The Boeing Company

Jack C Shaw

Melville D McIntyre

Guy R Olbrechts

John F Gilbert

A plurality of inertial measuring unit (IMU) modules (41A, B, C and D) each comprising gyros and accelerometers (61, 65 and 67) for sensing inertial information along two orthogonal axes, are strapdown mounted in an aircraft, preferably such that the sense axes of the IMUs are skewed with respect to one another. Inertial and temperature signals produced by the IMU modules, plus pressure signals produced by a plurality of pressure transducer modules (43A, B and C) and air temperature signals produced by total air temperature sensors (45A and B) are applied to redundant signal processors (47A, B and C). The signal processors convert the raw analog information signals into digital form, error compensate the incoming raw digital data and, then, manipulate the compensated digital data to produce signals suitable for use by the automatic flight control, pilot display and navigation systems of the aircraft. The signal processors include: an interface system comprising a gyro subsystem (47), an accelerometer and air calibration data subsystem (50) and an air data and temperature subsystem (52); a computer (54); an instruction decoder ( 56); and, a clock (58). During computer interrupt intervals raw digital data is fed to the computer (54) by the interface subsystems under the control of the instruction decoder (56). The computer includes a central processing unit that compensates raw digital gyro and accelerometer data to eliminate bias, scale factor, dynamic and temperature errors, as necessary. The central processing unit also modifies the gyro and accelerometer data to compensate for relative misalignment between the sense axes of the gyros and accelerometers and for the skewed orientation of these sense axes relative to the yaw, roll and pitch axes of the aircraft. Further, accelerometer data is transformed from body coordinate form to navigational coordinate form and the result used to determine the velocity and position of the aircraft. Finally, the central processing unit develops initializing alignment signals and develops altitude, speed and corrected temperature and pressure signals.

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Kirkland, WA, United States of America

Jack C Shaw