Ameer Randolph
Concorde was a supersonic aircraft with a cruising speed of Mach 2.02, which is twice the speed of sound. While it was an engineering marvel, it was not without its problems, one of which was high fuel consumption. Concorde's fuel consumption was a problem throughout its operational life, with some estimates suggesting it burned up to 2 tons of fuel during taxiing alone. However, once it reached its cruising speed, Concorde became the most fuel-efficient aircraft ever built.
| Characteristics | Values |
|---|---|
| Fuel consumption rate | 5,638 Imperial gallons (25,629 liters) per hour per British Airways; 4,800 US gallons per hour (18,000 liters) per hour at Mach 2 and an altitude of 60,000 feet (18,000 m) |
| Fuel consumption compared to other aircraft | Four times that of the Boeing 747; 4 times more than the 747 on a per-passenger basis; 4.2 times more than the 747-400; 4.1 times more than the 787-9; 3.5 times more than the A350-900; 1.7 times more than the A380 |
| Maximum fuel capacity | 95 tons |
| Fuel used for taxiing | 2 tons |
| Fuel used for cooling | Acts as a heat sink for the air conditioning and hydraulics |
| Fuel tank count | 8 |
| Fuel transfer during flight | Fuel is transferred between tanks to maintain trim and balance |
| Fuel flow rate | Fuel is delivered to the engines at suitable flow rates, temperatures, and pressures |
| Fuel tank de-aeration | Required for tanks used during the climb due to Concorde's high climb rate |
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What You'll Learn
Concorde's fuel efficiency at Mach 2
Concorde's fuel efficiency has been the subject of much debate. While some argue that the aircraft's fuel consumption per hour per unit of thrust was poor, others claim that when flying at Mach 2, it was the most fuel-efficient engine ever built.
At Mach 2, an aircraft experiences much higher air resistance, which increases the fuel burn per unit of thrust. Concorde's engines were designed to tolerate such conditions without surging, making them extremely fuel-efficient at high speeds. Additionally, Concorde's powerplants were efficient at twice the speed of sound, contributing to its fuel efficiency at Mach 2.
However, Concorde's high fuel consumption during taxiing and takeoff cannot be ignored. It is estimated that Concorde burned up to 2 tonnes of fuel just to taxi to the runway. Furthermore, Concorde's afterburners, used during takeoff and when accelerating to break the sound barrier, resulted in a fuel consumption rate of 32.5 litres per second.
When comparing fuel efficiency, it is common to consider the total fuel used divided by the distance travelled and the number of passengers carried. Concorde carried far fewer passengers than other aircraft of its time, and its high fuel consumption per passenger contributed to its high operating costs. British Airways, for example, faced yearly operating bills of around £1 billion due to Concorde's expenses.
In conclusion, while Concorde may have had the most fuel-efficient engine ever built at Mach 2 speeds, its overall fuel efficiency, especially when considering the number of passengers carried, was not its strongest selling point. Concorde sold something far more valuable: time.
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Fuel use during taxiing
Concorde consumed a significant amount of fuel during its flights, and this was especially true in the early stages of the flight. It is estimated that Concorde used around two tons of fuel during taxiing, which is the period between leaving the gate and taking off. This amount of fuel is comparable to that used by a Boeing 737 during a London-Amsterdam flight.
The high fuel consumption during taxiing was due to the use of the aircraft's afterburners, which were only used during takeoff and when accelerating to break the sound barrier. The afterburners resulted in a fuel consumption rate of 32.5 liters per second.
To manage the high fuel consumption, pilots would only use two of the four engines during taxiing. Despite this, the fuel economy of Concorde was not optimal, and it had high operating costs.
While Concorde's fuel efficiency improved significantly after reaching Mach 2, the overall fuel consumption, including taxiing, was a contributing factor to its demise and retirement.
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Fuel consumption rate vs other aircraft
Concorde was a groundbreaking aircraft, but its high fuel consumption was a significant issue throughout its operational life.
Concorde's fuel consumption was up to four times that of the Boeing 747. According to British Airways, Concorde's fuel consumption rate was 5,638 Imperial gallons (25,629 litres) per hour. In comparison, the Boeing 747-400 averages 14,400 litres per hour. The New York Times compared the fuel consumption of Concorde and the 747 on a New York to Paris flight in the late 1970s and found that Concorde used four times as much fuel. When comparing fuel consumption per passenger, Concorde becomes even less efficient, as it only carried 100 passengers, while the 747-400 carries over 400.
Concorde's high fuel consumption was due to several factors. Firstly, it was designed for supersonic flight, which made ground operations and takeoff particularly challenging and fuel-intensive. Concorde also had a unique tailless configuration for a commercial aircraft, which contributed to its high fuel use. Additionally, Concorde's afterburner use was different from other commercial supersonic aircraft, such as the Tupolev Tu-144, as it used afterburners for a more significant portion of the flight, impacting fuel efficiency.
