Hinge moment formula. Hinge moments of aircraft controls. Connecting the hydraulic booster using a reversible circuit
moment Msh, aerodynamic forces acting on the control element relative to its axis of rotation. In aerodynamic studies, the hinge moment coefficient (see Aerodynamic coefficients) msh is usually used, equal to
msh = Msh/(qSbA),
where q is the velocity pressure, S is the surface area of the control, bA is its MAC. Sh. m. occurs when the control element (OU) is deflected (characterized by the value of the derivative msh(δ) of the Sh. m. coefficient by the angle (δ) of the deflection of the op-amp) and when the angle of attack (α) changes (characterized by the derivative msh(α) of the Sh. m. coefficient m. by (α)). The dependences of msh(δ) and msh(α) on the angles (δ) and (α) are in the general case nonlinear, therefore an important characteristic is the maximum value of the msh in the considered range of angles of deflection of the op-amp and angles of attack. The noise level depends on the geometric characteristics of the op amp, flight modes, etc. When passing through the speed of sound, the noise level increases significantly. The value of the Sh. m. determines the force required to deflect the op-amp; a reduction in this effort is achieved by compensating for Sh. m.
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Moment- m. moment, moment, minute; | time, time, short urgent time. force, in mechanics: the product of force and a plumb line. - inertia, inertia, the force of body resistance to movement. alny,........
Dahl's Explanatory Dictionary
Articulated- hinged, articulated. 1. Adj. to a hinge, which is a hinge, arranged on hinges, using hinges. Hinges. Swivel joints. Hinge chain. mechanism.
Ushakov's Explanatory Dictionary
Moment- Favorable, important, profitable, main, long-awaited, dramatic, significant, historical, crisis, critical, culminating, intense, unforgettable,......
Dictionary of epithets
At the Moment Adv. Razg.- 1. Very quickly, immediately.
Explanatory Dictionary by Efremova
Articulated Adj.— 1. Correlative in meaning. with noun: a hinge connected with it. 2. Inherent to the hinge, characteristic of it. 3. Hinged, with hinges.
Explanatory Dictionary by Efremova
Moment- -A; m. [lat. momentum]
1. A very short period of time; moment, moment. Only one m has passed. Through m. find yourself somewhere. Lower your hand only to m. Moments of joy, pain, inspiration.
2.........
Kuznetsov's Explanatory Dictionary
Differentiation of the exchange rate at the time of opening— SPLIT OPENING A noticeable spread in stock prices at the opening of trading in the exchange session. This situation sometimes arises in cases where important information relating to a particular........
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Moment— - 1. specific, discrete point in time; very short period (
interval) time; 2. a separate side of a phenomenon.
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Moment of Import- date of acceptance by the customs authority of the customs declaration in relation to the cargo.
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Moment of Entry into Force— In reinsurance: certain
amount of funds for
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retention requirements........
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Moment of Fulfillment of the Seller’s Obligation to Transfer the Goods- seller's responsibility
hand over
the goods to the buyer are considered fulfilled: 1) in
the moment of delivery of the goods to the buyer, if the contract provides for an obligation........
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Moment of Shipment- - accounting
the date recording the shipment of the product to the buyer; when shipping products to a non-resident recipient - this is the date of delivery to the authority
transport or communications.........
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Moment of Transition- fixation
export and
import of goods by
the moment of crossing the border, the transfer of property from one hand to another, that is, the moment of transfer of property.
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Moment of Transition of Goods Across the Border— accounting
export and
imports are carried out according to
the moment they cross the state border. THE MOMENT OF TRANSITION OF GOODS ACROSS THE BORDER for export is considered: 1) for......
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Delivery time— - the date of delivery of the products to the carrier or communication authority, indicated by a stamp on the transportation document or document of the communication authority, the date of the acceptance certificate or receipt........
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Moment of Sale— - receipt of funds into bank accounts for goods, work or services, and for cash payments - the day the proceeds are received at the cash desk.
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Moment of Sale of Goods — -
the moment at which
goods shipped or released to the buyer are considered sold. From an accounting point of view
accounting moment of implementation is time........
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— -
point in time at which
products shipped to the buyer are considered sold (
shipment or
payment for products).
Establishment of M.r. products........
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At the time of opening— AT THE OPENING Refers to an order to a broker to buy a security at the `US.o.` price of the exchange. There is no price limit. However, if the order concerns a purchase or sale........
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Payment in Cash At the Time of Delivery— CASH ON DELIVERYA purchase made on the condition that
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time of delivery It is necessary to distinguish between such
terms of sale and conditions of cash sale,........
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Utility At a Time— TIME UTILITYUsefulness of a product or service at a certain moment
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Preacuisition Profit (profit at the time of acquisition)— The retained earnings of a company before it is acquired by another company. Profits at the time of acquisition are in principle not subject to distribution among the shareholders of the acquiring company........
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Moment— Borrowing from German, where Moment is from the Latin momentum, going back to the verb moveo - “I move.” Related words: mobile, furniture, etc.
