The only reason I'm aware of why designers include a fuel dump capability is when they design a landing gear system which cannot handle the maxmum takeoff gross weight.  This is often the cse on large jets -- think of an airliner which may have a gross weight double that of its typical landing weight.  In this case, a landing required immediately after takeoff would require a fuel dump, which could easily be a 15 minute process.

 

I know of no cases where designers include a fuel dump provision to reduce post crash fires.  That's not to say the idea is without merit, but I would not bother with it.  Instead, I would take measures to prevent inadvertent fuel release after a survivable crash.  I'm not sure how to do that -- would a flexible fuel line (say, steel braided) be less likely to tear than a hard aluminum line?  Would a silicone fireproofed fuel line be less likely to rupture (those puppies look pretty indestructible)?  What about a header tank -- I imagine that five gallons of fuel just above your knees is not a good place for a fuel leak (and yes, my airplane has the header tank).

 

But dumping the fuel before an off-airport landing?  I don't think I would do that, but that's just me.

 

- Rob Wolf

 

p.s. the NASA test in the early 1980's involved a remotely-piloted Convair 720 with an anti-misting additive in the fuel.  As I recall, the remotely piloted airplane did not hit the intended point on laning and thus the objects intended to puncture the tanks, well, ithey pretty much ripped the wings apart, releasing the fuel all at once.  This was a test failure and the explosion-inhibiting anti-mist additive was not adequately tested.  Needless to say, they did not repeat the test.