Canard-Elevon Interactions on a Hypersonic Vehicle

Abstract : Airbreathing hypersonic cruise vehicles are typically characterized by long, slender bodies with highly coupled engines and airframes. For a case in which the engine is underslung (below the center of gravity), a large elevon control surface is typically necessary to trim the vehicle. The elevon is usually placed at the rear of the vehicle to yield a large moment arm. However, the drawback is that the elevons can cause large perturbations in lift and other undesirable effects. Canard control surfaces are placed on the forebody of the vehicle to counteract these effects as well as aid in low-speed handling. This study looks at how the canards affect the flow over the elevon control surfaces and, in turn, the controllability of the vehicle in general. A two-dimensional analytical formulation is developed and compared with both a series approximation solution and a computational fluid dynamics Euler flow field solution. The effect of the canard on the elevon, measured using the elevon effectiveness ratio, decreased as the distance between the control surfaces increased. In general, higher Mach numbers combined with higher canard detection angles resulted in a greater effect on the elevon. Adding a thickness correction, as opposed to assuming that the airfoils were at plates, actually decreased, on average, the accuracy of the model when compared with the computational data.