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.
I wanted to get back to the 3D printer this week, but my time was better spent in the shop working on the slats. I did manage to get the 3D scanner to work, but more on those later.
Slats are aerodynamic lift assisting devices attached to the front edge of wings. There are many types of slats and methods to accomplish the same aerodynamic principles. Large commercial aircraft often have hydraulically activated slats that extend on command from the wing. Some aircraft have slats that automatically deploy when the right conditions exist for it to be beneficial. In both cases, these are overly complex to design and build and not very common in light aircraft. Slats benefit STOL aircraft because in normal cruise, the profile of the wing acts the same as a wing without slats. However, at higher angles of incidence, such as in climb or descent, the slat forces air from below to the top of the wing, increasing lift dramatically, allowing much slower stall speeds (and steeper climb/approaches typical of STOL aircraft).
On Zenith STOL aircraft, the slats look/work like this:
I've learned the importance of gathering all my parts/materials before starting to build a section, so I started by laying out all the parts I have made so far for the slats. There are four to build, 2 inboard and 2 outboard - just like the flaps. I just noticed in the picture below I'm missing one of the slat doublers.... hmmm. I'll have to double check my count.
With a good idea of what's needed and what I need to still make (skins), I had another look at the plans.
The slats are a fairly simple structure to make without too many parts - this keeps them very lightweight. Like the flaps, accuracy is important so that the pick-ups match the attach points on the wings. Also like the flaps, it took some sleuthing to deduce the "distance between slat supports" by flipping back and forth several times between the slats diagrams and the wing diagrams. Not sure why Zenith couldn't just place the measurement on both pages! Each of the drawings have different points of measure. If this was a match drilled hole kit, no issue but for a scratch builder it takes some figuring!
Next I started laying out the skins. The width of the skin for a completed slat is deceiving as it curves on both the top and the bottom around the ribs. As a result I was disappointed to find that I can't fit two slat skins on every sheet, it's about 20mm too wide.... argh! I'll use the remaining metal on other parts but it would have been much quicker and nice to get two skins from each sheet. While I had the rolls out, I got all four slat skins measured and cut to size.
Full size 4x12 foot sheets are cumbersom to work with, so I cleaned up the bench a bit in order to make room, which was long overdue anyhow.
Other parts I still needed to make were the slat support brackets for attaching to the wings. These are traced from my card stock template onto 040 aluminum and cut out roughly on the bandsaw. From there they get ground down to size and sanded smooth.
Here is a pic of the four skins rolled up and the slat support brackets all ready for their turn in assembly.
I put away the skins for now and started to formulate a plan to assembly the first inboard slat. The general construction of each slat consists of a 025 slat doubler angle, 3 slat ribs and 2 slat support brackets. The slat doubler is essentially the spar of the slat.
Each of the slat support brackets also has a doubler made from a bent piece of standard 025 "L" angle. I decided to make up all eight at thee same time, 4 left/4 right. It starts with a 120mm long piece of L angle.
Measure out 50 mm and 80 mm in the centre of the bend where the relief holes will be. Use a centre punch to make a dirll point:
This notched piece of hardwood makes an excellent backer for drilling the holes so the part doesn't wander:
Use snips to make relief cuts to the edges of the holes:
Next was trying to decide how to make all the support brackets consistent with the ribs. The plans call the back edge of the support bracket to be 140 mm from the nose of the rib and that the rear lower edge of the rib be 28 mm elevated. So I figured the best way was to layout a rough sketch of the dimension lines on a board and trace out where a rib sits in relation to the bracket. This should ensure consistency for each rib that needs a support bracket and doubler. At the top right you seen the curved doubler (more on this later).
I struggled for a couple of minutes to figure out how I was going to place rivet holes from the inside of the rib, through the support bracket and into the doubler on the opposite side. The I figured out if I used a right side doubler inside a left side rib (and vice versa) I could trace lines on the inside where the doubler would be approximately. Now I know the holes I'm drilling will mate up with the doubler.
