Continued working on the right wing. Got the upper outboard skin mostly matched drilled to the ribs. I've only pilot drilled the skins at the spar and rear channel as I will need to fit the nose and trailing edge skins first, the right size them as a group.
first thing was laying out the rivet spacing on the upper surface as per the plans:
On of the keys to good rivet spacing is knowing where the rib fluting is. Marking it out ensures two rivets between each flute. I marked the distance of each rivet back from the spar centre-line so I can easily transfer the same measurements to the other ribs which are the exact same:
A3 holes clecoed before right sizing to A4 across the top of the wing chord. This really makes the curve of the wing apparent:
With the ribs confirmed as right size, the rear channel is drilled out to A3, waiting for trailing edge skin:
Next up was the upper inboard skin. This makes up the panel that covers the fuel tank. It's installed much the same way as the outboard skin. I'll wait to drill the rear channel here too:
finger clamps help to keep everything straight for pilot hole A3 clecos. Again, I'll wait to drill these up to A4 when I'm ready to add the upper root skin as there is a root angle to attach at the junction of the two skins that help form the taper to the root:
The main upper skins are now complete:
After cutting the 2nd fuel tank skin, I roughly laid out the tank ends and some other parts I needed on 025 for the fuselage. Minimal waste is the goal:
The next steps are joining up the two halves of the fuel tank form template and the two halves of the tank end aluminum templates:
Confirmed the templates match the measurements of the plans. This is very similar to the templates and forms of the wing ribs:
The form template fits well on the outside of the inner wing rib and this confirms the extended tank will fit in the wing bay as I expect. Kinda cool to see it work :)
With that confirmation, I laid out the aluminum templates on the pre sized 025 section. Then I used the centre punch to mark the relief corners:
I also punched the inboard tank ends where the plans show the out-port of the fuel tank. I've yet to completely decide on how this will look on my system with regards to the fittings, lines etc. But the out-port will be here:
To remind me where I made punch marks, I circled them as I went. Always drill and debure the holes before making relief cuts - so much easier
All four ends laid out for the fuel tanks - one left, one right:
Templates cut out, awaiting final relief holes and corner cuts:
Seeing as I only have four ends to make, I decided some pine boards would be just as easy to use and much cheaper than expensive 3/4 inch plywood pieces.
Stacked two boards and traced the form template on the top one. Screwed the boards together.
Cut the template line out on the bandsaw. Fresh pine getting cut smells real nice :)
Once I sanded the edges to the correct size, I marked the edges for rounding off on the router:
Both sides of the form, edge rounded and beveled on the sander for springback allowance on the aluminum blanks:
The rest went the same as the wing ribs, except the forms needed to be clamped around the periphery as there are no tooling holes to use like the wing ribs. Holes in the fuel tanks are not welcome here for obvious reasons! Next step will be start laying out the bends for the wing tank skins.
Before I move forward on the tank construction, I need to finalize what needs to be built into the tanks, including fittings for the filler neck, the out-port where the fuel will travel to the engine via the fuel line and where the quick drains will be mounted (more on this later).
The other thing I need to decide is how to monitor fuel tank levels - this is the kind of stuff I love to figure out, but also keeps me awake at night. The plans call for a float type fuel level sender similar to what you have in a car fuel tank. Essentially it's a float on an arm connected to a sweep contact that changes electrical resistance or voltage in the fuel sensing circuit, which is fed to a gauge on the dash similar (simply) to this:
The drawing above is simple enough, however there are two flaws for this to work in my airplane. There isn't room between the top of the tank and the upper wing skin for the the sliding contact/arm pivot. Second flaw, related to the first is the plans call for the same float arm system, but mounted in the side of the tank. All I can think of is why would anyone want to cut an unnecessary and large hole in the side of the tank? That's just asking for trouble with leaks and the builders forums are chock full of stories regarding just that.
So, like the trim control and lighting, I'm going to create my own Arduino solution. I've been doing some research on other methods to measure liquid quantities (the level) in a container (the tank) without being invasive (cutting holes).
My challenge is to find a method that can provide accuracy over 190mm of fuel tank thickness (top of tank to bottom) at it's thickest point and not require holes in the sides or bottom of the tank where it can leak fuel.
There is some limited information on the interwebs about using ultrasonic sound waves to measure the distance from the sensor to the fuel, but that requires a large range between full and empty to be accurate and again would require a sensor at the top of the tank, something I'm trying to avoid. The math to make this work and the shape of the tank doesn't make this easy.
I briefly thought I could make something like this I found on Amazon. It uses a float that slides up a column open/closing magnetic reed switches as it rises/falls, but it would still require a hole and mount on the top side of the tank and a bunch of circuitry to complicate things:
I've decided to try something like these. A pressure transducer that measures the weight of the fuel in the tank inline with the fuel out port via pressure. These transducers are fuel proof and output proportional voltage in a linear ratio to the pressure sensed - solid state, no moving parts and maintenance free They come in various pressure ratings and configurations, but most importantly are threaded the same size as my planned fuel fittings.
The outputs from the transducers can be read and interpreted by the Arduino microcontroller and with some simple programming the Arduino can output a signal for a readable gauge in the cockpit (one for each left/right tank).
What I want for gauges is really up to me as they can be displayed on a LED panel by simply programming whatever images I want to use as the display.
I could go with something simple such as the traditional automotive gauge on the right, but I kind of like the sweep/ribbon style on the left. The numbers in this example represent percentage, but could be made to show litres/gallons as well - it's all customizable in the programming.
I started to play with LibreCad to make my custom display. I created the sweep and used Microsoft paint to colour each section of the arc. Each arc represents a reading correlating to what the Arduino is reading, giving me a moving gauge as fuel is consumed.
The LED display uses low resolution bitmaps for display, but they can be in colour. I plan on green for anything more than 1/3rd full, yellow between 1/4 and 1/3rd orange then flashing red for anything less than 1/4 to draw attention to it. I might even have the programming sound an aural alarm as well.
A simple animated GIF shows what a declining tank would show (with an added funny at the end):
Progress is leading to more thinking and I love it. It's the true core of what this adventure is about.
Next up, flipping the wing over and fitting the bottom skins and mocking up the fuel tanks for welding and fittings.
Thanks for following along.
