CHT Part #4 more notes


I received an email from a builder that gave me a moment to pause and think about communication, and what people are willing to read into things. The letter was sent by a good guy, and I have deleted his name because I want people to focus on the comment, not who said it. Here is the sentence from his email:

 “In view of your modification of the inlet size for the Wagabond, would you recommend I do the same on a standard two-piece nose bowl for my plane?  Did you make the mod preemptively, or was the Wagabond running hot?  Thanks in advance”

Now, all this week I have been writing about cooling, and specifically linking to many articles that I have written in the last 20 months. The photograph and caption listed below is in a story that was directly linked to a few days ago. Read it and see if you think I the Wagabond was running hot as the letter writer asks:

Above, a real world proven Corvair system, the Wagabond cowl. Note that the air inlet is a simple 4.875″ hole in the cowl. This aircraft has flown at the record gross weight for Corvairs, it has always lived in Florida, it has a very large airframe with plenty on drag to spare, and yet it never ran hot, even with a front alternator and no inlet cooling rings. Why? because Corvairs have excellent cooling. builders can either utilize this success or they can ignore my suggestions. If they chose the latter and it doesn’t work, they rarely see the problem as a people issue. For some reason, a fraction of builders will focus on stories of people who has trouble with one-off ideas rather than looking at all the people who are flying proven ideas without issue.


This while series started because I was angry about people offering the unfounded opinion that Corvairs inherently ran hot, and that the cowls we offer and the way we teach people to cool the engine does not really work. Over the last several nights the stories I have written have been to counter these ‘opinions’ with facts and data, and offer links to show that this cooling is not an issue with Corvairs. The last sentence in his note indicates to me that some people are not really reading what I have to say, and my words are competing with a predisposition on their part to still believe that there is something wrong with the cooling as we build it.

I don’t blame the letter writer. He is exposed to many people talking about Corvairs, and at times it is hard to keep sorted out who has an ‘opinion’ and who has been testing and flying. This is why I was annoyed in the first place with people who have never owned a flying Corvair spreading rumors that “Corvairs need 6″ inlets”. On one hand it is just a lot of background static, but I am of the opinion that some of it sticks even when the recipient doesn’t consider nor remember the source. If you are new to a subject, be very discriminating when you choose to listen to people. Adopting perspectives, even partially based on false opinions it at best, a tremendous waste of time and energy.

To me, the really ironic thing is that their are other alternative engines that really do have cooling issues that are very hard to solve. The Corvair is nothing like that. Yet the ‘buy it in a box’ imported engines with actual cooling issues probably generate less internet discussion than the Corvair does on this topic. Part of the reason is that the people buying those are largely shopping for an appliance, and people coming to corvairs are supposed to be here to learn about a machine. The latter should generate more discussion, but talking about things is not the same as learning, especially when much of the conversation is opinion, and when fact must compete with rumor during the phase where the new builders understanding just developing.

The post I put down last night was number 365 since we started this blog. Give or take, that is a quarter of a million words. If I tasked you with typing a 250,000 words that were educational and entertaining or gave you the option of building a two place kit aircraft, which would get done first?  I type about 20 wpm, (not counting time spent staring at the keyboard) so I could build the plane much faster. I still consider the time well spend, under one condition: People actually read the content.-ww

CHT part #3, Letters, notes, sources and inlets.


Here is another block of information on CHT and cooling, along with data from flying pilots. This is a collection of notes and loose ends that adds a little more dimension to the first two parts.


Above, The Wagabond nose bowl last night about 3am.  I have been having a run of insomnia lately, and have been dividing up the hours in the middle of the night between writing, doing a little work on the Wagabond and reading Morris’s Colonel Roosevelt, a rich biography of TR from when he left the White house until his death. When I am this tired, I don’t make customer parts, but I will work on my own basic stuff like nosebowls. Last night it was more than 70F in the hangar. Not a bad temp for glass work. I bonded in the inlet rings seen above. They not only give the cowl a much better look, they are also functional. A lot more air will flow through a 5.125″ tube, even a short 1.5″ long one, than will flow through a 5.125″ hole in a flat plate. These rings are made out of PVC pipe, but you could actually make them out of just about anything.  This is the biggest size I think any Corvair needs, even on heavy slow climbers like Zenith 750s. This original one piece nosebowl is dimensionally the same as the two piece models we sell today. It has an altered line where the sheet metal of the cowl meets the nosebowl to make it fit the Wagabond better and the ‘tunnel’ in it is the beginning of the shape that flows into the J-3 airbox/filter that the plane is set up to use.


Above, a detail look. The white ring is PVC, it is bonded in with West System epoxy thickened with silica and flox. The section of paint stick and the sheet rock screw are just working as a clamp. If you look close, you can see that the tube flares out slightly on the ID near the end. It isn’t needed, but it will not hurt. Epoxy theoretically doesn’t stick to PVC, but it will get a mechanical bond if the surface is rough enough. This nose bowl is 10 years old. It may look a little rough, but well made glass parts hold up even on hot engines and over long lives. If you look closely, the marks show that it was vacuum bagged into our mold. the part had the image of the bagging plastic in many places.


Above, a bigger view. I ran 3 sheet rock screws through the part to pin it to the table after I covered the table top in plastic sheeting to prevent sticking. The screw holes don’t matter because they are in the section covered by the spinner. The two inlet rings are being clamped down by the sticks until they hardened. You can immobilize many things to a wooden work bench this sheet rock screws. Again, 5.125″ is probably too big on all except the slowest climbing planes in hot weather.  Inlets size doesn’t cool by itself, it has to be matched with outlets and good baffling.


Mail and comments:


Letter from 2,850cc 601XL builder and flyer Ron Lendon:

Ron with his plane at Brodhead 2012.


WW, it’s not that I don’t enjoy the reading I miss the succinct data and would like to have a place to quickly look it up.  Perhaps in my spare time now that the plane is flying with the correct carb. No I didn’t volunteer to do it. The calibrated CHT gage you allude to, is it available to those of us with short attention spans also?  I have the Westach gage and rarely see the CHT temps go above 350F on hard climb in the more temperate climate we have here in Michigan.  I’m using the ring type connection at the GM location.”

Ron, I looked on Ebay and other places to see who was selling Mil.surp. gauges but didn’t find anything noteworthy. I found mine at the Oshkosh flymart. Get a look at this link, it is to Dakota Digital, a company that makes all their stuff in the USA.


