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!
Busy couple of weeks at the shop since my last blog update.
After finding the fuel sensor assembly gasket dimensions weren't scaled correctly I redid the CAD drawings and cut new ones that have wider surface areas while maintaining the center hole diameter and the outside dimension of the sensor plate:
Original test gasket laid on top of new gasket. This should improve hole edge tolerances. It will shrink the access hole a bit in the wing tank skin, but I believe it is worth the trade off:
With the fuel sender mounting holes already drilled to full size for the well nuts, I needed to come up with a way to secure the new gasket and drill mounting holes at full size instead of upsizing them as I went. I took some scrap plywood big enough to fully sandwich a sensor gasket and drilled an index hole in the plywood at opposite corners of the original gasket:
Opened the sandwich, put the new gasket in place using the index holes as a guide, then screwed the sandwhich down tight to hold the new gasket for drilling:
Placed the fuel sensor assembly on top and indexed it over the gasket using the same index holes:
Used the sensor plate as a guide, pilot drilled then right sized the holes in the gasket sandwich:
Much cleaner result and the hole edge distances are now improved.
Tsped the gasket in place to confirm the holes do indeed match up on the skins and traced out the new access hole dimensions on the tank skin:
Removed any non-pertinent lines after corning drilling the new access cut-out:
Dremel tool with cut-off wheel to final shape the access hole, then filed the corners and final deburred the edges:
Took a quick peek at the truss head screws inside the tank that hold the drain bung and gasket. This is where the fuel will drain from the tank for pre-flight testing and any future required fuel tank maintenance if necessary. Very pleased at how the gasket I made fits, but I'll add some sealant on the screw heads as well:
With all the cutting and fitting of access holes, filler necks and other outlets complete, I can finally move onto the dreaded sealing of the tank seams. This process has been keeping me awake at night figuring out order of operations and how to do many things at once.
First, I fully cleaned the tank inside surfaces to remove any contaminants or markings and used Scotchbrite pads to scuff the joining surfaces on all seams inside and out where sealant will be applied. This included a full wipe down with lacquer thinner to remove any other oils or residue that could impede the correct adhesion of the sealant or curing of the sealant once applied.
Next I hand placed all the A3 squeeze rivets in the bottom seam of the tank on the outboard side and used tape to hold them in place so I could flip the tank upright.
Tank on the bench with rivets placed in the lower seam, the back edge and front side of the tank.
Next up was preparing the ProSeal sealant. It gets mixed 10 parts sealant (big can) to 1 part activator (small jar) - this is done by weight not volume so I used a gram electronic scale to measure out exact ratio of each and once in the same mixing container, stirred them together to start the sealing process. Working time of this sealant is about 2 hours after mixing depending on ambient temperature with early cure time of 7 hours once applied. Full cure time is suggested as 1 week before applying any pressure or liquids to the tank.
I was so wrapped up in applying the sealant to the outboard tank side lower seam I didn't take any pictures of the process. Needless to say, it's messy and stinky stuff to work with and anyone using it can tell stories of it getting on everything so I wore old clothes I didn't mind throwing out if needed.
A peek inside the tank after it sat overnight shows that the sealant I applied in-between the joints did squueze out exactly as I planned into the inside seam of the tank - perfect!
Same with the sealant between the front upper edge and the folded angle I had to add:
I used the remainder of the sealant I had mixed up to cover the rivet tails on the tank fill neck flange and it cured up very nicely. It doesn't look pretty, but it's inside the tank where no one sees it and is fuel tight which is the real goal.
With the outboard tank side started, I started on sealing the inboard tank side which included copious amounts of sealant on the fuel line outlet bung. I figured to to do it first where I had 360 degree access to it before the tank side gets placed in the tank skin:
Here is a progress shot for the inboard tank side. Same as the outboard side, hand placed rivets, secure them with tape on the outside of the tank. To apply the sealant easily, I used some large bore disposable syringes filled with sealant - kind of like a miniture caulking gun and ran a bead of sealant on the inner side of the rivets as I want the majority of the sealant to move inwards as I squeeze the rivets:
As you can see in this picture, sealant squeezes out between the seams on the outside as well as coming up through the rivet holes. A good complete seal on the seam and the rivets. More sealant applied arounf the fuel outlet bung as well.
Extra sealant doesn't go to waste (it's way too expensive to throw away!) so I added some around the fuel drain bung screws as well. Anything to improve the fuel tightness of the tank. You can also see how the sealant squeezed properly into the inner seams of the tank:
While I let the inboard lower seams cure, I placed the right tank into the left wing and finished fitting the fuel sensor assembly and gasket for the tank in anticipation of bringing the other wing out of storage.
The new version of the gasket fits perfectly and I could drill the sensor plate and gasket out to full size mounting holes right on the tank this time instead of the plywood sandwich shown earlier:
I took the Dremel tool and a grinding wheel to both fuel sensor assemblies and carefully cleaned up the sharp weld edges where the fuel sensor wiring may come into contact to prevent chafing with vibration. No issues any more.
Next I repeated the process for the top seams of the tank. As there is little room to waggle the rib into place onto the rivets, this time I laid down the bead of sealant on the rib, folded down the top tank skin then hand placed the rivets into the holes. Messy, but effective as I needed to do both inboard and outboard sides and the front edge as the top skin laid down. This sealant gets on everything!
Once mixed it can't be stored, so to use up each batch I made (40 grams at a time) I started sealing the outside of the tank edges - rivet heads and rivet tails:
I purposely went sealant heavy on the inside corners to ensure the corner plates I added formed a fully tight corner - again, none of this gets seen inside the wing so it doesn't need to be pretty.
First section of the top seam, working forward from the back corner of the tank. The sealant clearly is doing it's job at the rivet holes.
Forward edges done, sealant on top of squeezed rivets:
Extra sealant on the front corners
All edges sealed and left to cure. An inspection mirror inserted inside the access hole shows excellent sealant fillets on all the inside seams.
Picked up a couple of nylon NPT plugs for each of the outlet bungs. These will tightened in place when I pressure/leak the tank. Nylon seals well but won't damage the aluminum threads of the bungs. Permanent thread sealant will be added once the final fittings are in place.
Got the final truss head screws I wanted from Fastenal and used them to seal the fuel sender plate with the gasket. All part of sealing the tank for testing.
Fuel sensor in place - the relief grinding I did makes a huge difference in helping the sensor wire to lay flat across the top of the tank and to prevent chafing.
Fuel tank test fit in the wing, first time completely riveted and sealed - nothing changed, tank shape still the same and sitting in proper position for fittings and filler neck - YES!
