Patent GB-572983-A (GB)
Title: Improvements in or relating to aircraft navigational instruments
IPC: G01C21/20
Filed: 1942-01-08
Abstract: 572,983. Navigational instruments. FERRANTI, Ltd., and CLUDERAY, E. S. Jan. 8, 1942, No. 331. [Class 106 (i)] An aircraft instrument for computing the N, S, E and W components of wind drift comprises a presettable timing device for intermittently or continuously varying in accordance with wind magnitude the period of reciprocation of movable members appropriate to the respective directions, a presettable direction device for controlling the extent of travel of each of the movable members or members geared thereto in accordance with the cosine of the angle between the wind direction and N, S, E or W, together with the separate summating of one-way movements of the members. A wheel 1 carrying a heart-shaped cam 2 is driven from a clockwork or electric motor 3 under the control of an escapement 4. Held against the cam 2 by a spring 5 is a rack 6, the stroke of which may be adjusted by a variable stop 7 set in accordance with wind speed. The rack gears with a pinion 9 geared through a one-way 'disc 10 to a snail cam 11 which bears against a pair of spring arms 12, 13 carrying contacts 14, 15 in series with a battery 16 and an electromagnet 8. The direction device comprises a face cam 17 which if developed forms a half-sine-wave shape extending over half the circumference, the other half being straight. This cam is set by a knob 19 having a pointer moving over a compass scale. There are four similar mechanisms 20 ... 20<111> for wind drift. When the magnet 8 is energized, the rack bar 20 is permitted to move longitudinally a distance limited by the cam 17 and is returned by the spring 22 driving through one-way device 24 and gears 25, the pointers 26 of a counter. In operation, the stop 7 is set according to the magnitude and the knob 19 according to the direction of the wind, thus the timing of the making of the contacts 14, 15 depends on magnitude and the stroke of the rods 20 on the direction, the counters 26 summing up the components in the directions N, S, E and W. Instead of having four mechanisms 20, two mechanisms may be employed for NS and EW components, the cam 17 having two sine wave troughs each extending over half the surface. Air position indicators of the type described in Specifications 572,598 and 572,733 may be used in conjunction with the present invention. Furthermore, the apparatus in these Specifications may be converted into wind drift computing devices by substituting a presettable timing device for the air log, and a presettable direction device for the compass. The drift mechanism 20 may drive through a one-way drive one sun wheel of a differential gear, the second sun wheel being driven by the air position indicator while the arm carrying the planet wheel drives the counter. Where the air position indicator embodies two mechanisms instead of four, it may be necessary to subtract the correction for wind drift. In this case, the spindle of the direction device operates a clutch to drive the sun wheel of the differential gear in the correct direction. In a final form, Fig. 5, the presetting timing device is as in Fig. 1 and the rack 20 drives through a one-way device 23, 24 a disc 44. The direction device 19 positions a cam 50 having two sinewave grooves 49 working guided slides 47, each of which carries a friction ball 46 located between the disc 44 and a roller 45 driving the counter 26.