Good few days at the shop since my last update.
Now that I know the final position of the fuel tank in the wing bay, I can finalize the "packing" around the tank that prevents it from moving around left and right inside the wing.
The space between the tank wall and the rib is a bit larger than a couple strips of cork will fill.
A grabbed a small block of wood I had lying on the bench and discovered it makes a good model for the size of high density foam block I plan to use.
Also with the tank in final position, I can confirm the hole drilled in the lower wing skin for the fuel drain is centred on the fuel drain bung. To see this closely without flipping the wing over I used a remote mirror and zoomed in with my cellphone camera:
The image is a bit blurry, but the bung is perfectly centred on the pilot hole in the lower skin.
The drain fitting is a 1/2" nut, so I want the hole in the skin large enough to allow a 1/2" socket to turn the drain fitting into the bung when installed, or easily pulled in the future for maintenance if required.
Drilled the drain hole out to just larger that the diameter of the 1/2" socket. It clearly fits cleanly in the hole from below.
The drain plug put in the drain bung on the tank. This is just finger tight, eventually it will have thread sealant and tightened accordingly.
Once fully threaded into the bung, the drain plug will sit just proud of the lower wing skin providing easy access for testing the fuel for contaminants during pre-flight checks.
Like on the right wing, I needed to trim some of the trailing edge away from the wing tank bay. Laid out the trimming line using painters tape and drilled A5 holes at the corners for strain relief.
Used a scrap board of thin plywood to protect the rear channel and ribs underneath the trailing edge while drilling the corner reliefs and cutting along the painters tape edge with a Dremmel cut-off wheel. Much easier that using metal snips in these tight confines.
Finished drilling out the trailing edge to rear channel holes.
Lifted the upper wing skin, deburred all the holes and primed the trailing edge where it tucks under the upper wing skin.
Brought the threaded fuel neck, threaded tank flange, drain bung and fuel sensor mounting plate home so I could measure them and create 2D CAD drawings of the gaskets I wanted to make. To save some material I nested the fuel drain bung gasket inside the fuel sensor plate gasket (the inner rectangle gets cut out as extra anyhow).
Exported the 2D CAD file to a SVG (scaled vector graphics) file that can be used by the CriCut machine to make perfectly sized gaskets.
Did a cut test of the sizes on card stock and although the cutter depth should have been a bit deeper (to make cleaner cuts), then general fit is perfect for each fitting.
Found a supplier able to provide square foot sheets of Buna-N rubber at 1/16" thickness. Bought 2 sheets for less than $13 total including tax.
Buna-N or Nitrile rubber is a durable and fuel/oil/chemical resistant material commonly used in the petrochemical industry for making gaskets and o-rings. This material is perfect for my application.
The reason I chose a 12" x 12" sheet is that it is the maximum width the standard strong grip adhesive CriCut cutting mat will accept.
Concerned that the edges of the Buna sheet might catch on the positioning rollers of the CriCut machine, Brenda recommended I tape the edges down with painters tape as a precaution.
A Google search revealed that CriCut recommends a "Deep Point" blade for rubber sheets - the standard cutting blade is designed for lighter weight materials Brenda picked up a Deep Point blade at the craft store.
The adhesive mat with Buna sheet loaded into the CriCut machine without issue - a good first sign this was going to work.
For those who haven't seen a CriCut machine in action, here's a video of it in action cutting my gaskets.
Once complete, the mat returns to the loaded ready position. (I didn't let the video run to the end). If you look closely, you can see where the cutting head did it's magic.
Brenda helped me take the finished gaskets off the mat - very pleased how they came out!
Perfect dimensional gaskets for each assembly! Very VERY cool!
Once back in the shop, I proceeded to drill the gaskets out for mounting. I wasn't sure the CriCut could carve holes with this small a diameter, but it probably could. I wanted to match them however with the threaded holes already on the drain bung.
The easiest was to match up the holes was to clamp the drain bung onto a spare board with the gasket blank sandwiched in between, then drill out the gasket mounting holes just slightly smaller than the machine screws - this will ensure the gasket stays tight on the screws.
For the fuel sensor plate gasket, I built a temporary "box" of 2 x 2 blocks to support the gasket blank while I drilled the location of the gasket mounting holes..
