Main and tail rotors. Application. Features of the structural layout of the main rotor hub components and hinges B. Wheel turning mechanism
Main and tail rotors
1. MAIN ROTOR BUSHING.
The main rotor hub is designed to transmit torque to the blades from the main gearbox, as well as to perceive and transmit to the fuselage the forces and moments occurring on the main rotor.
The Mi-8T main rotor hub has five blades with spaced and rotated horizontal hinges, vertical hinges, a flapping compensator and a centrifugal overhang limiter.
The flapping compensator serves to reduce the amplitude of the flapping movements of the blades and the tilt of the main rotor cone. The design of the sleeve is made so that when the blade flaps at an angle relative to the horizontal hinge? the installation angle changes by the amount ??=-k?, where k is the swing compensator coefficient. Thus, when swinging up, the installation angle decreases, and when swinging down, it increases.
The centrifugal overhang limiter is designed to prevent blades from hitting airframe structural elements at low rotor speeds.
Basic technical data:
The horizontal hinge spacing is 220 mm.
The vertical hinge spacing is 507 mm.
Horizontal hinge offset 45 mm.
Coefficient value
swing compensator 0.5
The maximum upward swing angle is 25? ± 30"
Downward swing angle (overhang from the plane,
perpendicular to the axis of rotation of the HB):
When focusing on the bracket 3°40"...4? ± 10";
With emphasis on pawl 1? 40"±20"
Angles of rotation relative to the VSh:
Forward rotation 13? ± 15"
Back against rotation 11? ± 10"
The angle of inclination of the NV axis forward is 4? 20"±10"
The diameter of the HB bushing is 1744 mm.
Height 321 mm.
Bushing weight (dry) 610 kg
Lubrication of bushing components:
1). Horizontal and vertical hinges:
TS-GIP oil at atmospheric temperature T H above +5° C;
TS-GIP and? AMG (SM-9) at T H = -50? +5° C.
2). Axial joint:
MS-20 at ТH above +5°С (short-term reduction of ТH to -10°С is allowed for up to 10 days);
VNII NP-25 (SM-10) at stable low T H = -50? +5 °C (a short-term increase in T H up to +10 °C is allowed for up to 10 days);
The main rotor hub includes the main structural components:
Bush body;
Axle joint housings;
Blade rotation levers;
DSP (in the eyelets of the brackets);
Hydraulic dampers VSh.
The bushing body is made of high-strength alloy steel. It is a cast part with internal involute splines for installation on the main gearbox shaft. The housing is centered on the shaft by two cones: the lower one is a bronze split one and the upper one is steel, consisting of two halves. The splines are lubricated with NK-50 grease. The entire package is tightened with a nut using a special hydraulic wrench and secured with pins.
The body has five (according to the number of blades) wide lugs lying in the same plane at an angle of 72? to each other. The centers of the lugs are shifted in the direction of rotation by 45 mm along the axis of the horizontal hinge. The lugs in connection with the bracket form horizontal hinges. To fill and drain oil from the joint, there are holes in the bushing body that are closed with plugs. The top plugs are also used as lugs when removing the bushing.
In the upper part of the body there is a flange to which the reservoir of hydraulic dampers of the vertical hinges is attached with studs, and in the lower part there is a hole for the fixation pin of the swash plate arm bracket.
Each eye has bosses that, together with the bracket bosses, form upper and lower stops that limit the flapping movements of the blades. The lower stops are removable, which allows them to be replaced during operation in the event of defects (hardening).
The bracket is a cast part of a box-section with two pairs of mutually perpendicular platforms. The eye pads are designed to connect the bracket with the bushing body and with the axle hinge pin. The connection with the bushing body forms a horizontal hinge, and with the trunnion - a vertical hinge. The parts of the centrifugal overhang limiter are mounted inside the bracket, and in its lower part there are eyes for the pawl axis of the centrifugal overhang limiter.
The axle joint journal is a steel forging consisting of a head and a shank with a threaded section at the end. The head has a central bore for mounting vertical joint bearings. In addition, the head has stops that limit the vibrations of the blades in the plane of rotation and two brackets for attaching the vertical hinge damper. The axial hinge parts are mounted on the shank and then tightened with a nut.
The horizontal hinge is designed to unload the butt part of the blade from a variable bending moment by allowing the blade to oscillate in the vertical plane.
The horizontal hinge is formed by the articulation of the lugs of the bushing body and the vertical lugs of the bracket. The design also includes:
Two needle bearings;
Thrust ring;
Two bronze washers;
Seal details.
The outer races of needle bearings are installed in the housing eye and secured with nuts. Between the outer races there are two bronze washers, between which a steel thrust ring is installed. Bronze washers act as sliding bearings, transmitting axial forces that arise when the blade deviates from the direction perpendicular to the axis of the horizontal hinge.
Axial fixation: the horizontal hinge pin rests against the wall of the bracket eye with a split insert ring, and on the other side is secured with a nut and is secured against rotation by a segment key.
The pin is equipped with internal races of needle bearings and chrome-plated rings, along which reinforced cuffs operate. Needle bearings absorb the largest loads from the action of the centrifugal forces of the blade.
Rice. 26 Main rotor hub.
1-shaft nut; 2-upper cone; 3-hydraulic damper reservoir; 4,17,25-cork; 5-sleeve body; 6-bracket; 7,28,73-thrust ring; 8.74 bronze washer; 9-trunnion axle hinge; 10,31,59,63,67,82,71-nut; 11.72 - outer race of the bearing; 12.69-inner race of bearing; 13,18-ring; 14,20,40, 62,70-O-ring; 15-finger vertical hinge; 16-glass; 19,38,64-cuff; 22-nut of the axial joint housing; 23-oil reflective ring; 24,30-radial ball bearing; 26,79,80 - spacer sleeve; 27-row roller bearing; 29-axial joint housing; 32-stop; 36-washer; 37-plug; 39-nut of the vertical hinge pin; 41-springs; 42-counterweight; 43,56,83 - grease nipple; 44-axis pawl; 45-dog; 46-stop; 47-lower cone; 48,49-locking plate; 50-screw locking plate; 51-locking pin; 52-mortgage ring; 53-earring; 33,34-adjusting ring; 35 Belleville Spring; 54,60-needle bearing; 55-finger; 57-finger earrings; 58-hydraulic damper; 61-bracket; 65-ring horizontal hinge; 66-key; 68-finger horizontal hinge; 75.81-ball bearing; 76-roller of the blade rotation lever; 77-cover; 78 roller bearing; 84-blade rotation lever; 85-bolt; 86-bushing.
The bearing cavities are sealed with rubber sealing rings and reinforced cuffs. Oil circulation is carried out using special grooves under the influence of centrifugal forces. A pressure compensator can be installed in the filler plug, which, when the oil pressure in the joint increases (as the temperature increases), prevents oil from being knocked out through the seals thanks to the rubber working element.
On one side, the finger is connected to the hydraulic damper earring using a needle bearing. Here, on the side of the earring, to protect the internal cavity of the finger from moisture entering the finger, a rubber plug is inserted. On the other hand, a plug with an eye is installed on the finger to connect a clamp for fixing the blades in the parking lot.
The vertical hinge serves to unload the butt part of the blade from variable bending moments by allowing the blade to oscillate in the plane of rotation.
The vertical hinge is formed by the articulation of the horizontal eyes of the bracket and the axle hinge pin. The design of the vertical hinge is fundamentally similar to the horizontal one. Two needle bearings are mounted in the cylindrical cavity of the axle head, consisting of outer and inner races with a set of needles. The outer clips are attached to the trunnion, the inner ones are put on the finger. To absorb axial forces, bronze washers are provided, located between the ends of the outer races and the thrust ring.
There is a glass inside the hollow finger. The glass has radial holes and is fixed at the top of the finger. A plug is screwed onto the finger, which closes the hole for filling oil into the joint. Oil enters the needle bearings through the holes in the cup, drillings in the pin and in the inner races of the bearing. The hinge seals are rubber rings.
Rice. 27 Axial hinge.
1-Pressure compensator; 2-Cork; 3-Cup; 4-Magnetic plug.
An oil can is screwed into the lower part of the glass, through which oil is injected into the vertical hinge during initial filling (during assembly). When injecting, oil flows to the needle bearings, displacing air from the joint through a bypass valve located in the axle stop. Oil is refilled directly into the glass through the filler plug.
The axial hinge is designed to allow changes in the installation angles of the blades.
The axial joint is formed by the connection of the trunnion and the axial joint body.
In the head part of the axle there are two flanges for fastening the hydraulic damper brackets. There are also bosses here that limit the rotation of the blades around the axis of the vertical hinge. The internal cylindrical cavity of the head part is used for mounting needle bearings of the vertical hinge.
The trunnion has a shank with a threaded section at the end. The axial hinge bearings are installed and secured on the trunnion shank. The thrust roller is designed to perceive centrifugal force and two radial balls are designed to perceive bending moments transmitted from the blade.
When assembling, the trunnions are sequentially put on the shank:
Axle joint housing nut with collars;
Separator with two rows of rollers;
Thrust ring;
Oil reflective ring;
Radial ball bearing;
Radial ball bearing;
Trunnion nut.
Spacer sleeve;
The trunnion nut tightens the entire assembled package and is secured with a retaining ring.
During assembly, an adjusting ring with two disc springs and a protective washer (to preload the bearings) is first installed into the axial hinge housing, then a shank with parts is inserted, after which the entire assembly is tightened with a housing nut, which is locked with a plate.
The axial joint is sealed with rubber rings and cuffs.
Are the roller bearing cage seats angled? = 0°50" to the radial direction. Due to this, when the angle of installation of the blade is cyclically changed, the separator, together with the oscillatory-rotational movements of the blade, slowly turns towards the inclination of the rollers. The separator makes a full revolution in 50–80 minutes of rotor operation at an oscillation frequency of 3–3 .5 Hz (190?200 rpm of the rotor) and the angular amplitude of oscillations is 4.5?5°.Continuous rotation of the cage ensures that the bearing ring raceways are fully involved in the work, and also reduces the number of repeated stresses experienced by individual sections of the raceways. This ensures the durability of the bearing and increases the service life of the axial hinges and the rotor hub as a whole.
The body of the axial hinge is made in the form of a glass, on the bottom of which there is a comb with eyes for attaching the blade. At the other end of the glass there is a thread for a nut and a flange, to which the blade rotation lever is attached with four bolts. The bolts are relieved from shearing forces by bushings. The end of the turning lever has a cylindrical cavity in which a roller is mounted on a double-row ball bearing and a roller bearing, which is held from displacement by a cover. An oil can is screwed into the lever to lubricate the CIATIM-201 bearings. A pin is installed in the eye of the roller on two bearings, connecting the blade rotation lever with the swashplate rod. The body also contains:
Transparent cup;
Drain plug;
Filling plug with pressure compensator.
The pressure compensator consists of a housing with holes, a cover and a membrane. When the temperature and pressure of the oil inside the axial joint increases, its vapors squeeze out the membrane and escape into the atmosphere through the holes in the housing.
Vertical hinge damper.
The vertical hinge damper serves to dampen blade vibrations in the plane of rotation in order to prevent “ground resonance”, as well as to eliminate blade shock loads that occur during vigorous rotation of the rotor.
The damper is of a hydraulic type; its operating principle is to absorb the vibration energy of the blade and dissipate it in the environment in the form of heat.
The vertical hinge damper consists of the following main parts:
Cylinder; - shock absorber;
Lid with glass; - compensation valve;
Bronze bushings; - fittings;
Rod with piston; - sealing parts;
Bypass valves; - corrugated cover.
The damper body includes a cylinder and a cover. The steel cylinder, using axle pins and needle bearings, is fastened with tight-fitting bolts to the brackets, which are installed on the bosses of the axle hinge pin.
On one side there is a hole in the bottom of the cylinder for the passage of the rod. On the other side, the cylinder is closed with a cover with nine bolts. A glass is attached to the lid, covering the open end of the rod. Bronze bushings are pressed into the bottom of the cylinder and in the cover, along which the rod moves.
The rod is made integral with the piston on which the piston rings are installed. The piston has eight bypass valves (four in one direction, four in the other direction). Each valve includes a valve body with nut, cone, seat and spring. The spring, resting against the nut, presses the cone to the body seat.
A stop body is screwed onto the threaded end of the rod, to which a shock absorber consisting of two steel plates and rubber vulcanized to them is attached with six bolts. The shock absorber serves to soften the impact on the rear vertical hinge limiter when the main rotor is launched.
The stop body is connected to the horizontal hinge pin using an earring. A corrugated rubber cover is attached to the stop housing and the cylinder, protecting the hydraulic damper rod from contamination. The sealing of structural elements is ensured by rubber rings. The hydraulic damper cover has a boss in which a compensation valve is placed, which includes three balls (two large and one small) and grooves in its design. The grooves perform the following functions:
A compensation tank is connected to the damper through a fitting and hoses;
Through channels drilled in the thickenings of the cylinder walls, they are connected to both cavities of the cylinder.
The compensation valve ensures that the internal cavities of the cylinder are replenished with working fluid, as well as air bubbles are removed from them.
Rice. 28 Vertical hinge damper
1,14,19-Bronze bushings; 2-Finger; 3,13,20,28-O-rings; 4-Plug; 5.7-Large balls; 6-Small ball; 8,16,27-Valves; 9-Cork; 10-Glass; 12-Fitting; 15-Valve body; 16-Cone; 17-Spring; 18-Nut; 21-Case; 22-Shock absorber; 23-Stop housing; 24-Cylinder; 25-fluoroplastic ring; 26-Piston ring; 29-Bolt; 30-Cap.
The hydraulic damper reservoir, designed to replenish possible fluid leaks and drain the compensation system, is installed on the main rotor hub on studs. The tank is of a cast design made of AL9 with a glued plexiglass cap, which provides good visibility of the presence of oil in the tank. Liquid (AMG-10 hydraulic oil) is added to the tank through the filler neck with a lid on the cap. The liquid level should be no higher than the mark on the reservoir cap and no lower than the lower edge of the cap.
Hydraulic damper operation:
When the blade oscillates in the plane of rotation, the cylinder moves and liquid flows from one cavity to another through the calibrated holes of the bypass valve cones. In this case, hydraulic resistance arises, which dampens the vibrations of the blade.
At the same time, the increased pressure of one of the cavities presses on the large ball, pressing it against the seat, while the cavity is disconnected from the compensation tank. The large ball of the compensation valve presses the second large one through the small one - this ensures the connection of the low-pressure cavity with the compensation tank.
With an increase in the amplitude of vibration of the blade relative to the vertical hinge, the increase in force on the damper rod decreases, which eliminates an unacceptable increase in bending stresses in the butt of the blade. This is ensured by the opening of the bypass valves when the pressure drop in the cylinder cavities increases to 20–28 kgf/cm?.
Centrifugal overhang limiter.
The centrifugal overhang limiter is designed to prevent impacts of the main rotor blades on the tail boom at low rotation frequencies (spin-up and stop of the main rotor, helicopter parking).
The stops must provide sufficient angles of rotation relative to the horizontal hinge when tilting the main rotor cone while controlling the helicopter, while the blade should not touch the stops. However, when the main rotor is stopped or at low rotation speeds, the blades have a significant deflection under their own weight due to the lack of tensile centrifugal force. Ensuring the required clearance between the tip of the blade and the tail boom at low rotor speeds is the task of the centrifugal overhang limiter (DOS).
Rice. 29 Centrifugal overhang limiter.
1-Counterweight; 2.5-Fingers; 3-Spring; 4-Traction; 5-Dog.
The DSP is located in the main rotor hub bracket and structurally consists of:
Counterweight with spring;
A dog that serves as a movable stop;
Finger – axis of rotation of the pawl;
The rod that connects the counterweight to the pawl.
When the main rotor is not working and during its spin up to 108 ±3 rpm, the spring holds the counterweight and the pawl in the position in which the blade is on the stop: the overhang angle is 1? 40". When the rotation speed reaches 108 rpm, the counterweight, under the influence of centrifugal forces, begins to rotate, stretching the spring, and rotates the pawl. At a frequency of 111 rpm, the pawl completely moves away from the bracket: the overhang of the blade is limited only by constant stops, which allow it to deflect downwards by 4?.
When the NV speed drops to 108 rpm, the mechanism reverses and at 95 rpm the pawl returns to the position corresponding to the blade overhang angle 1? 40".