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Moment of the Beginning of a Collective Labor Dispute- - the day of communication of the employer’s decision to reject all or part of the employees’ claims or failure to communicate by the employer in accordance with Article 4 of this Federal.........
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Moment of Transition— - recording the import and export of goods at the moment of transfer of property from one hand to another, crossing the border, that is, at the moment of transfer of property.
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Moment of State Succession- the date of replacement by the successor state of the predecessor state in bearing responsibility for international relations in relation to the territory that is the object......
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Moment of Realization, Moment of Sale— - the point in time at which the products shipped to the buyer are considered sold (shipment or payment for the products). Establishment of M.r. products are recorded in the accounting.........
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Moment of Actual Detention- the moment of actual deprivation of freedom of movement of a person suspected of committing a crime, carried out in the manner established by the Code of Criminal Procedure of the Russian Federation (clause 15 of Article 5 of the Code of Criminal Procedure of the Russian Federation).
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Torque— , rotating action of force. Thus, when the turbine turns the generator, it creates a torque along the axis of rotation. Power of a rotary engine, for example, a FOUR STROKE........
Magnetic Moment— , measurement of the force of a permanent magnet or current-carrying coil. It is the maximum turning force (turning torque) applied to a magnet, coil or electric........
Scientific and technical encyclopedic dictionary
Aerodynamic hinge moments are the moments of aerodynamic forces acting on the controls relative to their axes of rotation. A hinge moment is considered positive if it tends to deflect the rudders or ailerons in a positive direction.
Airplanes use reversible and irreversible control systems. For aircraft with a reversible control system, the entire hinge moment or a certain part of it is balanced by the efforts of the pilot applied to the control lever. In aircraft with an irreversible control system, the entire hinge moment is perceived by the steering gear (booster), which deflects the controls.
The hinge moment of any control element is equal to
where is the hinge moment coefficient;
Accordingly, the area and average aerodynamic chord of the control;
Flow braking coefficient in the tail area.
In modern aircraft, which have large control surfaces and fly at high speeds (velocity pressures), the hinge moments are large. The magnitude of the hinge moment can be reduced by reducing its coefficient using aerodynamic compensation of the controls. There are different types of aerodynamic compensation: axial, internal, servo compensation, trim compensation (Fig. 11).
 |
Rice. 11. Main types of aerodynamic compensation and trimmer operating diagram:
a - axial; b - internal; c - servo compensation; g - using a trimmer; 1 - axis of rotation; 2 - compensator; 3 - steering rod; 4 - trimmer; 5 - trimmer control rod
Axial compensation is most widespread due to its simplicity of design and sufficient efficiency (Fig. 11, a). In addition, it has virtually no effect on the effectiveness of controls.
When the axis of rotation shifts back from the leading edge, the part of the steering wheel located in front of the axis of rotation (compensator) creates a hinge moment of the opposite sign. This leads to a decrease in the total moment. If the axis of rotation is aligned with the center of pressure of the steering wheel, then the hinge moment will become equal to zero - full compensation will occur. With further displacement of the axis of rotation back, overcompensation will occur and the sign of the hinge moment will change.
During a long flight in any mode, it is desirable to reduce the hinge moment to zero. Trimmers are used for this purpose. The trimmer is an auxiliary surface mounted on the rear of the control and has independent control. To obtain a zero hinge moment, the trimmer is deflected at an appropriate angle in the direction opposite to the deflection of the control. (Fig. 11, d)
Rudders and ailerons
The controllability of an aircraft is assessed by the effort that the pilot applies to the control levers. The magnitude of these efforts depends not only
from the kinematic diagram of the control system,
but also on the magnitude of the aerodynamic moments
relative to the axis of rotation of the rudders and ailerons that arise when they are deflected.
The concept of a hinge moment. The hinge moment is the moment of the aerodynamic load of the steering wheel relative to its axis of rotation:
Distance c.d. steering wheel from the axis of rotation.
Rice. 7.2. Hinge moment
Hinge moments always counteract the deflection of the steering wheel, and therefore cause forces on the control levers, which are overcome by the pilot.
The hinge moment is considered positive,
if he tends to deflect the rudder (aileron) in a positive direction (elevator - down, rudder - to the right, right aileron - down).
The value of Msh depends on the shape and size of the rudders (ailerons) and their deflection angles. Airspeed
and density of the environment and is determined by the formula:
M w = m b q,
where m is the hinge moment coefficient;
S - rudder area in m;
b - average geometric chord of the rudder;
q = 
- velocity pressure in the rudder area in .
Modern high-speed aircraft, which have large controls and fly at high speed pressures,
the hinge moments are large.
Aerodynamic compensation of the rudders and ailerons serves to reduce the forces on the control levers by reducing the hinge moment.
The principle of any aerodynamic compensation is to bring the aerodynamic force that occurs when the steering wheel is deflected closer to the axis of rotation of the steering wheel.
The following types of aerodynamic compensation exist:
a) axial compensation;
b) horn compensation;
c) internal compensation;
d) servo compensation;
d) trimmer.
