Ameer Randolph
The weight of aviation fuel is a critical factor in flight load calculations. While smaller aircraft typically measure fuel in gallons, larger aircraft measure it in pounds, as weight is a constant factor that helps determine how far a pound of fuel will take the aircraft. The weight of jet fuel depends on various factors, such as its components and temperature. As a rule of thumb, one US gallon of jet fuel weighs about 6.47-7.01 pounds at 59°F (15°C). This translates to approximately 30,000-700,000 pounds of fuel for commercial aircraft carrying 5,000-100,000 US gallons. For example, a Boeing 800 with a fuel capacity of 6,875 gallons can carry about 44,481-48,194 pounds of fuel.
| Characteristics | Values |
|---|---|
| Weight of one gallon of aviation fuel | 6.47-7.01 pounds at 59°F |
| Weight of one pound of aviation fuel | 0.143-0.155 gallons |
| Jet fuel density | 0.775 g/ml to 0.840 g/ml at 59°F (15°C) |
| Jet fuel weight calculation | Take the total weight of the fuel and drop the last zero. Divide that number in half. Add those two numbers together. |
| Fuel burn unit | Mass (weight) |
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What You'll Learn
Jet fuel weighs 6.47-7.01 pounds per gallon
Jet fuel is typically sold by the number of pounds rather than gallons because weight is important for flight load calculations. Fuel is burned by mass (or weight) and not volume, and its density varies with type. For example, JP-5/8 jet fuel has a density of 6.8 pounds per gallon, while JP-4 has a density of 6.5 pounds per gallon.
Using pounds is also more accurate for fuel burn calculations. When an aircraft flies at high altitudes, there are significant differences in fuel density due to temperature swings. However, smaller aircraft usually measure fuel volume instead of mass because they only use one type of fuel with a consistent density. For example, avgas has a density of 6 pounds per gallon.
The weight of jet fuel is also important when considering the fuel capacity of aircraft. For instance, a Boeing 800 can hold about 6,875 gallons of fuel, weighing 44,481-48,194 pounds. Most commercial aircraft can carry 5,000-100,000 gallons of fuel, which translates to approximately 30,000-700,000 pounds.
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Fuel is burned by weight, not volume
Aviation fuel is a catch-all term for a variety of fuels used in aircraft, including jet fuel, avgas, and sustainable aviation fuel. Jet fuel, for example, is typically a mix of extremely refined kerosene that burns at temperatures of 49 °C (120 °F) or above. The weight of a gallon of aviation fuel depends on the type of fuel and its density. For instance, the density of Jet A-1 kerosene at 15 °C is 804 kg/m3 (34.69 MJ/litre), while the density of Jet TS-1 kerosene at the same temperature is 787 kg/m3 (34.00 MJ/litre).
When it comes to aircraft, fuel is typically burned by weight rather than volume. This is because fuel density can vary with temperature, affecting the range that can be achieved from a gallon of fuel. Weight, on the other hand, remains constant, allowing for easy calculations of how far a pound of fuel will take the aircraft based on known consumption rates. This is particularly important for large aircraft like airliners, which load a specific amount of fuel for each trip, factoring it into their total payload.
The use of weight instead of volume in fuel calculations also helps with quick computations regarding maximum landing weight, especially during busy or stressful events. Additionally, the actual energy contained in the fuel is measured by weight, making it a more accurate measure for fuel burn. Pounds have become the universal standard in fuel units, likely due to the Gimli Glider accident in 1983, where an Air Canada Boeing 767 ran out of fuel due to confusion in fuel measurements.
While smaller airplanes typically use gallons when discussing fuel amounts, larger planes are more concerned with weight. This is because small planes that max out at 50 gallons and fly a few hundred miles aren't as affected by fuel expansion as larger planes that hold tens of thousands of gallons and fly thousands of miles. Additionally, smaller planes may not have the instrumentation to measure fuel weight accurately, relying solely on volume measurements.
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Fuel density varies with temperature
The weight of aviation fuel depends on its density, which varies with temperature. For instance, jet fuel is a gas turbine fuel used in propeller and jet fixed-wing aircraft and helicopters. It has a low viscosity at low temperatures, limited ranges of density and calorific value, burns cleanly, and remains chemically stable when heated to high temperatures.
The density of jet fuel at 15°C is 804 kg/m3, while at 250°C, the density is 1292 kg/m3. This means that the volume of jet fuel increases with increasing temperature. For example, 100 litres of jet fuel at a density of 757 kg/m3 at 100°C will have a volume of 92 litres at 15°C.
