A Close Formation Flight Test for Automated Air Refueling

S.M. Ross, M. Pachter, D.R. Jacques, J. Raquet

Abstract:	A close formation flight control system was designed for aerial refueling and flight tested in the first fully autonomous close formation flight. A United States Air Force C-12 (Beechcraft King Air) operated as a simulated tanker, and a Calspan LJ-25 (Learjet) was flown autonomously, simulating a refueling receiver; both are shown in Figure 1. The aircraft accomplished all of the close formation tasks required during air refueling. A carrier-phase differential GPS (DGPS) was designed to provide relative position information, and a micromechanical inertial measurement unit (MEMS IMU) was used to provide angular information from the lead aircraft. In this paper, the air refueling problem is explained, and the navigation requirements and system models are outlined. The concept of the control frame is developed, and the control laws are stated. System specifics of initialization and formation position change techniques are also detailed. The modifications to the aircraft that were required for flight test are listed, and simulation is used for risk mitigation of factors such as time delay, turbulence, unexpected bank angles and roll rates, sensor noise, and sampling rate differences between hardware components in the system. Of the several difficulties during flight test, two stood out of interest to the navigation community. The pitch and heading channels of the IMU failed, forcing a simple heading estimation system to be quickly designed, simulated, and installed. The DGPS also had an anomaly, which was erroneously analyzed as excessive sensor noise. This resulted in a reduction of the total aileron loop gain, which adversely affected performance during dynamic maneuvers. The flight test results are summarized, with representative performance plots. The completed work represents a significant step toward the capability of autonomous air refueling on an unmanned system.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	662 - 673
Cite this article:	Ross, S.M., Pachter, M., Jacques, D.R., Raquet, J., "A Close Formation Flight Test for Automated Air Refueling," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 662-673.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In