Category: Fuel Tank

Yesterday I brought the left fuel tank indoors and inflated it with 1 PSI of air. The workshop temperatures are just to volatile this time of year to get a solid reading. I left it overnight and checked it this morning. It now has 1.12 PSI of air in it! The increase is due to temperature and atmospheric pressure increases, but no leaks, yay! Finally, it has passed the test. Hoorah!

During the tank test I was browsing the Van’s website over the weekend (as you do!) and realised there is an 8 to 12 week lead time on the fuselage! Add on to that the sea freight shipping time and UK customs time and it’ll be nearly Easter before it arrives! Yikes, I better get it ordered or there’ll be nothing to do in the new year! First though, there are some choices that need to be made before the order is placed.

1. Tail or nose wheel.

This is a big and highly controversial issue. I’ve only ever flown nose wheels but the Van’s is a better aircraft as a tailwheel. I’ve literally spent months deliberating what to go for. On Sunday night I finally decided. It will be a tailwheel to begin with. If I really struggle, or simply don’t like it, I can fairly easily change it to a nose wheel if need be.

2. Tip up or slider

A much easier choice on the form was the canopy. I’d already decided a long time ago that I want a tip up canopy. Yes, the downside is it can get very warm in there without ventilation but the unobstructed view is what flying is all about for me.

3. Wheels & brakes

The wheels and brakes in the kit are ok but there is a lovely upgrade offered by Beringer with better, smoother, bearings, a hand brake and anti locking regulator. Very nice. So I will purchase these later on instead of using the Van’s stuff. For now I asked Van’s to remove the brake master cylinders from the kit. I did ask for right brake pedals though so I can share the flying with other pilots.

4. Air vents

The standard air vents provided by Van’s are plastic, fragile and leak profusely. I asked Van’s to remove those too and chose to go with Steinair’s AV1625B much nicer aluminium ball vents. Again I’ll get a pair of those later in the project.

5. Aileron trim

Although not required it is possible to add either an electric or manual aileron trim. Although I’ve flown several planes with aileron trim, I’ve never used it. I think it will be very rare that I need it but it was pennies so I decided to go with manual trim and have the option if I need it.

6. Fuel selector

The standard Van’s fuel selector is literally a lever that selects left or right fuel tank. It looks circa Victorian industrial era! Looks aside though there is an ‘off’ zone between the left and right setting where the fuel flow is interrupted during tank selection. I’ve chosen to leave that lever off the kit order and will purchase an Andair fuel selector instead as that has no off zone between left & right selection. Oh and it looks much nicer too!

7. Steps

I chose not to add a step to enter the plane. Being a tail wheel plane the step up onto the wing isn’t that high so I don’t think it’s worth it. Again, it’s easy to add in the future if I change my mind.

I think that’s it! A culmination of many, many months of deliberation, pontification and debate. But finally the order has been placed.

Ask other Van’s builders and owners and you’ll get a 1,000 reasons why my choices are right/wrong. At the end of the day it’s my plane and this, I think, is exactly how I want it.

I’m so excited I won’t be able to sleep between now and Easter!

It feels good to reach mile stones, not just because I’ve been working relentlessly on the fuel tanks week after week. It feels good because, frankly, it’s the most fun part of building a plane. Assembling parts of the plane is a small reward for all the hard work. Mind you, equally as rewarding is colouring in another section green on the progress meter.

I’ve coloured the right fuel tank green in this picture because, in today’s session, it passed last nights pressure test. So I applied JC5A jointing compound to all the mating faces where the tank would be touching the wing.

Once that was done I carefully placed the tank on the right wing and gently lined it up with the screw holes in the leading edge and spar.

I didn’t force it in place but instead seated all the bolts that hold it on the wing.

I systematically tightened the bolts only so far as they just touched the metal work. I didn’t want to tighten them all the way yet. Next I started at the leading edge forward screws and screwed the tank skin to leading edge and spar. Working from leading edge to inboard rib.

In both cases I used my electric drill set to screwdriver mode with the torque and speed set as low as possible. Once they were all in place I went over all the bolts and screws again with the torque ratchet set to 15″lbs for the AN509-8R8 screws and 25″lbs for the AN3 bolts.

