Sylvie Willis
The amount of fuel a plane uses on a journey depends on a multitude of factors, including the type of aircraft, the aircraft's empty weight, the payload, the efficiency of the engines, the flight path, and weather conditions. For example, a Boeing 747 burns approximately 1 gallon of fuel per second, which amounts to 36,000 gallons over a 10-hour flight. On the other hand, the Airbus A380, the largest passenger aircraft, consumes approximately 4,600 gallons of fuel per hour. While take-off is often considered the most fuel-intensive part of a flight, cruising accounts for a significant proportion of fuel usage, especially on longer flights. With the growth of air travel, improving fuel economy and reducing corresponding CO2 emissions have become crucial for climate sustainability.
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What You'll Learn
Fuel burn varies across different flight stages
The fuel burn of an aircraft varies across different flight stages. While several factors influence the amount of fuel burned during a flight, the flight stage plays a crucial role in fuel consumption.
Let's break down the different flight stages and understand how fuel burn varies across them:
Taxi Out
The "taxi out" stage refers to the aircraft's movement on the ground from the gate to the runway before takeoff. During this stage, the aircraft is using fuel to power its engines and move towards the runway. The amount of fuel burned during taxi out can vary depending on the distance to the runway, the speed of the aircraft, and the time spent taxiing. In busy airports, longer taxi times can lead to increased fuel consumption.
Takeoff
Takeoff is often considered the most fuel-intensive stage of a flight. During takeoff, the engines work at their maximum capacity to generate the thrust needed to lift the aircraft off the ground. This stage requires a significant amount of fuel to overcome gravity and achieve the required speed and altitude. However, it's important to note that the duration of the takeoff stage is relatively short compared to other stages, which affects its overall fuel consumption.
Climb
During the climb stage, the aircraft ascends to its designated cruising altitude. While the engines may not be at full power, they still consume a considerable amount of fuel to maintain a steady ascent. The climb stage typically has a higher fuel burn rate per minute compared to other phases of flight.
Cruise
The cruise stage, where the aircraft maintains a constant speed and altitude, is generally the longest phase of a flight. This stage usually accounts for the majority of total fuel consumption, especially on long-haul flights. Cruising at higher altitudes offers thinner air, reducing drag and allowing engines to operate more efficiently. However, the fuel burn rate per minute during the cruise stage is typically lower than during takeoff and climb.
Approach and Taxi In
The "approach" stage refers to the descent and manoeuvring of the aircraft as it prepares for landing. During this stage, the engines may be throttled back, reducing fuel consumption. The "taxi in" stage involves moving the aircraft from the runway to the gate after landing. Similar to the "taxi out" stage, fuel is used to power the engines and navigate the aircraft to the gate.
It's important to note that while these are the general patterns of fuel burn across different flight stages, the actual fuel consumption can vary based on various factors such as aircraft type, weight, engine efficiency, flight distance, and weather conditions. Additionally, shorter flights may have a higher proportion of fuel burned during non-cruising stages due to their shorter cruising time.
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Jet fuel vs diesel
The amount of fuel a plane uses on a journey depends on a multitude of factors, including the aircraft's empty weight, payload, engine efficiency, flight path, and weather conditions. For instance, a Boeing 747 burns approximately 36,000 gallons of fuel over a 10-hour flight, while the Airbus A380, the largest passenger aircraft, consumes about 23,000 gallons in a 5-hour flight.
Now, when it comes to jet fuel vs. diesel, it's important to understand their similarities and differences. Historically, jet fuel and diesel were quite similar in extraction, production, composition, and application. However, over time, they have diverged, particularly in terms of composition and use.
One of the main differences is their composition. Jet fuel, typically Jet-A, is a specific type of aviation turbine fuel, while diesel is a specific fractional distillate of petroleum fuel oil. Jet fuel has a higher sulfur content and is considered "drier" than diesel, which affects its lubricity. This higher lubricity is acceptable for gas-turbine engines commonly used in aviation but may require additives if used in diesel engines.
