In order to avoid the imposition of excessive acceleration in a direction parallel to the normal axis of an aircraft the control system for a power‐operated elevator 12 includes an artificial feel unit arranged to impose force on the pilot's control column 8 in response to such accelerations. In the arrangement shown in FIG. 1 an accelerometer 1 is placed with its axis parallel to the aircraft's normal axis, its output being fed to main and rate amplifiers 2, 21, respectively, controlling the output of a generator 3 driven by a separately excited motor 4, the generator driving a torque motor 6 connected to the control column 8 by a belt 7. The provision of the rate amplifier 21 ensures that the force applied to the column 8 will be high if the acceleration is changing rapidly even though the instantaneous magnitude of the acceleration may be low. The circuit is so arranged that positive acceleration produces a forward stick force, so that if the machine is flown hands‐off by the pilot accelerations tending to be built up by gusts will be automatically relieved. A trim control 23 may be fitted to the main amplifier 2.
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