1/2 A glo engines appeared not long after the glo plug was introduced in 1947. Everyone seemed to want to jump onto the bandwagon. Early 1/2A engines were made by McCoy, Vivell, Herkimer (OK Cub), Atwood (Wasp), Holland (Hornet), O&R (Midget), K&B. Then Leroy Cox made them all mostly obsolete with his 1/2A line.
On the Continent, small diesels of about 0.75cc had a long history, but they were almost unknown in the U.S.
K&B Manufacturing, in 1949, produced a 0.020 engine, followed by others of 0.035 and 0.049 cuin. I bought one of the first K&B :"Infant" engines from John Broadbeck at his factory in Gardena, CA. It was 0.020 with a metal propeller, which had to be straightened after every flight.
This K&B .049 appears new, and performance might improve with breaking-in. Right now it runs on;
SIG 25% nitro, 10$ castor and 10% synthetic
Kaysun 5 1/2" 2 1/2" pitch plastic
I could not use a tach indoors (with fluorescent lights), but estimated about 12K RPM. Not very exciting!
Floyd