The frequency of the main rotor at which the DSP is triggered during spin-up is higher than when it stops due to a change in the arm of application of the centrifugal force when the counterweight is rotated. Due to this, the actuation process occurs without delay, thereby eliminating impacts on the movable stop in its intermediate positions.
MAIN ROTOR BLADES.
The main rotor is designed to generate lifting and driving forces in all flight modes, as well as to create longitudinal and lateral moments of helicopter control.
The Mi-8T helicopter is equipped with a five-blade main rotor, which consists of a hub and blades.
The bushing is designed to fasten the blades, transmit rotation to them from the main gearbox, as well as perceive and transmit to the fuselage aerodynamic and inertial forces arising on the main rotor. The bushing is installed on the main gearbox shaft.
The main rotor blade is designed to create lift.
The main rotor blades are attached to the hub body with two bolts each, using horizontal, vertical and axial hinges. Vibrations of the blades relative to the vertical hinge (in the rotation cavity) are damped by hydraulic dampers. To protect the blades from icing, they are equipped with electrothermal anti-icing devices. In addition, the blades have a pneumatic alarm system for damage to the side members.
Main rotor data:
NV diameter 21.3 m.
Direction of rotation clockwise (top).
The area swept by the NV is 356 m2.
Fill factor 0.0777.
Weight 1285 kg.
Basic technical data:
Blade chord 520 mm;
The blade shape is rectangular in plan with a geometric twist:
at the end of the blade (section No. 22).
Blade weight 135 kg.
Blade profile between sections 0...1 - NACA-230, 2...3 - NACA-230-12, between 4...22 to 50% of the chord -NACA-230-11 increasing its ordinates from the chord by 1 mm, and from 50 to 95% change of ordinates to 0 according to a linear law.
Structurally, the blade consists of the following main elements:
Spar;
Twenty-one tail section;
Tip;
ending;
Anti-icing system;
Spar damage detection system.
The spar is the main power element of the blade, which absorbs aerodynamic and mass loads that arise when the rotor pitch changes.
The spar is a hollow beam with an internal contour of constant cross-section, made of aluminum alloy AVT-1 in the shape of a blade tip in accordance with the theoretical profile. The surface of the spar is hardened by cold hardening with steel balls on a vibration stand. In this case, the depth of the cold-worked layer reaches 0.3–0.4 mm, which significantly increases the service life of the blade.
Rice. 22 Main rotor blade.
a) Plan view of the blade; b) Butt part of the blade; c) Section of the blade; d) The end of the blade.
1-pin connector; 2-tip; 3-charge valve with spool; 4.12-plug; 5-pressure alarm; 6-bolts securing the tip to the spar; 7-spar; 8-compartment blade; 9-contour light lamp; 10-removable end piece; 11-plates of balancing weight; 13-sealant; 14-clamp; 15-screw stop; 16-anti-flutter weight; 17-compartment liner; 18 honeycomb core.
To increase the rigidity of the structure, the upper and lower flanges of the spar have smooth thickening ribs inside. The first of them from the toe of the spar are used as guides for installing anti-flutter weights.
In total, in each blade to obtain the necessary transverse alignment, which is necessary to increase the critical flutter speed, in the toe of the spar between compartments No. 18? 22 eight counterweights (anti-flutter weights) 400 mm long and weighing about 1 kg each are inserted. Each counterweight is rubberized, which allows it to be tightly inserted along the front stiffeners into the cavity of the spar. The centrifugal forces of the counterweights that arise during rotation of the blade are perceived by a screw stop screwed along the thread inside the end part of the blade.
The end part of the spar is closed with a plug consisting of two halves (plug and clamp), between which there is a sealant. When the halves are pulled together, the sealant is squeezed out and seals the end part of the spar. The plug has 2 bolts and 2 studs on which the balancing weight plates are assembled.
The end of the butt part of the spar is also closed with a cover installed on 9 bolts and sealed. The cover has a plug connector for supplying power to the heating elements of the blade anti-icing system and the contour fire, as well as a charging valve designed to pump air into the spar cavity. On the rear wall of the spar, near the end of the butt part, a pressure alarm is installed for the spar damage alarm system.
A cover is attached to the end cap with screws (and to the spar) to cover the wires running to the plug connector.
The blade spar damage signaling system is pneumatic with a visual pressure indicator. The system includes plugs installed at the ends of the spar to seal the internal cavity, a valve with a spool and a pressure alarm.
The pressure alarm consists of:
Transparent plexiglass cap;
Aneroid sensor element;
Red cylinder.
The aneroid sensitive element is a bellows, inside of which there is an inert gas - helium with a pressure of 1.05? 1.1 kgf/cm?.
In operating condition, the cavity of the spar is under increased air pressure: air is pumped through the charging valve with a hand pump with a pressure p spar, which should be 0.15 kgf/cm? greater than the pressure p SPL the alarm starts to operate. The internal cavity of the signaling device body communicates with the cavity of the spar. If cracks appear in the spar or its seal is broken, the air is released and the pressure in the cavity of the alarm body is equalized to atmospheric pressure. By forces of elasticity and internal pressure, the bellows opens and pushes the red cylinder into the visibility zone through the plexiglass cap.
Rice. 23 Blade pressure indicator.
1-plexiglass cap; 2-cylinder; 3-sealant; 4-gasket; 5-guide ring; 6-guide; 7-body; 8-aneroid sensitive element; 9-plug.
The pressure of the injected air depends on the temperature ТН and pressure РН of atmospheric air and is determined by special monograms and graphs. At temperatures ТН< -40°С давление воздуха в лонжероне р лонж должно превышать давление срабатывания сигнализатора р СПЛ на 0,25 кгс/см?.
The tip is designed to attach the blade to the bushing and consists of a comb and two jaws.
Using a comb, the blade is attached to the axial hinge body with two bolts with a tightening torque of 8...10 kgf m.
The tip is attached to the spar with cheeks using 9 through bolts and 12 (6 on each side) bolts with bushings. The bushings are designed to relieve bolts from shearing forces. In addition, in places where through bolts pass, in order to prevent deformation of the spar, there is a textolite spacer.
When installing the tip, an MPF-1 adhesive film is applied to the spar, and the ends of the cheeks are coated with VITEF-1NT sealant to prevent electrochemical corrosion.
For transverse balancing of the blade, a counterweight (eight bars of 40 cm each and weighing 1 kg) is inserted into the toe of the spar. The centrifugal forces arising during rotation of the blade are perceived by a screw stop installed inside the spar at the end of the blade.
The tail part of the blade is formed by separate compartments. In total, the blade includes 21 tail sections. The compartments are glued to the trailing edge of the spar and are structurally exactly the same.
Each compartment consists of:
Sheathing;
Tail stringer;
Two ribs;
Honeycomb filler.
Rice. 24 Tail section of the blade.
All components of the compartment are glued together with VK-3 adhesive film.
The ribs are made of 0.4 mm thick aircraft material. At the junction of the rib to the spar, the back of the rib is bent and represents a tab that is glued to the rear wall of the spar. The skin, 0.3 mm thick, is made of avial, at the tail stringer it is not cut, but curved around it. The stringer itself is textolite.
The honeycomb core is made of aluminum foil with a thickness of 0.04 mm and forms a hexagonal honeycomb on a side of 5 mm. On compartments No. 16 and No. 17 in the area of the tail stringers, flaps are fixed in the form of plates 40 mm wide and 1.5 mm thick, which serve to regulate the cone of the main rotor blades.
The compartment is glued to the rear wall of the spar with VK-3 adhesive film.
The compartments are not secured to each other, but to prevent air flow, inter-compartment liners are placed between them, made either of sponge rubber or in the form of duralumin rubberized boxes.
The tip (end fairing) ensures smooth flow around the end part of the blade.
For mounting blades
use special
device
The end fairing consists of fixed and removable parts. The fixed part is glued to the rib of the last compartment. The removable part is mounted on screws, has a cutout covered with a plexiglass lamp and a titanium reinforcing plate. When the removable part is removed, access to the mounting unit for the balancing plates (steel for weight balancing) and to the contour light lamp mounted on the bracket is available.
Electrothermal blade anti-icing system. The heating pad consists of:
Six layers of insulating fiberglass;
Metal heating elements;
Power wires;
Connecting bars;
Surface anti-abrasive rubber layer.
The heating elements are powered by current through a plug connector to which the power drives are connected. The other end of the power drives is soldered to the busbars of the heating devices. On the toe of each blade, in sections 5 m long from the end, split metal (stainless steel) fittings are glued to protect the toe from abrasive wear. A layer of polyurethane 0.8...1 mm thick is applied to the fitting.
2. TAIL PROPELLER
The tail rotor is designed to create a thrust force, the moment of which relative to the center of mass of the helicopter balances the reaction moment of the main rotor, and also provides the ground moment for controlling the helicopter.
When the helicopter is in directional equilibrium, the moment of thrust of the tail rotor relative to the helicopter's center of mass is equal to the reaction moment of the main rotor.
When the pitch of the tail rotor is reduced or increased, which is carried out using foot control, the thrust of the propeller changes accordingly. The helicopter's directional balance is disrupted, and the helicopter turns left or right depending on which moment is greater - the reactive moment of the main rotor or the thrust moment of the tail rotor.
When flying in the self-rotating mode of the main rotor, when there is no reactive moment of the main rotor, the helicopter is subject to a moment from the friction forces in the main rotor shaft supports, in a direction coinciding with the direction of rotation of the main rotor. In this helicopter flight mode, for directional balance, the thrust force of the tail rotor must be directed in the opposite direction, and its moment relative to the helicopter’s center of mass is equal to the moment of the friction forces in the main rotor shaft supports. Therefore, the tail rotor is reversible and can be used not only as a pusher propeller, but also as a pusher.
The tail rotor is also an element of the helicopter's static directional stability, since in flight the disk swept by the propeller has a positive effect on the stability of the helicopter.
To ensure uniform distribution of thrust over the disk swept by the tail rotor in conditions of oblique flow, the propeller hub has combined horizontal joints of the “cardan” type, which allows the blades to make flapping movements relative to the plane of rotation of the hub. However, as a result of the deviation of the plane of rotation of the tail rotor during flapping movements of the blades, the unevenness of rotation inherent in a simple cardan appears.
The presence in the design of the rotor hub of a flapping compensator with a coefficient of K-1 leads to a decrease in the amplitude of the flapping oscillatory movements of the blades and, consequently, reduces the uneven rotation of the tail rotor. To change the pitch of the blades, the propeller hub has axial hinges. The tail rotor is driven from the main gearbox using a transmission.
The tail rotor blades have an electrothermal anti-icing device that ensures normal operation of the propeller in icing conditions. The direction of rotation is clockwise when looking at the helicopter from the tail rotor.
The tail rotor consists of a hub and three blades.
Basic technical data
Screw diameter, m................................................... ........ 3,908
Swept area, m 2 ……………………………… 12
Fill factor………………………………0.135
Weight …………………………………………………… 121 kg.
Tail rotor bushing.
The tail rotor bushing is designed to secure the tail rotor blades and impart torque to them from the tail gearbox shaft, as well as to absorb aerodynamic forces and moments that arise when changing the pitch of the tail rotor, and transmit them through the gearbox to the end beam.
Basic technical data:
Bushing type………………………………………………………. cardan with combined main shaft.
Direction of rotation…………………………………... clockwise when viewed from the tail rotor.
Compensator coefficient
swing k ……………………………………………………… 1.0.
Deflection angles of the bushing from
neutral position:
To the hub flange……………………………………………. 10? ±10? ;
To the leash cross ………………………………………… 12? +20?/ -10? .
Full range of rotation angles
blades relative to OS…………………………………….. 29? +1? 40?/ -1? ;
The smallest angle……………………………………... - 6? +1? 10?/ -50? ;
Maximum angle………………………………………….. 23? +30?/ -10? .
The tail rotor hub consists of the following main components:
Hub with flange for fastening to the tail gear shaft;
A cardan, including a yoke, a cardan body and a bushing body;
Axial hinges, ensuring rotation of the blades when changing the pitch of the tail rotor;
Leash with a slider and rods for rotating the blades.
Bushing lubrication:
1). Axial joint:
MS-20 at outside air temperatures (ТH) above +5 °С (short-term reduction of ТH to -10 °С is allowed for up to 10 days);
MS-14 at T H = -15? +5 °C (possibly SM-12);
VNII NP-25 (SM-10) at stable low T H = -50? +5°C (a short-term increase in T H up to +10°C is allowed for up to 10 days);
VO-12 all-season at T H = -50? +50 °C with replacement every 200 +10 hours of bushing operation.
2). The bushing bearings are lubricated through grease nipples with CIATIM?201 lubricant.
The hub is used to attach the bushing to the output shaft of the tail gearbox and transmit torque to the tail rotor cardan.
The hub of the hub is made of steel, made in one piece with a flange, which is attached to the flange of the output shaft of the tail gearbox using eight bolts. The fastening bolt nuts are tightened with a tightening torque MZ = 8 +3 kgf m.
The hub is equipped with a swing limiter and a crossbar, tightened with a nut and a lock washer.
Inside the hub there are involute splines along which the slider moves. The slider guides are two bronze bushings pressed into the hub bores.
Lubrication of the bushings and spline joint is carried out by CIATIM-201 through a grease nipple made in the yoke fastening nut. The lubricant is refilled until fresh lubricant flows out of the safety valve installed in the hub flange.
The cardan is designed to ensure the flapping movement of the blades relative to the plane of rotation of the tail rotor, imparting torque to them, as well as transmitting the thrust force of the tail rotor to the tail gearbox.
The cardan includes, made of high-alloy steels:
Traverse; - cardan body; - bushing body.
Rice. 30 Tail rotor bushing.
1. Slider; 2, 12. Bronze bushing; 3. Hub; 4. Swing limiter; 5, 11, 31, 36. Nut; 6, 32. Tapered roller bearing; 7, 38, 41 Adjusting ring; 8, 33, 37. Cup (bearing housing); 9, 40, 43. Reinforced cuff; 10. Grease fitting; 13. Rubber cover; 15, 30. Cover; 16, 27 Double row ball bearing; 17. Pin; 18. Leash; 19. Adjustment rod; 20. Spherical spherical plain bearing; 21. Oil tank; 22. Bolt; 23. Cap; 24. Cork; 25. Special screw; 26. Cap nut; 28. Roller; 29. Needle bearing; 34. Cardan housing; 35. Traverse; 39. Washer; 42, 44. O-ring; 45. Nut of the axle joint housing; 46. Bulk roller bearing; 47. Thrust ring; 48. Double row roller bearing with cage; 49. Trunnion nut; 50. Thrust roller bearing; 51. Thrust bearing ring; 52. Axial joint housing; 53. Bushing body.
The traverse has two trunnions, on which the internal races of tapered roller bearings and adjusting rings are mounted using nuts. Adjusting rings provide the necessary preload of the bearings. The outer races of the bearings are pressed into the cups. The glasses are mounted in cylindrical grooves in the cardan housing. The bearing cavities are protected by cuffs and closed with covers. Bearings are lubricated by CIATIM-201 through grease nipples installed in cups.
The cardan body is made in the form of a cross and also has two axles, which are located perpendicular to the traverse axles. Tapered roller bearings are mounted on these axles, the outer races of which are pressed into the cups. In turn, the cups are installed in the bores of the bushing body and secured with nuts. The cavities of the glasses are sealed with rubber reinforced cuffs and closed with lids. The covers have grease fittings through which CIATIM-201 lubricates the bearings.
The bushing body has three trunnions, which together with the axial hinge bodies form the axial hinges of the bushing.
The sleeve cardan is a combined horizontal hinge and provides freedom of deviation of the sleeve body relative to the plane of rotation of the tail rotor at an average angle of ± 11? in any direction.
The axial hinge is designed to ensure rotation of the rotor blades when the propeller pitch changes.
The axial joint is formed by the articulation of the bushing body journal and the axial joint body.
In addition, the hinge design includes:
Trunnion nut;
Thrust bearing ring;
Thrust roller bearing with cage;
Double row thrust bearing with cage;
Thrust ring;
Axle joint housing nut;
Bulk roller bearing;
O-rings;
Reinforced cuff.
The axial hinge assemblies are mounted on the journals of the bushing body. A thrust ring is pressed onto the axle, which is the inner race of the bearing with bulk cylindrical rollers. The bearing absorbs radial loads, while the nut of the axial hinge housing acts as the outer race.