No update for a couple of weeks, but that doesn't mean I've been idle on the project. Picked up six sheets of 020 aluminum last week. They are 12 feet long and fit (barely) in the back of the family truck. The shipping materials actually weigh much more than the aluminum itself. Lots of straps to hold it in and a cheap fabric red flag on the end to keep it (closer to) legal.
I griped a bit about this on Facebook (who doesn't). It's very hard to understand why raw aluminum made here in Ontario is shipped out of country to be processed into sheets, then sold back at a premium here in Ontario. I'm all for North American jobs, but this is a good example how much manufacturing base our country has given away since I was born.
Off to the shop last Saturday. Nothing better than a hot tea in my Canuckmug.
The wing skeleton takes up much if not all the workbench and the other workbench is being used for Ron as he works on the Aeronca Scout finishing touches before it gets painted. A roll of plush carpet on the floor makes a good cutting mat:
First wing skin cut to size and rolled out on the skeleton. This one is the upper outboard skin:
Lined up, the pilot A3 holes at the spar clecoed in place. With those secure, the skin naturally curves down across the wing ribs. It actually starts looking like an aerofoil! Sweet!
Marked up the rib lines and the cross L lines that define the rivet lines for both. The cross L's help stiffen the skin over the wing bays. The whole skin will come off again once I finish the pilot holes at the spar, to drill pilot holes for the ribs and L's.
Spent the rest of the day making the L's and helping Ron install the new windshield in the Scout. Learned a bunch about drilling windshields so they don't crack - this will be handy when I install mine.
I also started working on the fuel tanks. I've got the first tank skin cut to size which is just a large folded rectangle (think four sided rectangular box). I'll need to make the tank sides and the wooden form to bend the edge flanges for welding it all up.
I managed to secure a copy of the drawings for the extended fuel tank. I put these into LibreCAD. This is the template for the wooden form directly from the dimensions in the plans. The tank will fit in the first wing bay between the first and second wing ribs, main spar and rear channel:
The template for the aluminum sides was derived form this using the drawing tools available in LibreCAD - I learned a few new tricks how to make parallel lines, offset by 6 mm which leaves room for the flanges. It's very close in shape to the wing ribs, just a bit smaller. I also created crosshairs on the drawing where the relief holes at the corners are drilled and also where the fuel outlet of the tank is, including allowances for the fold of the flanges:
You may recall from a previous post, my wife Brenda bought a CriCut Maker craft printer/plotter/cutter. I have a fair amount of time to think while driving to/from work sites and it donned on me to ask if the CriCut could accept native .DXF files that LibreCad produces and if it does, could it cut these templates from Bristol board?
Turns out, it CAN! I wish I knew this a long time ago, it would have saved me a ton of time cutting templates from converted PDF files, but the CriCut is fairly recent in the crafters market. Oh well, still have lots of templates still to make!
The CriCut can cut and print up to (almost) 12 inches wide by 24 inches tall with a little margin included in that. My wing skin templates had to be sliced down a bit in order to fit, but I was able to get the most important shapes (the complex curves) plotted and cut.
It starts with a standard piece Bristol board, cut down to 12 x 24 inches:
The CriCut uses an adhesive cutting mat - something similar to 3M Post-It notes on a larger scale. I laid the mat on top of the marked Bristol board to make sure it fit correctly. (The whimsical black cartoon cat and logo on the inside of the machine lid is something Brenda added herself, using vinyl and made on the CriCut):
With the Bristol board cut to size, it gets stuck down on the mat to wait loading into the printer:
The Design Space software for the CriCut takes a bit of getting used to, but isn't too difficult to figure out. As I stated above, to make the upper wing skin tip template fit, I had to slice it in half in LibreCad and import both halves into Design Space.
Follow the directions on Design Space to choose and load your material, and press go. The CriCut cutter automatically checks depth of the cutter and goes about making the cuts defined by the DXF file:
Almost impossible to see in the picture below but the cutter follows the lines of the uploaded DXF file. Once the cutting is complete, unload the mat:
Bristol board isn't one of the default materials in Design Space, so I just chose the heaviest card stock listed and asked the machine to cut with more pressure. Almost completely through and enough to easily remove the cut outs:
Emboldened by my success, I make the template for the outboard wing nose skin. It too turned out perfectly:
Here is what I got done over the course of about 45 minutes. Like I said, the machine and software make it easy to create perfect templates. On the bottom are the two template pieces that make the tank sides. You can even have the CriCut print and cut on the same piece just by choosing what you want done with each line segment. You can see the crosshairs I spoke of above, drawn right on the template.
Back in the shop for the day tomorrow. Goal is to get the pilot holes drilled in this upper outboard skin, make the upper inboard skin and drill it (it covers the fuel tank) and maybe get the blanks made for the tank sides.
I'll need to obtain the hardware for the tanks soon. These include the fuel outlet fittings, the quick drains and the fuel filler necks. Lots to think about :)
Thanks for reading, stay tuned for more.
Well, Saturday has come and gone again, but still making progress on the right wing skeleton. Not a lot to show as much of what I did today is repetive work.
You may recall last week I started adding the flapperon arms to the rear wing ribs, using the same template method I used for the slat supports on the nose ribs. Today I wanted to continue this process and finish the other three for the right wing.
It's at this point that I remember, the first one I did is the only one where the rib flanges face inboard - on the rest or the rear ribs they face outboard. My template for the first won't work on the other three.
No matter, I just used the same process with the template facing the other way. To make the A5 rivet hole layouts consistent, I used a scrap piece of 016 to make a hole template for spacing the rivets the same as the first:
The process works well and things go faster with each one made. The other three came out perfectly:
With everything right size hole drilled, time to take it all apart, debur and scuff with ScotchBrite (I need to get some more!):
Clean with lacquer thinner and prime. I always prime anywhere two metal surfaces are sandwiched together. The main spar ends of the ribs will also be done when final holes are drilled. The flap arms and slat brackets will be done in gray primer as they are outside the surface of the wing skins. Something else I need to get more of - grey primer!
All six rear ribs primed, four with flap arm attach points, two without. Five nose ribs, four with slat attach points, one (closest in picture) with tie down ring bracket attach point. The 6th nose rib will be primed before final assembly. The root ribs will be primed in grey are they can be seen from the cockpit.
Also getting green prime are the nose skin support Ls and lower skin support Ls.
