What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Fuel on belly

Drippy

Well Known Member
Guys,

I have a question - I over the last few months I have seen these streaks on my belly. The photo is of the bottom of the fuselage along where the spar connects the two wings.
x9p9bDJrSZugMzkE_DvUMg


I said fuel in the title but I am not 100% sure what the fluid is .. . as you can see it has a blue tint but doesn't evaporate right off like 100LL and there is a bit of grit to it dark specs.

My first step was to pull the cover off the tunnel - no noticeable streaking or leaks. I did have an issue back in March when I did my annual I found leaking around the stopper (not sure what you call it) screw in my stock Van's Fuel Valve. At the time I tightened and torque sealed - in my recent inspection there was no leaking here or anywhere else I could detect.

One other possible area for fuel was a leak in the Right Tank along the in board rib joint about 2 inches forward of the vent. Fuel from this leak flowed down, aft and inboard along the spar - gear leg. I repaired this a month or two ago and cleaned everything up. There is no indication of fuel leak now - though I pulled the tank to make sure there was no leaking along the spare and found zero indications of a leak - also performed a pressure test no bubbles and it held pressure no issues.

One idea is that there might be fuel mixing with the grease from the gear leg??? But I don't figure out why the streaks would only be at the center of the aircraft and not all along the belly leading out to the streaks in the center.

d7D_lPIoTly2BcMc-EMDyg
 
Last edited:
Sorry let me try again.

Belly:

https://photos.app.goo.gl/trpxqR78gaWxfNk69

Right Gear Leg:

https://photos.app.goo.gl/kFBNTbfkpYYnqd2t5

Note- on the gear leg I whipped off the bluish tint - before tanking the photo - not sure why?????

The stuff on the belly sure looks like fuel stains to me - it appears to be right along a seam. Which seam is that? It looks like it might the one under the spars, in which case you could have a fuel leak in the cabin under the seats or in the tunnel where your plumbing goes from your fuel selector to the tanks.

The landing gear looks like grease. During construction grease is used to help insert the gear legs into their mounts.
 
Check the lines at the tunnel bulkhead fittings on both sides. Same for the lines connecting to the selector valve.

Tom
 
Agreed on the fuel leak.

Get it all naked, get everything out of the way so you can get to all your lines, and turn on the boost pump, and start touching fittings looking for a wet spot. Depending on the age and type of fuel hoses, the leak could be within the walls of the hoses themselves as well, and dripping out the end of the firesleeve.
 
Pull the seats and inspection panels, with that much on the belly I think you'll be able to find the leaking fitting pretty easily.
 
After you clean up the tunnel and check for obvious fitting issues, put a layer of white paper towels on the bottom of the tunnel. This “witness” paper will help isolate the leak(s) if any remain.

Carl
 
After you clean up the tunnel and check for obvious fitting issues, put a layer of white paper towels on the bottom of the tunnel. This “witness” paper will help isolate the leak(s) if any remain.

Carl

Yep, this is how I found a leak in the tunnel of our 10.

Lots of things in there to leak but not a lot of room to work at tightening things. Or room to even look for the leak.

Tunnel side access panels are nice.
 
Tunnel photos

Guys,

Thank you for all the great inputs- I pulled the tunnel cover see the photos below.

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn





I didn't see any significant blue staining. There was a little right under the inlet of the pump but I believe that is old from when I had a split fuel line - damaged in filter removal for cleaning - long story:-(.

I pressurized the system up to ~30PSI with the electric pump - but was only able to pull from the left tank - remember I pulled the right tank looking for a leak.

My plan it to put fuel back in the right tank and pressurize that side of the system after wrapping everything in tissue (leak detector).

Any other suggestions - I am definitely open to ideas.

Thanks up front for all the help.
 
Last edited:
Go under EVERY fitting with your finger or a clean white paper/cotton towel. You will find somewhere green/blue residue ... then follow that. I had the same ... but went flying twice, until I looked it over. If there is a fuel smell, then you have a leak.

Check it prior the next flight, don't risk anything!
 
