Zenith 701- Corvair reference page, November 2013

Builders,

Here is a single location page that has number of links to information specific to the Zenith 701 / William Wynne-Corvair Combination. In brief, we flew the combination in 2007, and it does work. Our test aircraft weighed 677 pounds ready to fly (without fuel) and more importantly, was well within the CG envelope for the plane, and we didn’t have any ballast in the plane to achieve this. If the number sounds slightly high, consider that we publicly weighed it on electronic scales, and I am reasonably sure that 50% of the empty weights listed for 701’s outright fabrications.

Both the 601 and later the 750 installations we do have been very popular, but the 701 has not proven to be. We have about 12 active builders working on the combination, but it isn’t likely to ever be popular like the 601/750. When people hear this they jump to the conclusion that the 701/Corvair combination didn’t work. They do this without thinking that you can see several examples of Corvair powered 750’s on: Zenith 750 / Corvair reference page, October 2013 and they clearly work, so obviously the same engine will fly an aerodynamically similar plane that is 20% smaller and lighter with 30% less wetted area. The 701/Corvair was not the ultimate performance nor the maximum useful load the 701 could achieve, but it worked well, and it works infinitely better than any engine a builder will never afford. If you would like to start with a simple three page spec sheet on the engine, read this link first: Basic Corvair information

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Our Corvair powered 701 taxis out before its first flight, 2007. Gus Warren at the Controls.

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The actual reasons why the combination has limited popularity are two fold. First, the 750, it’s newer big brother, is a better plane and product for most builders needs and skills, and it has completely out stripped 701 sales since it’s introduction. Second, 701’s tended to be the project of grass roots- working American builders. The 2008 recession hit these people particularly hard, and they are the last to feel any of the recovery. Many of their projects are dormant while these builders put family first. I encourage all of these men to stick it out. We are here for the long run and will assist them when ever they are ready.

On the mechanical side, one of the cornerstones of our 701 installation is being made of our proven  production parts. The installation uses our regular off the shelf components with only two exceptions, it has it’s own motor mount and its own stainless exhaust system. Even these parts are not totally unique, they are closely related to our other production parts. This commonality allows builders an easer build and installation, and it also means that the track record and flight data from our other flying Zenith installations also benefits 701 builders.

The engine in our 701 test aircraft N-9569S, was a standard 2,700cc production enginebuilt in 2006. We made no attempt to lighten the engine or use special parts, nor did we build a larger displacement engine. We wanted the weight and the performance to represent what a base line builder spending $4,500 to build an engine could expect. Later we installed an Elison Throttle body injector, a Weseman 5th bearing and a larger oil cooler. Even with these developments, a builder could still replicate this engine for $7,400 working from our parts and manual.

While the installation is not “main stream” it is still a viable option, a good match to specific builders. Many new builders get focused on what is popular with most builders. That will work for them also only if they have the same budget, goals and desires as other typical builders. “701 Builders” is a very broad group of individuals, each with their own set of circumstances. If you are one of them, you only need to find the right engine for just one guy in the whole group: You.

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Above, the 701 on display in the Zenith booth at Sun N Fun 2010. It was the 7th consecutive year we had a Corvair powered plane on display in the Zenith booth at the airshow. We are supporting Zenith builders for the long run.

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This page has an abbreviated look at our Corvair program. For an over view with a little more depth, get a look at either of our other two Zenith reference pages, as they have sections discussing our support programs and a fuller description of the installation components available:

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Zenith 750 / Corvair reference page, October 2013

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Zenith 601/650 – Corvair reference page November 2013

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I will be glad to answer further questions just email WilliamTCA@aol.com or call 904-529-0006. You can also check our two websites, https://flycorvair.net/ , http://flycorvair.com/ . The first is our ‘newspaper’ the second is our ‘library’ and ‘store.’ The links below are stories that already appear on these two sites, they are just arranged here to support this introduction to Corvair power for 701 builders.

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The organization of this page follows this outline:

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1) – Time line of N9569S, our test bed 701 airframe.

2) – Popular Corvair engine options for Builders

3) – 701/Corvair installation components

4) – Photo essay of our development work on the 701, 2006-2010.

5) – Builders working on the combination

6) – Notes on poor products to avoid

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1) – Time line of N9569S, our test bed 701 airframe.

