Gentlemen, How does one determine the percentage of size increase in a plane for a modification? I have a GP U Can Do .60 I like this plane but would like a gas engine. I know of one guy that did a weight reduction mod on a G23 and flys this model. To me it seems like too much weight up front even though it does fly at the resulting in a heavier model which changes the light 3D features. This is the plane I like so it seems that this is the plan for a scratch build. Right now with a Saito 100 it carries just under 21 oz. up front. I would like to know what the percentage increase in size would be required to carry an engine of app. 46 oz. and I'm sure you would have to consider the weight of additional support equippment that gas requires as well. Is this a practical approach or are there other aspects in design to consider? If it is as simple as just increasing the size of the design as is I would like to pursue it. I greatly appreciate any feedback on this. Joe

Here is a litle practical help -
a 46 oz gas engine ?
I don't think so
3x16=48 ozs- typical 40/50 cc engine. and the ignition and batt will up this another 8 ozs--
if you are new to all this - stick with a in cowl Pitts style muffler - simple -a bit noisy but it works
The model for really sparkling performance - ready to fly -- 13 lbs --TOPS
You can do it - I have done em at 11 lbs.--but I have built lots of light weight aerobats
as for total area - shoot for about 1300- 1500 squares .
will it work?you bet your a-- it works .
If all you are after is hover and flips - use a fat airfoil - easy to make strong
if you want to include good snaps spins etc - use a tapered foil about 15% at root (max ) and down to 12% at the tip
this will snap better as it will stall before simply mushing around.
Someone will probably offer a good "formula" but scaling is kinda an art form . - this is a hands on, known entity.
choose the engine - THEN pick the size.
(Believe it or not - that's how it was done in full scale for many years )

Dick, Thanks for the response. The engine is a 3W 24 at 2.89 lbs. w/ ignition. Without designing a plane around this I was thinking of sticking with the design of the UCD.60 and wondered if I could just increase the dimensions in a stick build project and end up with the same plane only larger. I'm looking to find the percent in size increase required. Thanks, Joe

good luck- my recommendations were for more powerful engines
The model designed by Wolfgang Matt for that engines -is about as large as the 24 will handle
Wolfgang is a first class designer - and he is worth copying if you get lost on your project.