Modeling, Simulation and Flight Testing to Support Proof of a Stratospheric Dual Aircraft Platform Concept

Dual-aircraft platform (DAP) is a novel atmospheric satellite concept that features two glider-like unmanned vehicles connected via a thin adjustable cable allowing them to sail back-and-forth, without propulsion, using modest levels of vertical wind shear. This paper presents the results of an initiative to demonstrate this novel flight concept through simulation and flight testing at Embry-Riddle Aeronautical University (ERAU). A realistic simulation environment, described herein, was developed to support the development and testing of flight control systems. This environment includes nonlinear aerodynamic models for the aircraft, a multi-element cable dynamics model, propeller-motor thrust model, control surface actuator models, and time-varying wind profiles. This simulator offers both pilot-in-the-loop control and autonomous sailing flight control, and an interface to provide visualization cues. A flight test program was also initiated to support validation of the DAP concept. Glider-like unmanned aircraft were assembled, instrumented, and flight tested in an effort to physically demonstrate the sailing mode of flight. The test scenarios described here focus on the capability to sail with one aircraft (i.e., fly without propulsion) while "towing" (i.e., pulling on) a moving truck as an intermediate step towards the more complex scenario of sailing with two connected aircraft. The ongoing transition of this flight test program from manual to autonomous control led to development of a formation flight controller and evaluation of the accuracy of onboard wind estimation techniques.