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The story started in 2006 when we bought the kit directly from the factory. We were there to hold “Corvair Day”, and we used the occasion to bring home a complete airframe kit. 30 months before in 2003 we had picked up our own personal 601XL  kit, and we had it flying in early 2004. With the 601 program up and running, we decided to try the 701/Corvair combo. We did this with the support of Sebastien Heintz, the president of Zenith. He had a great number of 701 builders who were not comfortable with the escalating costs of Rotax 912’s and he was encouraging people with proven engines to develop affordable installations that would serve his builders.

Sebastien has a simple standard for alternative engine providers: Before they tell his builders how great their engine is for his families airframe designs, they should buy their own, and finish and test it. Sounds simple enough, but 80% of the companies selling engine installations have never owned nor tested the combinations they sell. Some of them have never owned any kind of a test bed aircraft, nor flight tested anything. You would think that no one would buy such products, but people do all the time. Our 701 was the second kit we bought from the factory, and we had a very through in house test program planned.

Picking the kit up in 2006- From right above, Nick and Sebastien Heintz, and Caleb .

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In that era we operated with a crew we called “The Hangar Gang.” As a team we had hammered out a string of Corvair R&D projects: My Pietenpol, The Skycoupe, Our 601XL, and the Wagabond, in addition to assisting in completing a number of friend’s Corvair powered planes like Gordon Alexander’s Pegzair and Phil Maxson’s 601XL. I felt pretty sure that we would knock out the 701 in short order,  so that is where we started in the spring of 2006.

 Above, The “Hangar Gang”, with our 601XL, built in 90 days including developing the FWF Corvair installation. The was the first tail wheel XL and the first with dual sticks. The plane was built as an after hours project by 3 or us. L-R, Grace Ellen, myself, Kevin , Whobiscat, Upson, Gus Warren, and Dave the Bear.

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Simply put, the 701 came at the wrong time. It took 17 months to finish the plane, an eternity by our standards. We had a lot going on outside the hangar; Four of us got married, 2 bought a house, one had heart surgery, and one got a corporate job. Near the plane being completed, we sold it to a super-wealthy aviation investor who owned a lot of turbine helicopters, but suddenly found himself in need of an LSA plane. The FAA set a Jan, 10th 2008 deadline as the last day you could legally register a professionally built E-SLSA plane, so the arrangement was on the up and up. However it was a poor match because the owner, whom I had known for a number of years, turned out to be the wrong guy to own any plane with the word “experimental” on the registration.

E-LSA was a stupid category for a number of reasons, one of them being it only had a 5 hour test period, not 40. We agreed to do all the flight testing, and Gus Warren did all the first flights. Things went relatively smoothly, but owner had a very different idea of what constituted ‘tested’. We had only one single serious issue where the owner did not set the timing with a light, Gus later did a flight and made a precautionary landing because the engine had way too much advance. Learn a lesson here: all planes need to have only one person in command, and that goes for on the ground also. Neither maintenance nor flight is correctly done by committee.

Over time we worked all the development we needed, and fully turned the plane over to the owner. He had sporadic interest in it. We borrowed the plane back in 2010 and updated it with a big clean up, installed a 5th bearing and took it to Sun N Fun, where we displayed it in the Zenith booth all week. We returned it to the owner, who made some changes I thought were foolish. To my relief, in  2011 the owner said he wanted to sell the FWF. in a week or two we found a 601 builder to buy it. He actually paid the same amount of money I had charged the Zenith owner in 2007. Five years after we picked up the kit at the factory, this closed the R&D part of the 701/Corvair story.

I share this in plain language for several reasons. I want every builder considering the combination to have the full picture, not an industry-typical 4 page brochure with bumper sticker length slogans instead of facts. I also want new builders to understand that even professionals like me make wrong turns and have issues to deal with. If the road to building your own plane has not been perfectly smooth, welcome to the club. Only a person who has never built a plane, or has reason to BS you would claim they never had a detour in plans or an aggravating day. Homebuilding is all about learning, and then putting that understanding into action and material. The people that taught me my skills and what it means to be an aviator were honest and plain spoken, and had little time or tolerance for ‘nice’ and ‘polite.’

After I had been in aviation for 20 years, I made a strong attempt in letter and deed, to thank them individually for what they had shared. For many of them, my expressions of gratitude arrived too late, they had passed. I would never again have a chance to look them in the eye, shake their hand and thank them. I was left with just the hope that emulating their honest and plain spoken ways would respect these men a failed to sincerely thank in person.

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The 701 testbed in the Zenith booth at Sun ‘N Fun 2010. This was the last public display of the aircraft. But this time the great interest of Zenith builders had shifted to the 750, and we already had customer-built, Corvair powered 750s being finished.  The project had provided a lot of good data, but it came at a large cost in both dollars and man hours that we knew by 2010 were not going to result in broad sales. This said, the testing, data and combination are all still valid, and can be of use to the right builder.

