Fuel tank leak tests

This week the Proseal had set up enough on both tanks that it was leak test time.  I set up my manometer test rig so that I could put 1psi of pressure on the inside of the tank.  There is a poor picture of it below.  I tested the right fuel tank first and it failed.....grumble, grumble, grumble.  As I mentioned in a previous post the back baffle is the hardest because you have to blindly rely on the baffle "pushing" a bead of Proseal into a nice filet.  The plans say not to use more than 3/16" bead of Proseal (diameter) and to put the bead just below the holes.  Well that's what I did...I thought... but it seems I must have put the bead a little too far below the holes which means the Proseal never made contact with the baffle.  Now I have to cut a 5" hole in that bay of the tank, reach in, add more Proseal, and then rivet a cover plate over the hole.  Its not a hard task and it's amazing how many people have had to do this exact same repair.

The left fuel tank is still attached to the manometer and doing well.  Once I have determined that there are no large leaks (like the one in the right tank) I will add about 5 gallons of 100LL fuel to the tank and let it sit in various positions.  100LL fuel has a blue dye to it and because of its viscous nature it will find holes that water will not.  So, I will let it sit a day or so in each position and then look for blue dye seeping from rivet holes or other sealed locations.

I brought both tanks into the house for a few days where its much warmer so that the sealant would cure faster.

Here is that horrible picture of the testing manometer.  You can see the plastic tube that gets hooked up to the vent fitting.  That tube drapes down to the floor and then back up (taped to a broom handle to keep it relatively rigid).  I put about 45" worth of water into the tubing and then use the air stem attached to the drain flange (on top as the fuel tank is stilling bottom up) to put enough air into the tank that the water level rises.  27" of water difference between the two sides of the loop is equivalent to 1 psi of pressure in the tank.  Then I watch the water level to see if there are any leaks.  Initially the water level started to drop indicating a leak so I sprayed the tank down with soapy water.  No leaks were indicated so I checked the manometer again and the water level had stabilized.  Best guess is that the tank is still cooling down from being inside the house.  Several hours later the water level had remained stable.

Oh yes, in the mean time I finally got around to cleaning up the edges of the bottom wing skins and clecoing them in place for final drilling.

Fuselage is in the house!

Big week this post!  Amy took a little vacation with her mother so I decided to take the week off myself.  I have lots to do and this seemed like a good time to get some of it done.

Leading off the week was my trip to Oregon to pick up my fuselage kit.  Its here but still not inventoried since I don't really have a place to store all the loose parts.  The kit comes in small "packages" of parts that once unwrapped need to be stored.  I have 30 days to do the inventory and I hope thats enough.  After 30 days I guess its on my own dime if a part is missing.

I also started the annual inspection on the RV-9 this week.  I changed out my spark plugs, did the compression tests, and pretty much finished the engine "group".  I also replaced my brake pads on both wheels while I was doing the undercarriage.  There was still a lot of pad left but I had ordered the parts so I figured it was a good time to do it.  I also finished most of the cabin group and that included finishing the heated seat wiring as well as machining a shim that took up a little of the design slack in the aileron linkage.  Overall things are looking good but I still need to finish the tunnel as well as the wings.

Finally, I sealed up the left fuel tank.  The rear baffle is in and now I have to let it sit for a week or two so the Proseal can cure.  Then its leak test time.

This is the storage location for the cabin cover.  It took far too much time to rig up a safe way to hoist that up and then secure it.

Left fuel tank with vent line installed. 

Left fuel tank with rear baffle in place.  Still no rivets but there is a cleco in every hole!

Same as the picture above but from a side view.

Left fuel tank - almost done

This week I almost finished sealing the left fuel tank.  I kinda ran out of steam (energy) today before I got the back baffle installed.  I got all the ribs, vent lines, and related details completed but I was tired of breathing Proseal and MEK through a respirator so I called it a day.

Stiffeners riveted and sealed on the left fuel tank.

Here is the tank almost ready for the back baffle to be dropped in.  The fuel level sender still needs to be installed and a few shop heads still need to be encapsulated with sealant before the final baffle install.

Left fuel tank - Sealing process described in detail with photo's

Tonight I took a few extra pictures of the sealing process I use (not easy to do with very sticky rubber gloves on).  Van's recommends that you buy two orders of sealant (about a quart total) to complete the RV-10 fuel tanks.  So far I have completed the right fuel tank with the left tank well on its way and I've used maybe 1/2 of the first batch.  So, I assume they expect that you will use far more than I think is necessary. 

Below are some step by step pictures and description of how I am sealing the tanks.  Granted this is only one part (the fuel cap flange) but the steps apply to all mating surfaces.  The idea is to get two barriers of sealant so that if one fails the second will prevent fuel leaks.  Some areas this is not really possible but in most it is.

End ribs with fuel penetrations installed/sealed

First step is to get the tools out.  This is a 10cc syringe that I use as a mini caulking gun.  Oh, and lots of rubber gloves...

Syringe loaded up with enough Sealant for tonight's sealing steps.  Tonight I installed the fuel cap flange and the drain flange.

There are really only a couple of places that fuel can get out on this fuel cap flange.   Past the skin/opening interface and past the rivets.  In this picture you can see that I put a bead of sealant around both the outer and the inner rings to act as double barriers for the first situation.

Its not really visible in this picture but this batch of sealant prevents the fuel from leaking past the rivet holes.  This is a bead of sealant around each dimple.  The fuel flange will sit on top of this area.

Each rivet needs to be sealed as well so in this picture I am dabbing sealant into each dimple on the outside of the skin using a q-tip twirled in sealant.  This is done just before I put the rivets in place.

Rivets pushed into place and the area around the rivets is gently cleaned up with MEK so that the tape used to hold the rivets in place (and protect the skin while back riveting) sits tight against the rivets and skin.

