The 5 cc Drone Diesel is arguably one of the best model diesels ever to originate in the USA. This very well-made fixed-compression design was manufactured in two quite distinct variants between early 1947 and mid 1949. It enjoyed considerable competition success until the arrival of competing glow-plug engines like the Fox 35 in 1948. Those lighter and more powerful models spelled the doom of the Drone, causing the termination of its manufacture in mid 1949.
The first model Drone featured a plain bearing, while the second variant had a single ball-race at the rear of the crankshaft journal. Both glow heads and variable-compression heads were offered as accessories. Contrary to well-established urban myths, both fixed-compression versions of the engine started and ran extremely well if handled correctly. The full story of the Drone diesels, including the correct approach to operating them, may be found in my earlier in-depth article on the late Ron Chernich's "Model Engine News" (MEN) web-site.