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Above, the 2,700 cc Corvair, in our original configuration on the Zenith 701. An inherently simple engine, It’s opposed six configuration makes it the smoothest of available power plants. It has outstanding cooling because GM put a tremendous amount of cooling fins on it and  gave it a factory CHT redline of 575F. All of our engine parts are made in the United States.

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2) – Popular Corvair engine options for Builders

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If you are new to Corvairs, lets quickly cover some ground: General  Motors made 1.8 million Corvairs. brand new parts, including billet cranks, forged pistons, valves bearings,  virtually every single part inside is currently made and readily available, and will remain so. Rebuildable Corvair engines are plentiful, and much easier to find that Lycomings or Continentals. We have been working with Corvairs for 25 years, and there is no shortage of core engines or parts. If you doubt this for a second, Google “Corvair engine parts.”

The Corvair makes an outstanding aircraft engine because it is a simple, compact, direct drive, horizontally opposed six cylinder, air cooled engine. It is robust, and ‘flat rated ‘ from it’s automotive output. The engine runs equally well on automotive fuel and 100LL, and it does not care about ethanol. In its 53 year flight history, more than 500 experimental aircraft have flown on Corvair power.

The engine can be built in three dispacements with three respective power outputs. They are 2,700cc / 100HP, 2,850cc / 110HP and 3,000cc / 120HP. The two smaller displacements weigh 230 pounds, the larger actually weighs 8 pounds less because it uses lighter cylinders. All engines are completely rebuilt from very high quality parts before flight. They are not just removed from cars. The parts we use are specifically selected to convert the engine for the rigors of flight use. Forged pistons, Inconel valves, chrome rings, ARP rod bolts and many other components are upgraded in the rebuild.

To absorb the propeller and flight loads a “5th bearing” is added. It is a billet housing with a very large bearing from a V-8, bolted on the end of the case.The ignition is redundant and utilizes two 40,000 volt systems, one driven by digital electronics the size of a match book, the other by a traditional set of points. The engine is direct drive, it has no complex reduction unit. It makes good thrust because it has more than twice the cubic inches of a Rotax 912. All of the systems on the engine are intentionally patterned after those on Lycomings and Continentals, because they are the  model of success in proven aircraft power plants. People who do not acknowledge certified engines as excellent models of success are often just zealots.  To succeed in experimental aviation you need dispassionate information not emotional opinion.

One of the unique features of the Corvair is that it can be built at home, from our information and parts and a locally acquired rebuildable engine, or it can be purchased from us, test run with logs. 90% of current builders are building their own engine at home. Only 10% of the builders opt to have us build their engine. We have happy to serve both builders. In either case, Corvairs are the best match for builders who want to understand and be the master of their engine.

Because of the plans built vs production engine nature of the Corvair, there are large variations in how much builders budgets run. Below is a quick look at the differences. Keep in mind, these budgets are for first class, completely overhauled, zero timed engines with 5th bearings, starting, ignition and charging systems. We have clever builders who have built and flown engines for less than $3,000, but this not representative of main line builders. The numbers below are much better for Zenith builders to budget on.

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2,700cc / 100HP typical homebuilders budget: $6,500- Same engine assembled and run from us $9,750

2,850cc / 110HP typical homebuilders budget: $7,500- Same engine assembled and run from us $10,750

3,000cc / 120HP typical homebuilders budget: $8,500- Same engine assembled and run from us $11,750

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If you are attracted to the concept of building your own engine, but have not built motors before, Good.  About half of our builders have never built any kind of an engine before. Our main work is teaching people what we know and providing the parts to work with. Our system does not require anyone to be a machinist nor to have previous engine experience.

The procedure of building an engine in your shop follows this format:

1) Get a conversion manual and DVD’s from us, use them to find a rebuild able core engine locally. Disassemble this engine following the steps in the DVD.

2) Send the crank and heads to our approved facilities for rebuilding and modification. They come back ready to ‘bolt on.’ Other parts of the engine are cleaned and inspected. The parts to convert the engine are ordered from us, many of the standard rebuild parts like lifters and gaskets are available from local auto parts stores. We do not ‘middle man’ anything you can directly buy.

3) Assemble these parts according to the manual and DVDs. There is no machine work required, only basic tools are needed, and a few specialty tools like a torque wrench. Many builders attend our free Corvair Colleges and directly learn hands on skills. You can even bring your parts and assemble them under our supervision, and test run your engine on our equipment. College attendance is a plus, but not required. Our methods work without direct training; a good number of engines are built and flown each year by builders who have never met me in person.

