If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
Corvair conversion engines - cracked crank link
Richard Lamb wrote: Cal Vanize wrote: The issue us addressed in this page: http://www.flycorvair.com/crankissues.html The date on the page is 15 January 2006 - just released information. Ron Webb wrote: Do you have a link for the broken cranks? I cannot find anything about broken cranks on the "Corvair authority" site. http://www.flycorvair.com/ I did find the following statement: "I have never seen a cracked head, cylinder, case, crank or rod in the hundreds of Corvair engines I have inspected. It is a very strong engine." The Corvair engine has been flying since the early 1960's. Seems odd that ANY flaw would only now be being discovered. that dose seem like a lot of broken cranks... Three out of five cranks cracked. All with 200 or less hours. That's a small sampling, but not very good results. The article does indicate that the cranks were from engines in planes that were flying. That's the good news. But does that also mean that the engines need a teardown and inspection as part of every oil change? |
#2
|
|||
|
|||
Corvair conversion engines - cracked crank link
"Cal Vanize" wrote The article does indicate that the cranks were from engines in planes that were flying. That's the good news. But does that also mean that the engines need a teardown and inspection as part of every oil change? If you are running a conversion that is different from William's conversions, it could be a good idea. g If people take the time (yeah, lots of it) to read the whole article, you will notice a few things, and I will attempt to point out some of the more significant (to me) points. Biggest point. Do not use corvair engines outside of the recommended operating parameters. Some sub points. Biggest one, don't use longer prop extensions. Big time no-no. Others include, don't use heavy props, or hand carved props. Don't overstress the prop with some aerobatic maneuvers, or hard landings. Make sure the crank is properly ground. Oil systems must provide for consistent oil flow to all parts, at all times; stay away from two line cooler and filter systems. Use low RPMs and big props, rather than smaller props and higher RPMs. Avoid detonation, which is easy to let happen, if treated like an aircraft engine. Obey all points of his conversion manual. Nitrated cranks are a good way to add an extra margin of safety, when obeying the conversion manual, but the other examples that have followed the manual have been OK for long operational periods, even without the nitrated cranks. Avoid other's add ons, like extra bearing hubs, as they have not been tested. I am sure I missed some points, or miss stated some, but if you are using corvair power, it would be wise to investigate what this man has to say, and not take my word on it. I remember saying a long time ago, that I would feel better (or something like that) if a redrive was used to take the stress off of the crank. I think I will still stand by those words. Of course, It would need to be a properly researched and tested redrive, which at this time, does not exist. -- Jim in NC |
#3
|
|||
|
|||
Corvair conversion engines - cracked crank link
On Wed, 18 Jan 2006 19:17:35 -0600, Cal Vanize
wrote: Richard Lamb wrote: Cal Vanize wrote: The issue us addressed in this page: http://www.flycorvair.com/crankissues.html The date on the page is 15 January 2006 - just released information. Ron Webb wrote: Do you have a link for the broken cranks? I cannot find anything about broken cranks on the "Corvair authority" site. http://www.flycorvair.com/ I did find the following statement: "I have never seen a cracked head, cylinder, case, crank or rod in the hundreds of Corvair engines I have inspected. It is a very strong engine." The Corvair engine has been flying since the early 1960's. Seems odd that ANY flaw would only now be being discovered. that dose seem like a lot of broken cranks... Three out of five cranks cracked. All with 200 or less hours. That's a small sampling, but not very good results. The article does indicate that the cranks were from engines in planes that were flying. That's the good news. But does that also mean that the engines need a teardown and inspection as part of every oil change? These were also 40 year old cranks of unknown provenence, pulled out of old car engines that may have been thrashed to within an inch of their lives in previous "inCARnations" |
#4
|
|||
|
|||
Corvair conversion engines
Let's say you have to replace the engine 4 times to get 2000 hours. You are
still saving money over the cost of a Lyc or Cont and there is no guarantee they will make it to TBO either. "Cal Vanize" wrote in message ... As my research continues, I have been investigating possible engines for a 601XL. The Corvair engines looked like a good candidate. The reports seemed very good and the engine was surprisingly inexpensive for initial purchase and long-term maintenance. The stated expected TBO is 1500 hours and the Corvair Authority website documents the use of a Corvair engine in a 601XL. Everything seemed OK until yesterday when I read the most recent updates on their website. Seems that the "untreated" automotive cranks have been cracking in a very short time. Nitriding seems like the only solution. But with standard cranks cracking at under 100 hours, what would be the expected life of a nitrided crank. Twice as long, four times as long, eight times as long? This would still fall short of the 1500 hour TBO stated by the Corvair Authority. Does anyone have any first hand experience with Corvair conversion engines? Any info on their realistic life and reliability? TIA, CV |
#5
|
|||
|
|||
Corvair conversion engines
But would you have to replace the engine?
