Low-wing tanks typically have fuel supply lines at the bottom. For external drop tanks, I thought they came built with internal lines that mate with the plane.

enter image description here

That appears to be the case for more modern tanks – though I'm not sure yet – based on a mid-50s patent. Earlier patents (image shown) that correspond with WW2, as far as I've seen, don't mention any relevant internal structures. And two Wikipedia articles weren't helpful:

Most I could find was an F-86 manual on Google Books. And it mentions the jet engine providing compressed air into the tank to draw fuel (the mechanism isn't yet clear to me, but I'll pursue that later).

For now, WW2 aircraft. For example: Where electric motor compressors used instead of bleed air? Were there internal tank structures that assisted?

If there are differences between implementations, then the most common/typical would do or the typical American-fighter implementation (to assist with references since they're typically much easier to find).

  • $\begingroup$ If you have a pump onboard the airplane that is able to apply suction to a line built into the tank, it would seem that pressurization of the tank would not be necessary. I suspect that this is the system that was used with piston-engine aircraft in WW2. Clearly there must be a line to the low point in the tank regardless of whether the feed is due to pressurization or suction. I don't really know anything about it though. $\endgroup$ Apr 22, 2020 at 21:35

1 Answer 1


Like the F-86, air is supplied into the tank so the fuel can be pushed up. On the P-51, the source of the air was the vacuum pump (the one used for the flight instruments), providing 5 psi of pressure.

Knowing this, the two connectors, pressure and fuel, can be seen in many photos.

enter image description here
Source: P-51 manual

And the two connectors:

enter image description here
Source: ww2aircraft.net

  • 4
    $\begingroup$ Curious as to which point the lines broke free when the tank was dropped? $\endgroup$ Feb 10, 2021 at 13:32
  • $\begingroup$ Using the pressure side of the vacuum pump, that's clever! $\endgroup$ Nov 1, 2023 at 20:20

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