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.
It has been almost a month since my last blog post, but work continued on the slats over that time. No real need to blog about it as the process was the same for all four with the exception that the outboard slats were slightly longer externally. The internal skeleton and assembly steps were the same.
A pciture of the last slat on the bench awaiting trailing edge bend before debur, prime and rivet.
Also in the last couple of weeks I played a bit more with the 3D printer. It seems I've run into an issue with the filament jamming in the extruder. Very frustrating stepping away to do other things while the printer works on something, just to come back and find nothing coming from the nozzle!
I took the extruder apart and it was clear it wasn't feeding correctly as evidenced by the "knot" of melted filament between the extruder and the hot end.
I spoke to a work colleague who is very invested in 3D printing as a side business and showed him some pictures. There are two things that most commonly cause this are a gap between the hot end feeder tube and the extruder, or worn extruder parts. As the extruder parts are 3D parts themselves from the manufacturer, his suggestion was to spend some money to upgrade to an all metal extruder and hot-end.
Looking further into this, I decided to not to proceed any further with using this printer. The printer is not mine (it belongs to the local library) and I'm not quite ready to invest the time or money to upgrade something that is already esentially obsolete. I still plan on printing parts for the airplane eventually, but this printer is has become a bit of a distraction from the airplane itself. Also, newer model printers are getting cheaper by the minute and easier to use with built in functionality that makes printing exactly what I need more sense, so I'll look at investing in one of my own eventually. I've accomplished what I set out to do - proof of concept and making it functional again for the library. 3D scanning is also functionally feasible, but it too needs more time to getting it working the way I want it so it too will be shelved for the meantime.
A question came up from another builder on the forum on how I've managed to bend the trailing edges so cleanly. The entire procedure of assembling the slats can be seen on a previous blog post but for the sake of explanation, I used a small diameter rod along the inside of the fold held in place with some spacers Ron and I came up with. The are scrap strips of 0.016 aluminum with a a small curled up end.
I used wide painters tape to hold the strips in place, the curl of the strip against the rod. The picture make sit look like the curl is taller than the rod, but it is not. If it were, it would leave a mark on the inside of the skin so caution is warranted here
Strips and tape are cheap, good to have several across the entire width of the slat skin:
The inboard slats (the shorter ones) eventually tuck inside the outboard slat enough to be riveted together once they are mounted on the wings. Here they are back to back and upside down on the bench lined up but not yet tucked together - this really gives the idea how long and wide the wings will be!
Looking at my "completed sections" drawing, I'm pleased to be "mostly done" the control surfaces.....
.... and happy to see an empty bench, even for a few minutes! Now to begin one of the bigger sections both in size and number of parts - the WINGS!
I brought a fresh roll of 0.032 (on the bench) and 0.042 (coiled beside the bench) down from the storage barn, to start laying out the components for the wings. Like everything else, I want all the parts made and ready to use in assembly to minimize the time on the bench.
First up, the wing spar webs from 0.032. The two spar webs are almost a full length section of a sheet and requires accurate cutting so the spar assembly is straight and true. They make up the centre part of the spar between to 6061-T6 angles on the top and bottom (more on later).
I cut the first web using a plunge saw with metal cutting wheel and it turned out fairly decently. The saw isn't as accurate or clean cutting as I would like leaving me some extra work with a hand file to clean up the cut edge by hand before deburring and sanding smooth. With a bit of work, it eventually cleaned up nice and straight. I cut the second spar web by hand using the large hand shears - it took longer to cut, but I found that if I was careful I could be more accurate cutting by hand and it took a lot less time to debur and clean up the cut. I used each side of the factory edges of the sheet to be and edge for each spar web giving me a perfect factory edge to measure from..
With the spar webs cut to size, I measured and cut out the tapers at the inboard ends of the spars where they will meet the wing (the bottom of the spar web faces the ruler in the picture below)
The thickness of the 0.032 and 0.040 sheet make them awkward to roll/unroll, so it makes sense to cut the other pieces out while the sheet is on the bench.
