The whole operation of fuel transfer and management is watch over and controlled by the Flight Engineer, from his panel on the flight deck
The correct centre of gravity (CG) placement is vital to Concorde. The cruise speed cannot be attained with the centre of gravity at its take-off value, add to that Concorde cannot be landed with the CG at the supercruise position. It is as important as flap/slats to other aircraft; in the case of Concorde it’s even more important as subsonic aircraft can always make a flapless landing, unlike Concorde.
A general rule of aircraft design is that everything is duplicated, in the case of Concorde there are three CG indicating systems, and some critical things are quadruplicated, there are four pumps available in Tank 11 which guarantee forward movement of fuel, and therefore CG, which enables flight at approach and landing speeds, two pumps powered from electrical systems, one from the left-hand hydraulic system and one from the right-hand hydraulics.
Before Concorde takes-off, the flight engineer will start to move fuel from the forward trim tanks to the rear trim and collection tanks, this will continue during the acceleration through Mach 1 and onto eventual Mach 2. During this process around 20 tons of fuel is moved and this results in a shift of the CG by 6ft (2meters). This will neatly balance the change in the centre lift of the aircraft.
As Concorde reaches the end of the cruise and during the deceleration stage, the reverse happens; fuel is pumped forward to the wing transferred forward trim tanks. This moves the CG forward again and the therefore the lift moves forward. When Concorde has lands, the engineer starts to pump more fuel into the forward fuel tanks, this is a standard practice to correctly balance Concorde, so that she can be unloaded without and stability problems, as Concorde is heavier at the rear and this has to be corrected.
Concorde needs this fuel transfer system to achieve the necessary efficiency in high-speed flight, but it also provides several extra benefits for the aircraft. The ability to put the aircraft’s weight in the right place throughout the flight, which means that very little use, is made of pitch trim. This is a bonus for the pilot, for large trim changes are a real nuisance, tending to make accurate flying very difficult. Another bonus comes oddly enough, from being able to put the aircraft deliberately a little out of trim. On take-off and landing, the CG is placed slightly further back than it needs to be. As a result the elevons go down to counteract this rearward weight shift, in doing so increase the camber of the wing.
LOAD LIMIT CONTROL
During the normal mode of fuel trim transfer, fuel is pumped either from tanks 9 and 10 into tanks 11, 5, and 7 to obtain a rearward CG shift, or from tank 11 into tanks 9, 5 and 7 to obtain a forward CG shift. The trim tank contents are pre-selected on two load limit selectors, one for tank 9 and 10 and the other for tank 11. Any fuel in excess of the trim tank requirements is transferred into tanks 5 and 7. The load limit control channels are duplicated and each one automatically continues controlling should the other channel fail.
The collector tanks are replenished from the main transfer tanks 5, 6, 7, & 8 in a sequence that minimizes the movement of the aircraft centre of gravity
The main transfer sequence is manually initiated using the pumps in tanks 5 and 7. Each collector tank is equipped with main and standby 115V AC electric motor driven pumps. The electrical loads of the fuel system are supplied from the aircraft’s electrical power system via circuit breakers on the distribution busbars. The main AC and DC circuit breakers are located above the equipment racks on both sides of the flight compartment; the essential AC and DC circuit breakers are located forward of the racks on the left side.
The main transfer sequence is:-
Tank 5 – Replenishment tank 1 via the left-hand pump, and tank 2 via the right-hand pump.
Tank 7 – Replenishment tank 3 via the left-hand pump, and tank 4 via the right-hand pump.
When tanks 5 and 7 are empty, the pumps in tanks 6 and 8 continue the transfer by:-
Tank 6 – Replenishment tank 1 via the left-hand pump, and tank 2 via the right-hand pump
Tank 8 – Replenishment tank 3 via the left-hand pump, and tank 4 via the right-hand pump.
Transfer of fuel from the auxiliary tanks 5A and 7A is into their respective main tanks 5 and 7.
The trim transfer system is used to redistribute the fuel in the trim tanks and main transfer tanks so that the aircraft centre of gravity can be moved to optimum positions for take-off, subsonic and supersonic flight.
The trim transfer is normally automatically sequenced and controlled from the Flight Engineer’s Panel; however there is a forward transfer override control available to the Pilots for use in abnormal circumstances requiring a rapid forward transfer of fuel.
The aft trim tank (Tank number 11) has four pumps two of which PUMP GREEN and PUMP BLUE are powered by their respective hydraulic system. Thus forward transfer capability is available using electric or hydraulic power.
The trim transfer system is augmented in the aft trim condition by a reduced level operation in collector tanks 1 and 4. As tanks 1 and 4 are located well forward this moves the aircraft centre of gravity further rearward. The resultant rearward centre of gravity is the optimum for minimum trim drag in supersonic cruise
CG POSITION INDICATION
Each CG indicator is derived from any one of three channels. The main channel is the one normally used with Standby 1 and Standby 2 channels availably in the event of a main channel failure. Each channel has its own CG pack in which the CG position is computed using fuel quantity information and other fixed and manually introduced inputs.
The main channel uses fuel quantity indication from all tanks in computing the CG.
Standby 1 channel uses fuel quantity indication from only those tanks on the left-hand side of the aircraft and channel A of tanks 9, 10 and 11. For computation purposes the sum of the left-hand tank moments is doubled.
Standby 2 channel computes the CG in a similar manner to Standby 1 but uses the tanks in the right-hand side of the aircraft and channel B of tanks 9, 10 and 11.
CG & MACH LIMITS INDICATION
Bugs on the CG indicators show the forward (fwd) and rear (aft) boundaries of the CG corridor relative to Mach number. Bugs on the Machmeters show the maximum and minimum mach limits relative to the aircraft CG position. Both the CG and Mach number band widths move relative to Mach number and CG respectively.
The limits display is provided by two identical but separate channels. One is contained in the Standby 1 CG pack and serves the Captain’s CG Indicators and Machmeters.
The other channel is contained in the Standby 2 CG pack and serves the First Officers Machmeter and the Flight Engineers CG Indicators.
CG & MACH LIMIT WARNINGS
CG and Mach limits warnings are provided at two levels of CG/Mach number values. The first warning activates at a normal boundary level and the second warning activates when the normal boundary limits have been exceeded by a further margin.
The second warning level is defined as an extreme boundary. Its purpose is to indicate when corrective actions, taken at the normal boundary warning, are not producing a rapid enough correction of CG/Mach valves.
The warnings are initiated through two separate channels; one in STANDBY 1 CG pack and the other STANDBY 2 CG pack. Both channels function the master warning system, but STANDBY 1 channel activates the pilots Machmeter/CG indicator warning and STANDBY 2 channel activates the identical warnings at the First Officers Machmeter and the Flight Engineer’s CG indicator.
For further information on the fuel system, click on the links below!
For further information about the Concorde fuel system, click on the links below!
Including – Safety & Cleanliness Precautions during Refueling. Water Check Operations, Magnetic Fuel Indicator, Types of Fuel and requirements
Approved Fuels and Additives for Concorde