The raceways of a double-row thrust bearing are the cemented ends of the trunnion nuts and the axial joint housing. It absorbs the main loads from the action of centrifugal forces and most of the bending moments. Are the bearing cage seats angled? = 0° 32? ±6? to the line of radii, therefore, when the axial hinge body swings to change the pitch of the tail rotor, the separator continuously rotates around its axis. As a result, the surface of the nut raceways wears out more evenly, which can significantly increase the operational reliability and service life of the axial joint.
A thrust bearing with a cage is also mounted on the axle nut, which, together with the ring, performs the function of preloading the axial hinge assembly by selecting the thickness of the ring.
The cavity of the axle joint housing is protected by a reinforced rubber cuff and rubber rings. The cuff is installed in the bore of the nut of the axle joint housing and is secured against axial displacement by a spring ring.
The axial hinge body is made in the form of a glass and has a comb for attaching the tail rotor blades. There is also a boss on the body, in the bore of which a blade rotation roller is mounted on needle and double-row ball bearings. The roller bearings are lubricated through the CIATIM-201 grease nipple.
An oil tank with a transparent control cup is attached to the axial joint body with a special bolt (red) to determine the presence of oil in the joint. There are holes on the reservoir and in the body, closed with yellow plugs, used for draining oil and refilling the axle joint. The oil level in the joint is checked using the marks on the control cup when the blade is pointing down.
The driver assembly ensures rotation of the tail rotor blades in accordance with the control action from the mechanism for changing the pitch of the tail rotor.
The node includes:
leash,
Adjustable traction.
The driver is pressed onto the slide and tightened with a nut, which is secured with a lock washer. The position of the slider mounting slot relative to the driver is fixed with pins.
A double-row ball bearing is installed in the slider head. The outer ring of the bearing is pressed through the flange of the cuff housing to the end of the slider by a threaded cover. The inner ring of the bearing with a sleeve is attached to the tail gear rod with a nut.
To lubricate the CIATIM-201 bearing, there is a grease nipple on the driver, and on the threaded cover there is a pressure limit valve through which used grease comes out when it is replaced.
The leash has three levers ending in forks, which include the ears of the blade turning rods. The blade turning rod consists of an eye, a rod and a fork. The connection of the rod ear with the driver is carried out using a spherical self-lubricating bearing. The part of the slider protruding from the hub, between the driver and the hub, is protected by a rubber corrugated cover.
When changing the pitch of the tail rotor by moving the rod of the tail gearbox, the slider moves and, with the help of a leash and adjustable rods, rotates the axial hinge to a given installation angle.
Tail rotor blades.
The tail rotor is designed to balance the reaction torque of the main rotor and ensure directional stability and controllability of the helicopter.
The tail rotor is mounted on the flange of the tail gearbox output shaft and is located on the right side of the end beam. Three-blade pushing propeller with pitch variable in flight. Structurally, it consists of a sleeve and three blades.
The tail rotor rotates from the main gearbox through transmission shafts, intermediate and tail gearboxes.
The tail rotor hub is of a cardan type with a combined horizontal hinge; each blade is fastened to the hub with two bolts. To change the pitch of the tail rotor, the hub has axial hinges that ensure rotation of the blades.
To protect against icing, the blades are equipped with electrothermal anti-icing devices.
The tail rotor blade is designed to create thrust force in order to balance the reactive torque of the main rotor and provide directional control of the helicopter.
Basic technical data:
Chord……………………………………………………….. 305 mm.
The shape of the blade in plan is ……………… rectangular, without geometric twist.
Profile………………………………………………………NACA-230M.
Blade weight…………………………………….. 13.85 kg.
The tail rotor blade consists of:
Spar;
Tail section;
Spar tip;
End fairing;
Anti-icing system heating pad;
Blade static balancing unit.
The spar is made of AVT-1 material and is a hollow beam with an internal contour of constant cross-section. The outer contour is machined according to the theoretical contour of the blade and polished in the longitudinal direction. The spar is strengthened from the inside by cold hardening. In the butt part of the spar, two parallel platforms are milled for installing the tip.
Rice. 25 Tail rotor blade.
1. Bracket; 2. Honeycomb filler; 3. Spar; 4. Heating pad; 5. Forging; 6. Hairpin; 7. Balancing plates; 8. Fairing (removable part); 9. Rib; 10. Fairing (fixed part); 11. Sheathing; 12. Tail stringer; 13. Bushing; 14. Bolt; 15. Tip; 16. Plug.
At the end part, two studs are riveted to the spar, onto which balancing plates are installed.
The tip is made of high-strength alloy steel 18Х2Н4МА and is used to attach the blade to the PB bushing. The tip is attached to the spar with eight bolts and using MPF-1 adhesive film.
A bracket made of AK6 material is attached to the rear wall of the spar in the butt part using VK-3 adhesive film and using two butt bushings for attaching the tip.
The tail part consists of:
Sheathing,
Cell block,
tail stringer,
End rib.
Fiberglass sheathing 0.4 mm thick made of two layers of fiberglass, glued top and bottom to the honeycomb block with VK-3 adhesive film.
The stringer is made of two layers of fiberglass and glued from the outside along the tail part of the blade to the skin, covering it from above and below. The front ends of the tail stringer protruding under the skin are sealed with putty, so that the aerodynamic quality of the blade is not reduced.
The end rib is made from avial sheet. The wall is glued to the outer end of the honeycomb block, and the shelves are glued to the casing of the tail section.
The connection of individual elements of the tail section, as well as fastening to the spar, is carried out with glue. The connection of the tail section with the spar is supported by a duralumin bracket.
Tip - the end part of the blade is covered with a fairing consisting of two parts:
Fixed part riveted to the rib,
The removable part, made of stainless steel, is attached to the spar with four anchor nuts. Removing it provides access to the balancing plates.
3. SWAVER.
The swashplate is a control mechanism designed to change the magnitude and direction of the rotor thrust force.
The change in magnitude of the resultant aerodynamic forces of the main rotor is carried out by changing the total pitch of the main rotor, i.e. simultaneous change in the installation angle of all blades by the same amount. The direction of the resultant changes by tilting the plane of rotation of the swashplate, resulting in a cyclic change in the installation angles of each blade, i.e. depending on their azimuthal position.
The swashplate is placed on the housing of the main gearbox VR-8A and is attached to it using a guide on eight studs with a tightening torque of 5–6 kgf m.
The swashplate consists of:
Slider guide;
Cardan (consists of outer and inner rings);
Swashplate;
Leash (two-link);
Bracket;
Five vertical rods;
Collective pitch lever with support;
Leash displacement limiter;
Rockers and rods of longitudinal and transverse control.
The slider guide is a hollow cylinder with a flange, inside which the main gearbox shaft passes. The guide is made of chrome steel 30KhGSA and has a chrome-plated outer surface along which the slider bushings slide.
The slider is made in the form of a steel cylinder. Inside it, bronze bushings are installed on rivets, with which it slides along the guide. CIATIM-201 lubricant is supplied to the cavity between the bushings through grease fittings. On the outer surface of the slide in its central part there is a flange to which the bracket is attached with studs.
In the upper part of the slide, two diametrically located holes are bored into which radial ball bearings are pressed. With the help of these bearings and two fingers, the inner ring of the cardan is pivotally connected to the slider. The bearings are lubricated through the slider's oiler at the same time as the bronze bushings are lubricated.
To protect rubbing surfaces from dirt and retain lubricant in the cavities of the slider and bearings, two rubber cuffs are installed in special grooves of the slider. On the outer ring of the cardan at an angle of 90? Two cantilever pins are attached to each other, to which longitudinal and lateral control rods are attached through ball bearings. The bearings are covered with rubber covers and lubricated through oil nipples screwed into the fingers.
The fingers are located in such a way that the attachment points of the longitudinal and lateral control rods to the outer ring of the cardan are shifted relative to the corresponding axes by 21? against the direction of rotation of the main rotor. This design solution achieves advanced longitudinal-transverse control, which is necessary for strict correspondence of the inclination of the axis of the main rotor cone of rotation to the deflection of the control handle.
The swashplate is mounted on the cylindrical surface of the outer ring of the cardan using a double-row angular contact bearing. The inner rings of the bearing are tightened with a nut locked with a stopper. The outer rings of the bearing are pressed by a flange to the inner shoulder of the bushing, pressed into the plate.
The bearing cavity is sealed by two (top and bottom) reinforced rubber cuffs. The upper cuff, in addition, is protected from water and dirt by a screen mounted on the nut. Bearing lubrication is carried out by CIATIM-201 through grease fittings and is controlled by the release of lubricant through a warning valve.
The swash plate is stamped from aluminum alloy in the shape of a five-pointed star. At the ends of the plate legs there are cylindrical bores and square flanges for mounting end hinges.
Each end hinge includes in its design:
Double row ball bearing;
Spacer sleeve;
Needle bearing;
The cavity of the end hinge is sealed with rubber rings and closed with a lid. The hinge rollers are connected by pins to the rotating rods of the blades.
The cardan is a universal joint consisting of an inner and outer ring.
The outer ring is attached to the inner ring of the universal joint using a second pair of pins and radial bearings. The bearings are lubricated with CIATIM-201 through grease nipples screwed into the bearing caps.
The common axis of the fingers connecting the inner ring of the cardan with the slider is located perpendicular to the common axis of the fingers connecting the outer and inner rings. With this connection, the outer ring of the cardan, and with it the swashplate, can tilt in all directions relative to the slide.
Rice. 63 Vertical thrust.
1. Upper fork; 2. Traction; 3. Lower fork.
Vertical rods include:
Threaded rod;
Upper fork;
Bottom fork.
In the internal cavity of the lower fork there is an axial hinge in the form of a double-row ball bearing, the cages of which are clamped with nuts. To protect against dirt, a rubber cover is placed on the hinge. The axial joint allows the upper fork to rotate relative to the lower one. The upper fork screws onto the threaded end of the rod and has a cut that allows it to be locked using a coupling bolt. This design makes it possible, if necessary, to change the length of the vertical thrust and, therefore, change the angle of installation of the blade.
Rice. 62 Swashplate.
1. Rocking fork; 2. Scale; 3. Nut; 4. Washer; 5. Roller; 6. Bushing; 7. Screw; 8. Longitudinal control rocker lever; 9. Slider guide; 10. Finger; 11. Ball bearing; 12. Case; 15. Cross control rocker fork; 16. Rubber cover; 17. Nut; 18. Ball bearing; 19, 20. Fingers; 21. Ball bearing; 22. Roller; 23. Lower traction fork; 24. Ring; 25. Rubber ring; 26. Cover; 27, 29. Nuts; 28. Ball bearing; 30. Rubber cover; 31. Oil can; 32. Glass; 33. Bolt; 34. Rod; 35. Upper traction fork; 36. Oil can; 37. Body; 38. Cuff; 39. Bearing; 40. Bushing; 41. Flange; 42. Cuff; 43. Ring; 44. Screen; 45. Nut; 46. Cardan outer ring; 47. Leash clamp; 48. Bolt; 49. Cuff; 50. Nut; 51. Hairpin; 52. Cover; 53. Axis; 54. Pin; 55. Finger; 56. Cardan inner ring; 57. Nut; 58. Leash earring; 59. Plate; 60. Lever; 61. Blade rotation thrust; 62. Cover; 63, 64. Fingers; 65. Oiler; 66, 68. Nuts; 67. Leash lever; 69. Body; 70. Fork; 71. Roller; 72. Finger; 73. Needle bearing; 74. Roller; 75. Ball bearing; 76. Bronze bushing; 77. Crawler; 78. Slider bracket; 79. Bronze bushing; 80. Cuff; 81. Finger; 82. Bolt; 83. Vernier longitudinal control; 84. Nut; 85. Lateral control scale; 86. Disc; 87, 88. Pins; 89. Bushing; 90. Axle; 91. Nut; 92. Earring; 93. Finger; 94. Collective pitch lever support.
I - on the transverse control rocker; II - along the cardan of the plate; III - collective pitch lever supports.
The swashplate is rotated by a drive.
The leash is a kinematic link consisting of a clamp (bracket), an earring and a lever, hingedly connected to each other. The presence of five hinges on the leash ensures rotation of the plate at any tilt and translational movement along with the slider along the guide. The driver clamp is attached to the lower part of the NV bushing body and is secured against rotation with a pin. In order to monitor the condition of the driver clamp and prevent its deformation from the landing site, a clamp displacement limiter is installed on the sleeve above the clamp.
The clamp displacement limiter consists of two half-rings, which are tightened with screws, two plates, which are attached to one of the half-rings using brass screws. The limiter is installed in such a way that the gap between the control plate and the swash plate clamp is 0.8–1.6 mm. If the driver clamp is deformed, it presses on the end of the plate - the soft brass screws are cut off, and the plate hangs on the safety wire. In this case, a section of the half-ring, painted orange, opens, which signals the beginning of deformation of the clamp. This allows for increased flight safety.
The bracket is stamped from aluminum alloy and is attached with studs to the outer flange of the slide. Steel bushings are pressed into the bracket boss. The following are installed on the bracket:
Longitudinal control rocker;
Cross control rocker;
Collective pitch lever.
The longitudinal control rocker has a roller to which, on one side, the rocker lever is attached with end splines and a screw, and on the other side, a rocker fork is installed on involute splines, which is tightened with a nut. The longitudinal control rocker arm has a hole for mounting a ball bearing. Using a bearing and a rocker pin, the lever is connected to the longitudinal control rod, and the fork is connected to the rod coming from the hydraulic booster.
Rice. 64 Fastening the collective pitch lever.
The cross control rocker is mounted on the bracket using an axle and two needle bearings. The bearings are lubricated by CIATIM-201 through grease nipples screwed into the bracket.
The rockers have adjustment scales and verniers to control the deviations of the longitudinal-transverse control rods, which allows you to adjust the control without the use of inclinometers with an accuracy of up to 6?.
The collective pitch lever is attached to the support through a shackle. The support is fixed to the main gearbox shaft housing. This fastening of the lever allows the bracket, together with the slider, to move strictly vertically along the guide, and not along an arc.
Basic data of the swashplate:
| Control knob position | Deviation of the control handle from the neutral position, mm | Swash plate tilt |
| Neutral (with the lock installed): - forward - left | -- | 2? ± 12? 0? thirty? ± 6? |
| Forward all the way | 170 ± 10 | 7? thirty? ± 30? |
| Back all the way | 160±10 | 5? ± 6? |
| Back to the hydraulic booster when the hydraulic stop is turned on | - | 2? ± 12? |
| All the way to the right | 155 ± 10 | 4? ± 10? |
| Left all the way | 157 ± 10 | 4? 12? ± 12? |
Main rotor hubs (ROH) consist of a body and blade suspension sleeves with hinges. The perfection of VNV largely depends on how well its main parameters are chosen. These parameters for hinge screws primarily include:
Spacing of horizontal and vertical hinges;
Parameters characterizing the kinematics of the NV, i.e. determining the nature of the change in the true installation angle of the blade from the angles of deflection of the blade in the flapping plane, rotation H, and the flapping compensator coefficient k, cf ist = /((3, £, k) ;
Parameters characterizing the load on the bushing bearing units;
Parameters that determine the damping moment relative to the vertical hinge (Bill) Мg~ fg , £,).
Helicopter rotors, depending on how they deflect the blade in the flapping plane, can be divided into three main types:
With horizontal hinges (HS) (2.4.1, a-d);
With elastic elements performing the role of the main shank (2.4.1, f, g);
Without GS or elastic elements replacing them (2.4.1, h).
In the latter case, the required compliance is achieved by selecting the appropriate rigidity characteristics of the butt part of the blade and the axial hinge (AH) of the bushing.
Changing the angle of installation of the blade is most often carried out by rotating it in the OSH. In some NVs of the second type, there is no OS, and the angle of installation of the blade changes due to twisting of the elastic element.
In the practical activities of helicopter companies, kinematic diagrams of bushings with different locations of hinges relative to the axis of rotation of the HB are used. By using different combinations of hinges, a number of specific problems of NV dynamics and the nature of loading of hinge joint bearings are achieved.