That was today's work, I'm almost ready for wing skins. I have 6 sheets of 020 aluminum on order and expect to pick it up this week or next.
I need to call Zenith on Monday to order some A6 rivets (apparently they are Zenith specific) and call ACS for a A5 strap duplicator tool.
My blog entries are sorted automatically by the publishing software I use in reverse chronological order. This is great for regular readers who get to see my latest posts on the front page. One of my regular readers pointed out that new followers might be better served however by starting at the beginning of this journey. In order to make that easier, I've added a button at the top right of the page which takes the reader right there.
Thanks to those that have been following since the journey began and for those just or recently joining me, thanks to you too.
Back in the shop today, getting more done on the right wing.
I started the day by deciding what i wanted to do next. The inboard rear channel doubler needs to be riveted to the channel. To do this, I first needed to drill the aft rib flanges out to A5. I could get the top two holes done, but the rear channel needed to be lifted to get the bottom ones because the table was in the way of keeping the drill straight.
Unlike the lower holes of the nose ribs at the spar, I made the room by removing the ribs from the spar but leaving them attached to the rear channel. I moved everything back to the edge of the table:
With all the holes in the rear channel upsized to A5 where necessary, I took the ribs off to drill the pilot holes for the lower skins to A3 on the inboard and outboard rear channels:
All holes are deburred and the parts for the rear channel are rubbed down with ScotchBrite.....
.....cleaned then primed:
To keep things straight for re-assembly with clecos, I finger clamped the rear channel to the top of the main spar:
It might seem I'm overdoing it with clecos but this is by design. Not only does this keep everything tight, but by adding a cleco in every hole I don't want to rivet yet, it prevents me from accidently doing just that and further not having to drill a perfectly good rivet out (a lesson I've learned already). The top of the doubler will be pilot holes for the top wing skin and top of the trailing edge skin, so I won't be riveting those yet. Same with the holes for the main ribs.
Same goes with the inboard rear channel doubler plate. I can't rivet it yet until I fit the first main rib (remember it tucks between the rear channel and the doubler plate). As a reminder, I filled those affected holes with clecos:
I decided it was better the lie the rear channel flat on the table to do the rivets on the doubler. Same process as every other long line of rivets - alternating holes, rivet between the clecos, then remove the clecos and finish the rest:
The centre channel doubler will be clecoed and riveted when I add the rear strut pickup. That will happen when the spar and wing skeleton get elevated up on square tubing. That will allow the flapperon brackets to be added as well.
With the rear channels complete and awaiting final assembly to the main ribs and wing skins, it was time to tackle the flapperon arms. First up was drilling the tip of the first one to A3 size. I didn't get a picture of the other three, but I did the same thing as the slat attach brackets for the nose ribs. Start with the first one, stack the rest together with a clamp and use the first as a pilot hole for the other three.
Using the same idea as the slat brackets, I laid out a work space. The plans call for the pilot hole to be 48mm below the lateral line of the wing rib back from the spar, and 894mm rearward from the spar.
To accomplish this, I laid the rib out on some boards and used a block (the purple one in the picture) as my "spar". With the rib in position, I traced it out on the board with a marker:
The crosshairs marked and A3 hole drilled on the lower board below represents where the pilot hole of the flapperon arm is positioned relative to the wing ribs as per the measurements described above:
A cleco holds the flapperon arm in position via the A3 pilot hole:
Pivoting the flapperon arm upwards and under the rib until the top edge of the arm meets the top of the rib flange as shown in the plans:
Remove the rib and the flapperon arm is in the exact position it needs to be:
Extending the lines of the flapperon arm "head" with marker lines makes it easy to reposition if necessary.....
....and allows me to visualize where the flapperon arm is relative to the rib when laying out the rivet pattern for attaching them together, This saves having to flip everything over and drilling from the arm side. A3 pilot holes are first drilled through the rib using the layout shown in the plans:
With the A3 pilot holes drilled, the arm is added back again, lined up and the pilot holes are drilled through the arm and clecoed to the board to keep everything straight and correct:
All holes, except the lower 4 are brought up to final A5 size:
The whole assembly if flipped over and a "L" bracket is added to support the lower wing skin at the rib/arm joint. The L is back-drilled suing the A3 holes then upsized to A5:
The skin support L in position on the flapperon arm:
The arm seems to stick out a long way to the rear from the rib, but it's deceiving to look at - the trailing edge skin still needs to be added to the aft of the rear wing channel. This will close the gap between the wing and flapperons substantially.
A good productive day. Next up will be the other three flapperon arms. With those complete, I can raise everything up on steel beams on the bench and start prepping the wing skins.
Even the little steps are getting me closer. Thanks for following along.
Back in the shop today. Made some moderate progress on the right wing.
I pleased that some of the lessons learned on previous sections are being applied in later sections. Since the start of this adventure, I've learned so much that some problems just seem simple now compared to before. Very satisfying.
One of the first parts I made for my plane were the root nose rib blanks. I remember being so proud of these and I should be - this wasn't something I'd done before. One thing that has obviously improved over time is the quality of my work and my eye for quality work. These original parts although fine, seem like I made them in a rush - perhaps caught up the excitement.
My originals are on the right. The tooling holes are too big and somewhat out of round. The relief holes aren't as accurate as they should be and the curve of the nose are kind of un-smooth.
I made some new ones (it took me a quarter of the time of the originals) and I'm very happy how they turned out - much nicer and certainly more accurate. The form block (I thought I was done with form blocks) fit really well with the proper size tooling holes.
To make these blanks, I used Ron's 701 templates as the design is the exact same. Unfortunately, Ron's 701 template has the tooling holes in the wrong spot on the forms, so I had to drill two extra holes to make the blank match the form. Not a huge deal, the forms made the nose ribs perfectly.
Placed on the spar in the correct position, it looks quite odd and stubby. The wing root tapers to the cabin roof line as does the wing nose skin.
For some reason, this small nose rib requires two A6 rivets, where the rest of the nose ribs along the wing use A5. I confirmed with some other builders who are using the kit that the plans are correct. I heard that Zenith used to use two A5 AND a bolt here! The A6 seems like overkill, but I'd prefer that than trying to fit a bolt.
To add to the strength here, a doubler plate is added across the spar web to connect the rear and nose root ribs. A5 rivets here too.