Next step is to add buffer strips to the sides of the tank to prevent tank movement in the wing especially when close to empty or less than full of fuel. I have some high density foam that I secured to the tank sides with high strength contact cement. Once dried I can literally lift the tank by the foam blocks.
Next close up the bungs with the nylon plugs and test the tank for leaks. If it passes the leak test, back into the wing it goes where I'll add the top cork strips and connect the fuel lines.
More to come :)
Good few days at the shop since my last update.
Now that I know the final position of the fuel tank in the wing bay, I can finalize the "packing" around the tank that prevents it from moving around left and right inside the wing.
The space between the tank wall and the rib is a bit larger than a couple strips of cork will fill.
A grabbed a small block of wood I had lying on the bench and discovered it makes a good model for the size of high density foam block I plan to use.
Also with the tank in final position, I can confirm the hole drilled in the lower wing skin for the fuel drain is centred on the fuel drain bung. To see this closely without flipping the wing over I used a remote mirror and zoomed in with my cellphone camera:
The image is a bit blurry, but the bung is perfectly centred on the pilot hole in the lower skin.
The drain fitting is a 1/2" nut, so I want the hole in the skin large enough to allow a 1/2" socket to turn the drain fitting into the bung when installed, or easily pulled in the future for maintenance if required.
Drilled the drain hole out to just larger that the diameter of the 1/2" socket. It clearly fits cleanly in the hole from below.
The drain plug put in the drain bung on the tank. This is just finger tight, eventually it will have thread sealant and tightened accordingly.
Once fully threaded into the bung, the drain plug will sit just proud of the lower wing skin providing easy access for testing the fuel for contaminants during pre-flight checks.
Like on the right wing, I needed to trim some of the trailing edge away from the wing tank bay. Laid out the trimming line using painters tape and drilled A5 holes at the corners for strain relief.
Used a scrap board of thin plywood to protect the rear channel and ribs underneath the trailing edge while drilling the corner reliefs and cutting along the painters tape edge with a Dremmel cut-off wheel. Much easier that using metal snips in these tight confines.
Finished drilling out the trailing edge to rear channel holes.
Lifted the upper wing skin, deburred all the holes and primed the trailing edge where it tucks under the upper wing skin.
Brought the threaded fuel neck, threaded tank flange, drain bung and fuel sensor mounting plate home so I could measure them and create 2D CAD drawings of the gaskets I wanted to make. To save some material I nested the fuel drain bung gasket inside the fuel sensor plate gasket (the inner rectangle gets cut out as extra anyhow).
Exported the 2D CAD file to a SVG (scaled vector graphics) file that can be used by the CriCut machine to make perfectly sized gaskets.
Did a cut test of the sizes on card stock and although the cutter depth should have been a bit deeper (to make cleaner cuts), then general fit is perfect for each fitting.
Found a supplier able to provide square foot sheets of Buna-N rubber at 1/16" thickness. Bought 2 sheets for less than $13 total including tax.
Buna-N or Nitrile rubber is a durable and fuel/oil/chemical resistant material commonly used in the petrochemical industry for making gaskets and o-rings. This material is perfect for my application.
The reason I chose a 12" x 12" sheet is that it is the maximum width the standard strong grip adhesive CriCut cutting mat will accept.
Concerned that the edges of the Buna sheet might catch on the positioning rollers of the CriCut machine, Brenda recommended I tape the edges down with painters tape as a precaution.
A Google search revealed that CriCut recommends a "Deep Point" blade for rubber sheets - the standard cutting blade is designed for lighter weight materials Brenda picked up a Deep Point blade at the craft store.
The adhesive mat with Buna sheet loaded into the CriCut machine without issue - a good first sign this was going to work.
For those who haven't seen a CriCut machine in action, here's a video of it in action cutting my gaskets.
Once complete, the mat returns to the loaded ready position. (I didn't let the video run to the end). If you look closely, you can see where the cutting head did it's magic.
Brenda helped me take the finished gaskets off the mat - very pleased how they came out!
Perfect dimensional gaskets for each assembly! Very VERY cool!
Once back in the shop, I proceeded to drill the gaskets out for mounting. I wasn't sure the CriCut could carve holes with this small a diameter, but it probably could. I wanted to match them however with the threaded holes already on the drain bung.
The easiest was to match up the holes was to clamp the drain bung onto a spare board with the gasket blank sandwiched in between, then drill out the gasket mounting holes just slightly smaller than the machine screws - this will ensure the gasket stays tight on the screws.
For the fuel sensor plate gasket, I built a temporary "box" of 2 x 2 blocks to support the gasket blank while I drilled the location of the gasket mounting holes..
Started with A3 holes which match the sensor plate and the fuel tank.
Gasket laid in position on the fuel tank over the sensor hole.
Fuel sensor plate clecoed back in place on the tank with he gasket sandwiched between.
Mounting holes were then drilled out to 5/16" diameter, the size required for the well-nuts that will be used to secure and seal the sensor plate.
Each mounting hole upsized to 5/16" then fastened with a well-nut as I went.
Complete fit up of fuel sensor plate (fuel sensor to be re-mounted in plate).
Pulled the assembly apart for deburring and noticed that my original inner line doesn't match the inside edge of the gasket?
Also noticed that some of the mounting holes in the gasket were too close to the edge of the gasket to effect a good seal. As a result one of the holes torn a bit too. Looks like I made a measurement error creating the 2D drawings in CAD. Thankfully I only cut one sensor plate gasket like this. I'll update the CAD drawing to widen the gasket and cut a new one for this tank and a proper one for the other tank.
Setting that aside, I drilled out the mounting holes in the threaded tank insert next, using a scrap of 016 aluminum as the backing plate (standing in for the fuel tank).
Threaded tank fitting now riveted in final position with the gasket. Sealant will be added to the rivet tails that secure it.
Outside front corner of the wing tank. Sealant will be added to the rivet heads on this side as well and won't be seen once the tank is inside the wing.
Test fit of threaded fuel filler neck and cap confirms inside flange still fits correctly. Thread sealant will be added here too. That should complete a fully sealed fuel fill assembly on the tank.
Fuel bung mounted on underside of tank with gasket. More sealant here on the machine screw tails and around the perimeter.
Next up, re-do of fuel sender plate gasket (CAD drawing already corrected, cutting to be completed still) and final seal up of tank edges. Once that sealant cures, the tank will be final mounted in the wing bay and cork strips added on top to support the upper wing skin.
