Back in the shop after a couple of nightshifts at work. The shop is definately where I like to be, working away on the airplane and away from the constant din of COVID doom and gloom. We are streaming music via a bluetooth speaker to avoid any outside news. The crazies that call 911 with stupid scenarios around social distancing rules are starting to really annoy me, but that is for someone to worry about right now while I'm on days off.
With everything on the flap assembly correctly drilled to correct size, it's pulled all apart again for deburring. I decided it was best to drill the flap pickups for the connector bolt while they are off the flap that way I can ensure consistent position of the hole. I noted these measurements in my plans (Zenith don't tell you the dimensions of the hole placement on the angle, just that it's an AN3 diameter bolt hole).
Placing the pick-ups back to back and clamping them together for drilling through makes for an easy way to make them consistent.
With everything deburred, I cleaned of the Sharpie markings off with acetone, scuffed up everything with a purple 3M Scotchbrite pad and wiped everything clean again. The aluminum sure looks clean now!
I was going to use Cortec primer again here, but decided interior pieces can be sprayed with green chromate based primer. I did any edge that would be in contact with other aluminum. Kind of wish I had done this with the elevator - much easier that the Cortec and easier to see coverage is complete. The outside surfaces of the flap pick-ups are done in grey paintable self-etching primer as they will be painted with the flaps later. For the flap spar, the outside of the flanges and the areas where ribs attach were also done.
I cleaned up the flap pick up holes as well using the same process. Green primer on the inside, grey on the outside. The grey primer looks thick in the picture, but it dried thin and smooth.
It doesn't take long for either primer to dry, so assembly can begin almost right away again. Kinda weird seeing everything in green but it will be inside the flap!
Here you can see the flap pickup angles painted primer grey.
A5 rivets here really tighten up this joint/structure. The entire weigh of the flap counts on this important interface.
With the entire inner flap skeleton now riveted, I added the skin back on and began riveting it all together again. This picture below shows the control horn and doubler in place, already primed and ready for riveting. It also shows the "toe-in" of the root rib and how the skin was trimmed to match. I took measurements and documented the rivet placement so I can match the other inboard flap.
Here is another close-up of the protruding flapperon pick-up angle. Really happy how the hole turned out. When prepping everything for final paint, I might consider filling the gap with some flexible putty or something to clean it up entirely. Not required but would prevent water or something getting in there.
From here, it's the process of riveting alternate holes on the bottom surface, working from the trailing edge forward towards the spar. Next, remove the remaining clecos, rivet any remaining holes and the bottom is complete.
Next time in the shop, I'll be flipping it over and drawing the nose skin down for temporary rivets across the top surface. It will be set aside and I can start the next one.
Only 3 more flaps to go. They should go much faster now.
Thanks for following along. Find your way to self isolate - make something!
Self isolation in the shop continues when I'm able. Progress has been steady and unfortunately when things are moving along well it's sometimes hard to remember to take more pictures!
I continued building up the first of the four flapperon sections. It's been slower than I like due to a couple of rework items, but the lessons learned will help make the other 3 sections go together faster.
With the skeletons built, it was time to layout the skins. I cleaned off the bench and laid out some soft pile carpet for rolling out the aluminum:
When I ordered the aluminum from Aircraft Spruce it comes rolled up, in this case four 12x4 foot sheets rolled up together. I only need one at a time and can get two flapperon skins (and more small 016 parts) from a sheet, so the other three were rolled back up for storage.
One of the challenges of scratch building is making some the more complex bends, particularly things that are long/wide such as flapperon skins. I had similar issues with the elevator trim tab - trying to accurately make 3 angled bends to the correct length between bends and the correct angle at the same time.
For the first flapperon skin, I decided to cut it about 20 mm wider than what the plans call for. My logic is that I can always trim an edge if needed. I started with the nose bend,using a piece of 4130 steel tube as the form and a long board to fold it over. At this width it's challenging - the nose bend is only short distance from the spar edge of the skin but very wide. It's quite a task even with a long board to bend it to 90 degrees like the plans describe. Same process as the nose skins on the stab and elevator. I got it over enough though to make the skin fold down tight with ratchet straps when ready.
To confirm the skin was the correct length, I temporarily finger clamped the skeleton to the skin. So far so good. I proceeded to drill some holes through the skin and into the spar, but when I bent the trailing edge, the skin wouldn't reach to the spar... ARGH! I measured it six times to make sure before making that bend.
To fix the issue, I decided to revise my order of operations and work backwards a bit. I knew the folded over skin was correct, I secured the long edge of the skin to the spar then reworked the nose skin a bit to start the bend earlier. It's kinda hard to explain and near impossible to capture in pictures, but it worked well.