I had to do some more thinking on how I was going to do the rest of the slat support brackets. While I thought on that, I made the first of 2 wing tie down brackets. The step drill worked to create the large loop where tie down ropes will attach when the plane is parked out in the open.
The assembly picture guides provided online by Zenith for builders are quite detailed. Designed for the kit builder primarily, they can be good for scratch builders to get a picture in their hed how the final assembly will look. Remember, most kit parts come pre-drilled. I'm doing all the drilling.
Here the tie-down bracket is mated to the number 5 nose rib, and it gets riveted to the back edge of the rib and will be tight against the spar.
Six A5 rivets will keep this together. I won't rivet this until I can cut the slots in the lower nose skin that allows this to protrude below the wing.
While I deburred the tie down and nose rib junction, I decided the best way to keep the slat brackets the same across the 4 different ribs was to use a wood template (just like I did for the support brackets on the slat ribs).
I started with the nose rib I did last week as my template. I laid it down on the wood and drilled through the front bracket holes then clecoed it down the wood. I then traced a rough outline of the nose rib and the slat bracket onto the wood.
Removing the original, I could now cleco a new slat bracket in the exact same position as the first.
The new rib is laid over the slat bracket in the exact position as the first. A measurement from the tip of the nose rib to the clecoed bracket holes proves it's exact like the other.
Flipping them both over, I can trace the outline of the slat bracket on the face of the rib. This allows the correct positioning of the skin support L. Drill through the L into the nose rib - these will be the holes for all three pieces.
Remove the support L and lay everything back on the template board and cleco the slat support. Back drill through the nose rib into the slat support, and cleco as you go.
I made quick work of the four slat support brackets and their support L. I re-added the support L to the assembly and drilled them all out to A4 (final size). The accuracy realized by this method is excellent.
Looking outboard from nose rib #1. I have #2 and #5 removed at this point for further fitting.
With the ribs, slat supports and tie down ring fit, I upsized the rib holes to A5 (final size), with the exception of the lowest holes. I'll need to wait until the wing skeleton gets elevated off the table or flipped over - I can't get the drill level because of the table.
Definitely a productive day in the shop.
I'm waiting to hear back from a supplier regarding some 020 aluminum sheets so I can start skinning the wings. It will be top skins first, followed by bottom skins, trailing edge skins and nose skins. Lots still to do, but progress none-the-less. I also need to order some A6 rivets (I better look to seem how many more I need!) and start thinking about fuel tanks and fuel line plumbing.
I happened to glance at the Zenith online parts catalogue today, looking for A6 rivets. Did you know ONE wing spar assembly is over $4000 USD if ordered as a complete assembly from the factory?!?! That's crazy! I have probably $400 CAD TOTAL of materials into both my spars. Sure, I've spent lots of hours of labour, but the lessons learned and fun had along the way - priceless!
Thanks for following along, stay tuned for more.
Yet another delayed update on my blog. December was real busy with work (back on temporary assignment in the tech side, Monday to Friday) and the Christmas season. I didn't get the chance to post any updates - but things are coming along nicely.
I clecoed the main wing ribs to the spar, in preparation for mounting the rear wing channel.
Finger clamped the rear channel into place - very pleased with how it fits on the ribs. The ribs do have slight upward taper towards the rear, so I propped up the rear channel on shims and made sure everything was perfectly level and square.
I didn't get a bunch of pictures of the rear channel root doubler. It's made from 0.125 aluminum plate and sits inside the rear channel at the wing root end. The root rib (on the right) actually attaches to the channel slightly outboard from the inboard end of the channel and on top of the doubler. I had a real hard time getting the rear channel to line up perpendicular with the main wing spar and ribs working outboard to the tip. Turns out the rear flange of the first full rib (shown on the left) mounts to the rear channel between the doubler and channel. It doesn't sound like much, but makes a huge difference the further outboard you go. The angled root rib allows for the difference in thickness of the doubler.
Brenda invested in a CriCut Maker machine for herself for Christmas. The machine is a plotter/cutter for home crafters/makers. It's really cool; it prints, it cuts, it can emboss. Check it out here:
I got my first lesson in how to use it. Essentially you upload .SVG (simple vector graphics) to the proprietary software, modify as you wish and let the Maker machine create your items. It's real simple.
I chose some public domain SVG files of some logos for Ron's airplane and used the Maker to cut them out of basic construction paper. I was amazed at how well it cut them out. It can cut adhesive backed vinyl too among many other materials. This will be AMAZING for doing custom graphics and registration letters for our airplanes! I already have some ideas about other uses to, including cockpit panel overlays - carbon fibre vinyl anyone? So cool :)
Sometimes, I'm like a kid in a candy store. Anyhow, back to the build (focus Jason... focus)...
I noticed a discrepancy in my plans. The overall picture of the wing skin rivets show A5 rivets along the rear channel from root to tip (top of red arrows), but the side view shows A4 in the rear channel (bottom of red arrows). A head scratcher....
Here is where the internet is handy. I posted the question to the Zenith Builders Group on Facebook and with a few minutes had a better idea what should be happening here (thanks Skip Rudy for the picture below). I further clarified this with Roger at Zenith, he advised me A5 to station 2040, then A4 out to the tip, or just A5 all the way out.
With the rear channel and rib attachment points pilot drilled to A3 hole size, I took the rear channel back off the wing assembly and drilled the top holes along the length. I was so pleased with my progress.... until....
....I remembered that I should have left the top holes at A3. In my mind I had the answer, these are supposed to be A5.... eventually :( This will make drilling the holes in the skin more time consuming, but not a huge deal. At least I know they are correct.
Next task is to start adding the nose ribs to the spar. This is done by back drilling from the rear of the spar into the nose rib using the pilot holes drilled for the main ribs. When brought up to A5 size, these holes will be the connection between the nose rib and main rib, with the spar web in between.
All the nose ribs in position on the spar, perfectly level with the top and bottom spar caps.
Had to make some small adjustments on nose rib number 5 in order to be clear from the forward facing spar web doubler flange. This doesn't affect any structure, but make the nose rib fit proper (picture just after the cut was made to the flange, prior to debur):
Nose rib 5 now fits where it should:
With the nose ribs in place on the pilot holes, it's time to make the slat attachment skin support angles. It starts with a piece of standard L. Five points are measured out according to the build instructions, then drilled out to A5 size:
Notches are cut to the edges of the holes with snips, then everything is deburred with sandpaper and small round files. This angle can now be bent to form a rounded support for the nose skin.
