Patent GB-987100-A (GB)
Title: Aircraft landing system
IPC: G05D1/06
Filed: 1961-07-07
Abstract: 987,100. Radio navigation. SPERRY RAND CORPORATION. July 7, 1961 [July 8, 1960], No. 24623/61. Heading H4D. In an aircraft landing system the craft is flown (automatically or normally) on the approach glide path under the control of signals from a radio-beam glide-path receiver until an altitude h 1  (Fig. 1) at which such signals cease to be reliable is reached whereupon the craft is flown under the control of signals derived by comparing signals representative of the actual rate of descent with a stored signal representative of the rate of descent at point h 1  until an altitude h 2  is reached and at this point a signal of constant amplitude is combined with the actual rate of descent signal and the combined signals compared with the stored signal to provide an error signal the correction of which by changing the angle of glide results in a " flare-out " of the latter to the point of touch-down. Figs. 2 and 3 show the general arrangement in which the receiver 10 supplies signals to the indicator 14 (and, if desired, to the auto pilot 26) via contacts 32 (Fig. 3) of the switching circuit 12 during the approach glide path the circuit 12 including a memory device 36 to which is supplied via contacts 34 a signal from generator 16 representative of the rate of descent of the aircraft. When the altitude h 1  is reached a comparison circuit 28, fed with signals from altimeter 24 and with a signal from a source 20 representative of altitude h 1 , ceases to supply an output so that relay 30 releases contacts 32, 34 against spring 35 and the actual rate-of-descent signals from generator 16 which are fed to a comparison circuit 38 via contacts 40 are compared therein with the stored signals from device 36, the circuit 38 providing an output signal to the indicator 14 via contacts 32 whenever the input signals differ. The craft is flown in accordance with indicator 14 until altitude h 2  is reached, this point being determined by a comparison circuit 42 (similar to circuit 28) fed with signals from altimeter 24 and a signal representative of h 2  from source 22. When the signals from 24 become equal to or less than that from source 22 circuit 42 ceases to supply an output and the consequent release of contacts 40 removes the actual rate-of-descent signals from the input a of comparison circuit 38 and supplies instead the output of a summing device 18 (Fig. 1) in which the actual rate signals from generator 16 are combined with a constant signal from generator 19. The output from circuit 28 displayed on indicator 14 is then an effective error signal and operation of the aircraft controls to re-centre the horizontal bar of the indicator 14 results in the craft flying through a flare-out manoeuvre. To prevent the touchdown point from " floating " between early and late positions (should the craft fly on a path which is parallel to but not coincident with the selected glide path) the inputs to the comparison circuit 38 are first integrated (Fig. 4, not shown) and sharp up and down manoeuvres when close to the ground are prevented by feeding back a proportion of the output of the comparison circuit to one of the inputs to cause the commanded glide path to " float " away from the memorized glide path by an amount proportional to the departure of the craft from the latter glide path and then " float " back to coincide with the memorized path (Figs. 4 and 5, not shown). Specifications 729,675 and 815,137 are referred to.