Got a confirmation e-mail today that my Zenair 750 STOL plans are on their way from the Zenair factory in Mexico, Missouri. Despite being a company founded in Canada, all plans come from the U.S. office of Zenair as they are numbered and serialised for each builder (makes sense really, the U.S. is a huge market for homebuilts.) It's also great way for the designer to keep track of customers and provide support.
With some luck, I should have them in my hands in 5 to 7 business days!
In my previous post "Time to get back at it" I mentioned spending a day in July at the Zenair Open Hanger day in Midland, where I met fellow Corvair engine builders John from nearby Angus and Jeff Moores of Newfoundland.
Here are a couple more pictures from that day that Jeff's wife was kind enough to send me.
Hoping to get back into the shop this week. More rivets to drill on the salvaged wing. Learn I will..... learn :)
First off, I ordered my plans set today! Hopefully it won't take long to be shipped from Zenair. Once I have them, I'll have my very own serial number and I can start going down the road of endless inspection paperwork that needs to be on file with Transport Canada. I'm trying to decide if I want to reserve a good registration (call letters) or wait and see what they assign..... but that's a bit premature.... ha!
Four more hours in the shop today. Continued to open up the salvaged 701 wing. Wasn't too surprised to find damaged structure inside. This is the top of the wing at the root where it attaches to the fuselage. It likely got twisted back from the impact out on the tip of the wing. Lots of rash damage, probably from improper handling after the crash.
Flipped the wing over and with some drill effort, off comes the wing root fairing, fuel cell inspection cover and lower wing skin. Whomever built this wing wasn't much of a craftsman (or craftsperson). Lots of rivets where they shouldn't be, and lots of rivets missing from where they should be. We also discovered the rear spar channel is way under gauge from what the plans call for. Seems like someone decided to take a shortcut.
Next step was to drill out the rivets holding in the incorrect rear channel:
It came out easy, but it too has holes in all the wrong places.
Easy to fix/replace, but after seeing this, we are truly wondering what else we are going to find.
Next up, straighten the inboard main wing rib (on the left in the above picture). It will require another strip of aluminium (called a doubler) to reinforce the damaged area after we straighten it.
I just two afternoon sessions, I've learned a ton thanks to Ron but I've got a ton more to learn yet!
Had a real great afternoon today speaking with and working in the shop of my new friend Ron. As I've stated before in my blog, the prime motivator of building my own airplane is about learning.
Ron is a long time builder and re-builder of aircraft, both certified and homebuilts. He has a very deep knowledge of all things in recreational aviation and most importantly wants to teach me some of what he knows.
Ron's current projects include rebuilding a Cessna 170, a short wing Piper and several Zenair projects. His thinking is to have me assist his group of builders repair a Zenair 701 as a very first step to learning metal aircraft construction. Perfect! What a fantastic way to get an introduction to building skills.
He gave me a quick tour of his workshop and we immediately went to work on removing the skins off a salvaged Zenair 701 wing that was badly damaged by a previous owner. This wing is being rebuilt.
We started by assessing the wing to determine the best course of action. We discussed what was salvageable as is, what could be patched and what would need to be cut away completely. As you can see in this picture, the damage is substantial.
After making some marks on the wing of what needed to be removed and a quick demonstration of the procedure required, I was drilling out the rivets. As you can see, there are a ton of them:
We also removed the lower wing skin closest to the wing root that was crinkled really badly. Again, a ton of rivets to drill out:
I wish I took more pictures, but I was having too much fun drilling rivets. Obviously today was just a tiny taste of what's to come for learning and building, but I'm hooked!
As we worked, Ron and I talked at length about my plans for building a Zenair 750 STOL. I explained my plans to put a Corvair engine in it and he was very interested in the combination.
Use of Ron's shop and taping into his experience building Zenair aircraft definitely confirms for me that this 750 STOL airplane is a do-able project that I can accomplish, and that by making some of the parts myself from raw materials (called "scratch building", as in "from scratch") I have the opportunity to save a bunch of time and money.
