I just ordered the Great Planes Giant Scale Super Chipmunk 1.20 ARF from Tower Hobbies. It's on back order until early November. I don't have any experience with gas engines, but it seemed to me that a 25cc Homelite conversion might work well in this. The Tech Notes recommend a .91-1.08 cu in (15-17.5 cc) two stroke, or a .91 -1.20 cu in (15-19.5 cc) four stroke. Seems like most of the available glow engines weigh between 31 and 35 ounces. These two conversions are between 53 and 64 ounces:

[link=http://www.firstplaceengines.com/MainFrame.html]First Place Engines[/link]

[link=http://www.gcbmrc.com/engines_25cc.htm]gcbm RC Models[/link]

How critical is the weight? I spoke with the president of GCBM and he thought this engine would work fine in the new GP Super Chipmunk. From what I've read, it seems you save just a little bit of weight by going with electronic ignition. Lighter than a magneto, but you need more battery for the eletronic module. Since I'd like to avoid spending the big bucks, it seems the price is right for the GCBM R/C 25cc at $210. What do you all think?

I also found a 25cc Homelite weed wacker in my garage that is in pretty good shape. I'll bet it has no more than 6 hours on it. Should I consider having it converted? Thanks for you help.

Marl Bell

Wing Ding I would not go with a gas engine on this model. The weight of the mag and or gas engine is going to take away from this models performance. A cap is an aerobatic plane and the 25 cc homie gas engine will not deliver the power to weight ratio needed. If you do install the 25 cc homie please convert it to glow (alcohol burning) and remove the ignition. You will get more power and it will run cooler and weigh less.
The other alternative is to follow the manufacturers suggestions on the recommended engine sizes. Believe them, they want the plane to perform well.

It all depends on what you want.

10 years ago, the power to weight ratios most people have now were unheard of. People thought I was crazy when I would put a .61 on a .40 size model to compensate for the high density altitude of my area. Now, if it won't accelerate vertically out of a hover, they say you don't have enough power, or you have too much weight. Things change....

I'm not familiar with this particular airplane nor combination, but once again it depends on what you want. If you have a thrust to weight ratio of 1:1 or better, it will be a good performer for normal aerobatics. If you want the newer style "3D" performance, you need at least 1.5:1 thrust to weight ratio. My "bottom line" for an acceptable (to me) gasser conversion plane is about 1000 square inches of wing area, and around 11 lbs. RTF weight. Anything less in wing area, or more in weight, gets "iffy" with these relatively heavy gasser conversion engines. Stay within those parameters or better, and you will have a nice flying airplane.

"SPEED COSTS MONEY; HOW FAST DO YOU WANT TO GO??"

Good luck,
AV8TOR

The plane I ordered is about 1000 square inches, but 13 to 14 lbs. Other folks also discouraged me from getting a gas engine for this size plane. I think I'm am going to put in a SuperTigre G2300. Similar performance and around the same cost as a gas conversion ($210). Thanks very much for the help.

Marl Bell

I think you shoud try Zenoah G26 if you want to put the gas engine in you plane . or try SPE40Z 40cc gas engine , same weigh as G26 , but more power .

the OS 1.20 4 stroke without the pump is the one recommended in the plans.  fits like  a glove and with a 16x6 it files wonderfully.

does anyone know where i can gt templates to rebuild a wing?