# Debate about Mark Langford's 3rd crank failure

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#### rbrochey

##### Well-Known Member
I am no engine expert but I have done quite a bit of research (relating to engines for different homebuilt aircraft types) including spending a good deal of time at the flycorvair site. I love those engines and wish I could use the Corvair engine in the Viking Cygnet I've started building. The site, the classes and what they are doing for the aircraft homebuilder is pretty remarkable, and I for one applaud those efforts. And the professional results. Thanks

#### BBerson

##### Well-Known Member
HBA Supporter
I would note that 6 cylinder aircraft engines are a bit more complex with torsional vibration.For example, the O-300* has 5th and 6th order crank dampers where the O-200 doesn't, yet use the same cylinders, I think.The O-300 main journal is also much larger, 2.247".It is important to note that all experimental engine/prop/airframe combinations are different. The torsional vibration may or may not be a problem.* the lower powered but similar C-125 doesn't need crank dampers.

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#### William Wynne

##### Active Member
George, good to hear from you. My goal isn't to make this group a permanent residence, I would just like to provide some insight, links, and maybe a "reality check." I would like to share a lot of reading links to have serious builders understand what kind of success people are having out there. If I can show builders the depth of material we have, there is a good chance I can get them to attend a Corvair College as you did, When they are there, surrounded by creative, outgoing and supportive homebuilders, many people will find their "home in Homebuilding."
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Mr 'Rbrochey ' : Thanks for the good thoughts, I have always liked the Cignet. Maybe one day it needs a big brother, sized for a Corvair....
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Mr Poppastie: We still don't use metal props. We used to offer guidance on how to reverse rotate a Corvair by using a different cam and gear set. Problem is that the once great made in California gear set has been outsourced to China, and they are now made of poo-poo with yardstick accuracy in the people's number 37 aircraft part and lawn furniture factory in throwdung province. Even if the rotating moment of inertia for metal props were ok, which it isn't, they are all still the wrong rotation for Corvairs without the gear set and reverse cam......BTW, We live in Florida on a little grass strip, but both my wife and I and our families going back a long way, are from NJ. We refer to Dad at "the real William Wynne" as I am Jr. He grew up in Passaic, Mom is from Irvington get at look at: William Wynne Sr. Turns 89 today | flycorvair.
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Mr "Bberson" Keeping the title of the thread in mind, let me point out that Mark Langford's plane, in every incarnation used a GM torsional Vibration Damper on the crank. Although there were several now-bankrupt LLC's that promoted rear starter systems that foolishly deleted the damper, Mark's system always used it. There isn't anyone knowledgeable who has seen the crank in person who suggested it was a harmonic failure. BTW, if you read Mark's website, you can see his plane was flown with accelerometers and a lap top to test for resonant frequencies, and it was show to be stunningly smooth.
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BJC

#### proppastie

##### Well-Known Member
Log Member
It was your foreum I was at. I really admire your passion, energy, and the fact you can earn living doing this. You have provided a way for many to enter the wonderful world of aviation. What you have done is very impressive. That you are there to invesdgate analyse and publish these problems says much for your integrity.