So after some weeks of debate, tomorrow I'm sending in my order to Zenair for a complete set of builders plans for a 750 STOL aircraft. Once I have them in hand, Ron and I are going to sit down and discuss a build plan.
I haven't posted anything to the blog because I've really not made any progress in the past couple of weeks, other than research stuff. Summertime is difficult.... hot and muggy and plenty of other family plans and activities to occupy my time.
Had a few minutes today though, so I thought I'd get out the core crankshaft I have safely stored in inventory and have a better look at it. One of the first items I'll be sending away for prep work, but it needs to be measured to see if it still meets factory specs.
This is the crank I inherited from the inventory I purchased in February. The previous owner had already completed some of the work to make it airworthy and it's in great shape:
The recommended prep work includes magnaflux testing for internal damage, straitening if required, heat treating for improved strength (ion nitriding) and grinding the piston rod journals to improve the fillet radiuses. Larger journal radii help prevent stress riser cranks from forming, which has led to broken crankshafts in the past. The process is quite common in certified aircraft engine cranks, so it's worth doing here.
One of the other processes that normally gets completed is to drill and tapping the centre of the end of the crank for a propeller hub safety shaft. Because the previous owner was working from the official plans, he had already completed this process with his machinist:
I opened my Corvair shop manual, and found the engine spec reference page. It contains all the measurements for the major engine components:
Using my digital caliper, I tried to measure as best I could the crankshaft main journals and connecting rod journals to see how close they are to factory. I really should be using a micrometer for this, but my calipers should at least let me know it's in the ballpark.
The manual says the connecting rod journals (they call them crankpin journals) calls for a diameter from 1.7999 inches to 1.800 inches. To make it easier to measure, I set and friction-lock my caliper to 1.7990 before placing it on the journal. This is slightly undersize, but as close to 1.7999 I can get. This way if the caliper slides over the journal without resistance, I know that it is below tolerance and no good for grinding. Anything larger than that leaves that much more room for the machining (good):
With my lovely assistant Brenda taking an action shot with the camera, I carefully measure each of the bearings:
It's real hard to get a good picture, but the caliper won't span the largest diameter of the journal, so we can deduce that they and the main journals (using the same measuring technique) are clearly above the minimum spec and can be used for conversion. I know it isn't a perfect measurement and my caliper may not be as accurate as a micrometer, but I think I'm in the ballpark at least.
I'm going to see if I can borrow a good micrometer from someone, or maybe buy one for myself to confirm this. Once I'm sure, off to Florida the crank will go for prep.
Next Wednesday I'm having my first shop lesson with Ron, another Zenair builder. He's rebuilding a Zenair 701 and has offered to let me help. What a great opportunity to learn and prep for my build.
More to come.....
Took an hour today to start cleaning up the push rod tubes that I removed from each of the cores:
First step was removing the old dry and cracked o-rings. GM used simple rubber ones which in the conversion process are replaced with Viton rings. Viton doesn't dry out with heat and remain supple over the course of the engine's life. Some were already cracked and missing pieces:
I rummaged around in my tool box and found the perfect thing to use. Don't ask me if I know how sharp the point is:
Some came off complete, but most came off in brittle little pieces:
Next step will be to clean them up. First a bath in Simple Green to get rid of the grime and grease, followed by a polish. The tubes are made of light steel with a zinc coating. GM left them bare, but standard practice for conversions is to paint and bake them white with high heat enamel to enhance cooling (or at least reduce heat transfer to the tubes from the cylinders). I've read online it's best remove the zinc coating and this can be done using an aggressive Scotchbrite pad or bench grinder wheel.
I haven't posted anything to my blog for a couple of weeks because I've been busy doing the other things in life that keep our family hopping at this time of year. Vacation, two birthdays, two anniversaries, the end of the school year, fireworks shows for Canada Day (another hobby of mine) and some camping. All this happens in the span of 14 days. But it's over again for another year.
