Sylvie Willis
Concorde was an engineering marvel, but its high fuel consumption was a problem throughout its operating life. With a fuel consumption of up to four times that of the Boeing 747, Concorde used an estimated two tons of fuel during taxiing alone. However, once it reached Mach 2, Concorde became the most fuel-efficient aircraft ever built. Its unique design, including a delta wing shape and movable nose portion, contributed to its supersonic success, but also posed challenges for fuel consumption during ground operations and takeoff. The distribution of fuel along the aircraft was strategically shifted to adjust the centre of gravity during acceleration and deceleration. Despite its impressive performance, Concorde's high operating costs and environmental concerns, such as fuel efficiency and noise pollution, ultimately led to its retirement.
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What You'll Learn
Fuel efficiency at supersonic speeds
Concorde's fuel efficiency is a topic that has attracted much debate. The aircraft consumed up to four times more fuel than the Boeing 747, and comparisons on a per-passenger basis further highlight this disparity, with Concorde carrying only 100 passengers compared to the 747's capacity of over 400.
However, Concorde's unique capabilities and design also come into play when assessing its fuel efficiency. Firstly, it is important to note that Concorde was designed for supersonic flight, which inherently presents challenges for fuel consumption during ground operations and takeoff. Indeed, it is estimated that Concorde used approximately two tons of fuel during the taxi phase alone.
Nevertheless, when Concorde reached its cruising speed of Mach 2, it became the most fuel-efficient aircraft ever built. At this speed, the drag coefficient is minimised, and turbojet engines operate at their peak efficiency. The aircraft's powerplants, slender fuselage, and complex wing shape all contributed to its exceptional supersonic range and fuel efficiency.
Additionally, Concorde employed an efficient cruise-climb flight profile, and its dedicated oceanic airways allowed for a slow climb as fuel load decreased during the transatlantic crossing. The distribution of fuel along the aircraft was strategically shifted during acceleration and deceleration to adjust the centre of gravity, eliminating the need for trim controls that would have increased drag at high speeds.
While Concorde's fuel consumption was a contributing factor in its eventual retirement, it is essential to recognise the trade-offs between speed, performance, and fuel efficiency. Concorde's selling point was not efficiency but the invaluable proposition of time, offering passengers unprecedented speed and comfort.
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Fuel consumption comparisons to other aircraft
Concorde's fuel consumption was a notable issue throughout its operational life. The aircraft's fuel consumption was up to four times that of the Boeing 747, as observed by The New York Times in the late 1970s when rising fuel prices created challenges for Concorde. This comparison becomes even more unfavourable when considering the number of passengers—Concorde carried 100 passengers, while the 747-400 accommodated over 400.
Concorde's high fuel consumption was particularly evident during the early stages of flight. It is estimated that Concorde used approximately two tons of fuel during a typical taxi. To achieve supersonic flight, Concorde required a significant amount of fuel during takeoff and ground operations.
Comparing Concorde's fuel consumption rate of 20,500 kg per hour to other aircraft further highlights the difference. 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. Concorde's fuel efficiency was similar to that of a business jet but lagged far behind subsonic turbofan aircraft.
While carrying a full load, Concorde achieved 15.8 passenger miles per gallon of fuel. In contrast, the Boeing 707 reached 33.3 pm/g, the Boeing 747 attained 46.4 pm/g, and the McDonnell Douglas DC-10 achieved 53.6 pm/g. The Airbus A380, a newer aircraft, boasts a fuel consumption rate of less than 3 L/100 km per passenger, equivalent to 78 passenger-miles per US gallon.
The high fuel consumption of Concorde contributed to its eventual retirement. The aircraft's operating costs were significantly impacted by fuel prices, and the challenges were exacerbated by its limited operation and the need to charge high fares to cover these costs.
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Fuel load management for centre of gravity
Concorde's fuel system and centre of gravity (CG) are closely linked and highly integrated in function. The Concorde uses fuel not only for the engines but also for aerodynamic stability.
The Concorde has a total of 13 fuel tanks with a maximum capacity of 31,510 gallons (119,280 litres) or 95 tons. Most of these tanks are in the wings, but the forward two and another in the tail cone are trim tanks used for storage and trim. Together, they hold about 33 tons of fuel.
The trim transfer system redistributes fuel in the trim tanks and main transfer tanks to move the aircraft's centre of gravity to optimal positions for take-off, subsonic and supersonic flight. During take-off and acceleration through Mach 1, fuel is pumped out of the forward trim tanks into the rear trim tanks and the collector tanks in the wings. This results in a rearward shift of the CG by 6 feet (2 meters).
