I can't believe how much work I got done in the past 3 weeks. Progress has been so good, I've been neglecting my blog in favour of keeping up the momentum on the right wing. I was off work this week for annual holidays, so was able to get four solid days in the shop this week alone.
I wanted to start on the trailing edges. Like the tops skins, they are made of two sections which join at the mid-way point of the wing in the same area as the strut pickups.
Cut the inboard and outboard trailing edge skins to width and length then I marked out the inboard edge where the trailing edge tapers and has a cutout to match the rear wing channel.
On the bender, I used the the 1/8th "shoe" to creat the trailing edge:
With all the top skins fitted and keeping the wing skeleton square I was finally able to release the spar from it's screw-down clamps and flip the entire thing over on it's back. At this point it makes sense to elevate everything up on square steel tubes:
I've temporarily added the required skin stiffener "L"s in each of the wing bays. The upper skin will need to come off for deburring later so I haven't final riveted these yet - that way I can roll the skin for storage if needed.
With the bottom side open for work, I could have a good look at the alignment of the flapperon arms in comparison to the rear channel and each other. The mid-wing joint at the rear channel and strut attachment point is quite a complex piece of joinery!
All four flapperon arms mount up correctly and line up close to perfectly. There is a bit of twist in the wing induced by the roundness of the upper wing surface, so I'm happy where the arms are at for now.
The lower inboard skin is the largest part I've made from of aluminum sheet so far - almost 3 metres long and 720mm wide. I rolled a full sheet of 020 out and made the necessary cuts - it was A LOT of cutting with shears, but at least it's a rectangle to start with before trimming the tapered inboard edge. Layout is marked on the sheet, including the areas for the cut-outs at the spar and rear channel whoch will allow access to the wing mounting bolts:
It even looks longer in the photo! No way in our shop to cut that other than by hand. We'd love a CNC or waterjet cutter for stuff like this, but where would we put it!
The wing skeleton is bolstered from below to bring the spar perfectly vertical again. With the spar both vertical and level from end to end, The lower wing skins can be added. It all begins with the first dill hole at one corner, then squaring it all up before adding more holes down the spar and rear channels:
With enough clecos to hold the skin square to the skeleton, I laid out the rib rivet lines and the lower skin stiffeners:
The skin was removed again and taken to another spot in the workshop (the floor!) to drill the A3 pilot holes as laid out. The skin is returned to the wing skeleton, re-attached by clecos and pilot holes are drilled throught the skin into the ribs, working from rear edge to front spar:
Man, there is a lot of holes to make and secure! A quick peek once in a while through the spar lightening holes confirms the rib holes are in the centre of the rib flanges and not near any rib fluting.
Eventually, all the rib line holes are upsized to A4. The spar and the rear channels remain as A3 until the nose skins and trailing edges are added. I've constantly checked the level of the wing across the spar and the rear channel, so far so good - it get better with each cleco I add as the whole assembly stiffens up:
With the skins drilled to A3 at the rear channel and the ribs brought up to A4, I removed the skin again and pilot drilled the spar. Then I re-attached the skin -again- and used the strap dupplicator to complete the skin holes at the spar up to A3:
With the inboard lower skin now firmly in place and square, I cut out the outboard skin and starting fitting it up in positiion, again using the strap duplicator where this skin overlaps the inboard one and at the spar:
The outboard skin has a very subtle curved edge on it which I was able to trace using the cardstock templates I created:
Looking ahead to the fuel line routing, I marked and pilot drilled where the fuel line will exit the rear channel - it's hard to see in the picture, but the pilot hole is just left of dead centre in the image below. This will be upsized to the required diameter once I figure out fuel lines and grommet sizes for the hole. There will also need to be holes in this area for wiring - but that can wait for now.
Next skin I prepared was the outboard nose skin. This has a very complex curve to match the wing tip insert once it is wrapped around the nose ribs. Another cardstock template I created from the plans is used here to trace the curve described in the plans:
The inboard nose skin is almost as long as the inboard lower skin, but only extends from rib number 1 to rib number 5. I cut it out from a sheet of 016 and laid it temporarily on top of the clecos to get a better idea if the length was correct and it was. According to the plans, it is a rectangle shape to start before it is wrapped around the nose ribs:
I notices in the assembly drawings however that the pictured skin they show was a triangular tab running between the 1st nose rib and the root rib (outlined in yellow on my picture):
My plans don't reference this at all. My plans do not show any rivet line layout in this location (which there would need to be) nor any dashed line to indicate this tab:
After some head scratching and discussion, both Ron and I feel a full root nose skin from top of the spar to bottom of the spar will be correct (as shown in the plans). Everything is covered, this isn't a structural piece and the plans version is actually cleaner aerodynamically, At the end of the day, the plans are always the final answer.
The procedure to fit the nose skin is multi stepped. First the skin is slid between the main lower wing skin and the spar:
Now the lower skin holes at the spar are used to back drill through the nose skin:
The same is done for the outboard nose skin:
Once all the holes are drilled along the spar of both nose skins, they are pulled out and cleco'd on top of the lower wing skins - this will be their final orientation.