Letter from 2,850cc CH-750 builder Blaine Schwartz:

Click on: ( Zenith 750 Builder Blaine Schwartz )

“William, Thank you for such an informative essay! Carl Sandburg once wrote: “Experience is the greatest teacher”. You are a first-class example of proving his premise. Blaine”


Letter from 3,000cc PC Cruiser builder Sarah Ashmore:

“I find it difficult to understand why anybody feels they need 6 individual CHT readings on a Corvair. Lycomings and Continentals have a CHT on each cylinder because each one is truly independent and subject to different cooling and heating rates. The Corvair is one big block of aluminum, a material which conducts heat rather well, so it should be fairly uniform in temperature regardless of what is going on in the cylinders. One on each head is good enough for me and I have already purchased the special size bolts along with the other hardware for the engine build. And cooling is not something I like to do the hard way either. My variation on the Personal Cruiser will have a 30″ wide firewall instead of the stock 22″ but I have your generic nose bowl and a set of generic Weseman baffles all ready to go on it. All I have to do is make sure I follow your recommendations on the cooling air exit and I would expect the test flights to have no surprises with regards to engine cooling. There is enough experimental in my aircraft already so I choose my innovations wisely. A good pair of articles in a long line related to engine cooling.”

Sarah, there are also a lot of certified planes like C-150s and 152s that don’t have any CHT at all. 6/cht-6egt combos mostly appear as an option on big injected engines in fast certified planes like Bonanzas, where owners are trying experiments in extreme leaning and early top end replacement. Although Dan Weseman has a 6/6 combo on his plane, just the other day he was saying “what is wrong with a little too much cooling?” implying that no one is setting a record here, so why not sacrifice a few mph cooling drag to have an engine that always runs very cool. It fits in with your idea of leaning to the proven side rather than the edge of the envelope.


Letter from 2,700cc 601XL builder and flyer Dr. Gary Ray:

Click on: ( 601XL-2700cc  Dr. Gary Ray )

“William, Thanks for this post.  I read and re-read everything but this brings all of the temps, measurement locations and expected results into one post.  I have my 601XL-B setup as you have shown and I am experiencing the same results.  Until recently, I have taken all CHT’s from beneath plug #3 and #4.  The highest temp I have ever seen has been 430 F on its maiden flight when I only measured plug #3 , otherwise it can get to 410 on high heat days during a 90 mph sustained climb.  I now record temps on both sides from the bottom #1 & #6 locations.  During the last 50 hours I am seeing a maximum temp of 315 F on the worst days and a spread between sides of less than 10 degrees.  Measurements show approximately 80-90 degrees lower temperatures between the top plug position and the lower GM position.  The gauge is a four channel MGL device for CHT and EGT’s and it produces comparable results to the temperature compensated analog meter I had used before.  It reads about 10 degrees higher and has a thicker washer type thermocouple which likely accounts for the slight difference.  In cruise at 3000 rpm, 9.75 degrees at the tip Warp Drive, 21.5 MP, 65 OAT,  CHT’s read 270 degrees.  EGT’s taken at 12 inches downstream from the last exhaust port are 1200 to 1300 and will go higher if leaned more aggressively which I do not do.
 Current Set Up: Maximum advance on the timing is set to 30 degrees, 100LL fuel only, Inlets size 4.75″ with inlet rings, Outflow is 3.5″ x 24″ which is 2.4X inflow area and the bottom edge is rounded.  Metal tape over cowl hinges above plenum and tight baffles. The Niagara oil cooler reduced maximum oil temps by 30 degrees (now 210F).  Normal climb is 90 mph.  If I see temps near 310 F , I increase air speed by reducing my rate of climb which seems to work.
 It is nice to know that there is such a large margin over normal operating temperatures before overstressing the engine.  The engine runs with a very low level of vibration.  Just how low is really apparent when I am in dead calm air.  This is when I start patting myself on the back for choosing the right engine.”

50 hours until CC#27 registration closes.


We have a shade over 48 hours until we close the registration on CC#27 which will be held in Barnwell SC November 8-10.


CC27 –


The Event also has it’s own Face Book Page:


Below is a link to a story I wrote about the specific skills builders learn at colleges. Read it and decide if you would rather learn these things slowly at home, or head to the college and have me teach them to you personally in one weekend. You can do it either way, but I an assure you that it changes the way you see yourself, from mere owner to builder and master of your Corvair engine to know these skills. It is hard to make an argument against learning them sooner rather than later.


Basic Corvair College Skills, examples of learning


Below is a link to my story about the “Cherry Grove Trophy”, which we present to the outstanding Corvair Aviator of the year each November. In 20 days there will be a new name on the Trophy, and a fresh presentation made at Saturday night’s dinner.  In other branches of aviation, the awards often go to the guy that wrote the biggest check or had the most political influence. In the land of Corvairs, we are not polluted by corruption like that. Our Trophy goes directly to the individual that set an outstanding example and gave back to others now building. Barnwell is the setting where you can meet these builders in person and understand that your place is beside them, In the Arena. Reading a membership magazine featuring aircraft no working man can afford, written by editors who would consign and condem you to be only a spectator is the antithesis of this. Read this story, contrast it to most industry magazines, and then decide for yourself: Spectator or Man in the Arena?


The Cherry Grove Trophy


Blast from the past, CC#19, Barnwell, 2010.  Builder Jeff Cochran stands with his running Corvair. Today this engine is flying in his Zenith 750.  He is planning on flying it back to Barnwell for CC#27. Progress is made by deciding that the time has come to advance your own dreams. You must choose this, it doesn’t happen without your personal action. If I am ever going to write your story about flying your plane, you must take action to start this.


” (2010)- Zenith 750 builder Jeff Cochran of Alabama supervises the run-in of his 2850cc Corvair, above.  The Zenith 750 is a large airplane capable of climbing at very low  airspeeds. This combination makes it brutally unforgiving on engines with inadequate cooling or light duty construction. The Corvair’s outstanding cooling and high quality  components make it impervious to installations that are the undoing of lighter engines.”

Pietenpol Mount on airframe


Piet builder Mark Chouinard sent in a photo of his Corvair motor mount on the front end of his plane. The airframe exhibits outstanding craftsmanship, and looks to be in the “light at the end of the tunnel” phase. From this point forward the pace of work tends to increase.