Started with A3 holes which match the sensor plate and the fuel tank.
Gasket laid in position on the fuel tank over the sensor hole.
Fuel sensor plate clecoed back in place on the tank with he gasket sandwiched between.
Mounting holes were then drilled out to 5/16" diameter, the size required for the well-nuts that will be used to secure and seal the sensor plate.
Each mounting hole upsized to 5/16" then fastened with a well-nut as I went.
Complete fit up of fuel sensor plate (fuel sensor to be re-mounted in plate).
Pulled the assembly apart for deburring and noticed that my original inner line doesn't match the inside edge of the gasket?
Also noticed that some of the mounting holes in the gasket were too close to the edge of the gasket to effect a good seal. As a result one of the holes torn a bit too. Looks like I made a measurement error creating the 2D drawings in CAD. Thankfully I only cut one sensor plate gasket like this. I'll update the CAD drawing to widen the gasket and cut a new one for this tank and a proper one for the other tank.
Setting that aside, I drilled out the mounting holes in the threaded tank insert next, using a scrap of 016 aluminum as the backing plate (standing in for the fuel tank).
Threaded tank fitting now riveted in final position with the gasket. Sealant will be added to the rivet tails that secure it.
Outside front corner of the wing tank. Sealant will be added to the rivet heads on this side as well and won't be seen once the tank is inside the wing.
Test fit of threaded fuel filler neck and cap confirms inside flange still fits correctly. Thread sealant will be added here too. That should complete a fully sealed fuel fill assembly on the tank.
Fuel bung mounted on underside of tank with gasket. More sealant here on the machine screw tails and around the perimeter.
Next up, re-do of fuel sender plate gasket (CAD drawing already corrected, cutting to be completed still) and final seal up of tank edges. Once that sealant cures, the tank will be final mounted in the wing bay and cork strips added on top to support the upper wing skin.
Very happy with the gaskets and how they turned out and I'll probably use the same method to cut some cork supports as well.
Stay tuned for more, thanks for following along.
No update for a couple of weeks, but that doesn't mean I've been idle on the project. Picked up six sheets of 020 aluminum last week. They are 12 feet long and fit (barely) in the back of the family truck. The shipping materials actually weigh much more than the aluminum itself. Lots of straps to hold it in and a cheap fabric red flag on the end to keep it (closer to) legal.
I griped a bit about this on Facebook (who doesn't). It's very hard to understand why raw aluminum made here in Ontario is shipped out of country to be processed into sheets, then sold back at a premium here in Ontario. I'm all for North American jobs, but this is a good example how much manufacturing base our country has given away since I was born.
Off to the shop last Saturday. Nothing better than a hot tea in my Canuckmug.
The wing skeleton takes up much if not all the workbench and the other workbench is being used for Ron as he works on the Aeronca Scout finishing touches before it gets painted. A roll of plush carpet on the floor makes a good cutting mat:
First wing skin cut to size and rolled out on the skeleton. This one is the upper outboard skin:
Lined up, the pilot A3 holes at the spar clecoed in place. With those secure, the skin naturally curves down across the wing ribs. It actually starts looking like an aerofoil! Sweet!
Marked up the rib lines and the cross L lines that define the rivet lines for both. The cross L's help stiffen the skin over the wing bays. The whole skin will come off again once I finish the pilot holes at the spar, to drill pilot holes for the ribs and L's.
Spent the rest of the day making the L's and helping Ron install the new windshield in the Scout. Learned a bunch about drilling windshields so they don't crack - this will be handy when I install mine.
I also started working on the fuel tanks. I've got the first tank skin cut to size which is just a large folded rectangle (think four sided rectangular box). I'll need to make the tank sides and the wooden form to bend the edge flanges for welding it all up.
I managed to secure a copy of the drawings for the extended fuel tank. I put these into LibreCAD. This is the template for the wooden form directly from the dimensions in the plans. The tank will fit in the first wing bay between the first and second wing ribs, main spar and rear channel:
The template for the aluminum sides was derived form this using the drawing tools available in LibreCAD - I learned a few new tricks how to make parallel lines, offset by 6 mm which leaves room for the flanges. It's very close in shape to the wing ribs, just a bit smaller. I also created crosshairs on the drawing where the relief holes at the corners are drilled and also where the fuel outlet of the tank is, including allowances for the fold of the flanges:
You may recall from a previous post, my wife Brenda bought a CriCut Maker craft printer/plotter/cutter. I have a fair amount of time to think while driving to/from work sites and it donned on me to ask if the CriCut could accept native .DXF files that LibreCad produces and if it does, could it cut these templates from Bristol board?
