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.
Good hours spent in the shop while I pondered how it could already be 19 years since that tragic September morning. I'm so happy we have the freedom to chase our passions.
Finished up the spar root and front upper strut fittings. Did the rough cutting on the band-saw to approximate shapes (the card stock templates shown in the middle were made early on this process in FreeCAD software):
Two spar root fittings after cleanup on the grinder and rough hand sanding. Final fine sand will be completed just before primer and rivets as I still need to fit them to the spar and drill the attach bolt holes.
Laid out the location of the wing attach bolt holes. It's important to be consistent here. Length of the wings from where they each attach at the cabin frame must be equal for rigging purposes when the wings are installed. The circled crosshair point is the centre of the bolt hole. My holes will be round, not sketchy round like the marker shows!
Right wing spar in the upright position. I clamped the spar attach fitting to the spar cap in the correct location ensuring the bottom lines up exactly flat with the lower spar cap and sticks out the appropriate distance from the root end of the spar as per the plans. I used a flat piece of tool steel to do this, the plywood of the table top isn't a reliable flat reference.
I laid the spar down and back drilled through the spar cap using a block of wood as a backer up to A3. The rivet spacing here is 20 pitch eventually up to A5 size:
Up sized the holes to A4, then removed the spar attach fitting for matching up with the one for the left wing spar:
My original plan was to stack one on top of the other and back drill through the top one into the other, but I figured the most critical dimension was the bolt holes. If the attach fitting to spar holes aren't exactly the same that doesn't matter as much as the bolt holes being equal.
Stacked the attach brackets on top of each other and pilot drilled the bolt hole location throught the top one and just starting into the lower one. Attempting to drill through both by hand can lead to out of round holes or slippage despite the clamp used to hold it down.
Then I used the drill press to final hole size each of them to AN7 which is 7/16 inches (I confirmed this in the plans and on the cabin frame attachment points to be sure). I also drilled out the A3 and A4 size holes required in the right attach bracket (not shown in this picture, but you can see them in subsequent photos at each end of the 20mm rivet pitch lines)
Next step was to start the left wing spar, following the same procedure that worked so well on the right wing spar.
With the spar caps and stiffeners added to the second spar, I wanted to figure out a way to make the spar tips exactly the same, i.e. both wings from root to tip exact same length.
It started by using a scrap of angle as a base line zero measurement point at the root end.
Placing the spars back to back (or spar top cap to spar top cap actually) I clamped them together in parallel at the root end and at the spar web outboard end. I confirmed the spar webs and caps are equal length.
With the right spar as the guide or "master" I added the matching left spar tip and clamped it in place. Essentially the left spar is now a mirror copy of the right.
Finger clamp at the far most tip end keeps things exactly where they need to be.
The left wing tip is pilot drilled to A3 to match the right. Final measurement confirms both wings are exactly the correct length as per the plans. Very happy.
With length confirmed correct, I fabricated the root doubler for the left spar. Here it is clamped in place for fit prior to match drilling and having the flange trimmed. It was easier to make the bend and trim it than guess at the width of the flange. Think smarter not harder my grampa used to say!
Flange trimmed and spar laid down again for layout of doubler rivet holes. Still need to trim the upper spar cap to match the taper of the spar web and doubler.
With the doubler in place and complete, it was time to compare the attach brackets again and confirm the bolt holes will have the same extension from the spar root. Lining the second (left) bracket up against the first (right bracker) while it is attached to the right spar and using a square confirms they are the same. Measuring the extension on the first (right side) confirms 39mm from spar root edge to the outisde of the bolt hole.
Using the same measuring points, I clamped the left attach bracket to the left lower spar cap and pilot drilled exactly matching the rivet spacing of the right wing. Double checking the bolt hole distance I confirmed both bolt holes are exactly same on both spars, meaning they are true mirror copies of each other for length. More happiness!
The twin spars lined up bottom to bottom. Very happy how these are so far, but I have a bunch still to do for these to be a complete assembly for the wing. Still need to trim the upper spar cap to match the taper too.
Next up, cutting and forming the 063 web doubler plates, adding the front upper strut angles and fittings. After that cutting the lightening holes and flanging them (that should be "fun"). Then it all comes apart again for debur, prime and re-assembly prior to final driven rivets.