#### BBerson

##### Well-Known Member
HBA Supporter
Mr Wynne, my comments on this forum are very specific in most cases for things which I have direct experience. And I don't claim to be an authority that knows all.
The topic of torsional vibration is complex, so I find it best to avoid absolute statements, while seeking comment from others.
With that in mind, I concluded the GM vibration damper is not designed for a propeller, and may help or make it worse.
Further, I concluded that external accelerometers do not work for proper crankshaft stress testing. A valid vibration analysis would require crankshaft strain gauges, as I see it. But I haven't seen a vibration test so I still seek info on how to do a valid crankshaft strain and vibration test because I would like to do it at my home shop.
Because any change in the system requires a new test to be sure.
But others have said a vibration analysis costs roughly $70,000, so I remain skeptical that a homebuilder can do this test properly. For certified engines, FAR33 requires crankshaft bending stress not exceed the endurance limit. For experimental, no strain testing is done in most cases and that is fine. However, the experimental engine operator should understand the risk of operating an engine without a vibration test. It might fail in 100 hours, 500 hours or never. Nobody knows. I understand this risk and operate with that in mind. So, I invite further comment about vibration analysis. #### slevair ##### Well-Known Member HBA Supporter I have easily built more than 100 Corvair engines, but never one that had a prop on it. I can build a 7500rpm 250hp track engine, but don't pretend to know any more about putting a prop on one than they do about racing. I would not even consider doing it without reading and learning all that was available on the subject from people with real world experience. I know first hand how expensive and hard won knowledge can be, and greatly appreciate people like W. W. that are willing to share it. Simply put; if you haven't tested it you don't know it. Ask someone who has. Scott LeVeque, LeVair Performance and Restoration (Corvair and Yenko specialists) #### BoKu ##### Pundit HBA Supporter ...there three items are all one piece, and there is no bending possible between them... No bending, as in infinite modulus? #### ekimneirbo ##### Banned Hello Double W....... I have really enjoyed what you posted here. As someone who recently purchased your manual and a few Corvair engines, I want to say that the volume of information available is both good and bad. From a potential builders perspective its great to read in depth history, but while trying to get my mind around what the latest updated information was..........I grew a little tired of searching. I had a lot of questions in my mind that I couldn't find answers to. It seemed that everything kind of revolved around Mark Langfords third break and an inability to find accurate commentary on how the rest of the Corvair world progressed or regressed from there. I'm not trying to be negative here, only to point out that there are probably many potential builders that may be in the same plight as myself. There just didn't seem to be any definitive info (that I could find) to get me past that point. That's why I'm very glad that you took the time to bring it all together for me in this posting....I learned more in 20 minutes here than I did in hours and hours of reading and searching. I would like to make a couple of suggestions. First, I would like to see you start a new thread in the Corvair section here on HBA and call it something like " WW Corvair Exerpts" or Updates . Then take just the postings that you have placed above and copy and paste them. Then make a "sticky" out of it so that it remains at the top of the Corvair thread. I think it would do much to cut the spread of misinformation and foster more interest in Corvair building. When ever you felt that some new information was pertinent, you could add it......but it would make it much easier for guys like me to get the info we want/need without being buried in interesting but not specifically helpful info. In other words, what exactly is the Corvair world like after the 3rd crank break. I know to me that seemed to be where the road ended, so I assume many others have grappled with that point.As I said above, you have answered my questions with these postings, so hopefully you'll make them an easily found reference for others. Second recommendaton.......invite all the people building and flying Corvair powered airplanes to send you pictures and info on their airplanes and post them on your site. I'm sure that others like me were not aware of how many successful planes are flying and that would be a great testimonial to them. Anyway, thanks for taking the time to set the record straight on what has happened and what is happening in the Corvair world. #### rv6ejguy ##### Well-Known Member Mr Wynne, my comments on this forum are very specific in most cases for things which I have direct experience. And I don't claim to be an authority that knows all. The topic of torsional vibration is complex, so I find it best to avoid absolute statements, while seeking comment from others. With that in mind, I concluded the GM vibration damper is not designed for a propeller, and may help or make it worse. Further, I concluded that external accelerometers do not work for proper crankshaft stress testing. A valid vibration analysis would require crankshaft strain gauges, as I see it. But I haven't seen a vibration test so I still seek info on how to do a valid crankshaft strain and vibration test because I would like to do it at my home shop. Because any change in the system requires a new test to be sure. But others have said a vibration analysis costs roughly$ 70,000, so I remain skeptical that a homebuilder can do this test properly.

For certified engines, FAR33 requires crankshaft bending stress not exceed the endurance limit.
For experimental, no strain testing is done in most cases and that is fine.
However, the experimental engine operator should understand the risk of operating an engine without a vibration test. It might fail in 100 hours, 500 hours or never. Nobody knows.
I understand this risk and operate with that in mind.

So, I invite further comment about vibration analysis.
Many good points here. As someone who has studied TV on my own installation and performed a mathematical analysis using the Holzer model, I'll make a few comments here:

There are 3 ways to prove that TV is not an issue with a particular engine, flywheel, gearbox (as the case may be) prop etc.

1. Strain gauge analysis
2. Mathematical analysis
3. A bunch of flight hours (like 20,000 cumulatively) on several engines of IDENTICAL configuration. A few hundred hours on 20 engines is a start but actually pretty invalid confirmation that the trend will continue.

# 3 is the least scientific but in the end, the real proof that TV is not an issue.
#2 can show that there are possible concerns and that an instrumented study is useful
#1 can save a whole lot of fuel and calendar time over #3

WW understands the significance of using identical configurations and that any small change can throw demonstrated reliability right out the window. Therefore he is stressing that everyone use a proven configuration and propellers.

