Patent GB-595589-A (GB)
Title: System for three dimensional orientation of an aircraft for blind landing, course direction and the like and apparatus therefor
IPC: G01S1/02
Filed: 1943-05-26
Abstract: 595,589. Radio navigation. NOLDE, G. V. May 26, 1943, No. 8391. [Classes 40 (iii) and 40 (v)] [Also in Group XXXVIII] An approach or landing system for aircraft (which may also respond to ground markers and give indications as to the presence of other aircraft and when landing may be effected), comprises a transmitter on the aircraft, a directional receiver on the ground whose directivity is periodically varied, a ground transmitter emitting signals controlled by the periodic output of the ground receiver, and a receiver on the aircraft responding to such signals and controlling an indicator. Certain parts of the system may be duplicated so as to give signals indicating the position of the craft in horizontal and vertical planes, i.e. in azimuth and in declination. The indicator on the aircraft may comprise two screens 67, 68, Fig. 3, on which light beams 70, 71 may be projected under control of the aircraft receiver and of lightdeflecting means moved synchronously with the means for varying the directivity of the ground receivers. Fig. 6 shows the system in skeleton, the upper part representing the apparatus on the aircraft and the lower part that on the ground. Signals from the aircraft transmitter 76 are received by the fixed aerials 42, 43 and 42A, 43A of two radio-goniometers, the search coils 38, 38A of which are continuously rotated (after being initially started) and are connected in turn (for periods corresponding to half a revolution of the search coils) to a receiver 72 controlling (in a manner described later) the modulation by an audio-frequency signal of the ground transmitter 74. The signals received by the aircraft receiver 75 are repeated by relay 53 over commutators 61, 62 alternately to lamps 50, 51, the light from which is reflected by mirrors 65, 66 to the vertical and horizontal screens 67, 68 (see also Fig. 3). The commutators and mirrors are driven synchronously with the search coils of the ground receivers by a motor, Figs. 4, 9 (not shown), controlled by a modulation frequency on the carrier from the ground transmitter. Ground equipment. This is shown in greater detail in Fig. 8 in which the search coils 38, 38A of the two radio-goniometers are driven through clutches by motors 36, 36A. The search coils are connected alternately by contacts of relay 79 to the radio-receiver 72. The ground receiver 77, in response to signals from the aircraft, controls magnets 47, 47A actuating the clutches driving the search coils. The ground transmitter 74 is continuously modulated by coil 83 with currents of supply frequency (for driving the motor on the aircraft synchronously with motors 36, 36A) and is also modulated by currents of a high audio-frequency from oscillator 82 under control of (1) receiver 72 and search coils 38, 38A, and (2) relays 86, 87 controlled by directive aerials 91, 93 of marker beacons. Operation. The ground operator sets the pointer of the azimuth goniometer to the prescribed course and the pointer of the declination goniometer to the desired glide angle. The goniometers are normally at rest, and the ground transmitter 74 normally radiates a carrier frequency a continuously modulated by a low audio-frequency synchronizing current. When the aircraft pilot reaches the vicinity of the beacon, he tunes his receiver 75, Fig. 9, to the frequency a and at the same time closes switch 80 to energize relay 55 to clutch in the motor 56 which is driven synchronously with the ground apparatus by currents passing filter 95 from receiver 75. At this stage, the ground transmitter 74 is modulated continuously by the oscillator 82, and the relay 53 of the aircraft receiver closes alternately (through commutators 61, 62), the circuits of the lamps 50, 51, Fig. 6, so that each lamp glows continuously through one half revolution of the commutators. This glow of the lamps and the synchronous movements of the mirrors 65, 66 produces a complete illumination of both screens 67, 68, Fig. 3, indicating that the aircraft has the right-of-way for landing. On receipt of this indication, the pilot releases switch 80 and closes switch 81, thereby maintaining a circuit for the clutch relay 55 and energizing his transmitter 76. This is tuned to frequency b so that the ground receiver 77 causes relay 180 to energize the clutch solenoids 47, 47A of the goniometers 38, 38A. The goniometers on the ground thus rotate synchronously with the mirrors and commutators on the aircraft. If the aircraft is on the prescribed course, the plane of the goniometer coil 38A will be perpendicular to the line of flight when the coil has passed through 90 degrees from its zero position, at which instant it will have a minimum of reception, thereby causing the transmitter 74 to emit an instantaneous signal causing the lamp 50 on the aircraft to light for that instant. During one half revolution of the apparatus, this will occur repeatedly and the image of lamp 50 will appear at the centre of screen 67 as long as the aircraft is on the prescribed course. Similarly, during the other half revolution, the goniometer coil 38 will control lamp 51 to project an image on screen 68. If the plane is to left or right, or above or below, the prescribed course, the image will be correspondingly displaced on the screens 67, 68. A meter 69, Fig. 3, controlled by the intensity of reception by receiver 75, Fig. 9, indicates roughly the distance of the aircraft from the landing field. The ground markers 91, 93 (at a distance of, say, half a mile and three miles from the landing field) control the indication on the aircraft in the following way. The markers are directive receivers having relays 88, 89 controlling relays 86, 87 having contacts 130, 135 connected to contacts of relay 79 and controlling the circuit of the modulating oscillator 82. When the aircraft is in the vicinity, relays 88, 89 open the circuits of relays 86, 87 so that the modulating oscillator 82 is under the sole control of the receiver 72. When, however, the aircraft is immediately above the marker 93, relay 89 de-energizes relay 86 which closes the circuit of oscillator 82 over contacts 133, 130 for half a revolution, so that the entire screen 68 glows while the aircraft passes over marker 93. Similarly, the entire screen 67 glows while the aircraft passes over marker 91.