DA40D - Right Tank Drained

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Karl
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Re: DA40D - Right Tank Drained

Post by Karl »

In theory fuel cannot transfer between the tanks with out the transfer pump running. With the pump running it can only transfer left to right. (assuming everything is connected correctly)
There are heater pipes and a one way valve, if either fails then fuel can transfer right to left but only really with the engine running.
BTW, a new amendment to the manual now requires the valve to be replaced every 1000hrs.

As the origional post said the left tank was full and the right tank showing empty this shows there is no connection between the tanks. Liquid finds its own level, so either both tanks would be empty or equal quantity.

Assuming the tanks were indeed full then the most likely cause would be a leak or theft of fuel IMO.
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Re: DA40D - Right Tank Drained

Post by Boatguy »

Karl wrote:In theory fuel cannot transfer between the tanks with out the transfer pump running. With the pump running it can only transfer left to right. (assuming everything is connected correctly)
The diagram and text are clear that left is main and right is aux.

Unless the cooler has a check valve, what stops gravity feed between them? I’m referring to the fuel system diagram posted earlier.
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Re: DA40D - Right Tank Drained

Post by Keith M »

Boatguy wrote:“Fuel that is not injected into the combustion chambers is routed through the AUX fuel tank (right wing) and fed back into the MAIN fuel tank (left wing). This way hot fuel from the rail is cooled and cold fuel in both tanks is heated.”

I don’t see why, fuel can’t gravity feed between the two tanks.
The link between the two tanks is via what is effectively a heat exchanger. Only if that was fractured would there be a direct connection between them, although I'm not sure if it runs under the cockpit floor, or behind the firewall. In the latter case, it would be too high for any gravity assisted cross flow.
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Re: DA40D - Right Tank Drained

Post by Boatguy »

The AFM says

“Fuel that is not injected into the combustion chambers is routed through the AUX fuel tank (right wing) and fed back into the MAIN fuel tank (left wing). This way hot fuel from the rail is cooled and cold fuel in both tanks is heated.”

If the “cooler” is a heat exchanger, then without running the transfer pump, how would fuel be “fed back into the Main fuel tank”?

Further with both tanks full at departure, returned fuel would have nowhere to go since the right tank has no relief valve, only a capillary which allows air into the tank.
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Re: DA40D - Right Tank Drained

Post by Karl »

Boatguy wrote:
Karl wrote:In theory fuel cannot transfer between the tanks with out the transfer pump running. With the pump running it can only transfer left to right. (assuming everything is connected correctly)
The diagram and text are clear that left is main and right is aux.

Unless the cooler has a check valve, what stops gravity feed between them? I’m referring to the fuel system diagram posted earlier.
Oppsss got my left and rights back to front.
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Re: DA40D - Right Tank Drained

Post by Karl »

Boatguy wrote:The AFM says

“Fuel that is not injected into the combustion chambers is routed through the AUX fuel tank (right wing) and fed back into the MAIN fuel tank (left wing). This way hot fuel from the rail is cooled and cold fuel in both tanks is heated.”

If the “cooler” is a heat exchanger, then without running the transfer pump, how would fuel be “fed back into the Main fuel tank”?

Further with both tanks full at departure, returned fuel would have nowhere to go since the right tank has no relief valve, only a capillary which allows air into the tank.
It is described as a cooling loop in the right tank. It is essentially just an aluminium pipe. The return fuel never enters the right tank it just flows though a pipe (cooling loop) that is in the right tank.
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Re: DA40D - Right Tank Drained

Post by Boatguy »

Ok, that makes more sense. And I found the descriptive language in the maint manual:
“The right tank has two adapters which connect to a pipe loop inside the tank. This is the cooling loop.”

So back to the OP, where did the fuel go? And does the plane have LR tanks?
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Re: DA40D - Right Tank Drained

Post by OriensFlight »

Perhaps it's time to pull out the fuel-measuring doohickey. I think its actual name is the "Fuel Quantity Indicator Calibrator" although some people call it the mechanical fuel gauge. I hear it's really fun to work with (sarcasm), so wear gloves.

Can your mechanic suggest a procedure? If I had to make one up, I'd measure the fuel level in both tanks, then fill the right tank to the same level as during the incident, then measure both thanks. Then I'd leave the plane sitting over night, and measure both tanks again in the morning. Then I'd fuel the left tank, check both tanks again, let it sit for some time, and then check both tanks again. If that didn't show any discrepancies then I'd taxi the aircraft to the run-up area and try to burn off a gallon, then measure again. I suppose one could go overboard on this sort of thing, but hey the fuel system is one of the more important bits of the plane. If after all that, and perhaps an hour flight, you can't get the thing to misbehave, perhaps chalk it up to the fueler having not properly reset the counter.

Let us know how it goes, an interesting mystery.
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Re: DA40D - Right Tank Drained

Post by Captain-random »

The aircraft was on a level concrete apron and filled right tank first.

No long range tanks.

The aircraft was filled to the top when I departed and after a 2 hour flight was filled to the top again with around 40 litres of JetA1 (which is roughly the correct fuel burn)

The day after the right tank indicated empty and after a further 1.5 hour flight took 22 usgals to fill to the top again. (It should have only taken 10us gals which show the tank was in fact nearly empty on takeoff)

I emailed the airport (a secure international airport) who have never had any reports of fuel theft and who’s light SEP GA JetA1 client numbers are very small (I can’t imagine someone in a King Air / TBM stealing 10us gals of fuel)

So I’m at a loss :S
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Re: DA40D - Right Tank Drained

Post by Boatguy »

- No LR tanks so the gauges should be telling you what is really in the tanks.
- Full tanks is 28US gallons, 14gal in each wing.
- Tanks were filled after flight #1 on day #1
- On day #2, right tank reads empty, meaning the plane now has only 14 US gallons of fuel, all in the left tank.
- 1.5hr flight should burn about 10US gallons @ 6.6gph (75% power).
- Upon landing, 22US gallons to fill both tanks. This sounds roughly correct if you started with an empty right tank as 14 - 10 = 4 in the left tank when you landed + 10 to fill the left tank and 12 to fill the right tank = 26 which is pretty close to the 28gal total capacity capacity.

So if this is the summary, I see only three possibilities:

- The right tank was not actually filled after the first flight. A 2hr flight should have used about 13 gallons or 50 litres, so the 40 litres sounds a little light, but could have filled the left tank. If you only drew from the left tank, then 40litres (10.5) gallons could all have been put in the left tank and the right tank was never filled. This seems the most likely.

- Both tanks really were filled, and 14gal of fuel leaked out over night. This seems highly unlikley as Jet-A doesn't evaporate well and smells awful. N125NG had a fuel link in the right tank at the wing root, but never enough to unload 14gal overnight.

- The fuel in the right tank was stolen by someone who used the fuel in a diesel vehicle (I agree no turbo prop is going to steal 10gal). Seems very unlikely at a secure international airport.

So my conclusion is that the right tank did not get filled after the first flight. I mean no disrespect by suggesting that you read the gauges wrong after the first fill up and/or didn't see the fuel in the right tank as you said you did, but the math works for the explanation that the right tank was never filled and the I can't think of another scenario that explains the situation.
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