Axial compensation consists in the fact that the axis of rotation of the rudder (or aileron) is shifted back so that the area located in front of the axis of rotation is 25-28% of the area of the rudder. Compensation is created by a part of the steering wheel located in front of the axis of rotation.
Fig.7.3. Axial compensation
When the axis of rotation shifts back from the leading edge, the part of the steering wheel located in front of the axis of rotation (compensator) creates a hinge moment of the opposite sign. This will lead to a decrease in the total hinge moment (Fig. 7.3,a). If the axis of rotation is aligned with the center of pressure of the steering wheel, then the hinge moment will become equal to zero - the steering wheel will be completely compensated. With further displacement of the axis of rotation of the steering wheel back, a hinge moment of the opposite sign will appear. This unfavorable phenomenon is called steering overcompensation. In aircraft manufacturing practice, overcompensation is not allowed, because leads to reverse forces on the control levers.
Axial compensation is widely used due to its ease of design and good aerodynamic characteristics.
| Fig.7.3. Horny compensation |
On modern aircraft, horn compensation is used relatively rarely, because creates an uneven compensation effect along the steering wheel span
and at large angles of deflection of the steering wheel leads to separation of the flow from its surface, causing shaking.
Internal compensation, widely used on ailerons, is carried out using a soft hermetic partition (diaphragm). Articulated
the moment decreases due to the moment of forces acting on the compensator located in the cavity
with narrow slits inside the tail (wing).
Rice. 7.4. Internal compensation
The upper part of the cavity is hermetically separated from the lower flexible diaphragm. The compensator is not flown around by the air flow, but is under the influence of the pressure difference that occurs in the cavity when the rudder (aileron) is deflected. The advantage of internal compensation is that the compensator does not introduce any disturbances into the flow, which is especially important at large Mach numbers.
The disadvantage of such compensation is the limitation of the range of deflection of the controls,
especially with a thin tail (wing) profile.
Servo compensator- this is an additional rudder, kinematically connected to the main rudder and the fixed part of the tail. When the steering wheel is tilted
in one direction the servo compensator is deflected in the opposite direction, as a result of which aerodynamic forces act on the servo compensator, reducing the hinge moment of the steering wheel.
Aerodynamic compensation, if properly selected, reduces the hinge moment, but does not reduce it to zero.
During a long flight in any mode, it is advisable to reduce the hinge moment to zero. Trimmers are used for this purpose.
Trimmer- an auxiliary steering surface, which is installed at the rear of the steering wheel or aileron, not kinematically connected with the deflection of the steering wheel. The pilot controls the trimmer directly from the cockpit. The main purpose of the trimmer is to balance the aircraft.
| Rice. 7.5. Servo compensator Fig. 7.6.Trimmer |
To obtain a zero hinge moment, the trimmer is deflected by an appropriate angle, opposite in sign to the deflection angle of the main steering wheel.
You can also reduce the hinge moment of the elevator by deflecting (rearranging) the movable (adjustable) stabilizer.
Adjustable stabilizer, installable
in flight at a certain angle of attack, it allows, during long flights at a certain mode, to reduce the required deflection angles of the elevators. This
significantly reduces the effort exerted by the pilot on the control stick.
At high flight speeds, the magnitude of the hinge moment is significantly influenced by air compressibility.
When moving from subsonic to supersonic speeds, there is a significant increase in both hinge moments and forces on the control levers. Controlling an aircraft without the appropriate devices in the control system becomes impossible.
Devices that perceive sharply increased forces on the control levers are called hydraulic boosters or boosters. If there is a hydraulic booster - an auxiliary mechanism that controls the rudders, the pilot controls only this mechanism, which is much easier. How to control the steering wheels.
On large aircraft, power steering is
currently the only means that provides acceptable forces on the control levers.
Rice. 7.7. Types of aerodynamic compensation
| Rice. 6.13. Servo compensator |
1. What is called static controllability?
2. What is called dynamic controllability?
3. With a high or low degree of controllability, is the aircraft “strict” in controllability?
4. What is meant by degree of controllability?
5. What provides longitudinal control of an aircraft?
6. What is called longitudinal controllability?
7. Why does the airplane turn toward the bank when the ailerons are deflected?
8. What is necessary to prevent a roll from occurring when the aircraft turns?
9. When and why is differential aileron deflection used?
10. What is meant by differential aileron deflection?
11. List the controllability features of high-speed aircraft.
12. What is called equality of ailerons?
13. What is aerodynamic compensation of rudders and ailerons used for?
14. What is the controllability of an aircraft?
15. How can controllability be quantitatively characterized?
Do I call them aerodynamic hinge moments? moments of aerodynamic forces acting on controls relative to their axes of rotation.
A hinge moment is considered positive if it tends to deflect the steering wheel (aileron) in a positive direction.
For aircraft with a reversible control system, the forces applied by the pilot to the control levers depend on the magnitude of the hinge moments. In automatic or manual control with a steering drive (booster), hinge moments determine the power of the steering drive that deflects the controls.