Very happy with the gaskets and how they turned out and I'll probably use the same method to cut some cork supports as well.
Stay tuned for more, thanks for following along.
A few weeks between blog entries but lots of progress on the fuel tanks.
I've been pondering the cut outs in the tank for the fuel senders and the fuel filler necks. Unfortunately neither of them can be cut in the upper tank skins using a standard hole saw (or at least one we have in the shop) so I needed to use the fly-cutter.
I adjusted the centre of the fuel sensor hole a little more forward on both tanks so the fuel sensor gets as close as possible to the front wall of the tank which is also the deepest part of the tank. This also gets the mounting plate to a location on the upper skin that is as flat as possible, important for sealing the mount to the tank.
I wanted to come up with a way of sealing the sensor plate to the tank that will not only be fuel tight but allow me to open the tank for inspection if needed in the future or if I ever need to service/replace the fuel sensor itself - not likely, but nice all the same having access to get a hand or tool inside.
I'll be securing the fuel sensor assembly to the tank using "well-nuts". These neoprene fasteners are used in the automotive industry to join parts together and seal holes. They are a neoprene tube with a shoulder washer and captive nut inside:
To test the plan I grabbed a couple of scraps of aluminum to represent the tank skin and the fuel sensor plate. The well-nut gets inserted in the hole up to the washer head (also helpful as it can't fall inside the tank). A 8/32 machine screw is threaded into the well nut and as it tightens down to compresses the washer head to seal the top of the tube.
The magic on the backside is that as you tighten the machine screw, the captive nut inside tightens up against the underside of the hole, compressing the neoprene tube and forming a seal on the underside of the hole. Good and fuel tight, but I'll add some thread sealer on the machine screw to be sure and my machine screws will have wider heads and be shorter in length.
Laid out the fastener lines on the underside of the fuel sensor plate. The well-nuts require a larger hole for insertion so I needed to ensure edge clearance would work. The fastener line will approach but not clear the sensor mount tube, but I can get a well-nuts close enough to each other to ensure a tight seal around the perimeter.
Usually the fly-cutter is used on a drill press. The tank is too bulky to mount safely on the drill press bed. I checked online and see several people cutting the sensor holes in the sides of their tanks using a hand drill - the key is to go real slow and keep the cutting head well lubricated with cutting oil. Mine worked out fabulously with the hand drill. Speed control is important here as a tear in the skin would be disastrous.
Back drilled pilot holes in the mounting plate at the corners first then placed it in the newly created hole. Once squared in position, used the pilot holes as a guide to match drill the tank:
Cleaned away most of the Sharpie lines and retraced the outer edge of the mounting plate. Then extended landmark lines from the corner pilot holes.
Mounted the sensor plate onto the tank, transferred the landmark lines onto the front of the plate and marked out the fastener locations:
Drill the balance of the fastener holes up to A3 using clecos to secure it as I went.
Very happy how this turned out. Waiting until I get an order of well-nuts in stock before I drill these out to the larger size. Once those are done, I'll cut out the access hole in the skin that the sensor plate will cover.
Now that the final size and shape of the fuel tank is established, it's time to make the fuel bay in the wing ready to accept and secure the tank from moving around. First up, two U shapped channels are added to the spar as front tank supports.
Thin cork strips secured to the support channels with contact cement to prevent vibration damage on the front wall of the fuel tank:
Rear support angle gets the same. These front and back supports have some spring to them holding the tank securely from moving back to front in the wing bay.
With the tank now in final position in the wing bay, I was able to peel back the top skin, reach inside and mark the location of the tank drain hole in the lower skin of the fuel bay (tank pulled up and forward to take this picture)
Here is the initial hole. Once I secure the tank completely, I'll flip the wing over and final size the hole to match the drain plug. Also needed to open the passthrough hole a bit to give more clearance for the fuel port fittings.
Flipped the wing over on it's back again so I could add the trailing edge to the wing and the last of the flapperon support arms.
The reason to wait on the last flap support arms is the complex joint where the lower wing skin, trailing edges and rear strut support meet. The inboard trailing edge needs to fit over the rear strut attachment first, then the outboard trailing edge, then the lower wing skins on top. Order of operations stuff keeps me up at night sometimes! With this done I can final rivet the lower wing skins and flap support areas that are already in place. The trailing edges are left clecoed together for now until final adjustments of the trailing edge position.
Wing back upright again with top wing skin lifted up to add the final flap arm in place and adjust the trailing edge.
Last flap arm placed in position for riveting
Trailing edge adjusted for straight and correct up/down relative to the flap arms, then clecoed to the rear channel. Fuel bay skin also put in place to match up with the trailing edge.
Cork strips added on the floor of the wing tank bay. The fuel tank will rest on these after the contact cement that holds them in place dres.
Some light weight to prevent the cork strips from curling up before they set.
The inboard strip will be fastened later once the final drain hole size is drilled out. I'll add a collar of cork around the final hole to help support the lower skin here.
One of the challenges of an un-welded tank is fitting it in the wing bay without clecos. In order to fit the upper wing bay skin over the tank, I can't have clecos sticking up, so I used a large amount of tape to secure the tank edges and fuel sensor assembly together temporarily so I can finalize tank position before sealing the tank up.
Like the bottom of the wing bay the space between the tank and upper skin will be filled and supported by cork strips, these ones will be cemented to the top of the tank once it is sealed.
Next was layout of the flush mount fuel filler neck and threaded mount flange - an order of operations that has killed off a lot of brain clock cycles in the past month. The key here is to align them with the tank in position in the fuel bay. The finished edge of the fuel neck needs to be far enough away from the edges of the wing bay skin, so I start the layout position there, keeping consideration of where the internal edge of the fuel tank are and how the threaded inner flange will mount in the tank.
My original layout called for a centering hole 60mm aft of the spar and 80mm inboard from the adjacent wing rib..
Once I had the upper wing skin in place, I realized that doing that would put the threaded tank flange too close to the side wall of the fuel tank to fasten and seal it correctly, so I moved the whole assembly inboard by another 10mm and drew another centering mark.
With the confirmed centre of the fuel filler assembly now confirmed, I drilled a A4 pilot hole in the upper wing skin through the gap between and on through the fuel tank itself. This centering hole now aligns both the outer fuel neck and the inner threaded flange.
The tank was removed from the wing again. Using the fly-cutter and hand drill, a 60mm hole was created in the tank based on the pilot hole drilled in from above the wing skin in the previous step.
