As I mentioned at the end of my last blog post, I want to scan some of the parts into 3D digital models.
I'm making almost everything from scratch on the build, including the small tip inserts for the slats and flapperons. Normally these come with a kit and are made of either fibreglass or more recently are blown plastic molds. I could just purchase these, but Ron has originals from a 701 which shares the same sie and shape of the 750 ones. Purchasing is easy but expensive and doesn't do anything for increasing my learning. Making my own may not be much cheaper in the long run, but certainly equal or less and making my own also means I can learn some practical skills that come from 3D modelling and printing.
First step in this process is to 3D scan the original tips. Again, I could just purchase a 3D scanner and get at it, but what fun would that be?
When Microsoft brought out the XBox gaming system, they shortly after released a sensor system that can detect player movements and translate that into interactive game play on the screen. I believe this was in response to the Nintendo Wii game system which had already broke ground and was first to market with this type of player interface. Microsoft took the best of what the Wii motion sensor did with infra-red (IR) and expanded it to include camera capable of sensing colour, faces and more refined depth of field. Enter the "Kinect".
In this past decade of electronic and programming experimentation, it wasn't long until someone (much smarter than me I'm certain) said "Hey, I wonder if there is a way to hack this XBox sensor and piggyback on what Microsoft developed for other things?" One of the first uses was for robotics control - robots that could see (sense) and recognize objects. This quickly led to 3D scanning for types of objects, both for item manipulation and avoidance (is the obstacle in my way too big to move or is it of a shape I can grab/push etc.)
These type of developments often branch out to other things, including 3D printing. Think about the possibilities! Being able to 3D scan a rare car part and print a replacement for example. Scanning and printing replacement bio-mechanical pieces (heart valves). Printing materials are also evolving - industry is now printing everything from concrete to rubber to aerospace alloys.
Like 3D scanning, 3D printing has come also come to the home/hobbyist workshop - makes sense, these home hobbyist are often on the leading edge of these things, at least initially. At thankfully for less knowledgeable people like me, they often share their knowledge online - thanks YouTube and Instructables.com!
So, where to get started. I picked up an XBox 360 Kinect sensor. It is the most current one being used by 3D scanning hobbyists and has wide ranging support.
The hack of the sensor requires 3 items. A 12 Volt power adapter (bottom left and middle), the male end of a USB cable (top) and the Kinect sensor itself (cable end on the right).
Normally the XBox console gets power and sensor data directly from the Kinect. As a result (and probably because Microsoft wants to control everything) the Kinect has a proprietary plug similar but not exactly like a USB end. The third party 3D scanning software runs on a Windows computer, so that requires a USB connection. So, my hack requires replacing the proprietary XBox connector with a USB and also injecting 12 Volt into the cable to replace the XBox console power.
I found this wiring diagram in one of the online tutorial videos. In this case, the author wanted to dual-purpose his Kinect sensor for 3D scanning and maintain it for gaming use. To do so, he added a switch in his diagram - I won't be doing this, I don't intend on reusing this for XBox, so I can eliminate the switch and the XBox end shown on the left:
First step was to clip off the unneeded end of the USB cable (the phone end in the case of my sacrificial USB cable) then strip off the outer jacket of the clipped end:
Strip back the outer shielding if there is some and the inner foil shield if there is some (cheap cables don't have these, that's why they are cheap!):
Trim away the two shields, leaving the traditional white (data -), green (data +), red (5V +) and black (ground) USB wires:
Repeat the process with the Kinect cable (cut off the proprietary plug and strip/trim the shielding:
First thing I noticed once the shielding was pulled back was an extra brown wire I wasn't expecting....hmmm.... I was expecting a gray wire. Wonder if the diagram is referring to the outer shield, it's kinda gray?
A little further reading in some of the comments on the YouTube videos and some of the instructables pages I quickly discovered that Mircosoft switched to a brown wire from gray at some point. Problem solved.
I tinned the wires first after stripping of the insulation - this makes soldering them together much easier when the time comes. I also added thin wall heat-shrink tubing to each connection which once I confirm everything is working, will be shrunk to tighten everything up. Next, solder white to white, green to green, red to red.
Next, add in the 12 Volt supply lines. Positive 12 Volt from the wall adapter to the brown wire (gray in the diagram). Lastly, black wire from the USB side, black wire from the Kinect side and Negative 12 Volt from the wall adapter (hard to see in the picture sorry).
Next, connecting to a computer and powering it all up - hopefully no smoke escapes! Unfortunately, my laptop doesn't have a graphics card that is supported by the 3D software, so I'll have to wait to get my home server back up and running to test this, but should be good!
Not much I like better than wiring projects, can't wait to do more of this on the airplane.
I'll file this in tools for now and get back to it soon. Want to get the 3D scanner working so I can scan the flapperon and slat parts I mentioned above then print them. Carbon fibre anyone? :)
A real good, full and productive day today at the shop.
I'm pulling together the last of the details about the elevator. Started off today by laying out the access hole for the trim servo:
The hole turned out well and deburred nicely. I think I may have to enlarge the hole some, but I've already cut my cover plate as per the plans:
The easiset way to make sure the cover plate is centred over the access hole is to extend the layout lines far enough, that layout lines copies to the cover can be lined up:
The plans call for A4 pulled rivets to secure the cover - I think I'll add riv-nuts like I did on the fuel tank cover of the 701 wing repair. I want access to the servo during routine maintenance inspections and drilling out rivets each time doesn't make sense to me.
Next up was figuring out how the elevator connects to the stabilizer. According to the plans, the centre elevator hinge requires a bushing between the attach bolt and elevator horn and the specs are described in the drawings below.
I cut a small length of bushing tube material and confirmed the diameter is 1/4 inch:
Initial width was brought close to 2.5mm using the bench grinder. Pro tip - hold on tight with a pair of pliers, the busing tends to go flying across the shop if you don't (this was my 3rd attempt!)
