We often take gravity for granted because it’s constant, but it plays a crucial role in moving fuel in vehicles like cars and airplanes. For example, a typical fuel system relies on gravity to draw fuel from the tank to the engine. In a high-wing monoplane like the one explained in How Airplanes Work, the aircraft would stall almost immediately if flown upside down, as gravity would pull the fuel down to the engine from the wing-mounted tanks.
So how do aerobatic planes, which perform loops and fly upside down, manage to get fuel from the tank to the engine? To answer this, I consulted Randy Henson, a pilot of the aerobatic biplane seen below:
Randy explained there are two methods to solve this issue:
"The first is the flop tube design used in my Pitts S-1T. The fuel tank is located in the fuselage, just in front of the pilot's knees. Inside the tank, a flexible hose with a weight at the end is used. When the plane is upright, the hose, or flop tube, falls to the bottom of the tank, drawing fuel. In inverted flight, the weight causes the hose to shift to the top of the tank (now the bottom), drawing fuel from there. This is a clever design as it only requires one tank, yet allows access to all the fuel regardless of the plane’s orientation. It’s commonly used in high-performance aerobatic planes that have the fuel tank in the fuselage.
"The second solution is the header tank, used in planes like the Super Decathlon, which is a high-wing monoplane. These planes have main fuel tanks in the wings, higher than the engine. In normal flight, gravity feeds the fuel from the wing tanks to the engine-driven fuel pump. For inverted flight, a small header tank is positioned near the pilot’s feet, connected to the main wing tanks. During upright flight, fuel flows into the header tank by gravity. The header tank is linked to the fuel pump, so when the plane rolls inverted, fuel flows from the header tank to the engine. A check valve in the line prevents fuel from draining back into the main tanks when inverted. The header tank typically holds enough fuel for about two minutes of inverted flying.
"My plane and most modern aerobatic planes are fuel-injected, though some older Pitts planes with pressure carbs can also fly inverted."
Explore these links to expand your knowledge:
- Aerobatics FAQ
- Aerobatic Airplanes
- How Airplanes Work
- How Becoming an Airline Pilot Works
- How Gas Turbine Engines Work
- How Ejection Seats Work
Buzz