Of course my mind hasn't strayed too far from my project and I'm starting to narrow down my decision on what airframe I want to build. In my post from last year "So Many Choices" I describe my thought process in this regard.
Just before I started vacation, I managed to meet up with Ron, a local home builder who has vast experience with building aircraft from scratch, from kits and rebuilding damaged airframes for others. He is currently working on a Piper Pacer, but he has offered me a spot on his build team and more importantly, the opportunity to assist him and another guy in building a Zenair 701. You can't ask for better chance to learn from someone that has "been-there-done-that". Ron is also keen to see a Corvair installation process, perhaps for future build of his own.
So, after much debate and thinking out the pros and cons I've decided 99.9% that I'm going to begin the process of building a Zenair 750 STOL (Short Take Off Landing). This aircraft has the best of everything I'm looking for:
One thing I really like about the home building movement is the willingness of others to share what they have learned and help others get started. It's a tight knit group of individuals and it's great having that support network when working through a build.
During my vacation, I got a call from another Corvair builder named John who is putting a Corvair in his Zenair 650. His engine was built for him by William Wynne and he is close to flying his 650 for the first time. He reached out to me after seeing I was also in Ontario in hopes of having another Corviar builder to bounce ideas off of (again, that built in support network is great). He also offered to put me in touch with yet another Corvair builder who is doing the same 750 airframe that I'm interested in.
I told John I was planning on heading to the Zenair open house being held in conjunction with the Midland RAA (Recreational Aircraft Association) fly-in being held this past weekend. We agreed to meet up in person and that's exactly what happened yesterday.
I arrived at the Midland Huronia Airport sharply at 9am Saturday morning. I was hoping to meet the Zenair staff before the crowds got too busy. I had the opportunity to speak directly with brothers Michael and Nicholas Heintz, sons of Zenair aircraft designer Chris Heintz. I explained my goals and mission and they answered any question I had. When I mentioned I was planning on putting a Corvair engine into the airplane, they were very positive about the combination which is extremely encouraging.
Michael advised me that a builder from Newfoundland by the name of Jeff Moores was coming that day to look at purcashing a Zenair 750 and was a Corvair builder as well. I've had conversations with Jeff via the Corvaircraft forums, as he has already built a Corvair for his Merlin ultralight, so it was great to meet him and his wife Dale in person. Shortly after, John walked over and introduced himself.
Jeff, John and I talked at length about each of our plans and how we are at substantially different phases of the build. having built both a 2.7 litre and 3.0 litre Corvair engin, Jeff offered some great insight to the differences and advantages of each. Considering none of us had ever met before in person, it amazed me how quickly we became friends - guess that's all part of being a builder.
We took a tour of the production facility where Michael explained the evolution of Zenair kits and how advanced the CNC production has become, even just in the last few years. The 750 kits are considered state of the art and are "match drilled" meaning all the holes in the pre-formed aluminum parts are already drilled for the builder, saving substantial time in assembly. It was clear from the tour that the kit quality is top notch, and I came away from the tour feeling very confident that this is a great project for an amateur builder like me.
As the morning progressed, each of us were offered a flight in the factory 750 demonstrator with Nicholas Heintz. This one is actually the 750 Cruzer model, which has a somewhat cleaner airframe (no slats, different wing, etc) resulting in a somewhat faster cruise speed than the STOL model, but the cabin dimensions and "feel" are the same. The demonstrator is equipped with a Jabiru engine (which is has approximately the same horsepower as what a Corvair would:
Now, I'm not sure what my goofy smile was from; the fact I was actually going flying or how pleased I was to experience the visibility this cabin design provides (and I wasn't even in the air yet!) but I suspect it was a combination of both:
A short time later and we were airborne! I was so wrapped up in the flight experience and speaking with Nicholas about the handling characteristics of this Cruzer model vs the STOL version, I didn't get any puictures, but I am really impressed with this aircraft. Smooth, stable and comfortable. The visibility is incredible in all directions and the bubble doors give that extra feel of roominess. One thing I noticed when I had the controls and entered a turn was the really nice visibility through the clear panel cabin roof:
Jeff's wife Dale took some pictures and videos of my flight and when they get a chance will send them to me and I'll post them. Here are a couple of more I took:
So things are starting to pick up speed. I'm definitely in the arena and the game is about to really get started!