Increasing the main gear spacing increases control efficiency and the permissible range of helicopter alignments, but at the same time the bending moments on the main gearbox shaft increase. From the experience of the domestic helicopter industry, it follows that it is advisable to have a minimum mainshaft separation, and obtain the necessary control margins by appropriately selecting the deflection range of the swashplate (SA). This approach makes it possible to create the most compact and lightweight design of the hub. An increase in the number of blades causes certain difficulties with placing the joints in the same plane, which forces the main shaft spacing to increase. The main factor that determines the minimum permissible separation of the propeller bushings of a conventional design is the provision of a restoring moment Mshtt created by the centrifugal forces of the blade. Necessary
take into account that MW depends on the blade flapping angle p.
Typically, the propeller spacing can be selected from the condition that the range of blade deflection angles in the plane of rotation (autorotation - takeoff) is 12-18°.
With the correct choice of kinematics, in this case the stability of the blade relative to the propeller is ensured. The offset of the propeller shaft at the accepted maximum angles of deflection of the blade in the plane of rotation cannot be reduced in this way and must be proportional to the maximum torque. The transition to modern blades from KM with str = 6-7 instead of str = 3.5-5, as on helicopters of previous generations, requires a certain increase in the offset of the propeller, necessary to maintain the range of deflection angles in the plane of rotation. This, naturally, entails a slight increase in the mass of the NV bushing. By moving the VS, a change in the vibration frequencies of the blade in the plane of rotation is achieved, which is associated with detuning from the “air” and “ground” resonance. The combination of the main shaft and the main shaft in the form of a cardan unit ensures uniform loading of the main shaft bearings in all helicopter flight modes (2.4.1, b).
When the NV blades are mechanically driven, torque M from the engine is transmitted through the bushing. The bushing perceives aerodynamic T and Q and inertial forces P and moments arising on the HB blades, and transmits them to the fuselage (2.4.2).
The mass of the sleeve sleeve is proportional to the centrifugal force of the blade and its length. Therefore, to reduce the weight of the bushing, it is advisable to reduce the length of the sleeve as much as possible. This is hampered by a number of restrictions. The length of the sleeve cannot be made less than the total size of the hinge units moved as far as possible towards the body. In addition, reducing the sleeve, especially for multi-bladed propeller bushings, is associated with layout difficulties.
The length of the sleeve is significantly reduced (for a given I piece) on the bushing with the order of the hinges “GSh-OSH-VSh” (helicopter “Chinook”, 2.4.1, c) and “OSH-GSh-VSh” (helicopter “Fletier”, 2.4 .1, d). The structural layout of the bushing with combined hinges is shown in 2.4.3 (S-58 helicopter).
The main indicators characterizing the perfection of the design of NV hinge bushings are:
Load-bearing capacity of GSh, VSh and OSh bearings;
The level of stress in parts subject to variable loads;
Resource and the possibility of its further increase;
Performance of dampers;
Bushing weight;
Manufacturability of parts and assemblies;
Simplicity and ease of maintenance.
Introduction….4
1 Analysis of the designs of helicopter rotor hubs….…5
1.1 Relevance of problems associated with servicing the three-joint hub of a helicopter main rotor...5
1.2 Types of helicopter main rotor bushings...7
1.3 Features of using elastomer bearings….…11
1.4 Comparison of a bushing with an elastomeric bearing with a bushing with hinged blades....14
2 Calculation of the NV bushing with a metal fluoroplastic bearing and the NV hingeless bushing....20
2.1 Physical picture of the main rotor loading….20
2.2 Operational and design loads….23
2.3 Selection and calculation of the main rotor hub......26
3 Development of technological maps for servicing the hingeless main rotor hub of the Mi-8 helicopter....49
3.1 Strategies for aircraft maintenance and repair.49
3.2 Maintenance of the hinged bushing of the main rotor of the Mi-8 helicopter….….55
3.3 Development of technology for servicing a hingeless main rotor hub based on an analysis of the operation of the main rotor hub of the BK-117 helicopter….75
4 Flight safety in difficult geographical and temperature conditions...80
4.1 Helicopter flight safety….….80
4.2 Impact on flight safety of operation in conditions of high and low ambient temperatures......81
4.3 Analysis of typical aviation accidents associated with crew errors and violations during landing in difficult weather conditions...84
5 Calculation and comparison of economic costs from the introduction of a hingeless main rotor hub...89
5.3 Calculation of operating costs for servicing the hinged bushing of the main rotor of the Mi-8 helicopter….…90
5.4 Calculation of operating costs for servicing the hingeless main rotor hub of the Mi-8 helicopter and comparison of the resulting costs with the costs of servicing the hinged main rotor hub.......93
6 Ensuring safety when replacing the main rotor hub on the Mi-8 helicopter….….…95
6.1 Introduction….….….….95
6.2 Work to replace the main rotor hub….….…96
6.3 Analysis and safety assessment when replacing the main rotor hub on the Mi-8 helicopter….….98
6.4 Development of necessary measures to ensure safety when replacing the main rotor hub on the Mi-8 helicopter….….101
Conclusion….….105
References….….106
Graduate work:
ANALYSIS AND DEVELOPMENT OF MEASURES TO INCREASE THE EFFICIENCY OF TELECOMMUNICATION ENTERPRISESGraduate work:
Feasibility study of measures to improve the efficiency of the transport sector
Introduction (excerpt)
One of the most loaded elements of a helicopter's structure during operation is the helicopter's load-bearing system, the main unit of which is the main rotor hub. Over the years of operation, the main rotor hub with hinged blades has proven itself to be a very reliable structural element of the helicopter's load-bearing system. However, due to the abundance of parts, lubrication points and inspection objects, servicing such a bushing is very labor-intensive and is carried out according to operating hours, that is, after a certain number of flight hours. This operating strategy is not always justified, since the replacement of an element is often carried out before it reaches a pre-failure state.
World experience in helicopter manufacturing has shown that when using other technological solutions for the design of the main rotor hub, such as a hingeless hub and a bushing with a metal fluoroplastic bearing and torsion bar, operation can be carried out more efficiently.
The options for implementing a hingeless main rotor hub and a main rotor hub with a metal fluoroplastic bearing on the Mi-8 helicopter, considered in the WRC, will make it possible to evaluate the possibility of increasing the efficiency of the technical operation of the main rotor hub.
Main part (excerpt)
1 Analysis of the designs of helicopter rotor hubs
1.1 Relevance of problems associated with servicing the three-joint hub of a helicopter main rotor
From experience in operating helicopters with a classic rotor hub design, it is known that this type of hub has a number of disadvantages. The main type of routine maintenance on a rotor with a classical scheme is regular replenishment and periodic replacement of lubricant in the articulated joints of its hub. The bushing hinge bearings operate constantly under the influence of variable and significant loads. To ensure lubrication of the rubbing surfaces of these hinges (horizontal, vertical and axial), special oils are used.
Oil in a certain amount is poured into the cavities of the indicated joints through a funnel or with a special rod syringe.
As the rotor operates for a certain number of hours, the oil becomes contaminated and its lubricating properties deteriorate. Therefore, the maintenance schedule requires periodic oil changes.
Failure to comply with oil change intervals leads to premature wear of the bearing surfaces and their failure. The same consequences result from the use of oil types not intended for bearing lubrication.
Practice shows that needle bearings operate most durable when lubricated with special hypoid oil, and ball bearings when lubricated with engine oil.
The general trend in the development of the development and design of helicopter rotor hubs is not so easy to consistently follow, since each specific helicopter company, as a rule, uses bushings of a certain design.
However, one can note the increasing complexity of the design of hub-carrying rotors with hinged blades while simultaneously improving their weight characteristics, reliability and fatigue strength, which is achieved by more careful study of the design details, taking into account a deeper understanding of the operating conditions of the main rotor.
Recently, much interest has been shown in the simplified design of the main rotor hub, in which the hinges are replaced by elastic elements. There are several ways to achieve this goal, differing in their fundamental and design features among different aviation companies. It is unlikely that when switching to a hingeless fastening of the blades, one can count on a significant reduction in the weight of the hub. The design improvements achieved are aimed at increasing efficiency by reducing production and operating costs and improving handling characteristics due to a significant increase in control power. These improvements were achieved at the cost of overcoming significant difficulties due to the complication of processes and calculations.
Weight perfection of the bushing, characterized by the coefficient:
, (1.1)
where mw is the mass of the bushing;
z - number of blades;
P - centrifugal force;
K - coefficient.
The weight perfection of the bushing is significantly increased due to: replacing steel with titanium alloys; the use of wire torsion bars in the design of the axial hinge (AHS) and self-lubricating bearings in the blade rotation levers; modernization of centrifugal overhang limiters; the use of spring-hydraulic dampers that reduce the variable loads acting in flight in the plane of rotation; some increase in structural tension taking into account modern structural and technological measures (Figure 1.1).
Figure 1.1 - Weight perfection of rotor bushings of various types
The desire to lighten the design as much as possible, reduce its cost and simplify maintenance in operation has led to the creation of bushings made of composite materials without conventional horizontal hinges (HS), such bushings are called hingeless.
1.2 Types of helicopter rotor hubs
Currently, eight main designs of rotor hubs are practically used, the kinematic diagrams of which are shown in Figure 1.2. Let's look at the most widely used bushing designs and determine the advantages and disadvantages of each design.
The classic design of a main rotor hub with hinged fastening of the blades: the attachments are attached by means of horizontal, vertical and axial hinges. In this case, a significant role is played by the size of the spacing (distance from the axis of the bushing) of the horizontal and vertical hinges, which determines the design of the bushing.
A rotor with combined horizontal hinges and vertical hinges is quite acceptable in terms of design and allows the use of a simple method for determining stresses.
.
a - classic three-joint; b - with combined GSh and VSh; c - with remote HS; g - with external main shank and high shank; d - on the cardan; e - with an elastomeric joint; g - semi-rigid screws; h - rigid screws
Figure 1.2 - Kinematic diagrams of main rotor bushings
However, a helicopter with such a main rotor is unstable, has unsatisfactory controllability characteristics, and is subject to the risk of self-excited vibrations on the ground and in the air. The hub of such a rotor is heavy and complex; it must also include vibration dampers for the blade relative to the vertical hinges and a stop-limiter that limits the movement of the blades in the hinges.
A main rotor with vertical and horizontal hinges having a small spacing has significantly better characteristics of stability and controllability, but to a certain extent, it has all the other disadvantages of a design with combined vertical and horizontal hinges.
A main rotor with a large spacing of horizontal and vertical hinges has excellent stability and controllability characteristics; by selecting an increased spacing of vertical hinges and corresponding damping characteristics, self-excited vibrations of the helicopter are eliminated. However, the hub and butt parts of the blades are inevitably heavier and more complex than those of a rotor with combined hinges. The large hinge spacing also attracts the attention of designers in connection with the problem of reducing flow stall on a retreating blade.
Schemes of rotor hubs with hinged blades, in addition to the fact that they differ in the relative position of the hinges and the amount of their spacing, may have other differences, for example, the eyes of the horizontal hinge can be shifted so that the axis of the vertical hinge does not coincide with the radial position of the longitudinal axis of the blade.
The main rotor hub with an elastomeric bearing has all the advantages of a hinged blade system with a significantly simplified hub design. An elastomeric bearing consists of alternating spherical layers of elastomer (rubber) and metal. Under the action of the centrifugal force of the blade, the elastomeric bearing is compressed, and the movements of the blades in the flapping plane and in the rotation plane, as well as changes in the blade installation angle, lead to a shift of the elastomer.
The main rotor hub on the cardan does not have complex elements characteristic of a scheme with hinged blade suspension and is, apparently, the simplest in design. It lacks vertical hinges and dampers to dampen vibrations of the blades relative to the vertical hinges. The disadvantage of this scheme is that it is not applicable to large helicopters due to the limitations associated with the constant taper angle of the main rotor blades. In addition, a main rotor on a cardan is characterized by a special type of instability such as aerodynamic flutter, called “wave” of the main rotor (from the wave-like trajectory drawn in space by the ends of the blades).
A rigid rotor has neither horizontal nor vertical hinges. However, in the absence of hinges, the blades can be attached to the main rotor hub rigidly or by means of elastic elements - torsion bars, therefore, such rotors should more accurately be called rotors with hingeless fastening of the blades. Rigid blade mounting can be used on small helicopters to avoid excessive variable bending moment acting at the blade root. The deflection of the blades in the flapping plane and in the plane of rotation of the main rotor, in this case, is carried out due to the elastic deformation of the blades themselves, which, therefore, must be made sufficiently elastic.
When the blades are attached to the hub by means of elastic torsion elements, the latter perceive the centrifugal forces acting on the blades and allow the blades to deviate in the flapping plane and in the plane of rotor rotation. A rigid main rotor has a number of advantages: it allows a significant shift in the helicopter's alignment, quickly responds to control and provides good helicopter stability characteristics.
It was experimentally determined that the control power of a rigid main rotor is twice as high as the control power of a main rotor on a gimbal, and theoretical calculations showed that a rigid rotor has 14 times greater control potential compared to a propeller on a gimbal. A helicopter with a rigid main rotor can have good longitudinal control without a tail unit.
The use of a rigid main rotor allows the use of a tilting pylon, which provides the ability to change the angle of attack of the main rotor and, thanks to this, the ability to install the fuselage in flight in a position corresponding to the minimum resistance of the helicopter, which is especially important for high-speed helicopters. In addition, the rigid fastening of the main rotor blades allows the aerodynamic load to be redistributed over the swept area of the main rotor (by lateral displacement of the helicopter's center of gravity) in such a way that it can be used to delay the stall mode on the retreating blade, reduce vibrations and increase the maximum flight speed of the helicopter.
1.3 Features of using elastomeric bearings
For a main rotor hub with elastomeric bearings, the flapping motion, movement in the plane of rotation and change in the installation angle of each blade is provided by one elastomeric bearing (Figure 1.3). To maintain a constant position of the geometric center of the elastomeric bearing, an additional self-lubricating bearing is used, which perceives only small transverse loads perpendicular to the longitudinal axis of the blade.
1- main rotor shaft, 2- blade, 3- elastomeric bearing.
Figure 1.3 - Diagram of a main rotor hub with an elastomeric bearing
An elastomeric bearing must perform the following four functions:
- perceive the full centrifugal force of the blade;
- provide a change in the angle of installation of the blade;
- ensure the flapping movement of the blade;
- ensure movement of the blade in the plane of rotation.
The simultaneous performance of all these four functions by one bearing is primarily only possible if the bearing has a spherical shape. A spherical elastomeric bearing consists of alternating layers of steel and rubber glued to each other. The centrifugal force compresses the entire bearing, which has a very high degree of elasticity during compression, higher than expected in calculation studies, which is a great advantage of this design, since it gives slight displacement relative to the axis of the main rotor of both the center of the bearing and the butt of the blade.
Changing the installation angle of the blade and its movement in the flapping plane and in the rotation plane causes a relative displacement of the metal bearing plates, limited by the forces arising in the rubber layers during their shear.
Compared to conventional hinges, an elastomeric bearing, in which the angular movements of the blades are carried out due to the shear of elastic (elastomer) elements, has the following advantages:
- the number of parts is reduced;
- simplifies maintenance;
- there is no abrasion, wear or slippage of rotating elements;
- contamination of working parts (pivot bearings) by dirt, dust, and water present in the environment has been eliminated.
Natural rubber is chosen as an elastomeric (elastic) element in an elastomeric bearing, which has a number of advantages important for performing the intended functions, while its disadvantages do not cause serious design problems.
The advantages of the selected material in this case are excellent strength characteristics. Disadvantages are: limited operating temperature range; sensitivity to light, ozone, oil pollution; aging.
Let us briefly consider the possible impact of the disadvantages of natural rubber, when used in an elastomeric bearing, on the performance of the product. The operating temperature range of the main rotor hub varies from approximately -54°C to +71°C. By means of certain additives to natural rubber, rubber grades have been obtained whose effective temperature range varies from -54°C to +82°C, which covers the operating temperature range of the bushing.
To determine the effect of elevated temperatures on the fatigue strength of an elastomeric bearing, 500-hour dynamic tests of the bearing were carried out at a temperature of 93°C. Figure 1.4 shows the dependence of bearing deformation on load before and after 500-hour fatigue tests. As follows from the graphs in Figure 1.4, after 500 hour-long tests at a temperature of 93°C, the degree of elasticity of the test sample remained within production tolerances.
