812,294. Gyroscopic apparatus. SMITH & SONS (ENGLAND) Ltd., S. May 24, 1957 [May 25, 1956], No. 16315/56. Class 97(3) In aircraft instruments (e.g. gyroscopes) which are monitored by devices affected by gravity, the monitoring means are modified a condition appropriate to straight flight to a condition appropriate to turning flight only if both the rate and amount of turn of the craft from an established course exceed given values. As shown in Fig. 1, navigation instruments for an aircraft consist of two identical gyromagnetic compass systems 100, 200, and two identical gyroverticals 110, 210. The gyromagnetic compass systems include pendulous magnetic field sensing devices 101, 201, comparators 102, 202 and directional gyroscopes 103, 203. When the heading indicated by the gyroscopes differs from the magnetic heading, a signal derived from the comparator causes precession of the gyroscope to reduce the difference to zero. The circuits for the correcting signals may be interrupted by switches 104, 204 controlled by relays 105, 205. The gyro-vertical 110 has pendulous devices 111, 112 indicating deviations from the vertical about the pitch and roll axes respectively, by means of electrical signals. The signal from the pitch indicator 111 is applied to a torque motor 113 to erect the gyroscope about the pitch axis. In straight flight, the signal from the roll indicator 112 is applied to a torque motor 114 to erect the gyroscope about the roll axis, the signal passing through normally closed contacts 115, 116 controlled by relays 117, 118. The relays also control normally-open contacts 119, 120. In leftward turning flight, when relay 117 is energized, the signal from the roll detector is disconnected and the signal from the pitch detector instead is applied to the torque motor 114. In rightward-turning flight, relay 118 acts similarly, but with the pitch signal applied in reverse sense. The gyro-vertical 210 is connected into a similar system. Each of the gyromagnetic compass systems is associated with a device, Fig. 2, for controlling relays 105, 117, 118 in one system and the corresponding relays 205, 217, 218 in the other system. The control device 130 shown is associated with system 100 and includes a repeater 131 controlled by the directional gyroscope 103, so that shaft 132 rotates in accordance with changes in the heading of the aircraft. Shaft 132 drives, through gears 133, the sun pinion 134 forming one input member of a differential gear 135. The other input member is a wheel 136, freely mounted on a shaft 137 co-axial with pinion 134, and carrying on a stub shaft a planet pinion 138 meshing both with pinion 134 and with a pinion 139 fixed to shaft 137. Shaft 137 drives the driving member 141 of a slipping clutch, the driven member 142 of which is slotted at 144 to provide, together with a crank 150 and a pin 145, a lost-motion connection to a shaft 146 which passes through an insulating plate 147 carrying bosses 148, 149 limiting movement of crank 149. A plate 151 fixed to shaft 146 carries insulating pegs 152, 153, 154, 155 which operate respectively four sets of spring contacts 156, 157, 158, 159. Each set consists of two pairs of contacts L, R on opposite sides of one of the pegs. Contacts 156 are so arranged that any appreciable movement of crank 150 from its mid position closes one pair of contacts 156L, 156R which energize the centretapped winding 161 of a two-phase induction motor 160 from an A.C. source 162. The other winding 163 is energized by an A.C. source 164 in quadrature with source 162. The circuit is so connected that a left turn of the aircraft energizes repeater 131, causing shaft 137 to turn in a sense to close contacts 156L, and this causes motor 160 to turn in a sense to re-open the contacts. A right turn causes similar effects for contacts 156R. Provided that the rate of turn of the aircraft is less than a fixed value, determined by the speed of motor 160 and ratio of the driving gear, and also that the deviation from an established course is less than a fixed amount dependent on the amount of lost motion between shaft 137 and contacts 156, the gyroscope monitoring is not affected. If either of these values is exceeded, plate 155 will move sufficiently to close contacts 157 R or L, 158 R or L, and contacts 159 R or L. Contacts 157 are arranged, when closed, to energize relay 105 to interrupt the monitoring circuit of the gyromagnetic, compass system 100. Contacts 158L, 259L (where contacts 259 in a device 203 associated with the system 200 correspond to contacts 159) are connected in series in the energizing circuit of relay 117, and contacts 158R, 259R control energization of relay 118. Closure of these contacts modifies the monitoring circuit of the gyrovertical 110 appropriately for a left or right turn. Since two similar systems are used, the normal monitoring is not interrupted unless both systems are consistent in their indications, thus reducing the likelihood of faulty operation.