When new guys set started they find it hard to visualize how much more productive per hour they will be in the second half of the plane. Your skills will be far better, you will find a work schedule and rhythm that fits your life, you will have many trusted fellow builders to share info and enthusiasm with, and with enough persistence, you can see the light at the end of the tunnel.

Photo: Come on CC28... that fabulous looking engine mount needs something bolted to it!  Like what you see?  Call William Wynne at

Mark’s plane is a traditional Pietenpol with a number of nice details. The landing gear combines traditional wire wheels from a straight axle gear with J-3 style independent suspension. Disc brakes are modern but appropriately sized. This view gives a good look at the Pietenpol’s structure. Mark has wisely left off the outter skins on the front of the fuselage until everything is built and rigged inside. The Gray powder coated Motor mount we made for him is one of our “High Thrust line” motor mounts. Below are some direct links to Pietenpol stories in our archives. The first three explain the concept of a high thrust line mount.


Pietenpol  Motor Mounts, P/N 4201(C)


Pietenpol  Products, Motor mounts, Gear and Instalation Components.


Pietenpol  Power: 100 hp Corvair vs 65 hp Lycoming


Three Pietenpol Motor Mounts


Making  a House Call on 1,000 Hour Pietenpol


New Pietenpol #3, Mike Groah, Tulare, California


New  Pietenpol, Gary Boothe, Cool, Calif.


Pietenpol review in pictures, 15 more Corvair powered Piets


From our Brodhead 2013 coverage: “After the Forum, we conducted a Tailgate Tech Seminar. Piet builder Mark Chouinard, extreme right, extreme tall,  listens as I answer questions. Mark picked up one of our high thrust line Piet Mounts for his project. Jim Boyer of California picked up another one at Brodhead for his Piet. That rounds out the first 10 of these new generation Mounts. While I have previously made Motor Mounts according to the original drawing, all of our Piet mounts from here forward will be high thrust line models.”


Corvair CHT, letters and notes.


We picked up several letters from friends on this topic. Let me share some of them and offer a follow up on the story.

Zenith 601XL builder and flyer Ron Lendon wrote:

“And after all that reading I’ll be dipped if I can find your recommendations for the temperature range your followers should be shooting for.  Try putting those details in too, OK?”

Ron, for a guy who made his own cowl and experimented with carbs, I would have guessed that you would have liked reading the information. The topic was the measurement location and test tools, not so much the values. For people with busy schedules and short attention spans, The numbers:

GM Factory limit, measured on bottom of head: = 575F

Highest temp I have personally seen in a Car, measured on bottom, without engine damage = 575F

Highest sustained temp I have personal seen on a CHT in a plane without any damage to the engine = 480F, measured on bottom of engine

Highest temp on bottom of engine  that builders should consider tolerable before stopping to rework cooling system = 420F

A reasonable goal temp in a hard climb that will still have a very wide margin of safety = 380F, measured on bottom of engine, easily achievable with our existing cowls and cooling designs, even in large planes.

Highest Temp that Dan Weseman saw on bottom of engine in full air combat maneuvers in 3100cc “Wicked Cleanex” = 375F

Typical Max climb/ 5 gal/hr cruise temp numbers in well prepped Zenith 601on 80F day = 375F/320F

My target goal, measured on bottom of engine, for gross weight Vx climb in 3000cc Wagabond, 100F day, 5″ inlets, 60mph, 1,600 lbs = 350F.

Lowest cruise temp recorded for a plane with a full cowl, measured on bottom of engine, Chris Smith 3100cc “Son of Cleanex” = well below 300F.

Lowest cruise temp recorded for a plane with a J-3 cowl, Jim Weseman, 3100cc Celibrity biplane = 250F


Above, Phil Maxon’s 601XL, finished in our hangar in 2006, flies over the Atlantic Ocean near Ponce Inlet FL. This aircraft was one of the first 4 Corvair powered Zeniths, yet is has never had any cooling issues. Corvair Cooling, especially on airframes like Zenith XL’s is not a mystery. Anyone who chose to follow our directions and used our designs did not have to be a pioneer. If you want your plane to work, just make it a clone of successful aircraft.


For readers with a little more time, get a look at the following links to stories I have written. I found them all simply by searching “Cowling” , “Cooling”, and “CHT” in the search block at the top right side of this page. If you are only going to read one story for right now, make it the last one, because it highlights the difference between measuring the CHT under the plugs and below the engine:


Cooling with J-3 style cowls. (Pietenpols, Cubs, Biplanes, etc)


Corvair Cooling, Three 2007 examples from our hangar.


Corvair Cooling, something of a human issue…..


Corvair Cooling



Measuring Cylinder Head Temps on Corvairs.


Right here and now I am going to make a very important point: I could put an engine on the run stand, hook up two of the finest CHTs, fuel the engine with pure ethanol free 94 octane gas, have it be ice cold and get ready to start it.  Then I could reset the timing from 30 degrees total to 44 degrees, (a number that people without timing lights often think “sounds good”) Start the engine, and take it to 2,700rpm.

It would take more than 3 minutes for the CHT to exceed 400F on the gauge. Long before this, the detonation would begin, and within 30 seconds of it really knocking, (which would be hard to hear over the prop,) the engine would blow out at least one head gasket, and crush down the ring lands on several pistons.

I could then honestly report “The engine had never exceeded 400F.” I could give many examples like this, and then we could have a lot of internet people offer opinions about the cooling system design we use, and some car guy is going to offer the “expert opinion” that the cowl needs 6″ inlets.  If you want to learn something in aviation, the discussion is going to have to be held at a higher level than that.

CHT is not something that can be discussed as an issues divorced from other operational parameters. I have seen people waste incredible amounts of time trying to solve a “cooling problem” who have not bothered to check any of the basics.

I have been doing this for a long time, and I still have no idea why some people get to the point of having 5 years of work and $30,000 in their aircraft project, but they refuse to drive down to their local auto parts store and buy a $39 timing light.

About a year ago, a guy contacted me who bought an engine I had built for someone else in 2005. He had it ground running on his plane. When I asked him what the timing was set at, he said he had no idea, he just assumed, without a single word to confirm this, that I had set the timing before mailing it to the original owner six or seven years earlier.