A quick check confirms the threaded male side of the filler neck nicely fits the tank
The upper wing skin is clamped onto the bench and the fly-cuttter is used to cut the upper flange hole. This is 70mm in diameter, larger to fit the finished rim of the fuel filler neck and allow it to sit flat against the wing skin.
With the inner threaded flange taped in place, I placed the wing tank back in the wing and added the wing skin back over the tank. This confirms the hole in the tank and the hole in the skin line up as expected.
Just for satisfaction, I threaded in the filler neck - this looks absolutely amazing!
Ideally, I want the tab that opens the flush fuel cap to face towards the rear like in the picture. This has 2 important reasons and 1 cosmetic.
When in the stowed position, the tab is less likely to get caught in the slipstream over the top of th wing and inadvertently pop up - not likely, but why risk it.
Secondly, I want the vent tube I plan to add to the cap to be at the front of the cap facing into the slip stream.
Cosmetically, I want both caps facing the same way - it's just more pleasing to the eyes :)
The fuel neck threads into the tank fitting and will tighten down as it goes, so to have the tight position line up with the above three criteria for the cap, I needed to figure out how far the neck threads into the tank flange exactly, then fasten the tank flange to the tank at that rotation.
I know the gap between the tank and the wing skin will be filled by cork gaskets. So I created three gaskets that will eventually be the ones installed.
Glued together with contact cement and laid in place where they will sit on the top of the tank.
Another layer of cork on top of the three. This 4th layer represents the wing skin aluminum (0.020) and a 1/16inch rubber gasket that will sit between the wing skin and the threaded fuel neck when it is in final position.
Once in tested position, I back drilled two of the tank flange holes - this is where the tank flange will be on final install.
Back drilled the rest of the tank flange holes. To hold the flange in place for final fit testing with the fuel filler neck on the wing, I popped a couple of A3 rivets just to hold it in place. These can be drilled out easily once I'm ready to add sealant on tank flange where it mounts inside the tank.
My mock-up worked perfectly. When I get the 1/16 thick rubber gasket material the gap between the threaeded tank neck and skin will disappear and the cap tab sits exactly where I want it to - excellent!
The wing is almost ready for final fit of of the wingtip, trimming the inboard end of the trailing edge and other minor clean up items.
I've been feeling a bit of what it called imposter syndrome.
YouTube videos of other builders out there show amazing work and the speed at which they are accomplishing their builds is something else to behold. It makes me feel a bit like my project is taking way too long some times and that I'm not actually doing anything or accomplishing anything. I'm not actually building something amazing, I don't actually have the skills to do this, someone else is the builder - I'm an imposter.
But as some people close to me keep reminding me - I'm not an imposter at all. I'm doing this and I'm creating most everything from scratch. Those YouTube builders for the most part are buying a kit that is pre-formed, pre-drilled and just needs to be put together. I'm creating a plane from pure raw materials. Looking back, i've done tons of work so far.
I'm AM doing this - no one else. I AM learning the skills and applying them. I'm not an imposter - I AM THE BUILDER!
More to come, thanks for listening!
Couple of updates to share. Got some work done early in March, then was away for almost 2 weeks for a work trip, then back in the shop yesterday for the day.
Both fuel tanks are now together awaiting sealant at the seams. I decided to keep the rivet spacing on the seams at 20 pitch - not required for strength, but will ensure the seams are tight and will squeeze the sealant out to the edges of the inside seam.
By placing the clecos on the inside edges of the tank I can test fit the tank in the wing.
It's a tight fit. I had to slide the rear corner of the tank inside the rear channel first, then slide the tank forward towards the spar..
With the tank forward as far as it would go, the fuel port on the tank doesn't completely line up with the passthrough hole, so some more trimming of the top forward seam on the tank was required so it can clear the wing spar.
When I originally cut and bent the tank skins I had the intention of having the tank and seams welded, so I wasn't concerned that the forward seam flange was a bit narrow. Now that I plan to rivet the tank together, the forward seam won't be wide enough to safely rivet.
To correct the issue, I cut the folded flange off, and bent a new flange that can be riveted onto the front wall of the tank and is wide enough on the other flange to accept a row of rivets to secure the top skin.
Once the rivet lines were laid and drilled out, I trimmed away the excess top skin to match the new flange. This brings the upper front edge of the tank close as I can to the plans (5mm overhang).
The right wing tank doesn't have the same flange width issue and I was able to create a rivet line in the original bent flange, then trimmed it the same way to match the left wing tank.
Got my fuel sender mounting plates back from Henri the welder. Very happy with the work he did. They look heavy, but are actually quite light and the welds are solid and fuel tight.
Next step was drilling out the passthrough hole where the fuel sender extends into the tank. A small hole saw is perfect for this.
Some simple trig math to figure out the centre of round plate. Bi-sect the circle in two places. Draw a perpendicular line from the mid point of each of the bi-sect lines. Where the perpendicular lines intersect is the centre of the circle.
Holesaw on the drillpress makes a nice clean hole:
Deburr and clean up some of the sharp edges with sandpaper and they are ready for the sending units.
Drill and tap the plate for mounting screws:
The mounting plate is thick enough to allow for four full threads to engage and holds the mounting gasket tight. I may add some thread locker when final installing these as I'd prefer not to have a nut that could come loose and fall inside the tank.
Next up I need to fabricate the rear channel fuel tank support angle. In the standard aircraft, the wing tanks are smaller and supported by a rear tank rib that runs laterally from the inboard and out board fuel tank bay ribs. With the long range tanks, an angle is added to the rear channel to secure the tank forward in the fuel tank bay.
Rather than create new from fresh stock, I realized I had some scrap ends of channel cut off the end of the rear channel when building up the wing skeleton. Although a bit thicker material, these will work perfectly.
Mark out where to cut the channel to create the angle and cut on the bandsaw:
The plans call for the angle to be mounted on the top of the rear channel, but this doesn't make sense to me as the trailing edge and fuel tank skin will then have a bump to overcome when they get attached. The only thing I can think of is that it is done that way to make mounting it easier. I going to mount mine inside the channel by securing temporarily with some epoxy so I don't need to cleco it in position as those clecos then will be in the way when I attach the trailing edge and fuel tank skin. Eventually rivets will hold it all together anyway.
With the tank rear support angle temporarily in place and the front edge trimmed correctly, the tank fits good, nice and square in the wing. A piece of adhesive cork will be put on the face of the angle (and elsewhere on the tank) to prevent rubbing:
Onto the fuel bungs.
Sometimes Google is your friend, sometimes it overcomplicates things. For the fuel drain bung, I want to secure it with five machine screws evenly distributed around the perimeter. So I searched Google on how to divide a circle into five equal parts.
