Rotorcraft performance enhancements due to a lower-surface effector

Although the application of advanced structures and Intelligent control systems on helicopters has seen a dramatic increase over the past two decades, the overall performance of helicopters, relative to fixed-wing aircraft, has been somewhat stagnant. This is due to many factors, one of them being the lack of innovative aerodynamic devices that can operate in the unique environment of a rotor. Research over the past 20 years has shown that in order to have a performance increase with the rotor, It must adapt to the changing environment around the azimuth. One method of doing this that is being researched is the use of miniature trailing-edge effectors (MITEs) on the blades of the rotor. MITEs are an extension of the passive high-lift device, the Gurney flap. Gurney flaps are small flat plates, between 0.5 to 5 percent chord, fitted perpendicular to the airfoil surface at or near the trailing edge of a wing or rotor blade. A MiTE is an active Gurney flap, which can be used to actively control the spanwise and azlmuthal lift and moment distributions on a rotor blade. Compared to traditional tralling-edge flaps, which are being explored for the same application, MITEs have the advantage of very low inertia and actuator loads. MiTEs have been the focus of experimental and validated computational fluid dynamics research and, as a result of these efforts, an unsteady aerodynamic model was created for MiTEs located at the trailing edge. In the present work, this model has been modified to account for MITEs placed up to 15-percent of chord upstream of the trailing edge. This model has been Incorporated into a rotor performance code to predict the effect of MITEs on rotor performance and explore their ability to extend the flight envelope of the RAH-66 Comanche. With the increased use of transonic airfoils as facilitated through the use of MiTEs on the outboard section of the rotor blades for stall delay, a 15-percent or more increase In the maximum velocity of Comanche Is predicted, or an eight-percent increase in the service ceiling could be achieved.