December 23, 2013 Leave a comment
December 23, 2013 Leave a comment
Here is an older story of testing from 2004. It is a good example of how our testing has been an integral part of the work we have done. Although the machinery is simple, the comparitive testing is sound and the meathod is valid. The information gathered in these tests has served builders for a nearly a decade. In the story I mention that the three of us totaled 55 years of work as A&P’s. Today that number is now 84 years of working experience.
O-200 Torque and Horsepower Testing
Here’s the O-200 on our dynamomemter, and your test crew from left to right, above: Gus Warren, Detroit Institute of Aeronautics, A&P 1990; Steve Upson, Northrop University, A&P 1976; yours truly, William Wynne, Embry-Riddle Aeronautical University, A&P 1991. While the way we dress may be slow to catch on in high fashion circles, we certainly know our stuff about all types of aircraft powerplants. This is 55 years of A&P experience working on engines in the field nearly every day. This experience, along with a good technical background, puts us in a good position to do real world testing.
On the left above is the Continental O-200 as removed from a 1959 Cessna 150. This engine is considered the standard against which all other 100hp class engines are measured. It is a direct drive 4-stroke, 4-cylinder engine of 200cid. It carries a horsepower rating of 100 at 2,750rpm. I have read that Continental produced about 50,000 O-200s. On the right is a 170cid Corvair engine. For size comparison, the O-200 is 32″ wide without the baffling. The Corvair is 28″ wide.
To adapt the O-200 to our dynamometer required making a new mount. Everything seen in gray, above, is part of that mount. The red cap at the center is a dust cap covering the bearing on which the mount pivots. This red cap is in exact alignment with the O-200’s crankshaft. This way, the rotation against the torque is in line with the crankshaft. The mount was made from a Corvair wheel, a pirated VariEze motor mount, some spare tubing, and a Corvair blower bearing. This bearing is at the bottom, and rides on a steel U channel. This provides additional support to the mount, and restrains it from turning full circle. The vertical element is a 1.5″ diameter steel tube. There is a pin on the back of this tube that engages the hydraulic cylinder. By comparing this mount to the blue Corvair bed mount seen in previous dyno tests, It is apparent how we can change the configuration in a few minutes. This is the charm of using the 5×4.75 bolt pattern wheel as the basic element.
The first photo on this page shows the engine with its stock McCauley prop. Above we see the engine fitted with our primary test prop, a 2-blade 60″ Warp Drive. Since we normally use this prop on Corvairs, the blades here are turned around to work as standard rotation pusher blades. This will effectively load the engine for torque testing. The prop is ground adjustable, so we can fully load the engine at any rpm we desire. The carburetor is an overhauled MA3-SPA. The engine has new Slick mags. It is less than 500 SMOH. We first tested the timing at 24 degrees as per the AD, and then tested it at the pre-AD setting of 28. Differential compression showed all over 70. The engine turned its full rated static rpm with the certified McCauley prop, indicating it was a very healthy engine.
Above is an overview of the test rig. We used two different methods to measure the torque output. First, we used a hydraulic cylinder. This cylinder is located just above and in front of the battery. Second, we measured it with a digital scale. The scale is located just out of view, but it is driven by the 8-foot metal beam clamped onto the mount. We had 4 feet of it extending on each side, so that its weight would not affect the scale reading.
Above is a closeup of the hydraulic cylinder. The braided line runs to a remote gauge. You’ll notice it’s on the opposite side of the stand now. The O-200 has a different rotation than the Corvair, requiring the hydraulic unit to be moved to the other side of the stand. The gauge reading was calibrated by hanging weights on a 4-foot lever arm in 5 pound increments. The needle valve on the output of the cylinder is required because pulses on the line when cranking the starter motor are so fierce, they will damage the gauge. This is true with both the Corvair and the O-200.
In the photo above, you can see the electronic scale sitting off to the side. Pressure is put on the scale by the vertical stick clamped to the steel arm. We’re going to refine this and make it a lot cleaner looking shortly, but for these tests, it worked flawlessly and provided repeatable accuracy. If you’re wondering how all this stayed together in the prop blast, you’re forgetting that the prop is functioning as a pusher. I was only concerned that some of the equipment would be inhaled. Although we got both methods of torque reading to agree, I feel in the future we’ll probably use the electronic scale more often because it’s subject to fewer variables. The dynamometer is also rigged for simultaneous thrust measurement, so we’re going to put the hydraulic unit to that function for simultaneous readings.
After a full day of testing, which included several dozen test runs, we came up with some surprising data. The engine performed substantially below its 100hp rating. I initially suspected that the engine was not performing at peak power, or that the test equipment was flawed. During the testing, we conducted all of the standard mechanics’ tests to evaluate the condition of an engine, including differential compression, timing, and fuel flow. All of these showed the engine to be in good condition. The most telling test was that the engine turned its full static rpm with the certified propeller. It would not do this if it were down on power. Keep in mind that we use a digital optical tach to ensure that there is no error in rpm measurement.
