# Drop tanks on WWII aircraft **URL:** \ **Category:** Factual Questions\ **Created:** [May 1, 2015, 6:43am UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973 "2015-05-01T06:43:59Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![obbn](https://avatars.discourse-cdn.com/v4/letter/o/d6d6ee/32.png) [@obbn](https://boards.straightdope.com/u/obbn)\ **Post date:** [May 1, 2015, 6:43am UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/1 "2015-05-01T06:43:59Z")
Hello Everyone, During WWII or fighters were unable to escort or boomers deep inside Germany because they lacked the fuel to do so. One workaround was the incorporation of disposable fuel ranks that could be jettison when empty or before engaging in a dogfight. I’ve always wondered how the fuel from these tasks was sent to the engine. Did each of the tanks have an internal fuel pump or was the fuel drawn by some sort of vacuum system? ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [May 1, 2015, 9:07am UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/2 "2015-05-01T09:07:36Z")
I had a notion of the answer, and now [I have tentative confirmation](https://books.google.fr/books?id=Fdeo9ZVg6dAC&pg=SA1-PA20&lpg=SA1-PA20&dq=%22drop+tank%22+compressed+air&source=bl&ots=abgy9V-DD0&sig=5SvKqip5kq3nGwFnOkdAdPaN9z4&hl=en&sa=X&ei=c0BDVaijNcP4UMvogLgL&ved=0CCcQ6AEwAQ#v=onepage&q=%22drop%20tank%22%20compressed%20air&f=false) (it’s the manual of the F-86, which is from slightly after WW2 - 1947 - but I suspect the principle was the same). No pump or anything like that inside the tank : they were designed to be disposable, and thus as cheap as possible (in fact some were made out of paper !). Instead the compressor of the aircraft’s engine was used to blow compressed air into the tank, which in turn forced the fuel out and into the fuel lines. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [May 1, 2015, 9:49am UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/3 "2015-05-01T09:49:57Z")
Why would the pump need to be in the tank? The regular fuel pump can suck gas from wherever so long as there’s the selector valve and relevant plumbing. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 1, 2015, 11:11am UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/4 "2015-05-01T11:11:53Z")
**Kobal2** ’s approach is still used today. But would have been a problem on piston-engine WWII aircraft. In those days they’d use a small tube facing into the airstream to provide some ram air head pressure into the tank ullage. All it has to do is push the fuel uphill a foot or so into the wing. Then you put a small electric pump in the wing to push it to the engine. As **GreasyJack** says, positive displacement pumps have some ability to “suck” fuel uphill as well. Pushing is definitely the better way to move any liquid, but it can be pulled some. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [May 1, 2015, 1:52pm UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/5 "2015-05-01T13:52:16Z")
It looks like in WWII [they used exhaust from some kind of vacuum pump to pressurize the drop tanks.](https://books.google.com/books?id=SfwqCTY9I6MC&pg=PA21&lpg=PA21&dq=p-51+drop+tank+vacuum+pump+exhaust&source=bl&ots=hPHBXAZOLZ&sig=wd2-hkyNjHdfD2xndNaRz5jloIU&hl=en&sa=X&ei=4oRDVfCbBcWbNtW_gPgC&ved=0CB4Q6AEwAA#v=onepage&q=p-51%20drop%20tank%20vacuum%20pump%20exhaust&f=false) Same system on the P-47 as well. ---
**Author:** ![Scumpup](https://avatars.discourse-cdn.com/v4/letter/s/ce73a5/32.png) [@Scumpup](https://boards.straightdope.com/u/Scumpup)\ **Post date:** [May 1, 2015, 1:56pm UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/6 "2015-05-01T13:56:24Z")
I built a few model airplanes when I was a kid. Mostly WWII fighters. The specs for the planes typically listed drop tanks as among the plane’s armaments. I presume this is because they could be dropped while still containing fuel. How effective were they in practice when this was actually done? ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [May 1, 2015, 2:35pm UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/7 "2015-05-01T14:35:12Z")
Well, I suppose they might land on somebody’s head, but that’s about it. Drop tanks make lousy incendiary devices. ---
**Author:** ![blondebear](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blondebear/32/1022_2.png) [@blondebear](https://boards.straightdope.com/u/blondebear)\ **Post date:** [May 1, 2015, 2:53pm UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/8 "2015-05-01T14:53:28Z")
> [@silenus](#): > > Drop tanks make lousy incendiary devices. But they did make decent [race car bodies](http://en.wikipedia.org/wiki/Lakester) back in the day. ---
**Author:** ![lieu](https://avatars.discourse-cdn.com/v4/letter/l/c2a13f/32.png) [@lieu](https://boards.straightdope.com/u/lieu)\ **Post date:** [May 1, 2015, 3:01pm UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/9 "2015-05-01T15:01:55Z")
According to Chuck Yeager, dropped tanks were pretty useful for target practice. > **[Chuck Yeager](https://www.facebook.com/permalink.php?id=465193060493&story_fbid=714091581958706)** > > Jan 15, 1945, was my 61st and last WWII mission. Andy and I were flying as spares. No one aborted so I took Andy on an aerial tour to Switzerland where we dropped our tanks and used them as target... ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 1, 2015, 3:20pm UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/10 "2015-05-01T15:20:59Z")