I explained that this was a very poor assumption, that even if I had, there is no telling that it wasn’t changed by the first owner, or bumped as it went in or out of the two airframes and was shipped around the country. I pointed out that if I said I unloaded a firearm before selling it to someone else 7 years ago, I would hope that no one would never say to me “I can point it at people today because you unloaded it half a decade and three owners ago.”

About a month ago I heard from the same guy, The engine still was not running evenly on both ignitions but he still had not checked it with a light. If someone presented me an engine that had a years ground running on it, but had never had the timing checked, I am going to flat out say that I would not fly it without tearing it down. Why? because you can check things the easy way with a timing light right away, or you can check things later the hard way with wrenches. Or of course there is the third option, which is just say “I am sure it didn’t hurt anything, It will be alright”

‘Sprint’ builder Joe Goldman wrote:

“William I as am not building my engine I would feel comfortable with 6 cht’ too know what is going on with each cylinder. Does the stock location average temps or would it indicate a particular cylinder over heating. You would not know which one, then how do you locate the trouble.”

Joe, we are friends and you know I think you are great, but lets get a little more thoughtful on this one. First, why are you not building your engine? If the goal of asking me a question is to learn something, then let me offer that building your own engine is the best way to learn many things. Honestly, what are 6 chts going to tell you that 2 are not? Lets say that flying along at 5,000′ and the CHT reads very hot. What are you going to do? Land, that’s what. If your right side CHT indicates an excessive number, please explain to me what knowing if it was #1 #3 or #5 is going to do for you at 5,000′. I have said it many times and many ways, but please know this well; You detect issues in the air, you land. Diagnosis is always done on the ground. The only guy who argues against this is the one who is going to rationalize some reason to keep flying. Each CHT sender cost more tan a Raytech thermometer. If the plane isn’t running right, land and use tools on the ground to look into the problem.

Besides, if you build and equip your engine correctly, you are not going to be flying around looking at issues in the air. Stop for a minute and honestly tell me what is going to happen to an engine, in flight which is going to make an individual cylinder suddenly go up in temp? If you were looking to tell which individual cylinder was causing an issue if your engine started running rough, you are a poor decision maker, and you need a better flight instructor. Any skilled pilot will tell you that the first thing you look for when your aircraft runs rough is the nearest airport. -ww

Cylinder Head Temperature measurement


In this story I would like to address CHT (Cylinder Head Temp) measurement on Corvairs. In the 20+ years I have been working with Corvair flight engines, I have written a great number of informative posts and stories on this topic, and I have also covered this in stories on cooling systems, instrumentation, human factors for lower time pilots and how CHT relates to detonation threshold.

My comments on these topics can be found in our manuals and on both websites. The information we have shared is from personal measurement on several of our own aircraft, dozens of test engines in extensive ground runs, comparative instrumented engines, and a data from a number of experienced Corvair powered pilots Like Dan Weseman and Woody Harris.  All of this has been collected and correlated with my professional A&P perspective, and often discussed at great length with other trained professional aircraft mechanics like Gus Warren and Arnold Holmes, whose experience includes extensive Corvair flight time, in addition to many certified aircraft engines. My data includes many aircraft that worked well, and a handful that didn’t. It is big picture, not myopically gleaned from looking at one or two engines, listening to stories and jumping to a conclusion.

I do not consider myself ‘brilliant’ about this topic. The value of my perspective comes from simple observation of data over a long period of time, working with builders and being in the best position to gather all the data. This is the opposite of just following a few stories that seem to support a pet narrative. Part of what motivates this story is hearing from builders who have been told a number of myths about Corvair CHT info.

One builder was told he “Has to have 6″ air inlets.”   Others have been told that the GM CHT locations don’t work.  None of this is supported by observed data, it is opinion from people who just think their pet theory is right. The myths are not always malicious in origin, but well intentioned and malicious myths are both myths just the same.  Two very prolific sources of this information are people jumping to conclusions based on little experience. If someone has never soloed a Lycoming, Continental nor Corvair powered plane, they can still have an opinion on CHT, it just isn’t worth sharing with builders who need factual, unbiased data.


Above, a Lycoming O-320 (160hp) cylinder that I own.  The 320 is the most respected and prolific light aircraft engine ever built. You are looking at the bottom of the cylinder, the 320 has both the intake port (left) and the exhaust port (right), on the bottom of the head. The arrow points to the CHT probe location. One of the people telling builders his view that under plugs was the only place for CHT obviously didn’t know that all Lycomings use this location, which is very much like the GM Corvair location.  For most Lycomings, the CHT limit is 475F. While I am thought of as a Corvair guy, Our hangar also contains a C-85 and an O-290, and parts of many other aircraft engines. My perspective comes from broad experience and spending time with aviation professionals with far better backgrounds.

A mechanic may be clever with EFI or experienced with vehicles imported from the fatherland, but if they have never turned a wrench on nor flown a Lycoming powered plane, their perspective is myopically limited. I really don’t know a lot about modern car maintenance, but I do know a fair amount about planes, and I know enough about both subjects to say that knowing one does not qualify you in the other.

On the table next to the cylinder is a 50 page Lycoming operations manual. You can down load it for free off Lycomings website. Every aircraft mechanic I know owns a copy and is familiar with the data inside. It is a great book, and even as a Corvair guy you should read it. Quite often, people will say things that are directly against the experience in this manual, even when they are Lycoming owners, speaking of Lycomings. For example, Dan pointed out to me that Lycomings leaning operation in the book is enrich it until it runs slightly rough and lean it only until it runs smooth, exactly the opposite of what most people think. Either you are the kind of builder who is inclined to follow the recommendations of the company that built 300,000 of the engine you are running or you are the kind of guy who is going to follow a story written in Flying magazine by a guy who has never pulled a cylinder off any aircraft engine.

For several years at Oshkosh there was an alternative engine guy who’s background was car racing who liked Gear Driven liquid cooled V-8’s. He started all of his forums by writing on the board “If Lycoming made a car would you drive it?” I spoke with him a number of times and read the stuff he wrote. He absolutely felt he had nothing to learn from Lycoming, (or most other experienced sources for that matter) He doesn’t write that any more. This is because he was killed by a mechanical failure while flying his plane. It was his second major accident. He killed his passenger also. I spoke with him after the first, and I will tell you he learned nothing from it.