Well, my buddy Guy had some progress in getting the last three broken studs out on the 110hp block.
The first one came out fairly easy once centre drilled. Looks like the threads are still intact and should clean out nicely:
Number two, not so much. The centre of the stud hole doesn't always line up exactly with the threads, so he stopped working this one with the end mill until we can decide if we want to re-tap the hole afterwwards:
I tried using a large EasyOut bit but the last of this stud won't come out and I'm wary of damaging the remaining threads. I've filled up the hole with some home-brew penetrating oil and will let it sit for a couple of days to see if it will loosen up before trying again. I think I might be able to use a tap and just clean it out, but I'll wait for now on this one. This is likely the worst of the bunch.
Number 3 was the most interesting result. Using an EasyOut, Guy backed the stud out carefully, but unforuntately it brought most of the aluminum threads with it. It was stuck in there real good:
Now, the beauty thing of all this is that all 3 holes are salvageable. There is enough room left between each of the damaged holes and the cylinder bores to insert either a Heli-Coil or TimeSert thread repair. They each have their strengths and pricing differences and from what I've read they each work well (click the links to check them out). I kinda like the TimeSert method better, just seems more permanent. This will mean cutting new threads on the end of the replacement studs with a sharp die to match the repaired holes, but that is common practice and an acceptable repair for a conversion.
If I can't get the number 2 one out cleanly, it will be easily removed during the drill/tap/insert process of the thread repair.
I'm stoked this is going to work and I can use this block for my engine <grin>.
On another note, I've added a running total time log on the lower right of my blog page:
One of the things builders like to keep track of is the amount of time spent on parts of the project. I've broken things down into basic groups and will try an remember to update it regularly. I considered purchasing a commercially available program like KitLog, but I prefer this blog format. The 25 hours showing under Engine is just a rough guess and doesn't include non hands on time like time I've spent online and in person looking for a core. I might consider breaking the chart down further, but I'm happy with it for now.
Next step, research where to purchase TimeSerts.
Got a call from my buddy Guy (correct pronunciation is Gee, which is french Canadian) . Despite his best efforts to remove the broken studs he is struggling a bit. He tried welding a nut to them but they just snapped off further down and now they are sitting close to flush to the block. This leaves no option but to drill them out using a milling machine and end mill bit.
Fussy, temperamental work with a fairly high risk of wrecking the threads if not careful.
After finding limited success using the weld method, he tried centre drilling the stud in preparation to back them out with an EasyOut bit. This proved to be very difficult because the studs are a hard material to drill, but he did manage to centre drill one of the three. The other two he's going to use the milling machine as it should be easier.
The next concern will be how to clean out the remaining debris from the threads that gets left behind. The conversion manual is very specific that the lower end of the studs is a special thread called 3/8"-NC5. So at this point I believe I'll need a 3/8"-NC5 tap to clean out the threads. Even an experienced machinist like Guy had never heard of this particular thread (he checked with his suppliers too) and suggested it will be expensive to obtain due to it's rarity.
While my buddy worked on end milling the holes, I decided do do some research.online. Although I wasn't able to find a tap or die that matached this unique thread, I did come across an online archive of GM production drawings that show the machining dimensions of a Corvair engine! I really love the internet!
This is where it gets a bit more confusing. According to the dimensional drawing showing the machining instructions of the casting, the stud holes are supposed to be tapped to a dimension 3/8"-16 UNC:
But how can that be? The hole and stud should be the same thread as the stud..... hmmm.
I sent an e-mail to the internet Corvair conversion forum seeking some guidance.
Not long after sending the e-mail, I got a telephone call direct from William Wynne (the Conversion Manual author and recognized Corvair guru).
