词汇与结构 The ailerons provide roll control around the airplane’s _________ axis. The ailerons are positioned by pilots’ control wheels.

which variable will be measured in the feedback control?______ will be measured in the feedback control.

DFCS can automatically operate the elevators and rudders to control the pitch and yaw of the aircraft.

Closed-loop control system is an automatic control system. Open-loop control system is not an automatic control system.

In many airplanes, the elevator is controlled by two cables: a “down” cable and an “up” cable. Normally, a break or disconnect in only one of these cables will not result in a total loss of elevator control. In most airplanes, a failed cable results in a partial loss of pitch control. In the failure of the “up” elevator cable the control yoke will move aft easily but produce no response. Forward yoke movement, however, beyond the neutral position produces a nose down attitude. Conversely, a failure of the “down” elevator cable, forward movement of the control yoke produces no effect. The pilot will, however, have partial control of pitch attitude with aft movement. When experiencing a loss of up-elevator control, the pilot can retain pitch control by: • Applying considerable nose-up trim. • Pushing the control yoke forward to attain and maintain desired attitude. • Increasing forward pressure to lower the nose and relaxing forward pressure to raise the nose. • Releasing forward pressure to flare for landing. When experiencing a loss of down-elevator control, the pilot can retain pitch control by: • Applying considerable nosedown trim. • Pulling the control yoke aft to attain and maintain attitude. • Releasing back pressure to lower the nose and increasing back pressure to raise the nose. • Increasing back pressure to flare for landing. Trim mechanisms can be useful in the event of an in-flight primary control failure. For example, if the linkage between the cockpit and the elevator fails in flight, leaving the elevator free to weathervane in the wind, the trim tab can be used to raise or lower the elevator, within limits. The trim tabs are not as effective as normal linkage control in conditions such as low airspeed, but they do have some positive effect — usually enough to bring about a safe landing. If an elevator becomes jammed, resulting in a total loss of elevator control movement, various combinations of power and flap extension offer a limited amount of pitch control. A successful landing under these conditions, however, is problematical.