I'm going to build a Butterfly, and put my OS .40 on it. Of course,
the Butterfly calls for a .10 to .20 sized engine, so mine will be
overpowered. Others have evidently flown a Butterfly with a .40 sized
engine and gotten away with it, though. I simply could not resist
purchasing the engine, and I will also not be able to resist purchasing
the plane. I remember reading a post by someone who was able to get a
Butterfly to rise off of the ground with a .25 sized engine.
Unless your field elevation is above 6,000 feet and the plane will be
carrying a heavy payload, what is the logic in this power choice? It
will fly fine with a .15 . . a .40 will just over stress the airframe.
If you can find me a sailplane kit with a wingspan which is greater
than that of the Butterfly, then I will be happy to purchase it.
Eventually, I will be scaling the Butterfly up, at which time I will
then have a more appropriate power match. In the meantime, I will be
Say, fellows, I just realized something. The Bird of Time has a
wingspan of almost ten feet. Perhaps this would be a better match for
my engine, even though I would probably still be overpowered. Does
anybody have an opinion about this?
I also bought a Butterfly at a swap meet and it had an old OS15 in it. This
engine is Ok but marginal in windy weather.
Your 25 will be more than ample. I have been very pleased with my Butterfly
as it seems to pick up thermals with ease and I have been getting 40 min
flights easy. Usually end up bringing it down as either my neck is giving
up or I get worried re battery or excessive height. prop size should be
about 9 by 4,5,6 pitch for a 25 engine
In case it was overlooked, the bird of time is a real non-motorized
sailplane and the butterfly is a gas airplane with a big wing.
Not that you can't put a motor on a bird of time, but it is drawing much
farther outside the lines than putting an oversized motor on a butterfly.
Proceed at your own risk in any event.
P.S. In any event use lightweight radio equipment
(servos,batteries,reciever) if possible to compensate for the extra engine
weight and put it towards the tail. You might want to build it, hang the
motor, and then figure out where to put the radio equipment and linkages so
it will balance at the designed CG without adding even more weight just to
One of the appealing aspects of the butterfly is it's gliding ability,
making it heavier with a larger engine (and larger/draggier prop) will of
course compromise that. Not to discourage you, by all means give it a go,
it should climb like a .
Thank you ,John..I had a 9by 5 on the engine, testing it, I picked
up the tail a bit, and snappped the prop,on the cement driveway. I was
that was a good prop size, and I guess it was. I am having trouble hand
it. It seems as though it is to heavy, and wont rise, and and hits the tall
climbing. My first Butterfly would rise at the slightest toss.
That's exactly the rig my son learned to fly with. It will fly the
batteries dead at 1/4 throttle, and will climb like a c-gas FF model if
you want to power up.Big, vertical spiral climb.
It climbs well at 1/2 throttle.
You can overload the wing if you try to get aerobatic at high throttle
settings--I know that for a fact.
You can easily hand launch it with that engine, and not have to heave
BTW-that was at 3500' MSL. It performs a little better here in Texas at
Saw about 20 of the Butterfly IIs scratch built over a two
year period from RCM plans. About 15 of them flew. All well with OS
.20FPs 9X5 props and a Higley heavy hub for balance.. The scratch
built BFs are much lighter than the currently kitted BF by DynaFlite.
A friend built the DynaFlite kit and it was a bit underpowered with
the OS .20FP therefore he switched to the OS .25LA and a 9X6 prop. It
flys extremely well now.
My own scratch built BF II is powered by an OS .26FS with 10X6
prop. I highly reccomend this power combo.
As well I am in the process of converting a second BF II into
"E" power using a brushless Astro 020 w 4.4:1 planetary gearbox and
matching speed control. Planned prop is 12X8. Calculated flight times
with this combo and 1320mah 3 cell LiPo pack, hands-off light @ 62%
throttle are expected to be in the 31 minute range.
I have also seen this plane fly many times with floats and in
the dead of winter on skis. All in all a great all around plane.
I am one who has done the Butterlfy with a .40. Here's the changes:
1) the firewall needs to be heavier and more firmly mounted.
2) the wing center sections need to be strengthened and stiffened
chose to fill the area in the center surrounding the main wing joine
tube with "Bondo lite" (its a BLUE automotive filler) and
double-webbed the spars THen I sheeted the center section completely
eaxtra bays each side and the full center panel from LE to main spa
top and bottom out to the polyhedral break.
3) the outer panels also need to be strengthened and stiffened. Shee
the upper side from LE to main spar.
4) Fiberglass the portion of the polyhedral break where the sheetin
meets using 0.5 oz cloth 2 inches wide. (thats almost a square o
5)The tailplanes need help.. double the 3/8 X 1/4 stock at the hing
line with another piece. (just add it on and gain the stab area.. it
the easy way and it works well) Do the same for the vertical stab.
Now the Butterfly has the strength for 1/2 throttle in level flight.
Full throttle aerobatics will still rip the wings apart. Jsut go ahea
and use an APC 12.25 X 3.75 to help prevent you overspeeding it. The
it should climb like a rocket. (I used 11X5 and shattered the win
pulling out of a dive using it to train Cub Scouts. (picture
available... has a few more mods, not related to just putting a .4
It makes a good piggy-back carrier or towplane for up to 100 inch spa
LIGHT sailplanes (such as Gentle Lady or Spirit) with a .40
This is really some excellent advice! I will study your post very
carefully, and make similar changes in my own Butterfly. I like the
idea of being able to fly at a lower throttle setting, where my engine
will be making less noise. In fact, I intend to eventually do a diesel
conversion, which should lower the noise level even more. If I break
the crank shaft, or other internal parts, I am prepared to replace
them, since I recently purchased a lathe, which I haven't even used
yet. Again, thanks for the excellent advice!
The United States of Texas