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LOT OF FUEL, BUT NOT ALL FOR THE ENGINES



In common with any aircraft the Concorde design has to ensure the stability of the aircraft over the complete speed range.

It is well known that, as an aircraft accelerates, its aerodynamic center of pressure moves backwards. On a lot of subsonic aircraft the tendency of the plane to pitch down is corrected by trimming the elevators, but there is an aerodynamic drag penalty associated with this gain in stability

For Concorde at Mach 2.2 a rearward shift of two meters in the center of aerodynamic pressure occurs.

The solution suggested is French :
it consists in using the fuel like mobile ballast.

The kerosene fuel is primarily contained in the wings, but two supplementary tanks are located in the fuselage, one in the front and the other in the back. They contain approximately a third of the fuel. In the climb and acceleration, fuel is pumped rearward into the tanks of the wing and tail. The centre of gravity will thus move back at the same time as the center of pressure. The idea, proposed by the engineers from Dassault, was implemented successfully on the Mirage IV.

Click on the picture to get a big version


In subsonic equilibrium (1)



In supersonic flight the aircraft "TENDS TO PIQUER" as the gentre of gravity moves back(2)



Classic solution is to rebalance the aircraft using the elevons but this increases the drag (3)



On Concorde the rebalancing is achieved by a system of fuel transfer,which makes it possible to readjust the centre of gravity of the aircraft to match the aerodynamic center of pressure both during acceleration when the c.g. moves back(4) and,



during deceleration, when the center of gravity moves forward again (5),



to move at the same time the centre of gravity (6).

Original article: Science & Life N°9 - June 1992.

This page has been corrected by Gerald Wilson - Lytham, Lancs., Uk - Thanks to him.


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The Fuel System

Concorde's multi-function fuel system also is complex, and in comparison, the 727's flight engineer panel is a piece of cake. One Concorde flight engineer described the fuel system as ". . . typically British. There are 13 fuel tanks, numbered one through eleven."

Fuel tanks 1, 2, 3 and 4 are engine feed tanks. Tanks 5, 6, 7, 7a, 8 and 8a are transfer tanks that flow into the engine feed tanks. The forward tanks, number 9 and 10, and the aft tank, number 11, are trim tanks used to move Concorde's c.g. fore and aft during cruise. Total fuel is 95,430 kilograms, or 209,946 pounds (approximately 26,400 gallons).

Concorde has four refueling points, two in front of each main landing gear. The automatic refueling system first puts fuel in the forward-most tank, tank 9, to ensure Concorde does not squat on its tail. Tank 11, the aft most tank is filled last.

But the fuel is used for other purposes besides feeding the thirsty Rolls-Royce Olympus engines. It also is used as a heat sink to cool hydraulic fluid and air passing through the air conditioning heat exchangers.

In flight, the flight engineer also uses the fuel to shift Concorde's c.g. as it accelerates. Shifting the c.g. aft (from 51 to 52 percent Mean Aerodynamic Chord for takeoff to 58 percent at 2.0 Mach) keeps the center of lift relatively stationary and the elevons relatively flush. This is extremely important as any control deflection creates drag and drag equals increased fuel consumption. During deceleration, for landing or as the result of an engine failure, fuel must be shifted forward.

Transfers are closely coordinated between the flight engineer and the pilot to maintain optimum controllability of the aircraft. With an outside temperature higher than normal, fuel can transfer aft faster than the airplane can accelerate. Likewise, in colder than normal air, Concorde will accelerate faster than fuel can be transferred aft. In either case, the fuel transfer is not a simple task of just opening a valve and turning on pumps.