We retested and calibrated the hydraulic cylinder system. It showed itself to be accurate. To doublecheck it, we came up with the digital scale system to corroborate the data. They both told the same story. As an A&P mechanic and a big fan of certified engines, I was very reluctant to conclude that the O-200’s 100hp rating is probably a “gross” rating, as opposed to a “net” rating. If you’re a fan of car engines, you probably know that in the 1960s, many car engines had gross hp ratings. These optimistic numbers had things like the fricitional drag of the engine and the accessories factored out. In the 1970s, net hp ratings became more popular. This is the power output you’d actually see at the prop flange. All of the numbers that we test are net. This is the only type of external measurement we can do. It is also the real world power output of the engine that you are going to use to go flying.
The torque peak of the O-200 occured at 2450rpm. The engine produced 160 foot pounds of torque. If you use the formula Torque x RPM / 5252 = HP, you’ll see the engine was producing 74.6hp. We established the torque peak by running the prop at many different pitch settings until we homed in on the peak of 160.
The hp peak of the engine was very close to its rated peak of 2750rpm. We tested numbers slightly higher than this. However, I was reluctant to run the motor in the 3000s because it’s above the engine’s redline, it’s a borrowed engine, and it’s a certified piece of equipment which will very likely go back into another certified plane. So it behooves us to operate it accordingly. At this rpm, we measured the torque at 144 foot pounds. Using the formula, you’ll see that the engine produced 75.9hp. Again, these are net horsepower numbers.
The temperature outside was 85F, and the RH was 60%. The pressure was almost standard, and we’re only a few feet above sea level. A rudimentary calculation to account for the temperature difference above a standard 59F shows that the corrected hp output of the engine is in the neighborhood of 80-81hp. Again, keep in mind we worked all day in an attempt to raise this output. If you’re reading this and thinking there’s something we’ve missed, I can understand that. It’s difficult to convey the work of three mechanics over a 12-hour period in a few paragraphs and photos, but I can assure you we left no stone unturned in our search. At the end of the day, I largely came to the conclusion that the 100 horsepower rating was a gross rating.
Keep in mind that I’ve been doing installations on planes for 10 years. In this time, we had numerous comparative studies which showed that the Corvair was a very powerful engine, and in many circumstances, could easily match the O-200. One which stands out in my mind was the break-in run of Mark Langford’s Corvair engine at Corvair College #3. He had a pusher prop from an O-200 mounted on his Corvair. The manufacturer of the prop told him on the phone that the Corvair could never turn up the prop to any substantial rpm. When it did, the propmaker was something between impressed and stunned. Even though Mark’s engine is a 3100, it was exceeding what the O-200 could do by a good margin. Over the years, a lot of circumstantial data like this makes more sense in light of finding that an O-200 has a far lower net output than previously suspected.
Does this mean that an O-200 is a bad engine? Does this mean that the VSI in every Cessna 150 isn’t telling the truth? Of course not. The engine is and remains the standard measuring stick of 100hp engines. They have worked for nearly half a century, and will continue to do so. This said, I can assure you from our dynamometer testing that standard displacement Corvair engines will exceed the O-200’s power output handily. This being true takes nothing away from the O-200’s status. It just puts numbers on the success we’ve seen with the Corvair motor over the years.
As a coincidence, a few days after the testing we had a visit from Al Jonic. I worked with Al on the installation of the V-8 in Jim Rahm’s Lancair IVP. Al won the EAA’s highest honor for engineering, the August Raspet Award, for this work. He’s a veteran of thousands of dynamometer runs. Although he’s used much more sophisticated equipment, he was duly impressed with our setup and approach. He offered to send us sophisticated programs to use to correct the conditions for standard day performance. He also offered 40 years of insight on the value of dynamometer runs, correction factors, and gross vs. net ratings.
This dynamometer testing is an ongoing business. I didn’t build it to run it a few times, and prove a few points. I regard it much more as an everyday tool. It takes all the talk out of engine building, and replaces it with hard testing. It is the perfect complement to our ability to rapidly flight test any modification. We’re currently running an entire series of Corvair engine tests. Most of these will be done by Corvair College #8. The Corvair is already exceeding the power output of the O-200. We’re just working to define by how much. When we have this data complete, we’ll put it all on the Web page here.
November 18, 2013 Leave a comment
Below are links you can click on in sequence that follow through a detailed series I wrote on Getting Started in Corvair building. They are detailed and long, but successful builders tend to spend the time to learn and make better choices. I wonder about people who decide to buy an engine or a plane of any kind after reading a 4 page sales brochure with less than 200 words on it. Hardly due diligence in a ‘flyer beware’ marketplace. If you would like to start with a simple three page spec sheet on the engine, read this link first: Basic Corvair information
Conversely, we offer a very detailed picture of exactly what Corvairs are about, what you can learn and achieve by building one, and the infinite ways you can build one that will conform to you needs, goals, skills, timeline and budget. The Corvair can be made to fit your project, you don’t have to rearrange your plans and budget to serve the company that is selling you an engine. Sounds funny when you put it that way, but that is just what most people do.
