Patent GB-766203-A (GB)
Title: Apparatus for measuring relative fluid velocity and displacement particularly air speed indicators and logs for aircraft
IPC: G01P13/02
Filed: 1955-02-07
Abstract: 766,203. Measuring fluid flow. COMPUTING DEVICES OF CANADA, Ltd. Feb. 7, 1955. [Feb. 24, 1954], No. 3502/55. Class 69 (1). Apparatus for measuring the flow of fluid relative to a body, and in particular and as shown in Fig. 1 an air-speed indicator or log for aircraft, comprises a vane device 15 rotatable about an axis 13 at right angles to the flow to be measured, means such as a propeller 14 for producing continuous rotation of the spinner 12 and hence of the axis 13 in the plane of the dotted circle so that the vane 15 aligns itself with the resultant relative velocity which is at an angle α to the flow to be measured, and computing and indicating means such as synchro transmitters 16 and 19 and receivers 18 and 21 responsive to the value of α and the angular velocity of the spinner respectively, feeding a computer 22 which by effectively multiplying the angular velocity by the cotangent of α obtains a value of air-speed for display on the indicator 23 and for use in the log 24. Fig. 6a shows a preferred form of vane device 15 in which the centrifugal effect tending to make the vane 15 of Fig. 1 set itself at an angle a = 90 degrees is eliminated by use of a cross-member set at right-angles to the fincarrying vane member; a counterweight 40 is attached to the other end of the axis 13. Other types of vane device are described and illustrated. Fig. 12 shows a typical complete system in diagrammatic form, in which the angular positions of the spinner and vane are followed by the shafts of motors 69 and 73 respectively, and the calculation V = R # cot α is effected mechanically (V = required air-speed, R = effective radius of vane, # = angular velocity of spinner). Synchro-transmitter 16 supplied with A.C. from the supply to its rotor has its stator output led through slip-rings 50 to receiver 74; the receiver rotor winding controls motor 73 through amplifier 79 so that the motor shaft sets itself in a position corresponding to α. Similarly synchro-transmitter 19, receiver 68, amplifier 70 and motor 69 ensure that the shaft of synchro-receiver 68 follows the rotation of the spinner, the coupling between the shafts of motor 69 and receiver-synchro 68 being effected by balls 71 engaging a disc 75 and a roller 80. The position of balls 71 is controlled by a mechanical resolver element 72 from the shaft of motor 73 so that disc 75 rotates at an angular w velocity -, and a cosine resolver element 76 sin a coupled to balls 77 between a similar disc 751 and roller 78 drives the latter at angular velocity #/sin α cos α, i.e. # cot α; the counter 81 thus can be suitably calibrated in air-miles, and a commutator 82 used to supply electrical impulses for remote logging. A modified computing system is described in which the resolving system 75, 751, 71, 77, 78 and 80 is driven, not by motor 69, but by a constant-speed motor through gearing controlled by a position difference vector signal from a differential transformer taking the place of receiver-synchro 68; in this case the value of the gear ratio can be arranged to operate an air-speed indicator. In a simpler arrangement the rotation of the spinner is used to generate a voltage proportional to # and the position of the vane controls a variable resistance which is made proportional to tan α, the current then being read off directly as the air-speed. The spinner 12 may be motordriven instead of propeller-driven; in this case the power supplied to the vane-driving motor is controlled by the angular position of the vane so that the latter lies between predetermined limits to ensure sufficient accuracy.