Fuel fraction

This article is about flight vehicles. For the topic in combustion physics, see fuel mass fraction.

In aerospace engineering, an aircraft's fuel fraction, fuel weight fraction,^[1] or a spacecraft's propellant fraction, is the weight of the fuel or propellant divided by the gross take-off weight of the craft (including propellant):^[2]

${\displaystyle \ \zeta ={\frac {\Delta W}{W_{1}}}}$

With a fuel fraction of nearly 85%, the GlobalFlyer could carry 5 times its weight in fuel.

The fractional result of this mathematical division is often expressed as a percent. For aircraft with external drop tanks, the term internal fuel fraction is used to exclude the weight of external tanks and fuel.

Fuel fraction is a key parameter in determining an aircraft's range, the distance it can fly without refueling. Breguet’s aircraft range equation describes the relationship of range with airspeed, lift-to-drag ratio, specific fuel consumption, and the part of the total fuel fraction available for cruise, also known as the cruise fuel fraction, or cruise fuel weight fraction.^[3]

In this context, the Breguet range is proportional to ${\displaystyle -\ln(1-\ \zeta )}$

Fighter aircraft

At today’s state of the art for jet fighter aircraft, fuel fractions of 29 percent and below typically yield subcruisers; 33 percent provides a quasi–supercruiser; and 35 percent and above are needed for useful supercruising missions. The U.S. F-22 Raptor’s fuel fraction is 29 percent,^[4] Eurofighter is 31 percent, both similar to those of the subcruising F-4 Phantom II, F-15 Eagle and the Russian Mikoyan MiG-29 "Fulcrum". The Russian supersonic interceptor, the Mikoyan MiG-31 "Foxhound", has a fuel fraction of over 45 percent.^[5] The Panavia Tornado had a relatively low internal fuel fraction of 26 percent, and frequently carried drop tanks.^[6]

Civilian Aircraft

Airliners have a fuel fraction of less than half their takeoff weight, between 26% for medium-haul to 45% for long-haul.

Model	MTOW (t)	OEW (t)	OEW Fraction	Fuel capacity (t)	Fuel fraction	Payload Max. (t)	Payload fraction
Airbus A380[7]	575.0	285.0	49.6%	254.0	44.2%	84.0	14.6%
Boeing 777-300ER[8]	351.5	167.8	47.7%	145.5	41.4%	69.9	19.9%
Boeing 777F	347.8	144.4	41.5%	145.5	41.8%	102.9	29.6%
Boeing 777-200LR[8]	347.5	145.2	41.8%	145.5	41.9%	64.0	18.4%
Boeing 767-300F	186.9	86.1	46.1%	73.4	39.3%	54.0	28.9%
Airbus A350-1000[9]	322.0	155.0	48.1%	124.7	38.7%	67.3	20.9%
Airbus A350-900[9]	283.0	142.4	50.3%	110.5	39.0%	53.3	18.8%
Airbus A350F	319.0	131.7	41.3%	131.7	41.3%	111.0	34.8%
Boeing 787-9[10]	254.7	128.8	50.6%	101.5	39.9%	52.6	20.7%
Airbus A330-300[11]	242.0	129.4	53.5%	109.2	45.1%	45.6	18.8%
Airbus A330-200[11]	242	120.6	49.8%	109.2	45.1%	49.4	20.4%
Airbus A330-200F	233	109.4	47.0%	109.2	46.9%	68.6	29.4%
Boeing 787-8[10]	227.9	120.0	52.7%	101.3	44.4%	41.1	18.0%
Airbus A320ceo[12]	79	44.3	56.1%	23.3	29.5%	20	25.3%
Boeing 737-800[13]	79	41.4	52.4%	20.9	26.5%	21.3	27%
Bombardier CS300[14]	70.9	37.1	52.3%	17.3	24.4%	18.7	26.4%
Bombardier CS100[14]	63.1	35.2	55.3%	17.5	27.7%	15.1	23.9%
McDonnell Douglas MD-11F	286.0	112.7	39.4%	117.4	41.0%	92.0	32.2%
Ilyushin IL-76TD-90VD	195.0	92.5	47.4%	90.0	46.2%	50.0	25.6%
Boeing 747-8F	447.7	197.1	44.0%	181.6	40.6%	132.6	29.6%
Concorde[15]	185.1	78.7	42.5%	95.7	51.7%	12.7	6.9%
Virgin Atlantic Globalflyer[16]	10.1	1.6	16.1%	8.4	82.9%	0.1	1.0%

General aviation

The Rutan Voyager took off on its 1986 around-the-world flight at 72 percent, the highest figure ever at the time.^[17] Steve Fossett's Virgin Atlantic GlobalFlyer could attain a fuel fraction of nearly 83 percent, meaning that it carried more than five times its empty weight in fuel.^[16]

See also

• Mass ratio