The cone was arranged so that the wing twisted progressively outwards towards the tips creating negative incidence, and hence negative lift, in the outboard sections, creating overall stability in both pitch and yaw. A single control surface on the trailing edge of each wing tip acted as combined aileron and elevator. Dunne had an advanced qualitative appreciation of the aerodynamic principles involved, even understanding how negative lift at the wing tips, combined with steep downward-angled anhedral, enhanced directional stability.[5]