Aircraft elevator control

In the early days of flight, eontrol surfaees of aireraft were operated by eables eonneeted between the eontrol eolumn and the elevators and ailerons. Modern high-speed aireraft require power-assisted deviees, or servomeehanisms to provide the large forees neeessary to operate the eontrol surfaees. 

Hydraulie servomeehanisms have a good power/weight ratio, and are ideal for applieations that require large forees to be produeed by small and light deviees. 

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An aircraft has three controlling surfaces to regulate these three movements (see Figure 12-18). The elevators control the pitch of the aircraft. They are located in the horizontal tail section. The ailerons control the roll of the aircraft, whereas the rudder controls the aircraft s yaw from the vertical tail section. The other parts of a typical aircraft are the cockpit, wings, fuselage, tail section, and flaps. 

Longitudinal control of an aircraft is achieved by elevators and a horizontal stabiliser surface. The latter is positioned by a stabiliser trim control and actuation system. A main part of this system is a ballscrew actuator that is equipped with two hydraulic motors to rotate the ballscrew through a reduction gear. If the stabiliser is not moved, it is held in place by the actuator. To this end, an electro-mechanical, power-off engaged brake (POB) is mounted to each motor shaft. The brakes are engaged if the associated motor is shut off or if the system has to be stopped after a failure is detected. 

On the A3 80 and the subsequent aircraft, the final stage was reached the mechanical connection between the controller and the PHR cyhnder is removed. The ultimate rescue redundancy is similar to that of the A340-600, but it ensures the control of the rudder, a pair of elevators, and a pair of ailerons, on the basis of yoke side-stick and pedal orders. The technology is now analog. 

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