Earlier this week we had a number of posts on the issue of spark plugs, centered on a hard miss under full power experienced by Guy “A.” I had another two calls with him after he changed to AC R44F plugs that were gapped to .035″. He now reports that the issue appears to be resolved, and he could not get the aircraft to act up as it had before.
In this case, it is worth noting that Guy “A” had previously flown his plane with NGK plugs with out issue. Was the issue the gap, the dirty condition or? In my perspective, he likely could have gone back to a new set of NGK’s correctly gapped and the issue would have likely disappeared. But. you have to ask yourself, by what margin?
I advocate the AC plugs because they are the ones designed for the engine, and GM owned both AC and Corvair. This is my beginning point, but the strongest case I can make is that I have never seen an issue in a Corvair flight engine caused by an AC plug. Because of our central location on the flow of information on Corvairs, I have access to many more case histories than any single builder, in addition to our own testing, and a lot of road miles for comparison. I have good evidence that the AC plugs will work perfectly under a wider range of conditions in a Corvair flight engine than any other plug that builders commonly consider.
If you work outside the engine world, it is often easy to forget some concepts that seem simple on paper, but are often forgotten in a frustrating search for an issue in the hangar. Rule#1 is always Go Back to what you know will work. If you have an issue like a hiccup, and part of your set up is different from the norm, then reset your engine to the norm. In this case, the plugs we are speaking of cost a whopping $9.00 for the whole set. If you have an issue with two variables, or what you suspect are two variables, being able to absolutely eliminate one of the for nine bucks is a diagnosis tool that only a foolish mechanic would not utilize. In the aviation world, you can’t let something like brand loyalty to plugs that worked in your motorcycle color your perspective. Your allegiance has to belong to what works. Experimentation is good, but it always has to be done as the expansion of the envelope from a set up that works perfectly. If what you have doesn’t work flawlessly, then fall back to the known until it does. A number of guys resist this, which would be fine if we were shade tree car guys wrenching on hot rods. But this is flying, and it can be for keeps, and most professionals don’t fool around with biases, brand loyalties nor reasons of ego or saving face.
Many experimentals have a lot of outstanding details. But good aircraft are not made of 99% excellent. They are made of 100% airworthy. The plane having the issue is outstanding, you could easily call it 99% excellent. But with a 1% detail like the incorrect plugs gapped wrong or dirty, it is not 100% airworthy. As builders, it is important to get the basics 100% right. I included the Guy “B” story to illustrate that this spark plug story isn’t a Corvair story at all. A nearly identical mistake in reverse on a certified aircraft produced the same result, a plane, that until the detail is corrected, is not airworthy. Both pilots made a simple mistake and missed a basic element. One of the things I would like to point out is that Guys “A” and “B” have more than 10,000 flight hours between them. Would a beginner have made the same mistake? Could have, but I have been training people to build engines a long time, and in my experience, new guys are very detail oriented because they take nothing for granted. If you think about human nature, you can see how guys with a lot of time around different kinds of planes may get complacent about details. If your new to planes and engines, don’t let this story spook you. If you just approach this in the proven format and not add creative touches like other brands of plugs, you will not have this kind of issue. Arm chair commentators will find that last sentence boring or manipulative. For those of us who will fly something other than a key board or an arm-chair, I point out that reliability is supposed to be more boring than unnecessary risk, and yes, I am trying to convince people to at least start with proven set ups.
One of the people I keep counsel with on Corvair experience is Dan Weseman. I was speaking with him about CC#24 plans when this issue came up. He commented to me that he had never had a single issue, even once, with an ACR44F plug, and they have been the only ones he has ever flown in a Corvair. Arguably, no one has flown the Corvair harder than Dan. He pointed out that the AC’s not only work flawlessly, they are also the least expensive plug on the market. He didn’t really see any motivation for working with any other plug.
In an average year, I will get 200 emails asking about things like constant speed props and elaborate injection systems. If you read all of them, it is easy to tell that 95% of these come from people with little experience. If I lined up these 95% and asked them to install a distributor and time it, or to explain to me how you could tell if the engine was on the top of the exhaust stroke of compression by looking at the motion of the rockers,(both things we teach at Colleges,) I am sure these people would be at a loss. Is there anything wrong with their dreaming of injected constant speed planes? Of course not…if the extent of what they came to aviation to do is dream about things. Conversely, if actually achieving things is the goal, dreaming can not take the place of a rock solid foundation of the basics.
None of us were born knowing this stuff. I am glad to teach it to anyone who wishes to learn instead of day dreaming. I can make a very good argument that the builder who creates and masters the operation of a basic aircraft, is a lot safer, and will experience far greater rewards that any builder operating a plane he really doesn’t understand, or is sketchy on the details of a complex aircraft’s function. The guy with the most basic plane has won the game. The guy who consigns himself to daydreaming has not lost the game…..he wasn’t ever playing. Once the basics are mastered, then moving forward can be done with the understanding that you are not posing or posturing as your own mechanic, you actually have earned the confidence in yourself, the real reward for knowing the subject. -ww