4) The test run serves several purposes. We teach people to build one of  three specific models, and we teach them to use specific parts. Not only are these proven, but it also allows me to verify from a remote location that the engine was assembled correctly. A builder can report his static rpm, CHT, oil temp during the test run with his Warp Drive prop at the specified setting, and I can confirm the output and assembly of the engine without seeing it personally.

If you would like a sample of the information on working your way through the above four steps, get a look at this: Getting Started in 2013, part #1, Crankshaft process options.

I have broken down building a Corvair and installing it on your airframe into 42 “groups”. The previous link is about  ‘Group 1000’ the crankshaft. If you would like to look at every part that goes into a Corvair, along with the conversion parts we sell, look at Groups 1000 -3300 at this link to our catalog: http://www.flycorvair.com/products.html

All builders get started with a conversion manual. The first part of the above link is about manuals and DVD’s.  The direct link to the manual is: http://www.flycorvair.com/manual.html. almost all builders looking for a rebuild able engine also order the Disassembly  DVD, which covers core engine selection visually. The direct link to it is: http://www.flycorvair.com/videov.html We encourage everyone to get started with information, even if you are pretty sure you would like to purchase a production engine from us. If you eventually buy an engine from us, we directly reduce the price to rebate all the money you spent on manuals and DVD’s.

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Links to related stories:

a) – Corvair Weight story: Corvair vs O-200…. weight comparison

b) –  Samples of our production engines:  2012 Corvair Engines For Sale: 100, 110 and 120 HP

c) – For an explanation of ‘flat rating’ and a Zenith engine build : Shop perspective: Mastery or ?

d) – A story about engines running on our hangar Dyno: http://www.flycorvair.com/thrust.html

e) Engine of builder now working on Zenith airframe: World’s Strongest 3,000cc Corvair, built by Greg Crouchley

f)  2.700cc engine we built for Becky Shipman’s 650: Shipman Engine at CC#22

g) A story about the evolution on 120HP Corvairs: 3,000 vs 3,100 cc Corvair engines.

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In the photo above, the 701 mount appears slightly distorted by the camera angle; it actually has no down thrust in it.

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3) – 701/Corvair installation components

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The two parts that are unique to the 701 installation are the mount and the exhaust system. Other than this, the parts are common to our Zenith 750 installation.  We are glad to make the mount and the exhaust on a special order basis. The pricing on these items are the same as the equivalent 750 parts. For all of the other parts, refer to our “Zenith 750 reference page” or our regular catalog of parts.

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4) – Photo essay of our development work on the 701, 2006-2010.

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Below are a sequential chain of photos, mostly taken in our Edgewater Florida hanger that was our base from 2003-2007. All of these photos and their captions are on Flycorvair,com, our traditional website. They were in the “Hangar Update” monthly news section. I have put the original captions in Blue, and clarifying comments from today are in black.

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Where we started: “The 701’s firewall rigidly mounted at a 17 degree angle on the build up stand, above. This is the beginning of developing the 701 firewall forward package.”

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“In the above photo, Scott Thatcher’s 601 engine does jig duty in the construction of our CH701 motor mount. Like all other mounts, it began as a standard Tray. Long and careful study of the installation, and our experience with installing engines in airframes played into adjustments in the location as small as 3/16″. An engine hoist suspends most of the weight of the engine, and a scissor jack stabilizes the engine over the heavy duty shop table. The alignment was checked many times before the tubes were tacked in place. The mount and engine were then removed from the stand. The mount was finish welded on the bench with a Tig welder, using great care to minimize warpage. It was then reinstalled on the stand, and normalized with a gas torch. After cooling, I made a jig off the mount to capture its dimensions.

These are but a few of the steps in the long-term development of an engine installation that can be replicated by other homebuilders. Any one-off installation is comparatively easy. A good example is the Skycoupe. When working on its installation, I knew that there would probably never be another one. Thus, no jigs or tools were made, nor consideration given to the multitude of factors that would make the path easier for others who would follow the installation. It only had to serve well on one plane. Conversely, the Corvair/701 installation may prove to be popular. Our experience pays off here and will later allow rapid development of a highly refined installation pending positive flight testing.”

