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Corvair Engine Conversion

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Engine conversion corvair

CORVAIR AIRCRAFT ENGINE CONVERSION

The following page shows what I went through to convert a 1965 aircooled Corvair engine into an experimental aircraft engine. I plan to install it on my Zenith 601XL, but I bought the engine cores long before I decided on that aircraft. Since experimental aircraft are one of my hobbies, I knew I would eventually need it. Being able to understand that a large part of the cost of a new certified engine has to do with legal expenses and lack of economies of scale, I've always been partial to auto conversions. It's a price driven decision.

It's a pretty common aircraft engine conversion. It was original made by GM, the parts are inexpensive and still available, it's a aircooled six cylinder engine that produces about the right amount of horsepower for a sport aircraft so it's a pretty good choice.

FORWARD

I guess I could start off with some liability statement... there is an inherent danger to experimental aircraft, what I do is not what I recommend you do, buyer beware, you get what you pay for, etc. Also, I am not in anyway affiliated with any other company selling or handing out expertise, parts, or advice and I'm not making any recommendation for or against any item by showing it here. This is just a record of what I have done and although I may make suggestions, I am in no way providing a guarantee or acceptance of your liability.

Also, I do have to tip my hat to those who have come before me and have been kind enough to share their experiences and lessons learned. Thanks to all and specifically to William Wynne and Mark Langford.

And yes, what I have done to my engine conversion will be counter to common practice in some ways: I will be providing a fuel injection system. I will be providing a single coil. I will have a computer that controls both fuel delivery and spark control. I will require a single high pressure fuel pump. If I lose electrical power the engine will quit. If the computer dies, the engine will quit. If my fuel pump dies, the engine will quit. Yep, I know.

CRANKSHAFT

I do have to mention one thought and it concerns the crankshaft. It is the crankshaft which limits the ultimate maximum horsepower that a converted Corvair aircraft engine can deliver. Increasing horsepower requires an increasingly large propeller and increases the bending loads on the fourth journal and bearing. John Brannen did an analysis (of which I studied and found to be pretty close) which showed that the bending forces due to the gyroscopic and asymmetric loads are many times larger than the twisting load due to the application of work. In a car, the crank only sees the twisting load. Even with a perfectly balanced and symmetric propeller, huge asymmetric loads are applied at angles of attack other than 0 degrees (P-Factor). The gyroscopic loads are equally large based on the typical props we are using and typical maneuvers that we are flying.

It's a matter of lateral bending that is generated by the prop that must be absorbed by the fourth journal and bearing. Actually, it will eventually be absorbed entirely by the journal. As the bearing wears, it eventually allows the journal to bend as much as necessary to absorb the full force.

It's another engineering balance: You could run the engine at 200 HP with a huge propeller; but the tradeoff would be that the P-Factor and turning rates would have to be excessively limited. Since we generally don't limit our maneuvers based on maintaining the structural integrity of the engine, the propeller size and horsepower should be limited.

Based on historical evidence, this is a reliable 90 HP aircraft engine.

MASTER CHECKLIST

I have made a master checklist of all items and actions needed during the conversion process. Costs, alternatives, and notes are provided so it's a hell of a checklist (if I do say so myself). The method I use to check off items is to fill in the Actual Prices column. Just looking at mine, you can see which alternatives and which parts I choose by the cost of the item ($0.00 means I did something that required no cost, like cleaning a part, or I chose not buy something).

Corvair Master Checklist


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JANUARY 2004

After a year or so of on-and-off searching, I found someone in Alabama who had several. His father collected the engines for experimental aircraft. He wasn't an airplane guy and wasn't interested in Corvairs. So after a few emails with him, I decided to drive down one weekend. I got four 110hp engines, all were complete, three were '65-'68, one was a '64. I got an extra crank, an extra set of heads, three 12 row fin oil coolers, an extra set of pushrod tubes, an extra set of valve covers, two side draft motorcycle carbs, and a gascolator for my Model-A. It was $400 for the engines, the rest he just loaded into my truck for free. I paid cash and gave his buddy $20 for helping us load the engines. The following is a few pictures of where these babies were hidden...

One in the barn, one in the weeds in front of the trailer...

Corvair Engine Conversion

and two more in the trailer.

Corvair Engine Conversion

This is how you get four engines in a Ford 150. Also, it's well over 1000lbs and that makes for an interesting interstate ride home:

Corvair Engine Conversion

AUGUST 2005

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