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What is the function of a flap load limiting (relief) protection system?
  • A
    To retract the flaps when exceeding the limiting speed of the currently selected flap position.
  • B
    To increase the aircraft`s angle of attack such that the limiting speed of the currently selected flap position is respected.
  • C
    To reduce flight deck workload by automatically selecting flaps.
  • D
    To increase the lift of the aeroplane.

Refer to figure.

There are numerous types of flap designs which increase lift and drag in varying amounts. For light aircraft the most popular type is the plain or camber flap. For large transport aircraft the most used is the slotted Fowler flaps. (see different types in the image in the annex)

In the cockpit there will be a selector where the pilot selects the desired flap setting, the input from this selector will be the input for the slat/flap control computers which control, test and monitor the operation of the flaps and slats. This computer’s output will be the input for an electrically controlled hydro-mechanical unit, a hydraulic motor, which drive the transmission which moves the flaps. The position of the flaps is measured with sensors and is indicated in the cockpit. The flaps are protected against asymmetric operation, runaway and over speed.

The flap load relief system, or load limiter will retract the flaps to an intermediate position when the airspeed exceeds a predetermined speed. Once the speed has decreased below this speed, the flaps will be automatically returned to the selected flap setting.

If the main hydraulic system fails, the emergency operation might be via an alternate hydraulic system or an electric motor which operates the same gear train as the normal operating system.

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