Aircraft fuel systems do more than carry energy for the engines. They store fuel in wing and center tanks, move it through pumps and lines, and help keep the airplane balanced in flight. A well designed fuel system also gives pilots control over which tanks feed which engines.
This matters because fuel is a large part of an aircraft's weight, especially at takeoff.
Key Facts
- Fuel weight = fuel volume x fuel density.
- Approximate jet fuel density = 0.80 kg/L.
- Total fuel = left tank fuel + right tank fuel + center tank fuel.
- Fuel imbalance = left wing fuel mass - right wing fuel mass.
- Center of gravity moment = weight x distance from reference point.
- Engines need a steady fuel flow, so pumps and valves maintain pressure and routing.
Vocabulary
- Wing tank
- A fuel tank located inside an aircraft wing, often between structural ribs and spars.
- Center tank
- A fuel tank located in the fuselage or wing center section that often feeds fuel before the wing tanks.
- Fuel pump
- A device that pushes fuel through lines toward the engines at the needed pressure and flow rate.
- Crossfeed valve
- A valve that allows fuel from one side of the aircraft to feed an engine on the other side when needed.
- Fuel transfer
- The controlled movement of fuel between tanks to manage supply, balance, or aircraft center of gravity.
Common Mistakes to Avoid
- Thinking each engine can only use fuel from the tank on its side is wrong because crossfeed valves can route fuel across the aircraft in many designs.
- Ignoring fuel balance is wrong because uneven left and right fuel loads can create a rolling tendency and increase pilot workload.
- Assuming the center tank is always used last is wrong because many aircraft use center tank fuel first to reduce wing bending loads in a planned way.
- Treating fuel as only engine energy is wrong because fuel mass also affects structure, cooling, center of gravity, and flight planning.
Practice Questions
- 1 A left wing tank holds 3200 L of jet fuel and the right wing tank holds 3000 L. Using 0.80 kg/L, what is the fuel mass imbalance between the wings?
- 2 An aircraft has 2500 kg of fuel in the left wing, 2500 kg in the right wing, and 4000 kg in the center tank. If both engines together burn 2400 kg during the first hour, and all of it comes from the center tank, how much fuel remains in each tank?
- 3 Explain why pilots and aircraft systems might transfer fuel between tanks during a flight instead of simply using fuel evenly from every tank at all times.