Then the fuel flange laid on top of the skin with the rivets poking through the holes.  Notice that there is already a bead of sealant showing up around the outer edge.  Thats barrier #1.  The rivet sealant is barrier #2.  Each opening actually has two barriers of sealant on them so that if one fails the second should prevent leaks.

And finally this is the "cap" of sealant that I place on top of the shop head of each rivet after it has been set.  This acts as the second barrier for the rivet holes.

This is the drain flange inside the fuel tank with the sealant cap applied.

And this is the outside of the same drain flange.  If you look close you will see sealant around each rivet as well as the edge of the flange.  This is after I had used some MEK to clean up the excess sealant that squeezed out.

Right tank curing, Left tank on the bench

I managed to get the right tank to the point where I need to let the sealant cure for a week or so before a leak check.  Now its on to the left tank.  Much of the prep work was already done (cleaning up edges, riveting nut-plates on the Z brackets, making the new anti-rotation brackets) so this should go a little faster than the right tank.  As of today I managed to assemble, final drill, trim, countersink, disassemble, debur, and dimple all the parts.  Next up is the reassembly with sealant.  I hope to get it to the point of a leak test in the next week because the RV-9A annual inspection is due in March and I plan to start that the first full week of March. 

Hopefully it will warm up a bit before then because the hangar is darn cold right now with an outside temp in the 20's.

Took this snapshot from one of the security cameras in my hangar this morning.  Notice the temperature INSIDE the hangar is 30.5 degrees Fahrenheit.  Brrrr.  I'm not going to be doing the annual in those temps that's for sure.

Riveting complete, now it waits for sealant curing.  I left my fuel tank caps at the hangar so I used some tape to cover the fuel inlet while it waits.

The other end of the tank with rubber gloves covering the fuel outlet and the return line fittings.  Not really sure why I didn't just use a finger from the glove instead of the whole glove....

Right fuel tank, almost done

I spent a lot of time on the right fuel tank this past week.  In fact since this was a nice 3 day weekend I spent the majority of it in the garage.  I got the right fuel tank sealed up and almost rivet complete before my back decided it had had enough for the day.  A little more riveting on the back baffle and then its time to let the Proseal cure enough for a leak test.  :-)

Ribs cleco'd in place with sealant.  Took a whole box of cleco's but the skin is nice and tight.

Inside view of the cleco'd tank.

And this is about 6 hours later.  All of the ribs are riveted with the exception of the farthest forward 3 rivets on the top side.  I still have to install the tank attach bracket before I can fasten the aft half of the inboard rib.

Top of the tank in the same state as the picture above.  I could not reach those last 3 cleco's on each rib so I took the fuel tank to the airport and had Harry help me finish those rivets.

Top J-Stiffener riveted in place.

Inside view of J-stiffener riveted in place.  Still have not finished encapsulating the shop heads with sealant in this picture.

Aft rib half riveted in place.  You will notice the fuel return fitting and the vent fittings installed in this picture.

Outboard rib with the extended range fuel transfer fitting installed....with LOTS of Proseal...I kinda went overboard on this one.

I took this picture so you could see the vent line end.  I curved it a bit around the fuel filler opening and then bent it up close to the skin.  This should allow less fuel to burp overboard when the fuel expands due to heat.

The vent line fittings are encased in Proseal (after torquing them down) to make sure there are no leaks that might limit how much fuel I can put into the tank.

Outside of outboard rib.  Not much Proseal here because there is a nice filet of sealant on the inside (see pictures above).

This is a vent line snap bushing penetration.  I put a little left over Proseal on the vent line and the fitting to keep them from vibrating and possibly cutting through the bushings.  Not likely but hey, I had some extra Proseal.

A nice shot looking into one of the fuel bays.

Fuel level sensor and float installed.  This is the empty position with the float on the bottom of the fuel tank.

And this would be the full position.

And this is how things stand as of this evening.  The Z brackets are riveted on and all thats left are the side rivets that should be pretty easy to install with the squeezer.  No Proseal required on these so I guess I am pretty much done with Proseal for this tank.

I poked my phone camera into the fuel filler opening to take a couple of pictures of the back baffle seal.  It looks pretty good in every location I can see.  Only a leak test will tell for sure though.  This picture is looking outboard at the end rib.

And this picture is looking inboard at the 2nd rib in.  The top left "line" is the baffle seal and you can see a bead of Proseal along the entire length which is exactly what I was hoping to see. 

Proseal Take 2

Still working on the right fuel tank.  I did get to fly this week though.  Harry, Jeff, Paul, Mark and I met at Jefco for a little breakfast and then Harry, Jeff, Mark and I flew on up to Friday Harbor to meet up with some Fall City folks.  (Ben, Kathy, Jeff, Salima ,Larry, Mary, Dave).  We walked down to the water front to have some lunch.  It was a very nice day for flying and it showed as the sky was full!

Parked at Jefco for breakfast.

Harry and Jeff off my left wing on the flight back home.

Fuel cap base with sealer and cleco's

Back side of the fuel flange.  Nice cap of Proseal over each rivet shop head.

I got a little carried away back riveting the fuel cap...I forgot to add the tape to protect the skin so it scuffed up a bit.  No biggie since the skin has to be scuffed for paint anyway.

Finished up the stiffeners on both sides of the tank.

Stiffeners back side with nice cap of Proseal over rivet shop heads.

Stiffeners after I had back riveted them but before removing the tape and cleaning the heads a bit.

Stiffener rivets cleaned up a bit shows the proseal around the head of the rivet.

Fuel drain port sealed and cleco'd to the outside bottom skin.

Fuel tank drain flange on the outside of the fuel tank.  Riveted but not yet cleaned up completely.