Turns out, it CAN! I wish I knew this a long time ago, it would have saved me a ton of time cutting templates from converted PDF files, but the CriCut is fairly recent in the crafters market. Oh well, still have lots of templates still to make!
The CriCut can cut and print up to (almost) 12 inches wide by 24 inches tall with a little margin included in that. My wing skin templates had to be sliced down a bit in order to fit, but I was able to get the most important shapes (the complex curves) plotted and cut.
It starts with a standard piece Bristol board, cut down to 12 x 24 inches:
The CriCut uses an adhesive cutting mat - something similar to 3M Post-It notes on a larger scale. I laid the mat on top of the marked Bristol board to make sure it fit correctly. (The whimsical black cartoon cat and logo on the inside of the machine lid is something Brenda added herself, using vinyl and made on the CriCut):
With the Bristol board cut to size, it gets stuck down on the mat to wait loading into the printer:
The Design Space software for the CriCut takes a bit of getting used to, but isn't too difficult to figure out. As I stated above, to make the upper wing skin tip template fit, I had to slice it in half in LibreCad and import both halves into Design Space.
Follow the directions on Design Space to choose and load your material, and press go. The CriCut cutter automatically checks depth of the cutter and goes about making the cuts defined by the DXF file:
Almost impossible to see in the picture below but the cutter follows the lines of the uploaded DXF file. Once the cutting is complete, unload the mat:
Bristol board isn't one of the default materials in Design Space, so I just chose the heaviest card stock listed and asked the machine to cut with more pressure. Almost completely through and enough to easily remove the cut outs:
Emboldened by my success, I make the template for the outboard wing nose skin. It too turned out perfectly:
Here is what I got done over the course of about 45 minutes. Like I said, the machine and software make it easy to create perfect templates. On the bottom are the two template pieces that make the tank sides. You can even have the CriCut print and cut on the same piece just by choosing what you want done with each line segment. You can see the crosshairs I spoke of above, drawn right on the template.
Back in the shop for the day tomorrow. Goal is to get the pilot holes drilled in this upper outboard skin, make the upper inboard skin and drill it (it covers the fuel tank) and maybe get the blanks made for the tank sides.
I'll need to obtain the hardware for the tanks soon. These include the fuel outlet fittings, the quick drains and the fuel filler necks. Lots to think about :)
Thanks for reading, stay tuned for more.
Another successful week in the shop.
I continued to work on forming and flanging wing parts. Last blog post I had started the forming of wing ribs, starting with the root ribs. Here they are out of the forms - I'm happy how they turned out and using the hardwood dowel to work the metal flanges into the flutes on the forms made forming the curvatures of the flanges much easier.
As I mentioned before, I'm using Ron's 701 nose ribs forms. The trick here was to pre-flute the blanks as the 701 forms don't have flute channels cut in them.
In the vice, I start by bending the flat trailing edge flange over as it is straight and does'n require any fluting. Then the bottom flange, working forward towards the nose.
as I got close to the nose, I carefully worked the nose flange over, drawing the aluminum across. The metal backing plate on the forms really helps in the this regard.
A little cleanup with a small tack hammer backed up by a body work anvil and some tweaking with the fluting pliers and the nose ribs are ready for lightening holes.
Six left and six right, enough for both wings
Lightening holes are cut on the drill press using the fly-cutter, set to the diameter of the flange dies (which are exactly to plans - in the case of the nose ribs is 115mm)
Lightening holes cut and deburred, awaiting flanges.
Next up, the wing ribs. I used the exact same process here as the root ribs with a couple of modifications. I stacked all the blanks together and drilled the pilot holes as a stack to ensure consistency in the forms. Each of the ribs has 3 lightening holes, however two of the blanks have no third hole, so I pilot drilled those separately from the rest, but using the same layout as the others.
First blank/form in the vice and from here the forming is the same as the root ribs - using a hardwood dowel to massage the flutes. All ribs are made from the same form, regardless of lightening hole requirements. I added a small clamp at the tail end of the form to keep the forms tight.