I duplicated the same process for the opposite side slats. In order to keep parts together with their mates, I put a alphanumeric mark on each set of parts. Slat support "J" matches up with rib "J" and doubler "J"
here is a better look at a curved doubler as it would be oriented under the rib and slat support. The doubler provides extra skin support around the slot that will be cut for the slat bracket.
Each inboard and outboard slat has 3 ribs. The outers have attach brackets and support doublers, the middle rib is just a rib. I'm pondering adding a doubler to the middle ribs to further support the skin. They are real easy to make and attach and weigh nothing.
Here are the ribs for the inboard and outboard right side slats. The one in the foreground shows how the doubler creates the sandwich of the rib and support bracket go together. Again, I decided to complete all 8 at the same time as I had the layout and process readily available.
Next up I started figuring out how I was going to bend the skins. Slat skins from the factory come pre-bent and it's important to be accurate here. A few test strips of 016 measured out according to the plans, bent then adjusted and bent/tested again to correct errors had me in good shape. I documented where the bend lines are compared to the plans once the skin is actually bent.
With the lines laid out, I made sure to mark each line with an bend order number, where the bend setback would be and what radius.
Clamping the long straight edge down to the bench makes it easy to scribe the long bend lines.
The underside edge of the skin needs a corner relief cut at each end to allow the tip insert to fit correctly. Measured the required cut and corner drilled first to make a clean inside corner when cutting:
The first bend must be the middle one as the throat of the bender isn't deep enough to make the bend from the other end of the skin if I make the small (2nd/3rd) bends first. After measuring several times to confirm the first bend (everything counts on the first bend being correct) I placed it in the bender and used a long piece of 025 doubler as a forming shoe. It worked perfectly.
Placing the slat doubler inside the bend confirms the bend is correct and true. I pulled the slat doubler out past the skin to show the match in this picture.
The second bend adds the up angle on the lower part of the slat. Again the bend here needs to be exact - too narrow, the next flange will be too wide. Too wide and the next flange will be too narrow.
More double and triple checking and the 2nd bend turned out perfect.
Here is the skin back in the bender getting ready for bend number 3. This bender can bend aluminum sheet up to 025 easily, but is really designed for lighter/softer aluminum trim coil/flashing/soffit which is can be bent to sharp 90 degree corners. To adapt to bending smoother radii required of aircraft aluminum, we insert a pre-bent strip of aluminum called a "shoe" to help form the bending sheet around the shoe to create the correct radius. In this case, I use a "shoe" of 020 to bend the skin around, leaving a perfect 1/8" radius in the skin.
Careful measurment and planning leads to a perfect set of bends - very pleased how it turned out!
Next I needed to figure out how to lay out the rivet lines for the slat doubler that fits inside bend # 1 (the 90 degree corner). I placed the doubler on the edge of the bench and slid the skin over top. The goal here is to make the rivet lines line up with the centre of the slat doubler flanges. So measure the middle of the flange.....
..... then slide the mark on the doubler to the skin edge and mark the skin.
Do the same at both ends then connect the marks with the straight edge. Voila, a perfect rivet line.
The first rivet is placed 30 mm in from the edge of the skin which is also the centre line of the inboard rib. From there, the rivet spacing is 50 mm. Rivet locations marked with black marks along the rivet line. These continue across until meeting the location of the centre rib. Then the same process starts 30 mm in from the opposite end on 50 mm spacing towards the middle.
Next I'll flip the skin around the do the same layout for the other side of the flange of the skin/doubler.
Overall a productive couple of days in the shop. More coming soon!
As I mentioned in my previous blog post, I volunteered to assess, repair as needed and make functional again a 3D printer that belongs to our local library, in exchange for the use of it to experiment printing some parts for my airplane. The primary issue reported by the library staff was that it wouldn't print and they suspected it was a plugged extruder nozzle. They don't have the knowledge or salary dollars to assign a staff member to investigate further, so the printer sits idle and unused.
