Patent GB-703864-A (GB)
Title: Improvements in or relating to aircraft navigation systems
IPC: G05D1/02
Filed: 1951-06-06
Abstract: 703,864. Radio navigation. SPERRY GYROSCOPE CO., Ltd., DOVE, F., and NISBET, R. H. June 6, 1952 [June 6, 1951], No. 13376/51. Class 40 (7) Relates to navigation systems of the type disclosed in Specifications 690,985 and 691,017 for enabling an aircraft to make an asymptatic approach to a ground track defined by a radio localizer beacon in which signals proportional respectively to the displacements of the aircraft from the track and to sin e where e is the deviation of the heading of the aircraft from a preset heading are combined to control an indicator and/or an automatic pilot. In such systems when the aircraft is displaced so far from the track that the displacement signal exceeds the maximum deviation signal, the aircraft tends to turn continuously in a circle and this is prevented according to the present invention by generating a second deviation signal proportional to cos and utilizing this as the control signal when the displacement exceeds a predetermined magnitude; such control signal preferably includes an adjustable fraction of the first deviation signal but alternatively it may include the unmodified first deviation signal and/ or the displacement signal. With such a control system the aircraft will approach the track obliquely for large displacements at " an angle of attack" defined by the ratio of the two deviation signals and will then converge with the track asymptatically. The control signal may also include a signal proportional to the banking angle. The change in the control signal is effected by relays controlled by the displacement signal and by a switch 29, the positions of the relay contacts shown in the drawings corresponding to a normal control, i.e. (s + sin e) with relay coils 31, 32, 33 de-energized. For small displacements an A.C. displacement signal proportional in amplitude and phase to the magnitude and sense of the displacement is produced by the radio receiver 1, 2, 3 and applied through relay contacts 31e, 32e to a mixer 5<SP>1</SP> where it is combined with a first deviation signal (sin e) from the rotor 6 of the relayer 5 coupled to the gyromagnetic compass 6, the resultant signal being combined at 1b with the A.C. output from the roll (i.e. bank) pick-off 17 detected at 20, and applied to an indicator 22. A D.C. displacement signal from the demodulator 26 is applied to polarized relay 24 whose armature 25 is maintained in a non-contacting centralized position 34 by a centralizing spring when the displacement is less than the predetermined distance but when the displacement exceeds such distance the relay operates and makes contact 27 or 28 depending on the sense of the displacement. If contact 27 makes, relay 32 is energized to open contact 32e, close contact 32c and change over contact 32d thereby excluding the displacement signal from mixer 5<SP>1</SP> and applying thereto a fraction of the sin e deviation signal from potentiometer 23 and a cos e deviation signal from the Selsyn rotor 7. If contact 28 makes, a similar control signal results but the phase of the cos # deviation signal is reversed. In order to ensure that relays 31 and 32 do not become again effective should the aircraft cross the track to a position beyond the predetermined displacement on the other side, the three-pole relay 33 is provided whose coil is energized when either coil 31 or 32 is energized to close holding contact 33a and open contacts 33b, 33c thus preventing coils 31 and 32 from becoming energized again until switch 29 has been opened and closed again manually.