Slat attach brackets are next. I scribed some Sharpie lines 10mm from the edges. Where they intersect is the attach holes where the slats will attach.
I stacked all four needed for the right wing, clamped them together and pilot dilled them to A3. Final holes will be drilled when the slats are attached to the wings.
I didn't capture in pictures how I got the slat attach bracket and skin support angle positioned on the first nose rib, but I used the same thinking as I did with the slats, seen on a previous blog post here
It turned out very well. This should go a long way to making the slats equal, straight and easy to install when the time comes.
Attachment in place, waiting on others to be completed (I'll likely use this one as the template for the rest). Will need to come off for debur and prime before final rivets. I might leave the rivets until the nose skins are cut and fit.
It's really starting to look like a wing with each passing shop session.
I've placed an order for more 020 aluminum as I am just about ready to skin this wing. Also need to order some Tefzel wire for the nav/strobe/landing lights and some plumbing pieces for the fuel system. So much to think of!
When a build like this all seems overwhelming (and it sometimes does - trust me), it pays to stop and admire the work being done. I sat on a stool for a quick drink of water and couldn't help notice the symmetry of the lightning holes in the nose ribs when looking in from the tip to the root. I can't believe it was over 3 years ago that I cut these rear and nose ribs out and debured the blanks. Unreal!
Thanks for continuing to follow along on my journey. Your support means a lot to me.
It's been a while since I posted, but progress continues on both wing spars. As I stated previously, I want both main spars complete and ready for ribs before starting to add the other wing structures. The wing takes up a substantial part of the work area, so the left spar when complete will go to storage while I build up the right wing. Once the right wing is skinned, it will swap into storage and I'll build up the left.
All the bucked rivets in the right wing spar are done, so it was time to final hole drill the left wing spar in prep for debur, prime and final reassembly.
This picture was taken around Halloween. The black A5 clecos and copper (orange) A4 clecos reminded me of the season!
Unfortunately, one of the holes in the spar web doubler came through very close to nicking the spar cap. Thankfully it didn't, but this will make it impossible to have enough clearance to drive the rivet with the bucking gun. Solution was to drive the rivet from the other side - not ideal, but perfectly acceptable according to the build standards.
With all the holes now complete, it comes all apart for debur, prime and reassembly.
When I was reviewing the drawings, the question of dissimilar metal corrosion (called a galvanic reaction) came to mind. Galvanic corrosion (also called bimetallic corrosion or dissimilar metal corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. The electrolyte in this case can simply be environmental humidity. Salt water exposure would be worst case scenario.
The aluminum spar attachments are made of aluminum. The connection points on the struts and front of the cabin frame are 4130 steel. I did some research on the forums and it seems most people just ensure they have good prime/paint on both parts and/or powder coating on the steel parts.
So what does the aerospace industry do? They anodize their parts.
Anodizing in the simplest of terms is a process of increasing the thickness of the natural oxide layer on the surface of a metal part. This thickened oxide layer renders the part non-conductive electrically, thereby preventing galvanic reaction with other metals. The anodized aluminium layer is grown by passing a direct current through an electrolytic solution, with the aluminium part serving as the anode (the positive electrode). The current releases hydrogen at the cathode (the negative electrode, either lead or aluminum) and oxygen at the surface of the aluminium anode, creating a build-up of aluminium oxide on the part.
This doesn't however change the dimensions of the part as the layer is nano-metres thin.
Sounds complicated, but is actually simple enough to do in the shop. There are literally dozens of YouTube videos online showing different methods for doing this. Many home hobbyists do this when making parts for their car, computer cases, flashlights etc.
I managed to find a good article in KitPlanes magazine which was simple enough I thought I'd give it a go for my strut pick-ups and spar attach brackets. In the end, if it it didn't work, I can always just prime and powder coat where necessary. The over-riding mantra of my build is to learn, so this is something worth trying.
There are several components needed for the home anodizing process, which I'll try and detail here in pictures.
I scored a small aquarium air pump at the thrift store - 2 bucks. A new piece of air tubing for $3 and a air-stone for making bubbles in the electrolyte $5 from the local pet store. The purpose is to agitate the electrolyte, essentially circulating the solution as the process happens.
Distilled water which makes up the majority of the electrolyte solution. A thrift store kettle for $5 - I should have bought a larger one as the parts once complete need to be boiled in distilled water for an hour to seal the anodizing coat (more on this later). Baking soda to neutralize the electrolyte bath acid and also to contain any spills.
The main electrolyte bath tub.
The main rinse/neutrailizing bath - warm distilled water/baking soda solution:
My electolyte bath is a 10% solution of Muriatic acid and distilled water. I followed the measurements closely and all the warnings of adding the acid to the water slowly. Never add water to acid - always acid to water. The thermal reaction is easier to control by adding acid a little at a time - it can be explosive if you do it the other way around! Pay attention closely to the instructions. Muriatic acid is nasty stuff, so wear gloves, goggles and breathing mask. Make sure to use a well ventilated area.
Before the parts can be anodized, all residual oils, markings and natural corrosion must be removed. The easiest was to do this is using household amonia. Again, proper gloves, googles and respirator mask - this stuff is hard on the eyes.
I proped everything up on some bent metal strips to allow full circulation around the parts. The parts sit in the bath for a while.
For the negative plate in the anodzing bath, I used a piece of scrap aluminum sheet that had too many dings/creases in it to be useful for anything else. I cleaned it with lacquer thinner and made sure it was completely dry before bending it to shape inside the acid tub. The more surface you can expose to the bath and parts the better, so it's bent up both sides of the bath.
Checking back on the ammonia bath, the parts are starting to bubble - a good sign that any contaminants on the surface are being lifted away. I don't have any pictures, but once I was satisfied they had soaked long enough (about 30 mins), I used a clean 3M scrub sponge to wipe them down, then a spray bottle of distilled water to rinse them off. A good indication that the part is completely clean is when the water spray refuses to stick to the aluminum and jut flows off. Water beading on the part means contaminants remain. Mine parts just flowed the water freely. It's important to not touch the parts at this point without clean gloves as any natural oils on your skin will contaminate the part again.
