In the Rex line we have 2 new 15cc engines.

The R91HR1 (picture on the left) is developed for use in helicopters and has therefor a completly redesigned crankcase so that it can be a direct replacement for an 15cc OS-max sized engine.

The R91F is an updated airplane version of the discontinued R91HR helicopter engine.
Includeding the updates is the new crankcase which is similair too the R91HR1 helicopter engine.

Both engines have an ring-type piston which is casted from a specially developed aluminium alloy, while the sleeve is made from iron.

More information about the R91F.
More information about the R91HR1.