Patent GB-1204899-A (GB)
Title: Inertial navigator
IPC: G01C25/00
Filed: 1967-12-08
Abstract: 1,204,899. Inertial navigation. UNITED AIRCRAFT CORP. Dec.8, 1967 [Dec.14, 1966], No.55945/67. Heading G1C. An inertial navigation system comprises a stable platform provided with at least a pair of accelerometers with orthogonally diposed horizontal sensitive axes and an azimuth gyroscope, a manual control providing a command signal in accordance with the desired ground track of the craft on which the system is mounted, a torque responsive to the command signal for torquing the azimuth gyroscope and thus by means of a followup system the platform until the sensitive axis of one of the accelerometers is aligned with the desired ground track and a further follow-up system responsive to the other accelerometers for preventing deviations of the craft from the desired ground track. The system is described with reference to its use in a craft such as a helicopter which flies between and hovers at selected points to allow, for example, the lowering of a cable suspended sonar dome into the sea at each selected point. The platform is stablized by three gyroscopes and three accelerometers are also provided arranged with orthogonal sensing axes in the normal way. At each selected point whilst hovering the platform is levelled and the gyroscopes are calibrated for drift and earth rate. Whilst at each point the pilot manually sets controls for latitude, desired ground track heading for flying to the next point, distance to the next point and magnetic variation; if true headings are being used. A gyro-horizon controls the altitude of the craft in pitch and bank and its altitude controlled by a sonic altimeters. A flux gate provides craft azimuth in formation and input signal representative of earth rate is arranged to allow for the effects on the platform of Cariolis acceleration. In this way the platform is arranged to rotate in azimuth at each selected point to bring the sensitive axis of one of the accelerometers into alignment with the desired ground track heading to the next selected point. On operation of a single control the sonar dome is raised and the craft accelerates along the desired heading to a selected air-speed below its cruising speed, then climbs to a desired cruising altitude and further accelerates to fly to the next selected point. During this process signals representing air-speed and avaiable engine output are fed to the system to monitor its operation. A rate-of-turn gyro and slip-skid accelerometer are also provided to minitor the course followed by the craft. As the craft nears the next selected point, the system creates a phantom point beyond and at a lower altitude that the desired point and the craft glides towards this phantom point until close to the desired point when by means of relays under control of the altimeter and air-speed inputs the craft is directed to and hovers at the desired point and the sonar dome is lowered to the desired depth in the sea. In this way the time taken to fly from one point to the next is reduced, and of course, the platform altitude is corrected at each point and aligned in azimuth with the ground track to the next selected point. Means are also provided for keeping the sonar dome cable vertical at each point and for aligning the craft with the ground track to the next point whilst the sonar dome is lowered.