All my wing ribs formed and lightening holes cut awaiting debur and flanges. The two wing ribs on top are the two that only require front lightening holes, the rest underneath have three holes.
Took the day Thursday to travel to Sudbury and pick up a sheet of 063 aluminum and some flat stock needed for the wing and strut pickups. I also grabbed a small chunk of 0.188 plate for the fuselage pickups. This supplier is much cheaper than Aircraft Spruce and much closer to home.
I was pleasantly surprised to find the sheet came on a well strapped pallet which fits nicely in the back of our truck. Over packaged for a single sheet, but it didn't cost anything to me, so that's good!
When back at the shop Friday, I planned on cutting off the pieces I need immediately for the spar doublers. I laid out the rough dimensions while the sheet was still on the back of the truck. This allowed me to nest them a bit and save waste. All set to rough cut but unfortunately mother nature had other plans and a downpour forced me to abandon the plan and just unload the sheet off the truck for next time in the shop.
The flat stock is perfect for the spar and strut pickups, and the flat plate works for the rear wing/fuselage pickups.
I'm so fortunate to be able to use the tools and jigs and bending equipment of Ron's, it's saving me untold hundred of dollars. One of the best examples of this are the flanging dies Ron had custom made at a machine shop.
In the front of the picture below are the two halves of the 115mm diameter flange die - female side on the left, male on the right. It's easy to see the shoulder on both that creates the flange on the lightening holes.
The process is easy. Place the blank over the male side....
Invert the female side and place it on top (carefully - the dies are heavy tool steel and dropping them will permanently damage the blank and maybe the die as well!)
A shop press would work well here, but two large C clamps and the bench-top edge work just as well. Make sure to use two clamps the same so equal turns on the handles makes even clamping force on the dies. I did four turns on each at the same time, going about a half turn each time and it worked well.
The distance to compress the dies together isn't much. Top photo before compression, bottom photo at the end of travel.
Take the dies apart and the flange is complete - total time about 2 minutes each once I got into a rythym.
The process is repeated for the wing ribs, using the correct flange die size where appropriate.
The smallest flanging die only requires a single C clamp centered over the hole. Credit to my daughter Caitlyn for taking some of the following photos of me working!
After about 90 minutes, all the wing, wing tips, root and nose ribs for both my wings are now flanged and ready for fitting on their spars.
Something really cool looking about the symmetry of wing and nose ribs laid out side by side on the table
Next up, I'll get the 063 spar web doublers cut from the sheet I bought, bent and fit one to the spar. Then I can proceed to add the spar pick up, the strut angle and strut pickup. With everything fit, I'll drill/flange the lightening holes, begin drilling all the holes to correct A5 and A4 where needed. After that, disassemble, debur, prime and reasemble for final riveting. Just a few more steps!
Thanks for following along, it was a productive week indeed!
It's been some time since my last post, sorry. I do however have some progress to report on.
I took some time last week to start digging deeper into getting the 3D printer working. YouTube and Google are well known sources of information (as everyone knows - duh!) and there are tonnes of tutorials and "for Dummies" content out there, including how to calibrate and start printing with this early generation HicTop Prusa printer.
First thing I learned was that any design 3D model must be converted to G-code by intermediary software. G-code is the machine language used by 3D printers, milling machines, etc. to interpret the 3D design in a way that can be understood by the machine, i.e. how to move the stepper motors in each of the 3 axis, how/when to extrude the filament and the path the print head must follow.
The software that does this for 3D printing is generally referred to as "slicer" software.
I loaded up the official 3D test file from the HicTop website which comes as an "STL" file. The test file is a 4 leaf clover shape. In a nutshell, an STL file stores information about 3D models. This format describes only the surface geometry of a three-dimensional object without any representation of color, texture or other common model attributes.
These files are usually generated by a computer-aided design (CAD) program, as an end product of the 3D modeling process. “.STL” is the file extension of the STL file format.
The STL file format is the most commonly used file format for 3D printing. The true meaning of the file extension .STL has been lost to the mists of time.
It’s widely believed to be an abbreviation of the word STereoLithography, though sometimes it is also referred to as “Standard Triangle Language” or “Standard Tessellation Language”.