A proper vibration analysis can be carried out today for much less than $70K, Dan Horton proved this 10 years ago. You need someone savvy in the field to help with this. I studied this whole issue in some detail a couple of years back. While it appears that most of the crank failures were due to bending loads, you simply don't know what contribution TV might have been to these failures without a math or real world instrumented TV analysis. TV remains the single most ignored and misunderstood issue with regards to automotive engine use in experimental aircraft IMO. Last edited: #### proppastie ##### Well-Known Member Log Member TV remains the single most ignored and misunderstood issue with regards to automotive engine use in experimental aircraft IMO. TV (torsional vibration).....does that include resonance vibration analysis? Or how are they different. Give us the short version if possible #### rv6ejguy ##### Well-Known Member TV (torsional vibration).....does that include resonance vibration analysis? Or how are they different. Give us the short version if possible Usually we can collect all relevant TV/ resonance information with a Wheatstone Bridge on the propeller shaft. We are mainly concerned with the resonance aspects which can cause much higher than nominal amplitudes. #### William Wynne ##### Active Member Mr Bberson and Mr: Boku Just so that everyone reading this understand your specific experience with Corvair flight engines, please start your next response by taking 20 seconds to answer my 6 yes or no background questions below. I think in the absence of your real names, perhaps you would like to share your experience: . Have you ever: (1) Seen a Corvair engine turn a propeller in person? (2) Seen a Corvair powered plane fly in person (3) Flown in a Corvair powered aircraft yourself? (4) Fully rebuilt a Corvair flight engine yourself? (5) Completed and flown your own Corvair powered plane? (6) Attended a Corvair College and met me in person? . Mr. Bberson you wrote: "I concluded the GM vibration damper is not designed for a propeller, and may help or make it worse. Further, I concluded that external accelerometers do not work for proper crankshaft stress testing." Mind if I ask if you did this without ever running a single test on a Corvair on your own? Are you aware that the durometer of the elastomer in the damper is not original? Is your conclusion on what works for testing based on running these tests to FAA standards personally? Just to be fair, you can read my bio and find out that I was once in charge of certification of MT props in North America, I am fairly well versed in what at takes to get a prop approved as an STC on a certified plane in the US. Have you done direct work on testing props to FAA standards as a paying job? Let me point out that if you have a porche engine in your Grob, it isn't certified to FAA standards, it is allowed by joint agreement, so I hope you spend an equal amount of time on VW and porshe sites discussing their crank issues. For 25 years I have been telling people in every book I have written that flying isn't safe, and it can't be made safe. Any comment you may have about risk awareness for People who will actually be using Corvairs is superfluous. . Mr Boku, I note that you are a glider guy, and have a project to make Composite taperd wings for RV series aircraft. How are those wings coming? Since neither those have much to do with Corvair engines, I am interested to know what your specific interest in commenting about Corvair engines is. Perhaps the goal is to just show that you know engineering terms? Maybe any reasonable person who read my comment would understand that with the props we use, the loads are low enough that there is no significant flexing between the 4th and 5th bearing. That us a useful reality, I don't think most people find discussions of "infinite" something they are going to use to build a plane. . Here is the Reality Check: On any discussion of structural analysis, there will always be people like who want to show up and claim they can do a calculation, or someone could run a test to predict behavior. If you are new to engineering, understand this basic tenant: ALL calculations, mathematics, and evaluations have elements in them that make them a MODEL of what they are describing or measuring. In the case of aircraft crankshaft, all of these models, even with the best of equipment, are approximations. They can not model the system perfectly, and they are a simplification that can't begin to evaluate factors like variations in materials, surface finish, harshness of pilot input, or something really complex like an intermittent misfiring cylinder. . Here is the Good News: flying the plane is a 100% accurate model for flying the plane. No theory nor calculation is as reliable a predictor as several hundred hours of flight time. Thus anyone who is really interested in buiding a plane, with an engine, can have a good degree of confidence that it will work, if they build a clone of an engine prop combination that has worked over hundred of hours. This is the subject of this story: Understanding Flying Corvairs Pt. #6, 98% DNA not enough. | flycorvair . So if you are reading this, ask yourself if you got into experimental aircraft to Learn Build and Fly, or did you get into it so that you can hear engineering opinions form people on the net without real names, who will not be using a Corvair themselves, who may have never even flown behind one.On this date in 1953, 31 men got together in the lobby of a small Midwestern airport and founded an organization called The Experimental Aviation Association. They were men of action not talk, men of real testing rather that theory, men how actually accomplished things, not people who criticized the work of others without offering their own alternative. In the course of building you will encounter many people who will try to make you settle for the path they settled for. How tragic it would be to have a chance and a desire to be a real builder, but be dissuaded from this path by a person on the internet with no name, one you can never meet. Your day, Your Life, Your Choice. -ww. #### proppastie ##### Well-Known Member Log Member WW this is a tough crowd here I am amazed at the expertise here, you being part of the amazingness. #### rv6ejguy ##### Well-Known Member TV (torsional vibration).....does that include resonance vibration analysis? Or how are they different. Give us the short version if possible Usually we can collect all relevant TV/ resonance information with a Wheatstone Bridge on the propeller shaft. We are mainly concerned with the resonance aspects which can cause much higher than nominal amplitudes. #### BBerson ##### Well-Known Member HBA Supporter . I openly invite anyone who still has questions to ask them, or write me, -ww. Rather than answer the comments with professionalism, It seems you prefer to attack commenters personally with insults such as my 5000 posts. I suppose the moderators with 8000 posts are here to spew nonsense as well, according to you. I don't find any usefull info in your responses. So enjoy your adventures on the forum. I suggest a look at the forum rules. #### WonderousMountain ##### Well-Known Member Thank you ww for commenting here, Your posts are in violation of several rules This forum is not on!y the largest builder forum, it's also the most challenging. IMHO, Mark's engine is cursed #### Vision_2012 ##### Well-Known Member ... Your posts are in violation of several rules This forum is not on!y the largest builder forum, it's also the most challenging. IMHO, Mark's engine is cursed What did WW say that was "in violation of several rules"? Please review rules 9 and 14, Mr. Wynne recognizes that opinions, humble or not, can be contrary to the reputation of engine performance. Unfortunately, opinions can lead people to do stupid things to their engines and get hurt. None of his challenges were personal or in bad taste. I find challenges to my thinking can lead to my personal growth. Rule 15, advertising products and services when supporting a technical point being made IS allowed. And, as far as I know, cursing at engines don't lead to broken cranks. #### autoreply ##### Well-Known Member Thank you ww for commenting here, Your posts are in violation of several rules This forum is not on!y the largest builder forum, it's also the most challenging. IMHO, Mark's engine is cursed Putting my moderator hat on: If you feel that a post crosses the line, please use the triangle on the left side of a post to report it and the moderators will look into it. Moderation will not be discussed in the topic concerned. Now putting it off again: @ William Wynne, as a user of HBA; I'd advise you to avoid some aspects of your replies that come across as a bit condescending. It breeds irritation, while a straightforward and clear truth will always rise to the surface on HBA. I for example have never been near a Convair in person, yet most certainly have the background to say more than a bit about certain aspects of it A proper vibration analysis can be carried out today for much less than$70K, Dan Horton proved this 10 years ago. You need someone savvy in the field to help with this.
Yep. About 20K Euro's (25KUS\$) is a good rate from a reputable institute with the instruments to do a full TV analysis.

