As we get to the last of the flap repair (for this wing anyhow) I'm learning more skills that will come in handy later for my build.
So far, I've had the opportunity to work with blind "pop" rivets (the predominant style in the Zenair line of aircraft) and solid "bucked" rivets. Both have their place and use.
Last night I started working with flush rivets. Designed with a smooth flat top they too are bucked or squeezed to form a bond between two sheets of metal. The advantage these have however is that they leave the top surface smooth and thereby more aerodynamic. It also looks real cool! Most modern metal aircraft use this style for aerodynamic reasons. They are particularly handy around windows trim and landing gear plates where thickness tolerance of adjoining parts is important.
In the case of our flap repairs, we wanted to come up with a way to clean up the trailing edge and correct the ham-fisted attempts at a straight edge by the original builder. Ron made up a sleeve which will be flush riveted to the trailing edge.
It starts with marking out the rivet lines and drilling small #3 holes, the size of the rivet shank:
Next, the hole is very carefully countersunk with a bit in the cordless drill:, to a depth that matches the shoulder of the rivet. Holes for larger rivet are usually countersunk using a dimpling tool, but this tool works here:
Here is a picture of a typical flush rivet. Note the smooth flat top, angled shoulder and round shank:
Making the hole match the rivet so it lies flush is the goal here. Too shallow and the rivet won't lie flush, too deep and it can't hold the bond adequately enough nor be completely smooth on the surface:
Work a little at a time, test fit often and eventually the rivet will sit perfectly flush with the surface... smooth!:
Now repeat 30 times along the trailing edge :)
Ron and I flipped the wing over on the bench and I removed the damaged nose skin:
I know at this point I shouldn't be surprised by anything I find with this repair, but this was interesting. There was a "perfectly" blended rectangle, held in place by rivets and covered by the magic of cheap paint located at the back edge of the nose skin. It is hard to make out in the picture below but I really didn't notice until I took off the skin what it actually was, so I don't have a before picture.
Once the skin rivets were removed, and the damaged nose skin removed did the curious patch reveal itself, again nothing surprises me anymore:
My only guess is that this was some sort of Mickey Mouse access panel to get at the wing strut mounts, but I can't for the life of me figure out how anyone thought this was an acceptable patch..... jeebus.
On a happier note, I recently confirmed my attendance this fall at the Zenith Factory open house in Mexico Missouri. It's a two day drive from here, but most importantly William Wynne will be there demonstrating the build up of Corvair engines. As a bonus I'll be able to take my core items for assessment and perhaps send my heads away for rebuilding at the same time. Can't wait to atttend and learn even more!
Next up, more finishing work on the wing repair and prepping the bench for slat building.
Been a while since I posted, but the new job is taking up most of my days and weekends are escaping us because now the outdoor work around the house begins. Excuses aren't welcome, but the grass doesn't stop growing.
Much earlier in this blog (my first post actually - click here) I spoke of all the work my mentor Barry Morris and I put into trying to promote and develop the South River / Sundridge Airport. Unfortunately, Barry passed away before seeing the local municipalities get their acts together on this important community asset.
I honestly thought all was lost regarding the airport. Three times the municipality almost sold the property to non-aviation interests who wanted to turn it into a number of non-aviation purposes. How disheartening.... however....
I'm ecstatic to say the property was sold to a couple of business men that are enthusiastic aviation people who want to continue to develop the property PROPERLY as a municipal airport, including paving a runway and installing lighting. "Build it and they will come...." is a quote from the 1989 "Field of Dreams". How perfectly appropriate!
On the 12th of May, the new owners, in conjunction with COPA and the local flying club hosted a fly-in pancake breakfast. Ron, his wife Donna and I attended and joined the fun.
Over 40 aircraft from all over southern Ontario attended, it was wonderful! The new owner couldn't wipe the smile off his face! There are a bunch of photos on the airport Facebook page. I was way to busy chatting with friends to take a bunch of pictures but here are a few:
Of course one of the more interesting planes that arrived was a newly kit built Zenair 750 STOL, just like I'm building. Spoke at length with the owner who has about 80 hours on the airframe after completing it last year just south of us in Emsdale. The biggest thing he recommended was keep at it. There is a ton of stuff he still wants to do cosmetically (more paint, etc) but he's having way too much fun flying! He let me sit in it too and I'm even more convinced that I've made the right choice :)
The chance to see another completed 750 was a real good motivator!
The 701 flap repair is almost done. Some final trimming to be done, but the skin wrapped real nice and the joining patch turned out real smooth. Happy to be moving on to building my own flaps shortly and not fighting with other people's mistakes.
Ron has never been very happy with the pinched trailing edge design of the wings and flaps on the 701. The original builder (as I've been saying all along) never really paid attention and the trailing edge isn't nearly straight enough. The pinched rivets called for in the plans really add a lot of drag too.
The plans in the 750 model I'm building wraps the skins forward to the spar, making the trailing edge much cleaner both in appearance and more importantly aerodynamically. Every little bit helps!
To clean things up, we'll be adding a trailing edge strip and attach it with flush rivets. Here, we're fitting the trailing edge "cover". The first one worked real well, I'll add a picture when the one is done.
We plan on building flaps and slaps at the same time for three new 701's and my 750 and new slats for this repaired 701. This sounds like a ton of work and it is, but there are huge time savings because they are dimensionally the same, meaning we only have to set up jigs once.
I spent a couple of hours the other night bending my slat ribs on the forming block. The 750 slats are identical to the 701, so I didn't need to make my own forms for this. The only adjustment needed was one tooling hole on the tail end which is different:
So they turned out ok, but will need some clean up. Not a big deal, but not a nice as I would have liked.
Next up, finish skinning the 701 wing extension. Here is a graphic of what I have complete and ready to assemble (highlighted in blue). Lots of stuff ready to be bent still.
Thanks for reading :)
Flap repairs continue. With the tightness of the skin and short bend radius, making the skins align squarely across the spar and ribs is a challenge. Careful application of ratchet straps helps, but doesn't leave a lot of room for drilling and clecos.
I took a couple of nights off and when I came back, Ron had striped the paint on the 701 wing, the original parts of the inboard flaperon and the entirety of the outboard section.
Went back to the shop this afternoon. Ron was away so I thought I'd tackle some of my parts. We plan on building our new slats and flaperons together, taking advantage of common assembly jigs. In order to do this, I need to get the balance of my flap and slat ribs done.
Due to the tight radii of the nose section, I was concerned how the aluminum would bend. It took some finesse, but I got them done. Happy with how they turned out!
A big part of this project is going to be taken up by drilling, clecos, drilling again, deburring clecos, rivets..... more to come.... stay tuned.
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!
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.