ORIGINAL: tripower222
Ok here is the scoop,</p>
I have been out of model flying for 18 years and wanted to get back in. About a month ago I bought a 1/4 scale Sig Cub 105'' wing span (not clip wing) on ebay. the plane has a converted weed wacker engine on it that seemed to run ok befor flight. I purchased and built a set of Sig 1/4 scale floats for it and gave it a try.
All worked out great except !!!! DANG!!!! she is way under powered, almost couldn't get off the water and once it did super slow climb.</p>
Info:
The plane weighs 18 lbs 2oz. ready to fly with half tank of fuel (14lb. 8oz. plane, 3lb. 10oz. floats)
The engine turned a 16x6 prop 6700 rpm static and a 16x8 prop 6600 rpm I used th 16x8 for the flight.</p>
Now as for choosing the motor I looked at the Zenoah G26, the Fuji Imvac BT24 and the CRRC 26cc weight is really of no concern as the plane is balanced well and they are all lighter than the current engine an would likely need to add the weight back for balancing anyway
Obviously power is my main concern. I don’t see a HP rating on the Zenoah nor would I put much faith is manufacture HP comparisons from one MFG to another. I was looking for experience to help with that.</p>
Also electronic ignition or not?</p>
Let me say that the difference in cost on all these engines is not a big deal to me I just want to get it right.
It seems there is really no weight advantage by my calculations (if it mattered in my situation) by the time you put the ignition module, battery, and wiring in place of the magneto it’s a wash and certainly less dependable (with the hassles of keeping the battery charged). My question to the experienced is, is there really a difference performance either power, smoothness, or idle that would make it worth it?
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If you sat down and calculated the airspeed of the model flying with 6" of pitch at 6700 rpm, you might be surprised to learn that that combination is flying your Cub at just a hair above stall speed. I would drop to a 15x10 or 12 and then reset the engine's needles.
You might discover that you do not need another engine at all. Just because the engine peaks out at 6700 rpm, doesn't mean that it can't pull a heavier prop without losing much rpm and providing a huge increase in performance. Gassers are a bit different in this regard than our old standby glow engines. I wouldn't give up on this engine just yet.
While some of the other 26cc engines you mentioned "might" be a little stronger, what you will really need to make a substantial difference is an increase in displacement to 40cc or greater. This assumes that you have tried my prop recommendation and it wasn't enough to make you feel warm and fuzzy. I would even consider a Turnigy 52cc engine. Good luck.
Ed Cregger