Aerodynamic Testing of a Circular Planform Concept Aircraft

Abstract

Auburn University has entered into collaboration with Geobat Flying Saucer Aviation Inc. for aerodynamic and flow visualization studies of the Geobat aircraft. The aircraft model that was tested consisted of a circular planform with a central opening. A circular disk with an airfoil cross-section in the streamwise direction can offer distinct advantages of a circular planform configuration such as the reduced influence of tip vortices and hence lower induced drag. The aerodynamic challenges of such planforms include longitudinal and lateral stability, controllability and handling qualities partly due to the unique dynamics of wake vorticity. Wind tunnel testing was conducted to study the longitudinal stability of the Geobat aircraft. Studies include analysis of both a solid flat disk and one with similar geometric characteristics of the Geobat. The Geobat was tested with and with out a leading edge transition strip to determine the difference between laminar and turbulent flow over the model. Multiple flap and elevator deflections were tested for both cases to help determine longitudinal stability characteristics. For comparison, a highly stable and conventional aircraft model, a Cessna 172, was also tested under the same conditions. After comparing, it was found that the Geobat model yielded much better stall characteristics than the Cessna 172 while pitching moment trends show a far less stable aircraft. Comparing the laminar and turbulent testing, aerodynamic data shows that the transition strip does not affect the longitudinal characteristics below the stall region. This illustrates that the flow over the model is already turbulent in nature. This can be seen in the flow visualization tests where a crescent shaped separation bubble was located at the leading edge tripping the flow to turbulent. Also distinct recirculation near the cockpit and trailing edge of the control surfaces was also observed.