Once the torques were double checked I popped the fuel cap in (so I don’t lose or break it) and took a step back to admire nearly a years work!

The wing is starting to look like it might actually fly one day!

Later this week I plan to spray the left tank with primer like I did the right tank so I looked for anything else I could spray with primer at the same time. I spotted the wing walk doublers which would be perfect for primer so I degreased and washed them. I hung them up to dry.

Once the left tank is ready I will spray it all together with these doublers.

That’s all for today.

Last night I put the left fuel tank on test again. It’s been sat for about 4 days since the ‘mega fix’ so the sealant should have cured enough for a test. Like previous times I inflated the tank to 1 PSI recorded the temperature and atmospheric pressure and left it overnight.

This morning I returned to the tank to find it had held pressure pretty well. It had only dropped from 1 PSI to 0.9 PSI but so had the temperature so it’s hard to tell if it’s a leak or just the affects temperature.

One possible place that it could be slowly leaking is the cork gasket between the access panel and tank so I decided to follow Van’s advice and seal that with tank sealant instead. I also called Nigel, my inspector, and talked through the tank leaking problems with him.

In particular, I explained the possibility of the ‘drinking straw’ affect causing air to travel along the skin to baffle seam. He agreed it was a possibility but, like me, said it was impossible to know for sure.

I saw a fantastic fix for this on another blog which involved injecting Class A (runny) sealant into the tank near the joint where the original leak was. I very much liked the theory and Nigel said there was no harm in trying it. So I did by first taking a blunt 14 gauge needle and bending it 45 degrees.

I drilled 1/8 hole in a test piece of aluminium to be sure the needle would fit which it did with good room to move it around. Next measured the length of the needle from bend to tip and marked the drill point on the tank based on that measurement. I applied positive pressure to the tank to help push any shavings outward and, with the shop vac close by the drill bit, drilled the 1/8 hole.

After deburing the hole and cleaning the area I angled the tank so that the joint was facing the ground. The theory is that the sealant would flow into place. I then mixed up a runny batch of tank sealant. I used the syringe to suck up the sealant, fitted the bent needle and inserted it into the tank. I squeezed sealant slowly out while twisting the needle left and right in an arc fashion.

I repeated that about 3 or 4 times to get a good amount of sealant in there. Once that was done I got an AD-41H closed blind rivet (as used previously on the tank baffle) and twirled it in sealant. I put the rivet in the hole and popped it with the rivet popper.

After that I gently relocated the tank at even more of an angle to encourage the runny Class A sealant to flow directly down into the corner.

All this left tank testing work had me doubting if I had properly tested the right tank so I put that on test again too just for fun. It’s ready to be fitted to the wing so I thought it best to test before I do that.

That’s enough work for today.

Well this left fuel tank is really getting on my nerves now! After yesterday’s failed pressure test today I decided to do all I can to fix the tank one last time. If this doesn’t work then the only option left is to cut a hole in the tank and fix it from the inside. Of course, I really want to avoid that level of drastic action.

I did have a thought about why this is happening. I think that, because I didn’t fix the original leak from the inside, the very first leak I plugged from the outside is causing the air to route in between the baffle, sealant and skin and find any rivets that aren’t completely sealed. I’ve effectively created a kind of drinking straw with one end being in the tank. The only way to plug that end of the straw is to cut a hole in the tank and put sealant on the inside.

Before I take that drastic action I first mixed up a large batch of sealant and covered every rivet head on the skin side. I’m now completely out of tank sealant and need to get some more ordered.

Once that was done I hooked up my manometer to my vacuum pump so I could accurately measure the vacuum in the tank and then created a -1 PSI vacuum in the tank by pumping the air out using the red handles vacuum pump.

I also screwed the dust cap on the schrader valve and sealed up the fuel filler cap using an off cut of a plastic carrier bag.

Then I (repeatedly) checked the rivet heads and every other possible place on the tank for leaks. Wherever there was doubt I put some more sealant. However small it seemed, I piled on the sealant.

