The Conceptual Design of a Tailless Sailplane Having a Stabilizing Fuselage

Abstract

A conceptual design of a tailless Standard Class sailplane is presented in this paper.  Longitudinal static stability requires a negative pitching moment gradient with respect to the lift coefficient and a positive pitching moment at zero lift.  The former depends on the position of the center of gravity with respect to the neutral point of the aircraft, while the latter, in the case of tailless sailplanes, is obtained by designing the wing to take over the stabilizing function normally provided by the empennage.  The two methods employed to achieve this, often in combination, are the use of an airfoil with a positive moment coefficient about its aerodynamic center, and the aft sweeping with washout of the wing to provide the needed positive pitching moment at zero lift.  The idea introduced here explores a fuselage design that helps to support the stabilizing function.  The pressure distribution around the fuselage is tailored to contribute to the stability of the vehicle.  To determine the overall benefit of this concept, the cross-country performance of the tailless aircraft is predicted and compared to that of a current conventional sailplane.  It is found that the conceptual design is predicted to achieve performance levels comparable to those of conventional designs.