Combat Engine size

Can any of you "older" combat fliers tell me why the maximum
engine size was decided to be a 36 when the rules were written
I guess in the fifties? What other 36s were out other than
the McCoy 36?

Although the old McCoy was actually labelled a 36, it's my understanding that several of the engines popularly referred to as 35's were .357/.358/.359 actual diplacements, and even the old Mac was slightly under the full 36 size. So I have to guess that the choice was made that way just to avoid any potential rules-lawyering from folks who used engines CALLED 35's but actually smaller, protesting against someone with an engine larger than .350 displacement.

Kiwi

Kiwi is mostly correct. Back then they actually tore the winner's engines down and checked the engine size(s) at the nationals and some other large conteste At some time back then there were two sizes. B was below .30, and D was .30 and over. That didn't last long as the D size pulled very hard and broke away easily. so many local contests limited D size contests to 35 , and later to 36. I heard that there was a large manufacturer that backed their engines VERY well had a hand in determining the 36 size. I have no way of checking this out though so it is strictly hear say.
Bigiron

For a long time an ignition 0.60 was legal in combat. They figured 60% of the displacement on ignition engines which gave the effective displacement of 0.36

The 60 % displacement rule is still in the rulebook for the use of four cycle engines. New rule book, page 31, Paragraph 11.1-- top RH corner of the page. So you can still use a 60 four cycle in combat with the same lines that you use on the 36s.
WOW talk about a battering ram----
Bigiron

That is interesting. With a 4 stroke 60 you could go to 1000 sq in and have a nice flying model. 11-8? prop 11-10?

Would that be with an 11/42 prop to get the speed up to 100 using only 10,000 rpm?