Yup, I said it..... no, I can't speak german... thanks Google translate.....ha ha!
The Corvair authority William Wynne talks extensively on his blog about different carb applications in a Corvair conversion and the importance of keeping things simple.
The dual (and sometimes quad) factory Rochester carb setup on a Corvair car engine not only complicates matters (syncing throttles arms, etc) they were never designed for altitude compensation and mixture settings required in an aviation application. The converted Corvair engine falls into the same horsepower range roughly equivalent to typical medium Continentals and Lycomings, approximately 100 to 120HP. This requires a fuel delivery system capable of delivering an air to fuel ratio capable of supporting this demand.
Fuel injection? I believe the advantages (no carb icing, small increases in HP) are FAR outweighed by the complex system components (injectors, return fuel lines, pumps, electronics, sensors, etc). Keep it simple.
The MA3-SPA carb as found on the O-200 continental and O-235 Lycoming is the definition of simple. They haven't changed much since the 1940's and Marvel Schebler continues to make new ones today - in other words it works, simple. Overhauled to new specs it's the perfect carb for my conversion.
Finding one that is both inexpensive to obtain and overhaul becomes a problem due to this popularity. A good core for rebuild can be found in the three to four hundred dollar range then count on six to seven hundred dollars to overhaul it. Expensive, but not an area I want to save money on - engine reliability is important in flying! The recommended overhaul shop (D&G Supply in Michigan) also will convert specific O-300 carb models to the Corvair specifications.
Armed with this knowledge, I've been searching online for a suitable core.
A couple of weeks ago while surfing E-Bay, I came across a listing for an O-300 Marvel Schebler carburetor that would be suitable for my engine. It's clearly an older one, but again the model number matches the acceptable models for conversion and the pictures showed well.
Like anything on E-Bay, Kijiji or Craigslist it's a buyer beware mentality. One has to consider the odds and what it's going to cost to ship. In my case, the core I was interested in had no reserve pricing but the shipping costs weren't cheap - it was in Germany! This compounds the pricing with the Euro being somewhat strong against the Canadian dollar. Worth a shot.
With this in mind, I did the responsible thing and figured out my maximum bid would be about 100 Euros. I watched the days count down and was pleased to see my bid of 40 euros was enough to win! With shipping and currency conversion the total costs came to $112 Canadian. Not bad and certainly better than what I expected to pay for a core.
"Mein vergasser ist angekommen" (which means "my carb has arrived") on Friday and I picked it up at the post office yesterday. My first look had me really worried as the box had a crushed corner and was split open at the top:
There was a sticker on the box from Canada Post stating the box was damaged by the forwarding shipper. Not good. One of the fears shipping any item overseas or otherwise is theft. Hope there isn't just a bag of sand in here!
Opening the box, I smiled a bit finding a note from the seller:
Opening the box further, it came apparent that the shipper used a lot of bubble wrap to protect the carb on it's journey, but more importantly there is a carb inside the wrap!
It's definitely old, but everything seems intact and the throttle/mixture arms move freely. The accelerator pump seems seized but that's typical of something that has been sitting on a shelf for a long time and that will be repaired as part of the overhaul.
The data plate is intact and shows this is a model 10-4895 MS carb, typically used on O-300 engines. This is a good carb for overhaul and conversion to the required specs for my Corvair!
Glad I found this. It will be sent for overhaul this fall.
Back to the shop soon.
Good day in the shop yesterday. Worked exclusively on the 701 wing repair and tip extension.
Lots of practice driving solid rivets in the spar extension caps. Ron showed me a great trick on how to secure the work piece to the bench that's I'll have to remember for my wing spars. By the time mine are done on the 750 I'll have driven over 400 of them!
Here is the completed spar tip extension:
More pictures showing the installation of the new wing and nose ribs. For now we've got them clecoed in place temporarily until the flap and slat extensions are complete. Once these are done we'll line them up properly prior to drilling the mounting brackets.
Amazing how solid riveting the front and back splice plates on either side of the spa web and caps make this a solid extension with no flex in the joint. Exactly what we want!
Finally starting to see the light at the end of the tunnel with this wing. Next up begin the skinning process..... and more learning :)
Spent 4 hours in the shop yesterday bending a large group of tail parts for my 750. Nice to get back there. Here's what I got done:
Here's a diagram of what I've got done so far (completed parts shaded in blue):
Happy with how these parts turned out, but need some more practice to make them perfect. Back to the shop in a couple of days. Spars and various fittings to be cut out then I'm ready to start building the tail group.