In between watching the pressure and topping up sealant I also prepared the right wing walk doubler skin by scuffing and dimpling it ready for primer.

Then I went back to checking the left fuel tank, topping up sealant and checking pressures again. Once I’d done as much as I could on the tank I went back to preparing the wing walk doublers only this time it was the turn of the left. First job was to trim it to size using my giant shears.

Then I deburred the edges of the doubler on the scotchbrite wheel and deburred the rivet holes using the hand tool. Next I scuffed and dimpled it so it too is ready for primer.

I went back to check on the tank pressures one last time and made a note of the fuel tank pressure, air temperature and atmospheric pressure on the tank. Unfortunately the pressure seems to be still dropping (very slowly) and for the life of me I can’t see where else it could be coming from. Oh well, it looks like I’m definitely going to need to cut a hole in the tank later this week. I decided to leave the vacuum on the tank and leave it to cure overnight before making a final decision.

Just before lunch Richard and I decided to pressure test the left tank. We gently inflated the tank and checked. It seemed to hold pressure at the lower PSI. However, as we inflated the tank the pressure seemed to drop again as we inflated. Richard grabbed the soap water spray bottle and began checking for leaks. To my horror he found three more rivets leaking! Aaargh! This tank is so annoying! Thankfully though, it wasn’t from either of the previous fixes.

I quickly mixed up some sealant while Richard hooked up the vacuum pump and started removing air from the tank. I dried the tank and then applied sealant all over the three rivets. We left the vacuum in place again like I did on the previous two occasions.

I also used a razor blade to clean away the left over sealant from the previous fix. I started in the middle of the rivet and worked outwards. The idea being that I didn’t displace the sealant that had wicked in under the rivet head. I used a scotchbrite pad to tidy up the area.

After that Richard left and I made a start on priming the right fuel tank. First I covered the outside of the fuel tank with brown paper and masking tape to prevent the outside tank skin from getting primer overspray.

Once everything was nicely taped up I mixed some PR30B etch primer and sprayed the tank.

I left that to ‘flash off’ for an hour or so and then mixed up some PR143 and sprayed the final coat if primer.

The tank looks great primed!

That’s it, I need to let the primer cure for at least a few days and then I can fit the tank to the spar.

Just before heading off to work today I thought I’d pop up and check on the left fuel tank pressure and see if it was holding pressure. I turned on the manometer to find, to my dismay, that the pressure had dropped to 0.4 PSI. I was gutted. Is this tank jinxed or what?!

I inflated the tank back to 1 PSI and did the soap water test. I was fully expecting the previous fix to have not worked but it seemed to be holding well. So I used the soap water test to check around all the other rivets. Then I spotted it…

Grr, so frustrating! I quickly dried the tank and applied the vacuum again. I mixed up some Class B tank sealant and dabbed it all over the rivet head. I then used a lollipop stick to force the sealant in and around the rivet as much as I could. Once that was done I returned the vacuum to 1 PSI and left the tank for a few hours.

I popped back at lunch time and released the vacuum pressure so that the sealant that had wicked would set where it seeped in around the rivet. That’s it for today, now I need to leave the sealant to cure and test again. Fingers crossed.

Well the right tank has been on test since Thursday and I was keen to see if it had held pressure or not.

Using the digital manometer I checked the pressure and was delighted to see that, after 36 hours, the tank pressure had risen! This happens because the outside air pressure has risen causing an increase of pressure in the tank.

I wrote the results on the tank like I did all the others just for the sake of completeness.

That, I think, means the right tank has passed the test! Yay!

Next I tackled fixing the left tank leak. It is leaking along the top baffle to skin joint. After some considerable thought and discussion with several people I decided to go with the vacuum method. This involves connecting a vacuum pump (I found a cheap brake bleeder on Amazon) to the vent tube and sucking the air out of the tank until I was near 1 PSI of negative pressure.

Then I mixed up some Class A PR1440 sealant which is much more liquidy than Class B sealant and ran a bead along the entire join and rivet heads.

After a short while I could see that the vacuum was working and sucking sealant into the gaps where there were leaks.