Maybe just a crank overhaul every 4-500 hours, in the middle of winter, after a good snow storm, nothing else to do. |
#6
|
|||
|
|||
Corvair conversion engines
I just think hanging a prop on a crank directly is a non-starter in the first place...especially on a crank and case not specifically designed for this in the first palce. Maybe a good redrive and flywheel would be a better way to go? |
#7
|
|||
|
|||
Corvair conversion engines
"Bret Ludwig" wrote in message oups.com... I just think hanging a prop on a crank directly is a non-starter in the first place...especially on a crank and case not specifically designed for this in the first palce. Maybe a good redrive and flywheel would be a better way to go? That is my opinion, also. -- Jim in NC |
#8
|
|||
|
|||
Corvair conversion engines
When it really gets down to facts, most often aircraft engines really
don't cost any more than auto conversions and the aircraft engine appears to be more reliable. No redrives needed, redundant ignition and lots of other things that makes them better. I was a firm believer in auto engine conversions but i haven't seen many last a long time except for the Subaru and Rotax engines. Morgans wrote: "Bret Ludwig" wrote in message oups.com... I just think hanging a prop on a crank directly is a non-starter in the first place...especially on a crank and case not specifically designed for this in the first palce. Maybe a good redrive and flywheel would be a better way to go? That is my opinion, also. |
#9
|
|||
|
|||
Corvair conversion engines
I just think hanging a prop on a crank directly is a non-starter in
the first place...especially on a crank and case not specifically designed for this in the first palce. Maybe a good redrive and flywheel would be a better way to go? That is my opinion, also. -- I partially agree. I agree that hanging a prop directly on the end of an automotive crank, even if you put it on the flywheel end, is a recipe for a short tbo even at low power and for a high failure rate at high power. (If you only use it to push an airboat around the local swamp, you can keep a couple of bottles of skin-so-soft in your tackle box.) However, switching to a traditional aircraft powerplant may not solve the problem. You really only have the full value of testing, experience, and service history when you mate an unmodified engine to an airworthy propeller with which that engine was certified--and preferrably in a combination used by a large number of aircraft in regular service for a reasonably long time. Remember the crankshaft problems in some of the Cessna 172's soon after the change from the Continental O-300 to the Lycoming O-320. (I think it was an early 160HP version, but have long forgotter the dash number--and the problem was promptly solved.) There have been other "teething" problems as well on various engines... In the special case of a KR-2, which was the subject of at lease two of the Corvair engines torn down and inspected, the plane sits too low to swing a 70+ inch diameter propeller; and IIRC was originally designed for VW engines swnging 52 inch diameter propellers. I have heard that the KR-2S sits enough higher to accept a larger prop, possibly 60 inch diameter. That seems to negate the reduction drives, although a shaft drive, similar to the one Steve Whittman developed for his V8 powered Tailwind, could be interesting. BTW, the plans are still available--I think Aircraft Spruce still sells them. Also, Revmaster (and possibly others) offers an aircraft engine based loosly on the VW dimensions and a Jabiru could work--especially with a 3 blade prop... |
#10
|
|||
|
|||
Corvair conversion engines
On Thu, 19 Jan 2006 15:35:13 -0500, "Morgans"
wrote: "Bret Ludwig" wrote in message roups.com... I just think hanging a prop on a crank directly is a non-starter in the first place...especially on a crank and case not specifically designed for this in the first palce. Maybe a good redrive and flywheel would be a better way to go? That is my opinion, also. What isn't there can't break. That's my reson for a direct drive 'vair insted of a geared Soob - same weight - same HP. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Book Review: Converting Auto Engines for Experimental Aircraft , Finch | Paul | Home Built | 0 | October 18th 04 10:14 PM |
P-3C Ditches with Four Engines Out, All Survive! | Scet | Military Aviation | 6 | September 27th 04 01:09 AM |
What if the germans... | Charles Gray | Military Aviation | 119 | January 26th 04 11:20 PM |
Corvair Engine Conversion Breakin Success | Dick | Home Built | 1 | January 11th 04 02:06 PM |
Corvair Conversion | Gig Giacona | Home Built | 17 | October 27th 03 09:43 PM |