Another key difference lies in their application. Jet fuel is designed for turbine engines, which are used in aircraft, whereas diesel fuel is designed for piston engines typically found in motor vehicles. Turbine engines, such as those in planes, continuously compress air, ignite it within a combustion chamber, and expel exhaust through an expansion turbine. On the other hand, piston engines use the familiar cylinder and piston arrangement and can have either ignition or compression fuels.
Despite these differences, there are cases where diesel fuel is used in aircraft gas-turbine engines, and jet fuel powers diesel engines, especially in ground support fleets at airports. This practice is economically viable due to the convenience of using a single fuel type and avoiding the need for diesel refueling outside the airport premises. However, using jet fuel in diesel engines may come with higher operating costs and require technical additives for long-term functionality.
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Fuel efficiency of different aircraft
Fuel efficiency in aircraft is a measure of the transport energy efficiency of an aircraft. It is typically expressed in terms of energy consumed per unit of payload over distance. The two most common metrics are kilograms per Revenue Tonne Kilometer (kg/RTK) and kilograms per Revenue Passenger Kilometer (kg/RPK).
Fuel efficiency is increased by improving aerodynamics, reducing weight, and improving engine brake-specific fuel consumption and propulsive efficiency or thrust-specific fuel consumption. For powered aircraft, the optimum glide ratio (where the sum of parasitic drag and lift-generated induced drag is minimal) must be balanced with thrust efficiency. Newer aircraft tend to be more fuel-efficient than older aircraft, with the average fuel burn of new aircraft falling 45% from 1968 to 2014. Newer aircraft feature sleeker aerodynamics, lighter materials, and optimized components. Engine performance has also improved, with modern engines producing more thrust at lower burn rates.
Aircraft size also affects fuel efficiency. While one might assume that larger planes are more fuel-efficient per passenger due to economies of scale, this is not always the case. For flights over the Pacific, smaller twin-engine widebody aircraft like the Boeing 787 and Airbus A350 are more fuel-efficient than very large four-engine aircraft. This is because four-engine aircraft tend to have higher wing weight and smaller engine fan diameters, and because they are operated with relatively fewer passengers.
Among the most fuel-efficient aircraft are the Boeing 787 'Dreamliner' and the Airbus A350. The 787-9, in particular, was the most fuel-efficient aircraft on 2016 transpacific flights, with 39 passenger kilometres per litre of fuel, or 60% better than the A380. The A330neo is also notable for its fuel efficiency, with claims that it is 14% more fuel-efficient than the ceo. The A350-1000 is another highly efficient aircraft, carrying more passengers for a higher density, lower-cost long-haul option.
Fuel efficiency can also be improved through operational procedures such as maintenance, routing, and flight planning and execution. For example, excess fuel increases consumption, with each extra tonne burning about 30 kg per hour. AI is also being used to enable real-time route optimization based on changing weather, predict when engines need servicing, and identify optimal traffic patterns.
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Fuel economy improvements
The amount of fuel used by a plane on a journey depends on a multitude of factors, including the aircraft's empty weight, payload, engine efficiency, flight path, and weather conditions. Fuel is often the single largest cost for aircraft operators, so improving fuel economy is a priority.
Aerodynamic Design
Aerodynamic improvements can increase fuel efficiency. Winglets, for example, are small surfaces that lift air vertically, reducing the amount of air flowing around the wingtip and lowering drag. Wingtip fences, thicker fuselages, and longer, slimmer wings can also reduce drag and improve fuel efficiency. NASA's "double bubble" D8 concept involves relocating the aircraft's engine to the top of the plane toward the tail, significantly decreasing drag and increasing fuel efficiency.
Weight Reduction
Reducing the weight of an aircraft can lead to significant fuel savings. Even small changes in weight can make a difference. Aircraft manufacturers are exploring ways to reduce weight, including replacing heavy wiring in non-avionic systems with lightweight wireless transceivers.