 Another person using that same engine wanted to put it back in production, after the accident, but he was killed by a similar engine failure. I just read a nice magazine story about a very nice Australian aircraft using the same gear box. A small postscript at the end of the story said that he was killed by a gear box failure. Same magazine had a press release from a new guy who bought the gear box assets to make more of them. You don’t need a crystal ball to predict the next chapter.

Don’t have anything to learn from Lycoming? They made plenty of successful geared engines like the GO-435, the IGSO-480 and the IGSO-540. No, they didn’t make cars, but evidently being a ‘race car driver’ doesn’t qualify you to make geared engines either. People who claim that they don’t have anything to learn from the successful experience of people who preceded them tend to attract followers with the same mindset. A harmless social phenomenon when the topic is flower arranging, interior design, modern dance or fashionable footwear.  When the topic turns to subjects with consequences, like aviation, builders who plan to die at home in bed with all of their great-grandchildren in the next room, tend to learn from others.


Above, the GM Corvair CHT location. Most common question: “Is it on the same spot on both heads?” Yes, because there is only one head. There is no such thing as a right or left Corvair head until we weld the pipes on the intakes, so this is on “both” heads. In 95 and 110 engines it is threaded 3/8″-16. An easy way to put CHT here is to use a 10MM spark plug ring CHT terminal and hold it down with a 5/8″ long bolt with a washer. This will work great. All Corvairs with the exception of ‘Spider’ and ‘Corsa’  high performance models had an idiot light in the dash that was tripped at 575F by a sender screwed into this hole. I had a guy who had never owned a Corvair tell me that the 10mm ring would not work because “it needed to touch the bottom of the hole” Really? the GM sending unit didn’t, and it read just the same.

For another view of a Corvair powered plane that is slow climbing, but runs cool, read this story: Gary Burdett, 2,850cc Zenith 750, now flying. (engine selection)  I personally verified the temps that Gary is getting by independently measuring them in person, on his plane, at Corvair College #26.  I heard from a guy who said he didn’t think it could run that cool, that both Gary’s instrumentation and mine must both be wrong. This comment came from a person who has never seen the plane nor the engine, has no idea where the temps were taken from, nor does he have a running engine nor a pilot’s license, yet he is still quite sure he is correct, unwilling to even entertain the possibility he is wrong. Some people you are just not going to reach, and that is OK. Plenty of people who stayed on land back in Spain felt that if Columbus had just sailed a little further, he would have fallen off the earth, and nothing Columbus did was going to change their minds.

Above, an eight year old photo from the old hangar in Edgewater. In the foreground, my 1966 140HP four carb Corsa, behind it Kevin’s 1965 180HP turbo Corsa. Both of these cars have factory CHT gauges. The factory turbo cars did not use a waste gate, they just had an oversized turbo and a very specific muffler, and the result was a very simple system that did not go into boost until the car had some serious rpm, the throttle mostly open and the CHT over 400F. Below this, the head dissipates the heat energy the turbo needs to make boost. The engine will not make its full output until it is up in the 500F range. Granted, they didn’t have to run this way for a hour at a time, but I have met people who don’t believe that Corvair engines were run that hot in the cars without damage. They hold this opinion even though they have never driven a turbo Corvair and seen the CHT gauge with their own eyes. I have driven 120,000 miles spread over the 4 Corvairs I have owned. At the time the Photo was taken, Kevin owned 7 other Corvairs, Grace had her 65 van, Gus had a ’67 Monza and Dave had a ’69 Monza. I felt that our ‘hangar gang’ was qualified to comment on Corvair operation.  I have met many people who have never owned a Corvair with strong, but incorrect opinions about how the engines ran in cars. Explaining the basis of my observed experience to the contrary, they often stick to their opinion, they are more comfortable with any antic dote  that seems support their opinion than a mountain of contrary evidence. This is especially true if the person in question is a car mechanic.

Corsa models, (140 and 180 HP) have the hole threaded 3/8″-24, same as a Lycoming. To make the 95 heads on my plane compatible with standard Lycoming probes, I have helicoiled them for 3/8″-24 threads. The probes I am using are Electronics International P-101s with A-101 quick detach fittings. They are in the Aircraft Spruce catalog on page 523.


If a guy wants to share an opinion about temp measurement that is contrary to mine, it might be worth asking what kind of test equipment he us using. If he looks at the head of an engine he did not see run and wants to jump to a conclusion, or he wants to use internet data from a builder who never set the timing with a light or is running a non aircraft carb, it probably isn’t going to be as accurate as I can collect in person.

From my tool box, top row, Fluke two channel digital type K temp meter, accurate to less than 1/2% of reading, compares two probes simultaneously, reads all common aircraft probes. Digital type K contact thermometer, 0-1,200F, accurate to 1 degree. Westach CHT, common in aircraft, not accurate source of info, but commonly quoted on net. Bottom, two Raytech non-contact thermometers. accuracy limited to surfaces that don’t have shiny finish, tends to read too high in many circumstances. OK for quick check looking for cold cylinder, but weak on data gathering. Small spark plug item: Original AC thermistor from 140/180 HP Corvair. Same part actually used on many certified aircraft such as Twin Comanche.


Above, the instrument panel in our Wagabond, in the process of being wired. The gauge in the lower right is the CHT. It is a very accurate military unit with a little stamp on the back that says “Calibrated MCAS Cherry Point.” It takes type K thermocouples and need no power at all to read, it is independent of the electrical system of the plane. There is a hole under the gauge for a left /right switch.

I like traditional gauges, and 2 CHT’s in the stock location make sense to me. You can also run 2 CHT’s in the stock location with many Glass Cockpit displays. If you want to run 6 CHT’s, then you are probably going to run them under the plugs. If you do this, know that we have gathered plenty of data to say that these will actually run hotter than the CHTs in the GM location because they actually read the temp of the plug as much as the temp of the head. They can be a little pain during a plug change, and if you are not careful, you can over torque one in a plug hole with a helicoil or a time sert in it, and the sending unit will stick to the top of the thread and extract it when you unscrew the plug.  One way to avoid this is to run a copper washer, then the sender, then the plug, but this is even more likely to show the temp of the plug. I have wired plent of planes for 6 CHTs, I am not enough of a zealot about it to really care about what other people would like in their planes. Dan has 6 CHT’s under the plugs in the Panther and it works great.

