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!
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.