lets say an airplane needs to get to a certain route but doesnt have the fuel to do and it needs to store in the anti-shock bodies. Is it possible?
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3 Answers
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Yes, and there have been cases of this. Tip tanks of the period when aircraft flew already supersonic and jet engines were still very thirsty are a good example. Below you see the area-ruled tip tank of the F-5.
F-5 tip tank (picture source).
Now that @voretaq7 got me thinking, I should also mention the "Doppelreiter" fuel tanks (slipper fuel tanks) which were used on some German fighter airplanes in WW II. They were mounted above and behind the wing, and to everyones surprise they had little impact on the top speed of the airplanes, and in case of the Me-309 helped to increase it slightly. They were the first practical application of Küchemann carrots and worked much like the flap track fairings of today's airliners.
FW-190 A with Doppelreiter tanks.
answered Aug 25, 2015 at 7:10
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2$\begingroup$ Not sure if that's quite what Ethan was asking about (I took his question to mean repurposing anti-shock bodies around other fuselage protrusions), but certainly if you're forced to have a fuel tank that can't be embedded in the wing or fuselage you want it shaped to create the least drag possible (we saw the beginning of this with even older designs, this drop tank from WWII for example). $\endgroup$– voretaq7Aug 25, 2015 at 16:12
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4$\begingroup$ @voretaq7: Yes, Ethan probably thinks only of the flap fairings, but tanks are good Küchemann-bodies in their own right. Messerschmitt experimented with additional fuel tanks which were put on top and aft of the wing, and to everyones surprise the planes flew faster with them than without. They were called "Doppelreiter" and were the first practical Küchemann-bodies. $\endgroup$ Aug 25, 2015 at 16:53
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Fuel is stored in fuel tanks, which typically have two requirements:
- They must be sealed so as to contain the fuel in all probable flight attitudes.
(Ideally they will keep it contained in a few improbable ones too.) - They must have appropriate plumbing to get the fuel to the engines.
(There are some exceptions to this, but fuel in a tank you can't use is not helpful in flight.)
Anti-Shock bodies are typically not fuel tanks - they meet neither requirement as they are not watertight (fuel will just pour out of them), and there's no plumbing to get the fuel out of, or for that matter into them.
As "Exhibit A", take a look at the anti-shock bodies around the 787 flap tracks & actuators- Note that the anti-shock body is hollow, but unsealed. Any fuel (or water) in here would simply pour out the trailing edge when the flaps are extended.
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4$\begingroup$ I guess the more interesting question would be: Is it feasible to seal these hollow bodies to make them watertight? The additional plumbing would definitely need changes but does not seem too onerous. The real crux is "Is it worth it?" If one really needed more fuel to add range I'm sure expanding the primary tanks themselves or adding a fuselage tank might give you more bang for the buck than squeezing in a few hundred liters into the shock bodies. $\endgroup$ Aug 25, 2015 at 6:39
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3$\begingroup$ @curious_cat As you'll note from the photo the anti-shock bodies on an airliner wing may be hollow but they aren't empty (there are already hinges, actuators, hoses, etc. in them, all taking up what would be fuel capacity). By the time you got done sealing the area (in such a way that doesn't interfere with its normal movement in flight) and adding plumbing you probably wouldn't get much usable fuel out of the equation. A bigger tank in the wing or fuselage generally wins out in design. $\endgroup$– voretaq7Aug 25, 2015 at 16:03
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$\begingroup$ @curious_cat: Well, if your antishock bodies aren't being used as flap-track fairings or what have you, using them for additional fuel tankage is perfectly feasible, but not many airliners today have antishock bodies that aren't already playing double duty as something else. $\endgroup$– VikkiAug 16, 2019 at 21:06
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In at least one case, yes!
The Convair 990 jetliner (a derivative of the earlier Convair 880) had large, prominent antishock bodies on its upper rear wings, easily seen in this photograph of a retired NASA 990:
(Image by NASA, via Stahlkocher at Wikimedia Commons.)
These antishock bodies - particularly the larger inboard ones - also served as fuel tanks, and held the aircraft's fuel-dumping apparatus. Wikipedia sums it up nicely:
One change from the 880 was the large anti-shock bodies on the upper trailing edge of the wings to increase the critical Mach and reduce transonic drag. The inboard shock bodies, which were larger, were also used for additional fuel tankage. Later during the design period, Convair modified the design to include fuel in the outboard pods as well, but during the initial test flights the extra weight caused the outboard engines to oscillate in certain conditions. The pods were redesigned once more, and shortened by 28 inches (710 mm), causing increased drag. The inner set of pods also served a secondary role as fuel dumps for the fuel tanks, and the outlet pipe is prominent.