I took a scrap of cardstock, and following the multistep process learned how to divide the circle, transcribe arcs off tangents, re-measure from arc to bisect angle, then scribe from intersecting angles to arc the outer circumference where the five hole locations I need will be. Really cool, bit how can I do that on the bung itself? This is too complicated for what I'm trying to do. Can someone say "Squirrel" !!
Can this be done easier with a protractor and simple math? Yes young Jedi, easier it can be (Master Yoda rolling his eyes)....
Draw a circle using a grade-school protractor. 360 degrees divided by 5 is 72 degrees. Mark five locations on the circle 72 degrees apart.
Centre the bung on the circle.
Use the five tangent lines to mark the drill holes on the bung with the centre punch at each of the five locations.
Drill the five holes.
Learn he will. Maybe.... LOL
With the bung now drilled out to A3, I centred it over the tank drain hole and secured it with clecos:
Satisfied with the location and fit, I took the bung off the tank and expanded each of the holes to 5/32 on the drill press and tapped each hole in turn to accept a 1/4 inch 10-32 stainless machine screw. The mount holes in the skin need to be slightly larger to clear the threads of the screws:
When final installed, sealant will be added underneath the screw heads and between the bung and the tank skin.
Next up, securing the fuel tank output bung fitting.
I needed to drill where the skin, tank rib and bung will meet.
With the location determined in the tank seam, I removed the rib from the tank and clamped the bung into place. I then back drilled through the rib flange and into the bung just enough to mark the location of the holes.
The bung was then put in the vice on the drill press and drilled just deep enough for tapping for machine crews the same as the drain bungs.
The holes in the skin and rib flange were opened up slightly for the 10-32 machine screws. With sealant this will secure the fuel bung very well, but I'll add some thread locker as well.
Test fit the fuel tank again with the new rear support angle and the finger strainer in place and it's coming together. Thread sealer will be added once this is final installed. Still some fitting to do in the wing bay (spar fuel tank support channels), but very pleased how the tank fits so far.
Next up is fitting the fuel sender assembly and the fuel fill neck and cap.
The fuel sender plate is inverted on the top of the tank so I can trace out the shape on the upper tank skin and determine how it will mount.
The red "panel" line represents the out dimension of the fuel sender assembly. The inner red circle is the rough estimate of where I intended the sensor to go. The inner green box roughly represents the access hole I'm going to create. I will be nice to be able to look and reach inside the tank should the need ever arise in the future. For rigidity, I may narrow the lateral width of the access hole a bit, I'll make the decision once I determine how this will be sealed and secured to the tank skin.
So this wing assembly has gone much faster than the first, but total time has been almost equal to the first as I figure out the fuel tank and associated wing plumbing. Hope to finalize this wing in the coming weeks and get the bench clear for the fuselage assembly.
Stay tuned for more, thanks for following along.
Finished laying out the outboard nose skin. This area has a double row of rivets along the spar line into the wing tip end of the spar:
Also drilled the main spar out to A5. The amount of aluminum swarf created by this project never ceases to amaze me - I can't imagine how much debris is created by the match drilled factory kits!
Ron and I went to visit with Henri, a local builder and master welder that Ron knows and who is also an aviation guy. His shop is next level - he is building a six seat CompAir 6 which will go on floats. He too is doing an "auto conversion engine" which is an 8 cylinder twin turbo diesel with 6 bladed propeller. Unlike my Corvair which has a proven method, he's doing all this design and testing himself. His work is amazing and has to be seen to be appreciated.
After much tongue wagging over his shop and project, we had a look at my fuel tanks. Although Henri says welding my fuel sender assemblies would be no issue, he wasn't comfortable attempting to weld my fuel tanks. The concern is the thin 025 aluminum will most likely warp beyond easy correcting with the heat of welding. Based on this, his suggestion was to seal and rivet the tanks and after a bit of research, that process is equally effective without the risk of warpage. Kit builders get their tanks from the factory pre-welded but they are expensive to order as individual parts especially the long range versions I want.
When I was forming the tank sides, I followed the same method as the wing ribs which included relief holes at the corners. I originally thought these wouldn't be a issue as welding the tanks would fill in these spaces easily. Sealant isn't capable of covering this big of a gap between parts, so I needed to come up with a way to "fill" the holes that wouldn't also change or interfere with the assembly of the tank.
A piece of 025 "L" can be formed to back the outward facing corners of the tank side panels. A 45 degree notch in one leg of the L allows the angle to be bent to the same angle as the corner, and some light brazing welds the angle into a corner:
This picture shows the concept better. This is the same angle in the vice prior to bending the second corner:
The completed angle backer, brazed closed and sitting in place. This will be treated with sealing compound before being riveted with the tank skins. This will effectively close the corners of the tank sides:
The front corners of the tank side. By placing on the outer side of the the tank wall, it doesn't change the geometry of the corners and the tank skin will still fit correctly.
When sitting in place, I marked where the ends of the corner backers would be, then transfered that mark to the outside of the tank skin so I could lay out the rivet lines:
On the bottom side of the fuel tank, there is one flute in the side wall and several on the top side. I made a mark to remind me that I won't be able to rivet here:
Laid out the rivet line. A3 rivets on 2omm spacing worked well and avoided the aforementioned flute mark. I shortened the rivet spacing at the corners to account for the corner backers.
Cleco clamps hold the skin in place on the side wall. Line up the wall and drill A3 holes along the rivet line:
Same process for the front of the tank:
I didn't drill near the tank outlets. I'm going to drill and tap the outlet fittings for stainless screws. With sealant between, the screws will tighten the fittings against the skin for a leak proof outlets:
Repeat the process for the inboard lower side (shown on the right):
Very pleased how the bottoms and front turned out. They will be the first to be sealed once I get the sealant from Aircraft Spruce in a couple of weeks.
Flip the tank over, and repeat the process, starting at the rear of the tank (3 rivets on 15mm spacing) and working forward, bringing the top tank skin down tight. There are 5 flutes to avoid here, but the spacing at 20mm continued to work out well:
Then the inboard side:
Cleco clamps are very handy here!
The front edge was originally going to be welded, so edge size wasn't a concern. Now however, I'll need to bend a 025 L and install it.
I've read many concerns from kit builders that their factory made tanks are slightly out of square, but this rivet/seal method seems to keep the tank much more square and straight.