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In 2006, Grace and I bought our house on an airstrip 90 miles north of Edgewater. I commuted back to the old hangar for 14 months to finish projects there and because I gave my word to our friend who I leased the hangar from that I would do 4 full years there. The hangar was $2,200 a month and it was a long drive, but I was determined to live up to it. ” Above is a photo of the actual 701 flight engine sitting on the mount. This project is continuing at the main hangar in Edgewater. Work progresses on it between regular orders.”

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“Above is a photo of the 701 airframe in the main Edgewater hangar. This illustrates how we tackle complete airplane projects in 2007. The 701 is being built as an E-LSA, which allows it to be built 100 percent for hire, unlike amateur builts, which must meet the 51% rule. The owner separately contracted us to build the firewall forward package for his airplane. Gus Warren of Fly With Gus separately contracted to build the whole airframe.”

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“You can see above how close the Corvair’s center of gravity can be brought to the firewall. Geometry of this mount was carefully worked out to allow the use of our Intake Manifold and a Niagara cooler. When W&B and flight testing data comes back, we’ll have more information. The key to a successful 701 installation is not simply how much the engine weighs, but how close you can bring the engine to the CG.”

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We later switched the plane to having the oil fill in the Valve cover like all our other installations. “Above is a top view of our 701 engine installation. It is also being fitted with the new Oil System. No oil components on the firewall make the 701 installation much easier with its very limited firewall space. An oil filler neck is custom welded into the Top Cover of this engine. It is made from a 1″ aluminum tube, and has a Moroso O-ringed aluminum cap welded into it. This was done for potential cowling clearance when we were thinking of a super narrow custom 701 cowl. At this point, we’re steering toward a 601 style cowl on the 701. We want to get this one flying and gather flight test data. We’re trying to keep as many of the parts for the 701 installation common to the 601 to avoid a long development. We’ll have more commentary on this installation when it’s done and flying.”

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“This is a view of the lower portion of the 701 installation. Although I had my doubts, Kevin found a way to rotate and trim our CNC bent stainless pipes for 601s into a slightly different configuration that neatly fits into the 701’s mount. This engine will be equipped with an Aero-Carb.” Engine was later switched to an Elison EFS-3A that worked a lot better.

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“Above is a photo I shot in Edgewater last week. The airplane is more finished than the photo depicts. The leading edge slats and flight controls, not seen in the photo, are complete and have been mounted. The glass is out of the plane to facilitate the detail work. One builder wrote to ask if it would take a long time to develop installation components after the combination is tested. The engine uses a lot of parts from our existing catalog. The Nosebowl is the same one we use on 601s. The sheet metal to mate it to the 701’s airframe will be different, something reminiscent of a Thorp T-18. All the engine parts, including the Baffling, oil cooler and oil system, Starter, Gold Hub and alternator are our standard parts. The exhaust system is made from 601 Exhaust pieces in a slightly different orientation. The only truly unique pieces are the motor mount and lower intake manifold. Even the prop and spinner bulkhead arrangement is the same as the 601.”

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“Above is a good look at the detail quality of the 701 engine installation. Over the years, our installations have gotten cleaner and cleaner through Manuals, Colleges, Forums, and this Web site as well as http://www.ZenVair.com. We’ve shared this information with builders everywhere. It not only looks clean, it’s technically correct and flight proven in every way. The 701’s installation differs from a 601 in only minor details. The oil filler is welded into the Top Cover, the Intake Manifold is segmented for installation. But by and large, it utilizes nearly all our flight proven parts, which will yield smooth flight testing and easy replication by builders everywhere. This installation has a 2002 Niagara cooler, the Gold Oil System and our standard Baffle Kit. The large sending unit is for oil pressure instrumentation in the glass panel, below.”

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“N9569S has a completely stock 701 airframe which will allow apples to apples performance comparison. We have the airframe set up for a 66″ 2-blade Warp Drive prop with nickel leading edges. The thrust testing section of our Web site compares this prop’s performance against a Rotax 912S with an in-flight adjustable prop. It is hard core, direct comparison testing like this that gives me great confidence in this combination.”

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“Sitting on the firewall above is the black box for the Stratomaster Enigma glass cockpit in the 701. This view shows how tight we have the Corvair to the firewall. Despite its proximity, there are no complex assembly or maintenance tasks like there would be trying to pull a mag off the back of an O-200 in this airframe. Having the aircraft within the forward CG limit is very important to achieving maximum performance from the 701 airframe.”

We later had a number of issues with the MGL instrumentation on this plane. MGL specified senders that were poor quality, and when the oil pressure sender partially failed I wasted a full day trying to track down the error, including pulling the engine complexly out of the airframe. The owner installed a MGL fuel Flow sender that was a plastic barbed fitting, something that no one should put in any flying fuel system.

