The study of a regional airplane's emergency remote servo-control specifics in longitudinal channel

Dynamics, ballistics, movement control of flying vehicles


Аuthors

Terekhov R. I.

Central Aerohydrodynamic Institute named after N.E. Zhukovsky, TsAGI, 1, Zhukovsky str., Zhukovsky, Moscow Region, 140180, Russia

e-mail: corporal@mail.ru

Abstract

In this article servo-control means the principle when control levers are coupled with their control tabs rather than main control surfaces. Control tab is a small surface located in control surface tail section. Its deflection causes the hinge moment occurrence, which moves the control surface.

The purpose of the emergency servo-control consists in ensuring redundancy of a mixed flight control system. The study was conducted for regional aircraft with two independent hydraulic systems and two elevators for longitudinal adjustment and control. Two conventional electrohydraulic servoactuators (EHSA) provide each elevator deflection in the main control mode. Each elevator has a control tab with electro-mechanical actuator (EMA) for emergency control in case of both hydraulic systems failure, when all the EHSAs switch to damping mode.

The estimated value of control tab’s own hinge moment is significantly less than elevator’s hinge moment. Such small-sized EMA of low weight could be used to control tab deflection.

The description of elevator deflection dynamics includes the non-linear dependencies of both elevator’s and control tab’s hinge moments, damping force caused by EHSAs in damping mode, and elevator aerodynamic damping.

After the loss of hydraulic power, the elevators move under the hinge moment. It could result inthe exceeding the operational values of angle of attack or normal g-factor of the aircraft. For smooth and safe transition between control modes, the control tabs in main mode should be controlled so as the elevator hinge moment close to zero. Furthermore, such deflection of control tabs allows reduce the EHSAs load during the flight.

The handling quality of an aircraft being in servo-control mode depends on a considerable degree on the actuator damping coefficient. In the course of the study the acceptable range of actuator damping coefficient values necessary to provide the required handling qualities in emergency control mode has been determined. Flight simulator study with test pilots involved proved that aircraft handling qualities in servo-control mode ensured the safe flight continuation and landing.

Keywords:

longitudinal control channel, control tab, hinge moment, actuator damping coefficient

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