As the parts are left to air-dry, I prepared the anodizing tub. I connected the negative lead from the power supply to the aluminum plate in the tub (the cathode).
The process is hard to capture, but the next steps are to hang the parts in the electrolyte acid bath from aluminum wire. The parts need to hang freely, not touching the other parts or the cathode. The positive lead from the power supply is connected to the parts via the hanging wire. The circuit is now complete and the power supply is engergized. The airpump is also turned on. The following pictures are of the anodizing bath well underway. The electrolyte solution is fairly cloudy by this point, making it hard to see the parts.
The voltage and current applied is calculated with an online tool, using the total square area of the parts to be anodized and what thickness you want the anodized layer to be. This gives you the starting voltage and current and how long the circuit needs to run.
As the anodizing takes place and the oxide layer builds up, the current slowly diminishes to almost zero as the parts no longer can conduct the current. A good indicator other than the readings on the power supply is the distinct reduction of bubbles coming off the parts.
Very close to the time to shut off the circuit, the bubbles coming off the parts took a dramatic downturn as expected. I waited for the time to run out and stopped the power to the circuit and the air pump. The parts are carefully lifted out off the acid bath and immediately dunked in the soda bath to neutralize the acid on the parts. With gloves on, sloshing the parts around makes sure the acid is fully removed from the parts. Once satisfied the parts are "neutral" they get boiled in fresh distilled water to seal the oxide layer. It's at this step that some people add dye powders to the boil to colour their parts. Iwas thinking of doing this, but decided colour wasn't import as I was going to prime/paint the parts as well.
Overall the process of anodizing went ok and I learned a lot. In hindsight, I'm not sure it's worth all the effort when prime and paint will suffice. There is also anti-galvanic paint on coatings that they use in marine applications. I'll look into those as well. The complexity of the system and process turned out to be too big a distraction from acutally building. It would have probably been easier to send them out to an anodizing shop, so my foray into anodizing is over, but in the end I'm smarter about it now than I was.
With the left spar primed and reassembled, I finished bucking the last of the rivets in the spars.
The spar pick-ups have been primed at this point on top of the anodizing I did. I need to order some AN bolts to go with them and the strut pickups (should be here next week). They look fantastic!
With the spar now essentially complete, it is time to start lining things up to ensure the spacing of the ribs match the spacing of the slat and flapperon pickup brackets.
I stood the spar up and anchored it to the bench. I started to add the ribs temporarily using small clamps at the spar and masking tape:
With the ribs in place temporarily, I clamped the nose rib slat attach brackets. These are only in the lateral position for now to allow for lateral measurement. They actually sit up higher on the nose ribs when mounted.
I did the same for the flapperon brackets at the tail of the rear ribs. Preliminary measurements show that the slat and flapperon bracket positions are perfectly matched to the slats and flapperons. This allowed me to drill the pilot holes in the spar for the ribs.
Next up for assembly is the rear wing channels - an inboard and outboard.
I previously had these channels bent by a professional shop as we don't have a suitable bender available at this length. The inboard channel has a support angle across the top. I laid out the angle rivet spacing and drilled out to A3:
The inboard and outboard channels are joined by a splice channel at the rear strut pickup point.
I laid out the splice channel, drilled out the holes to A3 as per the plans.
With the holes complete through the splice channel and the rear channel, I laid out the rear strut pick up. The plans aren't completely clear on the placement, but with a little figuring I was able to confirm the placement.
I clamped the strut pickup in place to the splice channel and backdrilled through the splice channel, ensuring accurate line up of the holes for the entire assembly:
The rivet spacing is tight here and one of the holes is actually for an AN3 bolt. Before drilling the holes out to A5, I finished adding the strut pick-up AN6 bolt hole:
Moving the clecos to the underside, clears room to work with the drill to brig the holes up to A5 size. The far right row of rivets is where the tail end of a wing rib attaches through the channel and splice channel. I'm leaving them as A3 until I fit the rib. I'll have to decide if I want to debur, prime and rivet this section first, or wait until final fit up of the wing ribs.
I did the same at the root end of the rear channel. Lay out the rivet pattern, then back drill through the root plate (a .125 plate inside the channel) that supports the rear channel attachment to the cabin frame.
With the placement of the nose and rear ribs confirmed earlier, I could drill the remaining pilot holes in the rear channel for for the rear rib attach points. Until the wing ribs are in place, I'll wait to debur and prime everything before riveting. After this picture was taken, I drilled everything out to A5 size and trimmed the outboard end of the channel to length and taper (more on this later).
Before final layout of the wings, I decided it was probably best to confirm the work table was completely flat, so I cleaned it off completely. It still was very flat and required almost no adjustment. It was weird to see it so empty!
Making sure the spar is completely straight laterally, vertically and no twist is critical. This is accomplished by using the flat table as a reference. The right angle towers are placed at each end across the rear face of the spar and secured to the table. A tight string line between the outer uprights gives a straight line reference for the other uprights. My spar is straight in all dimensions.
The camera shot give the impression this is far from vertical. It is, confirmed by inclinometer - the view is an optical illusion.
With the spar completely vertical and straight, I started to add the rear ribs. I back drilled through the spar web and into the rear rib flange, using an upright bubble level to ensure the rib was square up and down.
Very happy how this is going. The ribs are a perfect match to the spar. Once I have all the rear ribs in place, I'll remove them one at a time and repeat the process for the nose ribs one at a time, back drilling them through the rear of the web.. This will ensure they too are lined up exactly correct.
Lots to go on the wings, but they are starting to come together. I'm back to Monday to Friday schedule at work, so I should be able to get to the shop more regularly, perhaps one or two nights a week and a full day on the weekend. Hopefully my blog will keep up!
Thanks for following along.
Limited time at the shop this week as I concentrated on some home/cabin maintenance that needed to be done.
Pulled the right wing spar assembly apart again for deburring and prime. Took almost an hour just to scuff everything with Scotchbrite, and clean down with lacquer thinner in preparation for prime:
The self etching primer dries fast, but I decided to let everything cure for a couple of days. When I came back to the shop, I was ready to reassemble the spar.
I cleaned off the bench completely in order to make room for the assembly process.