Careful hand sanding brings it down to the correct width of 2.5mm
This is where things got a bit confusing. The plans clearly show the bushing extending on either side of the elevator horn - 2.5mm is barely wide enough to protrude out each side of the horn? Should the bushing rotate in the elevator horn? Right now, my bushing is almost a press fit in the horn with very little to no movement. The bolt rotates freely in the bushing. I'm guessing the bolt rotating in the bushing is better than the bushing rotating in the horn - easier to replace a worn bolt/bushing than a horn?
Also, I've been told that any bolt involved in a moving assembly should be drilled and cotter pinned or safety wired. The plans call for a nylon lock-nut here, but I'm kind of leaning towards a drilled AN3-5 and appropriate castle-nut and pin.
An email to Roger at Zenith cleared things up nicely. The bolt should clamp the bushing and the horn rotates around the bushing, not the busing around the bolt. Roger was kind enough to send a reference page that explains all this:
So, as counterintuative as this is, now I know what the correct assembly should look like (just like the plans). One difference is that the reference page explains the dimensions better. If you look closely the bushing should protrude a minimum of 0.5mm on each side of the horn when the nut is tightened.
To make the bushing rotate freely, I ran the bushing tube on the belt of the bench sander to very slightly reduce the diameter, only enough so that it would rotate freely in the elevator horn, and then cut it to the correct width:
I test fit the hinge and everything looks good. I used a non-locking nut temporarily to hold everything together, the proper nylon lock nut will be added at final assembly. Just enough clearance and no slop in the hinge - very good.
Next up, I had to devise a way to accurately place the hole for the outboard hinge pin in the wing fences. To do this I made a template for each side using card-stock paper. To make a clean hole that doesn't tear open and also matches the 3/16 diameter of the outboard hinge pin, I placed the card-stock between to thin scraps of wood, clamped it together and drilled through:
Placing the template over the pin, I now have a convenient place to mark a reference line (the wing fence rear rivet holes) - sorry, took a pic from each side as I was doing this:
Black reference marks on the card-stock where the rivet holes are:
Connect the reference marks and voila - when laid across the wing fence, reference marks line up with rivet holes and the drilled hole in the card-stock shows where the hinge pin hole will be. Easy! From here, I drilled out the hole to 1/4 inch, in anticipation of adding a bushing:
The plans don't call for a bushing on the pin, but there is room for one and I'd prefer that for smooth rotation and protecting the aluminum of the wing fence.
To make the require bushing I added the inside washer then measured out the pin to where the other washer will be inboard of the cotter pin hole - turns out to be about 6mm between the washers when assembled:
It's hard to position this completely as the clecos protrude out from the hinge pin plate, but this is close enough for now. Unlike the centre hinge, this bushing is free to rotate in the wing fence and around the outboard hinge pin. It will be well lubricated and I may add some more washers on final assembly to tighten up any slack:
With the Arduino trim control pretty close to final set up, I wanted to double check the power source as it will be in the plane.
The aircraft will have 12v DC nominal power from the Corvair engine, so I need a way to regulate this down to 5V for the Arduino board and the servo. Welcome to the "Buck Converter" - it takes up to 48V DC input and brings it down to a flat regulated output of the users choice.
The brass set screw on the potentiometer allows the user to set the output. The beauty is the output remains a constant flat voltage, regardless of changes in the input (say when the alternator is charging the battery circuit). Once set, I'll add a drop of LocTite to prevent it from changing due to vibration.
For testing purposes, I borrowed a 12V utility battery from Ron and hooked it up to the converter, and the converter to the Arduino test board:
The Arduino trim system runs exactly as it would powered by the USB cable - perfect!
I might use the converter below for powering the trim system. The trim system doesn't draw a tone of current (very little actually). This converter does the exact same thing as the one above, just not as bulky as the other one - reducing the footprint even further. The converter above might be better suited for powering LED landing/nav/strobe lights. Arduino will be used for lighting control too.
Next up, I started working on the mounting bracket for the trim servo. I grabbed a previous incorrectly bent bracket to re-purpose as my mount:
Once cut down to size, I laid out the lines for the servo mounting hole:
A cutoff wheel in the Dremel and the air-saw made cutting the mount hole easy:
With the bracket built, I can work on getting it mounted inside the elevator. I haven't got the push-rod or connectors yet, so I'll wait until I have those to mount the servo. I'm not sure this will be enough support for the servo either. The plans call for the Ray Allen trim servo to be riveted directly to the elevator skin - I'm thinking I might do a rework on my mount to attach it to the elevator spar.
What I could do in the meantime is fabricate and mount the trim control horn. I cut the piece a long time ago and bending such a small part was challenging but I got it done fairly quickly:
The control horn will be riveted to the trim corner. The horn end will be drilled once I know the size/type of push rod connector I'm using.
It took a long time to get to this stage and I'm almost ready to.... pull it all apart for deburring, priming and reassembly! It's nice to be able to move the elevator up and down now that it's attached to the stab - no binding, no grabbing. Nice and smooth! Really like how the fences turned out too!
With the horizontal tail group getting close to completion, it will soon head to storage. Next up will be the slats and flaps - both parts of the control surface systems on the wings.
I've been spending a lot of time considering creating a 3D digital model of the slat and flapperon tips. Normally these are blown plastic inserts or made from fiberglass and way to expensive to buy from Zenith. My theory is that I should be able to print them on a 3D printer - possibly even out of carbon fiber!!
To create a 3D model easily, it should be possible to scan an original (which are the same as the 701, which Ron has several in stock). Wouldn't that be cool!
There are many commercial grade (read expensive) 3D scanning tools available to buy. But what if I could hack a 3D camera sensor that used to belong to a Microsoft XBox gaming console? Yup, we can do that thanks to YouTube tutorials.