I removed the outboard lower skin and using the strap duplicator, I created the A3 pilot holes in the spar tip. Eventually, there will be two rows of offset A5 rivets here (the flange die is keeping the skin flat to the nose rib below as I drill them out):
I re-attached the outboard lower skin, sliding it below the outboard nose skin - this too will be it's final position. The three clecos at the spar hold everything square, but I'll wait to drill the second row of A5 rivets where nose and lower skins overlap once I have the wingtip trimmed and in place:
Speaking of wingtip, you might recall I decided to wait on trimming the outboard top wing skin until the wingtip is in place. I decided to trial fit the cardstock template and although still in very rought layout, it looks promising!
The yet to be wrapped overhanging nose skin doesn't leave a lot of room between the workbench and the counter!
To give myself (and Ron) some room to work, I sued a couple pieces of twine and tied the nose skin loosely down and out of the way. This gave me the room to work I needed to layout and pilot drill the nose ribs:
Next up is the strut support angle. This is a piece of 032, bent in an L shape which helps transfer the load of the wing strut back and across the wing rib and wing structure.
In the picture below you can see the lateral skin stiffeners temporarily mounted on the outside of the lower skin. The eventually will be inside the wing, i just have them there to help keep everything firmly in place while I was pilot drilling the rib holes. Perpendicular to that is the strut support angle which mounts on the outside of the wing. According to the plans, the support angle is supposed to only go as far back as shown, about 40mm short of the the lateral stiffeners - this makes absolute no sense to me. Why would they leave it short of the lateral support? I double and triple checked the plans and it clearly shows it short like the picture below..... strange choice by the designer.
I decided to deviate a little here. I'll extend my support angle back to meet the lateral supports. It adds more strut support with very little work or weight penalty and I'm not adding any new holes or rivets in doing so:
Once bent, each end of the 032 strut support angle is tapered:
Before adding that support angle to the lower wing surface, I'll need to know exactly where the strut support protrudes through the wing at the spar so I can fit them together properly. So until that was done, I set it aside for the moment and focused on the jury strut angles which needed to be attached.
Jury struts are diagonal braces that run between the middle point of the main wing struts and the wing. That triangular structure adds even more rigidity to the wing structure. The jury struts attach to the wing with simple (so I thought) 025 brackets. I made the ones I needed way back when I had some scrap 025 metal cut-offs from the wing rib blanks (that was a couple of years ago - jeez time is flying by). They are the ones on the left below.
Turns out the scaling I calculated back then was skewed and the original PDF cardstock templates I created was incorrect. I tried using them and bending them as per the plans and made several bad ones before deciding it was time to re-do the templates new (shown on the right). The CriCut Maker does this so much better than manually scaling a PDF to print on cardstock!
Below, the proper size front jury strut brackets, match drilled, one pair for each wing.
One set of rear jury strut brackets get match drilled holes as well:
A pilot hole drilled in the centre of the lower flange:
Mounted in position on the wing at the main spar. The other two pilot holes are made using the strap duplicator (not shown):
A long A3 bolt is used to help line up the second bracket where i mounts on top of the lower one:
Matching pilot holes drilled from below through the upper bracket and secured by a cleco for drilling of the other 2 pilot holes:
Secured to the wing. The bolt is not the correct one that will be used here, it was only temporary to help align things:
Next up was the tie-down ring and how the nose skin needs to be trimmed at the number 5 rib to allow it to protrude below the wing (sorry about the crappy picture):
I measured the distance from the spar forward to where the tie-down ring would pass through the skin and marked everything out on the skin. The tie down ring has not been riveted yet to the rib, it is only clecoed in position for fitting at this point, that can be done later from above:
Using a Dremel wheel, I cut out the slot a little at a time until the tie-down ring fit nice and snug:
I used the same methods for the wing strut pick-up pass through point:
Now I can fit the strut support angle as I know where it meets the strut support laterally. Again the duplicator is very handy here:
I'll need to create new 063 strut support brackets which mount under the strut attachment plates. I don't show it above, but I ran into the same issue where the part I made isn't correctly scaled. More to come on that.
Next up was the flapperon arm slots at the rear channels. This time I measured and used a 1/8 drill bit to create the upper extend of the slot and used metal snips to create the slot up from the trailing edge of the lower skin to the hole. That worked very well.
The skin and fapperon arms are very well supported on both sides here - four A4 rivets in the rib and four more A4 rivets in the flapperon support angle on the opposite side of the arm:
This wing is really getting close to be ready for final debur and riveting of the lower skins. Next up is trailing edge skins and maybe a trail fit up of the root nose skin.
When not at the shop, I'm still tinkering with a way to use an Arduino and a pressure transducer to measure fuel quantity in the tanks. I picked up some fittings and some 3/8 diameter poly pipe to use for simulating a fuel tank level sensing device. I'll need to make a decision soon if this is going to work like I expect it to. I think I'm going to need a lower range sensor, bt have found a decently priced source for them online. More on this to come.
Well, I've been hacking away at this blog well past my bedtime. I'm exhausted be very happy with what I got accomplished since my last post.
Thanks for following along.
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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.