RU2471674C2 - Airborne vehicle aerodynamic focus control element - Google Patents

Abstract

FIELD: transport.

SUBSTANCE: invention relates to aerodynamic elements for stabilisation of airborne vehicles. Airborne vehicle aerodynamic focus control element includes airfoil fixed on shaft, steering machine and linkage for transmission of hinge moment from shaft to steering machine rod. The linkage transmits hinge moment generated by air foil to steering machine rod via one or more its members which are mechanical or pneumatic springs.

EFFECT: invention is focused on providing relation between mass centre position and aerodynamic focus position.

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Description

The invention relates to aerodynamic stabilization organs of aircraft (see the encyclopedia "Aviation", the scientific publishing house "Big Russian Encyclopedia", Central Aerohydrodynamic Institute named after Professor N.E. Zhukovsky, Moscow, 1994).

The closest in functionality to the prototypes are classic stabilizers and destabilizers. These aerodynamic surfaces are designed to provide a rational degree of longitudinal static stability, characterized by the distance between the position of the aerodynamic focus of the aircraft (LA) and the position of the center of mass of the aircraft.

An essential feature of the proposed solution, which coincides with the essential feature of the prototype, is the provision of the aerodynamic focus of the aircraft with respect to the center of mass of the aircraft rational in terms of stability and controllability of the aircraft.

The disadvantages of the prototypes include the lack of the ability to control the position of the aerodynamic focus depending on the current position of the center of mass and current flight conditions.

The technical result, the solution of which the invention is directed, is to ensure at each moment of flight the desired relationship between the position of the center of mass and the position of the aerodynamic focus.

The specified technical result is achieved through the use of effects of static aeroelasticity, for which the aerodynamic surface is made rotatable and provided with a shaft connected to the steering machine via a linkage. The lever mechanism that transfers the articulated moment from the shaft to the steering machine contains one or more links, which are mechanical or pneumatic springs. In this case, parallel mechanisms transmitting the articulated moment from the shaft to the drive bypassing the spring elements are absent. The focus position is controlled by moving the steering machine rod, which leads to a change in the tension or compression of the spring.

Distinctive features of the proposed control is that it is made in the form of a rotary aerodynamic surface connected by a linkage to the steering machine, and one or more links of the linkage are mechanical or pneumatic springs.

Let two identical aerodynamic surfaces (AP) be placed symmetrically to the right and to the left on board the aircraft. Figure 1 shows the left surface. Let in the initial position the axis of the rod 2, coinciding with the axis of the spring 4, passes through the axis 8 of the shaft 6, i.e. the mechanism is in a dead position. In this case, the movement of the stem of the steering machine 9 cannot cause the rotation of the AP, but only pulls or compresses the spring 4. Let also the axis of rotation 8 of the shaft 6 be located in front of the point of application of the resultant aerodynamic forces acting on the AP.

The case when the steering machine pulls a spring. With a positive angle of attack of the aircraft on the AP, a negative aerodynamic hinge moment will act, which tends to reduce the angle of attack of the AP relative to the flow. As a result, this angle will become smaller than the angle of attack of the aircraft. Obviously, the lifting force arising on the AP will be the greater, the greater the tensile force in the spring, but when the force in the spring decreases to zero, the AP will turn into a weather vane, and its lifting force will become zero. Thus, pulling the spring more or less, we change the bearing capacity of the AP from zero (weather vane) to a value that almost corresponds to the rigid attachment of the AP to the aircraft (maximum tension force). In this positive angle of attack of the aircraft will correspond to the positive lifting force of the AP. If at the same time the AP is located in front of the center of mass of the aircraft, it will be equivalent to a conventional destabilizer, the area of which is greater, the greater the spring tension, if the AP is located behind the center of mass, then it is equivalent to a conventional stabilizer, the area of which is greater, the greater the spring tension.

The case when the steering machine compresses the spring. If reducing the force of spring tension to go to the zero level and begin to compress it, then the picture will change as follows. With a compression force not exceeding a certain critical level, and with a zero angle of attack of the aircraft, the angle of deviation of the aircraft will be zero. When a positive angle of attack of an aircraft occurs under the influence of a negative aerodynamic articulated moment, the AP will turn by a negative angle. If the spring had not been compressed, the AP would move to the vane position and its rotation angle would be equal to the angle of attack with a minus sign. But the force compressing the spring will make the AP move further, so that the final angle of rotation of the AP will become larger in magnitude than the angle of attack. As a result, the AP will acquire a negative angle of rotation relative to the incoming flow, and the lifting force acting on the AP will become negative. If at the same time the aircraft is located in front of the center of mass, then the moment created by the aircraft relative to the center of mass will tend to reduce the angle of attack of the aircraft, and the aircraft will perform the same function as the classical stabilizer (aerodynamic surface rigidly attached to the fuselage behind the center of mass of the aircraft) . Note that the flight of the boom with the plumage in front can be stable, and with the plumage behind it unstable if the plumage is arranged as described above.

Thus, in the considered example, an increase in the spring tension shifts the focus of the aircraft forward if the aircraft is located in front of the center of mass of the aircraft, and shifts the focus of the aircraft back if the aircraft are located behind the center of mass of the aircraft. An increase in the compression force of the spring leads to the opposite effect. The change in the force in the spring is carried out by moving the actuator stem.

The ability to control the position of the aerodynamic focus during the flight using the proposed stabilization body is demonstrated by the following example of figure 2 and figure 3.