With the skeleton now located correctly inside the skin, I could scribe the spar centreline along the bottom side. Ron has a really nice long straight edge made from 032 that works perfect for this:
I drilled out the flapperon pick-up angles to A5. I was about to remove them and realized the importance of marking where they go back as everyrthing will need to come apart for cutting the holes in the skin and for eventual debur and priming. I figured a simple matching alpha character on the spar, the nose rib and the angle would work well for this.
While on the bench I measured out where the rib centre lines were and drilled them to A3, working from trailing edge to spar, keeping everything flat and tight. The inboard root rib can be seen in the foreground along with it's "toe-in" rivet line. Next was A3 holes through the skin and in the spar and nose ribs.
Again, I missed taking a picture, but to layout where the pick up angles protrude through the skin, I placed and example angle in position against the spar and nose rib, traced it to define the hole then drilled the corners from the inside of the skin to the outside. With the holes now defining the edges of the angles. I used the Dremel and cutooff wheel to open the L-shaped holes from the outside.
With the top and bottom ribs and the lower spar secured and the fit of the angles through the skin confirmed as good, I started the gentle process of wrapping the nose skin over with ratchet strap. With a long board to distribute the load across the width it went fairly easily and the skin curved around the nose ribs really nice and even. The short edge extended well past the spar leaving me clearance to drill new spar holes.
Here is the nose skin wrapped and in the correct position, spar holes drilled to A3 and strapping removed. Very happy how it looks, leading edge is correct in profile and perfectly straight.
Here is a closer look showing the new spar line on the skin (green) and the extra skin that will be trimmed off (anything right of the thick black line to the right of the A3 silver cleco)
Finished drilling the A3 holes out to A4 on the top side, flipped it over and drilled the bottom side A3 out to A4. A close look up to the first rib line you can see the flap attach angle poking up from the spar below.
With most everything now the correct hole size, I confirmed my markings where the inboard skin will be trimmed to match the root rib.
Everything comes apart again for trimming:
So here was another problem. I traced the "toe-in" line around the nose on top and on bottom and figured where they meet would be where the skin needed to be trimmed back to. Wrong! It's actually a complex curve as the nose isn't actually perfectly round. Damn. The tip of the root rib won't be covered by the nose skin - it misses by about 5mm.
Again, not many pictures of what I mean, but a couple of nights pondering what to do, I realized the best course of action was to move the rib inboard slightly and make up the difference. This meant a new rib attach angle which would be easy. Only problem was I had already drilled the holes in the skin into the rib flange, and they wouldn't match anymore..... hmmmm guess I need a new root rib. So back to the form blocks and dead-blow hammer again.
With a new root rib, it was a simple matter to mount it 5mm more inboard with a new attach angle, drill through the existing skin holes into the rib flange. Now the skin wraps correctly over the root rib tip - problem solved. It doesn't change anything on how it will mount to the wing and interface with the flap actuator rod either. Phew.
Next was adding the flapperon control horn to the root rib. I removed the new root rib again and traced where the control horn would attach to it. I used the spar attach holes to secure it with clecos, then drilled the other river attach holes to A4. Decided to use the drill press for more accuracy.
Here is the bracket in place, drilled out to A4. It fits flush against the root rib and in line across the top surface of the flapperon (which is upside down on the bench in this picture).
Next issue.... The plans call for a L doubler in the corner formed by the control horn and skin, secured by four A5 rivets. Unfortunately, I'd already drilled four A4 holes (circled in red) as I misread the rivet specs in the plans, mistaking the root rib for a full rib (at the other end). I could just drill these holes out to A5, but then the support doubler wouldn't be in the right spot and would interfere with the control horn bolt which goes through the trailing end of the horn (approximate position shown by the gold arrow in the picture).
I made up the doubler of the correct length and placed it where it needs to go, leaving room for the control horn bolt. By offsetting the A5 rivets and placing them between where the A4 holes are, and up-sizing the spar hole to A5, I can accomplish the goal and meet the plan requirements. The hole near the bolt will remain as an A4 rivet.
A little back drilling through the horn and doubler up to A5 and it looks good to go Crisis averted.
Assembly of everthing is now complete. It's recomended to leave the control horn bolt hole and flap pickup brackets undrilled until they are ready to be fitted to the wing. Also, the inboard flapperon splice plate that connects to the outboard flap splice plate is attached during final assembly. This allows for final offset of inboard/outboard to be done in final rigging.
Guess what's next..... it all comes apart for final debur and prime, then back together again for final fit and riveting. Then I start the process (hopefully quicker this time) on the other inboard flapperon.
It's good to be in the shop :) Thanks for reading, more to come.
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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.