Weapon IMU transfer alignment using aircraft position from actual flight tests

This paper presents results from a study of weapon inertial measurement unit (IMU) transfer alignment using the aircraft´s navigation system position data. The alignment process consists of first establishing a navigation solution (position, velocity and attitude) using the raw IMU outputs, then via a Kalman filter algorithm estimate errors in the weapon navigation data using aircraft navigation system data as observations. The aircraft´s navigation system data is used to initialize the weapon´s navigation solution. The results presented in this paper are based on using the aircraft´s position data as the filter algorithm´s observation. Using flight data, it is shown that a weapon´s navigation frame can be aligned to an accuracy of less than 1 milliradian. The alignment error is determined by assuming that the total difference between the weapon´s post-alignment free-inertial position and the aircraft´s position is the result of horizontal navigation frame tilt error alone. The affect of the aircraft´s flexible structure during higher maneuver levels is illustrated