Isn’t this sort of what a NACA duct is trying to do?
EuroFlyer wrote:
The fuel in the tank isn’t just calmly sitting there like the clever engineers seem to assume.
That’s funny 
I don’t need no stinkin’ engineers anyhow!
EuroFlyer wrote:
I don’t know why his thread is so long. There is no doubt the low pressure area above the wing is strong enough to suck the fuel out of the wing. It is strong enough to lift the plane into the air, for heavens sake.
I don’t believe anyone is suggesting that fuel will not leak, when a cap is missing or ill fitting or for that matter ruin your day! but some like to reconcile how that happens, with what they understand regarding physics.
It’s my understanding:
That if a liquid is placed in an open rigid container, and the ambient pressure surrounding that container is reduced, the liquid will basically stay put. (Putting aside the effects of vaporisation).
The point being, there must be one or more ADDITIONAL factors, and if so what are they?
Well …I had it, the fuel caps where not fully tight due to old worn out rubber seals didn’t notice until an event happened, a little while after I bought the aircraft. I changed them the moment my passenger mentioned is this normal to see a vapor trail behind the right wing…..did it go fast, yes… I lost about 20 liters on 10 min flight….the tanks where no full btw…..So pls check the condition of your rubber fuel cap seals :-). Physics don’t matter I see the difference :-)
Ted wrote:
the liquid will basically stay put. (Putting aside the effects of vaporisation).
The point being, there must be one or more ADDITIONAL factors, and if so what are they?
Well, exactly. It will NOT stay put. That’s the whole point. If it would stay put, in a tank standing still, the suction wouldn’t do anything.
But the tank moves, quite a lot. As you can see in any of the many videos when you enter “tank sloshing” in youtube. Here’s one of them. It shows a truck tank moving forward. Now imagine a tank in an airplane, rocking all directions:
You will see, that during the sloshing quite a bit of the fuel will form waves touching the upper side where the tank hole is. If there’s a hole, and suction, that liquid will be sucked out.
To calculate that, you neither need Venturi nor Bernoulli. It’s a flow dynamics problem, involving Euler and Lagrange and n-th grade formulas, which most likely are much more complicated than the average aviation engineer’s toolset.
We have a new data point.
A former poster here has just posted on a US behind-paywall site (COPA) an incredible story, where be forgot to replace both filler caps and lost about 1/4 of his tanks in a matter of minutes. He even got the fuel streaming out on a video.
Expensive filler caps too, at €750 total.
Probably had bladders…
The video is here
It is a “3D” video. You can rotate the viewpoint with the mouse, and (go to youtube for the bigger version) at 0:51 in the video, looking past the pilot, you see the filler cap flying off.
Curiously it doesn’t show the fuel streaming out.
Video is unavailable….. have you got the link to it on YouTube?
It’s been pulled by the person who uploaded it…
