Delta-winged aircraft

Delta wings are effectively swept, and tailless delta-winged types can be stabilised in the same way as other tailless aircraft. However, a major problem arises with supersonic tailless deltas, because the rearward shift of the centre of lift position has to be trimmed by a large up-elevator movement. This significantly reduces the lift, while increasing the drag. On Concorde, the prob­lem is mainly solved by rapidly pumping fuel from a front tank to a rear one, so as to move the centre of gravity back for high speed flight. The movements of fuel during any flight have to be carefully calculated before take-off. This method of stability control, though complicated, does result in efficient flight with little or no trim drag.

In addition, the shape of the camber line may be used to control movement of the centre of lift. In Chapter 1 we explained how the lift due to angle of attack, and lift due to camber, were almost independent. At low speeds, the lift coefficient and angle of attack are large, so the lift force is dominated by the angle of attack. The centre of lift will be about – of the way back from the leading edge (- chord position). At high speed, the lift coefficient and angle of attack are low, and the lift is dominated by the camber. By suitable shaping of the camber line, the centre of lift at high speed (low angle of attack) can be arranged to be at about the same position as at low speed (high angle of attack). The very pronounced droop of the leading edge of Concorde’s wing produced by the camber may be seen in Fig. 2.23.

Because of the problems of control and stability of tailless deltas, many delta-winged aircraft have a small tail, or a foreplane.