I would also open up the wing roots - its possible that fuel is leaking into the area between the spars.
 
Be careful pressurizing the fuel tank! you can not put much more than 1/4 to 1/2 PSI without distorting the tank and ruining it!

After owning 4 different Mooneys It for sure is a fuel leak.
 
I don't think he meant pressurizing the tank, just the system after the pump. When you add fuel to check the other tank pressurizing the system with the pump will only pressurize after the pump. No seed to turn the pump on if you tried that already. With fuel in the tank you should see leaks in the lines just from the fuel head pressure. Use a paper towel or a dry finger. it will show up if it is on a fitting. If it is running out as much as the picture shows, it is a fairly large leak.
 
Issue found?????

Thank you everyone for the good advice.

I put paper towel under all the fitting in the tunnel and under the seats and used the fuel pump to pressurize the system - swapping fuel tanks frequently as I have the VAN’s fuel valve and am suspect of it.

Initial we didn’t find any obvious leaking but further inspection with a paper towel discovered a little leak from the connection between the selector valve and the filter. Removing the tube we found some cracking in the flare. We then replaced the original tube with braided line:).

My concern is that the fact that this wasn’t a big leak - the volume doesn’t seem to equate to what was seen on the belly.

One theory is I may also be getting fuel coming through the fuel vent and it is running along the leg and then down that seem????

Thanks for any other suggestions.
 
Thank you everyone for the good advice.

I put paper towel under all the fitting in the tunnel and under the seats and used the fuel pump to pressurize the system - swapping fuel tanks frequently as I have the VAN’s fuel valve and am suspect of it.

Initial we didn’t find any obvious leaking but further inspection with a paper towel discovered a little leak from the connection between the selector valve and the filter. Removing the tube we found some cracking in the flare. We then replaced the original tube with braided line:).

My concern is that the fact that this wasn’t a big leak - the volume doesn’t seem to equate to what was seen on the belly.

One theory is I may also be getting fuel coming through the fuel vent and it is running along the leg and then down that seem????

Thanks for any other suggestions.

Mike - where in Vermont are you located? Did you build the aircraft or buy it? I’m at KMGJ in NY - more than happy to help you take a look at it if youre down this way at all or if come up your way. I’ll be headed up to KBTV sometime in the next few weeks to check out an LX7 that a company my friend works for is purchasing.
 
Sounds good

I will send you a PM with my contact info but we actually are blessed with two RV10s at FSO - Franklin County Airport in northern VT. We are about a 30 minute drive north of BTV and most of us actual live or work in Burlington but commute to our planes.
 
One theory is I may also be getting fuel coming through the fuel vent and it is running along the leg and then down that seem????

Thanks for any other suggestions.

I would expect any leaking going on in the wing root area would create blue staining on the bottom of the wing root fairing edges.

Does your fuel vent line run into the cabin? Typically that exits on the bottom of the wing root fairing.

Larry
 
Fuel Vent

No fuel vent isn’t vented to the cabin it is stock - built to plans or at least as well as I can:).

Maybe not my best theory.
 
A couple more things to check...

I'd take a look at the induction airbox (FAB) overflow drain tube and mechanical fuel pump rupture drain tube. Both of those tubes should exit the engine compartment just aft of the firewall. Either of those could be putting fuel on the belly.
 
Fuel leak

Pictures definitely look like a slight fuel leak to me. But the best post by far was AIRGUY saying “get naked and look for wet spots”. Maybe he wasn’t trying to use a play on words but I laughed out loud, good for morning coffee humor.

Seriously though, it does look seem to be fuel leaking
 
When I first built my RV-10, fuel leakage was a big concern for me. I wrapped up every fuel line connection in the cockpit with white paper napkin material and taped it in place. Whenever I had the opportunity opening up the tunnel, I would snip off the napkin material and inspect for the tell tale 100LL blue witness stain. I never found a leak and attribute that to careful flaring and torque on the B nut. I also used Del-Seals on all the flare fittings.
 
Back
Top