The brand of printer appears to be HICTOP which is one of many widely reproduced, made in Asia copies of a Prusa 3D printer. This is more common than one might think - there are literally hundreds of knock-off models on the market and this practice was commonplace at the time the unit was purchased by the library a few years ago. The market now has several different manufacturers competing for dollars.
No manual in the box, but I found one online to give me some hints for what to look for. Here is how I received it and what I found.
First up, an unlabled box of what appears to be left over/spare parts, typical of knock-off manufacturing, but this was likely where someone just dumped anything extra left over:
There appears to be a bunch of stuff in the box, leading me to wonder what's missing on the printer!
Some of the bags are labled, some aren't....
Initially I thought why would someone would keep (what appears to be) a broken cog-drive belt. Further looking at the HICTOP assembly manual I downloaded from the interwebs shows that the belt is left open ended for adjustment purposes (ties off on the chasis slides at each end). Learned something new.
Some extra split tube wiring conduit/loom that didn't get used.
The box has a tonne of filiment in it, however anything in a bag appears to be labled 3D "pen". I know the library was touting they had a 3D crafting pen, so I'll have to research if this also works in the 3D printer. It doesn't seem to be the same stuff - different diameter and texture, but I also know filaments comes in many different material types and diameters (you can switch nozzles on the printer), but for now I'll run on the assumption they are not compatible.
The printer itself looks well used (or well abused?) and typical of home built hobbyist kits. Everything seems to be in place and secure on first glance.
It looks like some attempts were amde to tidy up the wiring, either at the original build stage or later on - however it needs some attention. Probably what the spare wiring conduit loom was for:
Power cord seems intact. The other grey cable is an older style USB cable common in early versions of 3D printers, but nice and long.
Also typical are simple filament spool holders, in this case the model has a threaded rod with nuts on the end uprights:
The print bed is damaged but still flat. It's somewhat common practice to use glue sticks to spread a thin layer on the print bed for the printed item to stick to as the bed moves back and forth. I think the proper procedure is to clean the glue off between prints though. This glue is very thick and likely baked on over several heat/cool cycles of the bed.
Early users of 3D printers struggled sometimes to remove completed prints from the bed and I imagine the evolution to heated print beds (like this model) might have made hard adhesion of the extruded plastics even more prevalent. Looks like someone used a hard tool of some sort to remove prints and left some fairly deep gouge marks.
After cleaning up the glue residue a little, it looks like a previous user also dragged the print head nozzle across the bed when trying to print something, leaving a permanent hash shaped mark in the soft aluminum. In this picture you can also see the nozzle and heater is covered in old plastic debris. It also appears loose and freely turns on it's mounting pipe.
This printer has a small display screen and single control knob to both prepare and operate the printer.
With a bunch of initial tidy up, everything looked good for power up. There doesn't appear to be any master switch to control power on/off, so I plugged it in hoping to not see any blue smoke! The power supply groaned a bit then the LCD display lit up. The menu selection knob seems to be functioning correctly and I can navigate through the menus easily:
After a couple of minutes, the extruder began to spit out melted filament which I caught in a tissue. Seemed more of a drip than a push by the extruder, but maybe the clog managed to clear itself?
Using a socket on a drive handle, I removed the nozzle once it cooled down after power off:
The nozzle is most definitely blocked and this confirms the string that appeared was just melting debris. So the nozzle will need some serious attention.
A few more attempts to clean the bed while on the printer proved difficult, removing four anchor bolts and unplugging the electrical connector is easy. I'll take both to the shop where I have access to lacquer thinner which should make short work of the glue that appears to be baked on over a long time. Acetone will melt the blockage in the nozzle.
Looking down from the top, everything looks good externally, maybe a bit dusty from sitting. Looking left to right at the extruder assembly is the extruder cooling fan, heat sink fins, filament loading latch (hole) and the extruder driver motor). On the front of everything is another fan which is ducted towards the nozzle tip.
