I see posts as well as advertising that relate to "1/2a". What does the designation "1/2a" mean?

Thanks, Tom

.049 size engines, like those made by Cox. I don't know why they're referred to that way, so if somebody could enlighten me I'd appreciate it.

from my understanding there are clasa sizes (a b c) etc A was the smallest until micro RC stuff came out so they needed a new designator. since there is no letter before a they made it 1/2a

Almost, these were engine class sizes in the "old days" for free flight contests-way before R/C. 1/2 A is .049-.051.

Jetts

In the early 70's I experienced everything from pulse rudder to 1/2a pylon. I built and flew the Sterling mini fledgeling, Goldberg mini skylark, Ace GLH, ACE .10 Biplane, ACE Littlest Stik, ACE Dick's Dream, The QT, and The Joy Stick. G Mark had come out with a throttled .020 as I remember, and I built the Goldberg mini skylark as a twin. Cool!
Man, those were the days...