I picked up an almost brand new XBox 360 Kinect sensor bar for $15 dollars in Facebook Marketplace! Next up, hacking it to interface with my Windows laptop, scan example items, and print them! <Insert evil laugh here>
Thanks for following along, more to come!
Happy New Year everyone!
With the Christmas holidays over, its time to get back..... WAIT!!
Failed well pump at home - replaced/repaired.
Failing clothes dryer - replaced.
Updated home network infrastructure.... started and functionally complete, but need to do more.
Check engine light on the car and new front struts installed.
Back to work... shift shuffle meaning an extra day of work to balance out the hours....yay me.
So, unfortunately the shop has taken a back seat for a couple of weeks. However, I AM BACK!
First up, finishing the centre section drilling out to A5. There is no question the number of rivets make this centre section solid:
Drilled out the rest of the elevator skin and nose skin holes to correct size:
Caitlyn came over with me to the shop on boxing day to shoot some pics of me working. Here I've taken the nose skin off the elevator to prep the outer hinge plate/pins.
The plates are made of 4130 steel, so it's important to centre punch them so the drill bit doesn't wander:
A bit of WD40 helps cool the bit, 4130 is a lot harder to drill than aluminum:
First holes drilled and plates clecoed in place - back drill to A3 then A4, then A5:
Nose skins back on, back on the bench with the stabilizer to start lining everything up, and...
.... uh-oh.... some interference between the nose skins and the centre support brackets. Apparently this is a common problem which is easily remedied by trimming the nose skin slightly and trimming the back the rudder support plate edges to clearance the nose skin as it pivots.
The fit of the hinge pivot point is still bang on - good!
Before pulling them apart again, I used a sharpie to rough out where I need to remove some aluminum:
While I had some downtime during a nightshift at work, I rigged up the trim servo and Arduino controller along with an example rocker switch. I had set this aside for several weeks but I wanted to refine my programming code a bit. This is a refurb laptop I fixed up and it took some more work getting the proper drivers for the Arduino installed amongst other things, but once I had those my new code loaded up perfectly and it looks like I've got the system nailed down to do what I want!
I brought the mock-up to the shop to show Ron but decided it would be a bit easier to demonstrate by mounting it to a board. I've added some spare LED lights to represent a cockpit indicator and a suplus limit switch to represent a momentary contact switch. I also added a really fancy post-it note flag to the arm of the servo to make it easier to see in a video.
Here is a short video describing the components of the system, my reasons for doing so and a demo of what it currently is programmed to do. Be kind, I'm no Martin Scorsese HA!
I've been thinking hard on how to bend the elevator trim tab. It's 025 thick and quite long. In addition, it has some complex tight bends that will be hard to do effectively on the bending brake, so I had to really think out an order of operations.
Like I usually do, I made up a test piece from some scrap 025 and used it to judge if the plan dimensions accurately reflect the true fit of the trim slot. Unfortunately, they don't quite fit - the gap is too wide to be covered effectively by the piano hinge.
I had previously cut a chunk of 025 to the flat dimensions called for in the plans. This the same dimension I used for my mock up piece. This wasn't going to work. The challenge is making the strip wide enough to account for the bends, the depth of the trim tab, the fore/aft distance in the slot and the overlap where they meet the hinge......hmmm....
After much thinking over breakfast coffee it dawned on me - why constrain myself to the flat part size listed in the plans. Why not cut the flat dimensions a bit wider or taller, then trim once I'm happy with the fit? I hate wasting aluminum in this way, but if I oversize the flat dimension enough to clearly cover the trim tab and enough to make use of the cutoff for something else, there won't be any worse waste.
At minimum, I'll salvage the cutoff and my original flat piece for other things yet to be fabricated.
First bend is the small tab at the hinge joint. The bender does good work on this, but can't bend far enough closed on this radius, so I had to bend it down further by hand. Fastening it the bench and leaning on it with a 2x4 worked. Next I bent the lower angle on the bender - this one is much more open so it worked as expected.
I placed the sheet in the approximate position in the trim tab slot. Width is a bit close will trim it down a bit to avoid any interference with the trailind edge. It''s clear from this picture the sheet I cut is well wide enough to cover the return bend back to the hinge.
Next I started fitting the hinge. The key here is to align the hinge left to right to take best advantage of a full barrel at each end. The barrel of the hinge alse needs to fit snug up against the trim spar. I used a small spare piece of hinge to mark out the correct length and it fits perfectly to the spar laterally.
On top is the spare hinge, length marked in green and my new hinge below it marked in red where I want to cut it
A chop saw makes quick work of the folded hinge, cutting though it evenly and easily. For the next step I pulled the pin out and ground down one side of the hinge arms to accommodate the safety wire required at each end to prevent the hinge pin from working it out - that would be bad!
To allow for safety wire, the hinge pin is slightly shortened to be just long enough to reach the last barrel at each end.
I remembered someone online suggesting using the bench grinder to slightly chamfer the rod ends to make sliding it back down the barrels easier. Just a small thing but made all the difference when reassembling the hinge several times over the course of this work. I also plan on using similar hinge to close up the engine cowling which will be open and closed more frequently - more on that later.
I flipped the elevator over again. When I was drilling the elevator skin, I didn't drill the holes where the skin meets the trim spar because I was waiting to see how the hinge would fit. As it turns out, this was a good idea, it saved me having to drill twice. I marked out the 40 pitch hole placement, placed the un-drilled hinge between the skin and trim spar and drilled it out to A3 (picture is after layout hinge pin not placed as of yet).
With the hinge apart again, careful drill of a small hole through the last barrel at each end to thread the safety wire when final assembly of the trim tab is complete. In this picture, I've already drilled out the 40 pitch A3 holes on the spar side of the hinge. Folding it over on itself, I marked the holes though to the trim tab side of the hinge (black marker dots on the left), then used this as a centre line (black) for plotting my holes on that side. I decided to offset them 20 mm from the spar side (blue tick marks)
Flip the elevator back over for viewing and dry fit of hinge to confirm safety wire hole is accessible AND viewable, both for installation and for routine pre-flight checks. From here I removed the hinge again and drilled out the A3 holes on the trim tab side of the hinge as marked.