Remove a few screws and the drive parts of the extruder assembly comes off the carrier. This revealed a partly melted pieced of filament which looked like it had jammed in the feed tube. It came out easy with a small tug on the exposed end. I removed the set screw that holds the feed pipe and heating element (called the "hot end").
I had some other supplies to drop off at the shop, so I took the nozzle and print bed with me to clean them up.
Previously, I had purchased a ultrasonic jewelry cleaner at a thrift store. Turns out it's perfect for cleaning small parts like the printer nozzle. I placed it in the tray and added just enough pure acetone to submerge it.
The cleaner has a bright blue LED light that makes it hard to see anything due to the reflective stainless bin bottom, but I'm not complaining, the cleaner was less than $7.
A short video of the cleaner when on.
While the nozzle soaked and buzzed away in the cleaner, I used lacquer thinner and a paper towel to remove the mess of glue buildup. It worked well when let to soak a bit and "encouraged" with a plastic scraping tool.
Removal of the glue reveals even more deep scratches. I originally thought about sanding them out with some fine sand paper, but I'm concerned about damaging it further or worse taking out the flatness. I'll have to research options.
The long acetone soak in the ultrasonic cleaner worked very well. Little bits floating in the acetone were a good sign. A small piece of wire in the tip of the nozzle pushed the rest of the debris out along with some high pressure air from the compressor. All good again!
Next up, reassembly of the printer including improving/replacing the print bed. Stay tuned.
A really productive day in the shop today. Managed to finish off the last flapperon (inboard right). A milestone part of my build is complete. Here is a family pic of them all together:
The opposite end shows the open ends of the outboard flaps (on the left below). This is where the aerodynamic tip inserts will go during final assembly:
With everything complete on the flaps, I stacked them up for wrapping in plastic sheet to protect them:
Once wrapped up tight, they go up in the barn for storage until needed back out for inspection and set-up on the wings. Stacked on some of my rolled aluminum, from botton to top, my completed assemblies are stabilizer, elevator then flaps.
One thing I want to try is 3D printing some of my parts and the aerodynamic flapperon tips are the ideal candidate for this technology.
I wrote previously in my blog about 3D scanning some original parts and using the 3D model from the scan to print them. I discovered that although my home server has enough processing power and memory for 3D scanning, the video card currently installed does not quite have enough chops for the job. A replacement I ordered arrived last week from Amazon and I set to the task of installing it. For some reason, the server will not power up (it has been sitting idle for a couple of months while I waited for the new video card). Bummer, I will have to investigate this further before I can start experimenting with 3D scanning.
Meanwhile, our local library allowed me to bring home their 3D printer. It broke several months ago and they have no money in the budget to repair it or hire someone to fiddle with it, so I offered to see if I could get it working. No idea at this point what it will take to get it working (it is an early model) but I told them in return for trying some prints from my 3D scans, I would both work on getting it working for them and pay for any parts that might be needed. From what they have told me, the extruder nozzle is clogged and the print bed may be damaged.
Very happy to have the flapperons done. Next on the build table will be the slats which I am led to believe is one of the more challenging sub-assemblies of the entire build. But that is what I got into this for - to learn :)
In an upcoming blog I document the 3D printer un-boxing, rebuild and repairs.
Thanks for following along.
Good progress since the last blog entry. I finished up the second outboard flap and started on the last inboard one.
The skin is bent correctly and the rivet lines are laid out:
With the skin riveted in place, the nose skin is rounded over. Lengths of wood under the ratchet straps draw the skin down tight:
With the skin in place over the spar, rivet holes are drilled, alternating out from the middle of the spar to the ends - this helps fasten the skin evenly and avoid twisting.
