yet more fuel tank stuff to do

Long time no update, but work still getting done.  I apologize in advance if this blog entry jumps around a bit.

Trimmed the top side inboard trailing edge to match the other wing:

Then trimmed the outboard tops side trailing edge as well, in prep for fitting the wingtip:

The fuselage longerons that I ordered from Zenith back in December finally came back into stock.  I was down to visit Dad and we made a day of it heading to the Zenair factory in Midland to pick them up.  Four 13 feet long custom aluminum extrusions which will form the corners of my fuselage.

 
With the sealant cured for a week, it was time to test the fuel tank for leaks.  Nylon threaded inserts and teflon tape tightened into the drain and outlet fittings works well for testing.  They are soft enough they won't damage the threads on the tank:

Propped the tank up on some sawhorses and elevated the rear to simulate the "in wing" position.

Threaded in the fuel filler neck to act as a funnel and wrapped it in terrycloth to capture any spills.  I didn't want any stray water to make me question if the seams were leaking or not.

Based on the dimensions, the tank should hold very close to 15 gallons.  In order to measure accurately, I used a 500mm graduated flask.  Unfortunately although it is accurate, it took a very long time to pour the water from the Jerrycan to the flask and into the tank - 15 USG = 56.78 litres.  Ouch, this is going to take a while!

I hooked up my retro Radio Shack analog multi-meter to capture the changes in resistance of the fuel sensor as I filled the tank in order to map out what various fill levels mean on the sensor. 

​ That wasn't easy to read accurately, so I switched to a digital unit - much easier to read.

Filled the tank right to the maximum in order to test all seams.  Disappointingly I found a weeping leak on the top outboard seam about 2/3 of the way to the rear of the tank.  Argh, this was going so well.

Water pooled on the lower seam and was also evident on the newsprint I laid on the floor below.  Better to know now than later with fuel I guess, but this further delays getting this wing complete.

Drained the tank to fix the leak.  In order to make sure everything was completely dry before adding more sealant, I used a small pancake computer fan over the sensor hole and left it run overnight.  That worked extremely well. 

Flipped the wing over and finished trimming the inboard lower trailing edge to match the other wing.  Had to be careful here as the fuel and pitot/static lines already run inside the trailing edge.

Drilled the rivet holes where the inboard and outboard trailing edges meet.

Measured the other wing and matched the template for the outboard lower wing skin on this wing.  lots of notes to myself on the template!

Trimmed the outboard lower trailing edge then installed the wing tip support angles on the rear wing channel and on the wing tip spar extension:

Test fit the wing tip and made some small adjustments for better fit.

Main wing strut pick-up riveted

Laid out the plan location for the fuel access cover on the underside of the wing on the inboard lower wing skin.  The original plans require this access near the main spar where the side mounted fuel sensors are installed and serviced from (oval on the left).

I'm not using side mounted sensors, so I decided to move the access cover closer to where my outlets are, which are further back due to the expanded tank size.  This gives me good future access to the fuel tank outlet should I need to ever change out the finger screen.

Original location in red on the left, new location in blue on the right (fuel drain hole above that):

I've also been making up some of the smaller parts needed for the fuselage as I find the time waiting for sealant to cure, etc.  I had a perfect piece of 025 to use for the two longeron gussets.  Most times when there are two, you can mirror them and save material. This is a good example of that:

One thing I observed when the tank was full of water - how much the tank flexes as water (fuel) moves side to side and back and forth.  Over time, that flexing will likely lead to stresses on the seams and fittings that will leak.  I decided to add a centre inside rib made of 032 for stiffness.  It means some more rivets in the tank skin, but with tight fit rivets and sealant they won't be an issue.  I added some passage holes in the new centre rib to slow flow of fuel from one side of the tank to the other.  The rib will not only stiffen the tank to prevent flexing, but also slow the sloshing of fuel - an internal baffle.

To further bolster the seal I buried a tab of 025 in the sealant as I riveted the rib in place, then covered it all in sealant again (the rear section done, front to be done in the picture):

I've decided to go a different route with the sealing of the fuel sensor plate.  As much as I thought the well-nuts and buna gasket would be enough to properly seal the plate to the tank, the well-nuts can not provide enough tension in this application to hold the plate against the gasket.  Disappointing as this would have been excellent it it had worked.  Back to the thinking board.

​Switching tracks again, drilled out the rear rivet holes on the wing tip:

Unfortunately, the pilot holes on the forward portion of the wing tip did not line up well with the forward attach angle.  Had to drill this one out and replace with a wider one which worked perfectly.

Back on the fuel access cover, I confirmed the new location wasn't interfering with anything where I planned to put it. 

To secure the panel, I picked up some Tinnerman clips from Aircraft Spruce.  These are very handy!

I needed to make sure the inside edge of the fuel access hole left enough space for the clip to be covered by the edge of the cover plate.  As shown below, the original hole oval left no room at the outer edge:

I adjusted the inner oval, making it 5mm narrower than the original - this left enough space to cover the clips and be a viable access hole.  I laid them all out, focusing on the front and rear edges and corners:

Clecoed the template on top of the cover plate and drilled the holes for the clips out to A3:

​Used the cover plate as a template to match drill the hole locations for the clips:

Enlarged the holes in the lower skin at the access hole location to the size needed for the clips and the #8 stainless screws that will secure the cover plate.  This picture is deceiving as it shows the original access hole size (the inner oval):

 
Hole saw to cut the access hole, centered on the pilot holes from the template:

Forward end of the access hole the same way.  The mark connection between the holes via tangential lines:

I find a line of masking tape is a good guide for cutting straight lines with the Dremel cutting wheel:

Access hole cut and ready for deburring:

Cleaned, scuffed and primed:

Clips in place and underside of the access cover primed and ready for attachment:

Once the prime was set, I used the edge roller to slightly curve the access cover plate edge downwards.  This makes the cover sit tight against the skin when screwed down:

Marked the forward end on the underside of the cover plate.  You can see the curled edges well in this picture.  I also filled the pilot holes with A4 rivets to clean those up.

Really pleased how this went, looks really good!

For the fuel tank sender plate, I've decided I to use rivnuts to secure it and ProSeal sealant as the gasket.  I kinda overthought the whole access to the tank thing, so this will be more permanent.

Rivnuts are hole inserts that are pulled just like a rivet but allow a machine screw to be used in the hole.  With the holes I drilled for the well-nuts too big to fill with traditional rivets, these rivnuts will work fine and really will secure the sensor plate properly to the tank skin.  Ron already has the tool to pull these, so I picked some up at Princess Auto to use.

I had to drill out the mounting holes a bit more to accommodate the 1/4 inch rivnuts, but the edge distance to where the sensor mounts in the tank is still acceptable.

Mixed up some ProSeal and applied a thin bead around the mounting holes and perimeter of where the sensor mounting plate will be using a small syringe:

Didn't get any pictures as I went as the ProSeal is messy and I didn't need it getting all over my cell phone.  Here is the final result with all the holes squeezed tight with rivnuts.  I'll have to get some 1/4-20 machine screws to fill in the centres, but very happy this is going to work.

Had some ProSeal left over from this batch, so sealed around the rivnuts for good measure and smoothed out the edges of the sensor plate.  This is messy stuff, but no question about leaks!

Maggy the shop dog decided she wanted a selfie as we were wrapping up for the day (got to love the 0's safety glasses)!

Lots of stuff done, more to do as always.  Wing is almost ready for flip back upright, then the wing tank will be fitted, along with the rest of the wing tip.

Thanks for reading, stay tuned for more!