During supersonic flight, the centre of gravity moves rearward, which is optimal for minimum trim drag. As the Concorde decelerates to subsonic speeds, fuel is pumped forward into the wing transfer and forward trim tanks, moving the CG forward. Additional fuel is often pumped forward after landing to maintain balance during unloading.
The fuel transfer process is controlled from the Flight Engineer's Panel and is usually automated. The panel allows the engineer to set up automatic transfers that stop when the correct quantities of fuel have been moved to the correct tanks. The centre of gravity displays on the instrument panels show the pilot the CofG limits for the aircraft's speed.
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Fuel as a heat sink for air conditioning
Concorde was an engineering marvel, but its high fuel consumption was a persistent issue throughout its operational life. It consumed up to four times more fuel than the Boeing 747, with a fuel consumption rate of 20,500 kg per hour. This, along with high operating costs, safety concerns, and noise pollution restrictions, contributed to its eventual retirement.
The high fuel consumption of Concorde was particularly notable during the early stages of flight, with the aircraft using approximately two tons of fuel during the taxi phase alone.
Now, let's discuss the concept of "Fuel as a heat sink for air conditioning." This idea is being explored as a potential solution for future aircraft designs to address cooling demands without resorting to conventional cooling systems that can cause excessive drag.
A heat sink is a passive heat exchanger that transfers heat from a device to a fluid medium, often air or a liquid coolant, allowing the device's temperature to be regulated. In the context of aircraft, fuel can be circulated underneath exposed surfaces to enable steady-state cooling. This approach can meet the cooling demands of hybrid electric aircraft, which have peak heat loads of 120 kW.
Two primary concepts are being investigated for using fuel as a heat sink. The first concept involves actively circulating hot fuel below the wing surfaces to maximize heat exchange with the ambient air. This approach takes advantage of the available wing surface area for optimal cooling. The second concept utilizes heat exchangers placed inside the existing fuel tanks. By adding heat to the fuel tanks, the fuel itself acts as a heat sink, absorbing and dissipating the heat generated by the aircraft's systems.
These fuel-based cooling concepts aim to enhance the efficiency of future aircraft by reducing drag associated with conventional cooling systems while effectively managing the thermal demands of hybrid electric propulsion systems.
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Fuel consumption per hour
Concorde's fuel consumption was a topic of much discussion throughout its operating life. The aircraft consumed up to four times more fuel than the Boeing 747, as observed by The New York Times in the 1970s. This comparison becomes even more pronounced when considering the number of passengers—Concorde carried 100 passengers, while the 747 accommodated over 400.
Concorde's fuel efficiency is best understood by examining its fuel consumption per hour. During its cruising speed of Mach 2.02 (approximately 1,338 mph or 2,154 km/h), Concorde's fuel consumption was 4,800 US gallons per hour or 18,000 litres per hour. At this speed, Concorde achieved optimum fuel consumption, as turbojet engines are more efficient at higher speeds.
However, Concorde's fuel consumption during the initial stages of flight was notably high. On average, it burned an estimated two tons of fuel during taxiing, which is attributed to the challenges of ground operations and takeoff associated with supersonic flight.
When comparing Concorde's fuel efficiency to other aircraft, it is essential to consider not only fuel consumption per hour but also the distance travelled and the number of passengers carried. Concorde's unique selling point was not efficiency but the significant reduction in travel time it offered.
In summary, Concorde's fuel consumption per hour was indeed high, especially during the early stages of flight. However, once it reached its cruising speed of Mach 2, it achieved optimum fuel efficiency for its time, showcasing the trade-off between speed and fuel economy in supersonic flight.
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Frequently asked questions
Concorde consumed 4,800 US gallons of fuel per hour (18,000 litres per hour) at Mach 2 speed and an altitude of 60,000 feet.
Concorde's fuel consumption was up to four times that of the Boeing 747. When compared to more modern aircraft, Concorde's consumption of 20,500 kg per hour is much higher than the 787-9 (5,400 kg per hour), the A350-900 (5,800 kg per hour), and the A380 (12,000 kg per hour).
Yes, due to Concorde's lower passenger capacity of 100, compared to over 400 for the 747, the per-passenger fuel consumption was even higher than the per-hour consumption.
Yes, Concorde burned up to 2 tonnes of fuel just to taxi to the runway.
Yes, Concorde was designed for supersonic flight and achieved optimum fuel consumption at Mach 2.02 cruising speed, with turbojet engines being more efficient at higher speeds. Additionally, Concorde's cruise-climb flight profile and distribution of fuel along the aircraft during acceleration and deceleration helped improve fuel efficiency.
