Patent GB-379429-A (GB)
Title: Improvements in and relating to echo altimeter apparatus for use on aircraft
IPC: G01S7/526
Filed: 1931-06-16
Abstract: 379,429. Echo-sounding apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Rice, C. W. ; 1161, Lowell Road, Schenectady, New York, U.S.A.) June 16, 1931, No. 17504. Convention date, June 16, 1930. [Classes 13 and 118 (ii).] In apparatus for determining by the echo method the altitude of aircraft, the emitted sound is produced by a pressure-operated device supplied with gas from a reservoir connected to a cylinder of the internal-combustion engine of the craft. Means are described for eliminating undesired noises from the received sound and for determining acoustically the angles of inclination and of banking and also the distance from vertical objects. The transmitter comprises a whistle 6 having a frequency of from 2000 to 4000 cycles per second and situated in a directing cone 7 in the fore part of the craft. The cone may be mounted so that the direction of its axis can be varied. The whistle is operated by compressed gas obtained from a cylinder of the engine and stored in the reservoir 9. A valve 24 allows gas to pass into the reservoir 9 when the pressure in the reservoir is below that in the cylinder. The ignition of the gas in the reservoir is prevented by a chamber 26 having baffles 27. A float 28 allows the escape of condensed moisture from the reservoir. The whistle is controlled by a valve 8 actuated by a cam 10 driven from a shaft 151 through gearing 12 and a pair of friction discs 13, 14, the position of the disc 13 being adjustable to vary the speed of the cam 10. The echo is received by a cone 2, Fig. 3, insulated from the craft by felt rings 30 and connected by a tube 3 to a stethoscope 5, Fig. 4. In the apex of the cone 2 are a number of holes 32 leading to a space 33 filled with felt and having vent-holes 34. High pressures caused by waves of low frequency, e.g. craft noises, or by changes in atmospheric pressure are thus prevented from entering the tube 3. A further sound-filtering device for lowfrequency waves is interposed between the tube 3 and the stethoscope 5 and comprises a tube having holes 35 opening into a container filled with cotton waste and divided into partitions by felt washers 37. A vent 38 communicates with the atmosphere. In an alternative form of filter, the construction is similar but the holes 35 are spaced apart a distance corresponding to half a wave-length of the received sound and the connections can be adjusted along the tube until the desired sounds only are transmitted through the filter. When the valve 8 is operated an electromagnet 50 releases a pointer 46 observable by the operator, the pointer making one rotation adjacent a dial 45 graduated directly in depths. The pointer may have two speeds and the dial two scales. In the embodiment shown in Fig. 7, two receivers 52, each connected to one ear of the pilot, are provided and the inclination of the craft is estimated by the binaural effect. Receivers 51, connected to the tubes 3 by cocks 55, may similarly be used to ascertain the banking angle. For finding a horizontal distance, e.g. from a cliff, receivers 57 mounted on the wing may be used.