Onwards! Thanks for following along :)
Another successful week in the shop.
I continued to work on forming and flanging wing parts. Last blog post I had started the forming of wing ribs, starting with the root ribs. Here they are out of the forms - I'm happy how they turned out and using the hardwood dowel to work the metal flanges into the flutes on the forms made forming the curvatures of the flanges much easier.
As I mentioned before, I'm using Ron's 701 nose ribs forms. The trick here was to pre-flute the blanks as the 701 forms don't have flute channels cut in them.
In the vice, I start by bending the flat trailing edge flange over as it is straight and does'n require any fluting. Then the bottom flange, working forward towards the nose.
as I got close to the nose, I carefully worked the nose flange over, drawing the aluminum across. The metal backing plate on the forms really helps in the this regard.
A little cleanup with a small tack hammer backed up by a body work anvil and some tweaking with the fluting pliers and the nose ribs are ready for lightening holes.
Six left and six right, enough for both wings
Lightening holes are cut on the drill press using the fly-cutter, set to the diameter of the flange dies (which are exactly to plans - in the case of the nose ribs is 115mm)
Lightening holes cut and deburred, awaiting flanges.
Next up, the wing ribs. I used the exact same process here as the root ribs with a couple of modifications. I stacked all the blanks together and drilled the pilot holes as a stack to ensure consistency in the forms. Each of the ribs has 3 lightening holes, however two of the blanks have no third hole, so I pilot drilled those separately from the rest, but using the same layout as the others.
First blank/form in the vice and from here the forming is the same as the root ribs - using a hardwood dowel to massage the flutes. All ribs are made from the same form, regardless of lightening hole requirements. I added a small clamp at the tail end of the form to keep the forms tight.
All my wing ribs formed and lightening holes cut awaiting debur and flanges. The two wing ribs on top are the two that only require front lightening holes, the rest underneath have three holes.
Took the day Thursday to travel to Sudbury and pick up a sheet of 063 aluminum and some flat stock needed for the wing and strut pickups. I also grabbed a small chunk of 0.188 plate for the fuselage pickups. This supplier is much cheaper than Aircraft Spruce and much closer to home.
I was pleasantly surprised to find the sheet came on a well strapped pallet which fits nicely in the back of our truck. Over packaged for a single sheet, but it didn't cost anything to me, so that's good!
When back at the shop Friday, I planned on cutting off the pieces I need immediately for the spar doublers. I laid out the rough dimensions while the sheet was still on the back of the truck. This allowed me to nest them a bit and save waste. All set to rough cut but unfortunately mother nature had other plans and a downpour forced me to abandon the plan and just unload the sheet off the truck for next time in the shop.
The flat stock is perfect for the spar and strut pickups, and the flat plate works for the rear wing/fuselage pickups.
I'm so fortunate to be able to use the tools and jigs and bending equipment of Ron's, it's saving me untold hundred of dollars. One of the best examples of this are the flanging dies Ron had custom made at a machine shop.
In the front of the picture below are the two halves of the 115mm diameter flange die - female side on the left, male on the right. It's easy to see the shoulder on both that creates the flange on the lightening holes.
The process is easy. Place the blank over the male side....
Invert the female side and place it on top (carefully - the dies are heavy tool steel and dropping them will permanently damage the blank and maybe the die as well!)
A shop press would work well here, but two large C clamps and the bench-top edge work just as well. Make sure to use two clamps the same so equal turns on the handles makes even clamping force on the dies. I did four turns on each at the same time, going about a half turn each time and it worked well.
The distance to compress the dies together isn't much. Top photo before compression, bottom photo at the end of travel.
Take the dies apart and the flange is complete - total time about 2 minutes each once I got into a rythym.
The process is repeated for the wing ribs, using the correct flange die size where appropriate.
The smallest flanging die only requires a single C clamp centered over the hole. Credit to my daughter Caitlyn for taking some of the following photos of me working!
After about 90 minutes, all the wing, wing tips, root and nose ribs for both my wings are now flanged and ready for fitting on their spars.
