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.