Patent GB-1029934-A (GB)
Title: Improvements relating to the automatic control of hydrofoil craft
IPC: B63B1/28
Filed: 1963-03-05
Abstract: 1,029,934. Automatic control of hydrofoil craft. UNITED AIRCRAFT CORPORATION. March 5,1963 [July 6,1962], No.8751/63. Heading G3R. [Also in Division B7] In a system for automatically controlling the altitude of a hydrofoil craft, the altitude error signal controlling submerged foils is modified by a signal, dependent on vertical acceleration of the craft, the magnitude of which is varied by means responsive to a short term average of vertical acceleration. As described, the controlled hydrofoil craft has two propellers, a rudder, two forward foils and an after foil, the foils having adjustable flaps. Pitch altitude. Signals from the pitch pick-off of a gyro-vertical 30, an after vertical accelerometer 36, and, possibly, a pitch rate gyro (not shown), are combined in an electronic control unit 49 which adds differential and integral components and controls hydraulic units 56, 58 respectively actuating the forward foil flaps in the same directions to maintain pitch altitude at a value chosen by the setting of a manual controller 44. The signal from the after accelerometer 36 has an integral component added and is applied to the system through an amplifier (not shown) the gain of which may be varied either manually, or automatically in dependence on the average of short term disturbances detected by a forward vertical accelerometer 38 so that damping is increased in rough short seas,. The sensitivity of pitch control is varied by signals from a craft speed detector 48 so that sensitivity is low up to the speed at which the hull becomes airborne and varies in correspondence with craft speed thereafter. Roll altitude. Signals from the bank pick-off of gyro-vertical 30 and a roll rate gyro 34 are also applied through control unit 42 to operate the forward foil flaps in opposite directions to maintain roll altitude at a value chosen by the setting of a manual controller 42. Altitude. The average of signals derived from a pair of radio altimeters 40 mounted well forward in the bow of the craft applied together with signals from a forward vertical accelerometer 38 through control unit 42 to control a hydraulic unit 60 actuating the after foil flap to maintain the craft at a height determined by the setting of a manual controller 46. Sea-state signals corresponding to the average depth of wave troughs below the mean sea level, obtaining by filtering the height signals, are also introduced smoothly into the system after lift-off by a programme unit (not shown). The signals from the forward accelerometer 38 have an integral component added and are modified in dependence on short term sea disturbances in the same manner as signals from the after accelerometer 36 which are applied to the pitch altitude control system. Both accelerometers are of the transistorised servo type. The outputs from the two radio altimeters are continuously compared with each other and with a short period average of their outputs so that any large variation, indicating a fault, is effective to disconnect the faulty altimeter. Steering. The craft is steered by signals from a manual turn controller 62 controlling a hydraulic actuator (not shown) operating the rudder. Stabilizing signals are added from a yaw rate gyro 32 through a high pass filter. Coordinated turns. Banking of the craft to suit the turn may be achieved by applying the product of signals from yaw rate gyro 32 and craft speed detector 48 through a low pass filter and limiter to the roll altitude control system. The same signal is also applied to the altitude control system to prevent the outboard foil broaching the water surface during a turn. The limits imposed by the limiter are automatically adjusted in dependence on the craft altitude and sea-state signals. Control console. A centralized arrangement of manual controls, visual indicators and test signals is described.