We had an almost hour long conversation about the conversion process, my overall plans and this particular issue regarding the studs among other things. He's very supportive of new builders like me that want to learn and his overall philosophy about home-building and being in the arena speaks to me.
He is an amazing person to speak with and very quickly confirmed that the GM drawings are correct, the stud holes are in fact 3/8-16 UNC. The reason the studs are slightly different is GM engineers wanted an interference (extremely tight) fit to ensure the studs would remain in place. Using a common 3/8-16 UNC tap would be appropriate to chase the debris from the holes.
Guy happens to have that tap (it's common) and I called him afterward to confirm what we know now to be correct. He's going to finish cleaning things up. In the meantime, I'll bring him the other half of the block and have him clean it up too. On the advice of William I'll also be contacting Dan Wesseman of FlywithSPA.com, William's recommended supplier for info on obtaining 12 new (to me) OEM matching long studs as the ones I have are too corroded to re-use.
To make things even better, Brenda tells me a fellow Corvair conversion builder called for me while I was at work and invited me to visit his shop near Barrie. He is building a Zenair 650 with a Corvair engine. It is almost complete at this point and offered to help answer any questions I might have along the way. I'll make contact with him tonight when I get home and maybe arrange a time to visit this weekend when I'm in the area for a family function.
Despite soaking those stubborn snapped studs in "homebrew", there is too little of them left sticking above the surface of the block to grab onto with a tool and back them out. For all I know, they'd come out now, but I got nothing that can grab onto them strong enough to turn.
I met up with my retired 911 buddy who is an accomplished machinist/welder/hobbyist to have a look at them.
He's taken my block back to his place for a couple of days to see if he can get them out. He figures he's got a couple of options to remove them and preserve the threads. I've told him to take his time and get to them when he can and he promised to be careful. Now that he sees my dilemma in person, he understands. He's the type of guy who likes a challenge and I have little doubt he'll be successful.
I've been pondering my options regarding the 140hp block I've been working on.
I'm getting concerned about the amount of corrosion on the camshaft bores. Originally I thought it was just transfer rust from the came, but it looks like it might be more.
In Corvair motors (and other major air-cooled engines) the camshaft rides in bearing-less surfaces bored into the block. These are polished surfaces and the cam rides in a coating of preassured oil provided by lubrication passages. In a running motor, it is critical that these bores are clean, smooth and round as possible. I haven't tried everything method I have in mind to clean these yet, but however it gets clean, I can't just grind away the corrosion and it looks like it's more than just stains. The risks are removing too much aluminium and making to bore over size - there are no options if that happens. Here are a couple of pictures of some of the spots I'm worried about:
The 140hp block needs a lot of work to remove the corrosion (these aren't the only spots, the cylinder bores are also poor), and it may just be a wasted effort if the cam bores won't clean up properly. So, in the meantime I've decided to have another look at the 110hp block and see if I've exhausted every effort to remove the 3 snapped studs that halted me last time.
I hadn't taken the case halves apart on the 110hp block, so that was the first step. Internally, it is much more promising. The cam bores are beautiful and will require a bit of polishing. Even better, all the mating surfaces look fantastic. I haven't measured any of the bores for specs, but they look near new and should check out okay:
Refreshed with information, I took the case half with the broken studs outside. Here are two seperate pictures of the 3 studs I've got to somehow figure out how to remove. As you can see, I haven't got a ton to grab onto:
Now, I'm not the first person to have this happen to their block. Some of the suggested methods are to weld a nut to the top of them and use a wrench or socket on the nut to back them out. Another is to drill the broken stud out carefully in the centre and use an "easy out" bolt remover like this:
I think I'll try the second method first and use the welded nut as a alternative if that doesn't work.
In preparation, I've soaked the three broken studs in some "home-brew" penetrating oil (see my previous posts) and I'll let them sit for a couple of days:
Maybe, with a little luck, I can use vice-grips and they will come out without having to drill or weld.
I've got a retired buddy who is amazing with machining, if that doesn't work I'll contact him for suggestions on the next course of action.
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.