Like the stab, elevator and flapperons, it's important to have a flat "surface" to assemble on. I placed the steel angles on the bench edges and lined them with painters tape to keep their surfaces smooth. Before adding the cross members again, I started the process of riveting the spar back together:
Acceptable practice for rivet placement is that the head of the rivet should be on the surface of the thinnest material being assembled. The centre spar doubler is 063 and the spar web is 032, so I started by first completing all the pulled rivets called out in the plans for the spar. To do this, I flipped the spar over and pulled the rivets from the aft side. I also attached the wing spar tip while in this position:
The root doubler and spar web are both 032, so it doesn't matter which way rivets are pulled and the plans don't have directions on this. I decided for consistency to pull them in the same direction the driven rivets will be along the spar caps:
Driven rivets are called out in the plans for most of the spar and depending on their location they have different lengths before being formed. The length is dependent on what thickness of materials are being joined. We don't have any rivets in stock that are correct length for some of the spar cap/spar web/centre spar doubler interfaces. There aren't many of them, so instead I used a rivet cutter to shorten a few longer ones (made -9 rivets which we have lots of into -7 rivets).
There are very specific standards with regards to properly formed driven (bucked) rivets. The formed tail of the rivet MUST be 1.5 times the diameter of the rivet tail once bucked.
I originally thought I'd be able to use the hand squeezer to form the rivets along the spar caps but I decided to test that theory first on some scrap material. This also confirmed I had the correct length of rivet for the thickness of the material (trust the plans but verify!). I used a piece of aluminum angle and 032 sheet to simulate the spar cap/spar web and discovered the A5 driven rivets are much too hard to squeeze by hand - I couldn't squeeze hard enough on the tool to get the correct formed head dimensions.
Putting the hand squeezer away, I got the air rivet set out and attempted to drive the first rivet. It went much easier than I expected and once I developed a feel for it, I got good at estimating the amount of time on the trigger to set the rivet correctly. The shank of an undriven A5 rivet is 4 mm in diameter, so the formed head needs to be 6mm in diameter.
It takes a bit more time than pulled rivets, but the evolution is the same. Place the rivet in open holes between the clecos, drive/form with the rivet gun/bucking bar then repeat on the next empty hole. I started with the top spar cap and measured each formed rivet for conformity as I went along. Once I had alternating holes done, I removed the clecos and filled in the rest. Next was the spar doubler and strut pickup angles. These were driven from the other side to respect thickness/rivet standards.
Then I repeated the process for the bottom spar cap:
Laying the spar down on the cross tubes of the bench confirms the spar is completely straight and true - very happy as everything that attaches to the spar is relying on this. It's amazing how stiff the assembly is and that without all the clecos it weighs much less too. The wing attach point still needs to be anodized before it gets riveted onto the spar, I'll be doing that this coming week.
Once I have the anodizing done on the wing and strut pick ups done, I'll add them to right wing spar - these have much longer rivets. Then I'll get all the spar cap holes on the left wing spar upsized to A5. Then the process of disassembly, debur, clean, prime and reassembly begins, followed by doing some more buckin' rivets!
Getting closer every day. Thanks for following along!
A couple of really productive days in the shop this past week, but not many photos to share.
Started the final fit-up of the upper strut fittings. The plans call for the strut fittings to extend 107mm from the lower wing skin. To make fit-up correct, I scribed a line 107mm from the rounded tip:
With the strut pickup held in position against the angle, it's a simple matter of lining up the scribed 107mm line with the bottom of the spar. The skin is 020 here, so the line is very slightly past the spar:
I drilled the strut/pickup interface hole as per the plans, but the plans don't really define the spacing of the mounting bolts that attach it to the strut angle. Base doin what I see in the plans, it appears to be evenly spaced, so that's what I went with. It started with A3 pilot holes in the pick-up:
Clamping the strut pick-up tp the strut angle in the correct position. The camera angle makes it look like the scribed line is inside the spar line, but it is actually where it needs to be. From here, I drilled through the strut pickup and into the angle. Once I had a couple of clecos in place, i removed the strut angle from the spar and took both to the drill press to enlarge the 3 pilot holes up to AN3 bolt size (sorry no pictures). The bolts will be added after everything is deburred/primed.
The next step was to take off the strut assemblies, the web and root doublers and L stiffeners to permit the spars to lay completely flat on the drill press. Without these doublers, the spars are fairly stiff, but they are still long and challenging to move around the shop. Must be careful not to introduce any unwanted twist.
To accomplish cutting of the lightening holes on the drill press, I set the spar on a movable workstand at the one end:
Fly-cutter in the drill chuck. The yellow tape flag has a written note on it as a reminder that the cutter was already set for 95mm diameter, but I double checked anyhow. The spar web sits flat on top of a piece of plywood that fits between the bottom of the cleco pins. It supports the back side of the web as the cutter scribes it's circle:
I used a level on the web between the drill press and work stand to ensure the spar was completely flat for drilling:
Started cutting the lightening holes at one end of the spar, then worked inwards to the next, clamping the spar to the plywood and drill press work area. Cutting with the fly-cutter is always an adventure, but securing the piece, lubricating the cutting head with a bit of WD-40 and using slowly increasing pressure goes a long way to making good clean circles.
There are 5 lightening holes inboard of the web doubler and 4 outboard. With the inboard ones done, I flipped the spar end-for-end and drilled the outboard ones. The I repeated this whole (hole?) processes on the 2nd spar.
I'm really pleased how the process I came up with worked out. It wasn't complicated and went fairly quick, but I always have a certain amount of trepidation when using the fly-cutter. If the cutter jams or grabs the material it could damage the web material beyond repair, meaning redoing the entire spar (a very expensive mistake). Thankfully, I didn't have any issues with either spar. Here they are, back on the bench awaiting deburr and flanging of the holes. You can see in the bottom right that I hadn't trimmed the spar cap of the left wing yet, but that has been done since this picture was taken.
With the lightening holes deburred, I followed the same process as the wing ribs. The flanging die and two large C clamps worked well using the corner of the bench to reach from both sides of the spar.
In order to accommodate the length of the spars, I had to switch corners of the bench. Maggie the shop dog/chief inspector was kind enough to move out of the way for me when needed - even if she doesn't look impressed in this picture :)
Even more so than when the lightening holes are cut, it's important that the spar is lying flat for flanging the holes. I used another piece of thin plywood to support the spar at the opposite end.
