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Formation Flight Control

Description: 3_plane_air

Formation flight has long been performed by birds for its social and aerodynamic benefits. The traditional "V" shape formation flown by birds not only helped communication between individuals, but also decreased the induced drag for each trailing bird, and thus reduced the energy required for flying. The benefits of formation flight have also been evaluated for manned aircraft. However, due to the associated levels of risk, human-piloted close formation flight are rarely sustained for a long enough time to fully appreciate the aerodynamic benefits. Therefore, reliable autonomous formation control can be an attractive capability for both human-piloted aircraft and Unmanned Aerial Vehicles (UAVs). In fall 2004, FCSL successfully accomplished a GPS-based autonomous formation flight control experiment using three turbine-powered YF-22 unmanned research aircraft.
In this particular formation flight configuration, a ground based R/C pilot maintained control of the ‘leader’ aircraft throughout the experiment. The GPS measurements of the ‘leader’ were transmitted to each ‘follower’ at 20Hz. The two ‘follower’ aircraft were initially flown under manual control until they reached a pre-determined rendezvous point behind the ‘leader’ vehicle. The on-board flight control system on each ‘follower’ was then commanded to take-over controls of the aircraft. The formation controller was designed with an inner and outer-loop architecture. The inner-loop served the functions of disturbance attenuation and attitude tracking control. The outer-loop nonlinear guidance and control laws were designed to minimize the forward, lateral, and vertical distance error by controlling the engine throttle and generating the desired pitch and roll angles to be tracked by the inner-loop controller. The horizontal (forward and lateral) components of the outer-loop controller were designed using a Non-Linear Dynamic Inversion (NLDI) approach, while the vertical channel of the outer-loop controller and the inner-loop were linear compensation-type controllers. With the combined effort of the inner and outer-loop controllers, two autonomous ‘follower’ aircraft were able to engage and maintain pre-defined position and orientation with respect to the ‘leader’.

Due to the complexity of a multiple autonomous aircraft experiment, the flight-testing program was divided into six major phases with increasing complexity and risk level:

    1. Initial flights for assessing aircraft payload capacity and handling qualitie
    2. Data acquisition flights for evaluating avionics performance and to collect data for aircraft parameter identification effort;
    3. Inner-loop controller validation flights;
    4. Outer-loop controller sub-system validation flights;
    5. ‘Virtual leader’ flights for evaluating the ‘follower’ formation flight performance with only a single aircraft;
    6. Multiple aircraft formation flight with two and three aircraft in autonomous formation flight.

The successful completion of the 3-aircraft formation experiment validated the overall design of the formation flight controller, the test-bed aircraft, and the on-board avionic system.

Recent Publications

Gu, Y., Campa, G., Innocenti, M., “Formation Flight Control,” Editorial, International Journal of Aerospace Engineering, In Press, June, 2011.

Gu, Y., Campa, G., Seanor, B., Gururajan, S., and Napolitano, M.R., “Autonomous Formation Flight – Design and Experiments,” In Aerial Vehicles, ISBN 978-953-7619-41-1, I-Tech Education and Publishing, Austria, EU, Chapter 12, pp. 233-256, January 2009.

Campa, G., Gu, Y., Seanor, B., Napolitano, M.R., Pollini, L., and Fravolini, M.L., “Design And Flight Testing Of Nonlinear Formation Control Laws,” Control Engineering Practice, Vol. 15, No. 9, pp 1077-1092, September 2007.

Seanor, B., Gu, Y., Napolitano, M. R., Campa, G., Gururajan, S., Rowe, L., "3 Aircraft Formation Flight Experiment", Mediterranean Control Conference 2006, June 28-30, 2006, Ancona, Italy.

Gu, Y., Seanor, B., Campa, G., Napolitano, M.R., Rowe, L., Gururajan, S., Perhinschi, M.G., and Wan, S., “Design And Flight Testing Evaluation Of Formation Control Laws,” IEEE Transactions on Control Systems Technology, Vol.14, No. 6, pp. 1105-1112, November 2006.