1-before dynamic tests 2 – after 500-hour dynamic fatigue tests at a temperature of 93º
Figure 1.4 - Graphs of the dependence of the deformation of an elastomeric bearing on the load
At extreme negative temperatures (-54°C), the hardness of the rubber increases sharply. The brittleness characteristic does not reach the critical point, which occurs at a temperature of (-62°C). Dynamic tests carried out at a temperature of (-64°C) showed that despite an increase in hardness by 22 times compared to hardness at room temperature, the bearing continues to operate normally without destruction.
One of the main advantages of an elastomeric bearing bushing is that it is lubrication-free, so there is virtually no risk of oil contamination of the elastomeric bearing. However, hydraulic fluid is used in the blade damper (when it moves in the plane of rotation of the rotor). To protect against possible contamination of the elastomeric bearing by hydraulic fluid and from exposure to sunlight and ozone, a protective bearing coating can be applied.
Rubber is characterized by a change in its physical properties over time, i.e. aging. The aging process is enhanced by exposure to factors such as sunlight, oxygen, ozone, heat, rain and other adverse environmental influences during helicopter operation. The aging process of an elastomeric bearing must be strictly controlled with storage conditions regulated to limit its aging from the moment the bearing is vulcanized until the sleeve with this bearing is installed on the helicopter.
Conclusion (excerpt)
In the final qualification work, the existing types of helicopter rotor hubs were analyzed, and strength calculations were made for a hingeless rotor hub and a rotor hub with a metal fluoroplastic bearing and a torsion bar. The results of the analysis proved the possibility of installing these types of bushings on the Mi-8 helicopter. Increasing the operating efficiency of the main rotor hub of the Mi-8 helicopter is achieved by significantly reducing the work on inspecting the fasteners and lubrication of the hub; these facts are discussed in a special part of the final qualification work. In addition, the service life of a hingeless bushing directly depends on its operating conditions and the results of flaw detection, while the main rotor bushing of the Mi-8 helicopter has a service life of 20,000 hours, after which it must be replaced. Economic justification for replacement.
The flight safety section is concerned with ensuring flight safety in difficult meteorological conditions. This is a very complex task that requires an integrated approach and careful monitoring of the implementation of the required instructions, analysis and elaboration of ongoing incidents. Flight safety when landing in special meteorological conditions can be achieved by complying with all requirements and instructions for helicopter operation, as well as by conducting additional pre-landing preparations that help improve the skills of the crew.
The economic justification for replacing the hub, discussed in the fifth part of the work, proves the feasibility of replacing the three-jointed main rotor hub of the Mi-8 helicopter with a hingeless main rotor hub.
In the section on safety and environmental friendliness of the project, facts affecting the safety of personnel when working at height are analyzed. Particularly noted are the risk factors associated with working at height when replacing a bushing, the impact of which is reduced by observing safety regulations.
Calculations of the economic costs of servicing the hingeless and articulated bushings of a helicopter main rotor showed. that the cost of servicing a hingeless main rotor hub is less than the cost of servicing a hinged main rotor hub, this proves the economic feasibility of replacing the main rotor hub with a hingeless one. In addition, the hingeless main rotor bushing has a significantly lower mass, and replacing the bushing will provide additional payload and thereby increase the economic effect of replacing the element of the rotor system. The annual effect from installing one bushing will be RUB.
Literature
1 Aerodynamics, flight dynamics, design, equipment and technical operation of helicopters. Directory. A.M. Volodko, M.P. Verkhozin, V.A. Gorshkov. –M., Military Publishing House. 1992.-556p.
2 Helicopter design. Textbook for Universities V.N. Dalin, S.V. Mikheev. - M., MAI, 2001. – 352 p.
3 Helicopter rotor hubs. Translation by M.A. Lerner. – M., TsAGI, 1972.-54 p.
4 Design of helicopter rotor bushings. Textbook Sokhan O.N. - M., MAI, 1981.-54 p.
5 Messerschmitt-Boelkow-Blohm Bo-105 1967 [Electronic resource] -Free access: h**t://w*w.aviastar.org/helicopters_rus/mbb-105-r.html Date of access (23.10.2010)
6 Design of screws for drive power units. Textbook for universities. F.P. Kurochkin. -M., MAI, 1980.-139 p.
7 Metal fluoroplastic bearings A.P. Semenov, Yu.E. Savinsky. -M. Mechanical Engineering 1976.- 192 p.
8 Technical Operation Manual for the Mi-8 helicopter, book 2, 1984.
9 Mi-8 helicopter (design and maintenance). V.A. Danilov Transport, 1988.-278 p.
10 Selection of rational design parameters for the torsion bar of the helicopter main rotor hub made of composite materials. Textbook for universities. E.A. Basharov.-M, MAI -2010.
11 Fundamentals of mechanics, design and technology for manufacturing products from layered composite materials. Textbook for universities. Yu.S. Pervushin, V.S. Zhernakov. -Ufa, 2008. -298 p.
12 Technical operation of aircraft. Edited by N.N. Smirnov - M.: Transport, 1997.
13 Technical Operation Manual for the Bk-117 helicopter
14 Design and operation of helicopters and engines. Tutorial for
Universities. Sudakov V.Ya. -M., Military Publishing House, 1987.
15 Flight safety analysis by aircraft type. State Center “Flight Safety in Air Transport” .- M. 2008-148p.
16 Economics of civil aviation. Textbook for universities Stepanova N.I., MSTUGA 2003.-103p.
17 Inter-industry labor rules when working at height. -M. 2004.
18 Instructions on labor protection during high-risk work IOT 0011-02, 2002.
19 Manuals on technical operation and repair of aircraft in Russian civil aviation. (NTERAT GA-93) - M., 1994.
20 Helicopter design. Textbook for aviation technical schools. YS Bogdanov, R.A. Mikheev. M., Mechanical Engineering 1990.-267 p.
21. Maintenance regulations for the Mi-26 helicopter, book 2.
22 Maintenance regulations for the Bo-105 helicopter
23 Handbook of aviation materials and technology for their use
Alexandrov V.G., Bazanov B.I., -M., 1979
24 Technical operation of helicopters. Textbook. Belyakov V.T. Military Publishing House, 1961 312 pp.
25 Computational and experimental study of the strength of elastic elements of hingeless helicopter rotors Golovanov A. I., Mitryaykin V. I. Izv. universities -Kazan: Aviation technology, 2001.
26 Fundamentals of design and manufacture of aircraft structures from CM Vasiliev V.V. - M.: MAI, 1985.
27 Optimal design of aircraft structural elements from CM. Dudchenko A. A. - M.: MAI Publishing House, 2002.
28 Composite materials: Handbook / Ed. V.V. Vasilyeva. - M.: Mechanical Engineering, 1990.
29 Design of helicopters Zavalov O. A. -M.: MAI Publishing House, 2004.
30 Methods of designing structures. Biryuk V.I., Lipin E.K., Frolov V. -M.- M.: Mechanical Engineering, 1977.
1) Needle bearings M and N (Fig._4.11.)
Rice. 4.11. Layout of the main components and hinges of the main rotor hub:
1- main rotor hub housing; 2- horizontal hinge; 3- swashplate rod attachment unit; 4- bracket; 5- blade rotation lever; 6- vertical hinge; 7-axis hinge; 8- blade; H, M - needle bearings of the horizontal hinge
of the horizontal hinge are located symmetrically relative to the perpendicular O1 O2, lowered from the center O2 of the vertical hinge to the axis of the horizontal hinge.
The middles of the bushing body lugs are shifted from the axis of rotation by a distance a = 45 mm. With this arrangement of the lugs, the horizontal hinge is rotated relative to the radial direction by an angle x. The angle x, equal to 5°4ў19ўў, was chosen so that in the main flight modes the resultant N of the aerodynamic and centrifugal forces of the blade would be directed approximately along the O1 O2 line. This ensures a more uniform load distribution between the needle bearings of the horizontal hinge and significantly increases their durability ; At the same time, the axial force perceived by the insert ring 51 and the nut 66 of the horizontal hinge decreases (see_fig._4.1.).
Rice. 4.1. . Main rotor hub:
1, 10, 19, 31, 39, 58, 62, 66, 81 - nuts; 2- upper cone; 3- compensation tank for hydraulic dampers; 4, 17, 25, 40 - plugs, 5.50 - bushing body; 6- bracket; 7, 8, 11, 12, 13, 18, 20, 22, 23, 28, 33, 34, 41, 51, 61, 64, 68, 69, 71, 72, 73 - rings; 9- axial hinge pin; 14, 65 - keys; 15, 44, 54, 56, 67 fingers; 16, 76 - covers; 21, 38, 63 - cuffs; 24, 30, 59, 70, 74, 77, 80 - bearings; 26- spacer sleeve; 27- roller bearing; 29- axial hinge housing; 32- locking plate; 35, 41 - springs; 36- washer; 37- plug; 43, 55, 82 - grease nipples; 45 - pawl of the centrifugal blade overhang limiter; 46- lower stop; 47- lower cone; 48, 49 - safety plates 52 - earring; 57- hydraulic damper; 60- bracket; 75- blade rotation lever shaft; 78, 79 - spacer bushings; 83- blade rotation lever; 84- bolt; 85 - bushing
2) Unit 3 connecting the blade rotation lever 5 with the swashplate is located at a distance from the axis of the horizontal hinge. Consequently, when the blade rotates relative to the horizontal hinge, it will simultaneously rotate relative to the axial one. In other words, if the blade makes flapping movements, its installation angle simultaneously changes. In this case, the installation angle changes in such a way that aerodynamic forces would reduce the change in the flapping angle. For example, if the flapping angle b increases (the blade “flies” upward), the blade installation angle j decreases, the lifting force of the blade decreases, reducing the flapping angle. Therefore, we can say that the main rotor of the Mi-8 helicopter has a wing compensator.
The operating principle of the swing compensator is shown in Fig._4.12.
Rice. 4.12. Scheme of operation of the swing compensator:
1- axis of rotation of the main rotor; 2 - horizontal hinge axis; 3- thrust to the swashplate; 4-axis rotation of the blade
Swing compensation is quantitatively assessed by the swing compensator coefficient:
For existing helicopters, the swing compensator coefficient is 0.4...0.6. Flight compensation allows you to reduce the angle of attack of the blade profile in azimuth 2700 and, therefore,. increase helicopter flight speed, prevent blade flutter.
General information.
The tail rotor is designed to create a thrust force, the moment of which relative to the center of mass of the helicopter balances the reaction moment of the main rotor, and also provides the ground moment for controlling the helicopter.
When the helicopter is in directional equilibrium, the moment of thrust of the tail rotor relative to the helicopter's center of mass is equal to the reaction moment of the main rotor.
When the pitch of the tail rotor is reduced or increased, which is carried out using foot control, the thrust of the propeller changes accordingly. The helicopter's directional balance is disrupted, and the helicopter turns left or right depending on which moment is greater - the reactive moment of the main rotor or the thrust moment of the tail rotor.
When flying in the self-rotating mode of the main rotor, when there is no reactive moment of the main rotor, the helicopter is subject to a moment from the friction forces in the main rotor shaft supports, in a direction coinciding with the direction of rotation of the main rotor. In this helicopter flight mode, for directional balance, the thrust force of the tail rotor must be directed in the opposite direction, and its moment relative to the helicopter’s center of mass is equal to the moment of the friction forces in the main rotor shaft supports. Therefore, the tail rotor is reversible and can be used not only as a pusher, but also as a puller.
The tail rotor is also an organ of the helicopter's static directional stability, since in flight the disk swept by the propeller has a positive effect on the stability of the helicopter.
To ensure uniform distribution of thrust over the disk swept by the tail rotor in conditions of oblique flow, the propeller hub has combined horizontal joints of the “cardan” type, which allows the blades to make flapping movements relative to the plane of rotation of the hub. However, as a result of the deviation of the plane of rotation of the tail rotor during flapping movements of the blades, the unevenness of rotation inherent in a simple cardan appears.
The presence in the design of the rotor hub of a flapping compensator with a coefficient K = 1 leads to a decrease in the amplitude of the flapping oscillatory movements of the blades and, consequently, reduces the uneven rotation of the tail rotor. To change the pitch of the blades, the propeller hub has axial hinges. The tail rotor is driven from the main gearbox using a transmission.
The tail rotor blades have an electrothermal anti-icing device that ensures normal operation of the propeller in icing conditions.
The tail rotor consists of a hub and three blades (Fig._5.1.).
Rice. 5.1. Tail rotor:
1- bushing; 2- bolts; 3- blade
Tail rotor bushing.
The tail rotor hub is designed to transmit torque to the blades, as well as to absorb forces from aerodynamic forces and transmit them to the tail boom. Tail rotor bushing (Fig.5.2.)
Rice. 5.2. Tail rotor bushing:
1 - slider; 2.12 - bronze bushings; 3 - hub; 4 - swing limiter; 5. 11. 14 31 36 45 49 - nuts; 6, 32, 46, 48, 50 - roller bearings; 7, 38, 41 adjusting rings; 8, 33, 37 - roller bearing cups; 9, 17, 40. 43 - reinforced cuffs; 10 - grease fitting; 13 case; 15 - cover nut; 16, 27 - ball bearings; 18- leash; 19 - blade turning rod; 20 - spherical bearing; 21 - bolt; 22 - oil tank; 23 - control glass; 24 - plugs; 25 - valve; 26 - cap nut; 28 - roller; 29 - needle bearing; 30 - cover; 34 - cardan body; 35 - traverse; 39 - washer; 42, 44- - sealing rings; 47 - thrust ring; 51 - thrust bearing ring; 52 - axial hinge housing; 53- bushing body
consists of a hub, cardan, axial hinges, a driver with a slider, and blade rotation rods.
Hub 3 of the bushing is made of steel, made in one piece with a flange, with which it is bolted to the flange of the driven shaft of the tail gearbox. The following are installed on the hub: swing limiter 4 and traverse 35, tightened with nut 11, which is fixed with a plate lock. The nut flange has an annular groove for installing an oil seal, which prevents dirt from entering the hub cavity. Inside the hub 3 there are splines along which the slider 1 moves. The guides of the slider are bronze bushings 2 and 12, pressed into the hub bore. Rubber sealing rings are installed in the inner grooves of the bushings. A grease nipple is mounted in nut 11, and a limit pressure valve is installed in the hub flange 3 for packing and controlling the lubrication of the spline pair.
The sleeve cardan consists of a traverse 35, a cardan body 34 and a sleeve body 53, made of alloy steel. The traverse 35 is mounted on the hub 3 with internal splines. The inner rings of tapered roller bearings 32 and adjusting rings 41, tightened with nuts 31, are mounted on two trunnions of the traverse. The adjusting rings 41 provide the necessary preload of the bearings.
The cardan housing 34 has the form of a cross, into the internal cylindrical bores of which steel cups 33 are pressed to install the outer rings of roller bearings 32. The bearings are protected from dust and moisture by rubber reinforced cuffs 40 and covers 30, secured against axial movement by retaining rings. An adjusting ring is installed between the cover 30 and the outer ring of the bearing 32. Grease nipples 10 are screwed into the threaded holes of the cardan housing and cover 30 to inject lubricant into the bearing cavity 6 and 32. On the outer journals of the cardan housing, the axis of which makes an angle of 90° with the axis of the internal cylindrical bore of the housing, steel rings are installed for sealing cuffs 9 and inner rings of tapered roller bearings 6. The outer rings of these bearings are fixed in steel cups 8 and 37, installed in the bores of the bushing housing 53. The glasses are secured in the bushing body with nuts 5 and 36, locked with lock washers. The bearings are preloaded by selecting the thickness of the adjusting rings 7, 38 and washer 39.
The hub cardan is a combined horizontal hinge common to all tail rotor blades. It provides an inclination of the plane of rotation of the hub body and blades at an angle from -8° to + 10° from the plane of rotation of hub 3.
The bushing body 53 has three axles, the angle between the axes of which is 120°. The journals together with the housings 52 of the axial hinges form the axial hinges of the bushing. A thrust ring 47 is pressed onto the axle, on which a special roller bearing 46, a nut 45 and a double-row thrust roller bearing 48 are mounted. The outer ring of the bearing 46, which receives radial loads from shear forces, is the nut 45 of the axial hinge housing. The thrust ring 47 is clamped to the trunnion by a nut 49, secured with a plate lock. The tightening torque of the nut is selected in such a way as to prevent the opening of the joint of this connection under the influence of centrifugal force and moments loading the axial hinge.