The distribution of fuel along the aircraft was carefully managed during acceleration and deceleration to shift the centre of gravity and maintain control at high speeds. Most of Concorde's 95 tons of fuel was stored in tanks in the wings, with additional fuel in the forward and tail cone tanks for trim and storage. During supersonic flight, the Centre of Gravity movement was critical, and fuel had to be moved around the aircraft to adjust for different speeds.
Concorde's fuel consumption compares unfavourably to more modern aircraft. For example, the 787-9 consumes 5,400 kg per hour, the A350-900 consumes 5,800 kg per hour, and the A380 consumes 12,000 kg per hour. These aircraft are more fuel-efficient than Concorde, which burned through an incredible two tons of fuel during an average taxi.
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Fuel distribution and weight
Concorde had a fuel capacity of 95 tons, most of which was stored in tanks in the wings. The forward two tanks and another in the tail cone were used for trim (balance) and storage, holding about 33 tons of fuel. Concorde, like most airliners, had multiple fuel tanks, but what set it apart was the need to transfer fuel between these tanks during flight to maintain trim and balance. This was necessary because Concorde lacked a full tail plane, a feature used by other aircraft to maintain stability during subsonic flight.
The Concorde's wing design was critical to its performance, but it also resulted in a shift of about six feet in the centre of pressure, which could cause a pitch-down moment if not addressed. Trim controls could have been used to counter this, but at the Concorde's high speeds, this would have increased drag, reducing efficiency. Instead, the distribution of fuel along the aircraft was shifted during acceleration and deceleration to move the centre of gravity, acting as an auxiliary trim control.
The Concorde's fuel system was designed to deliver fuel to the engines at suitable flow rates, temperatures, and pressures for all engine operating conditions. The use of separate tanks, along with internal bracing, reduced fuel surging. Due to the Concorde's high climb rate, the tanks that store fuel during the climb needed to be de-aerated to prevent issues with air in the solution. Only the red-coloured tanks (1, 2, 3, and 4) could feed the four Olympus engines, with the rest of the fuel transferred to these "collector tanks" from the blue-coloured "transfer tanks" (5, 6, 7, and 8). This arrangement ensured that the centre of gravity remained stable during flight, with two tanks ahead of it and two behind.
The Concorde's fuel also served as a heat sink for the air conditioning and hydraulic systems, helping to keep the cabin cool. During supersonic flight, a visor was employed to prevent high-temperature air from reaching the cockpit skin. To reduce skin temperatures, the majority of the aircraft's surface was painted white, a highly reflective colour that reduced skin temperature by 6 to 11 °C.
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Fuel tanks and transfer
Concorde had multiple fuel tanks, with most of its 95 tons of fuel kept in tanks in the wings. The forward two tanks, along with another in the tail cone, were used for trim and storage, holding about 33 tons of fuel. During the flight, fuel was transferred from tank to tank to maintain trim and balance. This is because Concorde did not have a full tail plane, which other aircraft use to perform this task during subsonic flights.
The use of separate tanks, along with internal bracing, reduced the amount of surging of the stored fuel. Due to Concorde's high climb rate, the tanks that store fuel during the climb needed to be de-aerated to prevent air in the solution from becoming a hazard. Only the red-coloured tanks (1, 2, 3, and 4) could feed the four Olympus engines. The rest of the fuel was transferred into them, and they are also known as "collector tanks". The blue-coloured tanks (5, 6, 7, and 8) are the main transfer tanks, keeping the collector tanks topped up.
The distribution of fuel along the aircraft was shifted during acceleration and deceleration to move the centre of gravity, acting as an auxiliary trim control. This was critical during supersonic flight, where Centre of Gravity movement is a crucial task.
Concorde also used fuel as a heat sink to cool the air conditioning and hydraulics. This was necessary as the fuselage heated up and expanded by up to 300 mm during flight.
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Frequently asked questions
Concorde consumed 5,638 Imperial gallons (25,629 litres) of fuel per hour. At Mach 2 speed and an altitude of 60,000 feet, this increased to 4,800 US gallons per hour (18,000 litres per hour).
Concorde's fuel consumption was up to four times that of the Boeing 747.
Yes, Concorde used fuel as a heat sink to keep the cabin and hydraulics cool. Fuel was also moved around the aircraft to shift the centre of gravity for different speeds.
Concorde burned up to 2 tons of fuel during an average taxi.
Yes, Concorde's high fuel consumption led to high operating costs and contributed to its eventual retirement. Rising fuel prices in the late 1970s also caused difficulties.