Hinge moment of any control
Msh = otsh5pdrA0I7> (10.112)
where tsh is the hinge moment coefficient; Sp, bdr - respectively the area and average aerodynamic chord of the control; kon is the flow braking coefficient in the tail area.
In modern high-speed aircraft, which have large controls and fly at high speed pressures, the hinge moments are large. The magnitude of the hinge moment can be reduced by reducing the coefficient tsh using aerodynamic compensation. Let's consider the main types of aerodynamic compensation.
Axial compensation. When the axis of rotation shifts back from the leading edge, the part of the steering wheel located in front of the axis of rotation (compensator) creates a hinge moment of the opposite sign. This will lead to a decrease in the total hinge moment of the steering wheel (Fig. 10.19, a). If the axis of rotation is aligned with the center of pressure of the steering wheel, the hinge moment will become equal to zero - full compensation will occur. With further displacement of the axis of rotation back, overcompensation will occur and change - . the sign of the hinge moment appears.
Axial compensation is the most common due to the simplicity of its design and good aerodynamic characteristics, but it is complicated by the fact that the position of the center of pressure of the rudder depends on the Mach number of the flight.
Internal compensation is close in concept to axial compensation and is more often used on ailerons (see Fig. ‘10.19, b). The hinge moment is reduced due to the moment of forces acting on the compensator located in a cavity with narrow slots inside the wing (tail). The upper part of the cavity is hermetically separated from the lower flexible diaphragm. The compensator is not flown around by the air flow, but is under the influence of the pressure difference that occurs in the cavity when the aileron (rudder) is deflected. The compensator does not introduce disturbances into the flow, which is especially important at high Mach numbers. The disadvantage of such compensation is the limitation of the range of deflection of the controls, especially with a thin wing (tail) profile.
Servo compensator is an additional rudder kinematically connected to the main rudder and the fixed part of the tail so that when the main rudder is deflected at a certain angle, the servo compensator deviates by an angle proportional to it in the opposite direction (see Fig. 10.19, c). In this case, aerodynamic forces act on the servo compensator, reducing the hinge moment of the steering wheel.
On light subsonic aircraft, horn compensation is used, which is a part of the surface of the steering wheel, placed in front of the axis of rotation and located at the edge of the control surfaces. The disadvantage of such compensation is the possibility of shaking of the empennage due to flow disruption at large rudder deflection angles.
You can also reduce the hinge moment of the elevator by deflecting (rearranging) the movable stabilizer.
Aerodynamic compensation, if properly selected, reduces the hinge moment, but does not. reduces it to zero.
During a long flight in any mode, it is advisable to reduce the hinge moment to zero. Trimmers are used for this purpose.
The trimmer is an auxiliary surface on the rear of the rudder or aileron, not kinematically connected with the deflection of the rudder (see Fig. 10.19, d). The trimmer is controlled independently from the cockpit. ■ ‘
To obtain a zero hinge moment, the trimmer is deflected by an appropriate angle, opposite in sign to the deflection angle of the main steering wheel.
When determining hinge moments, the only reliable method is experimental.
The results of experimental data processing show that, within a smooth flow, the hinge moment coefficients are Linear functions of the angles of attack (slung), the angles of deflection of the rudders (ailerons) and the trimmer
Approximate calculation formulas for estimating derivative hinge moments during design are given in.
The value of the hinge moment coefficient is significantly influenced by air compressibility. With the onset of the wave
Rice. 10.20. Approximate dependence of the coefficient tsh on the number M
crisis, the center of pressure on the control surfaces moves backward and the hinge moment coefficient at transonic speeds increases sharply (Fig. 10.20),
We are all accustomed to associating the concept of “reliable support” with a hard surface. For a car, this is the earth. It couldn't be stronger. Anyone can try and feel. Air is an unreliable substance, but it is, so to speak, the habitat of a large army of heavier-than-air devices, airplanes and helicopters.
Airplane L-410. The elevator and rudder servo compensators are clearly visible.
And it is precisely this that provides them with great opportunities, making the stay of these metal birds hundreds and thousands of meters above the ground quite comfortable.
The specifics, of course, are different here, and although certain terms used for machines moving on a hard surface on 4 wheels sound the same for an airplane, that’s where the similarity, in general, ends.
Stability, controllability, balancing, alignment. You can’t do without all this and much more in the air. Moreover, all these things are often interconnected.
To reveal its capabilities, the aircraft uses aerodynamic surfaces.
All movement and orientation in the air is based on the action of various forces and moments, most of which are of an aerodynamic nature to one degree or another. These forces and the moments they generate are formed during the interaction of aerodynamic surfaces with the air flow.
Forces and moments, different in places of application and influence, can be divided into useful and harmful. No one doubts this :-), as does the fact that the basis for improving the aerodynamics of an aircraft is the need to increase everything that is useful and reduce what is harmful.
All this is done in various ways and in connection with this there is such a thing as compensation. That is, it is likely that some undesirable effect cannot be eliminated, but can be compensated, which is generally equivalent to its elimination.