The raceways for the rollers of bearing 48 are the cemented ends of the nuts 45 and 49. The axes of the separator seats of this bearing are rotated from the radial direction at an angle equal to 0°26". When the screw rotates, the blades perform oscillatory movements relative to the axis of the combined horizontal hinge, and this causes not only the rocking motion of the bearing cage 48, but also its continuous slow rotation in one direction.As a result, the surface of the raceways of the nuts 45 and 49 wears out more evenly, which can significantly increase the reliability of the operation of this unit.
The preload of the bearing 48, which absorbs the centrifugal force of the blade and most of the bending moments, is carried out using a thrust roller bearing 50. The running tracks of the rollers of this bearing are the surfaces of the end of the nut 49 and the ring 51 installed in the housing 52 of the axial hinge. The cavity of the axial hinge is sealed by rings 42 and 44, as well as by a rubber reinforced collar 43, which is installed in the bore of the nut 45 and secured against axial movement by a spring ring.
The housing 52 of the axial hinge is steel, hollow, and has a comb on the outside for attaching the blade. In the bore of the side boss of the housing, a blade rotation roller 28 is installed on double-row ball 27 and needle 29 bearings. The inner rings of bearings 27 and 29 are tightened on the shaft 28 with a nut through an internal spacer sleeve, the outer rings of these bearings are clamped through the outer spacer sleeve in the bore of the body boss with a cap nut 26. Two radial ball bearings are installed in the roller head, the cavity of which is closed at the ends of the roller head with washers and is connected to the cavity of bearings 27 and 29 by axial drilling in the roller. There is a grease nipple on the body boss for lubricating the roller bearings 28.
To ensure lubrication of the axial hinge bearings, an oil tank 22 is secured to the hinge body with a special bolt 21. The tank body is made of polyamide. On the body there is a control glass 23 made of plexiglass, which allows you to determine the presence of oil. Bolt 21 has axial and radial drillings connecting the cavities of the tank and the axial hinge. On the body of the tank there is a blind threaded hole with a plug 24 made of polyamide for filling the tank with oil.
The driver unit, which provides a change in the pitch of the tail rotor, consists of a slider 1, a driver 18 and rods 19 for rotating the blades. The driver is made of steel, its hub is pressed onto the slider 1, fixed with a pin and nut 14. The driver has three levers that end with forks for connecting to the rods 19. A grease nipple is installed on the driver hub for packing lubricant into the bearing cavity 16. The slider is made of alloy steel in the form of a hollow roller with external splines connecting it to the hub 3 bushings. A rubber reinforced cuff 17 and a double-row angular contact ball bearing 16 are installed in the bore of the slider head in its own body. The outer ring of the bearing, together with the collar of the cuff body, is fixed by a threaded cover 15. The cover has a limit pressure valve to prevent overfilling of the bearing cavity with lubricant. A steel sleeve is installed in the inner ring of bearing 16, which is mounted on the rod of the tail rotor pitch change mechanism and, together with the ring, is tightened on the toe of the rod with a nut. The nut is secured with a plate washer, compressing it from four diametrically opposite sides and additionally installing a cotter pin. The cuff of the bearing assembly prevents the grease from being knocked out of its working cavity. The part of the slider protruding from the hub 3 between the driver and the hub is covered with a protective rubber cover 13.
The blade rotation rod 19, adjustable in length, consists of a fork, a rod and an ear tip. The thrust rod has a shoulder with turnkey flats in the middle part and ends with threaded sections at both ends. A fork and an ear tip are screwed onto the rod, secured with locknuts. The thrust fork is connected by a bolt to the roller 28, and the eye tip to the lever of the driver 18. The connection of the latter to the driver is carried out using a spherical hinge bearing 20 installed in the hole of the thrust ear. An oiler is screwed into the head of the pin that tightens this unit, through which lubricant is supplied through the axial and radial drillings in the pin and the inner ring of the spherical bearing into the cavity of this bearing. The pin is held in place by a pin to prevent wear. The spherical joint is protected from dust and moisture by a rubber cover.
When changing the pitch of the tail rotor, the slider 1, moving in the bushings 2 and 12 in the axial direction and rotating together with the hub 3 through the driver 18 and rods 19, turns the blades to a certain setting angle, thereby achieving a change in the pitch of the tail rotor.
Blade.
The tail rotor blade is all-metal and has a rectangular shape in plan. The blade has no aerodynamic and geometric twist, i.e. the contours of the blade sections are formed by the NACA-23OM profile and the installation angles of the sections are constant across the span.
Blade (Fig.5.3.)
Rice. 5.3. Tail rotor blade
1- butt tip; 2- foam liner; 3- rubber liner; 4- spar; 5- threaded bushing; 6- bolt; 7- bracket; 8- pin; 9- cell block; 10- casing; 11- tail stringer; 12- end fairing; 13- screw; 14- plug; 15-end rib; 16,19- studs; 17- anchor nut; 18 balancing weights
consists of a spar 4, a tail section, a butt tip 1 and an end fairing 12.
Spar 4 is made of aluminum alloy AVT-1 and strengthened by cold hardening. The outer surface of the spar is mechanically processed to obtain the required contour and polished in the longitudinal direction.
The tail part of the blade is glued to the rear wall of the spar. The tail part consists of a honeycomb block 9, a casing 10, a tail stringer 11 and an end rib 15. The honeycomb block is made of aluminum foil 0.04 mm thick, the package of which is processed in accordance with the contour of the blade and stretched to form a honeycomb in the form of hexagons with a side of 5 mm. On the outside, the honeycomb block is covered with a covering made of two layers of fiberglass 0.3 mm thick. Stringer 11 is also made of two layers of fiberglass and glued from the outside along the tail part of the blade to the skin with the ends sealed flush. The end rib 15 is made of avial. The wall is glued to the outer end of the honeycomb block, and the shelves are glued to the casing of the tail section. At the butt of the blade, the connection of the tail section with the spar is reinforced with a duralumin bracket 7, glued to the spar and tightened with bolts 6.
In the butt part of the blade, a steel tip 1 with liner 2 is attached to the spar, intended for attaching the blade to the propeller hub. The tip has a comb with eyes and two cheeks, between which the blade spar is installed. The tip is attached to the spar with a pin 8 and eight bolts 6 screwed into threaded bushings 5.
The internal cavity of the spar is sealed. In the butt part, a rubber liner 3 is glued into the end of the spar, along the contour of which sealant is applied. At the end part of the spar there is a plug 14 installed and there are holes for plates 18 of balancing weights, which are secured to studs 16 and 19. At the end part of the blade there is an end rib 15, to which an end fairing 12 stamped from aluminum alloy is attached with screws 13 through anchor nuts 17 . To prevent abrasive wear, a stainless steel pad is glued to the front part of the fairing.
The tail rotor blade is equipped with an electric heating element, which is glued externally to the toe of the spar and is inscribed in the theoretical contour of the profile. The heater is protected from mechanical damage by a layer of rubber and a stainless steel frame.
Maintenance.
Maintenance of the tail rotor, as well as the main rotor, involves preserving the protective coatings of the hub and blades, their integrity and reliability of fastening, maintaining hinge moments in the hub joints, timely detection of defects and their elimination.
Ice, snow, and frost from the surface of the blades are removed with warm air from a ground heater with a temperature not exceeding 60 ° C, followed by wiping the surface dry. Dirt is removed with a clean soft cloth soaked in warm water with a 3% solution of technical soap. Oil stains are removed with a cloth soaked in nefras, followed by wiping with a clean, dry cloth.
The tail rotor is monitored for: the absence of mechanical damage, the reliability of the locking of detachable connections, the operation of the propeller hinges, and the condition of the blades. If cracks are found, the tail rotor bushing should be replaced. Nicks, scratches and scratches up to 0.2 mm deep are cleaned with sandpaper, polished and coated with colorless varnish. When the grease is knocked out from under the plugs of the screw hinges, the plugs are tightened or the sealing gaskets are replaced.
Surface nicks, scratches and corrosion deposits without the formation of shells on the blade eyes are removed with emery cloth, followed by polishing with GOI paste and coating with primer. Scuffs and scratches are allowed on the paint coating of the blade casing material without damaging the fiberglass, followed by cleaning, priming and painting.
Quality control of the gluing of the skin to the honeycomb core, spar, stringer and rib of the blade, as well as the anti-icing device of the blade to the spar, is carried out by tapping with a hammer and by touch, without removing the blade from the hub. The area 30 mm wide from the tail stringer is not subject to tapping testing.
Tail rotor blades that do not extend to the edge of the compartment with a total area of no more than 16 cm2 with a single gluing failure of no more than 4 cm2 are allowed for operation if the gluing of the tail compartment skin with the spar is broken. A violation of the gluing of the skin with honeycomb filling should not exceed a total area of 30 cm2 on each side of the compartment with a single violation of the gluing not exceeding 5 cm2. In both cases, the distance between two adjacent violations must be at least 50 mm.
Dents on the tail part of the blade are allowed up to 0.5 mm in depth if there are no more than three of them and no more than one up to 0.8 mm. The tail stringer deflection can be no more than 3 mm. Smooth dents up to 0.8 mm deep and scratches up to 0.4 mm with a length of no more than 25 mm are allowed on the ends.
When monitoring the anti-icing device of the blade, non-gluing between the heating pad and the spar, as well as swelling of the rubber, are not allowed.
Maintenance of the propeller hub involves periodically measuring the clearance of the rollers and forks of the propeller blade rotation levers. At the same time, the clearance of the lever shaft in the thrust plane and in the plane of rotation of the screw is checked, as well as the axial clearance of the thrust fork relative to the lever shaft.
In the first case, the propeller blades are set to the maximum angle (the right pedal is forward all the way). A special device is attached to the visual oil control tank in the axial joint
(Fig.5.4.),
Rice. 5.4. Installation of a device for measuring the backlash of the rollers and forks of the steering rotor blades:
1,2,4 - indicator position adjustment screws; 3- bracket;;5- indicator; 6- fixing screw; 7- bracket
fixed with screw 6 on the tank plug. The indicator leg 5 of the device with a tension of 0.6 mm is brought to the spherical surface (point A) of the blade rotation shaft and tightened with screws 1, 2, 4. The angle between the measurement plane and the indicator leg should be no more than 10°. By turning the scale, the indicator arrow is set to “0”. By applying force clockwise and counterclockwise to the axial hinge body, the extreme positions of the indicator arrow are fixed. Based on the sum of the indicator readings, the roller gap is determined, which should not exceed 0.45 mm.
In the second case, in a similar way, the indicator leg of the device with an interference of 0.6 mm is brought to the cheek (point B) of the blade rotation shaft, after which the indicator arrow is also set to 0. By rocking the shaft in the plane of rotation of the screw towards and away from the indicator, the extreme positions of the arrow are fixed , the total value of readings of which should not exceed 0.45 mm.
After this, check the clearance of the lever shafts in the plane of thrust and in the plane of rotation of the propeller of the other two blades. In both cases, if a gap of 0.43 mm is detected, the feasibility of further operation of the tail rotor hub is decided.
The axial clearance of the thrust fork relative to the shaft of the blade rotation lever is checked using the same device. To check, by moving the indicator in bracket 7 and bracket 3, install indicator leg 5 on the surface plane (point B) of the fork with a tightness of 0.6 mm. After tightening screws 1, 2, 4, set the indicator arrow to “0” and, rocking the fork in the plane of rotation of the screw towards and away from the indicator with maximum force, fix the extreme positions of the indicator arrow. The fork clearance is determined by subtracting the lever shaft clearance indicator in the plane of rotation of the screw from the total readings of the arrow. The resulting value is the fork gap and should not exceed 0.2 mm. The axial clearance of the rod forks of the other two axial hinges is checked in the same way. The question of the advisability of further operation of the bushing is decided if there is a gap of 0.18 mm.
A double-row ball bearing, which ensures the independence of the reciprocating movement of the rod from the rotational movement of the screw hub driver, is a highly loaded structural element. Therefore, when performing maintenance on the tail rotor hub, the axial clearance of this bearing is measured. To perform the work, you should unlock and unscrew the slider cover and remove the cotter pin of the gearbox rod nut. Screw the cover 5 into the threaded bore of the slider
(Fig.5.5.)
Rice. 5.5. Installation of a device for measuring the axial play of the tail rotor rod bearing:
1- indicator leg; 2- body of the device; 3.4 - fixing screw; 5- device cover
devices with a tightening torque of 4 kgf m. Install fixture 2 on the hexagon of the cover and secure it with screws 4, and place an indicator in the bore of the fixture and, creating a tension of 0.4...0.5 mm, secure it with screw 3. After installing the indicator, move its leg 1 in the direction opposite to the indicator , and set the indicator arrow to position 0. Move the foot control pedals to the right and then to the left and record the indicator readings, the sum of which forms the gap value, which should not exceed 0.08 mm. With a gap of 0.06 mm, additional attention is required and a decision on the further operation of the screw is required. After checking, you should dismantle the device, install the rod nut cotter pin and tighten the slider cover with a torque of (8 + 2) kgf m, lock it and spray CIATIM-201 lubricant into the bearing cavity.
When checking the tightening torque of the nuts securing the tail rotor hub to the tail gear flange, use a calibration wrench. The nuts are tightened in cross alternation with a torque of 6...10 kgf m.
In the axial hinges of the tail rotor hub, at a positive temperature or when it briefly drops to -10° C, MS-20 oil is used, and in winter, at temperatures from 5 to -50° C, VNII NP-25 oil is used. To control the oil level, each of the blades is installed vertically downwards and the oil level in the axial joint is checked using control cups, which should not be lower than the control line marked on the cup and not higher than 15 mm from its upper edge.
If necessary, refill or replace the oil in the axle joints. When refueling, the blade is set to the rear horizontal position, and the left pedal is moved forward to extend the rod with the slider. Remove the plugs 1 on the axial hinge body and control cup (Fig.5.6.)
Rice. 5.6. Filling oil into the axle joint inside the tail rotor:
1- axial hinge plug; 2- balloon; 3- cap of the cylinder ventilation tube; 4- axial joint tank plug
and 4, and a device is installed in the housing hole, from the cylinder 2 of which the hinge is refilled with oil. After this, the blade is turned to; 15...20° up, the device is moved into the hole of the cup and oil is added to its upper level. When changing the oil in the axial hinge, the blade is set 10...15° above the horizontal position towards the fuselage. A container is hung on the axial joint body and plugs 1 and 4 are turned out to drain the oil from the joint. To fill the hinge, the blade is set in a horizontal position. In this case, the shaft of the blade rotation lever should be in the upper position.
Install the cylinder 2 of the device filled with clean oil into the threaded hole of the hinge body, having first removed the cap 3 of the ventilation tube from it. Unscrew the tank plug to vent the joint cavity and fill the joint with oil by completely draining the latter from the device’s cylinder. To speed up the filling of the joint, oil is compressed by the walls of the polyethylene container of the device while simultaneously closing its ventilation tube. After completely filling the joint with oil, check the oil level in the control cups of the tank. In a similar way, replace the oil in other axial joints.
The cardan joint, bearings of the rod, driver and rollers of the axial joints, as well as the slider splines are lubricated with CIATIM-201 grease by injecting it with a lever-plunger syringe through the grease nipples of the bushing units.
General information.
Transmission (Fig._6.1.)
Rice. 6.1. Helicopter transmission
1- engines; 2- fan; 3- main gearbox; 4 - transmission tail shaft; 5- intermediate gearbox; 6-tail gearbox
designed to transfer engine power to the main and tail rotors at the required rotation speeds corresponding to the most favorable operating conditions for the propellers.
The main transmission units are: main gearbox VR-8A, intermediate gearbox PR-8, tail gearbox XP-8, tail transmission shaft, main rotor brake and fan drive shaft 2.
Torque from engines 1 to the main gearbox 3 is transmitted through its two freewheels, which automatically disconnect one or both engines from the gearbox in cases where the rotation speed of the free turbines decreases or the engines (engine) stop. This is necessary to ensure that the main rotor switches to self-rotation mode for the purpose of landing the helicopter. The main gearbox transmits torque to the main rotor and units mounted on the gearbox.
The transmission of torque to the tail rotor is carried out by the tail shaft 4 of the transmission through the intermediate 5 and tail 6 gearboxes.
Main gearbox VR-8A.
The main gearbox is designed to transmit torque from the engines to the helicopter's main rotor, as well as to drive units mounted on the gearbox.