In general, the plug temp on #1 will read 60-80F higher in climb that the same cylinder with a probe simaltainiously  running on the bottom of the head. If anyone is speaking of CHT’s on a Corvair, and anyone comments on it without first establishing where the temp was taken and what kind of gauge was used, then they are not adding anything to the discussion. Quite often, if a builder mentions that their plane runs hotter than they would like, the first thing people like to chime in with is that there must be something wrong with the way we teach people to build cowls and cooling systems. In reality, we have people who are flying the same system successfully, so logic say to check these this first:

1) Is the timing set correctly with a light?

2) If there is a significant  L/R difference, especially at part throttle, and it has a flat slide carb like an aerocarb, Elison or a Rotec, it is the carb causing this effect. Butterfly style aircraft carbs don’t do this.

3) Does the cowl have inlet rings?

4) Does the outlet have a lip on it and is it 3X the size of the inlets?

5) Is the instrumentation correct?

6) Are they the correct spark plugs?

7) Is the fuel high enough octane?

8) is it a one of a kind prop? (these frequently don’t pump much air down near the inlets)

The above 8 points are the most common factors that keep the engine from running as cool as possible. Be advised that I have seen people break all 8 at the same time and still fly their plane without overheating it. God protects children and usually fools also. If you like the image of being 100 and meeting your great-grandchildren, I suggest not trying to discover the exact statistical value of “Usually.”  -ww

Steel tube fuselages part #2


A while back I wrote a story on the subject of design considerations for risk management in experimental aircraft. It was one of the most popular essays I put together in the 20 months we have been on this site.  If you missed it, you can get a look at it by clicking on this link:


Steel tube fuselages, “Safe” planes and 250mph accidents


Part of the above story is examining the structure of fuel dragsters in accidents, as they are something of an extreme example of steel tube aircraft fuselages. I was searching for something else on You Tube and came across this link,



which is a 500km/hr (300mph) accident in an Australian top fuel dragster. Total damage to the driver was a burned thumb. You may not be planning on having that kind of an accident, but it is visual proof of the value of simple concepts like steel tube fuselages and perhaps the idea of flying in a surplus Nomex jumpsuit or at least not flying in shorts and sandels.

On the way back from CC#26, Grace and I stopped by the giant Summit Racing warehouse in Georgia, exit 216 on I-75, (They are open 7 days a week 9am to 9pm). As I walked in I was surprised to see a restored version of Don Garlits’s “Swamp Rat 13” (the car blown in half in our original story) on display hanging from the ceiling. Hundreds of people a day go through that store, but I doubt that many of them know the significant history of the car or the role it played in the evolution of motor sports.  People drift through racing, aviation, and many other serious human pursuits with little appreciation of the depth of experience precedes, and is still available to them. I find everything a far richer experience when I have some understanding of those who pioneered their arena at a very high level of intensity.

Above, Don Garlits in command of Swap Rat 13. A very different era; Open face helmets and a 2,500 hp hemi in your lap.

3,000 vs 3,100 cc Corvair engines.


A number of builders just getting into Covairs miss the distinction between these two engines. Below I have a number of links to illustrate the difference, but in a nutshell, the 3,100 was the “big bore” option on corvairs between 1998-2008. It has since been largely superseded by the 3,000 cc Corvair with good reason.  There are still a number of 3,100s flying, and there will be for a long time, but very few, if any new ones are being built these days. A number of builders who previously flew 3,100s have elected to build a 3,000 as their next engine. There are reasons for this, and I will detail them below.

Above, the 3,000 cc Corvair that is flying in the Panther prototype. Notably, Dan Weseman successfully put several hundred hard hours on his 3,100cc engine in his “Wicked Cleanex, ” but opted for an all-out 3,000 cc Corvair in his aerobatic Panther. The engine both cary the same 120hp rating, but the internal differences make the 3,000 more durable, and it is far easier to build.

On the surface, the difference between a 3,000 and a 3,100 is simple: the 3,000 has a 92mm bore and the 3,100 has a 94mm bore. But the details go far deeper. The 3100 was originally developed for dune buggy’s in California, and piston/rod cylinder kits were sold by a number of companies in California. I bought one from Bob Sutcliffe in 1998, and his quality was good.  At early Corvair colleges we assembled at least 15 and perhaps as many as 20 of these engines. It was very apparent that the quality of the kits varied a lot. The other issue was that builders who knew nothing about engines spent lots of money on poor kits from California, and them brought them to Colleges and said “I just spent $5,400 with a dune buggy place that has never seen an airplane, and now I would like you to build this for me for free this weekend.”

The main problem with this was several fold, first, ‘free work’ isn’t what colleges are about; second, these engine required a lot of hand work and fitting to even be assembled. Often they had no standardization, and individual pistons and cylinders could only occupy specific locations on engines. The big one was that each of these engines required a custom set of pushrods to be made so the valve geometry was correct. We and others like Mark Langford repeatedly told people that this was not a first engine to build. Most people listened, but there was a certain type of person that just wanted a bigger engine although they were unwilling to learn the required detailed information to understand and assemble it.

Internally, the 3100 had many VW 94mm parts in it. Here are the things about that that I didn’t like: The pistons, even good ones made by Mahle, were cast. The VW wrist pin is 22mm, and the dune buggy mentality was to just bore out the Corvair’s .800″ (20mm) rod to take the larger pin and run it as a steel on steel no bushing floating pin. This worked, but was a poor way to do it. The California companies would occasionally send out a rod with a .060″ wall thickness around the pin and think nothing of it. These engines also had the head gasket cut so large that it broke into the upper head bolt areas. Using the VW pistons made the compression height wrong for the Corvair, requiring custom pushrods to correct it. The Compression on these engines was really too high to safely have Mr. average pilot run car gas in it. Many of the people attracted to them didn’t recognize that Mr. average pilot was a polite name for them. If you would like to read about 3100s that worked well, look at:

KR-2S at 700 Hours – Joe Horton


Zenith 601XL-3100cc Dr. Andy Elliott


Above is the 3100 of Dan Weseman in the Cleanex. This engine and the one in Chris Smith’s ‘son of cleanex went on to log about 500 hours each. Note the reverse gold oil filter housing on the engine. Have a look at four 3100s taking off in a row from Corvair College#16 in South Carolina, Langford, Weseman, Smith and Horton:


The first Correction actually came from Brady McCormick, Owner of the now defunct Magnificent Machine.  What Brady did was have a new forged piston made in 94mm. This was a good idea, and he incorporated the Corvairs deck height and pin diameter in his design, automatically correcting the geometry. But it still had the head gasket issue, and the piston design Brady chose was a light weight one for high rpm engines. It’s compression was still high, and It could not tolerate having a dish machined in it. Still it was an improvement, and perhaps 15 engines were built this way. Examples would be Jim and Rhonda Wesemans Celebrity; Mike Robitie’s Cleanex engine;( Guest writer: Phil Maxson, flying a 3100cc Corvair in his 601XL ) and several production engines we built like this one:

Brady’s pistons are no longer available, and the forging blanks they were made from have been acquired by Clark’s Corvairs as the basis for their USA made forged pistions. (They are only made to .060″ over bore now, and 94mm is a .264″ overbore)

Above Jim and Rhonda at CC#23, with Dan in the cockpit. the engine in this plane is a one of a kind reverse rotation Corvair, a 3100 with Brady pistons. Jim is a life long professional aircraft mechanic by trade, and a very clever guy. He had the experience to create a very unique Corvair for his plane. Most builders are far better off building an engine that is a regular “bolt together” experience. Jim and Dan developed their 5th bearing as a father/son team. Jim and Rhonda make Corvair cowling and baffling kits, but they made their best contribution to experimental aviation back in 1975…by having Dan. 



The actual permanent solution was having a better forged piston made, and reducing the bore to 92mm. In doing this we went to a different American manufacturer that specialized in pistons with thicker crowns that could have a dish milled in them. Below is a look at the 3,000cc piston top in a bore along with the head is designed to match.

Above, a 92mm/ 3,000cc Corvair set up. This is the final evolution of the big bore Corvair for aircraft use. Note how the head gaskets don’t break into the stud holes. The flat area on the head and piston are referred to as “the Quench”. There come very close to each other, making the charge burn much quicker with much less chance of detonation. The dish in the piston keeps the static compression low, ideal for running on car gas or 100LL.

The 3,000 cc engine is a far better engine for builders to work with. Although I can build any Corvair engine I like, and our 601XL had a very strong 3,100 in it, I didn’t hesitate for a second to switch to a 3,000 cc engine for our Wagabond. People who only know a little bit about engines often think that loosing 100cc is going backward, but in reality I typically de-tuned our 3100 because it had cast pistons and what I considered excessive compression. On the Wagabond’s 3,000 cc engine I am setting up to run at full power for as long as I like without having to retard the timing for car gas operation. Let this serve as a basic introduction to how the 3,000 cc engine has surpassed the 3,100 as the dominant big bore Corvair flight engine. For more 3,000 cc stories follow the links below.-ww


World’s Strongest 3,000cc Corvair, built by Greg Crouchley


Panther Prototype Engine 3,000 cc/120 hp to OSH


3,000cc Engine Running


Getting Started in 2013, Part #16, 3,000 cc Piston/cylinder kits


Flying Zenith 750 w/3000cc Corvair, Doug Stevenson, California


3,000cc/Billet Crank Shortblock, Destination: Waiex


New 3,000 cc Cleanex, Dale Williams, SC


11 Days left to sign up for Corvair College #27


I actually had not watched a minute of television in a long time, none of my trucks have a radio, and the only thing I have been listening to in the shop are old Neil Young and albums and a very well worn copy of Exile on Main Street. I looked at FB today for the first time in months, and I just found out that we now have a totally non-functional government instead of the usual basically non-functional government. My apologies for not recognizing the exact transition point. If any of you are just now finding yourself disappointed in all of the elected, let me say I admire how long you have held out hope and optimism.

Although I have a degree in Political Science and a pretty sharp knowledge of American history,  I didn’t actually come up with a solution, and didn’t think any of my comments would help, so I just turned the computer off, when back to the shop, made some parts, while listening to 1969’s Everyone knows this is Nowhere. I can assure you that listening to the guitar work on Cowgirl in the Sand in a national crisis may seem irresponsible, but it actually is just as effective at finding a solution as gluing your eyes to cable TV news. (Zero % effective) with the additional benefit of far lower blood pressure and I actually got some useful work accomplished. After 6pm I put in an hour wiring our Wagabond today. If you spent an hour on TV news or talk radio today, but didn’t do anything on your plane, try reversing that tomorrow and see if you feel better when your head hits the pillow tomorrow night.

We are just 11 days away from the sign up for CC#27 closing. The event is November 8-10 in Barnwell SC. I have a long standing policy on never allowing any talk about politics whatsoever at Colleges. If all of the people you know are spending their free time complaining about politics, I can’t fix it, but I can offer you a 72 hour, politics-free oasis. From what I saw in five minutes on FB, that is an oasis that is well worth heading for, even if you have to drive 1,000 miles.-ww

Above, Kevin Purtee and Shelley Tumino receiving the Cherry grove trophy at Barnwell (CC#24) last year. They hosted CC#22 in Texas in 2012, and are hosting CC#28 in February 2014 at San Marcos, TX. Don’t miss signing up for #27, it closes in another nine days, and February is a long way off.


CC27 –


The Event also has it’s own Face Book Page:

A visit to the insane asylum


It is surrounded by a fence and barbed wire. You need the gate code to get in.  The people inside tell themselves that the security is for their own protection, to keep others out, but if you go inside and listen to them, you understand that the chain link fence to keep them inside. Think I am speaking of a  serious mental institution?  I could be, but I am not. I am speaking of our local county airport. Don’t feel safe just because you live far away; I have visited countless small airports all over the country, and I am willing to say that most of them had plenty of nut jobs that needed to be fenced in. Follow my little adventure and understand a bit more about the mentally ill people who can be found at most airports….

Last month, My friend Doug was in town, and our task for the day was a simple one. Doug had heard about a Maule M-4-210 for sale at a municipal airport about 30 miles away. Both Doug and I own gliders, and we have been looking for a potent tow plane. Doug wanted to look at this one because it has a 210HP six cylinder Continental and a constant speed prop, and he could do a lot of things with the plane besides tow. The plane was said to be recently covered, fitted with a fresh engine and reasonably priced. The owner gave us a green light for a through inspection and invited Doug to fly it if he liked. It all sounded simple enough, but we made the mistake of going there on a Saturday, which is the day most of the inmates are at the asylum…..

Above is a photo of B.D. Maule and the prototype M-4. While the factory has been located in Georgia since 1968, This photograph was taken in Michigan were Maule was a long-established aircraft Company.


