fuel leaking from right wing?

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techbasset

fuel leaking from right wing?

Post by techbasset »

A question about a DA40NG rental:

There has been a persistent problem (i.e., twice) where a decent puddle of fuel accumulates under the right wing near the fuselage. Decent puddle = 8 hands of surface area or so.

When I reported this to maintenance, they claimed that it was leaking from the fuel drain because there was full fuel and there's a slight tilt on the ground to the right. I'm dubious of this because the puddle is not directly under the drain, and it seems like fuel is dripping from the dark grey strip 1-2 feet farther aft (the strip is also slightly warped and no longer well-attached to the wing). I don't see how fuel could be getting back there from the drain.

Has anyone ever encountered this? Is there a reason fuel would be leaking farther aft?
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Colin
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Re: fuel leaking from right wing?

Post by Colin »

In my year-long experience owning a DA42, I have had more fuel leak out than I ever *saw* in a decade of owning a DA40. I believe that the design of the fuel tanks for JetA must be a little more difficult. I keep wanting to insert something into the filler neck to tell line personnel where to stop. The first time it happened I thought something was horrible wrong and didn't fly the plane until I heard from the ferry pilot ("Yes, that happens all the time when you say 'top off,' tell them to hold it down an inch").

So I would be it is just overfilled.

When it comes out the vents (or overflow tubes, because I assume there are designated overflow tubes), it runs down the wing in all sorts of odd patterns.
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Rich
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Re: fuel leaking from right wing?

Post by Rich »

I think it's more likely that one of the fittings at the inboard end of the inner fuel tank. I had two different occurrences in my AVGAS DA40): 1 was the joint where the fuel sensor enters the inner tank. The other was for the auxiliary "low fuel" sensor. There is also, of course, the entry point of the fuel line.
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Re: fuel leaking from right wing?

Post by CFIDave »

It's considered "normal" for fuel to flow out of the vents on the right wing if you mistakenly fill it all the way to the top. I've seen this on my DA40 and DA42 (and I'm pretty sure the 62 will exhibit the same behavior). The leaking is made worse if the fuel nozzle is pointed inboard while filling at a high rate. Fuel coming out the vents will also run down the outside of the wing due to its dihedral.

Always tell fuelers to fill to only about an inch from the top of the tank.
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Re: fuel leaking from right wing?

Post by rivenmyst137 »

AFAIK, there are the fuel vents farther out on the wing, and there is the fuel valve closer to the fuselage. There shouldn't be any "vents" aft of the fuel valve on a DA-40NG, correct? Because the leak I was seeing is aft of the valve, and I have trouble seeing how fuel could be getting on the underside of the wing and flowing backwards since there's a decent air gap between the fuel valve and the underside of the wing. (Wish I had a picture...)
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Re: fuel leaking from right wing?

Post by Karl »

It is quite common for fuel to vent and run down the wing especially if the tanks are full to the very top.

It is quite easy to check. If it is venting, the fuel will be running down the lower surface of the wing until it reaches the lowest point, usually the wing seal, before dripping onto the ground.
However if the lower wing is dry and there is no evidence of fuel staining then it may well be coming from the inboard end of the tank. It should be easy for your mechanic to check.

On the DA40, if the aircraft continues to vent fuel after engine start or in flight then it is probable that the fuel non return valve is dirty and stuck partially open.
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