Patent GB-792346-A (GB)
Title: Pitch detectors
Inventor: COTTON MICHAEL BEN
IPC: G01C19/44
Filed: 1955-01-28
Abstract: 792,346. Gyroscopic apparatus. SPERRY GYROSCOPE CO., Ltd. Jan. 27, 1956 [Jan. 28, 1955; Feb. 9, 1955], Nos. 2679/55 and 3931/55. Class 97(3) In a gyroscopic apparatus for stabilizing aeroplanes or platforms carried therein, which is arranged even during a turn to respond appropriately to the control quantity from the pitch detector but having provision for eliminating, reducing, or compensating for the error in the control quantity attributable to the effect on the pitch detector of a component of centrifugal force directed along the fore-and-aft axis of the aeroplane during the turn, e.g. a pitch detector may have an axis of response which is automatically varied in direction in response to centrifugal force occurring during a turn. As shown in Fig. 1, a vertical gyroscope 1 has a roll detector 2 which supplies a controlling signal to a roll erection torque motor 3, and a pair of mercury switch pitch detectors 4a, 4b which control a pitch erection torque motor 5. The pitch and roll detectors 2, 4a, 4b are mounted on a follow-up platform 8 which is maintained level with the gyro casing by roll and pitch servomotors 9, 10 responsive to signals from pick-offs 11, 12. Pitch erection motor 5 receives signals from both detectors 4a, 4b in straight flight by way of a mercury switch 13. During turns, when the centrifugal force exceeds a given value, it acts on mercury switch 13 to cut out one of the pitch detectors. A pitch-roll switch 14 causes the roll torque motor to be operated by the pitch detector instead of the roll detector when the bank exceeds a given magnitude, in known manner. The pitch detectors 4a, 4b may be equallv inclined; but if the gyroscope is pendulous, the error is greater when turning in one direction than in the other, and the detectors have different inclinations, as shown. The error due to pendulous moment may be made such as to substantially compensate for errors due to centrifugal force in one direction of turn. in which case a single inclined pitch detector may be used. As shown in Fig. 4, the vertical gyroscope 1, with roll and pitch detectors 2, 4 controlling torque motors 3, 5 respectively, is suspended in gimbals 15, 16. The pitch erection motor 5 acts about an axis 17 which is maintained in alignment with the air path of the aeroplane, e.g. by a wind vane 21 acting through synchros 19, 20. The axis of pitch detector 4 thus lies in a substantially vertical plane containing axis 17, so that during a properly executed turn there is no component of centrifugal force acting along the axis of'the detector. For approximate correction, axis 17 may be tilted through a fixed angle during a turn, or may be set at a fixed angle with the fore-and-aft axis. The pair of pitch detectors 4a, 4b in Fig. 1, may be replaced by a single detector mounted on a cradle pivoted on the follow-up platform 8. The cradle is normally held by springs in a central position, but a magnet operated by the centrifugal switch 13 rocks the cradle to one tilted position or another during turns. The cradle also carries an accelerometer cut-out, which cuts out torque motor 5, in known manner, under excessive fore-and-aft acceleration. Alternatively, the cradle may be connected to a pendulum, and the liquid-type detector may be replaced by one of an electromagnetic type. In Fig. 9, tilt detectors 2a, 4d, each consisting of a pendulum and a selsyn, are respectively connected to windings 51, 52 of a resolver 50. In straight flight, the rotatable winding 53 is parallel with winding 52 and supplies signals derived from detector 4d only to torque motor 5. During a turn, winding 53 is turned automatically, and the signal produced therein is the sum of signal components from both detectors, which is equivalent to the signal which would be produced by a single pitch detecter with its axis of response parallel to the axis of secondary winding 53. In another embodiment, a bank-responsive switch feeds a biasing signal to the pitch erection torque motor whenever the bank exceeds a certain value. The signal tends to correct the error arising from the effects of centrifugal force on the pitch detector. If the error is compensated for turns in one direction by making the gyroscope pendulous, the biasing signal is applied only during turns in the other direction. In the embodiment shown in Fig. 11, the gyroscope is mounted in gimbal ring 54 which carries an armature 56 moving between the poles of an electromagnet 55, which is automatically energized when the aeroplane is banked. The armature 56 is shaped so that the corrective torque applied varies according to the amount of bank. Fig. 12 shows a pitch detector of the kind wherein an armature 57 swings over an E-type pickoff 58 the armature is mounted to swing about two axes at right-angles and is shaped to provide a corrected signal when acted on by centrifugal force. A liquid level pitch detector may also be modified; as shown in Fig. 13. A glass envelope encloses a drop of mercury in a space of V- section, together with a centre electrode 60 and end electrodes 61, 62. In straight flight the mercury drop moves in the vertex of the V, but in a turn the drop is carried up to thend end of the V, to move in a path skewed with respect to the normal path. Specification 715,313 [Group XXXV] is referred to.