Corvair engines?

[pacerpilot]

I've got about 80 hours behind a corvair now-and counting. It's in my (Jake Jaks) Pober Junior Ace. It's got the power to haul the 830lb airplane, two dudes, flight stuff, lunch and, 18 gallons of fuel. It burns 6gph at approximately 2700rpm. I've built many corvairs for dune buggies and couple aircraft engines (pre-nitride crank). No problems and very economical. However, if you go with a fast design it is recommended to add the "fifth bearing". This will add to the cost to build the engine obviously. As for the other "aircraft mods" their cost is in line with any engine. The crank will run about $500 to prepare. A new Airmotive carb will set you back a few bucks too. Other than that, you can fabricate most of the modifications (top plate, oil pan). Get William Wynnes information/plans. He has the info for getting machining and nitriding done in the plans book. FYI, you "can" spend $6500 on a corvair; but you don't have to.

[Max Torque]

I know of a number of persons that have had problems with the Corvair. Mainly crank failures also one, now possibly two cam gear failures.

C150L - Please substantiate the problem and failures. Thanks. I know of a couple of cranks breaking - most notably Mark Langford's. Also, what's the story (and substantiation) on the cam gears? Cam gears can be tricky to install correctly/properly.

[C150L]

Hi Max,

Hate to be mentioning names, but I had heard of Mark L having a couple broken cranks. If I recall, Mark might be the one I heard of that tended to push his Corvair to the limits, which might account for multiple(?) crank failures. Not positive but believe many crank failures I heard of happened in front of or in the front (forward) throw of the crank. I'm pretty sure one having the nitrided crank and fifth bearing cracked (causing forced landing) further back in the crank.

Friend of mine has one and he told me they found some aluminum in a valve cover and is suspecting it may have come from the cam gear. This engine has not been tore apart yet, so time will tell.

I know of another that had one cam gear go out and at least one crank let go. This one has been rebuilt, 5th bearing added and is flying again, with out issues.

I have to say, if I hadn't already, all these Corvairs I know of have been in the KRs. It was also suggested to me that it might be the shorter props and higher RPMs contributing to those failures.

I'm no expert on these engines. The one I put together (2 or 3) times has not broke a crank. I installed the Dan Wesseman 5th bearing on it as well. This is the one that has found aluminum in the valve cover and is suspecting cam gear.

I also have most of the parts needed to put one of these together for a plane project my son and I have. It will be a much slower plane and longer prop. I just a bit leery on going forward with this engine, given what I've seen in the KRs, but we're a ways off and will keep an eye open for new info. The KR I've worked on has the sweetest, most powerful sounding small AC engine imaginable. Sounds like a HEMI idling, waiting for the lights to go green and tear down the 1/4 mile at WIR. Full power kinda makes your heart pound. Maybe the new crank is all that needed.

Here's a couple good reads.

http://www.n56ml.com/corvair/break3/
http://www.homebuiltairplanes.com/fo...k-failure.html
http://www.zenith.aero/forum/topics/...corvair-engine

[Max Torque]

Thanks C150L. I know there have been some cranks that have broken. Then again, cranks have broken on Lycomings and Continentals also. From what I've gathered, the billet crankshaft available from Dan Wesseman looks to be the way to for anyone concerned about flying a stock crank. I recently met a guy who has several hundred hours on his Corvair (done according to William Wynne's instructions) powered 601. He just did a curiosity tear down and added a couple of upgrades and noted no problems inside. He said it's a great engine. Thanks again.

[C150L]

I agree. It could, should and may well be a great engine. I like all that I've seen but the KR(?) crank failures and at least one cam gear issue I've seen/know about currently has me a bit concerned. I may well be building one anyway. We have most of the parts needed. I want our project to bark/roar like my friends KR does when we turn the key.

[Bill Barker]

[QUOTE=C150L;44733]Hi Max,

I have to say, if I hadn't already, all these Corvairs I know of have been in the KRs. It was also suggested to me that it might be the shorter props and higher RPMs contributing to those failures.

There was some discussion about KR's on the Corvair website saying that KR builders seem to want unique engine installations and don't typically buy all the parts William Wynne has to offer. I would be careful of equating KR/Corvair safety to more mainstream installations that do follow Wiliam Wynne's tested recommendations.
Plus, there have been several LLC's selling questionable Corvair parts that have since closed shop. When we deal in vague information from forgotten sources, we muddy the conversation.

[Max Torque]

I totally agree about questionable parts and muddying the conversation. Not long ago, I learned about a Highlander that someone attempted to put a Corvair engine in that didn't turn out well. Checking into it more, it turns out the guy who did the installation did it his way with an engine of questionable condition, using questionable parts, and he did NOT follow William Wynne's instructions/guidelines/recommendations/etc. Of course, all most people hear about is that it was a Corvair engine that didn't work out.

I recently watched a Corvair powered Panther plane perform aerobatics for about 45 minutes straight. Engine sounded really good and it was great fun to watch.