What is so harmful that needs to be compensated for during an airplane flight? Yes, in general, there is enough of everything. But today we will dwell on the moment of aerodynamic forces, which, in my opinion, has a somewhat exotic name. This hinge moment. Its name does not seem to indicate a connection with aerodynamics, but in fact the connection is direct.
It's simple. Any control surface The aircraft is connected to the rest of the structure through a hinge. Deflecting during the control process, it experiences the action of an aerodynamic force, which, relative to the point of rotation of this surface (that is, the center of the hinge), precisely forms a moment, which, for obvious reasons, is called a hinge moment.
What does its magnitude depend on and what, exactly, is its harmfulness? Although it would probably be more correct to mention not only the harmfulness, but also the usefulness of the hinge moment. Therefore, let’s correct the question: what is its harm, and what is its benefit, if any?
About size.
The magnitude of the moment, as is known, is determined by the magnitude of the force and the leverage of this force. For our case, the magnitude of the aerodynamic force depends on the area control surface. And the shoulder is determined by its chord (the same as ), since the longer the chord, the farther the point of application of the force (that is, the center of pressure of the control surface) from the point of rotation (that is, the center of the hinge).
It is clear that with an increase in the geometric dimensions of the aircraft, requiring an increase in the required dimensions of the rudders, hinge moment also increases. It also increases with increasing angle of deflection of the control surface.
Scheme of the occurrence of a hinge moment.
In addition, the hinge moment increases with increasing . There are two reasons here. First is an increase in velocity pressure, causing an increase in aerodynamic force. Second the reason, which is more typical for high speeds, is due to the fact that during the transition from subsonic to supersonic speeds, the aerodynamic surfaces (including control ones) shift back (I mentioned this).
This displacement naturally causes an increase in the force application arm (relative to the hinge) and, ultimately, an increase in the value of the hinge moment. This value can be significant, so it’s time to remember the harm.
About the harm.
Hinge moment is certainly present, but on large aircraft or at high speeds (or both together) it can reach simply excessive values.
Since the generated force is transmitted to the elements of the control system, they certainly must have a certain strength in order to withstand all these loads. And an increase in strength very often means an increase in mass, which cannot be called a positive factor for any aircraft.
In addition, there is one link in the control system that, in general, cannot be strengthened or strengthened. This is the pilot, who perceives through the controls in the cockpit the effect of the hinge moment on the control surfaces.
Since the force created is transmitted through the elements of the control system to the aircraft control stick and pedals in the cockpit, when piloting the pilot will be forced to experience and overcome loads, sometimes very large, and under certain flight conditions (on the appropriate equipment, of course) may simply not be able to cope with control. Not enough muscle strength...
Unfortunately, it is common for a pilot, like any person, to get tired. Therefore, even if the values hinge moment not the table is grandiose, there is still almost always a need to reduce it, that is, partial or even full compensation, in order to relieve the pilot of unnecessary stress when piloting.
This most often means the presence of additional systems on the aircraft, that is, the same extra weight. Of course, it can be small, in the form of several small rods or electric actuators, but it can also be in the form of heavy hydraulic booster systems(more on this below), when the aircraft is forced to carry with it a set of massive booster blanks and a system for their maintenance. The harm is obvious :-). Well, what about the benefits?
Harmful and beneficial loads.
The flight mode of an aircraft in the general case can be either maneuverable, when the device performs any short-term evolutions in flight, or steady.
When an aircraft is in some steady flight mode for a long time, normal or abnormal (for example, in climbing or when the engine thrust is asymmetrical), then the pilot, depending on the conditions, is forced to apply some effort to the controls for just as long to maintain this mode (that is, the balance of the aircraft), thereby counteracting the hinge moment. These efforts are called balancing. They only tire the pilot, so it is advisable to get rid of them.
In maneuvering mode, the so-called maneuvering forces are applied. The nature of their occurrence is still the same, but the meaning is somewhat different. Of course, the pilot also gets tired of them, but you can’t get rid of them completely. Indeed, in accordance with this load, which the pilot feels on the control stick and pedals, he performs aerobatics. They allow him to judge the intensity of the maneuver, the overload and behavior of the aircraft.
This is exactly what it is benefit(albeit indirect) hinge moment.
Based on all this, various design solutions have been developed to combat hinge moment. The principle of their use largely depends on the nature of the loads that the pilot perceives through the control stick and pedals in the cockpit, that is, in general, on the flight mode.
Methods for compensating hinge moments.
First of all, we will talk about the so-called aerodynamic compensation.
Its essence lies in the beneficial use of the energy of the oncoming air flow. As a result of certain design decisions on the managers aerodynamic surfaces(rudders) conditions are created for the occurrence of a moment of forces of an aerodynamic nature, comparable in magnitude to the hinge moment, but directed in the opposite direction.
This newly arising moment partially or completely compensates for the hinged one, thereby removing unnecessary loads from the control stick and making piloting easier. The nature of its occurrence is similar to the nature of the occurrence of “our harmful” moment, and in essence it is exactly the same hinge moment, only arising in, so to speak, specially designated places.
Axial compensation.
