Myths about dual ignition and reliability


Last year, I had a pilot/owner of a Pietenpol powered by a Continental A-65 engine make the comment to me that he would not fly a Corvair because “It didn’t have true dual ignition” and that he selected a Continental because he had to “Have a really reliable engine”.  At a very surface hangar flying level, these comments seem logical, but lets take a look at them from a real practical level of an experienced aircraft builder, and see that the man who made these comments was living in a fool’s paradise provided by mythology that doesn’t hold up to practical inspection.


First let me say that an A-65 Piet can be a fine combination, it obviously works, and people have used the combination for many great hours aloft. If you own/fly/are building one of these, instead of rejecting my comments out of hand, read this carefully so that you can make good choices that will allow your particular plane to work well, because contrary to mythology, simply choosing any A-65 for your plane is not a guarantee of complete safety and happiness.


I was doing an electronic scale weight and balance on the plane. The owner was trying to say something nice about my work with Corvairs, but it kept coming out in sentences like “I really respect what you do, but I need a reliable engine.”  At times like that my stock response is “They are not for everyone” and “They are as reliable was the builder is willing to make them, just like any other engine.” He politely smiled, in the way people do when they are unwilling to think for 60 seconds about what they just heard.


The particular plane was about 660 pounds, but had a typical aft CG problem. The limit on pilot weight to stay inside the aft limit at 20″ was down near 145 pounds. The owner was 40- 50 pounds over this, but his counter was that he never flew it slower than 65mph, he never stalled it, and since the engine was an A-65 it was totally reliable, so he did not need to be concerned about power off CG issues. To him, the critical issue that made his engine a magically reliable device was the fact it had “the right kind of dual ignition with two spark plugs.”


When discussing what he could do about his CG issue my suggestion was that he could loose 40 pounds and put a metal prop on the plane. I said this because I knew that there was zero chance he was going to shift the wing on the cabanes. This guy didn’t build the plane, and didn’t strike me even being interested in building anything.  He didn’t touch the 40 pound idea, but he rejected the metal prop idea right away. The plane had a very nice looking wood prop on it made by a small production experimental prop maker. Our pilot said the way the prop looked made the whole plane for him, and he wasn’t going to use any other prop.  I pointed out that I thought it had too much pitch, diameter and area for 65 HP, I checked the full static rpm and it was only 2060 rpm. He jumped on this, saying “Everyone knows slower props are more efficient” and “Tony Bingeles’s book say to ‘keep your prop as long as possible for as long as possible’.” It was all I could do to point out his engine only made about 50HP at that rpm, that it would make more thrust, not less, if the rpm came up by 200, and ‘Uncle Tony’ and his ‘slogan’ were not about to cause a rewrite of Fred Weick’s classic work Aircraft Propeller Design.


I spent another intellectually painful 1/2 hour with this guy. I can type that line without fear of hurting his feelings because he told me that he never reads stuff on our website because the stories are too long for him. He went on to tell me that he and his 275 pound friend like flying the plane (based in Georgia), but it did have a very poor rate of climb on hot days. I tried explaining that it was mostly the prop but also things like his carb heat cable didn’t allow the flapper in the box to go all the way to cold. It was wasted words, because he kept coming back to how good the prop looked and that since his engine was an A-65, with two plugs, he never again had to think about reliability. I kept thinking about the line from Cool Hand Luke, “Some men, you just can’t reach.”


OK, here is what he didn’t get: If he is barely climbing out on a hot day at gross with the low rpm caused by the big prop, if he fails one mag, the plane will immediately have a forced landing. Sane people operating planes with dual mags know the exact weight and conditions that the plane has a positive rate of climb on one mag. Small engine, wrong prop, heavy weight, and hot day all add up to this guy hitting a tree off the end of the runway. You should never fly a plane with two mags at a condition that it will not climb on one. If you violate this, you are completely negating the advantage of dual mags and plugs. Airplane engines do not make full power on one mag, that is why they have ‘mag drop’ during the run up. Smart guys also understand that if you fly in a setting where it will not climb on one mag, then having two of them is statistically your enemy, not your friend.  If you understand that, you will know why Lindbergh chose an overloaded single engine plane and not an overloaded tri-motor for his flight.


Contrary to what this guy thought, the Corvair does have a dual ignition system. If you fail one side of our Corvair ignition, it still makes 100% power on the other. It does not have any ‘mag drop’ in the run up. He also missed that because they have 6 cylinders, Corvairs have been long proven to fly on 5, making it acceptable to have single plugs. Because we have a 40,000 volt ignition with a .035 plug gap, fowling a plug is very rare compared to a 10,000 volt mag with a .016 plug gap. In 2005 Gus Warren was our demo pilot. On the ground we tested the power output of the Corvair in our 601 as it ran on 5 cylinders. We then simulated this in flight to determine the max weight and OAT conditions we could have a positive rate of climb at. Testing showed that our powerful engine, turning a 2,700 rpm prop still had a 100 fpm climb rate on a 100 degree day on five cylinders …..when the plane was 200 pounds above the gross weight. It was safe for passengers in a way that the Pietenpol owner’s plane was not. The critical difference was that I knew this from a test, and the A-65 Piet owner didn’t even understand the concept.


Some thoughts on engine reliability: I was converting a Corvair builder’s oil case to a High Volume oil pump arrangement in the shop last week. On close inspection, I thought I saw a hairline crack radiating out of the fixed shaft bore. I looked at it with a 10X magnifier, couldn’t see anything conclusive, but there was a slight surface imperfection none the less. I had about two hours of work in it at that point between cleaning and machining. Without much thought, I tossed it in the trash can, went to the shelf (where I have about 50 more cores) and got another and started over.


