Patent GB-787818-A (GB)
Title: Aircraft guidance apparatus
IPC: G01S13/91
Filed: 1955-09-19
Abstract: 787,818. Measuring rate of descent of aircraft. SPERRY RAND CORPORATION. Sept. 19, 1955 [Sept. 23, 1954], No. 26723/55. Class 40 (1). An indication is given and/or a control is exercised in accordance with the difference between the desired and the actual rates of descent of an aircraft by apparatus brought into action automatically at a chosen height. As shown, Fig. 4, a radio-altimeter 21 at 100 feet puts a circuit 24 for delivering a D.C. signal corresponding with the rate of descent under control of a barometric altimeter 20. This signal, mixed with one from a vertical accelerometer (to deal with sudden changes in height), is compared at 27 with a steady voltage from 28 representing a chosen rate of descent. At 80 feet, indicator 89, which normally shows deviations from the glide path, is disconnected from the radio receiver and connected to the comparison circuit so as to show deviations of the rate of descent from that desired. The comparison signal may also control the automatic pilot. At 15 feet, the steady voltage from 28 is replaced by one from 33 representing a different desired rate of descent. Control of sequence by radio altimeter, Fig. 5A. Altimeter 21 delivers a continuous signal of which the frequency is proportional to altitude. This is converted to a stream of short pulses for triggering a single-shot multivibrator 119, 120 by triode and pentode amplifiers 112, 114, a cathode-coupled multivibrator constituted by tubes 116, 117 a differentiating circuit and an amplifier 118. Negative-going pulses at the output of 120 are suppressed by diode 121. Positive-going pulses are rectified at 122 and smoothed and produce at the output of cathode follower 125 a steady voltage corresponding to altitude. This voltage is automatically balanced by a uniselector operating by self-interruption under control of a test relay 126 and having one of its banks corrected to points on a potential divider. The other bank is connected to the terminals of manually-set switches 137, 138, 139 for selecting the heights at which the controls are exercised. Control of rate-of-descent indicator, Fig. 6. On the operation of relay 23 under control of the radio altimeter a continuous alternating signal representing altitude by amplitude is supplied from 20, amplified at 217, 218, rectified by a half-wave phase-sensitive rectifier and smoothed. The resulting signal after differentiation represents rate of descent. An A.C. signal from 40, representing by its amplitude and phase sense vertical accelerations of the craft is amplified by a pentode 41 with adjustable feedback and rectified by a full-wave phasesensitive rectifier. The resulting signal after integration also represents rate of descent (positive or negative) and with the other signal is applied to a tube 83. A steady voltage provided by potential divider 90, 91 and representing the desired rate of descent is applied to a similar tube and the voltages developed across the cathode resistors of these tubes are applied in opposition to indicator 89 after the operation of relay 32 at 80 feet. The value of the desired rate of descent voltage is adjustable automatically with a sensitivity control provided in the channel of the barometric signal by means of a ganged potentiometer associated with a diode 93 and also at will by means of a potentiometer 101 and a reversely connected diode 97. On the operation of relay 29 (at 15 feet) the potential divider 90, 91 is replaced by a direct connection to ground to give the final desired rate of descent. Specification 729,675, [Group XL. (c)], is referred to.