This is one of the most common types of simple aerodynamic compensation. Distributed axial compensation due to its simplicity and effectiveness, and also due to the fact that it does not reduce the effectiveness of the steering wheel itself. Its essence is that the axis of rotation of the steering surface is shifted back, closer to it (that is, the point of application of the aerodynamic force). In this case, the hinge moment is reduced by reducing the leverage of this force.
Axial compensation.
Such compensation is also used on multi-mode aircraft (equipped with a hydraulic booster system) flying at both subsonic and supersonic speeds. It is necessary for optimal unloading of the control system and reducing the required power of the hydraulic boosters at all Mach numbers of flight, as well as to ensure the possibility of an emergency transition to manual control in the event of a failure of the hydraulic booster system. Axial compensation all-moving stabilizers such aircraft are often carried out with " overcompensation».
This means that at subsonic speeds, the point of application of the aerodynamic force (the center of pressure) when the stabilizer is deflected is in front of the axis of rotation and contributes to further deflection of the stabilizer to its extreme position (that is, it unloads it). At supersonic speeds, the point of application of the aerodynamic force moves backward beyond the axis of rotation. But, due to overcompensation at subsonic levels, the force shoulder at supersonic turns out to be small, which means the force remains small. hinge moment.
Horn compensation.
Another type of simplest aerodynamic compensation is horny compensation. It is usually implemented on the control surfaces of fins and stabilizers of low- and medium-speed aircraft.
In this embodiment, the control surface is equipped with a so-called horny compensator. It is a part of this surface (protrusion) located in front of its axis of rotation and profiled so that in the neutral position it forms the tip of the fin or stabilizer.
And when the steering surface deviates, it moves into the flow (a horn appears) and an aerodynamic force is formed on it, the moment of which relative to the axis of rotation of the steering surface is directed in the direction opposite to the direction of the hinge moment.
The principle of horn compensation.
A significant drawback of horn compensation, which has significantly reduced its use in modern aviation, is the deterioration of the flow conditions around aerodynamic surfaces when flying at high speeds and at large angles of deflection of the rudders at various angles of attack, which causes a noticeable increase in drag and the occurrence of structural vibrations.
To reduce this effect, horn compensation can be used in combination with axial compensation. They complement each other and make it possible to expand the range of their application for various flight modes, especially since in design terms both of these options have a certain similarity...
Internal compensation.
With this method, the toe of the control surface is placed in a chamber inside the load-bearing surface (wing), which is divided into two parts by a flexible impermeable partition (also called balancing panel), connected to the sock and to the wing structure. At the junction of the steering surface with the carrier, narrow gaps are left, connecting the internal cavities with the atmosphere.
When the steering wheel is deflected, a pressure area is formed on one of its surfaces, and a vacuum area is formed on the other. Both of these areas communicate with the internal cavities through the indicated slots, as a result of which the flexible partition bends in the corresponding direction, dragging the entire steering surface with it.
The principle of internal compensation.
That is, a moment is formed directed in the direction opposite to the hinge control moment. This type of compensation is usually used on ailerons on high-speed aircraft. There is no sock outlet here control surface into the flow, thereby not increasing drag. However, there may be design difficulties in implementing such compensation on thin profiles.
Servo compensation.
Subsonic single-mode aircraft use so-called servo compensators(from the concept servo-, that is, an automatic auxiliary device) or flettners (named after the inventor, German engineer Anton Flettner). Such compensators represent a small control surface, installed along the rear edge of the steering wheel.
Structurally, everything is designed in such a way that this surface automatically deflects in the direction opposite to the deflection of the steering wheel. The aerodynamic force created in this case on the shoulder up to the axis of rotation of the compensator balances partially or completely hinge moment steering wheel
Since this shoulder is relatively large, even with a small surface area and small angles of its deflection, the magnitude of the moment that it creates is sufficient to effectively compensate for the hinge moment of the steering surface. But at the same time servo compensator somewhat reduces the efficiency of the steering wheel, since it “takes away” part of its surface to form a compensatory moment.
Aerodynamic servo compensators according to the principle of their management are divided into two kinds.
First view- this is the so-called kinematic. In it, the control of the compensator surface is carried out using a rod connected to the stationary part of the bearing surface. That is, the greater the steering wheel deflection, the greater the deflection of the compensator surface. In this case, the pilot cannot influence the process from the cockpit, but in ground conditions the control rod can generally be adjusted to different deflection angles.
Scheme of operation of the kinematic servo compensator.
Another circuit for a kinematic servo compensator. 1 - control rod, 2 - control surface, 3 - compensator.
Second type- more advanced - it is spring servo compensator. In its design, the main link is a double-armed lever that rotates freely on the axis of rotation of the steering surface. One arm of this lever is sandwiched between springs that have a certain tension. The second is connected to the main control rod and the compensator surface control rod.
While the load on the steering surface ( hinge moment) are small, that is, they do not exceed the tightening value of the springs, the entire steering wheel structure rotates under the action of the main control rod as a whole and the steering wheel is deflected without deflecting the compensator.
