Applying traditional wind tunnel testing to unconventional aircraft

AFRL aeronautical engineers collaborated with the Electronic Systems Center’s (ESC) Force Protection Program Office, Hanscom Air Force Base (AFB), Massachusetts, to conduct an in-house effort assessing the Desert Hawk small unmanned air vehicle’s (SUAV) performance and exploring potential improvements to that performance. Desert Hawk, also known as the Force Protection Airborne Surveillance System (FPASS), performs air base perimeter defense and other intelligence, surveillance, and reconnaissance tasks.

The team’s efforts to analyze Desert Hawk performance ultimately culminated in a wind tunnel test of the airframe in AFRL’s Vertical Wind Tunnel (VWT), Wright-Patterson AFB, Ohio. While the initial goal of the analysis was to increase Desert Hawk’s overall flight endurance by implementing evolutionary airframe improvements, preliminary results indicated that significant improvements to the aircraft’s endurance would require a clean-sheet redesign. The engineers then applied a traditional aeronautical engineering approach to characterize the Desert Hawk—and thus gain a better understanding of its performance and flight envelope.

To further enhance its knowledge of the aircraft, the collaborative team obtained a Desert Hawk flight article through prime contractor Lockheed Skunk Works and successfully tested it in the laboratory’s VWT (see figure). With the objective of improving Desert Hawk’s flying qualities and therefore its mission effectiveness, the team tested various thrust effects and a range of control surface deflections to produce a robust aerodynamic model as a baseline for future control system refinement.

Since the AFRL/ESC Desert Hawk collaboration began, Lockheed engineers have designed and flighttested two new iterations of FPASS. These new versions have provided greater endurance, increased airframe survivability, incorporated more sophisticated onboard sensors and observation systems, and introduced an improved ground-operator interface. Insights gained from the rigorous aerodynamic analysis and comprehensive VWT tests conducted in-house at AFRL will enable ESC and the Air Force SUAV community to generate more precise flight performance requirements and be smarter buyers in future acquisition programs. Results of the wind tunnel testing are expected to produce a higher-performance version of the evolving Desert Hawk/FPASS airframe.

Lt Milton Wancowicz III and Dr. Michael Ol, of the Air Force Research Laboratory’s Air Vehicles Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn_index.asp. Desert Hawk being tested in the VWT Reference document VA-H-06-02.