The specific gravity of jet fuel is also important in determining its weight. Specific gravity is the ratio of the density of a substance to the density of a reference substance, typically water. Jet fuel has a specific gravity of around 0.8, which means it is less dense than water and will float on top of it.
The net energy content of aviation fuels also depends on their composition. For example, BP Avgas 80 has a net energy content of 44.65 MJ/kg, while Kerosene type BP Jet A-1 has a net energy content of 43.15 MJ/kg. The energy content of the fuel affects its weight, as a higher energy content typically indicates a higher density.
Additionally, sustainable aviation fuel and blends of fossil and sustainably-sourced alternative fuels yield lower emissions of particles and greenhouse gases. These fuels must meet specifications for lubricity and density and must adequately swell elastomer seals in aircraft fuel systems. Sustainable aviation fuels are not yet widely used due to political, technological, and economic barriers, as they are currently more expensive than conventionally produced aviation fuels.
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Large planes use pounds, small planes use gallons
The weight of aviation fuel is a critical factor in flight load calculations. Large aircraft like airliners load a specific amount of fuel for their trip, factoring into their total payload. Small aircraft, on the other hand, almost always take off with a full tank, so weight calculations assume a full tank.
For large planes, fuel is typically measured in pounds as weight is a constant that allows for easy calculation of range based on known consumption. The actual energy contained in the fuel is also measured in pounds, making it a more accurate measure of fuel burn. Additionally, fuel density varies with temperature, and the range obtained from a gallon of fuel is not constant. For example, a Boeing 800 has a fuel capacity of 6,875 gallons, weighing about 44,481-48,194 pounds.
Small planes, on the other hand, typically use gallons to measure fuel amounts. This is because small planes usually have fuel measurement systems that measure volume, not mass. Additionally, small planes often use a single-density fuel, such as avgas, which has a consistent density of 6 pounds per gallon. As a result, volume is a simpler and more practical measure for small planes.
The conversion between pounds and gallons for jet fuel is approximately 6 pounds per gallon, though this varies slightly due to factors like temperature and fuel type. For instance, JP-5/8 jet fuel has a density of 6.8 pounds per gallon, while JP-4 is slightly lower at 6.5 pounds per gallon. Jet A1 fuel, the most common type used globally, has a density of 0.775-0.840 grams per millilitre at 59 degrees Fahrenheit, translating to 6.47-7.01 pounds per gallon.
In summary, large planes use pounds to measure fuel because it facilitates calculations, provides accuracy in fuel burn measurements, and accounts for variations in fuel density due to temperature changes. Small planes, however, favour gallons due to the limitations of their fuel measurement systems and the use of single-density fuels.
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1 US gallon of jet fuel = 0.143-0.155 US pounds
Jet fuel is typically sold by the number of pounds, and its weight is important for flight load calculations. The weight of jet fuel varies depending on factors such as its components and temperature. The density of jet fuel is influenced by temperature, and it is burned by mass rather than volume. As a result, weight is a more accurate measure of the amount of fuel available.
For Jet A and Jet A1 grade jet fuels, the density at 59°F (15°C) falls into the range of 0.775 g/ml to 0.840 g/ml, which translates to 775 kg/m3 to 840 kg/m3. Jet A1 fuel, commonly used in international aviation, has a slightly higher density than Jet A, which is primarily used in the United States for domestic flights.
Converting the density values to pounds per gallon, we find that one US gallon of jet fuel typically weighs between 6.47 and 7.01 pounds. Reversing this calculation, we can determine that one pound of jet fuel is equal to approximately 0.143-0.155 US gallons. This conversion factor is crucial for pilots and aviation professionals when calculating fuel requirements and load distributions for flights.
It's important to note that while gallons are commonly used as a unit of measurement for jet fuel, larger aircraft and commercial operations often utilize pounds as it provides a more accurate representation of the fuel's energy content and facilitates easier calculations for weight distribution and range estimation.
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Frequently asked questions
A gallon of aviation fuel weighs about 6.47-7.01 pounds at 59°F (15°C).
Pounds are a more accurate measure of how much fuel is available because fuel is burned by mass (or weight), not volume. Fuel density varies with temperature and fuel type.
Take the total weight of the fuel and drop the last zero. Divide that number in half and then add the two numbers together. For example, 8,000 lbs of jet fuel is approximately 1,200 gallons.
A Boeing 800 has a fuel capacity of 6,875 gallons, which weighs about 44,481-48,194 pounds.
Jet A is the predominant jet fuel used in the United States. Jet A1 is the most common jet fuel used globally.
