I spent a lot of time as a young lad flying various plane models with Cox .049 power. Mine was a Babe Bee .049 for control line and free flight, a generous Christmas gift (see below re cost vs wages) A favourite plane was Carl Goldberg Models' "Lil Wizard" for c/l. We flew these things for hours at a time in a local park. One day a guy came by with a Guillow Models B-17 with 4 Cox .049 engines! It was amazing. I don't think he flew it that day as he would just get all 4 engines sync'd and one would run out of fuel.
There was as I recall a Cox .049 R/C version engine advertised at the time, with I believe an exhaust port throttle, but I can't be sure about that due to passage of time.
Us kids were all covetous of the higher end Cox engines like the Black Widow but with even a humble Babe Bee going for about $20 at the time, almost half a week's wages for my Dad, the $60+ Black Widow was a distant goal. When I got my Babe Bee for Christmas I remember being very aware of how valuable it was and what a major gift it was. For kids doing hobbies with money earned at odd jobs at about 25 cents an hour, it was not likely we would get one.
I took care of the one I got for Christmas, and believe it or not I still have it! Should get it out and give it a snarl. I ran it once inside the service bay at my Dad and Grandfather's garage and I remember them running out of the office into the bay with horrified expressions (probably expecting some carnage) when it started. One of the neighbouring houses' occupants yelled over "what the hell was that?" It was that loud! Lots of reverberating noise in that garage, off the painted concrete walls.
Mufflers were not in the budget.
However, in a park and some distance off the ground they did not seem half so noisy.
Great fun, thanks for reminding me.