Reducing the rotation speed in the main gearbox is achieved by using three reduction stages.
The first stage consists of two driving cylindrical helical wheels, which are driven into rotation by the engines and are meshed with a third, common driven gear. The second reduction stage consists of two bevel gears with spiral teeth. The third stage of reduction is made according to the scheme of a closed differential mechanism, consisting of a differential and a closing differential circuit.
The main gearbox provides drive for a number of units, the operation of which is possible even in the event of a power plant failure. The kinematic diagram of the gearbox is shown in Fig._6.2.
Rice. 6.2. Kinematic diagram of the gearbox:
a - generator drive SGO-ZOU-4; b, d - drives of revolution counter sensors; c, l - drives of hydraulic pumps NSh-39M; d - drives from engines; e - freewheels; g - fan drive; ;z - main rotor drive; and - tail rotor drive; j - compressor drive AK-50TZ; m - oil unit drive; c-spare drive; 1-3 - generator drive gears; 4-9, 31-34 - gear wheels of unit drives installed on the left side of the gearbox; 10, 11, 16-toothed wheels of the first reduction stage; 12-15 - fan drive gears; 17 - differential driven gear; 18 - satellite; 19 - double gear; 20 - intermediate gear of the differential closing circuit; 21, 36 - gears of the II stage of reduction; 22, 35 - gear wheels of the tail rotor drive; 23-29 - gear wheels for driving units installed on the right side of the gearbox; 30-drive gear wheel for driving units; 37 - lower Nenets double gear; 38-drive differential gear
The main gearbox is installed on the ceiling panel of the helicopter fuselage and secured to the power frame units using a frame.
Gearbox (Fig._6.3.)
Rice. 6.3. Longitudinal section of the VR-8A gearbox:
1, 2 - driving gears of the second and first stages; 3, 5 - driven and drive shafts of the freewheel; 4 - separator with rollers; 6 - bearing housing; 7-spline bushing; 8 - spherical heel; 9-fan drive spring; 10, 13 - driving and driven gears of the fan drive; 11 - intermediate wheels of the fan drive; 12- fan drive cover; 14 - splined drive flange; 15 - front housing cover; 16, 29 - driven gears of stages I and II; 17 - gear housing; 18 - main rotor shaft housing; 19 - bell-shaped gear; 20, 45 - upper and lower rims of the double gear; 21 - satellite housing; 22 main rotor shaft; 23 - oil transfer pipe; 24 - cover; 25 - differential drive gear; 26 - satellite; 27-oil system manifolds; 28-idler gears; 30 - vertical shaft; 31 - tail rotor drive housing; 32 - driven gear wheel of the tail rotor drive; 33-spline drive flange; 34 - labyrinth seal housing; 35 - drive gear wheel of the tail rotor drive; 36- drive gear wheel of unit drives; 37 - mesh filter; 38 - gearbox tray; 39 - oil pipeline; 40- magnetic plug; 41, 42 - lower and upper oil transfer bushings; 43- spline bushing; 44 - housing of intermediate gears; 46 - double gear support
consists of the following main components: a crankcase, two freewheels, a main rotor shaft drive, a main rotor shaft, a tail rotor drive and accessory drives.
The gearbox housing is a power element that transmits aerodynamic forces from the main rotor to the fuselage.
The crankcase is cast from magnesium alloy. It consists of a gearbox housing 17, a main rotor shaft 22 housing 18 and a gearbox tray 38.
The gearbox housing 17 in the upper part has an external power belt with five flanges for fastening the sub-gear frame and a flange with studs for connecting to the housing 18 of the main rotor shaft 22.
Inside the gearbox housing there is a cylindrical bore with a flange for installing the lower half of the housing of 44 intermediate gears and a vertical wall with a bore for the rear roller bearing of the bevel gear shaft 1.
In the cylindrical bores of the front bosses of the housing there is installed a housing of bearings for the shaft of bevel gear 1 of the second stage and roller bearings of the driven shafts of freewheels.
The housing of gear wheels 2 and 16 of the first stage and freewheels, as well as the fan drive cover 12 are attached to the front shaped flange of the gearbox housing. A fitting for installing an oil pressure sensor is screwed into the side surface of the housing.
In the lower part of the gearbox housing there is a horizontal wall, into the central bore of which a race of roller and ball bearings of the vertical shaft 30 is pressed. In addition, the bearing cups of the bevel gear shafts of the unit drives are installed in the bores of the horizontal wall. The gearbox tray 38 is attached to the flange of the lower part of the housing.
At the rear of the gear housing boss there is a cylindrical bore for installing the tail rotor drive housing 31. There are flanges on both sides of the housing for attaching the side covers of the drives. In order to supply oil to lubricate the parts of the gearbox mechanism, channels with jets and nozzles are made in the walls of its housing.
The main rotor shaft housing 18 has a cylindrical bore and a flange in the upper part. A steel stepped race is pressed into the housing bore, into which a radial roller and angular contact ball bearing of the main rotor shaft are mounted. Holes are drilled on the body for the passage of bolts for fastening the support flange, which fixes the outer ring of the main rotor shaft ball bearing in the cage. The same bolts also secure cover 24 with an oil seal, covering the internal cavity of the crankcase from above. The conical reflector pressed onto the main rotor shaft together with the conical surface of the cover 24 forms a moisture-sealing labyrinth. Holes are drilled in the cover to allow passage of the swashplate guide mounting bolts.
At the rear of the main rotor shaft housing there are flanges for attaching the hydraulic booster bracket and the general swashplate lever bracket.
In the lower part, the main rotor shaft housing has a flange for connection with the gearbox housing. A breather is screwed into the side hole of the housing, connecting the internal cavity of the gearbox housing with the atmosphere.
The gearbox pan 38, which is also an oil tank, is installed in the lower part of the gearbox. The pan is cast from magnesium alloy, in the upper part it has a flange for fastening to the gearbox housing and an internal flange for installing mesh 37.
Inside the pan, a shaped wall with holes is cast, separating the cavity with heated oil draining from the gearbox housing from the cavity of cold oil. The pan has a number of bosses with channels for oil passage and a well for installing an oil filter.
An oil transfer bushing 41 is pressed into the central hole of the pan, into the grooves of which two oil pipes 39 are sealed. In the wall of the oil transfer bushing 41 there are holes for the passage of oil from the annular groove of the central hole of the pan into the annular cavity of the oil pipe. At the bottom of the pan there is a flange for attaching the gearbox oil unit.
A well is cast in the front part of the pan, into which a fine oil filter is installed. On the right side of the pan there is a flange for attaching the filler neck. A mesh filter and a lid are installed in the neck, held in the closed position by a traverse. To monitor the oil level in the gearbox, an oil level glass is installed on the filler neck. In addition, the pallet has a flange with a hole for fastening the oil supply pipe from the radiators and two threaded holes for installing oil temperature sensors. Three magnetic plugs 40 are located in the holes on the side surface of the pan, designed to catch metal particles entering the oil.
The main rotor shaft drive consists of freewheels, a cylindrical gear of the 1st stage, a bevel gear of the 2nd stage and a differential-closed gear of the 3rd stage of the gearbox.
The design of the main gearbox includes two freewheels, each of which consists of a sleeve 7, a drive shaft 5, a separator with rollers 4, a driven shaft 3, a housing 6 and oil sealing parts.
The freewheel mechanisms are assembled in the bores of the front cover 15, attached to the crankcase body. At the front, two housings of 6 ball bearings for the clutch drive shafts are attached to the cover.
The drive shaft 5 of the freewheel is made of steel, of variable cross-section, and is supported by two bearings: a ball bearing installed in the bore of the housing 6, and a roller installed inside the driven shaft 3 of the freewheel. In the front part of the drive shaft 5, splines are cut for installing a sleeve 7, which, together with the oil transfer ring and the inner ring of the ball bearing, is fixed to the drive shaft. To prevent oil from being knocked out of the coupling cavity, a sealing unit is mounted on the hub of the splined sleeve 7. The middle part of the drive shaft is a sprocket with 16 pads, which have a special profile with a cemented surface for the steel cylindrical rollers of the separator 4.
The freewheel separator is designed to simultaneously engage all rollers. The separator is mounted on the drive shaft sprocket and can move in the axial direction within small limits between split retaining rings installed in grooves on the cylindrical surface of the sprocket. At the rear of the separator there are projections that fit into grooves on the cylindrical surface of the drive shaft sprocket. This joint is used to limit the travel of the rollers with the cage when the freewheel is turned off.
Driven shaft 3 is steel, hollow, of variable cross-section. It is mounted on two bearings: angular contact ball and radial roller. The front part of the driven shaft is deployed into a cage having an internal cylindrical bore.
Bushing 7 is designed to connect the spring of the main engine drive to the drive shaft of the freewheel. It is made of alloy steel and has external spherical cemented splines in the front part, which are connected when articulated with mating internal splines of the engine spring.
To eliminate longitudinal vibrations of the drive spring, a spring is installed inside the cup, pressed into the bore of the clutch drive shaft from the outside, pressing the spring towards the engine through the heel 8.
The freewheel is turned on and off automatically depending on the rotation speed of the drive and driven shafts. When the drive shaft rotates, the rollers jam between the working surfaces of the drive shaft sprocket and the driven shaft race. In this case, the drive and driven shafts of the clutch begin to rotate at the same speed (clutch engagement). When the rotation speed of the drive shaft begins to decrease (which characterizes a decrease in engine speed), and the driven shaft, due to the inertia of rotation of the propellers and transmission, continues to rotate and overtake the drive shaft, the rollers will come out of the jam and will be installed in the cavities of the drive shaft sprocket (clutch disengagement).
From the driven shafts of the freewheels, the power of both engines is transmitted through the drive gears of the 2nd stage of the first reduction to the common driven gear 16.
The 1st stage cylindrical gear consists of two driving gears 2 and a driven gear 16.
The drive gear 2 has a cylindrical rim with external teeth and a hub with internal splines for mounting on the driven shaft of the freewheel. The driven wheel 16 consists of a gear and a support disk, which with its hub is pressed onto the hub of the gear and bolted to it. The support disk increases the rigidity of the driven gear while keeping its weight low. In the inner bore of the wheel hub there are splines for installing it on the shaft of the second stage bevel gear.
The driven gear 16 of the first reduction stage transmits the total torque from both engines to the shaft of the driving bevel gear of the 1st stage of the second reduction. Stage II of the gearbox consists of driving 1 and driven 29 bevel gears, as well as a vertical shaft 30.
The driving bevel gear 1 is made together with the shaft. It is mounted on three bearings: two radial roller and one angular contact ball. The inner ring of the rear roller bearing is secured with a nut on the wheel shaft, and the outer ring is installed in a cage pressed into the bore of the gearbox housing.
In the front part, the inner rings of the front shaft bearings with an adjusting ring between them are installed on the drive gear shaft, and on the splines there is a 16th stage I driven gear, secured with a nut. The outer rings of the front bearings of the gear shaft 1 are installed in a steel cage pressed into the cylindrical bore of the bearing housing. The outer ring of the roller bearing is pressed into the cage and secured against axial movement by a split retaining ring installed in the groove of the cage. The outer ring of the thrust ball bearing is installed in a cage with radial clearance and is secured against axial movement by a thrust flange mounted on the studs of the bearing housing. This installation of the ball bearing relieves it of the perception of radial loads, and the bearing perceives only axial loads acting on the gear shaft 1.
In the front part, inside the shaft of the drive gear 1, there is an internal collar, in the cylindrical bore of which involute splines are cut for installing the spring 9 of the fan drive.
The 29 stage II driven bevel gear is made of alloy steel and has a ring gear with case-hardened spiral teeth. In the wheel hub bore, involute splines are cut and there is a cylindrical cementing surface for installing the gear on a vertical shaft 30, which is made of alloy steel and has a diameter that varies along the length. The shaft rests on two roller and one angular contact ball bearings. The inner rings of the roller bearings are installed on the shaft, and the ball bearings are installed on the shank of the drive gear 36 of the unit drives. The outer ring of the upper roller bearing is installed in the central bore of the lower half of the gear housing and is secured against axial movement by a split lock ring. The outer rings of the lower shaft bearings are installed in one common steel cage, pressed into the central bore of the horizontal partition of the gearbox housing 17. The outer rings of roller and ball bearings are held against axial movement by a special flange attached to the partition studs from below.
On the outer surface of the upper part of the shaft 30 there is a thrust collar, a cylindrical part, a section with involute splines and a threaded section. The inner ring of the upper roller bearing is pressed onto the cylindrical part of the shaft, and a driven bevel gear 29 of stage II is installed on the splines; the parts are clamped on the shaft with a nut, tightened with screws screwed into the shaft 30 through the grooves of the nut.
Inside the upper part of the shaft 30 there is a cylindrical bore and internal involute splines. The outer ring of the lower roller bearing of the main rotor shaft 22 and the adapter spline sleeve 43 are installed in the cylindrical bore. A support ring is installed between them, limiting the lower position of the spline sleeve. The upward movement of the spline bushing is limited by a retaining ring installed in the boring groove of the upper part of the shaft 30. On the outside of the lower part of the shaft there is a shoulder, cylindrical and splined pads. The drive bevel gear 35 of the tail rotor drive is mounted on the upper splines of the shaft, which rests against the shaft shoulder through the adjusting ring. The ring provides the necessary adjustment of the gearing of the tail rotor drive. A thrust ring and an inner ring of the lower roller bearing are installed on the cylindrical section of the shaft. On the lower spline belt there is a drive gear 36 for unit drives, which carries the inner rings of an angular contact ball bearing on the cylindrical section of its shank. The parts installed on the lower part of the shaft 30 are tightened with a nut and secured against rotation with a plate lock.
The differential-closed transmission of the third stage of the gearbox consists of a driving spur gear, five satellites 26, a double gear, seven intermediate gears and a bell-shaped gear 19 with internal gearing. The leading link of the differential stage is a gear 25, which transmits torque to five satellites 26 installed on the housing 21, rigidly connected to the rotor shaft 22. From the satellites 26, part of the power is transmitted directly to the main rotor shaft 22, the other part of the power is transmitted from them through a double gear to seven intermediate gears, which rotate the bell-shaped gear 19 associated with the main rotor shaft 22.
The drive gear 25 of the differential stage of the gearbox is a steel hollow shaft, which has external involute splines in the lower part, and a cylindrical ring gear with cemented teeth in the upper part. With splines, it is connected to the gearbox shaft 30 through a splined bushing and is held from axial movement on one side by the inner shoulder of the bushing, and on the other by a support bushing installed in the bore of the splined bushing and secured with a special nut.
The differential satellite 26 is a steel spur gear with cemented external teeth. The satellites are installed in housing 21 on two radial roller bearings each. The ends of the satellite hub have slots to keep the special bolt that secures the satellite in the body from turning.
The satellite housing consists of two halves: upper and lower, connected to each other. Each half of the satellite housing is a steel disk with five cylindrical sockets for installing the outer rings of the satellite roller bearings. The upper half of the housing has a crown with internal splines for connection with the mating splines of the main rotor shaft and an external spline crown for installing a bell-shaped gear 19. In addition to the spline connection, the connection of the satellite housing 21 with the main rotor shaft 22 is carried out by two rows of special bolts.
The satellites are installed in housing 21 when its halves are installed. The inner rings of the roller bearings of the satellites are pressed onto the hubs of the satellites and secured with bolts, under the nuts of which steel support washers with end slots are placed. There are also end slots located on the inner end surface of the heads of the satellite mounting bolts. This allows you to rigidly fix the inner rings of the satellite bearings relative to their hubs.
The double gear consists of an upper gear 20 and a lower gear 45 connected by a support 46. The upper gear 20 is made of alloy steel and has an internal ring gear and a flange that connects the wheel to the support flange. The support is a disk, in the upper part of which there is a connecting flange for installing the upper gear 20, in the lower part there is a hub with a cylindrical bore in which splines are cut. The lower gear is hollow, in the upper part it has external splines with an annular groove, and in the lower part there is a cylindrical gear ring of external gearing. An outer ring of a radial ball bearing is installed in the inner cylindrical bore of the gear, which serves as a support for this gear. The inner ring of this bearing is clamped on the outer cylindrical surface of the splined sleeve 43 with a nut.
A double gear support is installed on the splines of the lower gear, which is secured against axial movement by plates that fit into the ring groove of the gear and are secured with screws to the inner flange of the support.