With the bend width confirmed, I used the bender to create the trailing edge bend. It's tight and the bender can only bend so far over. From here, a 2x4 it used to lean on it and bend it further down to match the first. This picture clearly shows the long side of the trim tab will extend well beyond where it should - just like I planned.
With it close to coming together I flipped the entire thing over and secured it to the bench. This gives a much better view of the planned overhang. A quick sharpie line down the length gives a good line for trimming away the excess.
I drilled both ends of the trim side of the hinge to the trim tab and one in the middle for good measure. With it clecoed together in these three spots, I ressembled the hinge halves, clecoed it to the spar/skin side. Next, I proceeded to drill the rest of the trim side of the hinge to the trim tab using the previously drilled holes as a guide.
Took the whole thing off the elevator (again) and used the duplicator to match the holes on the overlap trim tab skin. I love this tool!
With everything clecoed together again, I checked the movement - nice and smooth and no binding.
With everything good, drilled everything out to A4 final size
Voila! (gratuitous happy moment capture)
With a few more minutes to spare, I decided to put everything on the bench again and line it up. Before doing that, I made the modification to the centre hinge plate that will allow the elevator nose skins the room needed to move up and down. I also trimmed the nose skin slightly to avoid any interference with the centre hinge support bracket.
With everything lining up and measured correctly, and confirming the whole assembly is flat and level, I marked out where the centre hinge bracket meets the elevator hinge spar bracket. With those marked where they meet, I took them off their respective assemblies for drilling.
I started with an A3 hole which will be enlarged to the correct size next. Holding it together with an A3 cleco, I confirmed they won't interfere when the elevator pivots up and down.
I stopped here, because when I was reviewing the plans, I have concerns about the size and type of the bolt used as the hinge pivot. The plans call for an AN3 bolt and vinyl insert lock nut. Not only does this seem awful small diameter, I believe it would be wiser to up-size the bolt diameter to an AN4 bolt and use a castle-nut and cotter pin to secure it. This mod is an improvement, I'll have to do some research what size bushing that will require.
Very happy with what I've accomplished so far. Next up is finishing the elevator/stab connections and fitting the servo and trim actuator rod.
Thanks for reading :)
Back in the shop tonight, finishing up some of the smaller details on the elevator.
Got the motivation to cut the trim tab slot out of the trailing edge of the elevator. The plans call for a slot for almost the full length of the trailing edge. This doesn't leave much of the trailing edge remaining done this way, so after some discussion with Ron, I decided to shorten the trim tab somewhat.
Cutting the skin is tricky - have to be real careful not to damage the trim tab spar. I decided to drill some pilot holes to work towards, then clean the edge up close using a Dremel tool. It took several assemble/disasemble cycles to get it just right but it turned out nice a square. A round file helped to round out the inside corners.
I've decided to add some trailing edge ribs on the rear elevator skin and inside the trim tab as well. This not only supports the skin where I changed the cut, it also looks nicer and will be cleaner aerodynamically.
It took a few tries to get it right - there is no template in the plans for these, I'm making my own. I'm happy with the fit and feel.
Next on my list of small details was drilling the trim actuator hole in the trim spar and elevtor lower skin. The step dill was again very handy for this:
Took the spar out of the elevator skeleton to drill the matching slot:
Back together for final fit. The slot stays the same as the plans. I think I might try and come up with some sort of flexible cover for the trim actuator rod hole to prevent bugs, dirt, snow or rain from getting in there.
Started the initial fit of the elevator nose skins. These need to be in place to confirm the correct spacing between the elevator and the stab. Happy with the fit but surprised how much of the nose skin tucks under the rear skins - but that's what the plans call for and my nose ribs are correct!
With both nose skins temporarily in place, I set the elevator against the stab again to confirm (again) the alignment of the upper and lower horns and centre hinge bracket - all good.
Forward and rear brackets drilled and added - this really stiffens up the elevator centre assembly!
All in all a productive night. I'm headed back to the shop in the morning to continue to knock off the small details - it all adds up!
After a much too long break from working on the airplane, I'm back at it again. Not much has happened over the last couple of months in the shop. Returning to shift work has been harder to adjust to than I anticipated. Add to that the passing of my Mom, Linda in October and all the things to process both emotional and tangible - it's been tough to concentrate on anything else.
Mom was always one of the biggest champions of my dreams, including flying. She was my first passenger when I got my licence in 1995. I told the story of that day at Mom's Celebration of Life as it was one of my favourite memories of many during times I spent with her.
We went flying on a beautiful early spring day in a Cessna 150. Typical first passenger type of flight, showing off my newly minted licence by taking a tour of local sights from above. It was beautiful.
Mom always appreciated a good joke. When we were turning base from downwind, I pretended to look around the cabin like I'd lost something. Of course, Mom asked what I was looking for, to which I quipped "There should be a landing checklist in here somewhere, I might have forgot to bring it".
The look on Mom's face was priceless as she went from surprise, to fear to sly recognition that her oldest son was just trying to pull a fast one. Fast transition! She punched me in the arm and reminded me that landing checklists are important and I should have it memorized. I'm not sure she ever truly forgave me, but she probably did. She was that kind of person; kind, forgiving and loving. I miss her very much.
I also know she wouldn't want me to delay getting my plane built, even if she never got the chance to see it or fly in it. So this week I got back at it.
