Flight Test of an Active Flow Control Enhanced Vertical Tail

Abstract

The size of the vertical tail and rudder of a commercial aircraft is influenced by the requirement that the airplane must be controllable in the event of an engine failure. As a result, on twin-engine airplanes, it is typically larger than is required for lateral/directional stability and control under normal flight conditions. Despite the rarity of the need for this level of control, the airplane must carry this size vertical tail and rudder with it at all times. The primary impact of this is additional drag and weight that reduces the fuel efficiency of the airplane. Active flow control can be used to enhance the control authority of the rudder by mitigating flow separation on it at high rudder deflection and sideslip angles. This effect can be used to provide the required level of rudder control authority from a physically smaller vertical tail. As a result, fuel efficiency of the airplane may be increased due to the reduced size and drag of the smaller vertical tail throughout the operational envelope of the airplane. In April 2015, Boeing and NASA tested a pneumatic sweeping-jet-based active flow control system on the vertical tail of the modified Boeing 757 ecoDemonstrator. This test was the culmination of several years of development that included small-scale wind-tunnel testing, computational-fluid-dynamics simulations, a system-integration study, full-scale wind-tunnel testing, and the flight demonstration. The data from the flight test indicate that the flow control actuation may be able to provide an approximately 14% increase in side force at the maximum tested rudder deflection and at critical sideslip angles.