Next up, adding the front edge angle, fit the corner doublers and drill/tap/fit the outlet fittings. Very happy this complicated assembly (welded or otherwise) is coming together. I also heard back from the fuel cap manufacturer, I need to order the threaded flange for the tank that interfaces with the threaded tank neck. Not expensive, but wish there were better instructions or explanations as I would have ordered them with the caps and picked them up at the same time from Aircraft Spruce.
As always, thanks for following along.
After a week away for work, it was good to get back to the shop for some build time this past Sunday.
I received my adapaters that go between the fuel finger screen in the tank to the hose end fittings:
Loosely fit in position inside the wing bay:
Next, I needed to drill the large hole in the rear wing channel for the fuel line to pass through into the trailing edge. Laid out the location as per the plans, but moved the centre of the hole down a bit to allow the grommet to sit flat away from the doubler above:
It didn't take as much effort to create the hole with the bi-metal hole saw as I thought it would. This hole goes through the 040 rear channel and the .125 root doubler plate. A bit of sanding and it cleaned up nicely.
I primed the hole on both sides to prevent any corrosion between the channel and doubler:
Next up was adding the Swivel-Seal hose ends to the braided line. The process starts with the threaded collar. I protected the nice anodized finish by covering the vice jaws with tape first.
The cleaned end of the braided line is inserted into the back of the collar. It's a tight fit, but if you twist the line as you push it inwards it goes smoothly:
As per the instructions found online, the line gets inserted to just shy of the inner threads:
Next, the fitting gets mounted in the vice:
Push the collar centred and forward onto the fitting until the threads can start engaging:
Tighten the collar down on the fitting using a wrench while turning the braided line until tight:
It's a bit of a pain to get this large grommet in and sitting flat, but it is the perfect size for the braided line to pass through:
The braided line has a limit to it's bend radius, but I'll be well within the allowable limits once the trailing edge of the wing is in place. I will need to protect the pitot/static lines from abrading against the fuel line.
As I completed the fuel line for left wing, I fabricated the one for the right wing in prep for install once my tanks are ready. These fitting aren't cheap, but this is important for safety and they look good too:
Also got my flush fit fuel caps in from Aircraft Spruce. The factory finish on these is excellent, very pleased. Just need to figure out how to make the threaded flange fit the tanks. Email sent to manufacturer for guidance.
Prepping for the wing nose skin to be rolled up, I marked out the slots needed for the slat support brackets where they pass through the nose skin, using the same method as I used on the other wing:
Wing nose skin ready to roll over the nose ribs using ratchet straps. This went easier without the trailing edges in place:
Inboard nose skin drilled out to A3 at the spar once all squared up with wing:
Both inboard and outboard nose skins now rolled and attached. Still need to final rivet the slat attach brackets to the nose ribs, but at least I'm closer to closing up the wing.
Once the nose skins are final drilled and deburred, I'll add in the fuel tank angles to the back of the spar in the fuel tank bay. I'll need them welded up before doing that. Hopefully I'll have answers back about the fuel caps by then.
More to come, stayed tuned :)
As explained in a previous blog post, I've decided to use magnetic reed float style fuel senders to measure the fuel levels in the wing tanks. Much simpler to manage and accurately interpret the signals for display in the cockpit.
Figuring out the best position for the senders is a compromise between tank design and expected fuel position in different phases of flight. I also want them mounted in a way that the top of the sending unit doesn't require a blister or bump in the wing skin to cover it.
It makes the most sense to measure at the tallest part of the tank, but also consider the orientation of the tank. Wing dihedral means the fuel will accumulate towards the centre of the airplane, that's why the outlet is on the inboard side of the tank, so it seems to make sense to keep the sender in the inboard front corner of the tank. But that only makes sense if the tank remains in the same position in all phases of flight. What about when the tank tilts outboard in a turn? Or inboard?
So I believe the right thing to do is to have the sender furthest forware I can at the thickest part of the tank, and centred laterally in the tank. This should give the most stable level measurement regardless of bank angle as the mid point will stay the same or the average. More thinking on this required to confirm.
In the meantime, I do know I have to fabricate a way to mount the sender.
The "empty" level of the tank should be considered to be the distance above the bottom of the tank to the top of the fuel outlet - if the outlet of the tank is anywhere below the fuel level, the fuel line will draw air. I want my fuel indicator in the cockpit to show "empty" before this happens. I measured this distance and it is about 25mm, so for an extra margin of safety we'll design it at 30mm.
To simulate the top of the wing skin, I laid a piece of aluminum angle across the ribs approximately where the sender will be mounted. The goal here is to get an idea of how deep the recess will be in top of the tank for the sender.
The senders I've chosen at KUS-USA 6.5:" marine fuel senders, available on Amazon. There are many cheaper versions of these from various retailers online, but I wanted something I can easily replace if the need ever arises and KUS-USA has been in business for years, is the industry standard and I know the quality is good.
I was very pleased on the build quality of the units. The float is fuel/chemical proof, the sender assembly and mounting screws appear to be high quality stainless steel and it comes with a fuel proof neoprene gasket, not cheap cork or silicone. Even the sender wires are properly tinned from the manufacturer.
A reed style float sender works by having a series of reed switches and resistors inside the sealed stainless tube, which are activated by a magnet inside the float that travels up and down the outside of the tube. The position of the float in the fuel tank activates a certain combination of reed switch and resistor than can be interpreted by the fuel guage.
I clamped the unit into position on the aluminum angle with a wooden shim in between to simulate the space between the upper skin and the top of the wing tank skin:
A wooden shim placed on the bottom of the wing tank bay approximates where the bottom of the tank will be once installed. The fuel float in this position represents empty and although there will still be fuel in the tank at this position, the fuel will still be above the fuel outlet.
Next, I needed to fabricate the recess tube that the sender will mount in as shown above.
I started by creating the lower plate of the tube. I chose 0.125 thick scraps I had left over as I wanted something thick enough to tap threads in.
I'm sometimes amazed about what I remember from math class and more specifically geometry. One of the easiest ways to find the centre of any circle is to remember that 90 degree perpendicular lines drawn from the the mid point of any two bisecting lines will cross at the centre of the circle:
It works no matter how long the bisecting lines are:
I drilled out a pilot hole in the centre, then used a scrap of wood as a support for making the cut on the bandsaw. I can rotate the piece as I cut. It didn't create a perfect circle, but the bench grinder took care of any rough edges:
I used a large pilot drill on the first plate to create the sender passthrough and that worked, but for the second one I used a bi-metal hole saw on the drill press. Much easier and cleaner.