I had every intention of spending the entire day in the shop today. I'd taken the time last week to mark specific "shop days" on the calendar - days that are set aside for the shop and my build. A discussion with Brenda and our girls regarding my build led us to an agreement that these days are next to untouchable on the schedule so that I can make real progress this year. Obviously if something special comes up that can't be scheduled somewhere else my shop day can be compromised by moving it to another day, but the goal is to maintain a regular shop presence.
So, I discovered that "something special" can also includes those days when I physically can't go. Today was one of those days.
Last night at Natalie's Scout meeting, I tried to prove that I could still play volleyball like a 20 year old. A "I-used-a-could-do-that" type of thing. Needless to say I slept poorly last night and felt like I'd been run over by a Russian cargo plane today, so I missed the shop.
After some rest and feeling sorry for myself, I decided I didn't need to go over to Ron's and could at least get something done here in my own shop.
I pulled out something simple to work on - the flaperon rear ribs. These are simple flanged parts, really just smaller versions of the elevator rear ribs I made before (see my previous blog post here).
It starts with lining the forms up on the metal template. Unlike other templates, due to their size they don't have bolt holes for the forms. Just line them up and place the entire sandwich in the vice:
The soft faced dead blow hammer is used to gently form the flange over the edge of the form:
Turns out the flanges are a bit wider than the thickness of the form. With the short top-to-bottom height of these ribs, I had to devise a way to protect them when I inverted the form to bend the opposite flange. To do this, I added two blocks on each side. One of them had a small groove cut in it to make room for the opposite flange but still enough area to hold the forms:
As per the plans I need 8 left hand and 8 right hand rear ribs and I made a conscious decision to do only six right hand ones first in case I mistakenly made a right hand one when making the left hand ones. Hate to end up with extras - that would mean making replacement templates for each one I screw up. It's easy to see how this could happen, glad I thought of it ahead of time. Good trick to remember for later when I start working on all the wing ribs!
It's amazing! With a bit of attention to detail, I managed to bang out 16 flaperon ribs, all of equal dimensions and quality. Really cool.
16 complete ribs.... not bad for a day I didn't feel up to doing anything :)
I also got a new 14 tooth-per-inch blade for my band saw. Installing the new blade was challenging, but I learned on YouTube how to properly set the tension and blade guides for my model. Once I make some of the rougher cuts on the plate aluminum using the big industrial saw at Ron's shop, I can use my fine tooth band saw to make the final cuts.
I've said it before.... a little shop therapy goes a long way :)
p.s. Photo credits to my daughter Natalie.... thanks for making me look good!
Looking back this year I'm pleased about the progress I've made on my airplane build. I don't have a bunch of tangible things to show for it, but the amount of learning I've done, both with mistakes made and discovered, and with new experiences and skills learned is amazing.
Some of the 701 wing repair/extension stuff I accomplished this week:
Drilling and riveting the rear wing spar extension doubler sleeve (say that 5 times fast!)
Marking out the new wing rib to wing tip extension spar:
Tying back the wing skin to gain better access:
With room to work, laying out the proper location for the rear wing spar extension. Length is critically important for maintaining wing rib squareness:
Lots of A5 rivets here...
On the original 701 plans, each wing rib is full length from front spar to trailing edge of the wing. To enhance the strength of the rear extension spar, we've decided to split the wing rib at the rear spar. Here is the first one being held in place before being trimmed to fit. It will be fastened using the two inboard A5 rivets at the spar joint. Which I'll have to drill out as we hadn't thought this was the route we were going. Learning, right?
Installed after trimming with two new A5 rivets:
The wing rib attaches to a new bracket which also is attached to the spar sleeve with A5 rivets. Thankfully I waited to attach these after fabricating and fitting the bracket. Note the two rivets that are placed in reverse direction due to limited spacing inside the small rear rib section:
Here are the new ribs in place. The next rib went much easier as I didn't have to contend with the wing spar joint. The rear rib section still has to be fabricated and we have to decide on how to make the new flapperon pick-up bracket. I've still got to finalize the inside wing spar extension doubler, not happy with the fit yet. We'll wait for final squaring up and deburing before final rivets.
