803,575. Automatic steering control systems. SPERRY GYROSCOPE CO., Ltd. July 12, 1956 [July 29, 1955], No. 21926/55. Class 38 (4). [Also in Group XXXIII] An aircraft safety-device comprises means for deriving an electrical signal representing the divergence of a control surface from its long-term average position, which signal is applied to a relay or the like to produce a characteristic signal if the first-mentioned signal exceeds a predetermined value. The invention is applied in the embodiment described to a control surface 202 when operated by an auto-pilot 340. The pilot's control column 201 is connected by rod 255, lever 320, rod 282, and floating-lever 280 with the input 261 of a mechanically-operated valve 344 controlling, when a change-over valve 346 is un-energized, a fluid-pressure servomotor 210 connected to the control surface 202 by a rod 218. A follow-up rod 281 recentres the valve input 261 when the surface 202 reaches the appropriate position. When change-over valve 346 is energized, the servomotor 210 is controlled by a valve 345 operated by a transducer 208 energized by an amplifier 248. The latter is energized by a mixer 245, having for one input an answer signal derived from a potentiometer 207 positioned by the control surface, and for its other input a demand signal derived either from an auto-pilot 340 or from a potentiometer 206 driven by the control column 201, according to the position of a switch 341. The signals from potentiometers 206 and 207 are also fed to a differential 268, the amplified resultant energizing a slow response integrating motor 216SP11/SP which trims the datum of a spring feel device 216SP1/SP connected to rod 255. The change-over valve 346 is normally energized through a contact d2 of a self-holding relay D, so that the surface 202 is controlled by the auto-pilot 340 or the control column through an electro-hydraulic system. When the auto-pilot is in control, the control column 201 is centred by the feel device 216SP1/SP to a datum position set by motor 216SP11/SP. Due to the long term response of motor 216SP11/SP the position of the control column and hence the signal derived from potentiometer 206 represents the long-term average of the control surface position, and thus the output of differential 268 represents the deviation of the control surface from its long-term average position. This output is applied to a relay E, and if it is above a predetermined value, the relay opens a contact el, de-energizing relay D, opening contact d2 and de-energizing the change-over valve 346, so that the pilot's control column operates surface 202 through a mechanico - hydraulic transmission. A potentiometer 347 adjusting the sensitivity of relay E is driven by an airspeed or Mach number signal generator 348. A relay C can also de-energize relay D through contact cl, if the output of amplifier 248 is too high. Specifications 760,683, 803,572 and 803,574 are referred to.
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