This specific engine is unique in that it was designed to operate mounted vertical as a auxiliary power unit on airplanes designed to operate from remote locations or over the ocean. A Martin PBM Mariner used during World War Two may have used this engine to provide enough 28VDC power to start one of the main engines while at some remote South Pacific island. Incredibly compact and smooth running, the L-5 produces about 35 HP.
After the War, airplane enthusiasts obtained a few L-5 engines as surplus and attempted to convert them for use on small ultralight airplanes. There were several issues that made the conversion problematic. The oiling system and sump were setup for vertical operation and there was no provision for mounting and driving a propeller (as in thrust bearings or splined prop shaft)
These issues added some complexity to the rebuild, however using a pusher type propeller in an "airplane-style" mount and some modification to the oiling system allowed the Aero Telemetry team to complete this rare radial restoration in less than a month...it is most likely the only reliable running example in the world.