Online Community of Zenith Builders and Flyers
I have a question for those of you using, or planning to use the Corvair Engine.
After the recent failure of Mark Langford's engine, are you still planning on
using a Corvair?
I bought WW's book, DVD's, etc and had planned on going to a workshop
last year - unfortunately, I was not able to attend. As with many of you,
circumstances got in the way of my building plans.
I may now be in the position to again consider building (can't decide between the
650 and 750) but now am faced again with the "engine" decision.
My only beef with the Corvair was the age of the crankshaft, and this was before Langford's
third failure. Dan Weseman is apparently considering have a new crankshaft made from 4340 stock and the price appears to be reasonable.
Given all of this - I'd like to hear what those of you who are actually using, or plan to use this engine are doing.
I am building (slowly, life gets in the way) a 601XL-B taildragger. I plan to power it with a Corvair converted per the latest William Wynne conversion. I am waiting to build the engine until the airframe is almost done. I would rather not build the engine and then have it sit on a shelf for an extended period before actually using it.
My "slow build" has worked for me, just by luck. The "upgrade" package was developed before I got to my wings, so I can incorporate the upgrade as I build the wing and center section, rather than tearing it all apart for the upgrade. Same for my engine. I have been picking up nice core engines as I stumble into them and have attended a couple of Colleges. The crankshaft issues have developed and "cures" are maturing as I wait to build my engine.
Like you, I am very interested in Dan's new manufacture crankshaft. I may end up with a stock crank (I have one that measures to new tolerances and only has about ten thousand miles on it, the engine came out of a wreck in the late 60's and sat in a barn for fourty plus years before I bought it). Or, I may go with Dan's new crank. It will depend on what knowlege and wisdom develops over the next year or two before I build my engine, but it will be, for sure, a Corvair.
In case you have not found Dan's website, here it is. http://flywithspa.com/ You can read about the new crank, his single seat sporty plane that is in development and his parts for Corvair powered Sonexes on this site. Very interesting stuff.
I'm building a 601 XL-B TD. I will use a Corvair engine. I made that decision 27 months ago and I don't see a reason to change. The Corvair will have a 5th bearing. I don't think crank breakage has been an issue on the 601 series airframes. The KR2 users generally seem to stress the engine (crank) to a higher degree than the 601 users. Dan's web site has a good list of reasons why you may want the new crank, or not need it. For the projected price the new crank seems a good insurance policy. Even with the added cost of a new crank, the Corvair is a viable choice in overall cost, simplicity of installation, weight, and reliability.
I am building a 750 with a Corvair engine. I have followed WW's book, bought his parts (proven airworthyness is important to me) and attended a Corvair College where I finished building and ran my engine. I have a Roy 5th bearing on the front end with Falcon heads and a nitrided crankshaft and it purrs like a kitten. I did my homework and pleased with the result. I think your fear about the crankshaft is unfounded with Langford's failure being a one of a kind issue.
I am getting very close to mounting a corvair on my 750. Like the others I believe Mark's latest failure was due to pushing the corvair envelope. He had the 3100cc cylinders installed which places additional stress on the crank. Although there may be other failures at the #2 rod journal in aircraft installs I've haven't heard of any. Most of the crank failures at that location have been in cars, most while racing. I don't think there have been any cranks break at the #6 journal ( failure point) with any engine using the 5th bearing modification. That said there are a several hundred corvairs flying with no 5th bearing and an un-nitrided crank.
I'm planning on using a Corvair, 2700cc, nitrided crankshaft, Weseman 5th bearing, built by William Wynne himself. I've talked with Mr. Wynne about crank issues, and I read about Mark Langford's experiences, and I don't think there's much risk in the standard 100 hp configuration on a Zodiac that will be used to get from point A to point B. I agree with others that Mark was pushing the envelope somewhat. I'm glad that Dan Weseman is coming up with a new option that seems very sensible, and I would look at it if I was trying to get more performance out of the Corvair. When I look at the suggestions on Dan's site, I fall squarely into the "old crankshaft is OK" category.
I didn't realize Mark had another failure.