Something really cool looking about the symmetry of wing and nose ribs laid out side by side on the table
Next up, I'll get the 063 spar web doublers cut from the sheet I bought, bent and fit one to the spar. Then I can proceed to add the spar pick up, the strut angle and strut pickup. With everything fit, I'll drill/flange the lightening holes, begin drilling all the holes to correct A5 and A4 where needed. After that, disassemble, debur, prime and reasemble for final riveting. Just a few more steps!
Thanks for following along, it was a productive week indeed!
Busy couple of weeks since the last blog update, but lots to share.
I continue to assemble the wing spars and gather the remaining materials and make parts for the wings.
With the spar webs cut, it's time to layout the lightening hole locations along the web, and cut the spar cap angles. These form the top and bottom of the spar. It starts with a centre line along the length:
Measuring outboard from the root edge, I made a hatch mark for each of the lightening hole locations:
With the locations laid out, I stacked one spar web on top of the other, secured them with clamps and drilled pilot holes through both - this means all lightening holes in each spar are in exactly the same location.
Next up was cutting the bottom and top spar cap angles using the chop saw. I left them a couple of mm long to allow for filing and sanding the ends smooth as the chop saw cuts fairly rough..
Here are the first pair, roughly laid out on the right spar web. You can see in this picture I've marked up each of the webs with a Sharpie so that I keep everything straight as to which way is up/down/fore/aft and a rough idea of the lightening holes. This is important as I want to use the factory edge on each of the spar webs on the bottom edge of the spar and as my reference for measuring the height of each assembly.
With the lower spar cap lined up with the factory edge and clamped in place, I laid out the rivet lines on the spar cap angles. These holes will eventually be filled by A5 solid rivets. I measured and double/triple checked the layout to ensure everything matches the plans. It's easy to be off a couple of millimetres at the beginning that translates to being off several millimetres at the other. The rivet pitches also vary a bit near the middle of the spar too where the spar web doubler and strut pick-ups are located so those have to be carefully considered too.
Drilling all the A3 pilot holes in the spar caps left a LOT of swarf!
At the bottom of the spar at the root I only drilled one pilot hole to begin the process of lining up the spar cap angle. There are several holes and bolts needed here in the spar cap angle, but I have more components to add including the spar root doubler and the spar root pickup. It will be easier to back drill from the opposite side - pilot holes for spar root pickup will be laid out and drilled on the drill press for accuracy and ease.
To start the process of matching up the lower spar cap to the web, I used a straight steel block. The web sits on a board to back up the drill bit, tight against the block and under the spar cap angle. The spar cap angle is exactly even with the end of the web, forming a perfect corner. Drill through the pilot hole to A3 size - this hole will eventually drilled out and filled with an AN bolt.
I secured the inboard end of the lower spar cap with a cleco, then used the same steel block to line up the web and lower spar cap again moving outboard. A clamp kept everything straight as I drilled the next holes:
Every tenth pilot hole was drilled though the cap and web. A long piece of HSS square tube confirms everything is remaining straight as I go:
With the spar cab and web confirmed as straight and true, I finished drilling the rest of the holes between, checking for straightness each time:
I left the section un-drilled between each end of the spar web doubler location (shown as red angled lines). I'll wait to confirm fit of the doubler and the front strut pick up angle once they are made and fitted. I may back drill these like the spar root depending on how the fit up goes.
With the lower cap in place, i started to layout where the top spar cap will be on the web and the associated rivet lines. yes those are my red Crocs.... don't judge.
The upper spar cap is initially cut long enough to overhang the web where it tapers. This will be trimmed off later to match the doubler which gets added here at the root (more on that later). The rivet layout at this corner is non standard, so for my first hole, I chose the first standard rivet spaced on along the cap. I used a ruler underneath everything to make the spar height exactly 209mm as per the plans and secured it:
Pro Tip: Be careful your pilot hole isn't over top the ruler when you drill through the web! Better that than a finger I suppose!
With the spacing between spar caps confirmed and triple checked, I used a carefully cut wooden spacer to make each of the subsequent holes along the upper spar cap exactly parallel to the bottom one. I started with a wooden block close to the length needed to fit between the caps, squared the ends on the band saw, then slowly sanded each end until it fit snug but perfectly between the two.
