Patent GB-626124-A (GB)
Title: Improvements in or relating to navigation systems for dirigible craft
IPC: G05D1/02
Filed: 1944-11-24
Abstract: 626,124. Automatic steering control systems. SPERRY GYROSCOPE CO., Inc. , Nov. 24, 1944, No. 23500. Convention date, May 29, 1943. Addition to 599,254, [Group XL]. [Class 38 (iv)] Steering.-In a system, as in the parent Specification, wherein a craft is steered to follow a coarse defined by a radio transmitter and radio apparatus on the craft produces an output, proportional to displacement of the craft perpendicular to course, which is modified by apparatus determining the distance of the craft from the transmitter so that the output is substantially constant for a given displacement over a wide range of distances from the transmitter, the radio apparatus co-operates with a directional reference on the craft to control craft heading automatically. In Fig. 2 the loop aerial 12 of a radio direction finder 11, carried by a craft to be maintained on a course towards a radio transmitter is maintained automatically in the null position by a reversible electric motor 10 controlled. by signals from a radio receiver 9. A positional reference 13, e.g. an azimuth gyro or magnetic compass is also carried by the craft, and shafts 14 and 15, coupled to the positional reference and loop respectively, drive rotors 19 and 20 of a Selsyn receiver 17 and transmitter 16 respectively. The stator 21 of the Selsyn transmitter is supplied from an A.C. source and the course is set initially by adjusting its position by a knob 18 until the output of stator 22 of the Selsyn receiver is zero. Selsyn rotors and stators may be interchanged. Deviation from course results in relative movement of shafts 14 and 15 and a signal from stator 22 which is dependent in voltage and phase on the change of bearing of the radio transmitter. This signal is applied to a potentiometer 23, the output of which controls the rudder mechanism 28, through a phase-sensitive amplifier 41 and a reversible electric motor 43 adjusting an auto-pilot 40 as in Specification 526,980, to return the craft to course. During the correction a potentiometer 29 supplied from an A.C. source is adjusted from the neutral position shown by shaft 14 of the positional reference so that the craft is turned through a predetermined correction angle and returned asymptotically to course. A mechanical or electrical clutch 34 may be operated to declutch shaft 14 from the slider of potentiometer 29, whereupon springs 33 urge the slider to a central position. A range device 25 adjusts the potentiometer 23 so that its output and therefore the correction angle is proportional to the distance of the craft from the transmitter, thereby avoiding hunting when nearing the transmitter. The range device may be a clock mechanism when the time of the trip is known, an odometer when the distance is known, or a radio or optical distance computer. In a modification, Fig. 3 (not shown), the loop aerial is stabilized in azimuth by a reversible electric motor controlled by a phase-sensitive amplifier movement between shafts corresponding to shafts 14 and 15 of Fig. 2. Deviation from course then results.in a loop signal which co-operates with the signal from a non- directional aerial to produce a signal dependent in voltage and phase on the change of bearing of the radio transmitter. This signal is applied through slip rings to a direction-finding receiver comprising R.F., detector and A.F. stages with A.V.C., the final A.F. stage corresponding to amplifier 41 in Fig. 2. The A.V.C. applied to the A.F. stages provides the reduction in correction angle as signal strength increases when approaching the transmitter. In a modification, Fig. 4 (not shown), the modification of the correction angle is effected by a D.C. output from the direction-finding receiver controlling the output of a Selsyn receiver corresponding to receiver 17 of Fig. 2, through a thermionic valve circuit including a saturable reactor, a resistance-condenser delay network, and manual control. Control of the input -to this thermionic valve circuit may be by a range device operating a potentiometer. Specifications 503,317 and 523,953 also are referred to.