Control laws and the principle of automatic control system for managing the flight altitude

Automatic control of altitude in the general case related control device, ie simultaneous impact on the elevator and traction motors. However, if we assume that the flight speed is kept constant (eg, using AT), it can be considered a first approximation, the autonomous control system altitude with the elevator.

The automatic control altitude main signal in the control law will signal ACS deviation from a given height. However, the composition and structure of the signal control laws can be different depending on the type of aircraft and avionics capabilities.

Direct deflection of the elevator is piloting circuit ACS. In this case, the specified value for this circuit is formed by the trajectory path. If the controlled parameter aerobatic circuit uses the pitch angle, the laws of the formation of a given pitch can be:

;

;

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If the flight control law loop ACS with JOS

substitute the value of a given pitch in accordance with, for example, the expression, the deflection of the elevator can be represented by the relation

.

The resulting control law the main control signal in the loop stabilization height is the signal proportional to the height-keeping error. A signal proportional to the angle of pitch, provides vibration damping large longitudinal movement, and proportional to the angular velocity of the pitch - shock small longitudinal motion. Signals proportional to the derivative of the altitude and angle trajectory, enhance damping large longitudinal movement.

For maneuvering aircraft as a control parameter in the inner loop uses an overload (not pitch). In this case, the outer loop ACS generates a signal given excessive overload

Consider the dynamics of the output plane at a given height when using ACS.

Assume that the height of the airplane less than this. Then the elevator is deflected to pitch up in proportion to the mismatch. Longitudinal moment there that will cause the rotation of the aircraft to increase the angle of attack and pitch angle. As the angle of attack increases lift. As a result, the plane goes into a climb with the angle of inclination of the trajectory. As we approach a given altitude error signal is reduced, and the signal of the pitch increases. At some point, they will be equal. The elevator at this point will return to the neutral position. Upon further movement of the signal proportional to the angle of pitch, is more a signal proportional to the mismatch in height. The elevator is deflected by a dive. The angle of attack starts to decrease, there will be negative growth of lift, and the trajectory begins to curve downward.

Thus, in the absence of a signal proportional to the corner of the pitch, the return of the aircraft to the desired path is oscillatory.

In the ACS can be implemented as a pressure-stabilization modes and true (geometric) height. As a measure of the deviation of barometric altitude from the set, so-called proof-height KV - 11 KV - 16 or proofreader-height adjuster SGC. Measuring the true height by means of radio altimeters.

3.2. The dynamic properties of the system, " ACS - airplane" mode of stabilization altitude

The dynamic properties of the system, " ACS - the plane" is largely dependent on the control law implemented in the ACS. For definiteness, assume that the aerobatic circuit controls the pitch angle and trajectory - forms specified signal. We assume that the aerobatic circuit instantly fulfills predetermined pitch angle, ie always have the equality . Adopting this assumption due to the fact that the time control when managing pitch, usually on the order of magnitude smaller than in the management of the flight altitude.

For the analysis of the dynamic properties and the calculation of gear ratios to determine the transfer function . To derive the use of the following relationships:

;

;

;

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Block diagram corresponding to equation is shown in Fig.

Block diagram corresponds to the following transfer function

.

The analysis of the transfer function leads to the following conclusions:
- dynamic properties of the loop stabilization altitude above assumptions are described in the link of the second order;
- damping ratio is defined as the loop stabilization properties of its own aircraft and the gear ratio ;

- natural frequency of the circuit is determined by the speed of flight, the derivative of lift angle of attack and coefficient ;

- in the absence of external disturbances current height is given, that is, static error is absent.

For the calculation of transfer coefficients and you can use the default factors.