I copied the process all the way along, doing every tenth rivet and double checking the spar height each time. The caps are perfectly parallel and the spar height is bang on 209 mm. I finished of the rest of the holes to A3, skipping over the section where the spar web doubler will be. All the holes, top and bottom are A3, eventually will be up sized to A5 for solid rivets. The whole spar assembly as it sits now is already very strong.
Flipping the whole assembly over, I checked the rivet lines and confirmed the spar height as correct. I also started to formulate a plan for the spar root assemblies, spar web doublers and how to trim the upper cap angle taper effectively.
Next up is the spar tips. Made from 025, I bent these a while back when I was working on some 025 sheet work. They too have lightening holes, which I laid out and completed with the fly-cutter on the drill press.
Both tips with lightening holes cut and ready to be flanged. These holes are exactly the same diameter as the ones that will be in the spar web, so I marked the cutter with a flag note stating it was already set. Once I get the spar lightening holes cut, I'll flange them at the same time as these.
To ensure the spar tips are perfectly square and parallel to the spar, I flipped the spar back over and clamped a spare piece of angle to the bottom spar cap angle, measured exactly where the tip should overlap the spar end and marked it for pilot holes.
The red line on the left is the rivet line for the spar tip where it attaches to the spar web. The red line on the right is the rivet line station for the outer wing and nose ribs. It has a different rivet spacing, so I'm leaving that alone until the ribs are ready for installation. This will allow a small adjustment to compensate for any variance on the pickups in the slats, which will be installed on the wings later.
Four A3 holes evenly spaced between the spar caps. These will eventually be A5 pulled rivet holes.
Flip the spar back over. Layout the rivet holes in the ends of the spar caps as per the plans. Clamp it all together. I found it helpful to extend the whole thing over the end of the bench for this.
Back drill through the spar caps through the spar tip and secure with clecos:
Extremely happy with everything so far. The spar is dead straight, dead on 209mm tall throughout it's length and distance from root to tip is exactly as in the plans. Straight and rigid enough to stand on it's own! I'm waiting to pick up some aluminum sheet and flat stock later this coming week to make the spar pick-ups, the spar web doublers and front upper strut fittings..
I had a couple of hours for the shop one morning, so I decided to start modifying my wing rib templates. I've had these made for many months and now that I'm ready to start forming wing ribs I wanted to re-visit their layout. I'd experienced some issues forming the slat ribs and thought I could address this on the Wing ribs. I marked the location of flute relief on both the left and right side templates. This will eventually make forming the curves on the bottom and top of the ribs easier.
I started cutting the flutes using a small drum sander on the Dremel tool. It worked really well (more on these later).
Back in the shop the next evening, I started to form up the 032 spar root doubler. It was relatively easy to make as I had experience from installing a missing one on the 701 wing repair (click here for that part of my story).
It starts with bending a flange on the outboard end, then trimming the doubler to match the taper of the spar web, leaving enough width to bend a second flange to match the taper.
With the doubler bent correctly, I laid out the rivet lines for the upper perimeter and back drilled through the web out to A3, using the bottom spar cap angle as a guide to keep everything straight. (it's hard to see it here as it is underneath the inboard spar web):
Flip the spar over and lay out two rows of rivet lines, 5 rivets between spaced between the spar caps:
With the spar doubler drilled, clecoed and and confirmed as correctly positioned as in the plans, I removed it again in order to better see where I need to trim the upper spar cap angle. I marked a line on the angle using the web as my guide.
The next part was quite challenging - using the chop saw to make the accurate angle cut on such a long and un-wieldly piece of angle. I managed to get it close enough, but boy the chop saw makes ugly work of the cut:
The black line represents everything actually left to trim back for a perfect match to the spar taper. I used an angle grinder to gently remove more material using the spar doubler as a guide until it was perfect:
As I got close, I switched to a hand file, taking it down until it was perfectly level. Some final sanding to round off the sharp edges and it is complete:
Putting it all back together, I began laying out the rest of the root doubler rivets and drilling them out to A3. The plans here are kind of lacking about the spacing, but I believe I got it close to what is intended. These will be A5 rivets and the spacing I've left between them it well withing tolerances. I've written what I've used for measurements on my plans so it will be the same on the left spar.