With the file downloaded, I ran a free slicer program called Cura. Cura has many settings to customize a print but for this test, I went with the defaults with the exception of the filament diameter which I changed to match what I had loaded in the printer. Cura then converted the STL file to G-code, which was then exported to a SD card. The SD card gets placed in the printer and I started my first print (which as you will see below turned out pretty good!).
I asked Cura to add a base to the print called a "raft" - this is a small lightweight layer that is laid down first, giving a good base for the print to adhere to:
With the raft complete, the printer moves into position to create the 3D print, guided by the supplied G-code information:
Layer by layer, the extruder lays down a steady stream of melted filament, building upon the layer before it. I captured a video of it working here. This isn't sped up, it actually works at this speed (sorry about the noise!)
The test model is actually much taller, but to save on filament (and time), I stopped the print after a while as I was satisified everything was working as it should. I'm pleased as how well it turned out - nice and smooth and well defined shape wise:
Excited to try another print, I went back to the internet to find a 3D model for an airplane part I can use for my build. I'd seen someone had posted a trim cable fairing for Zenith aircraft. This fairing works as a passthough and strain relief in the tail of my airplane, or anywhere else that might be suitable.
I downloaded the free model (thanks to 3D model sharing site www.thingverse.com) and upoaded it into Cura Slicer.
Instructions from the original 3D modeller said they had best results when they inverted the model for printing and adding support structures. Support structures are somwhat like a "raft" described above and are used to support parts of the 3D model that overhang, preventing them from sagging or warping. First step is to invert the model:
Next I asked Cura to add supports. Here is a screen capture of the model showing all the layers including the supports (light blue). Cura allows you to show each layer of the print head path(in dark blue) - this is layer 133 of the print. You might notice adding support increases the print time and filament material used:
With the model exported to the Sd card, I started the printer again, this time with the new model I just converted with Cura. The following few pictures also show the second model in the set - a drill hole template that was included with the fairing model. It again starts with a raft for both:
The drill template is only about 15 layers thick, so when the printer finished it, I peeled it off the bed.
The printed item breaks away easily from the raft. The small scorch mark you see is actually extra filament that leaked out of the hot end print head and dropped on the printed piece (more on this later):
As I looked at the finished drill template. the printer chugged along building the fairing layer by layer. It's hard to capture the process as the bed and print head are constantly in motion:
Slowly the model starts to take shape:
Getting close to being complete, but you can see the print head is leaking badly!
After just over an hour, the printer head moves back to the home position and reveals the completed print!
Some room for fine tuning, but overall it seems like it turned out well!
I asked for the supports on the entire print as I didn't know any different, so Cura added them inside the throat of the fairing too. That will be easy to fix by cleaning it out with a small drill bit.
The print seems to have either warped or sagged at the one corner. It didn't affect the print in any way, but I suspect this requires another check of the print bed levels.
The main body of the print breaks away from the raft easily:
So do the supports. I'm printing these initial models with PLA (Polylactic Acid) which is different than most thermoplastic polymers in that it is derived from renewable resources like corn starch or sugar cane. Most plastics, by contrast, are derived from the distillation and polymerization of nonrenewable petroleum reserves. Plastics that are derived from biomass (e.g. PLA) are known as “bioplastics.” All the waste created by the supports and rafts can be recycled.
The base of the model is very smooth as it was last to print (model was printed upside down as per the suggestion online). The upper surfaces are a bit rough, but I think that's more to do with the support settings than anything and those can be adjusted.
The next models I tried printing were some edge markers. Unfortunately, they didn't work out well at all. I suspect I failed to set the model scale corrrectly and it looks like the extruder leak still needs to be addressed!
Overall, I'm really pleased that I got the printer working. I learned a tonne and I'm looking forward to doing some more with it. The possibilities are endless!
Back to the shop this morning to work on inboard slat #2. I followed the exact same process as the first slat and that experience made this one go much faster. I finished priming and assembling it back together:
After a hour or so in the slat box I finished riveting it together. Slat # 2 complete!
So, my completed parts picture is starting to fill in nicely!
