The OTM diesels were manufactured in the USSR during the 1970's. Although first introduced in 1972, their very simple plain-bearing radial-port design harked back to the 1950's. The series encompassed three models, all of which received "bird" names from their manufacturers. The most commonly-encountered design was the OTM 2.5 SOKOL (FALCON). It was accompanied by the OTM 1.5 STRYZ (SWIFT) and the OTM 0.8 KOLIBRI (HUMMINGBIRD). 

The 2.5 cc SOKOL appeared in 1972, evidently being the first of the trio to appear. It was manufactured at a plant in Kiev, Ukraine. The 1.5 cc STRYZ and 0.8 cc KOLIBRI seem to have appeared a little later, both evidently being manufactured at a different facility. The two smaller models were somewhat less consistently manufactured than the SOKOL, which was constructed to quite a good standard and ran very well.

The OTM engines were among the first such Soviet products to be produced with the primary intention of selling them on the world market as opposed to supporting the aeromodelling movement in the USSR. The SOKOL was produced in quite large numbers, finding its way all over the world. The other two designs also reached export markets, albeit in somewhat smaller numbers. Production seems to have ended in the latter part of the 1970's.

A full review of the OTM range will appear on this website in due course.