I upsized these to A4 with the exception of the 3 at the tip. I'll leave these as A3 until I can align the inboard root rib and nose rib. This assembly will only get stronger with the addition of the root attachment plate.
As per the plans, I added two standard L angles on the back of the spar at the required location. These add more torsional rigidity to the spar assembly as a whole.
First I marked the centre line of where the angle attaches at each location on the spar:
I cut and deburred two pieces of L to 209 mm long, then used the rivet holes in the spar tip as a guide as they are the same layout (4 rivets between the spar caps):
It doesn't show here, but I drilled pilot holes in each of the L pieces, then used the layout line on the web to align the L in each of the spots and drilled it out to A3. They too will become A5 eventually.
Ron had a look at the flutes I cut in my rib forms and suggested I widen and soften the edges a bit. To do this I used a hand file.
The file was very effective but left the flutes a bit rough.
A little hand sanding of each and they cleaned up nicely.
Both the wing and the root rib bottoms taper slightly up from the front bottom corner. In order to lay out the lightening hole and tooling hole locations correctly, I set up one of the forms on the bench and used a scrap of angle and a carpenters square as a straight edge for measuring against. As this is my first go at using these forms, I decided to do the two root ribs first in case I discover procedural issues. Better to change plans now if needed, but I think this will work.
The four vertical lines measured laterally from the square end. The tooling hole locations measured vertically up from the straight edge provided by the angle. I drilled the four holes out to 15/64ths diameter, same as the bolts I will use to clamp the forms together when bending the blanks into ribs. Left to right, the first 3 holes are also the centre of the lightening holes, the fourth is a tooling (bolt only) hole:
Flip the stack over, clamp the forms together straight and use the new holes to back drill though the other half of the forms, ensuring both left and right rib consistency.
With the forms and templates ready, I start to stack them and a blank together. From top to bottom in the picture below - right side form, left side form and wing root rib blanks. The blanks don't have holes yet and the stack is now pointing in the opposite direction (left to right - tooling hole, and 3 lightening hole centres).
Line up the root rib blank on one side of the form......
.... followed by the other form, lined up directly over top the other. Normally this alignment is accomplished via the bolts and holes. My blanks don't have tooling holes as I wanted the holes to first match on both forms otherwise what's the point?
With everything lined up exactly where it should be, I clamped the sandwich to the table and using the form holes drilled pilot holes through the blank:
This results in perfectly located holes - all four will initially be bolt holes for forming the rib.
With both root rib blanks having their tooling holes complete, I can bolt it all together and put it in the vise for forming:
Gentle and firm blows with the dead blow hammer, bends the flange over the sides of the form. A piece of hardwood dowel rod helps direct the forming blows, massaging the aluminum into the flutes, taking up the extra aluminum from the curve of the form and creating the desired shape across the top and bottom of the rib:
The flutes really help make the rib nice and straight, but it also make is tougher to remove the form. Not bad enough to avoid the flute work! Once out of the form, fluting pliers can be sued for final adjustment. Once flat and out of the form, the 3 forward bolt holes become pilot holes for the fly cutter.
Knowing the procedure works as I intended with the root rib, I repeated the hole alignment procedure for the wing ribs and it turned out perfectly. I'll get to pilot holing the rib banks soon in preparation to form the ribs..
The nose ribs of the 701 and 750 are close enough that I can use Ron's forms. I remembered this while looking for my nose rib forms - that's why I didn't make them for myself! Ron and two other builders were making their nose ribs at the same time, so they bolstered their form with a metal plate close to the nose. This absorbs and backs the small tinsmith hammer blows required to get the thin nose flange rolled over much better than the wood alone.
Ron's forms are already drilled for tooling and lightening hole centre, so the process changes only slightly. This time, I laid a nose rib blank on the drill backing board and centred the form on the blank.
With it clamped in place, I drilled out the holes, using the form as a guide. Then I repeated this step 11 more times for a total of 6 left and 6 right rib blanks.