With all holes now drilled, it all comes apart (AGAIN) for final debur, cleanup and priming:
The spar is primed on top and bottom flanges, the web in those places where ribs attach:
The skin is also cleaned, debur and primed:
I'm pleased with my attention to measuring detail. Rivet holes are perfectly centred in the nose rib and the flap pickup angle is cleanly passing through the skin:
All buttoned up awaiting final rivets before heading to storage and later inspection:
Outboard flap splice plate, drilled and primed, ready to be riveted to the inboard rib:
Final rivets complete on the underside and flap splice plate added. Lined up on the bench with it's opposite wing mate. Really pleased how these outboard flaps turned out.
So here is an updated "completion" diagram. 3 of 4 flaps complete!
Onto the second inboard (and last) flap. To fold the trailing edge, Ron helped me clamp it down using a long board. A 1/8th inch spaced inside prevents the trailing edge from getting crushed. The secret here is gently tightening each clamp in turn so the trailing edge remains straight and true. The square steel pipe helps keep everything down even
It didn't squeeze it down quite enough, but close enough to be drawn down flat to the ribs:
You may recall from an earlier post (see here) that it took a while to figure out the correct toe-in angle at the root of the inboard flap. In order to keep them the same and allow for any slight deviation from the plans, it's best to copy the first one I made. To do this, I used an adjustable angle protractor, measuring the trailing edge and transferring it to the skin of the second one:
After measuring again I laid out the rivet lines on both the top and bottom of the flap. The root and tip ribs already had holes in them from a previous attempt to skin it, but that first attempt led to a bad twist in the finished flap (long sad story). Rather than make a entirely new rib, I used the duplicator to match the new skin holes. With a couple on each end done, I took the skeleton back out and pre-drilled the skin rivet holes out to A3:
With the spar in place and square to the skin, I drilled through the skin and into the ribs, using the red centre lines on the rib to keep them square. Working up from the trailing edge and out from the middle keeps the skin nice and flat and straight, the weight of the square steel tube helps immensely - much better this time!
Next up, I'll flip everything over and begin the process of riveting the bottom skin to the ribs and begin bending the nose skin over to meet the spar, including laying out the flap angle pass-through holes.
One more full day in the shop this week should finish off the flap assemblies.
Thanks for reading, soon I'll have something new to show you besides flaps!!
It's been over a month since I last posted to the blog and I'd like to say I have a lot new to report but I don't.
Covid continues to limit travel but I still have access to the shop. I've been feeling a little discouraged lately about my airplane build project. It's getting done but sometimes it feels everything is moving slower than I thought I'd like when I started this journey. Perhaps it's the overriding doom and gloom of media, news and society right now bringing me down.
A couple of days ago, a story was posted to a blog I follow and it reminded again me why I'm building not just buying. It's about learning and mastering my passion, not about instant gratification. If I keep reminding myself of that truism and how much I enjoy being in the shop, maybe I can also remember that no matter how much no progress is, no progress is just that. Some progress, even a little gets me closer.
Anyhow, I have been getting to the shop this past month. Had a couple weeks of back soreness that continues to linger, but feeling better enough now to work on the plane regularly. Might as well, not much else to do at the moment.
A regular reader of my blog asked me for a picture of the flapperon control horn complete and attached to the inboard flap. Here it is, final riveted to the root rib, prior to closing up the nose for storage. I realized when I was looking for this picture, I had a few others from the past couple of weeks. I'm onto my 3rd flapperon (the 2nd inboard one) so I apologize if the order of the pictures is confusing. They really are all the same build sequence as what I've previously posted, but I'll add some comments to each,
Laying out another skin with the biggest straightedge you've ever seen. The weight of a square steel tube keeps it in place, small finger clamps at each end can't do the trick on their own:
An important aerodynamic principal is to keep all flaps exactly the same dimensions (I'm very close to the plans, but not exact). To accomplish this, I used the completed inboard flap as my template to lay out the next skins and where the skeleton sits inside the skin:
I used the bender to gently form the trailing edge past 90 degrees, then a wide board to press it down flat. Small wood pieces screwed to the table kept everything in place for the press down:
Here is how I drilled the flap pick up angles to the nose rib. Started with A3 moving up in hole size to A4 then A5 ensures a nice clean and round hole for riveting later. While I had them out, I did the remaining 3 flapperon skeletons the same:
With the skin bent, rivet lines laid out and confirmed by dry fitting the skeleton, I drilled the upper skin to A3, using a scrap piece of plywood as a backer to prevent damage to the lower skin (it's very easy to do, not much room between the two!)
