Patent GB-1225387-A (GB)
IPC: G01P5/175
Filed: 1968-05-03
Abstract: 1,225,387. Aircraft instruments. LEAR SIEGLER Inc. 3 May, 1968 [5 May, 1967], No. 21043/68. Heading B7W. [Also in Divisions G1 and G3] Generating linear mach number signal.-Airspeed q c  is determined by a pitot head 28 which operates through a mechanical linkage system 32, 42, 43, 44, 45 and 46 to rotate the rotor of a synchro 106 such that the output is proportional to log q c . Altitude is determined from ambient pressure ps by an aneroid diaphragm 60 whose motion is transmitted through a mechanical linkage system 62, 64, 66, 68 and 70 to rotate the rotor of synchro 80 such that the output is proportional to log.ps. The output from synchro 106 is connected via 142, 146 to the stator of synchro 80 and the arrangement is such that the rotor winding of synchro 80 produces an output via 150 which is proportional to the sine of the difference between the shaft angles of the two synchros. The output is therefore proportional to sine log q c /ps, which equals sine log. M, where M is the Mach number. The output signal is employed to control a synchro 174 by way of a motor 162, so as to furnish on leads 186-194 signals to control a computer. In accordance with the invention the signal is first linearized so that the output is a linear function of Mach number. In a first arrangement (that illustrated), the synchro 80 output is applied via an amplifier 148 and phase detector 152 to a function generator 154, of the diode, transistor or other type, which generates the desired linear output. This output then controls motor 162 by way of a D.C. amplifier/modulator and servo amplifier 158. Positional feedback information is provided from synchro 174 by way of gearing 176, 184 which controls a potentiometer whose output potential is applied to amplifier/modulator 156. In a second arrangement, Fig. 4 (not shown), function generator 154 is dispensed with and the feedback potentiometer is made non- linear such that the feedback operation results in the production of a linear final signal. The arrangements shown in Figs. 2 and 4 operate with D.C. signals. In a third arrangement, Fig. 5 (not shown), which makes use of a non-linear feedback potentiometer as in Fig. 4, the circuit is arranged for A.C. operation. Expressing measurements.-Rotation of synchro 106 in accordance with airspeed is also communicated over shaft 50 to a pointer 24 indicating against an airspeed scale 54. Rotation of synchro 80 in accordance with altitude is communicated over hollow shaft 52 (through which shaft 50 passes) to a Mach number dial 18 which is exposed to pointer 24 through an aperture 16 in scale 54. A cam 86 profiled in accordance with the function V mo  - M mo , where V mo = maximum airspeed and M mo  = maximum Mach number, operates through gearing 90-98 to position a pointer 20 which indicates the maximum allowable airspeed at the altitude at which the aircraft is flying. Automatic control of aircraft speed.-A manual control 25 positions a gear ring 118 carrying a pointer 22 to establish a desired airspeed, a synchro 110 driven from the gear ring via gears 112, 120 and 122 providing a signal representing the desired speed. The stator of synchro 110 is supplied with a signal representing the actual airspeed from synchro 106 and the arrangement is such that the output from synchro via 133 represents the difference between the desired and actual speeds. The signal is applied to a throttle control mechanism 139. To linearize airspeed error signals feedback is provided from mechanism 139 to gear ring 118, and thence to synchro 110, by way of motor 210, differential gear 201 and slipping clutch 214. The second input for the differential gear comes from manual control 25.