Mail Sack: Builder Questions, #1 RV-9?


Here is the first of a new series, where I take actual letters from builders and answer the questions here, where the answers can serve many builders. Because the writers sent in the questions as private email, I have trimmed their name off the email to respect their privacy. Their questions are in blue, I put the answer in black. You can click on the colored links in the answers to read stories with longer explanations.





Would you please answer some questions for me?

1. I have a Corvair conversion manual, #7856 that I purchased when I met you at the Arlington Washington airshow probably 6 years or more ago. It is a 2006 version. Is that still the most current version of the manual?

The manual has had many small updates since then, but if you read this site and keep up with the comments here, you do not need a new manual. Since 2006 we have written a very popular flight ops manual that you should consider.


2. I have found 2 engines – an RB and a YN. From your manual it appears that I could use everything minus the heads from the RB engine and the heads from the YN – if I bought both of them. Is this true or would you recommend waiting for a better engine?

The RB is a 140 HP manual transmission engine. If the crank does not need to be reground, you can magnaflux it and use it as it with a Dan Gen I bearing. Read this story: Getting Started in 2013, Part #5, ‘Allan Able’ short block. If the YN engine is a 1964 (it could be an un-useable 61-63) The heads will bolt on and work.


3. Would I have to re-nitride the crank from the RB engine or just do a magnaflux inspection?

See above.


4. In your manual and web pages you say that an engine should cost no more than $150 to $200. Is that still what most used engines are going for?

$250 to $300 is more common these days but plenty of guys who run adds on craigslist looking for engines pay less.


5. Has anyone used a Corvair engine in an RV-9 or -9A?

The only model RV that has flown on a Corvair was a -3. The guy had it on there and flew it for several years, but had issues. He had a turbo, injected 3,100, not really what I would call simple nor representative of how we suggest people do things. For all this work, it was not significantly faster than Dan’s 3,000 cc Panther prototype, which is totally reliable. You can’t really blame the engine for not being what some people wanted.


6. If not – why not? I think a 120 hp Corvair engine with the Weseman billet crank is a perfect fit for the RV-9. Even with all of the successful CH650/Corvair installations, I think the RV-9 is a better airplane than the Zenith, even though the Corvair engine would have to be moved ~7″ forward in the RV-9 to stay away from the aft CG limit.

Some people like Van’s products, others like Zeniths. You should build the one you like. I am sure the combination would work, but just about every RV-9 I have seen, including the one that belongs to my next door neighbor, has 150 or more HP.  RV-9 would probably be faster, but the Zenith would get off faster and might have a better climb rate.  It will take 1/2 the time to build a Zenith 650.  I have spent a fair chunk of time in person with both Chris Heintz and Richard Vangrunsven, and I will say that Heintz’s personal philosophy on individual choice appeals to me more. I have many friends with RV’s but I occasionally get tired of the element of the RV-fan club that attacks anyone who proposes something different, like putting a Corvair in a -9. Those people seem to forget that the RV-1 was a modified Ray Stitts design, and if Stitts had the same attitude, there would be no such thing as an RV-anything.  The guy who runs the Van’s Airforce website has made some very negative comments about freedom of choice in flying and turning people into the FAA. In 11 years of working with the Heintz family, I have never found an element like that. I don’t need everyone to love nor understand what I am doing, but it is tiring if the official attitude toward ‘experimental’ is negative.


7. Could you design and fabricate an engine mount for a Corvair/RV9 installation?

Yes. It would be easier to start with a an existing RV-9 mount to get the gear leg sockets already done. If you would like to see the geometry, it would be nearly identical to this one we built for the Wittman Buttercup:( )  there are several photos at that website. See picture below.


8. When will you hold the next Corvair College on the West Coast?

We are giving a lot of thought to having one in Chino, but I hope to have a California tour before the end of the year, even if we can’t organize a full blown college until 2015. -ww.




From 2009 “ Above, a motor mount for our Wittman Buttercup project. It is an intensely complicated Mount because it incorporates Wittman’s tapered rod landing gear sockets (the Buttercup actually uses RV-6 landing gear legs). I spoke on the phone with Earl Luce, the plans provider. He gave me all the operational data and weight and balance info for his O-200 powered plane, which I mathematically worked out to our own installation. The Mount resembles the O-300 mount for a Tailwind.  After completely welding it, I took it to our local powdercoater, and had it done in U.S. Navy gray. It is the 40th different Corvair Motor Mount Design that I have built.”


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 and in more than 50 magazine articles.

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