I think Mark had a few things going against him. I think his engine is one of the 3000cc modified engines. The original engine has 2700 cc, so he was getting a lot more HP. Second, he was using a long prop hub to fit his nosebowl, so the gyroscopic loads were causing greater stress. I'm not sure if he was using a 5th bearing.
I made a concious decision when I built my engine to 1. not go for the maximum HP instead sticking with the 100 HP configuration, 2, Keep the prop hub short, 3. Use one of the available 5th main bearings available, 4. Have the crank nitrided. I don't think any of the Corvair builders that have gone that route have had crank shaft failures.
My engine is complete, has been run on a test stand, and I still plan on flying with it sometime within the next year.
Mark was using a WW 5th bearing that incorporated a rear mounted thrust bearing. He also had a rear starter. He also twisted off his harmonic balancer keyway due to a loose bolt, chucked up the entire engine in a machine and milled a new keyway 90 degrees off from the original one, with the crank still in the engine. By his own admission, he usually flew at full throttle at all times. I think his experience was strictly a one-off, and there is absolutely no reason to doubt the "standard" setup that has been proven time and time again. If you chucked up an 0-200 into a milling machine and milled a new keyway in the crank, it would probably break too. My opinion is that his loose harmonic balancer that caused the original keyway to fail also caused some stress cracking in the crank. (strictly my guess.) I would personally rather fly a Corvair that I know every single nut and bolt about, than just about any other engine I can think of. I have a 100hp with a Roy 5th bearing, and I sleep very comfortably every single night. I'm looking forward to flying all around the country next year if I can git r' done.
I was concerned, too. But, what are your options? None are perfect.
Jabiru= cooling problems/valves, $20k
Rotax 912= 4 critical AD's $$$
VW = Prop flange, power
Revmaster 2100= power
Jab 2200 = same above, power
O200 = $6-20k+
O235 = heavy $$
90 percent of the Corvair failures are in KR's (what's up with dat). Mark's rear starter is the only crank failure with front bearing. Super easy to work on, cheap parts. Good support.
O200=used $6-10k Great engine. Hard to work on, expensive parts, valves stick.
Don't forget the UL Power - 16-20K depending on hp + 4K FWF package and full fadec - but, pretty new product and I only know of a couple flying - the Zenith factory demos. I got a ride in the 650 in June, felt like a really nice engine - but I could easily build a second Corvair as a "backup" and still come in well under that for 2 complete engines.
I think another reason the KR's may have problems is they have to swing a smaller diameter prop and thus the RPM's go up, so they cruise a lot closer to 4000 rpm. The 66" prop recommended for Zeniths will max out around 3400 RPM in climb and cruise is probably closer to 2900, so it is putting less stress on the engine.
IMHO, I think Jabiru "cooling problems" are history! I've got a recent-production 3300A (#2427) with the new heads that have a larger finned area due to deletion of the external oil lines. It was very easy to tweak the ram air ducts and extend the cowl lip (CH750) and the CHT's were fine. I was marginal on oil cooling, but my new design sump cooler duct has solved that!
I'm not advocating using the Jab for any particular application ... it's just that cooling is no longer an issue.
The crank is now a non-issue. If you are *really* concerned about it, Dan Weseman is selling brand-new billet-machined cranks that are radiused, nitrided, and have an extended nose bearing race for his 5th bearing, for a very reasonable price. I would fly a properly setup Corvair-engined airplane anywhere... water, mountains, you name it.
The huge plus to the Corvair, IMHO, is that if you spend the time to put together your own, you will have complete mastery of not only your home-built aircraft, but also the engine that drives it. You will not be "beholden" to anyone else for any maintenance. If you have the skills to build the plane, you have the skills to put the engine together too. It's well worth the effort... plus, you won't be limited to "wondering what is going on" under that little 3"x6" door where the oil goes, and if everything is still the way it should be. I have flown Rotax 912's for 2 years, and they are not all roses. The gearboxes can get whacky, the carbs can get out of sync, they are water-cooled and can overheat in hot weather, and they are very expensive.