CONCORDE · FUEL-BALANCE EXPLAINER · Educational
Trim by pumping fuel.
A wing that flies at Mach 2 does not lift from the same place it lifts from at 300 knots. Concorde’s answer was not a bigger tail: it was a flight engineer moving about twenty tonnes of fuel aft during the acceleration and forward again before landing. This page explains the mechanism from the sources that describe it, and marks exactly where the drawing stops being sourced.
01 / WHY THE LIFT MOVES
The wing lifts from further back at speed.
Heritage Concorde’s description of the fuel system starts with the aerodynamics: any swept wing designed to fly close to Mach 1 experiences changes in the pressure pattern over it as speed increases, and those changes always move the centre of lift rearwards. On a subsonic aircraft the resulting nose-down tendency is trimmed out with the elevators, at a cost in drag. Some of the effect on Concorde was cancelled by the wing’s camber and twist, “but there still remains a shift of about six feet to be accounted for.”
Instead of carrying that trim drag through a Mach 2 cruise, Concorde moved its weight to follow its lift: fuel was pumped aft to shift the centre of gravity rearward, and the resultant rearward CG was “the optimum for minimum trim drag in supersonic cruise.” Airbus lists the same idea among the aircraft’s innovations: the movement of fuel around the aircraft in flight to adjust its centre of gravity.
Sources: Heritage Concorde, “Concorde fuel system: General description”, opening paragraphs (© 2014 Stephen de Sausmarez and Heritage Concorde; paraphrased) · Heritage Concorde, “Concorde fuel transfer”, “Trim transfer” · Airbus, “The day Concorde flew into the history books” (2 March 2019), innovations list.
02 / INTERACTIVE DIAGRAM · TWO SOURCED END POINTS, A STRAIGHT LINE BETWEEN THEM
Accelerate, and follow the lift aft.
Slide from a standing start to Mach 2. The schematic centre-of-lift marker moves aft, fuel moves from the forward trim tanks to the tail, and the centre of gravity follows. Only the two ends of the slider are sourced figures; everything in between is drawn as a straight line and says so.
0 to 2.0 in steps of 0.05. Arrow keys move one step.
FUEL MOVED AFT Sourced end point
0 t of about 20 t at Mach 2
0.0 ft (0.0 m) CG aft of its take-off value, of about 6 ft (2 m) at Mach 2
What is sourced: about 20 tons moved and a CG shift of 6 ft (2 m) rearward by Mach 2, reversed on deceleration (Heritage Concorde, “Concorde fuel transfer”). What is illustrative: the straight line between 0 and Mach 2, and the drawn positions. No simulation of the flight is implied.
03 / THE TANKS, AS DOCUMENTED
Thirteen tanks, four jobs.
Concorde’s fuel was stored in thirteen sealed tanks integral with the wing and fuselage structure, about 95 tons in all; most of it in the wings, with the two forward tanks and one in the tail cone used for trim as well as storage, together holding about 33 tons.
| Group | Tanks | Role, as the source describes it |
|---|---|---|
| Collector tanks | 1, 2, 3, 4 | The only tanks that feed the four Olympus engines; the rest of the fuel is transferred into them. Tanks 1 and 4 sit ahead of the CG and 2 and 3 behind it, so their contents can vary without moving the CG. In the aft-trim condition tanks 1 and 4 run at a reduced level, which moves the CG further rearward. |
| Main transfer tanks | 5, 6, 7, 8 (auxiliaries 5A and 7A feed 5 and 7) | Replenish the collector tanks in a sequence that minimises CG movement; tanks 5 and 7 also receive any trim fuel beyond the trim tanks’ requirements. |
| Forward trim tanks | 9, 10 | Pumped into 11, 5 and 7 for a rearward CG shift; refilled from 11 (with 5 and 7) for the forward shift. |
| Aft trim tank | 11 (tail cone) | Four pumps, two electric and two hydraulic (one from each hydraulic system), so forward transfer, and with it the CG movement that permits approach and landing speeds, stays available on either kind of power. |
Source: Heritage Concorde, “Concorde fuel system: General description”, “Fuel tank structure”, “Engine feed”, “Trim & main transfer” · “Concorde fuel transfer”, “Load limit control”, “Main transfer”, “Trim transfer”. Paraphrased; the pages are © 2014 Stephen de Sausmarez and Heritage Concorde and reproduce nothing from an approved manual here.
04 / THE SEQUENCE OF A FLIGHT
Aft to cruise, forward to land.
- Before take-off
The flight engineer already starts moving fuel from the forward trim tanks to the rear trim and collector tanks. The cruise speed cannot be attained with the CG at its take-off value.
- Through Mach 1 to Mach 2
The transfer continues during the acceleration. Around 20 tons of fuel is moved and the CG shifts by 6 ft (2 m) rearward, balancing the change in the centre of lift.
- End of cruise and deceleration
The reverse: fuel is pumped forward to the forward trim tanks, the CG moves forward and the lift with it. Concorde cannot be landed with the CG at its supersonic-cruise position; the source compares the transfer to flaps on other aircraft, and notes that unlike a flapless landing there is no doing without it.
- After landing
More fuel goes into the forward tanks so the aircraft can be unloaded without stability problems: it is heavier at the rear on the ground.
- A bonus from deliberate imbalance
Because the weight can be put where it is wanted, very little pitch trim is used in flight; and at take-off and landing the CG is placed slightly further back than it needs to be, so the elevons droop to counter it and increase the wing’s camber.
Source: Heritage Concorde, “Concorde fuel transfer”, “Fuel transfer” narrative (paraphrased). The 20 tons and 6 ft (2 m) figures are the page’s own; Airbus confirms the principle but gives no tonnage.
