Disappearing Fuel M20M

[Awful_Charlie]

Here's a picture when my LR extensions were being fitted - the red outline behind the main spar is the extra capacity.

If you're losing 16 galls in 4 weeks (that's about a fifth of a pint per hour), then I'd suggest that could be evaporating with enough ventilation, and somewhere you'll find a pile of blue goo - which is where it evaporated from and not necessarily the leak. Something is going to smell though, but if you're outside (in in Europe, the hangarage problem is similar!) it could be difficult to detect. Does the fuel disappear all the way down to zero given enough time? From about half tank you're away from the outboard edge, so I'd start with a thorough check through the inspection holes in the wheel bays, and then whip the belly panels off and look outboard from there. I'd also try parking with the selector on the right or off - that will certainly tell you which side of the fuel selector (not forgetting the selector itself!) the leak is.

From memory, fuel flows from the LR through the main spar to the mains through a 3/8" pipe at the bottom inboard corner, but also through a pair of 3/4" holes about half way up the main spar when things are pretty full, there's a corresponding air vent pipe in the top outboard corner. The exact loading schedule isn't published as far as I know, but somewhere I got the figure that the first 30 galls in in the mains only, so assuming it is linear from there to full, then every gallon past 30 goes 0.57 to the original tanks and 0.43 to the LR

Good luck - keep us posted please

 

Edited March 4, 2018 by Awful_Charlie
More details & fix photo size/orientation

[DavidP]

30 minutes ago, Awful_Charlie said:

Something is going to smell though, but if you're outside (in in Europe, the hangarage problem is similar!) it could be difficult to detect.

There is no smell, even after the cabin is opened after an extended period of time, even in the warm weather we experience in Australia. I have even hauled my engineer out of the hangar to verify this in case my sense of smell was shot!

30 minutes ago, Awful_Charlie said:

Does the fuel disappear all the way down to zero given enough time?

Yes

30 minutes ago, Awful_Charlie said:

Good luck - keep us posted please

Will do, and thanks for the information. That's very useful!

Edited March 4, 2018 by DavidP

[ArtVandelay]

Will do, and thanks for the information. That's very useful!

Assuming you have dark colors on the underside of your plane:
Take a clean paper towel, start wiping the underside, checking it as you go, you will pick up blue die where avgas has evaporated.

[Piloto]

20 hours ago, kortopates said:

Extended tanks without the second filler port? What is your total fuel capacity?


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For the M20M, M20R and M20TN 130 gallons when filled to the top of the skin.

José

[kortopates]

For the M20M, M20R and M20TN 130 gallons when filled to the top of the skin.
José

Thanks, and still with the extra bay in front of the speed brakes?


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[Piloto]

David there is the possibility that the main tanks and maybe the auxiliary tanks bottom drain holes in the ribs were sealed when the tanks were resealed. What is your plane serial number?

José

[Piloto]

On ‎3‎/‎4‎/‎2018 at 10:22 PM, kortopates said:

Thanks, and still with the extra bay in front of the speed brakes?


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 I found some Mooneys can make up to 135 gallons total on a completely dry tank. It depends on the leveling on the ground. A tilted back Mooney will hold more than a level Mooney but the extra fuel may come out during taxing.

José

Edited March 8, 2018 by Piloto

[carqwik]

Either the fuel is stolen (unlikely since why only drain one tank all the time?) or there's a leak (for sure).  The leak is internal and the fuel is running out of the tank, down the spar and possibly down the the belly of the plane where it's evaporating so it never reaches the ground.  It is summer there now right? Open the battery access panel on the port side and look in at the belly...see if there are traces of fuel dye there.  Although there should be an odor of gas in the plane, perhaps your plane is venting itself due to wind and hence no smell?

 

[rpcc]

You are saying it can't be missing by someone removing fuel from your plane because the issue follows you around the country.  

You can't find evidence of fuel on the plane - stains, smells etc.  You can't see evidence on the ground.

If the fuel has moved from one tank to the other you should be able to verify that by sticking each tank. 

If you think its leaking you are looking for how approximately 3 shot glasses per hour departing your fuel tanks un noticed.  

Seems very strange.  Can you send us some pictures of your plane and location where you tie it down?  That may help - some of these guys have very sharp eyes.

How could you ever fly this with such doubt about your fuel system?  

 

 

[jlunseth]

Probably you know this, but if you have leakage in the wing it will flow to the wing root unless it finds a way out of the wing.  The wing root is under the floor inside the cabin.  You would expect to smell that, but it is pretty subtle.  It should be noticed at annual, the floor has to be removed to see it.  It can find its way out through the belly, one would expect blue on the belly if that were the case.