Design and Testing of Deflected Slipstream Airfoil for VTOL Hover Enabled by CoFlow Jet
Gecheng Zha, Yan Ren, William J. Fredericks, Siena Whiteside
Abstract
This paper reports a design and testing research work to demonstrate the performance of a Deflected Slipstream (DS) airfoil for VTOL hover, which is enabled by CoFlow Jet (CFJ) active flow control. A CFJ-NACA-6421 airfoil with a chord of 65 cm is designed and tested. The flap has 66.74%C with 4 Schubeler EDF DS-30-AXI (69 mm) fans used as CFJ actuators. The aerodynamic design includes the flapped CFJ airfoil with optimized injection and suction location and size, internal ducts, and matching the micro-fans as the CFJ actuator. The test was conducted using a frame to hold the airfoil section in outdoor environment to mimic static hover condition. The testing includes measuring lift and drag, which are used to calculate the flow deflection angle. Flow visualization with smoke and tufts were used to observe the slipstream deflection. The airfoil setup has the flap deflected upward to avoid ground effect. The deflected slipstream enabled by CoFlow Jet is proven to be very effective by both the force measurement and flow visualization. The slipstream deflection angle θ is always greater than the flap deflection angle β. For as low as a flap deflection angle of 78◦, the slipstream can be deflected to 90◦ - 120◦. A deflection angle of more than 90◦ will generate backward thrust.