Another view. A few more tiny details to finish up (nose ribs, trimming the rear spar to 45 degrees for the wingtip etc) then we'll start to skin the wing extensions and the areas that need replacing near the root where I made the repairs earlier. Progress!
2017 definitely has been a busy year in the shop.
My goals for 2018:
Happy New Year everyone..... all the best to you and yours and thanks for following along!
Been steadily working to complete the wing extension. Haven't had much change to work on my own stuff, just trying to get the 701 stuff done to make room on the workbench for the larger sheets of 0.032 and 0.042 thickness. I need the room to make the long spars for the tail. I'll likely do the wing spar webs at the same time. Likely going to try using a router to make the long cuts, but more on that later.
I reattached the original spar tip to take some measurements to confirm the lengths of the extended spars. It took a lot of figuring because the original builder (as I've stated many times before) wasn't really accurate with measuring his parts).
I temporarily added the first of two new ribs and clecoed the flapperon back in place to aid in measuring for the rear spar extensions for each:
A lot of time doing repairs is fixing the little things one comes across during the rebuild. Ron has told me that this plane was a mess of wrong measurements. As a result, it never flew straight as designed, so the original owner added fixed trim tabs all over the place. These "correct" handling issues by working against aerodynamic forces as the plane flies through the air. We want to start with a properly built aircraft and only add these if they are required. So this one on the flaps has to come off:
With measuring and measuring, checking and measuring again I made the new spar extensions. What took a long time was making the doubler sleeves that connect these to the original spars. Using some scraps of the same thickness, it took me 3 tries to get them exactly the right size. They have to fit on the inside of the spar to ensure the wing an flapperon skins have a continuous level surface to attach to. In the picture below, the inner sleeves are actually on top of the new spar extensions for the sake of the picture. This process will be repeated for the leading edge slats, then everything again on the second wing when we get to it.
That's it for now my dedicated followers. I've got some time set aside this week for the shop (between Christmas shopping and my paying job). Lots of lessons learned this past couple of weeks that will really be helpful when I start working on my stuff.
Stay tuned, next update coming before Christmas (hopefully).
Can't believe it's been over a month since I posted to the blog. The second half of October and first couple of weeks of November have escaped us. Unfortunately, I felt like I had't gotten anything done in that time, but going through my photos, I see there is more done than I thought.
I had to go away for a week due to work, but I decided to make good use of my evenings in the hotel. I took my wing rib blanks and final sanded them as I watched TV. Got some laughs and strange looks from my co-workers when I told them I was building an airplane in my hotel room!
When I cut out the rib blanks the bandsaw kinda chewed up the inside corners of the ribs:
So when I got home and back to the shop I came up with a jig for cleaning these up. I drilled a slightly larger hole in a scrap piece of wood and set the sanding drum up on the drill press to fit inside. This gave me a working surface almost like an inverted router:
The sanding drum cleaned up the corners really nice and I finished them off by hand sanding.
On preparation for finish bending of the tail group pieces, I had to drill the tooling holes in the forms. Best clamp them together evenly and drill each on the press:
When I tool out the tail group blanks, I noticed that I still needed to add the second tooling holes to many of them:
To save time and ensure accuracy, I decide to drill the stack of blanks together, using the available tooling hole as a reference point. A bolt and wing nut held the stack together and a form block and clamp were used to place the tooling hole accurately:
With the tooling holes established, the second bolt is added as well as the back half of the forming block. Here is an elevator rear rib bolted up and ready for bending:
The whole sandwich is mounted in the vice:
A soft faced (plastic) dead-blow hammer is used to round the aluminum over the edge of the forming block until flat:
Remove the form block and voila! My first formed part for my airplane! YAY!
Four of these ribs are required, so repeat the process 3 more times. Two left and two right complete:
I'm real happy how these turned out. They are pretty simple compared to some of the other parts in the tail group, but they are nice and straight, so my efforts to make the form blocks accurate paid off.
The next thing I wanted to do was get more of the thicker parts traced and cut out. Ron figured a 2 x 2 sheet of 0.125 aluminum would suffice for the parts I needed.
The sheet comes from the supplier covered in a thin plastic covering on both sides which is a pain to remove:
This particular piece of aluminum had been sitting around the shop for a while and fell victim to a few scratches and dings. Once I cleaned off the rest of the plastic and adhesive residue I circled any areas of concern and got to work tracing out the parts, nesting them as best as I could, starting with the flapperon arms:
Eventually I managed to fit 25 pieces on the sheet. It's tough to know the absolute best layout to minimize waste, but I'm only missing a couple of pieces which can be done later:
That's it for this update. Next up, more 701 wing extension work, bending more tail group parts and rough cutting the 0.125 parts.