In the picture below you can see the remaining 0.032 sheet after cutting out the spar webs (coiled at top of picture), the spar root doublers (bottom of picture) and the four rear spar channel blanks (middle of picture). The two thinner strips on the right at 0.040 blanks that will be bent into angles as inboard rear channel doublers.
The 0.032 rear spar channels and the 0.040 doublers are too long to bend at our shop, so I've taken them to the same shop who bent the flapperon spars for me previously. I'll get them back this week.
I also needed to cut out the left and right 0.063 strut support brackets (bottom right in photo below). So while I had the sheet on the bench I also cut out some of the other 0.063 parts for the fuselage - the fuselage parts will be put into storage until I need them, but at least they are done. I ran out of space on the 0.063 sheet I had to layout/cut the spar web doublers, so I'll have to get some more from storage to get these done.
So despite no blog updates, I have been working away. Control surfaces are "done" and work on the wings is underway. Looking at the completed parts picture I posted above I'm very pleased how far I've come since starting. I'm not sure I can put a concrete answer on how much I've got done, but of the approximately 275 aluminum parts to make, I've got about 145 done which is very roughly 53%. Understand that's just parts made, not bent, assembled, drilled, debured, primed, riveted.
As always, thanks for following along.
It's been some time since my last post, sorry. I do however have some progress to report on.
I took some time last week to start digging deeper into getting the 3D printer working. YouTube and Google are well known sources of information (as everyone knows - duh!) and there are tonnes of tutorials and "for Dummies" content out there, including how to calibrate and start printing with this early generation HicTop Prusa printer.
First thing I learned was that any design 3D model must be converted to G-code by intermediary software. G-code is the machine language used by 3D printers, milling machines, etc. to interpret the 3D design in a way that can be understood by the machine, i.e. how to move the stepper motors in each of the 3 axis, how/when to extrude the filament and the path the print head must follow.
The software that does this for 3D printing is generally referred to as "slicer" software.
I loaded up the official 3D test file from the HicTop website which comes as an "STL" file. The test file is a 4 leaf clover shape. In a nutshell, an STL file stores information about 3D models. This format describes only the surface geometry of a three-dimensional object without any representation of color, texture or other common model attributes.
These files are usually generated by a computer-aided design (CAD) program, as an end product of the 3D modeling process. “.STL” is the file extension of the STL file format.
The STL file format is the most commonly used file format for 3D printing. The true meaning of the file extension .STL has been lost to the mists of time.
It’s widely believed to be an abbreviation of the word STereoLithography, though sometimes it is also referred to as “Standard Triangle Language” or “Standard Tessellation Language”.
With the file downloaded, I ran a free slicer program called Cura. Cura has many settings to customize a print but for this test, I went with the defaults with the exception of the filament diameter which I changed to match what I had loaded in the printer. Cura then converted the STL file to G-code, which was then exported to a SD card. The SD card gets placed in the printer and I started my first print (which as you will see below turned out pretty good!).
I asked Cura to add a base to the print called a "raft" - this is a small lightweight layer that is laid down first, giving a good base for the print to adhere to:
With the raft complete, the printer moves into position to create the 3D print, guided by the supplied G-code information:
Layer by layer, the extruder lays down a steady stream of melted filament, building upon the layer before it. I captured a video of it working here. This isn't sped up, it actually works at this speed (sorry about the noise!)
The test model is actually much taller, but to save on filament (and time), I stopped the print after a while as I was satisified everything was working as it should. I'm pleased as how well it turned out - nice and smooth and well defined shape wise:
Excited to try another print, I went back to the internet to find a 3D model for an airplane part I can use for my build. I'd seen someone had posted a trim cable fairing for Zenith aircraft. This fairing works as a passthough and strain relief in the tail of my airplane, or anywhere else that might be suitable.
I downloaded the free model (thanks to 3D model sharing site www.thingverse.com) and upoaded it into Cura Slicer.