[SheepdogRD]

I totally agree about questionable parts and muddying the conversation. Not long ago, I learned about a Highlander that someone attempted to put a Corvair engine in that didn't turn out well. Checking into it more, it turns out the guy who did the installation did it his way with an engine of questionable condition, using questionable parts, and he did NOT follow William Wynne's instructions/guidelines/recommendations/etc. Of course, all most people hear about is that it was a Corvair engine that didn't work out.

First, let me correct some misconceptions. The Highlander mentioned was built by a professional aircraft builder as his personal plane. He did NOT use an engine "of questionable condition"; it was built by a reputable Corvair engine builder associated with William Wynne, following the Wynne procedures and using mostly Wynne-provided (or Wynne-recommended) parts. The primary differences? The aircraft builder installed an AeroCarb and an exhaust system modified to fit around the engine mount (which was also built to Wynne specs).

Head temperatures were always problematic. It was so hard to keep the Corvair engine cool in climbout that the builder finally removed it and installed the air-and-water-cooled Rotax engine the Highlander was designed around. Since the Rotax installation, he's flown his Highlander over 350 trouble-free hours. Yes, he installed the Corvair in the Highlander "his way", but there was no precedent-setting installation to follow.

None of this is an indictment of the Corvair engine. Using a carburetor and exhaust piping different from the Wynne recommendations probably affected cooling, and cowling design probably affected it as well. The airplane wasn't instrumented like a research project, so there's insufficient data to truly determine what the problem was. The builder simply looked at his aircraft, grounded despite all his attempts to keep the engine cool, and saw the prospect of a long and expensive struggle. He decided he'd rather fly than do engine research.

I planned to use a Corvair in my Highlander, too. I attended two Corvair Colleges, and thought they were worthwhile, educational and fun. The other Highlander builder and I both accepted the assurance that the Corvair "would be perfect" for our aircraft. I don't think we were misled; I think we just didn't ask the right question: "What airplanes comparable to the Highlander are using Corvair engines without overheating issues?" The answer would have been, "None, yet". That wouldn't have meant the Corvair wouldn't work in such an airplane, but it would indicate that the path to success would likely be longer, bumpier and more costly than if there were precedents.

The aborted Highlander installation simply presents a cautionary tale. Like most engines, the Corvair is better suited to some types of planes than others. Pietenpols have been successful with them, and I'd hazard a guess that a part of that success comes from terrific cooling because the heads are sticking out in the airstream. Faster airplanes like the KRs and Panthers -- with their higher speeds and thus increased airflow through the cowling -- have also been successful with Corvairs. It's the middle-of-the-road installations -- tightly-cowled, 100-mph STOL aircraft like the Highlander -- that are apparently more likely to see cooling issues. Perhaps those aircraft need much larger cowling openings so they can move more air over the heads. Perhaps they need larger carburetors to provide even more fuel flow in climbout for better cooling. Perhaps they need larger-diameter exhaust piping to provide better evacuation and thus lower head temperatures. That development work remains to be done. Until we see consistently successful installations in Highlanders, we don't have a path to follow. I'd expect to do a whole lot of testing and modifications to get a well-cooled installation in one of them.

The Corvair Colleges are proof that most of us have what it takes to build a Corvair engine and get it to run on a test stand. It's great fun to be there and have the support of so many engine builders working on very similar engines. Then comes the installation into the airframe. If someone has already flown a Corvair in an airframe like the one we've built, they've blazed the trail for us. But, when there's no successful precedent installation, we're pioneers. There's nothing wrong with pioneering -- that's the very spirit of experimental aviation -- but we know that pioneers are the guys with arrows in their backs. Anyone willing to accept the possibility of arrows can be a pioneer. Those who prefer a smoother path can let the guys who pioneer for a living -- like William Wynne -- do the research and develop a path to follow.

In the case of the Highlanders, we both were keen to see the Corvair work well. But, when the consistent overheating issues surfaced and no one had definitive answers on resolving them, we both saw the potential for an extended period with arrows in our backs. We'd have had to install far more elaborate instrumentation and keep making changes to the installations (carburetor? exhaust? baffling? cowling?) until engine temperature management was no longer a critical issue on every flight, and had become simply something to monitor. Neither of us wanted to go through a long period of research, development and testing, so we opted to change to a proven installation.

Again, none of this condemns the Corvair engine, not even in the Highlander. There are Highlanders flying with air-cooled ULPower and Jabiru engines, so someone may find a path to making the Corvair successful in them. We just haven't haven't seen anyone do it yet.

I still like the Corvair engine. I particularly like its smooth operation and wonderful exhaust note -- like a mini-Merlin engine. At most Corvair Colleges, you're likely to see planes with successful Corvair installations flying in for the gathering. If I were building one of those planes, especially a Panther -- which was designed for Corvair power -- it might well have a Corvair in it.

[pacerpilot]

I agree with Sheepdog, proper application is critical. If an engine isn't spec'd right, it won't work right. As for the crank issue, the few failures that have occured are in the little, fast, quick handling types. Put a corvair in the right plane and you don't need fifth bearings, etc.