Spent some time in the shop on a rainy day.
Managed to make the rear elevator trim channel. It's critical to ensure this is made straight and to the correct dimensions as the covering skin leaves little room for error. A millimetre too big or too small translates to many problems, so I want to make sure I get this right, and it will be good practice for bigger parts later on in the build.
Unfortunately I've learned the plans sometimes leave out the "developed length" dimensions on some of the parts. In other words, what the dimension is prior to bending (which changes the length or width of a part as it bends). Not a huge deal if you are buying a kit as these parts come pre-formed for you, but for a scratch builder like me it's a critical piece of info. The math to figure out this isn't overly difficult, but making it repeatable using different material thicknesses and bend radii could be tricky.
Looking at the Zenair builders website, I found a great spreadsheet put together by another builder that does the math for you. It asks the basics (thickness, flange and web lengths and bend radius required). Input these or at least the ones known and the spreadsheet returns the "flat" or "developed length" dimensions. It's these that you use for cutting the raw aluminum. Here is a look at how a bend is calculated:
The spreadsheet makes it easy to apply the math, in this case for a piece of stock being bent into a channel:
So in the example above, entering 18mm for both flanges, with a channel web length of 80mm, requiring 90 degree bends with 1/8 inch (0.125) radius bends in the material 0.016 inches thick results in a developed length (dl) of 112.01mm. Just adding 18+18+80 mm together doesn't account for the bend radii or the thickness. The other result is handy too. Measuring 16.41mm in from the edge of the flat material provides you the sight line for the bending brake. I'm obviously only going to get as close as a half millimetre to these dimensions, but that's well within acceptable limits. Perfect, right?
One thing I learned early on in the process of making parts for the 701 wing repair is to use the never ending supply of scrap corners to try the theory before actually bending the full size parts (cheaper to experiment on scrap!)
So, I measured out the required dimensions on scrap, used the markings to align the piece in the bender and voila! Perfect example of what the full size piece should look like - this channel has two flanges, on at 90 degrees and one at 105 degrees.
Repeat the dimensions on the full size piece and bend the same way. Perfect and straight!
Finished off the relief angles on the rear wing ribs and root rib forms:
With this done, I made some headway on the 701 wing extension. Next step was figuring out the inside web doubler.
It's a bit of a puzzle as it needs to be fitted to span the spar caps top and bottom, the spar web and the closest wing rib. Consideration also has to be given to where the spar cap rivets will come through this doubler.
After careful measurement, I drew out the initial shape of the doubler. The dotted lines running left to right are the distance between each spar cap. The vertical dotted line represents the flange for attachment to the win rib:
To make the doubler fit correctly by sitting flat on the spar web and over the spar cap flanges requires a technique called "joggling". A joggle is a rise in the surface of the metal to overlap the adjacent panel or other piece. It's also used in reverse to create a depression in a surface to allow another piece sit flush, such as an inspection cover.
Joggles can be made in numerous ways, but I found a real neat tool that can be made out of scrap aluminum plate.
First, I measured out a rectangle of 0.125 aluminum plate:
Measure out the piece for a flex hole and bend slot:
Drill a hole on the press with a step drill bit. Makes a nice clean hole:
Cut the bend slot to approximately the same thickness as the plate, in this case 0.125:
Grind and sand everything smooth.
To use the tool, insert the piece to be joggled in the slot:
From here you have a couple of options. Thin gauge metal could be bent by hand by pressing down on the top of the "X" formed by the piece and tool.
Because this piece was made of 0.025, I decided to use the better option of pinching it all flat in the vise. This provides a much cleaner joggle and both sides of the bend lay flat. It's hard to capture this in a picture and I forgot to show it in the vise, but here is the result:
I purposely left both the flanges on either of the joggles wider than needed as the important dimension was the distance between the spar caps against the spar web. The flanges can be trimmed after test fitting it in place.
What a great tool. I made it big enough to do anything that needs joggling on my plane as well.
Next up, trail fitting the spar tip extension inner doubler and fabricating the rear rib channel. I want to get my 750 wing and root ribs final sized so that I can finish sand them prior to bending.
Until next time!
