The bell-spanload, or bell-shaped lift distribution, gives proverse yaw for outer aileron deflections, a key factor in controlling a tailless vehicle. Study of bell-spanload applications have been limited to swept wings with elevon control schemes, relying on a well-tuned proverse yaw response for a differential elevon deflection. In examining unswept wings, symmetric outer control surface deflections have minimal associated pitching moment, allowing their use in adjusting the lift distribution to optimize for a wide range of flight conditions. Lateral-directional control of bell-spanloads can be improved by the use of an additional set of ailerons inboard of the mid-span vortices. The inboard ailerons provide traditional adverse yaw which serves as a linearly independent control vector relative to the existing proverse yaw outer surfaces; the two vectors are sufficient to define a parallelogram-shaped controllable region in the roll-yaw control space