Let me start by saying Doug is a very pleasant soft-spoken family guy who would blend right in with the other 50-year-old guys at your local EAA chapter. He never speaks about his credentials unless you pry it out of him, but having known him for a long time I will tell you he is a USAF vet, has most of the ratings you have heard of, is a graduate of a well-known aviation university, is an A&P, and is a skilled pilot in many kinds of antique and sport aircraft. I have watched Doug just smile while a private pilot lectured him on flying. What makes this really funny is what Doug has done for a living for the last 20 years: He has flown 9,000+ hours, mostly in single engine aircraft, in the worlds ‘hot spots’, where getting shot down and killed might be preferable to being taken into the ‘care’ of the locals.  He only vaguely mentions where work is, and he has never mentioned who he works for. (I assume it is the good guys because the FBI agent who questioned me as a security reference said so.)

We did a 45 minute inspection on the plane. In that length of time, a large number of inmates came by to tell us things. It would be inaccurate to say they came over to speak with us, because I didn’t detect that any of the listened to a word we said. I want to be accurate, and not imply that every thing people said to us was crazy. Out of 8 or 10 people, one guy came over just to ask what time it was. He seemed normal. Everyone else had something wrong with them. Below, in Red, are a sampling of things that were said to us. S.E Hinton famously wrote “Even the most primitive societies have an innate respect for the insane” abiding by this, we just nodded our heads when they spoke. My comments in Italics are just my thoughts, I didn’t really engage any of these people.

Guy #1 “Maule was a fine southern gentleman. he really showed them Yankees how to build a plane”

Reality: B.D. Maule was born in Ohio. He lived most of his life in Pennsylvania and Michigan. His aircraft company was started in Michigan, and he did not set foot in Georgia until he was 57 years old.

Guy #2 ” Every Maule ever built was made in Georgia”

Reality: The 1966 model we were looking at was made on the assembly line in Michigan. It said so on the aircraft’s data plate.

Guy #3 “If you want to tow gliders, you have to put a set of huge steel cables from the firewall to the tail post to take the load, otherwise you will pull the steel tube fuselage in half. I know this, I worked on a lot of tow planes (probably not true), and I judged airplanes at Sun n Fun for 15 years” (sadly, I know this to be factual.)

Reality: Gliders have a weak link in the rope so that you can’t break anything while towing. The breaking strength of the link varies with the weight of the glider, but it us just a few hundred pounds at most. The line it self is a piece of line that looks too light to hang clothes on. A single 1/16″ welding rod has greater tensile strength. The only cable that runs forward is the release cable that opens the hook, it is made of very fine cable and it is never under tension.

Guy #4 “That starter is brand new. The reason why it isn’t working is that you have the jumper cables on wrong”

Reality: Between us Doug and I have 48 years of being an A&P. The starter was not new, It was freshly spray painted, but this looked like it was done in place. It was a 90 degree drive style, which can cost thousands of dollars if you actually buy a new one. This one had a broken internal clutch spring. The guy making the claim was the plane owner, who was neither a pilot nor a mechanic, but felt his general expertise covered both subjects.

Guy#5 “The engine was overhauled by the skydivers on the other end of the field. When they were all done, some other guy signed it off. They do great work even though they are not mechanics. You don’t need to be to work on airplane engines, they are pretty simple”

Reality: This aircraft is type certified, and you most certainly need to be a mechanic or work directly under ones’ supervision to do anything substantial on such a plane. If you gave me a choice between having your average weed-smoking skydiver and Helen Keller work on my aircraft engine, I would choose Ms. Keller, even though she is deceased.

Guy#6 “The yoke only went about half way to the right because the avionics guys put the vacuum filter on wrong and the control column ran into it, it took a long time to figure out, but it wasn’t a big deal because they always put more control travel in these planes than you really need.”

Reality: the type certificate data sheet for every certified aircraft specifically states the exact control deflections. You are required to have every bit of it available. Good homebuilt aircraft plans also specify these exact figures.


Things to take away from this story:

1)  There is no ‘safe’ airport. Don’t think for a moment that because it happened in the south that you are safe because you live elsewhere. I have had hours like this at airports in every part of this country. Make your shop ‘safe’ from idiots. You wouldn’t let the biggest idiot at your local airport into your home, but if you read stupid things from unqualified people on the internet, you are essentially inviting the biggest idiot on the planet to come and work on your plane. Think that over. At least 50% of major mistakes on home builts originate as ideas from the net proposed by people the builder never met.

2) You will never help these people, do not engage them or try to speak with them. You are far better off pretending you don’t speak English. If they overheard you, then try quietly telling them that you are on an undercover assignment for the FAA. If they offer to help you with anything, ask them to hand you a tool, and then tell them that you used to have highly contagious “Genital Leprosy” , but the CDC in Atlanta is pretty sure you are in remission right now.

3) If you accept the premise that you can learn a lot and get smarter by hanging out with smart and clever people, than you must also accept the WW corollary that “Stupidity is a Contagion” Do not spend any time with these people, do not socialize, hang out with nor have a single thing to do with them. I directly attribute my 2001 accident to allowing my standards of what I did in aviation and who I did it with to be eroded slowly by being around idiots.

4) Your home built is a clean state. It isn’t polluted by the misguided effort of every previous owner who opted to have the cheapest person work on it rather than the best. Be glad you are building your own pure plane. If you let idiots talk you into incorporating stupid things into your project, then you might as well just go out and buy the worst used plane, owned by the biggest idiot at your airport. Keep your plane a thoroughbred.

5) Your are a clean slate. If you don’t know how to fly nor build a plane or an engine, Good. Then we can get you started right, and you will not have to undo any bad habits or false ideas. Succeeding in this game is all about picking the right people to learn from, developing good judgment, and then exercising it. You are not going to accomplish any of these things by spending time with the inmates at your local asylum, so just stay far away from them.

6) There are many great people in aviation, and over time you can make life long friends with many of them. Do not accept lesser quality in place of real aviators of skill, ethics and judgment. We have fun at Colleges because I have made sure we do not welcome nor tolerate idiots and fools. The definitions of those two words don’t have anything to do with how much a person knows about planes or flying. It has everything to do with character, and as a thoroughbred, even a green one, you deserve quality company. If you have already encountered your quota of fools, change your setting and find better people.