Work continues on the elevator and horizontal stab. There are lots of little things to complete, but it's coming along nicely. In order to mate them up, I had to finish adding the fences on the stab. Here they are lined up where they will be fastened on the stab. To ensure that both ends are exactly the same, I taped them together and dry fit them, marking out the rivet lines:
Quick fit check on the other end, before drilling A3 pilot holes through both
Pilot holes drilled then clecos to hold it in place to confirm measurements are correct and fence is equal all around the stab aerofoil:
The fence is 063 thick, same as the original outer hinge plates which are attached at the trailing end with A5 rivets, so I'm doing the same here (where the black clecos are). The A5 holes are already in the tip rib, so I used the rivet hole duplicator to match drill them on the fence. The balance will be A4 rivets. This combination will only improve the strength of the whole assembly.
Happy how the fence cleans up the whole end of the stab:
I flipped the stab over to make getting at the A5 holes easier
Once flipped, I noticed how tight the fence is to the tip rib skin rivets. I made a note to remind me to river the skin first!
With both fences attached, the stab looks real good!
With the stab fences in place, now I could place the elevator in line and see how they line up:
Even without the elevator nose skins on, I was real pleasing to see them "together" for the first time. Have lots to do yet, but it feels good to see the sum of the parts looking close to what they will be once done.
Also important was seeing that the measurements of the centre hinge is correct! It's a tight fit tolerance but I nailed the measurements perfectly! (Picture is not very clear, sorry. Just noticed the camera focused on an errant rivet stem)
I placed the elevator horns temporarily in place to confirm the alignment - all looks good.
BINGO! Correct spacing for the hinge bolt and bushing. So satisfying to know everything is correct!
Next I decided to take care of the elevator cable pass-through hole. It starts with drawing a centreline on the leading edge of the stab and a measured horizontal where the cable guard angle will be riveted on. Thank goodness for flexible rulers!
Sketch out the lines where the slot will be and draw the circles that make up the ends of the slot:
Pilot hole to prevent tearing of the aluminum - that would really suck!
A small step drill bit used carefully does a great job. With both holes done, simple straight cuts from edge to edge on the new circles to open up the slot.
The leading edge of the stab has a slight curvature to it where the cable guard mounts. So once I had the guard angle bent, I rounded it out a bit to match. This will be primed before riveting to the stab:
Not a bad prodcuctive couple of hours. Like I said above, it's nice to see the sum of all the little parts I've done and it's motivating me to get back in the shop.
Next up, nose skins and tackling the trim tab. I've managed to write some good code for the trim tab Arduino computer that will control the servo.
Thanks Mom and thanks to my wife Brenda for getting me moving in the right direction again :)
I consider myself so fortunate to have a workshop space to build my plane. This is solely due to the kindness and generosity of Ron and Donna.
When I first talked with Ron about building my plane, he only asked that I share in some of the labour around the shop, such as cleaning and organizing, helping with other planes on the go etc. One of the big ones every season is cutting, splitting and stacking firewood.
Over the past coupe of weeks, I've been over to the property where the shop is and worked with Ron and Donna to split up five backhoe buckets of hardwood and stacked it in the woodshed in preparation for this coming winter. Although it's physically tiring and my shoulders are sore the next day, I'm glad to help out, and there is nothing better than working in a warm shop in the winter months!
Work had me on the road quite a bit the last couple of weeks getting some more project sites up to the latest standard, and I've got two more road trips scheduled in the coming weeks before I return to the communications centre.
While passing through Kapuskasing one morning, I passed their airport. I noticed a Zenair 701 parked/tied down on the apron and made a mental note to stop on the way back through later in the day to have a look.
One the way back, I had enough daylight to stop to look. You may recall, Dad and I traveled to St. Hubert Quebec back in June (see this post). I spend a lot of time driving for my job, and I got to thinking about that trip and how one of the Buffalo Airways mechanics Ronny McBryan (Uncle Ronny) had traveled from Red Deer to St. Hubert and passed through Kapuskasing on the same route I was on.
With this thought in my head and just as I came over the rise in the road west of the airport, what do my tired eyes see? Is that an orange tail!?!? Holy crap! It's a Buffalo Airways C46 Curtis Commando C-GTPO!
Unfortunately, there wasn't anyone around that could get me closer for a look, but I was dumbfounded what could have led me to be thinking about Buffalo Airways just before spotting one of their iconic war bird era cargo planes - so cool!
Second unfortunate thing, I couldn't get anywhere close to the Zenair 701 either. Oh well, maybe next time.
Here is a brief look at what I've got done when I've been able to get to the shop.
I needed to way to fold the trailing edge flatter without creasing the skin. To accomplish this I taped two small diameter rods together end for end and secured it to the table. I added a strip of wood near the middle to ensure the rod stayed in place securely for the bend:
The rod is slightly bigger than the radius required, but can be folded flat more once the skin is in place:
Like the horizontal stab, I prepped the table with blocks, lined up in parallel. These will be my guide to ensure the skins are equal at the trailing edge:
Skins are placed on the skeleton and roughly lined up. Wide mouth ViseGrip pliers hold the skin square to the spar for match hole drilling to the factory drilled spar:
With everything double checked for square, the first of the spar rivet holes are drilled using the hole duplicator:
Happy with where everything lined up, the skins came back off again for mark-up. It takes a bit of figuring as the plans aren't very clear on the rivet spacing and there are some offsets to consider closer the trailing edge, but it's doable with a little thought:
With the layout complete and double checked against the plans and skeleton, the holes are pre-drilled out to A3 size and the skin is clecoed back to the skeleton. I centre-lined the ribs with red sharpie, making it easier to align the ribs beneath the skin for drilling.
I want to draw the skin down from the spar back to the trailing edge equally on both upper and lower sides. This will ensure the skins are flat to the ribs and will continue to flatten the trailing edge. The first 3 or 4 rivets back from the spar on this side - I'll flip it over soon and do the same on the other side.
With the skin secure with the ribs rivets, I went back and finished duplicating the spar holes out the A3.