> [@Scumpup](#): > > I built a few model airplanes when I was a kid. Mostly WWII fighters. The specs for the planes typically listed drop tanks as among the plane’s armaments. I presume this is because they could be dropped while still containing fuel. How effective were they in practice when this was actually done? More accurately, drop tanks were listed as something that could be carried externally. Nobody ever considered them weapons. I suspect folks at the model company just didn’t care enough to distinguish between “external stores” and “munitions” or “armaments”. ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [May 1, 2015, 7:53pm UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/11 "2015-05-01T19:53:04Z")
> [@bump](#): > > It looks like in WWII [they used exhaust from some kind of vacuum pump to pressurize the drop tanks.](https://books.google.com/books?id=SfwqCTY9I6MC&pg=PA21&lpg=PA21&dq=p-51+drop+tank+vacuum+pump+exhaust&source=bl&ots=hPHBXAZOLZ&sig=wd2-hkyNjHdfD2xndNaRz5jloIU&hl=en&sa=X&ei=4oRDVfCbBcWbNtW_gPgC&ved=0CB4Q6AEwAA#v=onepage&q=p-51%20drop%20tank%20vacuum%20pump%20exhaust&f=false) > > Same system on the P-47 as well. You gotta love how kludgy the engineering looks in retrospect : > [@](#): > > Fuel gages for the wing tanks are on the floor, to the left and right of your seat. The gage for the fuselage tank is mounted on the upper left side of the tank itself ; you’ll have to look over your left shoulder to read it “By the way did we mention you’re sitting right in front of a large container of highly flammable crap, with no insulation whatsoever ? All right, moving right along…” ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [May 1, 2015, 8:13pm UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/12 "2015-05-01T20:13:25Z")
> [@Kobal2](#): > > “By the way did we mention you’re sitting right in front of a large container of highly flammable crap, with no insulation whatsoever ? All right, moving right along…” Not quite as bad as pilots of the Komet. It used a two part hypergolic fuel. The oxidizer was so potent it would cause most things like flight suits to spontaneously combust, and the other part by itself was toxic. Forget the enemy-even a rough landing could kill you. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 1, 2015, 8:18pm UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/13 "2015-05-01T20:18:21Z")
ETA: Ref **Kobal2** … That last part hasn’t changed much. There’s no such thing as a safe place within a fighter; everything is jam-packed, everything is nearby and all of it is at risk. In the F-16 they stuck the flight control computers directly under the floor under the seat. They were small and individually redundant, but all mounted together in one non-redundant outer box. They stuck them right next to the pilot under the logic that any battle damage to either would probably get both. And it took both to keep flying. And there was a large fuel tank directly behind the bulkhead directly behind the seat. True, jet fuel doesn’t burn like avgas, but OTOH modern munitions are a lot better at starting big fires than 0.50cal MG was (were?). ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [May 2, 2015, 5:22am UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/14 "2015-05-02T05:22:51Z")
> [@Scumpup](#): > > I built a few model airplanes when I was a kid. Mostly WWII fighters. The specs for the planes typically listed drop tanks as among the plane’s armaments. I presume this is because they could be dropped while still containing fuel. How effective were they in practice when this was actually done? > [@silenus](#): > > Well, I suppose they might land on somebody’s head, but that’s about it. Drop tanks make lousy incendiary devices. As an incendiary device, drop tanks were not effective, HOWEVER, the 15th Air Force pilots in Italy discovered that a building or haystack drenched in aviation fuel was rather easily lit up when it was struck by incendiary or tracer rounds from their machine guns. While not the “usual” method of attack, they used it quite a bit. Whether their tactics were shared with other units to be used in France or in the Pacific, I have never heard. ETA: Listing a tank as"armament" may have had more to do with simply noting that on some planes the tanks were mounted on the same hard points from which bombs would be suspended for shorter, ground attack missions. ---
**Author:** ![Ranger\_Jeff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranger_jeff/32/2065_2.png) [@Ranger\_Jeff](https://boards.straightdope.com/u/Ranger_Jeff)\ **Post date:** [May 2, 2015, 6:56am UTC](https://boards.straightdope.com/t/drop-tanks-on-wwii-aircraft/718973/15 "2015-05-02T06:56:31Z")
Maybe dropping fuel tanks (perhaps weighted properly) from their hard points would be good practice for a pilot training to drop napalm?