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“A look at the carburetor installation on the 701. The 35mm AeroCarb is spaced off the Intake Manifold by a 1” fabricated spacer which has flow straightening vanes in it. Gus worked out very clean and simple throttle and mixture cable installations. Whobiscat sleeps under the plane.

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After I wrote the story below we found that the primary culprit in the running hot issues was that the owner had altered the ignition timing. This was my own fault for having more than one person in charge of flight testing, alterations and fine tuning. don’t repeat this mistake yourself. If people offer to help you with your plane, remember, no matter how qualified they are, you are still in charge. Above the cowl is tuff tested with yarn to check airflow at high angles of attack.

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“Many of the things pertaining to the combination, like the weight and balance, are very good. But the aircraft owner disliked the Aero-Carb, so we replaced it with an Ellison. This change provided more issues than it resolved, initially. Second, the engine had adequate cooling in February, but as Spring grew much warmer, we needed to rework the cowling. The Ellison’s sensitivity to vapor lock compounded this need.”

“As an E-LSA, the aircraft had a short, five-hour test period. Although it was legally signed off, we weren’t kidding ourselves that the 10 hours we had on it constituted a fully tested power plant installation. While builders were understandably clamoring for details, we hadn’t put out much information or anything up for sale. The day before Sun ‘N Fun, Gus took off from his hangar to fly the airplane over 100 miles to Sun ‘N Fun. Although the airplane had 25 flights on it, this was the warmest day on which it had flown. About 25 miles into the flight, Gus noticed the characteristic pinging of detonation and made the very wise decision to make a precautionary landing at a sod farm. The 701 airframe was designed to be operated in just such places, and the landing was a non-event.”

“Gus’ initial thought was to let the aircraft cool off, then fly back to the hangar. A courtesy phone call to the owner of the aircraft changed the plan and the aircraft returned to the hangar that same morning on a trailer. The story of the precautionary landing was carried on the Kit Planes magazine blog. Although it accurately and fairly reported the landing, many Internet aficionados colorized and expanded the story, including incorrect phrases like “engine failure.” I am careful with the things I write to be accurate. If I poked a hole in the radiator of a car and it overheated, I would refer to this as a cooling system issue, not an engine failure. It was mildly annoying to read the colorized reports and listen to amateur analysis from people who never saw the plane.”

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“Our initial setup on the 701 used an Aero-Carb breathing air from directly inside of the cowling. This functioned fine, except the owner of the aircraft did not like the fact that he had to manually turn off the fuel with the mixture control whenever the engine was shut off. The owner is an aviator of enormous experience. He’s owned dozens of aircraft of all descriptions, including a Lockheed 12, Grumman Tracker, Sikorsky S-55 as well as a number of turbine powered aircraft. He holds an A&P, IA, and most of the other ratings the FAA offers. Although the Aero-Carb and Ellison are both flat-slide carbs, they function completely differently. The Aerocarb was immune to under cowl temps because it has no diaphragm and stores very little fuel inside it. The Ellison, because its throat is larger, provided an immediate seat-of-the-pants difference in power output, but as the weather warmed up, it showed itself to be temperature sensitive. We put a blast tube on its diaphragm, and ceramic coated the exhaust to lower the under-the-cowl temp. Yet we resisted making a specialized airbox because the goal was to keep the installation as simple as possible so budget builders could follow it at home.”

“The continuous warm air introduction turned out to be a mistake. I feel it was a major contributor to a warm engine beginning to detonate. At power, the carb inhales 150 cubic feet of air per minute. If this comes from the outside, it has significant cooling effect on the carb body. If it’s warm air induction, that large quantity of air raises the carb temp by 80 or more degrees F. The external blast tube on the diaphragm will not overcome the volume of air going through the carb. The above photo shows the 701 system as it is flying now. The air filter is in the aluminum canister, and it primarily breathes cool air from the lower part of the Nosebowl. The feed hoses are 2.5 inch.”

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“The tuft tests of the cowl revealed it had low flow characteristics on the exits. A check of our Web site will show that many years ago, we put radiused lips on the bottom of the 601 firewall to improve cooling. Although it was not initially necessary in cool weather, we’ve since installed them on the bottom of the 701 firewall, and, more significantly, on the sides of the firewall where most of the air exits. These radiuses work in conjunction with the fixed flaps we installed on the cowl. Tuft tests and flight data showed that this made a tremendous improvement.”

