Here's a fascinating 2.5 cc glow-plug motor which was sent along by my good mate Miles Patience of England. We know what it is because it tells us very directly - it's identified on the case as a VB 15. Question is - where and when was it made, and by whom?? It's pretty clear that the engine is of Eastern European origin because it features a metric glow-plug of typical Eastern Bloc pattern.
Apart from the twin exhausts (one on each side), the thing that really stands out with this motor is the mounting arrangement. There are no beam mounting lugs - instead, there are two lateral pairs of mounting holes split between the rear of the case and the middle of the separate main bearing housing. When you stop to think about it, this would present a pretty significant mounting challenge in a typical model aircraft! Perhaps the engine was intended for some specialized application like tether car racing?!? The fact that the twin exhaust stacks appear to have been filed to fit a cowling suggests some kind of competition application.
Can any kind reader put us out of our misery?!?
IDENTIFICATION MADE! - Ken Croft put a name to the maker of this engine right away. It's an early example of the work of Eugene Verbitsky of the USSR (latterly of the Ukraine) from the late 1960's or early 1970's. He used the monogram that looks like VB on all his engines, which were primarily built for F1C (Free Flight Power) competition, a category in which Vebitsky is a multiple World Champion, winning the title in 1997 and 2011. Many thanks, Ken!!