I then added the reinforcing plate that Ron and I discussed over the centre spar box joint and duplicated the holes at the spar and added the new holes on the rear channel. This really tightens everything up, and the entire centre section will eventually be riveted to A5 size. The same reinforcement plate will be added on the other side as well:
One of the complaints early builder/flyers of the Zenair STOL aircraft was the lack of elevator effectiveness and authority at slow speeds - i.e. landing flare.
To help alleviate this, sever builders have added aerodynamic "fences" at the tips of the horizontal stabilizers. These help keep airflow on the horizontal tail and over the elevator, preventing the air from flowing off the tips.
Following the examples shared by other builders on the Zenith forums, I set out to create my own based on their designs.
First was laying out the 063 aluminum sheet. I placed the horizontal stab tip form on the sheet, along with the original outer elevator bracket. I want 1.5 inch fences all around, so I measure this on the flat (upper) side of the tip rib:
The bottom edge was easy, how to do the top? Make a tool of course!
A simple stick of wood, drilled out to accept a sharpie. Trace around and voila!
Important to have exactly sized fences for each side, so I rough cut out the first one, fastened it to another rectangle blank and final cut them together as a sandwich on the bandsaw. I rounded out the trailing edges a bit as well:
With the final cutting done, a quick pass of the sandwich on the disc sander and some final hand sanding to clean everything up, they turned out very nice! These will take the place of the elevator hinge brackets as well.... so if anyone wants to buy a pair of original outer hinge brackets, shoot me an offer.... hahaha!
More to come on the elevator skins, support plates and hinge assemblies soon.
Thanks for reading!
July was a washout with regards to getting anything done in the shop, so not much available content for the blog....
A home project to replace the shingled roof on our house with metal took up 2 weeks of my July holidays and work travels took up a good portion of the rest of the month. Day trips with family need to happen too. This Monday to Friday temporary assignment I'm currently doing at work is good that the work is both challenging and really interesting, but it only leaves weekends to enjoy the summer. As of last week, I've been advised that I'll be returning to shift work at the end of September. I don't want to go back to the communications centre, but on the bright side, my schedule during the week gets freed up substantially (4 days off every week), allowing me more shop time.
Speaking of work travels, I had a chance to check out the Chapleau Ontario airport. Although there wasn't much to see (MNR fire base was quiet), I did notice this cool sign posted by the local flying club:
July and the beginning of August hasn't been a total loss I suppose. I did manage to get some work done on the elevator and horizontal stab.
When I fastened the skin to the stab skeleton, I marked out where I needed to trim the trailing edge. The extra was on purpose - it allowed for proper length and square fit. Now that fitting is complete and correct, I can trim it back:
With the trimming done, the rear slot is cut. This is where the elevator cables pass through the stab:
I notched back the spar doubler a small bit, leaving clearance for the rivet. Everything was deburred, cleaned up and primed after this photo was taken. Fortunately only had two places where this was an issue.
With the stab skeleton ready, I deburred the stab skin holes on inside and outside - there are a ton!
Cortec primer on the rivet lines was next. I really like how it applies - next to no smell, easy clean up and cures almost clear:
With the primer curing, I turned my attention to the elevator skeleton. Some final measurements to ensure it's built square and it is ready to taken apart again for final debur and prime.
The elevator skins are made of 016 aluminum sheet, folded at the trailing edge and fastened to the top and bottom of the spar. It consists of two sheets of equal length meeting a the centre:
To allow the rudder to move left and right, the skins are cut out at the centre box where the rudder hinges are. It's difficult to perceive in this picture, but once folded the cut out makes sense.
It's important to radius the corners of the cutout, so I started with a centre punch then a pilot hole and followed that up with a 3/8 drill hole.
Cut outs complete for the left elevator skin. Easier to see how this will look when folded. Round file and debur tool to clean things up. This is a exposed edge, so I final sanded it with 360 grit:
Careful use of the bending brake got the fold most of the way, then I used a small diameter aluminum rod to finish the fold to the 5 degree bend called for in the plans:
I used the same piece of pipe to curve the elevator nose skins that I had used for the horizontal stab - much easier this time.
By this point the primer has cured on the elevator skeleton. Re-assemble and check for square - all good to final rivet. I'll wait to final rivet the tip ribs once the skins are on and I can align the elevator and stab hinges:
With the prime cured on the stab skin, it is reinstalled for final riveting. I've decided to river the curved side (lower) and leave the flat side open for inspection. It's kind of weird order - first place the skin over the spar pick ups and cleco everything down tight:
Flip everything over and cleco down the flat (upper) side:
Flip it back over and complete the riveting on the curved (lower side). Really happy how everything is coming together and how straight everything looks :)
The stab is essentially complete at this point. Remaining items to be done are final rivet the hinge assembly (waiting elevator match up), cable pass-through slot in leading edge and fairleads (rub strips). I've also decided to add wing fences to the stab tips which have valuable aerodynamic benefits and really cleans everything up. More on the fences later.
Next up, get the elevator skins fitted up, then cut the trailing edge for the trim tab and install the servo.
Thanks for following along, more to come soon!
I'm finding it more and more difficult to keep my blog up to date - I've accomplished much in the last few weeks. A lot of it has been routine fitting, drilling, cleco stuff so I haven't been taking many pictures. There are a few updates to share though.
With the one side partly secured with clecos, I moved the stab to the other bench. A large square steel tube was placed on the top to gently bend the skin partially into position before we tightened the ratchet straps to pull the skin down tight around the nose and upper surface.
Long strips of wood help spread the strap loads across the length allowing for fine adjustment. You have to be real careful here, too tight and the skin can collapse at the nose, leading to damaging kinks.
With the fit confirmed, I made a few reference marks, then it all comes apart and I can start the process of measuring the skin for holes. This is the only way to make sure the skin rivets are centered on the ribs as I don't have the luxury of pre-drilled skins.
Measure twice and then twice again, using the stab skeleton as a reference.