Spring servo compensator.
But as soon as the hinge moment reaches a certain limit value, which is greater than the tightening of one of the springs, the double-arm lever begins to rotate, thereby deflecting the surface of the compensator. That is, the entire mechanism seems to turn on automatically, thereby reducing the effort required to deflect the steering wheel.
It turns out that servo compensator This design can be used in almost any flight mode, because it works proportionally to the forces acting in the control system, and not to the angles of deflection control surfaces.
Anti-servo compensator.
Apparently we should also mention the so-called anti-servo compensator, although the functions of this device are directly opposite to our topic. That is anti-servo compensator does not reduce hinge moment, but on the contrary increases it. The compensator itself deviates in the opposite direction for a conventional servo compensator. By analogy with “overcompensation,” we can say that “undercompensation” occurs :-).
The operating principle of the anti-servo compensator.
Design of the anti-servo compensator.
Anti-compensator on the stabilizer of the Piper Ra-28-140 Cherokee aircraft. Stabilizer toe down - anti-compensator up.
This device is usually used on light aircraft that are not equipped with a separate elevator. Its functions are performed by an all-moving stabilizer. This design makes the light aircraft quite sensitive to control, so the anti-servo compensator “heavies” the control, that is, it seems to improve the feedback from the stabilizer to the pilot so that he does not “overdo it” and does not use excessive movements of the control stick.
Trimming.
There is another method of aerodynamic compensation of the hinge moment. But it stands somewhat apart from the rest. The fact is that all the compensators just described work with maneuvering loads (I spoke about them above), and this one is used to compensate for balancing loads (this was also discussed :-)).
The method is called trimming (from trim, which literally means “to put in order”). and in general, with its help, balancing loads on the controls in the cockpit can be reduced to zero. In this case, the aircraft is considered completely streamed.
Diagram of the operating principle of the trimmer.
In traditional trimming systems, the active structural element with this method is trimmer(actually the compensation surface), and the design itself (as well as its aerodynamic effect) is in principle similar to the design of the kinematic servo compensator.
Another diagram of how the trimmer works. Here 2 is a trimmer, 1 is an electric trimmer control mechanism.
Elevator trim tab.
Only the trim has its own control system (usually mechanical or electromechanical) and can be deflected by the pilot from the cockpit, who in this case, at will, selects or changes the amount of compensation.
There are also so-called unmanaged trimmers. They can be used on low-speed aircraft and are usually installed on the ailerons and rudders. They are most often manually bent plates and are used in the presence of any aerodynamic asymmetry of the aircraft.
The principle of operation of a non-adjustable trimmer on an aircraft aileron.
Non-adjustable trimmer on the rudder of the L-29 aircraft.
Uncontrolled trimmer on the launch vehicle of a training aircraft.
Non-adjustable trimmer on the launch vehicle of a light-engine aircraft.
The same type of plate is installed on the blades. They work on the same principle and serve to eliminate the so-called mistaper of the blades during rotation, that is, so that the blades do not extend beyond the surface of the imaginary cone formed by the rotor blades during its rotation.
Non-adjustable trimmer on a helicopter blade.
Such trimmers They are also bent manually based on data from special sensors obtained during ground tests.
In addition to the traditional trimmer design, trimming with the help of controlled (or mobile) stabilizer, although this method can no longer be classified as aerodynamic compensation. The angle of installation of the stabilizer is changed using a special mechanism, controlled by the pilot from the cockpit and not requiring any effort from him.
The principle of rearranging the stabilizer.
Mutual movement of the stabilizer and elevator.
During the process of repositioning the stabilizer, the angle of the elevator also changes smoothly to maintain the balance of the aircraft. All this continues until the aerodynamic force that reappears on the stabilizer becomes equal to the force on the elevator that was there before the shift began. In this case, the force on the control handle in the cockpit becomes close to zero.
Other systems.
In general, the use of a controlled stabilizer makes it possible to reduce the size of the elevator and, accordingly, the required effort to move it. This method is quite effective over a wide range of alignments and speeds, while the stabilizer has less drag than with traditional trimmer.
However, the stabilizer repositioning system itself has more weight compared to conventional trimming. In addition, there is a need to strictly follow the rules and parameters for installing the stabilizer before takeoff in accordance with the alignment of the aircraft. Failure to comply with these rules is fraught with serious flight accidents.
Adjustable stabilizer for Embraer ERJ-190 aircraft.
In addition to the adjustable stabilizer, there are other systems in which the perceived loads are reduced by reducing the area control surfaces, but without reducing the efficiency of the control systems themselves as a whole.
First of all, this is the so-called servo steering wheel. In this design the main control surface, that is, the steering wheel itself is freely suspended on its hinge and is not connected to the control system controlled by the pilot. But at its end, an aerodynamic surface several times smaller in area (outwardly similar to trimmer), which is called servo steering wheel and which is precisely controlled by the pilot from the cockpit.
Servo steering diagram.