When it was done, I wrote the builder an email pointing out that he would not be getting the same one back, but there was no core charge. It wasn’t a big deal because these housings are worth about $10.  Conversely, if a guy had been working on the accessory case of an A-65 which he wants to sell without logs for a profit, a case which is worth about $500, if he thought he saw a crack, exactly how hard do you think he is going to look for it? Think he is going to throw the case in the trash just because he suspects something is wrong with it? It is a nice thought that people have morals like that, but don’t bet your life on it. If you want an A-65 and one is being sold as “overhauled” but it doesn’t have logs or it is called “experimental,” it will not have the same track record as a brand new Continental. It is a myth that all engines that once were made by Continental 60 years ago still have the same reliability no matter what has happened to them since.


I have flown a lot of hours behind small Continentals 65, 75, 85 and 100HP. They can be very reliable, but just like a Corvair, it is the quality of the parts inside and the care they are assembled with that count. Suggesting that all A-65’s are reliable just because they are Continentals is just as dumb as suggesting that all Corvairs are less reliable because they were car engines to start. sixty years after the last A-65 was made, and 40 years after the last Corvair was made, each engine now has to be evaluated on its own merits. Do you trust a Corvair that you have learned inside and out that is made of almost all new parts or do you trust an engine that was assembled to make a profit and is being sold as “experimental only”? Your decision says a lot about your perspective. Self-reliant people like to know, but many people would like to be absolved of responsibility and just say “I don’t have to be concerned, I was told it was good.”


A guy on the Pietenpol list who used to be a Corvair builder 10 years ago, stated he switched to a Continental because he wanted something easier and cheaper and reliable. Aircraft engines are my profession, and I am going to categorically state that those are mutually exclusive concepts in propulsion. Example: Buy a legitimate overhauled Continental with logs; Easy and Reliable but not cheap.  Build a reliable Continental: Reliable but not Easy nor Cheap. Buy a $6000 Continental because it was said to be “Zero timed” even though it doesn’t have real logs; Easy, not cheap, not reliable- a ‘Unicorn motor’. People eternally looking for the easy way to build a plane rarely get them done. The people who finish are the ones who follow a proven plan, even if it seems longer than something touted as a short cut. The mentality of looking for the easy short cut is the real culprit. What gets the plane done is the willful choice to make steady progress on a proven path.


There is no free lunch in aircraft. Building a reliable small continental is just as hard to build as a Corvair, and arguable more expensive. Want a look at what is involved in a good Continental? Look at this link to Harry Fenton’s work: Read that and tell me it is significant easier than a Corvair. If you have not seen it, please read: Great lies from discussion groups…….part #1, including the comments section that has actual pricing on building a certified engine. Pay particular attention to my points about the insanity of expecting the reliability of a factory new Continental to be found in the lowest priced collection of parts that runs. -ww

7 Replies to “Myths about dual ignition and reliability”

  1. Reminds me of one guy at a Corvair gathering I attended awhile back – he said the Corvair would be more reliable if it had dual spark plugs. (I told him to research the history of aircraft engines and spark plugs to learn the why & how dual plugs were necessary in the early days of aviation and aircraft engine development). This guy also stated that he only flew behind “real” aircraft engines and that the Corvair needed magnetos because he didn’t trust flying an engine that utilized points…?! (Hmmm, I wonder what’s inside most aircraft magnetos?)

  2. With people like this one out there in aviation it is a wonder that we are able to maintain as good a safety record as we do. This guy sounds like a smoking hole just looking for a place to happen. Educating that guy was like teaching a pig to sing, a waste of time and it annoys the pig.

  3. I used to go out to the local airport on a Friday morning for a couple of hours to listen and learn (mostly BS). One morning while I was there, the mechanic was tearing down the engine out of a Cessna 210 that had an off airport landing. The engine had literally destroyed itself when one of the balance weights had come out of the crankshaft and started hammering the inside of the crankcase.
    The engine had been rebuilt in another state and was on a cross country when it came down in western Kansas. The mechanic showed me where the retaining ring that held the balance weight in the crankshaft counterbalance had broken in half allowing the balance weight to come out. He said the manual is very specific that the retaining ring be inserted in its groove under finger pressure only and not seated with a hammer.
    The engine is only as reliable as the person that assembled it.

  4. “Well, it’s one louder”….classic!! More is not always better. Think of how infrequently an automotive engine has a plug failure these days. I have removed plugs from vehicles so badly rusted that the shell separated from the threads upon removal but the engine did not come in with a misfire problem. One would never consider running plugs that long in any aircraft engine. So far I have changed my Corvair plugs twice in about 250 hours.

    William you are right on with your ignition system design. I remember reading your manual before I built my engine. I was very impressed with the logical design that contained redundant failure prone components. Plus, the high voltage available is much greater than a mag.


  5. Excellent Article William. It reminds me of the saying ” The man who doesn’t read has no advantage over the man who can’t read” If I have gathered anything from reading your manual and writings its that there is a balance of several factors that one seeks to achieve in building up an aircraft engine. Saw a Youtube video of a 385 horsepower covair engine and I thought that speaks well of the basic design but just couldn’t be successful in an aircraft application. I don’t understand how some people can give emphasis to one factor to the exclusion of all others. Frank Lloyd Wright could have just as easily been talking about designing aircraft systems when he said “Form Follows Function”

  6. It goes back to the old adage of are you really “listening or hearing”. To back you up with a similar phrase to Cool Hand Luke, “Some men, you just can’t reach.”
    is simply a chuckle and a response that “Some people just can’t be learned”!


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