There is plenty of room under the Eindecker’s cowl for the O.S. GF40.
Propeller Idle Maximum rpm
Zinger 18 x 8 1,920 7,170
Xoar 18 x 10 1,890 6,730
Zinger 20 x 8 1,740 6,580
Zinger 20 x 10 1,770 6,220
climbing only 50-75 feet. It is fun to fly, but you have to mind
your energy while maneuvering. Again, more than 17 pounds
is a lot of airplane behind a 26cc two-stroke engine.
All of that changed with the O.S. GF40. Although the full
throttle rpm remained similar, I was now flying with a 20 x
8 propeller instead of the previous 18 x 6. In addition to the
extra pitch, the propeller disk is now 23% larger. Combine
the two and you have a different feel as you roll into the
run can now
be as short as I
want. With full
power, I have
been off the
ground in no
more than 20
feet and climbing hard. The maximum climb rate now exceeds
1,200 feet per minute and the Eindecker can hover, although
that does look wrong!
The envelope for appropriate maneuvers has also been
significantly expanded. My loops, barrel rolls, chandelles, and
Immelmanns are all now large, open, and graceful. In stall turns,
the GF40 will pull as long as I ask, letting me stretch them out
to my heart’s content before I kick in the rudder to bring it
Another joy is that distinctive four-stroke exhaust note,
especially while dragging out the takeoff or floating by at
reduced throttle. Although you may not always need the extra
power, it is nice to know there is plenty in reserve, whether I
need to get out of a tight jam or simply want to have some fun.
I think a 22 x 6 propeller will be the sweet stick for lazy
WW I-style flying and I am already eyeing one of those
nicely finished WW I-style Xoar propellers. Given a modern,
lightweight, aerobatic airframe, the 20 x 8 propeller would be
my first choice.
I have no doubt that the O.S. GF40 will provide plenty of
pull for aerobatic models weighing in the mid to low teens,
and could easily fly sport- and scale-type models up to 20
pounds or more, depending on wing loading and expectations.
Its reliable starting, easy handling, and abundant power will
make this a ready favorite for anyone who appreciates a well-designed and precisely machined engine.
Thunder Power RC
(407) 277 1248
ZLog Recording Altimeters
74 Model Aviation APRIL 2014