Using the skin holes as a guide, I lined up the ribs and drilled them out to A3. The steel tube keeps things flat and tight. I also did the spar at this point to A3. I leaned later to wait on the spar holes until AFTER I rolled the nose skin around.....
In the picture below, the nose skin is already pre-bent. Here I've flipped the whole thing upside down to rivet the lower skin. Again, I used the steel tube to keep everything tight, I also clmped the trailing edge down to the bench under some strips of wood to help secure everything:
Ratchet straps draws the nose skin over. If I'd been smarter, I would have waited to drill the spar holes once both skin edges were in place, but using the hole duplicator worked ok. I'll do it that way on the next ones.
The outboard flap sections do not have a tip rib. The tip is occupied by a fairing that I've yet to make (3D print!?!?). To help keep the shape of the nose correct, I inserted a piece of steel tubing that approximates the curvature of a tip-rib nose if it were in place. This worked well to keep the skin straight to the spar:
With everything drille dout and square, all holes are upsized to final A4 size and then the whole thing comes apart..... again.
Clean everything up using purplle ScotchBrite pad and a little acetone, ready for priming:
Once the primer is dry, everything gets assembled again. At this point I added the flapperon connection splice plate on the outboard flaperron. After fitting, it too was primed. Again, the matching bolt hole in the splice pate doesn't get drilled until later when mounting both to the wings for final adjustment:
So, here is an updated pictogram of what is complete (in blue), a good barometer of progress I suppose:
Moving onto the 2nd outboard flapperon, it's pretty much wash. rinse, repeat. I did take some time to check the straightness of the flapperon spar. I set it up on the steel tube and used heave steel blocks to reference against. This gave me the chance to verify the measurements and ensure ther was now twist in the spar (a common issue with scratch build parts) that could lead to a twist in the flapperon once it is skinned:
Laying the skeleton on the skin gives an easy reference to where the rib and spar rivet lines will be:
The trailing edge is carefully pre-bent in the bender, then.....
..... folded over using a long board and down pressure squeezing. Inserting the skeleton for fit confirms everything matches the previous 2 flapperons:
Top side riveted to A3, nose skin pre bent and flapperon flipped over to river the lower side (just like the last 2):
With the skin in position, flapperon pick-up angles can be laid out on the skin and cut out (I "think" I already showed this previously?):
It's nice to have the company of Ron's dog Maggie in the shop. Company is probably too polite - she's more of a supervisor!
The third flapperon is now almost complete. One more inboard one to do, but I was wrong when I thought the 2nd, 3rd and 4th would go quicker. It doesn't. But progress is happening and I'm happy about it.
Maybe it was a sign of brighter days ahead, but the other morning when I entered the shop, I'd thought Ron had left a work trouble light on in the Cessna cabin:
Turns out the glow wasn't man-made at all (trouble light or fluorescent).... it was just the sun streaming in the window of the shop roll-up door. Life is beautiful isn't it?
In closing this blog entry, I want to quote the author of the blog I spoke of reading the other day:
“At any real level, flying is not a sport, a hobby, a pastime nor entertainment. It is An Endeavor, worthy of every hour of your life you invest; Those who dabble in it find only high cost, poor reward and serious risk. They are approaching it as consumers. Conversely, for those who devote their best efforts and their serious commitment, the rewards are without compare.” -ww-2006
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.
Ok, funny story.
I went to the local hardware store to pick up some items. I needed some stainless machine screws for the trim cover plate and Brenda asked me to pick up some paper towels for thous house. I also picked up some 6mm drywall vapour barrier plastic, and a large roll of duct tape. While standing in line, I noticed some work gloves on sale, so I add that to my cart.
