| This
group represents the first major evolution from the sticks and string
era of flying. In pure form, the actuator comprises an hydraulic
ram with a mechanically controlled servo valve. Feedback within
the actuator is via a mechanical linkage of fixed geometry. The
purpose is to provide more force at the control surface than a human
pilot can provide. Two hydraulic systems are often required to achieve
the desired level of availability. Current examples include the
new Nimrod MR4A flight control PCUs and the AB139 Helicopter's main
and tail rotor actuators. |
