Patent GB-301278-A (GB)
Title: Improvements in and relating to gyroscopic navigational instruments
IPC: G01C19/38
Filed: 1928-05-09
Abstract: 301,278. Henderson, Sir J. B. May 9, 1928. Gyroscopic apparatus.-Apparatus for use on aircraft &c. to indicate the rate of turning in azimuth, i.e. about the true vertical, the total angle of turn in azimuth, the banking angle &c., comprises a gyroscope constrained by torques proportional to the angular velocity of the craft about an axis fixed relatively to the craft (the virtual vertical) and means to derive therefrom a measurement of they angular velocity and/or displacement of the craft about an axis fixed relatively to the earth (the true vertical) and/or the angle between the two axes, this angle being the banking angles when the machine is properly banked. If # is the angular velocity in azimuth and # the velocity about the virtual vertical, then # = # Sec. a, a being the banking angle- Also if R is the radius of the turn. V the speed of the aircraft, I the moment of inertia of the gyroscope and # its angular velocity, and if T is the couple constraining the gyroscope, then Tan a = V<2>/Rg = V#/g and T = I##, hence Sin a = V#/g = VT/gI#. Sin a is thus proportional to T if V and # are constant or if V /# isconstant. This condition is realised by driving the gyroscope by means of an air-screw. The apparatus is divided into two parts, the gyroscopic instrument and the indicator. The former, contained in the casing 1, Figs. 1, 2, and 3, comprises a shaft 4 driven by an air-screw on the boss 5 and connected to the gyroscope 9 by a universal joint comprising a gimbal ring 11 and two pairs of pivot pins 7, 10. A short spindle 12 in line with the axis of the gyroscope enters a fork 13 pivoted on pins 14 the axis of which passes through the centre of the universal joint. A contact 15 on the fork 13 lies between contacts 16 so that the smallest precession of the gyroscope about the pins 14 due to turning of the aircraft causes the contact 15 to press on one of the contacts 16. The rate of turning is measured by the couple about the pins 14 which is required to separate the contacts. This couple is applied by springs 26 connecting the fork 13 to normally horizontal cranks 23 secured to shafts 22 to which are also secured the slotted cranks 21 engaged by pins 20 on a cross-head nut 19 carried by a screw shaft 18. With this. arrangement the restraining couple is proportional to the Sine of the angle of tilt of the springs and this angle can be equated to a by adjusting the springs by screws 24. Also the rotation of the screw 18 is proportional to tan a and therefore to V#. For operating the screw 18, a worm 27 on the shaft 4 drives a wheel 28 on a sleeve 29 carrying a pinion 33 gearing with a wheel 34 on the spindle 35 which is connected to the horizontal spindle 36 by gears 37. A worm 39 on the spindle 36 engages a wheel 40 on a spindle 41 which carries at its outer end a friction bevel wheel 42 arranged between similar bevels 43, 44 fixed to a spindle 45. The bevels 43, 44 form the armatures of magnets 47a, 47b one of which is energized when the contact 15 presses upon one of the contacts 16. The spindle 45 is thus rotated in a direction depending on the direction in which the gyroscope processes and its rotation is conveyed to the shaft 18 by gears 49, 50, 52, 54. The spindle 51 conveys its movement to a flexible shaft 56 leading to the indicator, this shaft being therefore rotated proportionally to V#. In order to obtain the value of # by integrating V#, correction must be applied for variations in V. This may be effected automatically by providing on the sleeve 29 a crosshead 57 on which is pivoted by trunnions 58 a governor flywheel 59. A plunger 60 slidable in the sleeve 29 has at its upper end an arm 61 held in engagement with the flywheel by a spring 64 and at its lower end carries a friction disc 65 which is engaged by a friction driving-disc 71 driven by gearing from the shaft 36. The disc 65 drives a third disc 73 which drives a flexible shaft 80 leading to the indicator. The design of the governor is such that if the axis of the flywheel could be tilted until it was at right angles to that of the sleeve 29 the disc 65 would lie at the centre of the disc 73 and the force of the spring 64 would be zero. In these circumstances the speed of the disc 73 is inversely proportional to that of the disc 71, i.e. it is proportional to <1>/V. The indicator, Figs. 5, 6 and 7, comprises a casing 81 and a dial casing 82 containing the pointers 88, 90, 92, 93, 94, 96. The pointer 88 is set by hand to the compass course to be followed and the pointer 90 indicates the deviation from the set course. The pointer 92 shows the rate of turning in azimuth, pointer 93 the total turn, and pointer 96 the banking angle when the machine is properly banked as shown by the level 87. The pointer 94 is a steering indicator and is moved proportionally to # + a#, a being a constant. In order to integrate # the shaft 56, which receives movement proportional to V#, drives a screw 101 on which is a nut 113 having pins 112 engaging a forked arm 110 which is fulcrummed about a pivot 114 adjustable along a screw 116. The arm 110 engages by pivots 111 with the spindle 106 carrying the planet mitres of a differential 105, this spindle passing through the sleeves 107 of the other pair of mitres and being splined into a sleeve 108. The sleeves 107 carry friction discs 122 engaged by a driving disc 119 which is driven from the shaft 80 and therefore rotates at a speed proportional to <1>/V. With this arrangement the spindle 106 is rotated at a speed proportional to the product of the displacement of the differential from its central position and the speed of the disc 119, i.e. proportional to V# x <1>/V, so that the total rotation of the spindle is proportional tq #. To convey the rotation of the spindle 106 to the pointers 90, 93, 94 a pinion 136 on the sleeve 108 gears with a wheel 137 on a loose sleeve 138 on the spindle of the pointer 93 and a pinion 139 fixed to the sleeve 138 gears with a wheel 140 on a sleeve 141 which carries frictionally 'the spindle of the pointer 90. A gear wheel 142 fixed to the spindle of the pointer 93 engages the wheel 137 frictionally by means of a spring 143 and, through an idler, drives a gear wheel 144 fixed to a sleeve carrying one input mitre of a differential 135 on the spindle of the pointer 94. To convert the movement of the screw 101, which is proportional to tan a, into a movement of the pointer 96 proportional to a a slotted crank 129 on the pointer spindle engages with a pin 128 connected by a link 127 to a nut 126 on the screwed shaft 124 driven by the shaft 101. The movement of the shaft 101 is also conveyed to the pointers 92, 94 by a pinion 103, which, through an idler 130 rotates a gear wheel 131 fixed to the spindle of the pointer 92. A second wheel 132 on the same spindle rotates a gear wheel 134 fixed to a sleeve carrying the other input mitre of the differential 135. The planet wheels of the differential are carried by the spindle of the pointer 94 which is thus rotated proportionally to # + a#. There is preferably provided another pointer coaxial with the pointer 94 and actuated by the steering gear of the aeroplane so that the pilot can steer his machine in such a way as to maintain these two pointers in alignment. Knobs 89, 91, 95 are provided for setting the pointers 88, 90, 93 by hand, the knob 95 also serving to set the # component of the pointer 94. As an alternative to the governorcontrolled means for compensating for variations in V, the disc 119, Fig. 6, may be driven at a constant speed by clockwork &c. and variations in V may be compensated by adjustment of the nut 115 by turning the milled head 118. The casings of both instruments may be pendulously mounted. Specification 213,023 is referred to.