Concorde

It seems fitting to conclude a discussion on the problems of flight, from sub­sonic to supersonic, with some comments on the design of the late lamented Concorde, because controversy on its cost, on its sonic boom and on its com­mercial viability have tended to obscure the cleverness of its design. Readers who have followed the arguments put forward in this book will surely be fas­cinated by some of its outstanding features. It would possibly be going too far to describe one of the main features of such a costly and sophisticated piece of equipment as simplicity yet, as we shall see, there is some truth in such a description.

The now familiar ogee (or double curve) plan shape of the wing gives both a large chord (27.7 m), with its advantages, and a large span (25.6 m), with its advantages.

The large chord means that although the wing is thin, very thin, from the aerodynamic (t/c) point of view (only 3 per cent at the root and 2.15 per cent outside the engine nacelles), and so has low wave drag; yet at the same time it is deep enough (83 cm) to give the required strength and structural stiffness, usually a difficulty with slender swept-back wings. The main advantage of the large span is the reduction of vortex, or induced, drag at all speeds.

The slimness of wings and body (the Boeing 747 Jumbo Jet is longer, higher and much fatter than the Concorde), and the limitation of speed to just over Mach 2, have kept down the temperature rise and made it possible to use alu­minium alloys, with which we have long been familiar, for most parts of the structure, instead of having to experiment with the more costly, and heavier, stainless steel or titanium alloys. The temperature rise in the structure is also reduced by using the fuel as a heat sink. The maximum landing weight is 1068 kN, and the maximum landing wing loading 4.786 kN/m2, less than that of many comparable aircraft.

The ogee plan shape has another advantage in that the stalling angle is so large that it is unlikely to be reached in any ordinary condition of flight; this is because the shape leads to the formation of leading edge vortices (without any vortex generators!), and so improves the flow in the boundary layer and gives smooth changes of lift and pitching moment with angle of attack.

On the wing there are no flaps, no slots, no tabs, no spoilers, no saw teeth, no fences, nor any other devices usually required for such a large speed range as from 65.4 m/s (at 18° angle of attack) to a true speed of 649 m/s. The only moving surfaces on the wing are the six elevons (combined ailerons and eleva­tors) which control both rolling and pitching – and very effectively too. The rudder has two sections, but is otherwise simple and conventional.

The large ‘leading edge’ vortices are useful when landing as lift continues to increase to large values with increasing angle of attack, the ‘lift boost’ and the ‘form thrust’ already mentioned in connection with highly-swept wings, and the large area of the delta wing gives a considerable cushioning effect when near the ground (two reasons for dispensing with flaps).

Perhaps one of the most interesting features, taking us back to one of the earliest ideas for adjusting trim is the movement of fuel between tanks, auto­matically between the main tanks for adjusting the centre of gravity during cruising flight and, under the pilot’s control, from forward tanks to a rear tank under the fin during acceleration to supersonic flight when the aerodynamic centre moves back, and vice versa when returning to subsonic flight.

Pilots report that it is only by looking at the machmeter that they know when Concorde is going supersonic.