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Do fuel tanks need to be pressurized? It's my understanding that the pressure difference between the outside air and the inside fuel would force the kerosene out of the fuel tank. What stops this from happening? And if fuel tanks do need to be reinforced to accommodate for this, how do planes with wet wings, like the B-52, handle the pressure difference?

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Fuel tanks don't need to be pressurized, though they can be. Unpressurized tanks are vented to the atmosphere, and so a large pressure difference never develops in the first place.

In pressurized fuel tanks, the tank is not open to the atmosphere, so fuel has nowhere to escape to. If the tank is kept at a significant pressure difference to the outside air, it of course needs to be reinforced.

The B-52's wet wings are vented to the outside air. If the vents are plugged bad things can happen.

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Do fuel tanks need to be pressurized?

In some cases they need to: off the top of my head I'd say for example the XB-70.

Due to the design top speed of Mach 3, the airframe could reach temperatures as high as 250°C (500°F). In order "to reduce the likelihood of autoignition, nitrogen was injected into the JP-6 during refueling, and the "fuel pressurization and inerting system" vaporized a 700 pounds (320 kg) supply of liquid nitrogen to fill the fuel tank vent space and maintain tank pressure" (source Wikipedia)

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