While checking out my stuff, I realized I had most of the makings of a murder kit! I mentioned that to the cashier whom I happen to know and we had a good laugh. No, I'm not planning anything nefarious!
With the machine screws in hand, I was able to secure the cover plate. Worked well, but I had to enlarge the holes a bit to make up for some slight offset in the rivnuts.
With everything done on the stab and elevator that can be done before fitting it on the fuselage, it's time to wrap them up for storage in the barn.
Nice to see an open bench again! I decided to start on the flapperons next, as I already have the ribs bent/formed. Can't believe it was over a year and a half ago I did them! (see this post).
The plans are quite detailed here, even though there are fewer parts. The flapperons are built in four sections, an inboard and outboard section for each wing. As such, there are left and right ribs with varying orientations, Like the stab and elevator, I found it easier to lay all the parts out for inventory before beginning.
In studying the plans, I came across a small discrepancy. The flapperon control horn (part 75A1-6) shows 2 different shapes. The overview assembly page shows it like this:
The part dimensional drawing matches as well:
But the assembly/rivet drawing shows a different shape (circled in yellow below).
I emailed Roger Dubert at Zenith who got back to me right away. Thankfully the dimensional drawing is correct and thankfully I won't have to remake mine. He was kind enough to include an updated rivet/assembly detail drawing as well. Not sure I saw this anywhere in the update pages. Problem (if it even was one) solved.
It's important to accurately place the ribs on the spar, as the flap bracket spacing must match what is on the wing when it is built. I decided to do the inboard flaperrons first, as they are slightly more complex. To start, I lined the left and right spars back to back and matched measurements for the rib attach points. These finger clamps are perfect for this task and this will make them the exact same.
Drilled the spar holes out to A3 to start, then back drilled through the spar into the rib flanges.
Here, the plans could use some clarity. No where do the plans tell you how far the outboard rib of the inboard flap stands-off from the spar. The dimension I needed is shown in yellow below.
The only way I can figure is to complete the root end then measure back to the outboard end. This will work as the root rib has specific placement and is "toe-in" a bit to match where the fuselage narrows behind the rear cabin post. At this point, I also used a sqaure HSS tube to act as my straight edge to make sure the nose ribs and line up parallel to the spar. This made measuring the "toe-in" easy too.
With the root rib in place and secured to the bench, I can measure back to the outboard rib and adjust as necessary. The measurement is defined by the width of the flapperon skin with the widest dimension measured from the tail of the root rib to the tail of the outboard rib. I marked this on the plans as I will need it again for the left side inboard flap.
The left inboard flap went much quicker, just had to remember the ribs face a different direction. I lined them up facing each other against the steel tube and everything is square and identical.
With the inboards done, the outboards went smoothly too. The rib placements are similiar, but the process is the same. This time the inboard rib is square to the spar (no toe-in) and there is no outboard tip rib. The tip is a fiberglass aerodynamic plug that is inserted later (I'm considering 3D printing it!).
Next were the flap attach brackets, made from 6061-T6 angle. 65mm long.....
....cut and beveled and corners rounded off. Still some fine sanding to do to clean them up before paint.
Marked for drilling.....
.... and drilled to A4. Until these are in position, I'll leave them at A4, but final rivets will be A5.
Here is the first one in place. The bracket needs to extend 26mm through the flap skin. This piece of wood I'm using is about 28mm tall, so this is correct accounting for the 0.016 skin. I'm happy with the fit.
Really happy with my time spent in the shop over the last couple of days. The flapperons are well underway and I'm looking forward already to the dreaded slats!
I was thinking I wasn't going to post the following video because I'd like to think fellow builders are a smart, rational and analytic group. But the more I see on the news about the ignorance of people regarding Covid-19 and the steps EVERYONE needs to adhere to it wouldn't surprise me that some still need the reminder. Take it for what it's worth. Be careful, be smart, be safe everyone.... FLATTEN THE CURVE!!
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.