Patent GB-793109-A (GB)
Title: Improvements in or relating to an electric analogue data computer
IPC: G09B9/20
Filed: 1955-04-28
Abstract: 793,109. Electric analogue calculating systems. GARRETT CORPORATION. April 28, 1955 [May 12, 1954], No. 12275/55. Class 37. [Also in Group XXXVIII] In an electronic analogue computor (applicable e.g. to the determination of the parameters of high-speed flight for aircraft) for continuously solving an equation wherein an unknown variable occurs in the second power and a first term must equal a second term; a closed electrical loop continuously evaluates the first and second terms in first and second computing sections wherein the first section comprises signal generating means energizing the input of a first network having a potentiometer varying the value of the generated signal in accordance with its wiper position responsive to the unknown variable; and the second section comprises a second network energized from a second signal generating means; a second potentiometer being connected in one or other of the networks of the first and second computing sections of the closed loop to vary the input thereto in accordance with its wiper position responsive to the unknown variable, and an impedance being connected between the respective outputs of the computing sections so that the voltage thereacross must be zero to satisfy the equation; there being provided a servomotor adjusting both potentiometer sliders together to produce an effect equivalent to the second power of the unknown variable in response to the voltage across the impedance until such voltage becomes reduced to zero. Fig. 1 shows an analogue computer determining the values of angle of attack at, angle of yaw yt, and airspeed V of an aircraft wherein a resistance potentiometer 18 is energized by secondary 12 of an A.C. excited transformer, and has a slider 20 deflected by cam 21 actuated over a linkage from pressure ratio measuring instrument 22 responsive to Psi/Pti where Psi = indicated static pressure and Pti = indicated total pressure at the aircraft surface, the cam contour being such that the slider voltage represents a function f of the Mach number M. A secondary 13 of the transformer energizes a resistance potentiometer 30 (whose slider is returned to earth and is manually adjustable in accordance with a constant boresight correction Za) and resistance potentiometer 32, which has a slider 33 deflected by cam 34 actuated over a linkage in response to instrument 22 so that the slider voltage represents a function f2 of the Mach number, and is connected to the junction of equal resistances 23, 24 in parallel with the output voltage of slider 20 to energize potentiometer 26 whose slider 27 is deflected by instrument 28 in accordance to the indicated angle of attack ai, measured in response to the local air flow and referred to the aircraft. Functions f1 and f2 introduce corrections necessitated by position errors of the instruments with regard to the aircraft, which are determined by flight test, while the boresight correction Za is necessitated by misalignment errors of the computor and its instrument within the aircraft as determined by aircraft tolerances, and is made at installation. The true angle of attack: which is thus represented by the voltage e(at) of slider 27 appearing across terminals 37. Potentiometer 40 is energized by secondary winding 14, and its slider 41 returned to earth is manually adjustable in response to a constant boresight correction Zy. Potentiometer 42 is similarly energized, and its slider 43 is deflected by instrument 44 measuring the azimuthal air stream according to the indicated angle of yaw yi referred to the aircraft, to develop a slider voltage e(yt) across terminals 45 representing the true angle of yaw given by: Secondary winding 15 energizes series resistances 50, 51 chosen so that the combined resistance is temperature variable proportionally to Tti, the total or stagnation temperature of the external air in degrees K., and so that the voltage developed across 5 is proportional to 1/Tti, this voltage being transformer coupled to potentiometer 54 having slider 55 deflected by cam 56 actuated over a linkage from instrument 22 so that the slider voltage represents f3/Tti = 1/T, where f3 is a function of the Mach number and T is the dynamic external air temperature in degrees K, and is applied to amplifier 57, whose output energizes potentiometer 60 in series with resistance 61 from the function of which negative feedback is returned to the amplifier input. The slider voltage is further amplified at 66 to energize a fixed negative feedback potentiometer 68, 70 connected in parallel with potentiometer 67, the voltage on whose slider 72 is connected to one end of the primary of transformer 78, the other end being connected to slider 76 of potentiometer 75 energized by secondary 16. This slider is deflected by cam 77 connected by a linkage to instrument 22 so that its voltage is proportional to M2, and the secondary difference voltage of transformer 78 is amplified to control the direction of rotation of servomotor 64 in accordance with the phase sense of the difference voltage and to readjust sliders 63, 72 until it is zeroized. Then: (the latter being represented by the voltage on slider 72) so that the angular rotation of the servo-system is proportional to V, which is represented by the voltage e(V) across terminals 98 connected to the slider of potentiometer 96 energized from secondary 16 and adjusted by servomotor 64. A potentiometer 101 having a slider 102 deflected by a static pressure measuring instrument 103 indicating Psi is energized from the output of amplifier 57 with a voltage proportional to 1/T, and it is shown that the voltage e (P/PO) at terminals 104 represents the ratio P/PO of absolute to reference air density at static pressure Psi. In a modification (Fig. 2) for determining true air speed V a secondary 110 of an A.C. energized transformer energizes variable resistance 111 adjustable in accordance with V in series with potentiometer 112, having slider 114 deflected by cam 115 operated over a linkage from a pressure ratio measuring instrument of the kind shown at 22 in Fig. 1, as a function f8 of the Mach number so that the slider voltage represents f8/V, and is compared in the primary of transformer 78 with the slider voltage of potentiometer 120, which is energized by secondary 110 over a potentiometer comprising resistance 50 varying in response to Tti, so that point 118 develops a voltage proportional to 1/Tti, variable resistance 111 and slider 121 are adjusted by servomotor 64 responsive to control circuit 122 and amplifier 82 energized from the secondary of transformer 78 until the total voltage across the primary of the transformer is zero, and it is shown that f8/V = V/Tti where f8(M) = f4/f3 as above, and the rotation of the servosystem is proportional to V which is represented by the slider voltage of potentiometer 125 energized from secondary 110 and adjusted by the servosystem.