For quite some time now I've been helping Ron rebuild the wings on a 701 - using this as a learning experience towards building my 750.
In an attempt to ramp up our progress on the repair so we can get back to building new airplanes, we've been working hard at the flap extension.
It's become a huge quagmire. NOTHING that the original builder matches the plans. We could forgive a little tolerances here and there - IF THE TOLERANCES WE EVEN CLOSE TO WHAT THEY SHOULD BE! Even worse, it seems to have been a real terminal case of TLAR.... "That Looks About Right".
We've been building any new parts for the repair and extension exactly as the plans call for. However when we add those as components of the flap extension, they seem to create more problems because the "good parts" of the original builder are not "good parts" after all. Assumptions...
For example, we've had to add 3 rear ribs and a couple of nose ribs. Perfectly sized parts according to the plans. But the originals are several millimeters bigger than the plans, so the new extension skin doesn't fit right, it won't wrap tightly down to the new ribs, nor will it remain straight (leading and trailing edges). There is no way to predict this as none of the "changes" the original builder made are to scale (nothing is larger or smaller by the same amount). Assumptions...
What does this mean for us? Hours of thinking and rethinking on how to get the job done. I know the extension is our idea, but really that should be just more materials - if the dimensions were right (or at least close) on the original, we wouldn't be fighting at each and every step of the build.... sigh.
We'll keep working on it and I'm certainly learning where to watch tolerances. So far the pieces I've made for my 750 are real accurate to what is shown in my plans, so I'm happy. Guess I'll have to wait and see how they go together in assembly but I have much more confidence than I do with this 701.
Speaking of assembly, someone on the Zenair builders website was kind enough to email me a copy of the latest revisions to my 750 STOL plans. I have "Edition 3" plans, but with any design they are updates and additions made by the Zenair factory. Most of these are small changes made to make things incrementally better and of those most come from builders suggestions.
Having a look a the 20 or so pages of updates he sent me initially made my mind spin:
After pondering these and truly wondering what the hell I was thinking when I decided to scratch build this airplane, I decided the best way was to set aside some time at the dining room table and make notes on my plans of the updates:
The entire exercise took me most of a Sunday morning with breaks here and there for food, water (and sanity), but I think I have a good handle on what is important and what isn't. I probably have more freedom to decide what changes I want to incorporate as I am still early in my build and I'm making my own parts so unchanged parts can be modified to match up with the new designed parts easily.
A lot of the changes are simply cosmetic and make the 750 STOL have more part commonality with the more recently introduced 750 Cruzer model.
Onwards fellow builders and thanks for continuing to follow along.
Not a huge update, but a few things to mention this week.
Ron and I got further along on the 701 wing repair the last two weeks. We are being really challenged by the mistakes of the previous builder's measurements and decisions on what was "good enough". We've compounded that by adding the wind extention, but we are getting it figured out.
The flap extension to match the new wing length is coming together nicely. Because this is an add on, wrapping the short flap skin is certainly fun...
Once we get the flaps skinned we can fix the spacing of the flap brackets. As most things on this repair, nothing is consistent, even between both wings. Having the flaps apart allows us to adjust where they meet the flap brackets. Make it right has been the goal all along.
The days lately have kinda blurred together with my new position at work, but I'm certainly not missing the shift work that's for sure. It has made it somewhat difficult to focus on my project, but things will improve soon as I adapt to my new job and this Monday to Friday schedule. What hasn't changed is the feeling I'm doing something great when I do get to the shop, even if Ron and I spend the hours just jawing about airplanes and flying.
I've long been following the online musings of William Wynne, the Corvair expert I've mentioned before. He wrote the following quote on his blog the other day and it really struck a chord with me:
“Hours in the shop working with your own hands cleanses the part of your sanity which modern life soils”
Indeed William.... indeed :)
It's safe to say that any flying machine is a collection of parts that are strategically placed and assembled to enable one to fly.
Although this is true, it's the little things that get accomplished over the course of a building project that make the difference in not only getting the plane built, but improves the overall quality and performance of the end product. It also contributes to the philosophy I spoke of last August on my blog: ( a-little-here-a-little-there).
Today I decided to pull out the Corvair heads and have a closer look at them.
You might recall that these heads are 110hp versions from a 1966 car. They are just as I received them from the seller - not filthy but certainly not clean either!
Any engine that is more than 50 years old is bound to be grimy. Air cooled engines like the Corvair have many, many cooling holes factory cast in between the head fins. Being small, they trap everything. Not good as the GM engineers counted on these being clear for optimum cooling. What the GM engineers didn't consider is that casting aluminum or other metals sometimes leaves "flash" where the moulding halves join up during the casting process. Either it was considered to costly to remove the flash or maybe they decided it was good enough. What I have experienced however is the massive range of acceptable "flash" tolerances - some heads have so much the cooling holes are almost closed over. With a small amount of dirt in there, they are effectively closed to cooling air.
Here is a look at the cleaner of the two heads. I've put a lightbulb behind to ease the viewing:
As you can see, the cooling holes are many and this head seems quite good. Some minor flash to clean up but generally good.
The 2nd head, despite being from the same casting lot as the first is terrible! I could only find one hole that was clear and even then it was almost closed over from flash:
Took an hour with a combination of small files and old steak-knives, but I managed to clean out the majority of the gunk from the cooling holes.
Both heads really do need a good pressure wash before I'll be able to remove all the flashing, but this was a good start. Removing the flashing is very important and goes a long way to improving cooling of the heads.
It's these little things that take time, but make a world of difference and counts towards the goal. Along those same lines, my father Jim and I have been working on an important submission regarding my mentor Barry. I don't want to say much yet but it's a little thing that also counts for something. Stay tuned for more on this shortly.
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.
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.