I could drive myself to madness by concerning myself with what the masses will or might do. In experimental aviation you don’t have to be concerned with what ‘most’ people are buying or doing (unless your goal is to be like everyone else rather that being yourself), you need only find the right path for you. Corvairs are not for everyone. The strongest appeal are to homebuilders with traditional goals of Learning, building and flying. Many people interested in experimental aviation today have short attention spans and shallow goals. They want to posses skills but are unwilling to learn; They want to have things but are unwilling to make them; they are unable to differentiate between going for a ride in a plane and being an Aviator.
If you want to learn, I have long proven I have things to teach; if you wish to build and be the master of your engine, we have a proven path; If you long to find your place among real aviators, we have a home for you. You do not need any prior experience, just a willingness to learn and a positive attitude. In 24 years we have shared our experience with hundreds of builders. If your goals match our strengths, we will be glad to work with you. -ww.
October 24, 2013 Leave a comment
A friend of ours who is building a Zenith 750 wrote in with a quick note asking about oil pressure gauges and senders. I pulled together this general set of notes on oil pressure measurement and instruments as a good resource on the general subject. Over the years Corvairs have flown with just about every kind of oil pressure instrumentation imaginable. Going back to my point of Principle vs Preference. On this subject, it mostly falls in the category of preference.
The Builders specific question was focused on sending units for electrical gauges, and their reliability. If I had to pick one brand over another, I will say that I have never had an issue with the senders that are used in Autometer gauges. VDO is usually trouble free, but I have personally had one mess up, and it caused a lot of work with it’s erroneous information. Goes without saying, I wouldn’t use one from the land of Chairman Mao.
Some people are concerned about mechanical gauges bringing oil into the cockpit, but in actual experience, I have never had an issue with it. The line itself is 1/8″ on the outside, but only 1/16″ on the inside, and I generally put a #80 hole in a restrictor, at the engine, so even if the line came off, the flow rate is about 1/2 gallon per hour. For the record, I have never seen even the poorest mechanical line installations leak. You can take the nut off at the gauge with the motor running, and it does not “spray” oil, it just oozes, and even when the engine is hot, the oil really isn’t after six feet of line.
Below is the close up of the mechanical oil pressure gauge I have in the Wagabond. In addition to all the other things I like about mechanical gauges, I like the fact the needle covers a 300 degree arc, allowing you to see very fine changes. The gauge below is $54.97 from summit racing.
Now get a look at the next part, which is an analog electrical gauge. My primary complaint beyond the fact it is electrical is that this type of gauge is only a 90 degree sweep, making small differences had to see. They also cost about twice as much as mechanical after you get the sending unit. It is priced at $69.97, but the sender is about $40. I buy Autometer because of the tiny letters at the bottom of the instrument that say “made in USA”
For Builders interested in digital instrumentation, Google the name “Dakota Digital”. Below is one of their instruments, but the come in many different varieties, all made in the USA. They have a website you can buy direct from, it has many choices. Just a reminder, never mention to anyone on the phone while ordering from a non aviation company that you are building a plane. Summit will actually black list you. The people answering the phone have $9/hr. jobs, so don’t jeopardize anyone’s just scraping by living by saying that on the phone, and having them get in hot water for not turning you in. It is an annoying fact of a litigious society, but you are not going to fix it by getting a single mother just above the poverty line fired.
If you would like to read a two part story about the simple panel I built for the Wagabond, get a look at these two following links:
If you would like to read a story about Andy Elliott PhD arguing with ww the A&P about instrument choices, look at this one:
The story below has comments on oil pressure errors in electronic instrumentation. That part is 2/3rds of the way down at the picture of the Corvair/701.
As you are looking at parts of the oil system, I have reprinted the numbering system of the parts in the oil system for reference here:
Rear oil case group (2000)
2001- Rear oil case casting
2002- Rear oil seal
2003- 5/16 hold down hardware
2004- 3/8 hold down hardware
2005- Case to block gasket
2006- Harmonic balancer
2007- Balancer bolt and washer
Oil pump and regulator group (2100)
2101- Oil pump assembly
2102- Oil pump gaskets
2103- Oil pressure regulator piston
2104- Oil pressure regulator spring
2105- Oil pressure regulator plug
2106- Plug washer
Below is a good article of flight ops with comments on oil pressure indications:
Below is a short guide on what oil to use:
Below is a visual reference to where we take the oil pressure on the Corvair engine:
Below has notes on how the pressure bypass works:
Have a pleasant and productive evening.-ww
October 16, 2013 Leave a comment
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:
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
October 15, 2013 Leave a comment
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
October 9, 2013 Leave a comment
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:
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: http://www.youtube.com/watch?v=y_1ov0DAbe8&feature=plcp
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.