Q16-3. What type of pressure supplies the force
HYDRAULIC (POWER BOOST) FLIGHT
necessary to operate the control surface in a
CONTROL SYSTEM
full power-operated system?
Power-boosted flight control systems are used on
high-speed jet aircraft. Aircraft traveling at or near
PRIMARY FLIGHT CONTROL
supersonic speeds have such high airloads imposed
SYSTEMS
upon the primary control surfaces that it is impossible
LEARNING OBJECTIVE: Recognize the
for a pilot to control the aircraft without
functions of the three primary flight control
power-operated or power-boosted flight control
systems (longitudinal, lateral, and
systems. In the power-boosted system, a hydraulic
directional).
actuating cylinder is built into the control linkage to
Different aircraft manufacturers call units of the
assist the pilot in moving the control surface. The
primary flight control system by a variety of names.
power-boost cylinder is still used in the rudder control
The types and complexity of control mechanisms used
system of some high-performance aircraft; however,
depend on the size, speed, and mission of the aircraft.
the other primary control surfaces use the full
A small or low-speed aircraft may have cockpit
power-operated system. In the full power-operated
controls connected directly to the control surface by
system, the force necessary to operate the control
cables or pushrods. Some aircraft have both cable and a
surface is supplied by hydraulic pressure. Each
pushrod system. See figure 16-1. The force exerted by
movable surface is operated by a hydraulic actuator (or
the pilot is transferred through them to the control
surfaces. On large or high-performance aircraft, the
power control cylinder) built into the control linkage.
control surfaces have high pressure exerted on them by
Q16-1. What type of flight control provides additional
the airflow. It is difficult for the pilot to move the
lift during takeoff and landing?
controls manually. As a result, hydraulic actuators are
Q16-2. What type of flight control system is used on
used within the linkage to aid the pilot in moving the
high-speed jet aircraft?
control surface. Figure 16-2 shows a mechanically
Figure 16-2.--Hydraulically powered elevator control system.
16-2