So Facebook reminded me this morning I hadn't posted to the blog in a little while but rest assured I've been busy at the shop.
First I had to tape together each of the four sections of wing rib templates and make sure the matched the plans. I used the form template as a rough guide and pinned both to the table for measuring:
After confirming the template is exactly as per the plans, I unrolled a sheet of 0.025" sheet and traced out 12 rear wing ribs and 2 root ribs. It's a bit of a challenge to arrange them to minimize waste:
It took about an hour, but I managed to get the big sheet cut down to manageable size then separated each of the ribs as rough cuts using the bandsaw:
Lots of final trimming and edge sanding in my future!
Work continues on my forming blocks. Now that I have them cut out and sanded to final size, the next step is to router a 1/8" roundoff edge on the inside (metal facing) edge. This prevents the aluminum from bending too sharply:
Next, I needed to figure out a way to bevel the outside edge of each form to create springback relief. Aluminum, particularly thinner gauges needs to be bent 6 to 10 degrees past 90 degrees in order to spring back to the intended angle. Turns out Ron still has the table adapater he made for his forms:
Here you can see a nose rib form sitting on the adjustment table just before I sand away the springback angles:
Here is a good picture showing the nose rib forming blocks, stacked as they would be in use. The routered edge and springback angles can clearly be seen:
Just to confirm everything matches up, I placed the aluminum nose rib blanks between the form blocks for a picture.... perfect fit and ready to start bending soon!
Encouraged by my success, I continued onwards with the rest of the form blocks for the tail group and they too are ready for bending aluminum blanks. Really pleased how these turned out:
Work also continues on the 701 wing repair. As part of the tip extension, two new full ribs will be inserted between the last factory rib and the wing tip. The necessitates cutting back the original rear rib channel:
Trimmed of the flanges of the existing rear channel leaving a long tab that will attach to the new wing rib we are inserting at this location. Once I have the wing rib in final position, this will be trimmed accordingly:
This new ribs will form the support for the wing skin extension joint and a second rib will provide the outermost structural pick up point for the extended flap and slat lengths. Here is the first extension rib test fit in place:
Next up, figure out where the second rib needs to be by determining where the outermost flap and slat pickups will be. Once I know that, I can make a new rear channel and also decide on the second part of the spar cap/web inner doubler. It will have to be attached to ribs too.... phew.
Progress... back to the shop again for the day tomorrow, hopefully to finish off the wing rib blanks and the wing rib form blocks. Thanks for visiting!
One of the things that I'm really enjoying about being in the shop working on airplanes is it gives me a great way to decompress from work as a 911 dispatch supervisor.
With new technology arriving every day at work, it becomes very difficult to champion change as a team leader in the communication centre. We're all feeling a bit overwhelmed and morale at work isn't the greatest right now. I think too that we all feel we were robbed of the summer as the leaves are already changing here in our part of northern Ontario. Winters tend to be fairly sedate (we don't use the "Q" word - that's how you summon death and mayhem in emergency services) and as a result nightshifts feel longer. It's no fun going to work in the morning when it's dark and coming home when it's dark.
Going to the shop for some plane therapy helps, so that's where I headed tonight.
I made working on the 701 wing extension a priority tonight as Ron wants to get that finished up so we can concentrate on both my 750 build and finishing off his Scout. Once they are complete I'll be able to get some stick time in both while we fly off the required post inspection hours. We're aiming for spring and that should be around the time I'll need use of the workbench for my wings and fuselage.
I've been working on the wing tip extensions. We decided to extend them by 18 inches and this requires extending the wing spar caps as well. These will be extended out to the tips, giving a much stiffer extension that what the plans call for.
Here I'm using the rivet pitch guide to centre punch mark the rivet hole locations.
After marking, and using the drill press to make the holes in each of the upper and lower cap angles, I backdrilled each of the spar cap extensions through the spar web extensionm adding clecos as I went to ensure the spar web cap remained in the correct place.
Take it all apart and debur all the holes on each piece (my new tool works great for that!). Then reassemble with clecos and test fit in position at the end of the wing spar. Perfect fit, tight and level!
Fit the front side spar web extension doubler and back drill through the web. Disassemble, debur, reasemble for final fit:
I've made the spar caps match the angle of the spar tips. Really like how they look and how they will secure the tip skins:
Great progress tonight...... not bad for 3 hours of therapy :)
Time until takeoff
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.