Plenary Lecture

The Οptimization of CUMULUS Micro Aerial Vehicle Aerodynamics by using the Adaptive Flexible Wing Tip Concept

Professor Boscoianu Mircea
Co-authors: Adrian Coman, Pahonie Radu
Aircraft Department
Military Technical Academy
81-83, G. Cosbuc street, 5 sector, Bucharest
ROMANIA
 

Abstract: We propose a numerical analysis for improving the aerodynamic, dynamic performances and the quality of flight of Cumulus fixed flying wing MAV. The aim is to extend the flight envelope (efficient reducing of minimum speed and a better behavior at high angles of attack near stall) by using a special flexible configuration at the tip of the wing. This adaptive flexible wing solution was propose for the first time at University of Florida (US) although not in this form. This solution utilized a combination of biological concepts and composite material to produce a thin undercambered, flexible wing and then analyzed the effects of the morphing mechanism in the wind tunnel. For Cumulus the central planform remains rigid but the tips will be modified for a flexible solution.
We propose also an innovative deep stall maneuver for emergency landing by using this adaptative flexible concept for Cumulus flying wing MAV previously developed and designed. A morphing MAV is generally accepted to be a small aircraft whose shape changes during flight to optimize performances especially in critical regimes. The morphing of the wing tips investigated here essentially acts like a control effector in that their shapes are changed to alter the flight dynamics. So we use the simple form of morphing: a twist of the wing tips.
The solution to generate this twist at the tips is to modify the membrane of the wing with a simple mechanism which is easily achieved by using standard actuation schemes. Twist can be achieved by connecting parts of the wing to a servo in the semi flexible fixed wing. Twist can also be achieved by embedding carbon fiber torque rods into the structure. Any method is good considering the small loading of the wing tips generated by the low flight speeds.
Miniature airplanes are extremely sensitive to wind gusts, but the using of the flexible wing tip concept produce an efficient improving of stability of flight and the capacity to react at critical regimes, typical for a MAV mission. This is achieved by the washout effect that takes place as the wing tip deforms when excessive load is applied during windy conditions. The span of the flexible wing tip is an important factor that is also

Fig.1 Cumulus flying semi flexible fixed wing MAV

taken under consideration and study. After experiencing a wind gust, the wing tip will return to its original shape. The washout effect reduces the induced drag on the wing tips of the wing and creates a higher lift to drag ratio . We are able to prove that the (semi) flexible wing has the ability to generate washout during aerodynamic loading. Having washout on a wing reduces the induced drag of the wing, and raises the lift to drag ratio of the aircraft. The extent of washout is determined by calculating the negative angle between the root chord and the tip chord.