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The 701 has a very narrow firewall compared to the 601/650 and 750. I initially thought that we would use a ‘gill’ shape like a T-18 or a Pitts to exit to cooling air. Tuff tests revealed that the shape of the wind shield and the proximity of it to the cowl side exits hurt this. On the 601/650 and 750, we use a traditional hot air exit of just the bottom of the cowl, and it has always worked right off the bat.

“The tuft tests also showed a significant amount of reverse flow where air actually entered the rear of the cowl and flowed forward. There’s a number of very successful aircraft that use the cowling style with gill exits like our 701 Cowl; notable is the Thorp T-18, which has been flying in great numbers for half of the powered flight era. But eyeball aerodynamics and basic comparisons don’t take the place of flight testing. The 701’s more vertical windshield much closer to the cowling makes a high pressure zone at the base of the windshield. The small crescent shaped rib attached to the upper part of the firewall in the photo acts as a dam to prevent this reversed flow. There is one on each side. Gus hand made them in an hour or so.”

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“The top view, as compared to earlier photos shows that the Top Cover, which had an oil fill welded into it, has been replaced by a Gold Top Cover. The oil fill is in the valve cover, just like all our other installations. This eliminated the need for an oil fill door in the top of the cowl. The oil cooler in the photo is a Niagara 2003. The plane flew its first 5 hours on a 2002 cooler, like the rest of our high performance cooler installations. Our 3100cc 601 installation flew several hundred hours on a 2003 cooler and it out-performs any other cooler flying by a long shot. It’s overkill on most installations. But in March, we opted to upgrade the 701 to this cooler also. This was an easy change because our Baffle Kits are designed to accommodate either cooler. This was part of the refinements to the 701 installation that were ongoing before Sun ‘N Fun.”

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“Above is a view of how tight the Corvair fits in the 701. The wires in the photo are part of all the test leads to evaluate temperatures on the engine. The plane has a very elaborate MGL set up with flight data recording. This allows us to download and replay any part of the flight. The two black tubes in the photo are part of the Motor Mount. These attach to the steel tubing behind the windshield. They have to be there no matter which engine a builder chooses. The Corvair balancer is only 6″ in diameter, and snugly fits between the tubes with 1/2″ to spare on each side. With the engine in this position, the plane is in the weight and balance envelope of the designer, without any ballast. Planes flown forward of the front limit will have poor slow speed performance, and be prone to damaging the nose gear on landing. Engines moved forward would thus require ballast, something no well designed package has.”

“Two people have told me they were planning on using a rear starter on their Corvair powered 701. When looking at these photos, it is easy to see that anyone planning on this hasn’t examined very closely the installation, or has not finished the plane. Gravity, math, numbers and our flying 701 trumps other peoples’ guesses at what the weight and balance will look like. Twenty years ago there were things I wanted to do in homebuilding that time showed were poor ideas. How I got to where I am today is by letting my allegiance be only to what flight testing has shown to work. Pet theories and predjudices rarely add up to a lot of hours flown. This is also a good photo of how the inherently compact Gold Oil System fits in the 701 installation.”

“The top view of the engine shows the compact and organized installation, featuring The Gold Systems and Our Baffle Kit. The great majority of Corvair powered 601s are being finished by their builders in their home workshops, not at our professional facilities. The point is that our systems are flight proven in numerous installations and have been highly refined to be easily installed and trouble free, even when put together by first-time builders.”

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“The above photo shows the new fixed cowl flap on the underside of the 701 Cowl. In addition to this, there is now room for exit air on the underside of the firewall. It is important to note that the several hundred man hours of testing and research that have gone into perfecting the 701 installation were done by myself, Gus and Kevin at no expense to the aircraft owner. The owners experience meant that he was not a regular homebuilder in search of a proven product. He was excited about the idea of being a facilitator and a pioneer of the Hangar Gang’s efforts. He was well aware that new systems are not brought out without teething problems. However, we had a clear understanding that the R&D would be done at our own expense.”

“There are many cases in sport aviation where people who didn’t know what they were doing tried to charge an aircraft owner for the expenses of their learning curves. As professionals, this is out of the question for us. We will gain back our investment by selling high quality parts to facilitate the installation. “

“With the modifications shown above, the aircraft is now a reliable, hot weather, turnkey performer.  Gus flew the airplane several times in one day after the modifications were finished and pronounced the installation completed. It was a long haul to get to this point. People who’ve read my writing know that I’m an advocate of rigorous testing. All too often, things that have flown on a single airplane a few trips around the pattern are labeled “Flight Tested;” our 701 project would have met this standard 10 minutes into its first flight months ago. Had we sold anything based on its initial configuration, or had we been working with a customer who felt he was buying a proven product, great disappointment certainly would have awaited. Even with our extensive, decades-long experience, it takes time to make stuff trouble free.”

