Heritage Concorde

Included on this page – Centre of Gravity (CG) - Fuel Transfer Systems – Refuelling Concorde and types of Fuel used!

Concorde, like most airliners, has multiple fuel tanks which have been detailed below. The only difference concerning Concorde is that during the flight, fuel is transferred from tank to tank to maintain trim and balance of the aircraft as Concorde does not have a full tail plane which other aircraft  use on a subsonic flights to perform this task. Any swept wing designed to fly close to Mach 1, experiences changes in the pressure pattern over it, these always have the effect of moving the centre of lift rearwards as speed increases. As a result there is a tendency to pitch down, and on subsonic aircraft this is trimmed out by an upwards deflection of the elevators, or, more usually, by moving the tailplane itself, as this cause less drag.

An aircraft such as Concorde flying at Mach 2 and above needs to do rather more, as the rearwards movement of the centre of lift is much greater. Some of the effects of the aerodynamic changes are countered by the gentle cambers and twists of Concorde’s wing, but there still remains a shift of about six feet to be accounted for. That may not sound much, but the forces involved (the lift) is opposing, and therefore equal to, the weight – which may be 170 tons at the time.

Moving the elevons up to compensate for this would obviously produce an appalling increase in drag, and would leave precious little further upward deflection available for control purposes. Instead, fuel is moved to change the internal weight distribution. In fact most of Concorde’s 95 tons of fuel is kept in tanks in the wings, but the forward two, and another in the tail cone, are used for trim as well as storage. Together they hold about 33 tons of fuel.

During supersonic flight, Centre of Gravity movement is a critical task, and therefore fuel is required to be moved around the aircraft to shift the Centre of Gravity for different speeds.

The fuel system and centre of gravity (CG) are inseparable, they are has one; CG and flight controls are also inseparable, they are as one. They are highly integrated in function but not automated in control.

The fuel is also used as a heat sink for cooling purposes. Surplus heat from the air conditioning and hydraulic systems from the constant speed drive and generator and also from the engine lubricating oil is rejected through heat exchangers to the fuel.

 

Concorde Olympus 595/ Mk 610 Engine Fuel information

Fuel Type – A1 Jet fuel

Fuel Capacity – 26,400 gallons /119,500 litres / 95,680 kgs

Fuel Consumption – (at Idle Power) 1100 kgs/hr (302 Gallons/hr)

Fuel Consumption – (at Full Power) 10500 kgs/hr (2885 Gallons/hr)

Fuel Consumption – (at Full Re-heated power) 22500 kgs/hr (6180 Gallons/hr)

Typical miles to the gallon per passenger – 17 Miles!

The fuel system on subsonic aircraft would be relatively straight forward: there will be one tank per engine, located in the wing in an area adjacent to the engine which it supplies, with then perhaps an auxiliary tank outboard in each wing, a belly tank and then maybe some sort of tail tank for the longer range.

Concorde has 13 tanks set into the delta wing and tail of the aircraft. Apart from using all space possible for tankage, its logic in not immediately apparent, but it’s vital to understand form before considering function. If you look at the picture (Fuel tank function) you will gain some idea.

RED TANKS – 1, 2, 3 & 4.

Only Red coloured tanks 1, 2, 3, and 4 can feed the four Olympus engines. The rest of the fuel is transferred into them, hence their alternative name “collector tanks”. If you can notice in the picture that tanks 1 and 4 are ahead of the CG with 2 and 3 behind, so no change of CG as their contents vary during flight.

BLUE TANKS 5, 6, 7 & 8

Blue coloured tanks 5, 6, 7, & 8 are the main transfer tanks. Their job is to keep the collector tanks topped up. Tank 5 and 7 are an operating pair; 5 supplies 1 and 2, while 7 looks after 3 and 4. Once again they are disposed symmetrically about the CG so that no CG changes occur during their operation – note that 5 and 7 are also accepting fuel from the tanks colored Green this fuel is part of trim Transfer. When 5 and 7 are empty, 6 and 8 take their place and function similarly. The remaining blue colored tanks in the picture, tanks 5a and 7a, are transferred into tanks 5 and 7 upon reaching Mach 2

GREEN TANKS 9, 10 & 11

Green coloured tanks are trim transfer tanks. It is their job to shift the CG aft by some 5ft during transonic acceleration, keeping it nicely matched to Centre of Pressure (CP). First, Tank 9 contents will be pumped aft to Tank 11. When that is full, the remainder of 9 will be shared between 5 and 7, where there will be room as they have been keeping the red tanks topped up since before take-off. Tank 10 will empty into 5 and 7, whereupon the CG should be just about right for Mach 2.