05 / CHECK · THREE QUESTIONS · Educational
Did the mechanism land?
Pick an answer; each one opens the evidence and where it comes from. Finishing all three records the result in My Hangar on this device.
0 of 3 answered
QUESTION 1 OF 3
Why was fuel pumped aft during the acceleration to Mach 2?
Evidence. The source describes the pressure pattern over a swept wing moving the centre of lift rearward as speed increases, a residual shift of about six feet after camber and twist, and a rearward CG that is the optimum for minimum trim drag in supersonic cruise.
“The resultant rearward centre of gravity is the optimum for minimum trim drag in supersonic cruise.”
Sources: Heritage Concorde, General description ↗, opening paragraphs · Concorde fuel transfer ↗, “Trim transfer”.
Why it matters. Weight placed where the lift is means the tail is not fighting the wing for hours at Mach 2.
QUESTION 2 OF 3
About how much fuel moved, and how far did the CG shift, according to Heritage Concorde?
Evidence. The transfer narrative gives both figures for the acceleration through Mach 1 to Mach 2. They are the two numbers behind the slider’s Mach 2 end point; the values in between are this page’s straight line.
“around 20 tons of fuel is moved and this results in a shift of the CG by 6ft (2meters)”
Source: Heritage Concorde, Concorde fuel transfer ↗, “Fuel transfer”.
Why it matters. Six feet does not sound like much until you remember the lift equals the weight of the whole aircraft: a small lever arm on a very large force.
QUESTION 3 OF 3
Why does the aft trim tank, tank 11, have four pumps, two electric and two hydraulic?
Evidence. The source explains that critical things are duplicated or quadruplicated: three CG indicating systems, and four pumps in tank 11 that guarantee the forward movement of fuel and therefore of the CG, which is what allows flight at approach and landing speeds. Two of the pumps are electric and one runs from each hydraulic system.
“Concorde cannot be landed with the CG at the supercruise position.”
Sources: Heritage Concorde, Concorde fuel transfer ↗, “Fuel transfer” · General description ↗, “Trim transfer”.
Why it matters. The redundancy tells you how critical the system was: the forward transfer was as necessary to a landing as flaps are on a conventional airliner, with no flapless-landing equivalent.
CHECK COMPLETE · Educational
Fuel as trim, in three answers.
Understanding the mechanism matters more than the count.
A personal study record on this device. Not a rating, an endorsement or a qualification of any kind.
06 / SOURCES & PROVENANCE
Sources and provenance
Sources & provenance 8 claims · 3 documents
Verified: read directly on the date given. Reported: from an enthusiast-run but engineer-sourced site, paraphrased; treated as reliable for the mechanism and as the only source for the tonnage. Nothing here reproduces an approved manual, and no simulator or performance claim is made.
Spotted an error, or have a document that settles a claim? Sources / suggest a correction
Documents
- Heritage Concorde, “Concorde fuel transfer”© 2014 Stephen de Sausmarez and Heritage Concorde; no edition date shown. Read September 7 and 8, 2026. Sections “Fuel transfer”, “Load limit control”, “Main transfer”, “Trim transfer”, “CG position indication”.
- Heritage Concorde, “Concorde fuel system: General description”© 2014; read September 7 and 8, 2026. Opening paragraphs on the centre of lift, “Fuel tank structure”, “Engine feed”, “Trim & main transfer”.
- Airbus, “The day Concorde flew into the history books”Newsroom story, 2 March 2019. Read September 7, 2026 (the site refused an automated re-read on September 8). Photographs © Airbus, not reused.
Claims
- VerifiedMoving fuel around the aircraft in flight to adjust its centre of gravity is listed among Concorde’s innovations
Airbus, 2 March 2019, innovations list.
- VerifiedFirst flight 2 March 1969 at Toulouse, André Turcat in command, 29 minutes, under 480 km/h
Airbus, 2 March 2019, body. Not used in the diagram.
- ReportedCentre of lift moves rearward as speed increases; camber and twist cancel part of it; about six feet remain to be accounted for
Heritage Concorde, General description, opening paragraphs.
- ReportedAround 20 tons moved during the acceleration through Mach 1 to Mach 2; CG shift 6 ft (2 m) rearward; reversed on deceleration; transfer begins before take-off; more fuel forward after landing
Heritage Concorde, Concorde fuel transfer, “Fuel transfer”.
- ReportedRearward CG is the optimum for minimum trim drag in supersonic cruise; collector tanks 1 and 4 run at a reduced level in the aft-trim condition
Heritage Concorde, Concorde fuel transfer, “Trim transfer”.
- ReportedThirteen sealed integral tanks; about 95 tons; trim tanks together about 33 tons; only tanks 1 to 4 feed the engines; 1 and 4 ahead of the CG, 2 and 3 behind
Heritage Concorde, General description, “Fuel tank structure” and “Engine feed”.
- ReportedTrim transfer 9 and 10 into 11, 5 and 7 (aft) or 11 into 9, 5 and 7 (forward); main transfer from 5 to 8 in a CG-minimising sequence; tank 11 has four pumps, two electric and two hydraulic; three CG indicating systems
Heritage Concorde, Concorde fuel transfer, “Load limit control”, “Main transfer”, “Trim transfer”, “CG position indication”.
- IllustrativeEvery value between Mach 0 and Mach 2 on the slider, the positions of the tank blocks and the markers, and the markers’ travel
Drawn by this page as a straight line between the two sourced end points; labelled so wherever it appears.
ABOUT THIS EXPLAINER
Educational. A focused, sourced explainer of one mechanism: fuel transfer as centre-of-gravity control. It is not a simulator, a flight manual or a performance model, and it makes no claims beyond the sources listed above.
All aircraft