WW2 aircraft drop tank question.

I'm been trying to find a detailed diagram or description of the plumbing that was used for jettisonable fuel tanks. In particular the fuel line connection between the drop tank and the plane.

That connection had to be tight enough so fuel isn't leaking or spraying out but not too tight so it can release when the tank was dropped and not cause the tank to hang up. I'm been trying to find detailed information about these connectors on the web but without any success. Funny how the old engineering knowledge can become hard to find.

Any help or directions would be appreciated.
 

marathag

Banned
I believe it was a barbed check valve to a short lengths of clamped rubber fuel line for pressure and pickup
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Thanks marathag. It looks surprisingly crude but if it worked what the heck. On that Mustang it appears that the connection was achieved by short lengths of rubber hosing bridging the gap between the metal piping and clamped by simple hose clamps. On both the pressure line and fuel feed line.

I wonder when the tanks were jettisoned if sometimes the ground crew had tightened those hose clamps a little too much so the tanks would occasionally hang up for a while dangling and swaying in the slipstream until the rubber tubing broke or was finally pulled off the metal piping.

There must have been other methods developed for connecting drop tanks I would guess.
 

marathag

Banned
1/2" rubber hoses won't hold up an empty 20 gallon tank for long on an auto once the main straps are released, only the 3" hose to the filler port is strong enough.
Now for aircraft, the slipstream at even 200mph would pull right out.

Later on, that was more a problem with jets being able to jettison when going above mach 1, but that's not a WWII problem to get something past the shockwave cone
 
The simple method of joining the pipes with a short length of rubber hose secured by hose clamps was evidently used for USAAF drop tanks. What other methods were used by other air forces? Did they all use a similar arrangement or some very different method?
 
I wonder when the tanks were jettisoned if sometimes the ground crew had tightened those hose clamps a little too much so the tanks would occasionally hang up
I couldn't give you a source, but I recall seeing occasional mentions of it happening.
 

Archibald

Banned
It still happens with modern drop tanks. The freakkin' things just don't detach, adding all that weight and drag to the aircraft.
 

Deleted member 94680

It still happens with modern drop tanks. The freakkin' things just don't detach, adding all that weight and drag to the aircraft.

Really? Where’s that happening?

In the British forces tanks, baggage pods, stores and anything carried externally is mounted on an Ejector Release Unit. Pyrotechnic cartridges provide force to pistons to jettison the store away from the aircraft, overcoming any envelope effect generated by the speed of the aircraft. It’s a reliable and well tested system.
 

marathag

Banned
Interesting question... I would have thought something on the order of a servo run quick connect fitting; but were they invented later?

Fighters like the P-47 still had handles attached to pull cables that ran out to the release pins in the shackles.
Bombers like B-17 had electrical solenoids, as they had the additional options of timed interval release, and the pilot had an 'Emergency Salvo' lever that would cycle the bomb bay doors and release all the bombs, independent of the Bombardier controls
 
Since aerodynamics was critical from the start, why weren't drop tanks more streamlined?

For subsonic flight a teardrop shape is ideal for streamlining. WW2 Allied metal drop tanks were usually teardrop shaped. The "paper-mache" drop tanks used in the ETO were more of a tubular shape with rounded fronts and backs. They were restricted to cruise and below speed only. But you would jettison them when going into combat anyway so their speed limitation wasn't that important.

Here are a couple of WW2 teardrop shaped 110 gallon tanks.

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As for quick-disconnects ... try to picture two tubes overlapping. O-rings prevent fuel leakage. When the drop-tank is dropped, the inner hose falls away. A spring drives a piston down to seal the aircraft side of the circuit. The pilot probably also has a second valve to isolate the drop tank circuit from the rest of the fuel system.

Drop tank shape is a compromise between volume, weight, streamlining, ease of ejection, etc.
Volume favours a cube.
Weight favours a spherical cloth bag.
Streamlining favours a teardrop. Pre-WW2, 3 to 1 taper was considered enough to minimize drag. Later, supersonic drop tanks were more like 10 to 1 (see Century Series fighters during the Vietnam War).
Ease of ejection was eventually solved with ejector cartridges (gun powder) installed in pylons.
 
As for quick-disconnects ... try to picture two tubes overlapping. O-rings prevent fuel leakage. When the drop-tank is dropped, the inner hose falls away. A spring drives a piston down to seal the aircraft side of the circuit. The pilot probably also has a second valve to isolate the drop tank circuit from the rest of the fuel system.

Do you know if this system was used on WW2 aircraft?

The purpose of the spring driven piston was to seal the pressure line going to the drop tank?
No need to seal the fuel feed return line?
 
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Archibald

Banned
It happened plenty of time in Vietnam, to Phantoms and other aircrafts. Admittedly, that was 40 years ago, and reliability is probably far better nowadays.

It just blows my mind that the Wallies build drop tanks out of papier-maché just not to give any scrap of metal to Nazi Germany.
WWII is really "Nazi Albert Speer is smart, so we have to be smarter than him."
 
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It just blows my mind that the Wallies build drop tanks out of papier-maché just not to give any scrap of metal to Nazi Germany.


WWII is really "Nazi Albert Speer is smart, so we have to be smarter than him."
Yes.

Avoiding giving the Nazis more scrap metal wasn't the main reason the Allied air forces in the U.K. used the paper drop tanks. Unfortunately the Allies were already supplying scrap metal in the form of numerous shot down bombers and fighters.

It was a cheaper source of one use only drop tanks. An economical move. It saved using Aluminum stock and metal worker resources. Why build resilient metal drop tanks for fighters if they're going to be almost certainly dropping them every mission? So build cheap one use "paper-mache" tanks that can be built out of cheap material by unskilled quickly trained workers.

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Plus, after a few hours, the fuel can't be recovered for Germen use.


I'm guessing that a half-filled paper-mache drop tank weighing around a few hundred pounds falling from thousands of feet would smash open like an egg on hitting the ground depriving the Germans of some free Avgas. Come to think of it so would metal tanks if they're heavy from unused fuel. If either paper or metal tank fell empty and light I still don't think they would be in very good shape as well.
 
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