One of the nice aspects of doing one is that you not only know (instead of just bet) that yours is not in danger, but that you have a range for prop inertias (and PSRU gear options) in which you know you are safe. Hammer=>nail for the rest of your reply...

#### rv6ejguy

##### Well-Known Member
"Here is the Reality Check: On any discussion of structural analysis, there will always be people like who want to show up and claim they can do a calculation, or someone could run a test to predict behavior. If you are new to engineering, understand this basic tenant: ALL calculations, mathematics, and evaluations have elements in them that make them a MODEL of what they are describing or measuring. In the case of aircraft crankshaft, all of these models, even with the best of equipment, are approximations. They can not model the system perfectly, and they are a simplification that can't begin to evaluate factors like variations in materials, surface finish, harshness of pilot input, or something really complex like an intermittent misfiring cylinder." WW

I'd have to disagree with some of your points about TV analysis WW. Your statement would seem to indicate that you've never done this sort of work nor seem to appreciate its potential usefulness. The Corvair, in a certain configuration, may or may not have a concern with TV. Without testing, you'll never know, end of story. If you have 10 identical flying examples with 2000 hours each and no failures you can have some confidence that there are no serious TV issues, when you have 50 flying examples with 2000+ hours each and no failures, you can have even more confidence that there is no issue. Since we are asking pointed questions here, how many Corvair engines flying have 2000 trouble free hours?

Actually, TV modelling or measurement analysis does not concern itself with things like surface finish, pilot input etc. It is done to know if peak loads at the various resonance points are likely to exceed the structural capabilities of the design.

The models are actually very accurate regarding critical loads related to resonance and you can model a cylinder out if you wish.

Instrumented testing using strain gauges is the recognized engineering method to validate a design, you could measure the forces with a cylinder out here as well. This is the method accepted by the FAA on certified engines and propeller combinations.

