The use of an inertial measurement unit in the flight testing of a small, remote-piloted air vehicle
Abstract
A 3 meter-span, unmanned air vehicle has been flight tested in order to find its dynamic modes of motion, in-flight Euler angles, and in-flight angles of attack and sideslip angles. Instrumentation included an inertial measurement unit, a GPS, and a 3-axis sonic anemometer. Before flight, the inertial measurement unit was calibrated for rotation rate, temperature, and acceleration. Each of these calibrations was linear. The dynamic modes were estimated based on aircraft geometry, mass, and moments of inertia. For the short period pitch, Dutch roll, and roll modes, the estimates were compared to results from flight and were found to match. The Phugoid and spiral modes were found to be impractical to flight test due to space constraints and atmospheric turbulence, respectively. The low wing loading of the UAV strengthened the influence of atmospheric turbulence on the rate gyro data. The Euler angles were calculated from rate gyro data and compared to other measurement or calculation methods, including a ground-based video camera and equations using GPS and sonic anemometer data. It was found that roll and pitch angle errors fluctuate around zero due to coupling between the Euler angle equations. Yaw angle, however, does not exhibit this behavior. It was established that Euler angle drift rates of less than 6°/s can be achieved through calculation from rate gyros and that better results may be obtained by updating the Euler angles with outside sources of information. The angles of attack and sideslip angles were calculated from rate gyro and GPS data and compared to sonic anemometer calculations. It was found that angle of attack calculated the former way did not match the sonic anemometer calculations due to error in pitch angle and possibly the GPS' slow, 4 Hz update rate. Sideslip angle did match the sonic anemometer data after accounting for error in yaw angle and GPS lag. These results can be used as a foundation for the improvement of cheap, light flight testing equipment for small UAVs.
Degree
M.S.A.A.
Advisors
Sullivan, Purdue University.
Subject Area
Aerospace engineering
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