Figure 2 shows the initial state of one of the possible variants of the stabilization body under consideration. We assume that in this state there is no aerodynamic articulated moment, and the force transmission mechanism is in the dead position, i.e. the hinges O, A and B lie on one straight line (although in the figure the line of the OAB coincides with the axis of the aircraft, this is not necessary). We believe that the draft AB is made in the form of a spring, the stiffness coefficient of which is denoted by k. Obviously, in the absence of an aerodynamic articulated moment, any positive movement of the steering gear rod x _w (i.e., any leftward shift of the spring end B) will correspond to the same steering angle deviation δ ₀ (initial installation angle).

Now consider the situation corresponding to the deviation of the steering wheel under the action of the aerodynamic hinge moment M _W at an angle δ from the initial position (Fig.3).

We compose the equilibrium equation in a variational form:

.Here Π is the potential energy of the spring,

.

In turn, ΔL is the increment of the length of the spring having the length L in the undeformed state (i.e., in the undeformed state AB = L).

In this way,

Using the Pythagorean theorem, we write the relation

(L + ΔL) ² = (x _W + L + OA-OA · cosδ) ² + (OA · sinδ) ² ,

from which we get:

After simple operations, the equilibrium equation will take the form:

The resulting equation is non-linear with respect to angle δ. However, for practical geometrical dimensions and small angles δ (δ <0.3 rad.), It can be linearized with almost no loss of accuracy. It is easy to obtain the following linearized equation:

We assume that for the hinged moment, the following linearized dependence is valid on aerodynamic forces:

Here ρ, V are the air density and flight speed, respectively

S is the surface area of the turntable,

- производная коэффициента шарнирного момента

- derivative of the coefficient of articulated moment

aerodynamic surface deflection angle 5.

Above, for simplicity, we assumed that the hinge moment M _W0 corresponding to zero surface lifting force is zero (this corresponds to a symmetrical profile). We also assumed that the derivatives of the coefficient of the hinge moment with respect to α and δ are equal to each other.

Substituting (5) in (4) and resolving the resulting equation with respect to angle 5, we obtain:

- скоростной напор.Here

- speed head.

We now write the linearized expression for the lift acting on the steering surface:

и

одинаковы.This expression is also approximate since it is accepted that the derivatives of the lift coefficient

and

are the same.

Substituting (6) in (7), we arrive at the final expression for the lifting force of the steering surface:

We rewrite this expression as follows

Here

The value of S _{e will} be called the equivalent area of the aerodynamic surface under consideration.

, k), условий полета (q,

), а также от перемещения штока рулевой машинки х_Ш. Последнее обстоятельство позволяет путем изменения х_Ш управлять величиной эквивалентной площади в процессе полета, а, следовательно, и положением аэродинамического фокуса летательного аппарата.From formulas (9) and (10) it follows that the rotary surface we are considering creates the same lifting force as a rigidly fixed (non-rotatable) surface with an area of S _E = S _E (x _W ). As you can see, the value of the equivalent area depends on a number of design parameters (L, OA,

, k), flight conditions (q,

), as well as from the movement of the steering gear rod x _Ш. The latter circumstance makes it possible to control the value of the equivalent area during the flight, and, consequently, the position of the aerodynamic focus of the aircraft by changing x _W.

We draw attention to the fact that, in contrast to the usual area, the equivalent area can also take negative values. This means that under certain conditions, positive angles of attack of the aircraft cause a negative lift on the surface we are considering.

We list the goals that can be achieved using the proposed aerodynamic focus control.

1. Optimization of flight control conditions.

Knowing at each moment of the flight the position of the center of mass of the aircraft, the Mach number and the velocity head, by controlling the value of x _Ш, it is possible to achieve an optimal (from the point of view of solving control problems) mismatch between the position of the center of gravity of the aircraft and the position of its aerodynamic focus.

2. Minimizing the power of the drives used for flight control.

The control system of any aircraft performs two functions.

The first function is balancing the moments of all forces relative to the center of mass. The balancing is violated due to a change in the position of the center of mass (fuel consumption) and on the flight speed (Mach number), i.e. it depends on relatively slowly varying parameters.

The second function is operational management, i.e. control for the implementation of the given motion algorithms (trajectories) and parry of unforeseen disturbances. This management should have sufficient speed.

The traditional control system, the executive bodies of which are, for example, rotary stabilizers, performs both of these functions by the same control elements (in this case, rotary stabilizers). In this case, the articulated moment of the stabilizers, overcome by the steering machine, must meet the requirements of balancing, and the speed of rotation of the stabilizers - the requirements of operational control. Since power is the product of the articulated moment and angular velocity, the product of these quantities determines the required power of the drives.

When using the controls considered here, the balancing function can be performed precisely by these surfaces, and the required speed of movement of the rod of the corresponding drive is determined by the rates of change of centering, pressure head and Mach number. Since these speeds are small in a number of important cases, the required power of the respective drives can be small. Due to the fact that the balancing function from the steering surfaces used for operational control is now removed, their areas and the corresponding hinge points can be significantly reduced. Thus, the total required power of the drives of all the wheels will be less than with traditional control.

3. New features in the layout of aircraft.

At x _W values corresponding to negative values of the equivalent area, the control in question, being installed in front of the center of mass of the aircraft, acts as a stabilizer, and when placed behind the center of mass, it acts as a destabilizer. This paradoxical property may be useful in a number of cases.

Claims (1)

The control unit of the aerodynamic focus of the aircraft, including the aerodynamic surface mounted on the shaft, the steering machine and the lever mechanism for transmitting the articulated moment from the shaft to the steering machine rod, characterized in that the lever mechanism transfers the articulated moment created by the aerodynamic surface to the rod of the steering machine through one or several of its links, which are mechanical or pneumatic springs.

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