Ron's forms do not have flutes cut in them, but Ron says they had no issues forming their ribs without flutes. I will need to know where the flutes need to be crimped using fluting pliers, so I marked out 6 left and 6 right for future forming:
A couple of parts I've yet to make are the front upper strut fitting and the spar root fitting (2 of each, one set for each wing). These are substantially thick pieces of aluminum, each a 1/4 inch thick.
One challenge scratch builders have is a good reference of materials needed for a build. Kits come with everything already cut and mostly bent. To make scratch building affordable, one needs to purchase materials in complete sheets then cut them down to size. Buying in bulk saves major bucks.
Thankfully, I received a really good spreadsheet from another scratch builder early on in my build process, which has been invaluable in giving me some idea of the materials needed.
I've been following along pretty closely to the spread sheet of material, but it sometimes has a bit discrepancy compared to the plans. But as we all know, the plans are king.
My spreadsheet states the spar root fitting is 38mm wide by 240mm long - this coincides nicely with the spreadsheet and can be made from 1-1/2 inch x 12 thick aluminum bar stock perfectly (38mm is 1.49606 inches, close enough for me!)
My spreadsheet also states the front upper strut fitting is 40mm wide by 203mm long. This means I'd need bar stock just over 1-1/2 inches wide (1.5748 inches). This sucks because the next width in bar stock is 2 inches, meaning a bunch of wasted material if I have to cut it to width.
I spent too many hours thinking about this and trying to figure out if maybe I'd be better to order some 1/4 inch plate and cut them all out from that, which means more work and chance for error. It was then I looked again at the plans and realized the spreadsheet is wrong. Both are 38 mm wide, meaning I can make all four from a single strip of 1-1/12 wide bar stock. Cool! (I've adjusted my spreadsheet!)
So the 1-1/2 inch bar stock has been ordered along with some 063 to make the spar web doubler and some 0.188 plate for the wing attach brackets on the cabin/fuselage. It pays to shop around, these materials are about a quarter of the total cost ordering it from Aircraft Spruce and 8 hours closer too! I'll pick it up this week from the supplier. I'll probably get them to quote some 020 that I still need for the wings and fuselage skins.
One material that is cheaper to get at ACS are aircraft grade hard rivets. What you see below is way more than I need, but it's good to have extras. $68 something including tax and the time to go get them. I was going that way anyhow to pick up something for Ron, so it saved us both a little on shipping too. The picture below is what I got for the money. The writing on the label is the weight in pounds, not the cost per rivet.
Another consideration I've been pondering is fuel capacity and what that means for my build. Will the standard size fuel tanks be adequate for my expected fuel burn and range? I need to think about this as it affects how and where the fuel tanks get installed in the wing.
I reached out to William Wynne, the Corvair guy and he advises I can expect to flight plan for an average of 6 gallons per hour fuel burn at normal cruise speeds. Looking at the specs from the Zenith website, standard dual wing tanks are 24 US Gallons (2 x 12 gal.) - meaning not including unusable fuel in the lines and any reserve I can expect about a 4 hour range on average.
The extended tank option from Zenith (plans sold separately?!) increases this to a total of 30 US Gallons (2 x 15 gal.) - an increase of about an hour of endurance. The tanks are essentially a little bigger but still fir in the same wing bay.
Some have added a second standard tank in each wing, meaning a total fuel capacity of 48 Gallons!
That sounds great, but there are some serious pros/cons to consider. Extra range and fuel is always a good thing. But how long do I want to a leg to be - i.e. will I need to stretch/pee/eat before 4 hours? It also costs more to make larger or dual tanks, and it complicates the plumbing of the fuel quite substantially. There is also the consideration it may decrease the usefull load (how much can I take in baggage and gear - fuel weighs a lot) and that it costs fuel to haul fuel.
I'm all for the extra range - it never hurts to have more fuel than I need. I'm just not sure it meets my mission and if I eventually plan to put the plane on floats, then what? That has impacts on gross/empty weight on it's own, without considering the extra weight of fuel.
I don't have to decide yet, but will have to soon. Maybe I'll reach out to Jeff Moores in NewFoundland - he has a 705 Cruzer on floats and see what his experiences are. I'm leaning towards the middle option for a slight increase in range without complicating the plumbing.
So.... long blog today. I hope you are enjoying following along. More to come soon including some decisions on fuel tank size.
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.