From left to right: Sender, lower plate and tube stock which will be used for the sender mount:
The sender mounting plate is just a bit wide to fit inside the tube:
There is enough material on the outer edge of the senders to allow a bit of grinding to fit inside the tube:
A look at the bottom of the fabrication where the sender protrudes through the bottom plate, prior to cutting the tube to size:
Next to fabricate was the top mounting plate. I've decided to make these extra wide for a couple of reasons. First and foremost, spreading the weight of the sender assembly across a wider area of the upper tank skin and secondly, giving me wide opening in the top skin should I ever need to look or reach inside the tank for maintenance/repair reasons.
Centred on the plate, two pilot holes to guide the fly-cutter (didn't have a hole saw big enough):
Cut the hole slightly undersize then used a Dremmel bit to slowly expand it until the tube fits tightly in the hole:
A rough estimate where the sender will sit in the tube, prior to cutting the tube to length. This is what the top of the assembly will look like on the tank:
Laid the sender beside the tube and roughly marked out where the float will bottom out. The float buoyancy means it sits about half submerged in the fuel. Also marked where the tank bottom is, top of the fuel outlet and where guage empty is.
Once confirmed, I can mark the tube where the bottom of the recess will be - this is where I need to cut the tube, the lower plate will attach here:
Lower plate, sender gasket and recess tube:
The mount tube assembly stack:
The mount stack upside down on the bench:
With the sender in place:
Next up was the mounting screw holes. To ensure the 0.125 bottom mounting plate was thick enough to be threaded, I grabbed some scrap and did a test. Drilled a 5/32" pilot hole and tapped it to 10-24 thread that matches the sender mounting screws:
The screw holds nicely and will do fine on there own, but I'll add some thread locking compound when I install these just to be sure. much nicer than trying to capture a nut on the back side.
With that determined, I laid out the mounting holes in the lower plate and tapped them the same:
Both sender assemblies as seen from the tank side ready to be fitted to the wing tanks once they are welded up.
Very happy how these turned out. I'll do a bit more research on tank posistion just to confirm I am on the right track, including simulating a tank using a shallow(ish) Rubbermaid tote and some water.
More to come, thanks for reading.
Good day in the shop today. Time to start plumbing the wing for pitot, static and fuel lines. 50 feet each of blue and yellow nylon line and 20 feet of Earls's Auto-Flex fuel line:
I'm not ready to get the fuel tanks welded yet, but they are taking up a bunch of room on the bench, so I "dismantled" them for storage. Before putting the skins away, I decided to drill out the drain hole.
Step drill brings the hole up to 18mm diameter:
The tank drain fitting will be welded here and eventually will have the drain valve installed.
Before flipping the wing upright, I cleaned up the bench completely. It was getting quite untidy with all the bits, pieces and other tools. I laid down some green tape runners on the lower skins to help protect the skins where they will ride on the steel bench tubes.
Ron helped me flip the wing over and I was pleased to see the tape runners I put on the upper skin helped prevent most if not any scratches:
The nose skins are just wider than the bench when they lay flat, so I tagged the corners with a bit of yellow tape . It won't protect the corner, but it catches the eye when walking by.
Here is a better look at the pitot/static tube inside the nose skin now that the wing is upright. As mentioned before, I'll need to trim the length a bit to leave room for the the union connectors:
Here the connector unions in place on the end of the tubes. They point right at the spar web, bending the tubes into the lightening hole isn't practical.
A couple of holes in the spar web are necessary for routing the lines, but I like this better as it is another way to support the lines as they pass towards the rear channel:
Grommets protect the lines in the holes. I won't be connecting the probes until later as I work on wrapping the nose skin. Blue line is pitot (airspeed) and yellow line is static pressure (altimeter, VSI etc.):
The lines pass through the wing bay and out through the rear wing channel, again through grommets to protect the lines:
Not all leght of this line will end up in the airplane, but I'm not cutting anything I don't have to (less cuts means less potential leaks/failure points). For now it stays coiled up. Eventually it gets routed through the cabin, under the seats/floor and up to the instrument panel. I'll likely need more union/elbow connectors, but that's a ways off yet.
Next I worked on laying out where the fuel line leaves the left wing tank and travels though the inboard wing bay rib and eventually through the rear channel and out inside of the trailing edge to the fuselage.
The outlet fitting isn't welded yet, so for test fit I taped it in place:
The inboard tank rib (side of tank) sits inside the fuel bay of the wing once part of a completely assembled tank:
I lightly clamped the rib in place. The goal here is to approximate the location of the pass through hole in the wing rib foward/rear, not the distance laterally (left/right):
I marked the location of the pass through using a Sharpie through the centre of the fitting then drilled a pilot hole in the wing rib:
Using a the step drill, I enlarged the passthrough hole a little at a time until the finger strainer fitting from the tank could fit through. The aluminum plate is a piece of scrap I placed on the lower wing skin to protect it from scratches from the drill chuck:
I traced the size of the fuel outlet fitting centred on the passthrough hole, then enlarged it a bit more. This will give me a bit more room when I install the tank. The fittings and line just need to pass through here, they don't actually fasten to the rib.
Looking at the wing tank rib, facing inboard with the finger strainer in place:
Looking at the finger strainer, outboard towards the wing tank:
I can't do much more tank fit up until I get the fuel caps and fuel level sending units I ordered.
Looking back inside the wing, I needed to come up with a way to support and protect the pitot/static lines from rubbing on anything from vibration. The lightening hole flanges of the nearby wing rib face toward the lines, so clipping them to the surface of the rib won't work.
Using some scrap 025 aluminum that was already bent 90 degrees, I created some stand-off brackets
While the standoffs dried after priming, I remembered I needed to final torque the forward wing strut attachment bolts - so much easier with the wing upright!
Some 1/4 inch cable clips facing back to back get rivetted to the standoff then the standoff rivetted to the wing rib:
Nice and tidy and secure from vibration damage:
The standoffs are perfect, very pleased at how neat this arrangement is. Once the final fit of the lines are done at the pitot/static probes, I add a wire tie on the lines to prevent them line from sliding back and forth in the clips if needed:
Gentle bends supported well prevent the lines from kinking. There is plenty of room inside the trailing edge for a large radius bend in the lines as they exit the rear channel:
Cable clips avery 11 inches spaces out nicely along the face of the rear channel as the lines head inboard towards the fuselage:
Tied the nose skin up a bit with some twine which allows anyone walking around the bench when I'm not working on the wing to do so:
Good productive day. Waiting now on some plumbing fittings, fuel caps and fuel senders. I've got to drill and grommet the fuel line hole in the rear channel, then I can fir the trailing edge. While I wait for my orders to come in, I'll get the nose skin slotted for the slat pick-ups and wrap the nose skin.