Instructions from the original 3D modeller said they had best results when they inverted the model for printing and adding support structures. Support structures are somwhat like a "raft" described above and are used to support parts of the 3D model that overhang, preventing them from sagging or warping. First step is to invert the model:
Next I asked Cura to add supports. Here is a screen capture of the model showing all the layers including the supports (light blue). Cura allows you to show each layer of the print head path(in dark blue) - this is layer 133 of the print. You might notice adding support increases the print time and filament material used:
With the model exported to the Sd card, I started the printer again, this time with the new model I just converted with Cura. The following few pictures also show the second model in the set - a drill hole template that was included with the fairing model. It again starts with a raft for both:
The drill template is only about 15 layers thick, so when the printer finished it, I peeled it off the bed.
The printed item breaks away easily from the raft. The small scorch mark you see is actually extra filament that leaked out of the hot end print head and dropped on the printed piece (more on this later):
As I looked at the finished drill template. the printer chugged along building the fairing layer by layer. It's hard to capture the process as the bed and print head are constantly in motion:
Slowly the model starts to take shape:
Getting close to being complete, but you can see the print head is leaking badly!
After just over an hour, the printer head moves back to the home position and reveals the completed print!
Some room for fine tuning, but overall it seems like it turned out well!
I asked for the supports on the entire print as I didn't know any different, so Cura added them inside the throat of the fairing too. That will be easy to fix by cleaning it out with a small drill bit.
The print seems to have either warped or sagged at the one corner. It didn't affect the print in any way, but I suspect this requires another check of the print bed levels.
The main body of the print breaks away from the raft easily:
So do the supports. I'm printing these initial models with PLA (Polylactic Acid) which is different than most thermoplastic polymers in that it is derived from renewable resources like corn starch or sugar cane. Most plastics, by contrast, are derived from the distillation and polymerization of nonrenewable petroleum reserves. Plastics that are derived from biomass (e.g. PLA) are known as “bioplastics.” All the waste created by the supports and rafts can be recycled.
The base of the model is very smooth as it was last to print (model was printed upside down as per the suggestion online). The upper surfaces are a bit rough, but I think that's more to do with the support settings than anything and those can be adjusted.
The next models I tried printing were some edge markers. Unfortunately, they didn't work out well at all. I suspect I failed to set the model scale corrrectly and it looks like the extruder leak still needs to be addressed!
Overall, I'm really pleased that I got the printer working. I learned a tonne and I'm looking forward to doing some more with it. The possibilities are endless!
Back to the shop this morning to work on inboard slat #2. I followed the exact same process as the first slat and that experience made this one go much faster. I finished priming and assembling it back together:
After a hour or so in the slat box I finished riveting it together. Slat # 2 complete!
So, my completed parts picture is starting to fill in nicely!
I put both outboard slats aside for the time being and pulled the outboard slat skins out of storage to begin laying out the measurements for both of them. They follow the same method as the inboard ones, other than they are longer than the inboard slats. The inner skeleton remains the same, it's just shifted a bit more towards the centre:
A couple of hours later and the outboard left is substantially complete. Next up I'll continue the process and bend the trailing edge.
More to come with the 3D printer. I'm really stoked to try the 3D scanner and print something from that!
Another 15 hours done on the wings. Stay tuned for more, thanks for following along :)
A really good couple of days in the shop this week.
With the first slat underway, I was time to begin the task of wrapping the top skin over the ribs. To make this easier, Ron has built a "slat box" as show below. Made from plywood, it is essentially a reverse or negative pattern of the top surface of the slats. Green painters tape is added to any contact point to prevent scratching the skins:
Before getting the slat mounted in the box, I had to tuck the underside into the folded over trailing edge. It's tight, and I used a thin piece of wood as a slide to get it tucked under. The resulting pinch of the trailing edge fold is enough to keep everything together for mounting in the box.
Now it fits in the box and can be strapped down to complete the final wrap over.
I used a piece of HSS tubing to act as my spreader across the rear of the slat.
A look inside the each end confirms things are close enough and I can begin drilling the top side rivet holes.
To access the top side (which faces down in the box) I tilted the box on it's side:
Strategically cut access holes in bottom of the slat box line up with the 3 internal ribs so I can get at least 3 rivet holes drilled through the skin into the ribs:
The fourth hole is to far down inside the box to drill it accurately, but that can wait until everything is out of the box.