I put both outboard slats aside for the time being and pulled the outboard slat skins out of storage to begin laying out the measurements for both of them. They follow the same method as the inboard ones, other than they are longer than the inboard slats. The inner skeleton remains the same, it's just shifted a bit more towards the centre:
A couple of hours later and the outboard left is substantially complete. Next up I'll continue the process and bend the trailing edge.
More to come with the 3D printer. I'm really stoked to try the 3D scanner and print something from that!
Another 15 hours done on the wings. Stay tuned for more, thanks for following along :)
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.
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!
So, a lot has been happening in the world in the last week or so.
The Novel Corona virus, better known now as COVID-19 has seen exponential spread across international borders from it's origins in China. Unless you have been living under a rock or are reading this blog in some distant, future archive (thanks by the way!), news and anxiousness is rampant about what is now officially declared a pandemic. People are scared, some more than they realistically need to be and world financial markets are feeling the squeeze.
Mandatory closures of schools, businesses and government facilities are becoming commonplace as we work to "social distance" ourselves from others. Large groups, social gatherings, events and meetings are highly discouraged if not outright banned Efforts are underway by people everywhere to prevent the spread of the virus and protect those who may not have the benefit of good health and the ability to fight off this particularly nasty bug - it can and has been shown to be fatal. Unfortunately there are those ignoring common sense which is leading to more anxiousness and unease. This has even lead to a very strange phenomenon of the panic buying bulk toilet paper!
I've said before how much my shop time is my happy time. It's my place to decompress from my emergency services job. While a good portion of society has been told to stay home from work, my colleagues and I continue to work shifts in a busy 9-1-1 communications centre and although the calls for service have yet to peak as I think they will, we are an essential service and will continue to come to work and answer the calls. It's scary but I think we'll come out the other side of this craziness better off as a society from the lessons learned.
So, what better way to practice "social distancing" and "flatten the infection rate curve" of COVID-19 ng than to get to the shop and work on my build! Here's what's happened since my last blog post.
A couple of weeks ago, I traveled south to visit Dad and made a side trip to Princess Auto and Aircraft Spruce for tools and hardware. I needed an inch/pound calibrated torque wrench and was happy to find a good quality one on sale - score!
I stopped at Aircraft Spruce and picked up my online order of the remaining aircraft hardware I need for the build, other than some back-ordered nut plates and stainless machine screws. Obviously this isn't everything I'll need (the interior will require some fabric fasteners etc), but what you see in the picture below is the lion's share of bolts, nuts, washers and cotter pins called for in the plans.
I've primed and final riveted the elevator outer hinge pins
With the elevator all closed up I started fitting the trim control rod and servo arm
Here is a good look at the servo arm and trim control rod. I'm not happy with how they fit together as there is too much slop or play between the pin and the arm, so I'll likely put some JBWeld metal epoxy in the arm hole and drill it out to match size the rod arm pin.
The rod as it comes from the hobby store is plenty stiff enough to work in this arrangement, but comes much too long. I attached the trailing rod end to the trim tab actuator bracket. With the elevator trim in the neutral position, I held the road alongside the rod end, trimmed the rod to length on the bandsaw and ground it smooth on the bench grinder.
I specifically left the rod long enough so that I can trim is shorter if needed. The plans call for the elevator to deflect 20 degrees up and 40 degrees down from neutral. Before I can set the system up, I'll have to thread the this end of the rod for the safety nut. I may change the "neutral" position of the servo arm to favour the 40 degree pull - it will take some playing around to get it just right. The servo programming is the easy part!!
Some final clean up of the stabilizer was completed and I temporarily closed it up with rivets, just like the elevator. The insides will have to be inspected by Tansport Canada before all the final rivets are done. Stabilizer fences are just temporarily attached for storage purposes and may need to come off to open it back up for inspection, but I may get lucky and they can stay on for final riveting.
The following pictures show the completed tail assembly with outer and centre hinge pins installed. It lined up perfectly and shows no signs of binding - very pleased! (it's sitting on the bench upside down compared to how it will be mounted on the plane - it just sits better that way).
So! The tail is now complete. I currently have roughly 150 hours of work into it. Once wrapped in heavy plastic it will join the rudder up in the storage barn. There's about another full day's work once it's cleared for final close up to complete, with a lot of that having to wait for fitting to the fuselage.