Both methods are used in conjunction in all sorts of related industries and followed up with usually many thousands of hours of actual testing under conditions more severe than the device is likely to see in service. This is the final validation step in the automotive world.

In the experimental aircraft world, often shortcuts are taken compared to the certified world to save time and money and often there is no consequence to that approach but I would not be so quick to dismiss traditional engineering analysis. Nobody in industry would ever approve a design for production without this these days. Most of us flying non-certified engines simply accept that there may be more potential risk in our decision.

This thread is about Mark's 3rd crank failure, a failure very different from the first two and nothing to do with bending loads introduced to the front of the crank by propeller loads or 5th bearings. A failure in this area could easily have TV as a contributing factor.

William, nobody is trying is discount what you have a achieved and offered to others with regards to flying Corvair engines. The accumulation and distribution of the information and lessons learned from actually building and flying them is a fine model to all others aspiring to do similar things with other automotive engine types. I applaud you with what you've done here.

Before you were on the scene though, Mark was on the bleeding edge of flying Corvair engines and putting on a ton of flight hours quickly and documenting his trials and tribulations in a modest, informative and readable fashion. I've followed all this for many years and your account here on HBA does not exactly agree with what Mark said here on his site: http://www.n56ml.com/corvair/break3/ww.html

As in any field, few people know everything about everything in that field. Everyone in that field has something different to bring to the table based on their experiences in it. As such, most of us can learn something from someone else. As in the early days, you were learning a lot about Corvair engines which other people in the field already knew about 20+ years before. Given my past experience with building Corvair engines, for example, I would never have used a reground, low hp, non-nitrided crank in an aircraft application when there was a far superior, production nitrided, alloy crank readily available. As I said in another post on this topic, GM developed that crank in response to cracks showing up on the original crank during durability testing on the turbo engine. Crank fillet radius was known decades ago to be a critical factor yet this was seemingly never checked until failures showed up. Hopefully our learning process never stops if we have an open mind and a modest one.

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#### William Wynne

##### Active Member
Ross,

My point was that yes, the loads can be determined, but there are variable on how individual engine assemblies that are built by amateurs of parts reconditioned by various vendors can take these loads. Also, a very smooth pilot can have a very different set of loads than one with harsher inputs, particularly in aircraft with light controls. My point is that the engineering model has a hard time evaluating these other variables. I may sound anti-engineering, but I am not, if you look an my website, you can see that my Father was the Director of Advanced Technology for Raytheon until 9/11. ( His office was on the 89th floor of WTC#2)
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My point about flying is that it tests the whole system and process. You may say that 2,000 hours are required for any indication, but I believe that most people who have seen many auto conversions, have looked at the fact we are trying the very stiff crank, low inertia prop/ no Psru approach. looked at the number of planes, particularly my point about out of 250 engines, there have been only 2 other Corvair/5th bearing events, and both had an identified external cause, would concede that we now have a set of suggested building and use parameters that apparently work. Ross, you can certainly think of countless engines people proposed as 'perfect' for planes that never made it to anywhere near the list of flying planes we have.
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Ross, the reason why we used the forged steel factory cranks (some where factory nitride ones before 2005), was simply that they worked from 1960-2004. There were very few cases of anyone breaking a crank, ever, and this was before 5th bearings. There are still several of these planes flying with 1,000 hours on them. While there have been countless comments saying that the issue was the increase in engine output, I will flat out say that the major culprit was a wave of builders who started in 1998-2002 getting flying, all using cranks that were ground at their location. about 10% of these had no radius at all after terrible local grinding I never saw. Having been around craftsmanship my whole life, I did not envision the poor level of work that had crept into industry in the 1990s. The factory base 8409 crank worked for Pietenpols and other planes in the 1960s because those cranks came straight out of junk yard cars and were never ground, and thus had the modest but acceptable GM radius. The Base 8409 forging and the factory nitrided 140/180 hp cranks are the exact same material, the latter just have a very surface nitriding. They have a better reputation, but this is primarily because the harder surface didn't wear, and when a guy was looking a rebuilding his core, he rarely ever needed to regrind a factory nitrided crank, and thus was not subjecting himself to the chance the local grinder was going to damage it while thinking he was making it better. This issue has not existed in many years, as the only to sources of crank grinding we have told people to use is Moldex in MI and the Wesemans, and both of these locations are one stop shopping with magna flux, nitriding and good grinding. Neither of Mark's first 2 cranks went to these shops. Examining Mark's issues without studying the processes that have been used in the last 7 years leads to false conclusions.
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