Put the box back upright and added some more blocks. This allows the force of the straps to transfer down more vertically, tightening everything up and I can begin to drill and cleco the trailing edge down on the underside:
Take the assembly back out of the box again and finish the top side rivet holes I couldn't access before. The finger clamp holds down the rear curve of the skin to the double bend flange underneath:
Layout the rivet line across the top rear. These will be A4 rivets with 50mm spacing:
To ensure I had everything locked down where it needs to be, I flipped everything over and drilled out everything to A4 on the underside:
Back ipright again, drilling the topside rear rivet line, A3, then up to A4 on 50mm spacing. I also completed the front rivet holes in each of the nose ribs. Everything is tight and square.
And it all comes apart again for final debur and priming:
One of the challenges I'm facing is how to make the inside of the slat structure accessible for the inspector to see my workmanship. The fold-over design of the skin makes leaving it open like the flaps, elevator etc impossible. I discussed this with Ron and confirmed with Roger at Zenith that adding a lightening hole on the flap ribs was acceptable here. I'm not looking to save weight, just want an easy way to see inside. This viewing can be done with a scope.
I carefully added some small holes in the centre of the slat ribs using a step drill. This will allow a camera scope inside.
I flanged the hole slightly to add strength:
I scratched off some of the primer doing the holes, but they cleaned up nicely and I re-primed them.
The new access hole creates a new small problem. The skin support L now protrudes over the hole:
the quick solve for this is to trim the L a bit before riveting. I also trimmed it back a bit on the top of the bend flanges to ensure clearance for the top two rivets.
Primed the skin and once dry started the re-assembly which goes back together fairly quickly
With everything drilled out to A4 and clecoed, the slat skin is tight to the ribs and looks good for riveting. The access hole turned out really nice - there should be lots of room to look inside using a scope.
Very pleased how this turned out using the steps I came up with worked well, I'll be following the same order when I build the other three. Again, I'm rather surprised by the size these are, it gives a good impression about the wing dimensions.
One to the next one, it all starts with alying out the bends. Thankfully I wrote down the measurements and bend order from the first one - that will make the next three the same.
Very happy how the first slat turned out considering how complex and tight the bending that is expected of the skin. It's not a complicated structure, but "fun" to do.
Back in the shop soon to get the rest of the slats done. I'll be continuing work on the 3D scanning/printing project too, exciting things coming up. Thanks for reading.
Back in the shop for a few hours this week, continuing work on the first of four slats.
When we last visited my progress (ha!) I had just completed laying out the first rivet line on the skin where it attaches to the slat support angle (pseudo spar). With that complete, I flipped the skin over on the bench and marked out the second rivet line.
With the slat support angle in correct position, I drilled out the rivet holes to A3 on both edges. The plywood edge of the bench works well to anchor everything. I waited to do the holes where the skin/support/ribs meet to ensure fit. All the holes will be drilled out to A4 eventually.
Flipping the clecoed assembly back over, I began the process of fitting the three slat ribs. The ribs fit as expected so I drilled through from the skin, through the support angle an into the corner of the rib:
I continued the process for all three the same way and the fit well. The rib flanging die works well as a weight to hold the skin upright at the edge of the bench as I double check alignment.
Happy with the alignment, I removed the slat skeleton from the skin and began the process to layout the underside rivet lines of the ribs:
The inboard rib is 30 mm in from the edge of the skin and rivet holes in the skin are laid out, centre punched and drilled to A3. There are 5 rivet holes along the underside on each rib including the one at the spar.. I'll wait to drill the last two near the rear of the slat until the skin is wrapped around the trailing edge and I know where it will meet the skin on the other side.
Redlining the centre of the ribs makes line up easier when drilling through the pilot holes of the skin. This picture makes the rib appear twisted for some reason, it is not. Weird. To do this, I've removed the slat pick-up bracket - it will be added later once the slot in the skin is cut.