I feel so productive and safe from the world's dangers in the shop right now. With all the temporary closures, I couldn't think of a better place to stay safe from COVID-19 - working on the some temporary closures or my own :)
Thanks for following along. Next up flaps and slats!
A bit of time in the shop this week. Dismantled the elevator (again) and deburred the holes now that everything is drilled to right size. It's points like this in a project that make you feel both accomplished and behind at the same time. You realize all the work you've done to this point by the number of holes you've drilled, but taking it all apart for deburring seems like a backwards (but necessary none-the-less) step.
Deburring the trim tab after it is bent is problematic. The holes for the hinge can't be drilled without having it bent to shape first. How to debur the holes on the inside angles (see yellow arrows)? Make a tool!
Normally we'd use a rotary debur tool, but access is too tight. To get access, I came up with this idea.
1. Slot a piece of wood
2. Insert sandpaper
3. Slide onto flange
4. Gently and carefully slide back and forth along the length of the flange. The goal here is to remove the burrs, not to sand the flange. It worked really well!
A follower of the blog had asked me why the elevator skin looked wrinkled in the pictures on the bench and the look of wrinkles is due to the protective plastic coating on the sheet aluminum. I've now peeled that back anywhere there are rivet holes so I can properly debur them. I'm leaving the remaining plastic on the skins to help prevent scuffs and scratches as I work with them off the skeleton.
With the elevator skin off the spar, now is a good time to fit the trim servo. The bracket I made will work, but now that I'm fitting it I've discovered something I hadn't thought of. If I have to remove the servo for replacement or repair, orienting it this way (mounting screws are sideways in the bracket) means it will be painful if not impossible to remove it through the access hole!
I decided it best to create a new bracket similar to the one Ron is planning for his 701:
It took a couple of tries to get it right, but it turned out well!
I'll need to add a grommet or strain relief at the pass-though hole to prevent the servo wire from chafing:
The servo will sit on an angle, parallel to the inside of the skin surfaces - the more direct the push/pull rod can be to the trim tab control horn the better.
As I sit on nightshifts at work, I have some time to ponder what else I can do with the Arduino. The ideas are truly endless and easy to implement. One thing that really excites me is the ability to display data on little screens. For example, here is a picture from the internet where an Arduino programmer has an OLED (Organic LED) panel emulating a basic cell phone display. OLED displays are super cheap and highly customizable and some models are capable of displaying in different colours.
Here is another example of a development board with an OLED display connected to an Arduino mini exactly like the ones I'm using. They are very small in size, but can be used to display lots of things at really bright contrast and resolution.
Here's an animated guage from the interwebs being used for something someone was developing:
If animation can be done, animation in colour can't be much more difficult.
I'm pondering a small display like this on my instrument panel, with a custom display graphic. Perhaps a overhead drawing/graphic of my airplane with animated lights that blink in co-ordination with my navigation/strobe/wig-wag lights! How cool would that be? Here is a (very) rudimentary idea about what it might look like. I can't animate this picture, but I think you get the idea - the red/green nav/beacon/strobe lights would blink or in the case of the landing lights alternate back/forth when in wig-wag mode. Maybe I can animate the prop too hahahaha!:
Maybe instead of the bar graph LED showing elevator trim like I already have planned, I can integrate the bar graph onto an OLED display, either by itself or with the light display above:
My engine gauges will be traditional mechanical versions - much more robust. Everything I propose here is for non-critical indications.
I've got a long way to go before I have to worry about this stuff anyhow, but it is cool to think this is easily and cheaply within reach for a simple hobbyist like me!
Some my regular readers might have noticed I've removed the countdown timer from the right navigation bar of the blog. I originally intended this to be a motivator for me. I had set the goal of first flight to be my 50th birthday, but that is never going to happen. I got behind in my build with changes at work etc., so I'm removing it for now as it doesn't reflect reality. I'll continue to strive to get the build done.
Next up, priming the elevator pieces and reassembly for riveting!
Thanks for reading :)
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? :)
Sunday was a good day in the shop, and both Ron and I can see the finish line with the 701 wing repair and extension. Just a few more small items to go.
As Ron gets close to covering his Aeronca Scout with fabric, we've been discussing his plans to make a fabric/pain rotisserie rig for the shop. You may recall from way back in this blog an engine stand I bought for my Corvair. With my engine parts in Florida for rework, we're going to modify my engine stand and Ron's engine stand to become the end pieces for the rotisserie. This rig will allow us to mount any fuselage, wing or other large parts for priming and painting and being able to rotate them will be very helpful.
