Minimum Complexity Uninhabited Air Vehicle Guidance and Flight Control System

The availability of commercial single antenna GPS units at low cost and discontinuation of selective availability of the system has cased an increased interest in flying a stable fixed-wing aircraft using GPS alone. Utilizing such an inexpensive sensor, along with a relatively simple processor, a flight control and guidance system could be developed that would be so inexpensive as to be practically disposable even for some commercial applications. A flight control and guidance system that can operate on single antenna GPS measurements is also a candidate as an ultimate backup mode for any uninhabited air vehicle or piloted airplane given failures of sensors. In this paper, necessary hardware and software developments will be described, as well as particular solutions explored in a flight test program. Introduction Today, computers with significant computational capabilities continually become less expensive. The economics of consumer electronics has also made inexpensive GPS units available. A remarkable notion is to develop a guidance and flight control architecture that utilizes a single antenna GPS as a sole sensor, resulting in a very low cost system, still capable of rudimentary waypoint navigation, altitude control, and approach courses. However, when developing a flight control system for an Uninhabited Air Vehicle (UAV) using GPS alone, several issues arise. These inexpensive commercial units typically have update rates of 1 Hz and significant latency. Also, position and velocity is less information than that conventionally used for flight control, where air data and gyroscopic instruments are commonplace. The challenge is develop algorithms for navigation and flight control which maximize the robustness, tracking bandwidth, and accuracy given this limited sensor capability. An architecture is proposed, which utilizes observers for bank angle and wind components to reconstruct this “missing” sensor information. The airplane is assumed to be statically stable, and with a short-period mode that is fast compared to the response of the autopilot. By these assumptions, angle of attack is effectively set directly by elevator position at a given airspeed. This architecture has been implemented on a small fixed-wing UAV shown figure 1. Figure 1. Low cost aerial vehicle, with avionics mounted above wing (GPS receiver), and in boxes on the sides of the fuselage (computer and battery) This model aircraft used for flight test is a Thunder Tiger Trainer 60 Almost Ready to Fly (ARF) training remote control model airplane with a 0.6 cubic inch engine. During the flight tests the onboard computer is installed under the wing on the right side, the power box under the wing on the left