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“Gus holds open the cowl of the 701 to show off the FlyCorvair.com engine installation.
In order to serve the most builders and get the best use out of all of our fully flight tested products, the 701’s engine installation is very close to a 601’s. The engine itself is identical. This 701 sports a Gold Prop Hub, Gold Oil System, Niagara Cooler and an Electronic/Points Ignition System. It also shares in common with the 601 the Baffle Kit, Corvair Nosebowl, 2- blade 66″ Warp Drive propeller, and most of the Exhaust System.”

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“Blast from the Past: Steve Upson Alive. During the final phase of 701 modifications and testing, original Hangar Gang member Steve Upson, above, spent the largest chunk of time at the Edgewater hangar that he has in several years. People who met Steve several years ago knew him to be an incredibly talented aircraft mechanic as well as a chain smoker and connoisseur of quantity over quality beer. This caught up with Steve several years ago when he had emergency heart surgery and an abrupt lifestyle change. Today Steve’s alive and well.”

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5) – Builders working on the combination

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We have a number of pictures in the archives of builder’s 701/Corvair projects. I am going to extract them and put them on this page as running updates. To get started, Let me share a photo of one of the best known builders working on the combination: Terry Samsa of MN.

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From Corvair College #20 in MI: Terry Samsa running his 2,700 cc Weseman bearing power plant on our test stand. Terry drove in from Minnesota, a 14 hour drive. At this moment, you can be assured that he thought it was well worth the trip.

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6) – Notes on poor products to avoid

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The 601/650 and the 750 reference pages both have a ‘Section 9’, sharing comments on parts and companies that no one should ever buy aircraft parts from. If you are even considering, for a moment, buying any Corvair part that I didn’t make, you need to read these sections carefully to know what you are getting into. Also, be aware that many of the things advertised on Barnstormers and E-bay Motors as “Built by William Wynne” have nothing to do with my work.

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Simple example: Look at the last photo on the 750 reference page of the destroyed plane. notice the broken motor mount. That was caused by the original installation’s rear starter requiring bent tubes in the mount to clear it. The people that made it didn’t ever take classes in Structures and Materials, nor did they teach Welding at Embry-Riddle. I did these things, and I know why that mount broke. You don’t need this type of education to build a plane, but morally, you need to know what you are doing before selling aircraft parts. None of the people who ran now bankrupt LLC’s meet this simple requirement.

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In the age of the internet, people comments last a long time and are also easy to fake. If you look around, you can find comments from alleged builders offering testimonials for all products, even ones from now bankrupt companies. Look at the dates, and ask if these people are even still building today. Very few of these comments come from experienced builders, and many other the people would have long retracted the comments in light of what they were stuck with. Only 25% of home builts get finished. The percentage that get done with products of bankrupt companies has to be a tiny fraction of this. If you want to win at this game, it starts with making good decisions about who you are going to work with.

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I am clearly going to state again, If you have parts from another company, one I consider to have been run by vermin, I will not knowingly provide you any advice, service nor sell you any part to ‘upgrade’ your motor, nor will I allow you to participate in our ‘Zenvair’ discussion group, or attend any Corvair College.  It isn’t out of spite, it is simply because choices in aviation have consequences, and if you choose to work with vermin or their products, you are going to live or die with that decision. You can’t ‘upgrade’ junk by bolting good parts on it. Band aids don’t fix diseased things, amputations do. Zenith does not offer advice not service to people who bought Savanna kits, and this is the same principle.

I could list every name of every LLC that was in business to cash in on Corvair builders dreams and plans, but it would do no good. Just this week I heard of a new one starting again, right from the same address where the last one left off. Let it suffice to say that if anything on your plane came from Valdosta GA, I genuinely wish you good luck, your going to need it.

It is a free world, and no one has to listen to my experience nor advice. If you don’t like my tone, what I look like, things I say or perspectives, you are free to use these as a reason to discount or ignore what I have to say. A long time ago I learned in aviation that I needed to listen to the perspective of anyone with experience they wanted to share, even if they were not someone I personally liked.  I have learned much of what I know from people I would not have cared to be friends with. Aviation has serious consequences, and it is foolish to just restrict yourself to learning from people you ‘like’ or find ‘pleasant.’

About William Wynne
I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at www.FlyCorvair.com and in more than 50 magazine articles.

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