Again, I don't have any photos of the assembly, but the process is the same as above - weigh down the skin with the metal tube, use the straps to draw the skin down tight. The only thing that's different this time is drilling through the skin holes and into the structure below. I worked from the nose back to the rear edge (right to left in the photo) and from centre section out to the tips. Each hole gets a cleco until the rear most holes, ensuring a tight and bubble free fit.
Spar lines front and rear are drawn and rivet holes drilled. These don't have to be done with the skin off as the spar is a straight line and on this side the spar isn't pre-drilled. Again, measure 3 times - it's important the spar holes are centred on the spar flange:
I'm happy with how this turned out. Next step was using the template I made earlier to start laying out the slots for the horizontal stab brackets
This cutting is very delicate. The skin needs to be trimmed to be flush with the spar so the brackets sit flat and vertical against the spar. Cutting the skin is fairly easy, but any damage to the spar will be fatal!
I traced out the approximate location of the slots using the template and confirming with the plans started a pilot hole
I used a Dremel tool and rotary burl bit to slowly expand the hole enough so i could see where the rivet holes in the spar for the bracket are:
With a confirmed visual and measured slot location, I redrew the hole on the skin and slowly used the burr and some gentle hand filing to get it to the correct shape and location, ever mindful not to cut or mark the spar. Round files make a perfect corner:
Eventually with patience, the stab bracket fits nice and straight in the hole and perfectly vertical and flush with the spar underneath (it's sitting a little low inside the stab here as I couldn't hold it and take a photo at the same time!)
With that experience, the second slot went well too. I cleaned up the ragged edges a bit using a Dremel sanding/cutoff disc. The slots still have to be deburred properly, but that will come when the skin is off for full deburring:
On another note, Dad and I travelled to St. Hubert airport outisde of Montreal to attend the first flight of a C47/DC3 know as C-FDTD. We've been following the epic journey of Mikey McBryan (of Ice Pilots fame) and his Plane Savers team as they restore to flight a WW2 D-day survivor - a DC3 that dropped paratroopers over Normandy on D-day and during operation Market Garden, and that was sitting derelict, falling victim to vandals and the passage of time being slowly destroyed by neglect.
Here are a few personal pics of that trip - motivational for sure! For a full experience and to see what an amazing accomplishment this is, checkout www.planesavers.ca - of particular interest, watch the YouTube segments from the beginning - awesome and well worth your time!
Here is a copy of the flyer they were handing out to guests:
What an honour to be there and share this with Dad and the thousands of others who followed the restoration was unbelievably amazing..... what a great feeling watching it take to the sky again! All I could think about were are brave young countrymen that participated in the D-Day invasion exactly 75 years prior - God bless them and thank you for our freedoms!
I was so happy to share this adventure with Dad. As I post this blog on Father's Day, I'm reminded how much influence Dad has had on my life, particularly a love for aviation history. Thanks Dad!
While in the Montreal area, I also picked up a left/right set of fibreglass wingtips for my 750. These retail for $160USD a piece and I grabbed this uncut pair for $100CAD. Steal!
So, it's been a productive couple of weeks. Next up, I'll finish the stab skin, get the stab brackets installed permanently and proceed to skin the elevator. Once I have it skinned, I begin the process to line them up together and drill the mount holes for the hinge points.
Thanks for reading, more to come :)
Got a chance for a few hours at the shop last night.
The plans call for the stabilizer skin to be pre-bent to 90 degrees prior to attaching it to the skeleton for drilling. Conventional wisdom from other scratch builders is that this can be a challenge to do right.... bending this incorrectly, either crooked or in the wrong spot on the skin can at minimum lead to challenges getting the skin to lay flat on the skeleton and at worst render this very large piece of 020 aluminum useless (kinks are easy to make in such thin skins). I been nervous approaching this step, but with a bit of prep and double/tripple checking everything it worked out well.
First step was to mark the skin with the bend line which represents the middle of nose curvature (done previously) and lay the stab skeleton in position to confirm alignment:
I had to find a long enough (10ft) length of hard wall pipe to use as the bending form, as Ron doesn't have anything long enough in the shop. I originally thought I'd need some schedule 40 iron pipe, but I managed to find this mild steel electrical conduit at Home Depot that will work fine:
To prevent the sheet from slipping, I used wooden blocks as clamps, screwed down to the table:
Some thought went into the placement of the pipe in relation to the line. The overall goal here is to pre-curve the aluminum leaving room to tighten the aluminum down, not to make the curve exactly the same as the nose ribs. The pipe gives the curved surface to bend against. So the pipe is not directly on the bend line, but where the bend begins. Once exactly straight, the pipe is secured at both ends with blocking screwed down and a strip placed in the end and screwed down to the table to prevent it from lifting:
It's hard to capture when both of us are lifting the skin and forming it around the pipe. We use a long piece of rigid steel tube to place even pressure across the width. It's bent a little at a time, readjusted under the pipe, bent again, shifted, bent until the 90 degree bend is complete. If you look closely at the end you can see the incremental marks we worked to:
The size/width of what will be the horizontal tail on my 750STOL is really evident when I stood the skin upright. At almost 9 feet across it almost touches the ceiling!
Placing the skin back on the bench and adding the stab skeleton confirms the bend is very close (enough) to make assembly move on to the next step.
In a previous post, I mentioned making a decision having to be made about which surface to fit first. While researching how to bend the skin, it became apparent most builders suggest easiest is attaching the flat side first and drawing the skin across the curved side, so that will be my plan too.
Another challenge faced by scratch builders is that nothing made by the builder comes pre-drilled. In my case this becomes compounded by the fact my factory spars have rivet holes already - so how am I going to match those blindly from outside the assembly?
First step was to drill though the existing spar holes to match the holes on the doubler from the outside - no problem, that part is easy.
Now how to proceed? I can't drill from inside the skeleton out through the skin, there isn't room for a drill inside the spar web that is big enough to drill straight and the strap duplicator won't reach that far.