If you look at diagrams 1 and 2, you will see how the Fuel Quantity Indicators (FQIs) and their pumps and valves are placed within the aircraft, and then relate them to the tank location. It must be stressed that none of the fuel on Concorde is for trim purposes only; it is all usable and multitasking, as it serves to cool engine oil, generator drive oil, hydraulic oil and aircon supply.

 

The fuel also needs extra care too. This is to prevent the release of entrapped air during high rates of climb in thin air, the fuel in tanks not in use  must be constantly agitated to provide gradual release – known as de-air process. Climbing through 42,000ft, vents are closed-off and tanks lightly pressurised to minimise evaporation losses in low pressure atmospheres.

Centre of Gravity (CG) and Fuel Transfer

 

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 are 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.

Refuelling Concorde

 

Fuel Loading

The refuelling of the aircraft is carried out to schedules which specify the fuel distribution according to the total fuel load and specific gravity.

When refuelling, the fuel must be distributed in accordance with these instructions.

Refuelling with Passengers on Board

Passengers must not be on board the aircraft when it is being refuelled with fuel which does not contain Shell ASA-3.

This limitation does not apply when “topping-up” Tank 11 to achieve the required fuel load.

Minimum Fuel Load for GO-around/Baulked Landing

A Go-around or baulked landing must not be attempted unless the collector tank total contents are greater than 2,500kg. The total must be divided approximately equal between the four tanks.

A baulked landing with 2 engines inoperative must not be attempted if the fuel quantity in each collector tank supplying operating engines is less than 1,250kg.

Approved Fuels and Additives

Fuels:-

(1)   Unlimited Use

Kerosine type, (AVTUR), fuels to the following specifications:-

D. Eng R.D. 2494 Iss. 7 Amd.1

AIR 3405/C Iss.4

ASTM D 1655-73 Jet A-1

3-GP-23 h

D. eng R.D. 2453 Iss.3 Amd. 1

(2)   Limited Use

The following fuels may be used on a non-routine basis when no fuel in the unlimited use” category are available:-

ASTM ES2-74 Jet A-1

And provided that the operational conditions are such that the fuel temperature will at no time, fall below -40deg.C:-

ASTM ES2-74 Jet A

Where the -40deg.C limitation specified above can be observed the following fuel may be used on a routine basis:-

ASTM D 1655-73 Jet A

For use of Jet B, Wide-cut JP4 type of fuel, see Conditional procedure entitled “Use of  JP4 type fuel”.

Additives

(1)   Icing Inhibitor

D. Eng R.D. 2451 Iss.2

Air/3652/A

MIL – I – 27686 E.

The maximum permitted concentration of additive is 0.15% by volume.

If any fuel heater is inoperative, use of fuel containing an approved icing inhibitor, at a concentration of not less than 0.1% by volume, is mandatory.

(2)   Corrosion Inhibitor

Hitec E. 515 in concentration not exceeding 21 mg/litre, (7.5lb per 35,000 Imperial gallons).

TOLAD 245 in concentrations not exceeding 34 mg/litre, (12 lb per 35,000 Imperial gallons).

(3)   Static Dissipator

In order to achieve a refuelling time of 20 minutes from normal reserve quantities to full tanks, Shell ASA-3 static dissipator must be present in the fuel at concentrations up to a maximum of 1.0 mg/litre, (0.35 lb 35,000 Imperial gallons).

If ASA-3 is added to the fuel, concentrations may only be used which result in the electrical conductivity of the fuel remaining within the specification limits.

(4)   Combined Additives

AL 38

This is a combination of 99 parts by weight of fuel system icing inhibitor and 1 part by weight of Hitec E. 515. The maximum permitted concentration is 0.13% by volume, provided that the fuel does not already contain either of the constituent additives. The use of AL. 38 is subject to the limitations specified for Hitec E.515.

(5)   Fuel Dye

Automate Yellow 662 or 662F

The maximum permitted concentration is 120 ppm by weight, (42 lb per 35,000 Imperial gallons).

(6)   Anti-Microbial Additive

Biobar JF, in concentrations not exceeding 270 ppm and with total boron content not exceeding 20ppm, may be used on an intermittent basis. It is permitted to burn off the treated fuel provided that the fuel is not contaminated by microbiological or other debris.

 

Function	Tank Number	Capacity (litres)	Quantity (kg)
Engine supply	1 2 3 4	5,300 5,770 5,770 5,300	4,198 4,570 4,570 4,198
Main Storage Tanks	5 6 7 8	9,090 14,630 9,350 16,210	7,200 11,587 7,405 12,838
Auxiliary Tanks	5A 7A	2,810 2,810	2,225 2,225
Transfer and Reserve Tanks	9 10 11	14, 010 15,080 13,150	11,096 11,943 10,415
Totals		119 ,280	94,470