The connection of the support with the upper gear wheel 20 is carried out along their flanges with bolts.
The lower gear drives seven intermediate gears 28, which are similar in design to satellites.
The idler gear housing 44 consists of an upper and a lower half. In the lower half of the housing there are seven slots for installing the outer rings of the lower radial roller bearings of the intermediate gears 28 of the differential closing chain. The outer rings of the upper roller bearings of these gears are mounted in the bores of the upper half of the gear housing. Both halves of the gear housing are connected to each other by bolts, attached to the gearbox housing and receive that part of the reactive torque of the main rotor that occurs in the closing circuit of the differential.
The intermediate gears 28 are in mesh with the bell-shaped gear 19 of the differential closing circuit. The gear wheel is 19-steel, bell-shaped, in the lower part it has an internal gear ring, and in the upper part there is a hub with internal involute splines and an annular groove. The bell-shaped gear is mounted on the splines of the upper half of the satellite housing 21 and is secured against axial movement by a lock. This installation of the gear 19 allows it to self-center during gear operation.
The main rotor shaft 22 is steel, hollow, in the middle part it is turned into a disk with external splines for installing and fastening the body of the satellites 21. On the upper part of the shaft adjacent to the disk there is an external collar, a cylindrical belt and a thread. An adjusting ring, an inner composite ring of an angular contact ball bearing, an adjusting ring, an inner ring of a radial roller bearing and a nut screwed onto the shaft thread are sequentially installed on this section.
An angular contact ball bearing takes up axial and radial loads from the main rotor, and a roller bearing takes up radial loads, partially relieving the ball bearing of these loads.
On the toe of the shaft 22 there is a thrust collar, involute splines and threads intended for installation and fastening of the helicopter main rotor.
The conical lower part of the shaft ends with a shank, on the outer surface of which there is a thrust collar, a cylindrical part and threads necessary for mounting and fastening the inner ring of the roller bearing of the main rotor shaft.
An oil transfer pipe 23 is pressed and fixed into the cylindrical bore of the lower part of the main rotor shaft 22, which is centered in the shaft cavity by two cylindrical belts located at its ends. The sealing of the oil cavity formed by the walls of the pipe and the main rotor shaft is ensured by rubber rings installed in the annular grooves of the cylindrical belts of the pipe. Inside the lower end of pipe 23 there is a reinforced rubber cuff and an oil sealing sleeve, secured with a locking ring. From below, a steel oil bypass bushing is pressed into the shaft pipe and secured with a stopper, along the inner surface of which six cast iron oil sealing rings of the bypass oil sealing bushing of the oil line 39 operate. In the bypass oil sealing bushing of the oil line and the oil bypass bushing of the main rotor shaft pipe, radial and axial holes are provided for the passage of oil.
The tail rotor drive consists of a driving bevel gear 35, a driven bevel gear 32, a drive housing 31, tapered roller bearings, a spline flange 33 and a seal assembly.
The driving bevel gear 35 has internal splines on the hub, with which it is connected to the splines of the gearbox shaft 30 with pre-heating of the gear before connection.
The driven bevel gear 32 is made together with a hollow drive shaft. In the front part of the wheel there is a bevel gear ring of external gearing. The inner ring of a tapered roller bearing is pressed onto the cylindrical part of the roller adjacent to the ring gear disk and clamped onto the roller with a nut secured with a plate lock. On the shaft shank of the driven bevel gear there is an outer flange, a cylindrical part and a spline section. An adjusting ring, an inner ring of a tapered roller bearing, an oil deflector and a splined flange 33 are installed here, which are clamped on the shank with a nut screwed into the internal thread of the shank and locked with a plate lock. A duralumin plug is installed in the internal cavity of the roller.
The 33 spline flange has a square flange with four holes for attaching the transmission tail shaft and an oil threaded shank. Slots are cut on the inside of the flange.
The tail rotor drive housing 31 is cast from a magnesium alloy; its outer flange is mounted on the flange studs of the rear part of the gearbox housing 17. An adjusting ring is installed between the flanges of housings 17 and 31. The outer flange of the drive housing 31 has holes for mounting pins and holes with pressed-in bronze threaded bushings for the puller. At the rear end, studs are screwed into the drive housing to secure housing 34 of the labyrinth seal.
On the surface of the drive housing, two cylindrical belts are processed, with which the housing is centered in the bore of the gearbox housing. Between the drive housing and the inner surface of the gear housing bore, an annular oil cavity is formed with a nozzle installed in the drive housing.
Steel cages are pressed into the bores of the front and rear parts of the drive housing, into which the outer rings of the front and rear tapered roller bearings are installed and secured. Labyrinth seal housing 34 is secured to the drive housing on studs at the rear. The housing 34 has cylindrical bores: an oil deflector is installed in the front, the two rear ones in combination with the oil thread of the spline flange 33 form a two-stage labyrinth seal.
The fan is driven by four sequentially connected cylindrical external gears 10, 11 and 13, installed in the cavity formed by the front crankcase cover 15 and the cover 12.
All fan drive gears are made of alloy steel and have ring gears and pins with axial holes for lightening. Each gear is mounted on two radial roller bearings. The inner rings of the bearings are pressed onto the machined cylindrical sections of the gear journals, the outer rings are installed in steel cages pressed into the bores of the cover sockets 12 and 15.
The pinion of the drive gear has internal splines for connection with the splines of the spring 9. The driven gear has a shank for mounting a splined flange 14, which, together with the oil deflector and the inner ring of the front roller bearing, is fixed on the shank with a special nut. The outlet of the fan spline flange 14 is sealed with an oil deflector and a two-stage labyrinth seal.
The drives of the gearbox units are used to ensure the operation of the main helicopter systems in the event of engine failure.
On the accessory drive cover, located on the left side of the gearbox, two D-2 sensors for revolution counters and an NSh-39M hydraulic pump for the backup hydraulic system are installed. The alternating current generator SGO-ZOU-4 is mounted on a separate flange of the housing.
On the accessory drive cover, located on the right side of the gearbox, there are installed: an AK-50TZ air compressor, an NSh-39M hydraulic pump for the main hydraulic system and an additional drive.
The drive of the units installed on the gearbox housing is carried out from a central gear with external gearing, mounted on the splines of the vertical gearbox shaft.
Drive gear 1 (Fig.6.4.)
The unit drives are driven by two cylindrical gears 3 and 10, mounted on the splines of the bevel gears 7 and 8.
The cylindrical gear 3, through a pair of bevel gears 6 and 7, transmits rotation to the units installed on the left side of the gearbox, and the gear 10, through a pair of bevel gears 8 and 9, transmits rotation to the units installed on the right side of the gearbox.
The bevel gear 7 is cantilever mounted on tapered roller bearings in a steel cup 5. Between the inner rings of the bearings there is a spacer sleeve and an adjusting ring 4, by selecting the thickness of which the preload of the roller bearings is achieved. The installed parts on the gear shaft are tightened with a nut.
The shaft shank of the bevel gear 7 has external splines on which the splined sleeve 2 drives the gearbox oil unit is installed. The splined bushing is secured against axial movement by a split retaining ring. The steel cup 5 is made together with a flange, with which it is secured with studs in the bore of the horizontal partition of the gearbox housing. An adjusting ring is installed under the flange of the cup 5, by selecting the thickness of which the gap in the meshing of gears 6 and 7 is adjusted.
Between the wall of the cup and the inner surface of the bore of the horizontal wall of the gearbox housing, an annular channel is formed for the passage of oil to lubricate the drive parts.
The bevel gear 8 is structurally similar to the bevel gear 7 and is mounted on studs in the right bore of the horizontal partition of the gearbox housing.
Drives of left cover units 1 (Fig. 6.5.)
receive rotation from the bevel gear 2, on the splined shank of which the drive cylindrical wheel 10 is installed and secured with a nut. From it, rotation is transmitted to the gear wheel 9 of the hydraulic pump drive, from which, through the double gear wheel 5 and 8, the gear wheels b of the sensor drives are driven into rotation. revolution counters.
The bevel gear 2 is mounted on two tapered roller bearings, the outer rings of which are pressed into the bores of the cup 3, and the inner rings with a spacer sleeve between them, an adjusting ring and a gear 10 are tightened on the wheel shaft with a nut. Glass 3 gear 2 (see_fig._6.4.)
Rice. 6.4. Cross section of the lower part of the VR-8A gearbox
1- drive gear; 2- spline bushing; 3.10 - cylindrical gears; 4 - adjusting ring; 5- glass; 6,7,8,9- bevel gears
It is structurally made similar to glass 5, installed in the horizontal bore of the left side of the gearbox housing and secured on the outer side with studs.
Drive units of the left side of the gearbox (see_fig._6.5.)
Rice. 6.5. Drive units of the left gearbox cover:
1 - drive cover; 2, 5, 6, 8, 9, 10 - drive gears; 3, 12, 16 - glasses; 4. 13, 19 - adjusting rings; 7-pin; 11, 14, 15-tooth generator drive rings; 17-labyrinth seal housing; 18 - generator mounting clamp
are closed with cover 1, cast from magnesium alloy and mounted on the studs of the gearbox housing. The cover has three flanges with studs for fastening the units.
The gear wheel 9 of the hydraulic pump drive is made together with a hollow roller, which is installed in the bores of the housing and cover on two ball bearings. On the output part of the roller, slots are cut for coupling with the unit roller. The hydraulic pump drive outlet through cover 1 of the left side drives has a two-stage labyrinth seal. The output parts of the drive rollers of the revolution counter sensors inside have square-section holes for coupling with the rollers of the revolution counter sensors. The sealing of the output parts of the rollers is made as an end seal, which includes a housing with sealing rings, a sealing sleeve with a spring and an oil seal.
The bushing design is five-blade, with spaced and rotated horizontal hinges, with spaced vertical hinges, with axial hinges.
The design of the bushing is made in such a way that when the blade flaps relative to the horizontal hinge at an angle Y the true angle of installation of the blade decreases by the amount Z = KY . Proportionality factor K called the swing compensator coefficient.
In order to reduce the overhang of the blades and create the necessary gaps between the blades and the tail boom at low rotor speeds, centrifugal blade overhang limiters were introduced into the hub design.
Rice. 3.4. Main rotor hub diagram
The bushing diagram is shown in Fig. 3.4. The figure shows:
1 gear shaft; 2 Bottom ring; 3 Bush body; 4 Top ring; 5 Nut; 6 Splines; 7 Vertical hinge pin; 8 Axial joint housing; 9 Axle joint pin; 10 Blade reversal thrust; 11 Horizontal hinge pin; 12 Eyelet; 13 Bracket; 14 Vertical hinge damper; 15 Damper mounting bracket; 16 Blade rotation lever.
lgsh – Spacing of horizontal hinges;
lvsh– Spacing of vertical hinges;
A– The point of attachment of the swashplate rod to the axle hinge arm;
Q– Aerodynamic force;
R– Resultant force;
Ftsb- Centrifugal force.
Basic technical data of the bushing:
§ vertical hinge spacing 507mm;
§ displacement of the middle of the horizontal hinge eye is 45mm;
§ the value of the swing compensator coefficient is 0.5;
§ upward swing angle from the plane perpendicular to the axis of rotation relative to the main shaft 24.5-25.5 0;
§ angle of overhang down from the plane perpendicular to the axis of rotation relative to the main shaft:
When focusing on the bracket 3 0 40¢-4 0 10¢;
When focusing on the pawl, DSP 1 0 40¢-2 0 .
§ angle of rotation relative to the vertical hinge:
By rotation 12 0 15¢-13 0 15 ¢;
Anti-rotation 10 0 50¢-11 0 10¢.
§ NV rotation speed at which the centrifugal overhang limiter (DSO) is activated:
When accelerating 105-111 rpm (52-55%);
When braking 92-98 rpm (45.5-48.5%).
§ angle of inclination of the NV axis (forward) 4 0 20¢-4 0 30¢;
§ diameter of the HB bushing is 1744 mm;
§ HB bushing weight 610 kg.
The main components of the main rotor hub are:
1. A bushing body having five lugs lying in the same plane at an angle of 72 0 to each other.
2. Five brackets, the lugs of which, in connection with the lugs of the bushing body, form horizontal hinges using pins and needle bearings.
3. Five axle hinge pins, which, in conjunction with the eyelets of the brackets, form vertical hinges.
4. Five axle joint housings mounted on the axle joint journals using bearings.
5. Blade rotation levers mounted on the axial hinge housings.
6. Centrifugal blade overhang limiters, mounted in the eyelets of the brackets.
7. Hydraulic dampers, which serve to dampen vibrations of the blades relative to the vertical hinges and are fed by hydraulic mixture from the compensation tank, the liquid level in which should be between the upper notch and the lower edge of the cap.
Note: The main rotor hubs of Mi-171 helicopters are equipped with axial hinges with a magnetic plug and an inspection cup. The oil in the joint should be transparent (the opposite wall of the cup is visible).
Fig.3.5. Main rotor hub hinges
1 – Filling hole of the axial hinge; 2 – Filling hole of the horizontal hinge; 3 – Filling hole of the vertical hinge.
Oil level in the bushing joints (from the edge of the filler holes):
v in horizontal hinges 30-40mm;
v in vertical hinges 25-35mm;
v in axial hinges 15-20mm.
During the flight day, it is allowed to reduce the oil level in the hinges:
v in horizontal hinges by 20mm;
v in vertical hinges by 20mm;
v in the axial hinges by 15mm.
Main parts of the main rotor hub
A. Building
The bushing body is articulated with the main gearbox shaft by splines 6 and secured to it with a nut 5 . The nut is tightened using a special calibration wrench. The body has five lugs 12 , lying in the same plane at an angle of 72° to each other.
B. Horizontal hinges
Five bushing staples 13 (Fig. 4.6) in connection with the housing lugs 12 using your fingers 11 and needle bearings form horizontal hinges. Displacement of the horizontal hinge lugs A, selected in such a way that in the main flight modes the resultant R aerodynamic Q and centrifugal forces F cb the blades were directed approximately in the middle of the horizontal hinge. This design ensures a more uniform load distribution between the GS needle bearings and significantly increases their durability. The basic design of a horizontal hinge is shown in Fig. 4.7.
Fig.4.7. Horizontal main rotor hub joint
1 – Eyelet of the bushing body;
2 – Horizontal hinge pin;
3, 7 – Rubber sealing rings;
4 – Needle bearings;
5 – Bracket eyes;
6 – Spacer rings
B. Vertical hinges
Five axle joint journals 9 (Fig.4.6) in connection with the eyelets of the brackets 13 using your finger V form vertical hinges.
D. Axial hinges
There are five axial joint housings on the bushing 8 (Fig. 4.6), mounted on axles 9 .
The design of the axial hinge is shown in Fig. 4.8.
Fig.4.8. Main rotor hub axial hinge
1 – Trunnion of the axial hinge; 2 – Rubber sealing ring;
3, 9 – Thrust nuts; 4, 8 – Ball bearings; 5 – Filling plug; 6 – Hinge body; 7 – Roller bearing; 10 – Comb;
11, 12, 15 – Spacer bushings; 13 – Drain plug; 14 – Rubber cuff; 16 – Inspection cup; 17 – Pressure compensator in the joint; 18 - Plug
Axle joint housing 6 has the ability to rotate relative to the axle 1 on three bearings. Two ball bearings 4 And 8 perceive bending moments from the blade, and the roller 7 – centrifugal forces.
There is a “comb” on the bottom of the axial hinge cup 10 with eyes for attaching the blade. The hinge is equipped with a magnetic drain plug 13 with viewing glass 16 . The oil in the joint should be transparent (the opposite wall of the cup is visible).
To the filler plug 5 pressure compensator installed 17 , due to the deflection of the membrane, increasing its volume with increasing pressure in the hinge.
At present, in accordance with the design modification, during the manufacture of the bushing, a corrugated rubber “stocking” is installed into the hollow axle OS, which performs the function of a pressure compensator (Fig. 4.8a, item 17). The pressure compensator in the hinge (pos. 17, Fig. 4.8) is dismantled.
Fig.4.8a. Axial hinge of the modified main rotor hub
17 – Rubber stocking
D. Blade rotation levers
The blade rotation levers are mounted on the axial hinge housings and attached to the rods 6 (Fig. 4.1) swash plates.
Note: When performing targeted periodic inspections of the ITS blade rotation levers, use a seven-fold magnification magnifying glass.