Photos by the author
O.S. combines the economy
of a gasoline engine with the
distinctive exhaust note only a
four-stroke engine can deliver.
As most AMA members are aware, O.S. Engines is well known and respected for producing some
of the finest model airplane engines
ever made. The company’s detailing is
exemplary and performance is first rate.
What you may not know is that O.S.
was established in 1936 to produce
miniature steam engines and also
introduced its first gasoline model
airplane engine that same year. Forty
years later, O.S. introduced the first
four-stroke engine to the RC market. It
was met with considerable success and
remains enthusiastically sought after by
Along the way, O.S. has given us a
staggering array of glow, gasoline, and
diesel engines. Its current line includes
67 single- and multi-cylinder engines for
aircraft, marine, and surface use. I can’t
recall a single negative conversation
about O.S. products during my 35
years in RC, and if I have had any, they
haven’t been numerous or memorable.
Last year, I discovered that O.S. had
released its first four-stroke gasoline
engine: the GF40. At 40cc, this engine
promises to be a welcome option for
modelers with larger aircraft looking for
the economy of a gasoline engine and
the distinctive exhaust note only a four-stroke engine can deliver.
I quickly learned that the GF40’s
power output is approximately
equivalent to that of the earlier O.S.
GT33 two-stroke engine, making it the
perfect option for those 25-30cc models
that deserve more power and a more
The O.S. GF40 arrived in a glossy,
durable cardboard box. The supplied
accessories include a silencer, electronic
ignition, and CM- 6 spark plug, along
with the manual. The propeller nut
features a collet-style locking nut to
help avoid throwing the propeller if the
The workmanship is pure O.S., with
a flawless appearance throughout.
The GF40 features a cast-aluminum
crankcase, cylinder, and head, all with
Step into the
71 Model Aviation APRIL 2014
firstname.lastname@example.org O.S. GF40 GAS EnGinE