matchlessaero

Just got my latest copy of FLY RC, and while reading the 'engine' column, I spotted Mr. AJ Coholic's name and his question. Of course it had something to do with 'small' airplane engines. The editor's response was pretty interesting too........

If you get this mag, check out the 'engine' column when you get it.

flyinrog

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yeah,saw that, they could have spelled it right though...so did ya see that 7" wingspan corsair? wow!.....

ajcoholic

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Hey! I didnt get my copy in the mail yet...

I did have a few emails with Dave Gierke (whom I respect immensoy when it comes to engines) but I didnt agree 100% with something that was said in the feb issue and asked him about it. Coincidentally, Clarence Lee also had something to say about the same topic in RCM the same month! It was regarding Nitro content and how it affects the timing of the engine (preignition or retarded ignition).

I still aint' clear about it all..... Dave is working on some theories and how the plugs have somethign to do with it, etc. Its not a simple answer it seems...

AJC

flyinrog

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dont get mad , but its Andrew Caholic in the mag, and he did kinda dance around the question with speculation......

Japanman

Hi, A.J

I am very interested in this- what was written?
I am not at all satisfied with the variety of explanations regarding plug heat and nitro and timing.

J.M

combatpigg

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Duke FOX used to have a news letter that was stuffed in with their mail order exchanges with the customers, it usually had some interesting stuff. Onr of the letters was a quick course about the way nitro works. It is chemical supercharging, it makes more oxygen molecules available, and surround the fuel molecule for a better PROBABILITY of ignition. Without nitro there is a higher rate of un happy marriages between the air and fuel molecules. Without nitro a 1cc cylinder will only fill to let's say, 90% during each intake cycle, so the combustible ignition point doesn't happen until the piston is very close to TDC. With nitro, the same 1cc cylinder will fill sometimes 110% , which will make the critical ignition point happen sooner. I am pulling these numbers out of the air to illustrate a point. The heat range of the glow plug should be looked at as the last step in fine tuning after the compression ratio is optimized for the nitro % you are using, if you are adjusted to a point where you are no longer damaging plugs, but just wearing out the elements, then it's time to play with heat ranges. Most model engines in our size range have pistons that dwell at TDC through 20 degrees of crank rotation, so the piston is whipped slightly past TDC. This is the critical time for peak combustion pressure to occur, no matter what nitro percent you are running. A cold plug delays the ignition timing, maybe, but it's biggest asset to me is it is able to withstand the punishment of high nitro, high rpm use better than a standard plug.