Engine Efficiency
Improvements in engine efficiency have been a key driver of increased fuel economy. Aviation researchers are developing hybrid-electric engines and lighter-weight engines, which can reduce the usage of traditional fuel. For example, Honeywell's hybrid-electric turbogenerator combines an HTS900 engine with two compact, high-power-density generators, reducing the reliance on traditional fuel.
Optimal Airspeed and Altitude
Endurance and range can be maximized by flying at the optimum airspeed and altitude. Generally, higher altitudes provide better fuel economy.
Operational Procedures
Fuel savings can be achieved through efficient operational procedures such as maintenance and routing. For example, the Airbus A350 consumes less fuel than the Airbus A380 due to its newer, more efficient engines.
By implementing these strategies and developing new technologies, the aviation industry is working towards reducing fuel consumption and minimizing its environmental impact.
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Fuel consumption per person
The fuel consumption of a plane on a journey depends on a multitude of factors, including the aircraft's empty weight, payload, engine efficiency, flight path, and weather conditions. The type of aircraft is also a significant factor, with larger planes like the Airbus A380 consuming more fuel than smaller planes like the Airbus A320. Additionally, the length of the flight plays a role, as longer flights will generally burn more fuel than shorter ones.
When considering fuel consumption per person, the number of passengers on a flight becomes crucial. For example, a Boeing 747 can carry up to 568 passengers, and during a 10-hour flight, it might burn approximately 36,000 gallons of fuel. This equates to 0.01 gallons per person per mile, resulting in 100 miles per gallon per person. On the other hand, a smaller plane with fewer passengers might have a lower fuel efficiency per person.
Comparing fuel consumption per person between different modes of transportation can be complex. While a plane carrying 200 passengers from New York City to Los Angeles would consume approximately 27 gallons of fuel per person, driving the same distance in a car with two passengers would result in a higher fuel consumption per person. However, if the plane is not flying at full capacity, the fuel efficiency per person decreases.
The efficiency of the aircraft also impacts fuel consumption per person. Newer aircraft like the Airbus A350 are more fuel-efficient than older models, resulting in improved fuel efficiency per passenger. Additionally, propeller planes tend to be more efficient than jet engines, with the Bombardier Dash 8 Q400 turboprop being a notable example.
With sustainability and climate change concerns, reducing carbon emissions has become a priority. While cruising accounts for the majority of carbon emissions on a flight, the contribution of taxiing, take-off, climb, and approach are significant for short-haul flights. Aircraft capacity and engine type also play a role in fuel consumption per person, with higher-capacity aircraft and more efficient engines leading to lower fuel consumption per passenger.
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Frequently asked questions
The amount of fuel a plane uses on a journey depends on several factors, including the type of aircraft, the distance travelled, the aircraft's empty weight, the number of passengers, the efficiency of the engines, the flight path, and weather conditions. For example, a Boeing 747 burns approximately 1 gallon of fuel per second, which amounts to 36,000 gallons of fuel over a 10-hour flight. On the other hand, the Airbus A380, the largest passenger aircraft, consumes approximately 4,600 gallons of fuel per hour.
Different types of aircraft have varying fuel consumption rates. For instance, the Airbus A350 is considered one of the most fuel-efficient wide-body aircraft, consuming around 38 pounds of fuel per nautical mile. In comparison, the Airbus A380 consumes more fuel due to its higher capacity and greater maximum take-off weight (MTOW).
While take-off requires the engines to work the hardest, cruising typically accounts for the majority of fuel consumption and carbon emissions, especially on longer flights. However, for shorter flights, the non-cruising stages of the flight, such as taxiing, take-off, climb, approach, and taxi-in, contribute more significantly to overall fuel usage.
The growth of air travel has outpaced improvements in fuel economy, leading to an increase in corresponding carbon emissions and a negative impact on climate sustainability. While the introduction of more fuel-efficient aircraft has helped, the lower airfares of low-cost carriers have resulted in a rebound effect, with more flights and larger overall emissions.