With the inboard rib close to the inboard skin edge, it was easy to start forming the curve of the skin. I used three finger clamps to secure the rib using the skin support L, using the redline visible through the pilot holes in the skin as the alignment reference. I further confirmed the alignment using a measuring square. The other two ribs were slightly more difficult to line up as I had no way to clamp them in place for drilling, but the skin was already starting to curve with the first rib so I managed to get them lined up well.
With all three ribs lined up, I drilled through the skin into the rib, starting at the 90 degree corner, gently pulling the skin across the rounded underside of the ribs. The other holes into the support L on the outer ribs will wait until the slat support brackets are installed because the slat support bracket thickness will change the location of any holes drilled now. It's hard to capture the curve of the skin in pictures, but it turned out well. I always pictured in my head that the slats were much narrower - seeing the initial assembly here makes me realize how wide/thick they actually are!
I want to make sure the slot for the slat in the skin is accurate and doing so took some head scratching. How do I mark out where on the skin the slot goes when I can't mount the slat attach bracket until the slot exists? It's compounded by the curvature of the skin and the tapering angle of the bracket. I also happens in two places, the inboard and outboard ribs on each slat section.
What I came up with turned out pretty good. I used a duplicate slat support bracket as an example.
Knowing that I really only need two reference points between any slat attach bracket and slat rib to determine position, I used the original slat brackets to drilled out two matching holes for each of the ribs. Shown marked below on the duplicate - two holes matched for the "G" rib and two holes matched to the "H" rib
The smallest diameter machine bolts I had on hand meant I had to upsize the holes in the example bracket a bit (hence the reason for a duplicate bracket - I didn't want to change the A4 size in my actual bracket).
The bolts are just long enough to make the bracket stand-off the rib to the skin edge so I can then scribe a line back from the edge to the rib. This gives me an accurate start and stop end for the slot I need to cut.
Here is the final picture with the slot cut, the attach bracket through the skin and mounted to the rib. I've also drilled for the rivets through the skin and into the support L. I'm happy how this worked. In hindsight however, this didn't work for the outboard rib as it was too far away from the skin edge to make this work. For the outboard slot, I just duplicated the same length and position as the inboard, slowly lengthening the slot until it fit well. the key concern is matching the rib holes and being equally positioned in reference to the opposite end of the slat section. I've accomplished that doing it this way, so I'll do the same again on the next slat. This picture also shows the curvature of the skin on the underside of the slat.
With the underside of the slat now secured, I began the process of laying out the rivet lines for the top side. This is a single row of rivets as there is no need for a support L on the top side of the slat.
I used a seamstress measuring tape for it's flexibility and made notes of where the centre of each rib flange was as well as where along the length of the spar the rib is. The inboard rib is easiest, as it is only 30 mm in from the edge of the skin. I measured all three and marked out rivet holes.
With the hole locations identified, I drilled the pilot holes from the inside which I will then back drill from the outside when the skin it rolled over the ribs. Again, I'll wait to drill any holes that double through the lower skin once I confirm everything is lined up.
At this point I also made the first bend in the trailing edge with the bender using a 020 shoe to maintain the required bend radius. In this picture you are looking at the top skin which curves over the top of the rib, forms the trailing edge and covers over the tail of the ribs (this will become more clear when I get the skin curved over the rib).
With the help of Ron and a long board, we bent the trailing edge over by hand as far as we could. The aluminum bar stock is taped in place to prevent us bending the trailing edge completely flat and the round rod inside the trailing edge helps form everything.
With the bend close, we needed to figure out a way to make a small crease along the trailing edge. This crease creates the return angle from the trailing edge to where the skin meets the tail of the ribs. We used a thinner board to clamp the skin down tight slightly inside the trailing edge while the rod remained inside the radius to give something to bend against.
I turned out great and I'll continue to take pictures as I move along. Next up will be moving the whole assembly to a specially created "slat box" that Ron built. we'll be able to tighten the top of the slat skin down across the ribs and drill through the pilot holes into the ribs. It should also be ready for the trailing edge rivet holes.
Thanks as always for reading! Stay tuned for more coming soon.
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.