I did get and answer about the rivet spacing on the spar web doubler from Zenith - my theory was correct and I can shorten the rivet spacing to 20mm without issue.
With most major fit up and drilling complete on the spars, next up will be pulling everything apart again for final deburring edges and holes and priming of the mating surfaces. Then I'll begin the process of reassembly with clecos in preparation for driving and/or squeezing the solid rivets. I want both spars complete and ready for wing ribs and skins. One spar with the assorted ribs and other parts will go into storage while I work on the other to make room on the bench.
Another item on my list is deciding on the best way to prevent dissimilar metal corrosion (sometimes called galvanic reaction corrosion) on the spar and root pickups. I'm considering some DIY anodizing of the aluminum parts using simple chemistry theory. More on this later :)
Thanks for following along!
More progress on the spars and associated parts for the wings.
While using the bandsaw and bench top sander for other parts, I cut out the fuselage side wing attach plates. The inside corners are 6.4mm radius which is too tight to cut on the bandsaw, so I used a 1/4 inch bit to make the holes, starting with a centre punch for accuracy:
With the holes done, I cut the rough shapes out with the bandsaw. The rest of the shape will be formed using the bench sander.
Here are the pair awaiting final shaping with the bench sander. These attach to the back top corner of the cabin frame. The rear spar of the wing attaches to the small round ears at the top left and right. The ears get drilled when the wings are installed. They are thick (0.188 plate) - quite heavy but very robust.
The 8 wing side slat pick-ups, 2 wing rear strut pickups and cabin attach plates are almost ready for prime:
Wing flapperon attach arms are all rough cut out awaiting final bench and hand sanding:
I cut the spar web doublers for both wings to size and bent the top flanges. The inboard and outboard sides of each doubler are not the same length, so before bending I checked and rechecked the dimensions and orientation and labled them on both sides to avoid any confusion to how they orient on the spar:
It's hard to see in the picture, but the right wing spar web doubler fits nicely on the spar in the correct location (both left and right spars are back to back and the one closest to the edge of the bench is actually upside down). If you recall, I specifically didn't drill all the holes in the spar caps in this area as I planned on doing them with the doubler in place to keep things accurate. To keep the upper flange of the doubler in line with the top of the spar I used a couple of pieces of straight tool steel to line everything up:
With everything double checked and aligned, the doubler is clamped to the front face of the spar:
With the doubler in place I scribed the rivet line along the spar cap to get a couple of the holes started. While I was at it, I laid out the rivet line that follows the inboard edge of the doubler. The more I can secure the doubler as I go, the more accurate the following steps will be.
No issue with the layout being 10mm from the edge of the web doubler, but the plans call for 12 A5 rivets at 25 pitch along this line and it has to be into the web between the spar caps on the other side. So according to math, this means I need 325mm of space between the spar caps:
(12 rivets + 1 extra space at one end) x (25 pitch) = 325mm.
I tried several times to see where I was going wrong on the spacing. The total distance between the spar caps as measured on my actual spar (which is perfectly accurate as to the plans) is 255mm (as shown in the red dimension line I added to the above picture).
With 255mm available and using the same math I can extrapolate the required pitch to make 12 rivets fit on a 255mm line by rearranging the equation to solve for pitch:
(255mm line) / (12 rivets + 1 extra space at one end) = 19.615 pitch
So..... not exactly the same and not an easy round number for pitch. 20 pitch is the closest, but that means I'd need:
(12 rivets + 1 extra space at one end) x (20 pitch) = 260mm.
But that assumes I need a full 20 pitch space between the edge of the spar caps and the first and last rivet in the line. So what I propose to do is keep them at 20 pitch for ease of measurement, but shorten the space at each end between the last rivet and the spar cap line enough to miss the spar caps, perhaps make the space at each end 18mm.
Man, I never thought all the math and equations I disliked in school so much would eventually come in handy! What I can confirm is there is no physical way to place a line of 12 rivets on 25 pitch on 255mm. I've sent an email off to Zenith to see if 20 vs 25 pitch is acceptable and I imagine it is but I'll wait for confirmation before drilling holes here.
With the first couple of holes drilled through the doubler, I flipped the whole spar over and back drilled through the spar caps from the backside of the spar on the confirmed rivet spacing.
With the doubler in place and secure enough, I started to fit the front strut angle. I'd already cut the angles to length when I was cutting the spar caps. Now I needed to figure out how to trim the upper end. As usual, I needed to pay close attention as the drawing can be hard to interpret and I'm working on the right wing strut angle (the plans show the left one as the example). I sketched out what I figured was correct, trimmmed it close and placed it in approximate place on the doubler to check if it made sense and would be oriented correctly:
I flipped the spar back over so the forward side was facing up. In order to ensure proper placement of the strut angle, I extended the rivet hole lines from left to right and up and down from where the bolt holes will attach the ends of the strut angle. The angle does not follow the edge of the web doubler, it actually starts at the top outboard edge and crosses the spar doubler lower edge and spar cap just inboard of centre:
I scribed a line on the lower side of the strut angle as per the measurements on the strut drawing. I also scribed a line across the bottom flange of the lower spar cap. When the two lines are aligned, the strut angle is clamped in the correct position. Lifting the spar upright, I back drilled from the spar cap side, through the web, the web doubler and the strut angle. The assembly is clecoed togther and the overhanging corner of the strut angle will be trimmed after:
Flip the spar end for end and follow the same procedure a the top end bot hole. Clamp and back drill through from the other side.
Maeasure again to confirm fit and all is good. Lay out the rivet spacing. Use a spring punch to pilot the holes, drill to A3 and cleco:
Stand the spar on the bench upside down. Here you can see how the strut angle doesn't follow the angle of the web doubler edge:
Mark the excess strut corner for trimming:
Remove the strut, rough trim with the bandsaw then bench sander to clean things up. Final sanding during debur will make this really clean.
That's it for this update. While I wait for an answer from Zenith regarding the web doubler rivet spacing, I'll get the lightening holes done in this wing and flange them and I'll start to fit the strut attach pickups. I'll probably drill what holes I do know out to A5 as well as the top and bottom A4 bolts in the strut angle.
As always, thanks for following along.
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.