The inboard nose skin is ready to be installed. I clamped the skin in place, lined up along the spar. To draw the nose skin tight, ratchet straps are used, pulling the skin tight across the ribs. It's important to place the straps directly over the nose ribs to prevent caving in the nose skin before it is riveted.
Straps are equally tightened until the nose skins lay tight against the nose ribs and spar:
Folded protectors distribute the force across the trailing edge, thin scraps of wood protect the surface skins from the ratchet and strap hooks.
Using the hole duplicator, I matched the new nose skin to the original spar holes on the upper side of the wing. These were drilled to final size, the nose ribs to A3 until final fitting. The 3rd rib is drilled, but missing clecos so I can fit the outboard nose skin where it will overlap the slat pickup.
Once measured up, the outoard skin needs to be slotted to allow the slat pickups to protrude through. The easiest way to do this is with a trim router and spiral up-flute milling bit. I laid the outboard skin out on the table and set clamped a straight edge in place as a guide. Two strips of plywood under the sheet on either side of where the slot will be cut support the thin aluminum sheet and are thick enough to raise the bit above the table
After cutting all 3 slots perfectly straight, a valuable lesson learned - even if you right down the measurement, that is no guarantee that what you wrote down is correct :(
I measured the first slot as 395mm from the inboard edge, but for some reason I wrote down 595mm. From that point on, every time I double checked before cutting the slot, I measured/checked it as 595mm. Bringing the sheet back to the wing, my error was immediately obvious.
After pacing around the shop wondering how I could have possibly messing up the measurement, Ron told me he could fix the error fairly easily with a simple patch - go ahead and cut the right slot. This is part of learning and too much sheet metal to start over.
With the correct slot cut, all the slots lined up perfectly with the slat pickups - minor crisis averted.
Before working on securing the top side of the outboard nose skin, we thought it best to finish securing the inboard nose skin, that would give us a solid reference point for the outboard skin. We flipped the wing over and end for end on the bench. To get the nose skin flat, a thin strip of wood is placed under the ratchet straps. Once lined up and tight against the ribs, I again duplicated the spar holes and drilled the ribs to A3 size. Everything lined up excellent.
Even this nose skin, as small as it is lengthwise makes the overall wing so much more rigid. A good sign.
While waiting to discuss my slotting error I also unrolled my 040 sheet and start marking out the 3 horizontal tail doublers I need. I was initially really surprised at the amount of tape Aircraft Spruce used to secure the roll, but quickly understood why! There is a bunch of pent up spring energy in that roll, and I had to be real careful about wrangling it onto the flat floor for measure/cutting. The longest piece I need from this sheet is 1440mm long, so it was safe to cut that length off the end of the 12 foot long sheet. I marked and rolled the balance back up (that was a task!) and put it back into storage.
Aircraft Spruce ships all their sheet aluminum with a protective plastic sheet coating on both sides. Depending on how long the sheet has been on the shelf, room temperature, and other factors determines how easy it is to remove this coating. I think next time I'll gently warm it with a heat gun or hair dryer - this stuff sticks too good. For now, I've only removed a few inches from the edge I'm cutting from.
Even cut down to length, this sheet is awkward to put in the bender for scoring, and it's thick enough to making scoring a very long process. Instead, Ron and I think we are going to try using the router we used on the nose skin slots to accomplish the long cuts. If this works as we think it will, we'll use the same process for the wing spars (032) and maybe the fuselage sides/tops - anywhere a long straight cut on a large piece of material is needed. As I said above the tool makes really clean cut edges that require little in the way of deburring.
One other thing I've been doing is adding some of the complex shapes from the plans into CAD. Like my smaller parts (ribs, plates, etc.), these will be printed out to provide templates. One example is the wing root nose skin. I use a free downloadable 2-D CAD program called LibreCAD - it is very simple and more importantly it will accept the X/Y co-ordinate system common in the Zenith plans:
If you like doing things in 2-D CAD, you can download a free copy of LibreCAD here.
For those that have been asking, my finger is healing up nicely :)
More soon, thanks for reading.
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.