I placed the stab skeleton back on the skin all squared up and marked some of the points on the skin where holes will have to be drilled. I really don't like this method as there is too much room for error if the skeleton shifts even the slightest over the length of the skin and there is no easy way to clamp it down.
Before drilling more than a couple of holes, I flipped things over on the bench, moved it to the edge where the top side can hang over the edge and secured the skin where the holes matched up at the one corner:
The trailing edge holes I can rivet from the outside and matching them up is easy with the duplicator. There isn't a good way to blindly drill holes in the forward spar that guarantees a tight fit of the skin and correct hole alignment - and no second chances.
This got me to thinking about a way to drill from inside like I want to. The only thing that I can come up with is buying a tool like this that will fit inside the spar, but man they are expensive and most require specialized drillbits:
I'll continue to ponder this until the next time at the shop and maybe Ron and I can come up with an alternative. Happy with how this stab is coming together so far and really glad the bending of the nose worked out so nicely.
Another thing that got done for each of the airplanes being built in the shop was the elevator hinge pins. Made form plate steel and a modified AN bolt, Ron put several hours into each of these. What you can't see from the picture is the tiny cotter pin hole drilled in the pin or the finite welding he did making these - excellent work. The black paint is a first coat of anti-corrosion primer:
Back to the shop this weekend for a whole day hopefully on Sunday. Got to keep moving this project forward :)
Thanks for reading
I worked this week on getting the elevator trim channel installed on the elevator skeleton. I went over the plans several times to visually ensure I was adding the trim to the correct side of the elevator (remember, I'm building it upside down to take advantage of the flat upper surface of the airfoil).
Again, the plans have to be interpreted correctly - in this case the position of the channel is determined relative to the trailing edge of the elevator. But, that can be difficult without the elevator skin installed as the fold of the skin at the trailing edge extends past the tail end of the elevator rear ribs.
To solve this, I made a small narrow strip of 020 aluminum and bent it exactly as the elevator skin would be - it looks rough but it is exactly the right length to simulate the trailing edge:
I placed the strip in position and clamped it with clecos to the spar as if it was a complete skin. Measuring back from this temporary trailing edge, gives me the position of where the elevator trim channel should be but gives me room to to see my work.
Even with the measurement confirmed, I was having a hard time getting the trim channel to fit correctly, until I got a look at the build pictures that come with the plans. Turns out the kit supplied channel has been joggled at the end, allowing it to sit inside the tip and inner elevator rib.
Once I joggled my channel (that sounds bad as I type it), it fit in the ribs where I needed it to. This automotive body panel air tool is very handy for this:
The middle elevator rib gets trimmed down to fit between the spar and the trim channel. It's attached to the trim channel by an appropriately sized L bracket.
With everything squared up thus far, a quick check of the elevator alignment to the horizontal stabilizer shows extremely close to the plans, so my measurements, cuts and bends are very good and accurate. Very, very happy.
Next step is to start cutting the skins. These are fairly large in size and the bench is pretty crowded at the moment, so I rolled out the 020 sheet and traced out the skin on the floor, leaving it a couple of millimetres wide and long - it can always be trimmed back once I have it fitted to the tail skeletons.
First up is the horizontal stab skin. Making it fit correctly is challenging as you have to make holes AND account for the curvature of the skin across the top (bottom) of the airfoil as well. A kit skin would already be trimmed and holes cut for the front and rear stab brackets. As a scratch builder, this isn't a luxury we benefit from, so we have to come up with a workaround. Time for a template!
First step I did was to mark the location of the front brackets on the spar:
In order to transfer these measurements to the skin, I made a template from scrap 020. I cut out the space needed for the rear bracket, keeping in mind the overlap that is required by the real skin past the spar (15mm):
I removed the front brackets and with the template now in place (clamped) where the skin will be including the curve, I drew a line with a straight edge to represent where the back of the spar is - the goal here is to simulate where the final skin will sit in relation to the brackets. It's better to make mistakes on the scrap than on the full skin!
Knowing where the brackets come through, I was able to measure-mark-create the matching holes in the template and gently open the holes a little at a time with a Dremel tool until the brackets can be reattached where they will protrude through the skin:
I'm very happy how this template fits and I'm very confident it will transfer the positions of the holes to the real skin. I'll use the template to cut the slot for the rear stab bracket before final fitting the skin, but for now I placed the skin across the stab skeleton to check the fit - perfect, nice and square with the outer tip ribs and has the correct overhang of the spar.
Now I've reached a decision point. Do I fit the skin on top first and tighten it down with straps across the flat bottom or vice versa? Both have advantages. I can work form the rear bracket at the spar, fit the skin over the front brackets and pull the skin tight across the nose. Or I can start at the spar on the flat side, secure it and draw the skin tight around the nose, over the curve of the top - essentially working in the opposite direction. I've read that drawing skins tight over a curve is easier, but that means fighting with the brackets.
Either way, the skin will need to be pre-bent at the line that defines the tightest curve first - at the nose with a 27mm radius. The plans show a 90 degree bend in the skin prior to wrapping it around, so I need to get that done first.
I flipped the skin over on the bench to mark the centre of the bend line as per the plans (checking very carefully to mark it in the right spot - right and square:
A long piece of factory edge aluminum clamped down with wood blocks makes a great straight edge:
With the scribed line, I slipped the sheet under the stab skeleton to where it overlaps behind the spar 15mm and the bend line coincides where it should.
The next step will be pre-bending the skin, but I'll need to obtain something close to 27mm radius and more than 8.5 feet long so I can clamp it to the bench. I was thinking a piece of 2 inch ABS plumbing pipe might work, but it may not be stiff enough laterally, so maybe a piece of steel pipe. Unfortunately, Ron doesn't have anything that long in house, so I guess I'm going shopping :)
Thanks for reading, more to come!
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.