I applied more sealant here and restored the vacuum to 1 PSI again. I repeated this step several times until it seemed to stop creating these gaps and holding negative pressure much longer.

Once that was done I put sealant on the seams and rivets of the right tank too just in case in case. Then I finally put sealant on the access plates of both tanks and screwed that in place for the final time. Now I need to leave the tanks for a few days for the sealant to cure.

Tonight I decided to leak test the right tank. It has been well over the Van’s recommended 48 hours to allow the sealant to cure properly.

I did this in much the same way as I did the left tank. Except that this time I connected a cheap Amazon digital manometer to the tank to measure pressure. The water method is OK and works fine but I’m a sucker for gadgets!

The hardest part of this process was adapting the clear 12mm hose attached to the tank to the 4mm fitting that was on the digital manometer. I tried all sorts of ways to adapt the fitting with what I had available. I finally settled on a shed load of PTFE tape around the fitting with the hose fitted by hand.

Once that was secure I used a normal bicycle pump to inflate the fuel tank through the drain valve using the Schrader Valve adapter that I purchased from Van’s.

I put the tank as close to 1 PSI as I dare go. It creaked a little as it inflated. Just like the left tank it deflated slightly with each inflation. My thoughts drifted between leak and air balancing inside the tank.

At about 1 PSI I disconnected bicycle pump and left the manometer to settle. It did at 0.963 PSI. I watched it for 5 minutes and it seemed to hold steady. After 10 minutes or so I noticed the pressure increasing! So I moved a thermometer near the test so I could see what was happening with temperature at the same time.

The rise in pressure seemed to correlate to the rise in temperature of the workshop. I also checked the regional air pressure and was stunned to see it at 1034 mb. That’s pretty high pressure for where we are.

I wrote the figures on the tank and decided to have a clear up of the ‘shop  while I waited for more news on the tank. While cleaning up the workshop I also, accidentally, started riveting the most outboard ribs of the two leading edges to the wing spars. This was fairly easily done using the hand squeezer but it took a ton of hand strength for some reason.

After about 45 minutes I checked on the tank again and was delighted to see that the air pressure inside the tank had risen to 0.984 PSI. That’s a fantastic start to the leak test. I wrote the figures on the tank for reference and called it a night.

Fingers crossed that holds pressure for a few days.

 

Started early this morning with two jobs on the agenda. Close the right tank like we did the left and then pressure test the left fuel tank. Again my Dad stopped by to help. Work wise was pretty much identical to the left tank. Clean the tank and baffle, check everything was ok and then lay tank sealant using the gun.

Then cleco and rivet the skin to baffle.

Then blind rivet top and bottom baffle to rib holes…

Then cleco and blind/solid rivet the z brackets.

And that’s the right tank done and left to stand for a couple of days while it cures.

By now it was almost lunch time so my Dad and I decided to leak test the left fuel tank before lunch. The plan was to fill a plastic tube with water to create a manometer, inflate the tank with air to no more than 1 PSI and leave for an hour or so and check it after food.

As we inflated I noticed that the water level rose and then sank slightly with each pump of air. We inflated to 1 PSI and disconnected the pump in case it was leaking at the pump. Sadly it still dropped. We reinflated and sprayed soapy water all over the tank looking for leaks. I was sure it would come from the inspection cover as that was still only corked on. Unfortunately it wasn’t that simple. We eventually found the leak…

Disappointingly it was right in the middle of the rear baffle. Probably the least accessible place possible. Well that put a kaibosh on the afternoon!

During lunch we researched our options of which there are a few. Van’s recommend loctite 290 or cutting a hole in the baffle to apply sealant from the inside then make a plate to close the hole. Some forums also recommend creating a vacuum and ‘wicking’ sealant into the hole from the outside. Lastly someone suggested removing a handful of rivets in the location, prise the skin and baffle apart slightly and pouring some thinned sealant in there before finally riveting back together. Each have their own pros and cons so I’m going to sleep on it for a day or two before I finally decide but I’ve ordered a vacuum hand pump and some loctite 290 from Amazon just in case! 😋