More to come, thanks for following along.
Fuel lines and fittings have arrived. Stainless braided Auto-Flex line and Swivel Seal fittings. Expensive but the peace of mind this provides is worth it. This is one area of the plane I refuse to compromise on. Very impressed with the quality of Earl's Performance products. With these in hand I can start laying out the fuel tank plumbing.
I've been wanting to figure out a way to measure the fuel level in the tank that requires no internal sensor - less holes in the tank means less chance for leaks. There are several stories on the builders forums about tank sensors mounted through the sides of the tank leaking or being terribly inaccurate, hard to service and generally failing.
I wondered if there was a better way, and I originally came up with the following. A very sensitive presssure transducer (the chrome unit with yellow label below) that will measure the "head" pressure of fuel in the tank via a "T" in the fuel line next to the tank. In theory this should work using an Arduino microcontroller to read the sensor and output a value to a gauge. Here is the assembly mocked up on the bench. From right to left - finger strainer (inside the fuel tank), tank fitting (through wall of tank), threaded adapter, threaded "T", coupler and pressure sensor), fuel line fitting elbow.
Testing of the system has proven difficult. I've been unable to get consistent readings from the sensor in a static set-up. The programming of the Arduino works fine, I'm just not happy with the accuracy of the output due to the very low spread between empty tank head pressure and full tank head pressure, which given the depth of the tank is about 1.5 PSI. I'd hoped a programming algorithm within the Arduino to amplify the input values and stabilize the readings would work, but it's become too much of a tail chase to get it right. From there I'd still need to figure out how to smooth the values to account for changes in atmospheric pressure (fuel changes "weight" with changes in altitude) and aircraft attitude - banking towards the sensor increases head pressure, banking away reduces head pressure.
In an effort to focus on the build getting moved forward, I've decided to abandon this concept in favour of a top mounted float sensor. Yes, this means another hole in the tank, but if mounted from the top, the risks of leaks is minimized and the ability to service the sensor if needed is much easier. More on this later.
So removing the pressure transducer from the fuel line leaves just the tank strainer, the tank fitting and the elbow. I'll need to order the fitting that goes between them, but they are inexpensive and easy to obtain.
The tank fitting is a one direction NPT thread. This picture shows the fitting as it looks from the outside of the tank.
These fittings were gifted to me by another builder. They are actually the larger style, so I need to modify them slightly to fit the tank side rib so the strainer sits nearest to the bottom of the tank as possible. Trimmed them using the bandsaw, then cleaned them on up the disc sander.
The smaller diameter of the fitting needs to fit through the tank rib from the inside. I don't have a drill bit this size to make the hole, so I had to improvise.
I confirmed the fitting was trimmed enough by laying in on the outer face of the tank rib:
I drilled a pilot hole equivalent to where the centre of the fuel strainer will be on the tank:
Used a large step bit to create the general shape of the hole almost up to full size in the tank rib:
Laid the fitting centred over the hole on the tank side of the rib and traced the final size/shape:
Clamped the rib to the bench elevated on some blocks, then used the Dremel tool with spiral cutting bit to carefully bring the hole close to size using the trace lines as my guide:
Filed the hole to final size to ensure a tight fit:
Here is the fitting in it's final position looking from the inside of the tank rib.
On the outside of the rib, the fit is really good:
With the finger strainer in place
Bending the tank skins can be tricky. It is paramount to ensure the bends are as tight as possible to the corners of the tank ribs to reduce any gaps that will need to be filled when the tanks are welded.
I wrapped and finger clamped one of the ribs with the seamstress measuring tape (very handy long ruler for any project) to get a general measurement of where the corners of the tank skin will be. This picture is of the second tank taken later in the day (left tank had already been through this process and I forgot to get a picture for the blog):
The throat depth of the wide bender isn't deep enough to get to the middle tank skin bends, so I needed to use the heavy bender. To allow full access we moved it out into the open floor area, rather than roll up the paint booth curtain (Ron is painting currently).
First I laid out the 025 skin and marked the approximate location of the first bend. Like the slat skins, order of bending is important here, working from middle out to ends. I've left the skin a bit long at each end to make sure it doesn't come up short once it is bent to shape:
The heavy bender allows for material to pass through, giving full access to the middle of the sheet:
First bend complete, next was measuring the second bend closely to make the corners tight
Finger clamped the ribs in position to get a good measurement where the next bend would be:
Second bend line laid out (note the little circled "2" I used to remind me of the bend order):
Back on the bench, I discovered the second bend was slightly overbent and the process on the bender had opened up the first bend as well.... I corrected both before moving forward, but swapped the bend order on the second tank which prevented this from happening again.
Left tank skin rear corners corrected and test fit shows good:
Marked out the location of the fuel filler neck:
Front side of the tank skin bent up to meet the top skin and close off the tank:
The front side of the tank skin needs to have a 5mm flange bent forwards to create the seam for welding. I puposely waited to bend this flange as I didn't know where the bend would be until I mocked up the tank:
I tipped the tank forward on its nose and clamped the forward tank skin onto a piece of aluminum angle at the bench edge:
Using a deadblow hammer I caefully bent the 5mm flange forwards to match the top corners of the tank ribs:
Reassemble the tank and use Cleco vise clamps to hold it together. Some final tweaking of the rib flanges squares it all up - very happy with the final shape! The extra material overhang on the top side of the skin will be trimmed back to match the flange.
Marked out the fuel tank drain location which is directly below the fuel line fitting. This is the lowest spot in the tank once it is mounted in the wing. It is from here that fuel is drawn during pre-flight to check for contaminants such as debris or water:
The right wing tank went faster now that I have the benefit of a process from the first. Fuel outlets are on the opposite side of the left tank (the face inwards towards the fuselage:
I drilled and sized the fuel line fitting for the right tank after creating the tank so we could move the bender back out of the way. The process for the fitting was the exact same as the left wing, just the opposite side of the tank:
Picture of the top front of the left wing tank. I've laid out the location of the top mount fuel tank sensor and the fuel filler neck.
Both tanks clamped together, resting on top of the wing and awaiting parts for the fuel filler neck and fuel level sensor. These will be fitted before final weld-up.
Very pleased at how the tank assemblies turned out, hopefully welding and subsequent leak testing goes as well. Getting ready to order the fuel filler necks, fuel caps and the parts needed for the fuel level float sensors.
This doesn't fit under either the engine or avionics category, I guess it is part of the wings? Maybe under other......
Thanks for following along, stay tuned for more.
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.