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

Might not have been enough power for the typical hollow log CL plane. Lots of taxiing or long glide from a hand-launch.