The servo steering wheel deflects in the direction opposite to the required deflection of the main steering wheel. The force that arises on it causes the freely suspended main rudder to deviate in the desired direction. This deflection will occur as long as the moment from the force is servo steering wheel won't balance hinge moment(the same harmful one that needs to be reduced) on the main steering wheel.
Such balance is possible due to the large difference in the arms of the forces acting on the steering wheel and servo steering wheel. In this case, the pilot on the control stick only feels the forces on the servo wheel, that is, very small, because he himself servo steering wheel has a small area.
The main disadvantages of control systems with a servo steering wheel are some delay in the deflection of the main steering wheel and the relative deterioration of its operation at low speeds.
Combined use of ailerons and aileron spoilers for lateral control.
Another example of using the same principle. This application aileron spoilers in the lateral control channel. These controls themselves are actuated by a separate system and do not affect the force on the aircraft control stick. But their parallel use with ailerons, in addition to a number of other positive aspects (a topic for another article :-)), allows one to reduce the area of the ailerons, and therefore the size hinge moment on them.
Using boosters in the control system.
As you can see, there are enough ways to compensate for the hinge moment. However, as mentioned earlier, its value increases with the size of the aircraft and its flight speed. Sooner or later, a moment may come when none of the existing compensation methods will be effective (especially for maneuverable loads).
To avoid this and increase the ability of a person to pilot an aircraft in various modes, on many modern high-speed (or large-sized) aircraft, hydraulic boosting is used in the control channels, the essence of which is that the pilot, by moving the control stick, affects only the movement of a small spool (servo valve), that is, a special control element in the automatic control system.
And this spool forms and exerts a control effect on a large hydraulic cylinder (booster), which is connected directly to the aircraft rudders.
However, to be more precise, according to the nature of the impact on this servo valve, hydraulic booster systems are divided into two kinds.
Scheme of a reversible type hydraulic amplification system.
First- these are the so-called reversible systems. The peculiarity of the principle of their operation (by the way, the same as in automobile power steering systems) is that in order to activate the entire system (starting with the spool-servo valve), it is necessary to apply some small initial force, which moves control surface together with the servo valve. Subsequently, the hydraulic boosters (boosters) come into full operation and the pilot uses the control in full.
The positive side of such a system is the fact that when using it, the pilot feels the same maneuvering loads on the handle and pedals in the form hinge moment. Not in full, of course, but this is enough for proper piloting. Its disadvantage is that at high speeds/sizes of the aircraft, the loads may increase so much that the pilot will no longer be able to make the initial shift to put the system into operation.
Scheme of a hydraulic amplification system of an irreversible type.
For such aircraft and flight modes there is second type hydraulic reinforcement systems - irreversible systems. When using such systems, there is completely no reverse effect of flight loads on the control stick, and the pilot does not feel even a small part of the loads that the control surface absorbs. All these loads are completely connected to the hydraulic booster.
But, as mentioned earlier, the pilot cannot be completely deprived of the sensations inherent in the entire control process. After all, with the help of these sensations he “feels” the plane, and without them this very control simply will not exist.
Therefore, on aircraft that use irreversible hydraulic boosters in control systems, special devices are used, included in the control wiring line, which simulate flight forces on the control stick and pedals. These are various mechanisms (spring) and hydraulic loading mechanisms, load control automatic machines.
Automatic control devices use data on the speed pressure obtained from total and static air pressure sensors, thereby creating a real picture corresponding to manual control.
They work together with the loading mechanisms and trimmer effect mechanisms, also simulating the operation of trimmers, as with completely manual control.
Helicopter trim mechanism.
The trimming effect mechanisms in this case are fundamentally similar to the trimming device on a helicopter. How to constructively perform it on a helicopter trimmers like airplanes is not possible, then unloading the helicopter control stick in the simplest case is performed using electromechanical spring unloading device.
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That's probably all. These are, in general, methods and technical solutions for limiting or eliminating the effect hinge moment in the aircraft control system. They all apply to one degree or another. Some often, some much less often, depending on the purpose and design of the aircraft and helicopter.
However, all technology, like control systems, is being improved quite quickly. Already now there is a tendency to transform the pilot (especially on modern airliners of the latest generation) from an actively piloting person to a passively controlling person :-), for which the computer thinks, and piloting is carried out by devices and automation systems subordinate to it, which include the trimming process is performed automatically.
Maybe... It’s possible... But, apparently not now... Not in the near future :-)....
In conclusion, some typical photographs on the topic, which I did not include in the text :) ...
Until next time.
Vought F4U Corsair aircraft.
The tail of a Vought F4U Corsair. Visible are the rudder and elevator servo compensators (external), and the elevator trimmer (internal). The rudders have axial compensation (certain structural similarity to horn compensation).
Operation of the LV and RV servo compensators on the Vought F4U Corsair aircraft.
Mechanical control wheel for the elevator trim of a Cessna-172 aircraft.
The cockpit of a Boeing 737 Classic. Wheels (steering wheels) for controlling the rearrangement of the stabilizer on the middle console.
Airbus 320-214 cockpit. The pitch trim controls are clearly visible (wheels with white marks).