ORIGINAL: Rcpilot
How do you scale up a kit?
Do you use a percentage? 10% more wing cord and 10% more span? And 10% longer fuselage? 10% larger tail surfaces?
I had some basic design ratios once, but have lost the file. Somebody had pics posted of span/cord ratios and span/length ratios. Ratios for square inches of tail surface too wing area.
I have a kit that I want to do this with. I want to keep the fuse width the same so my cowl still fits, but I want to stretch the overall length of the fuse and wings to accommodate a larger engine (gas). Not sure if I should make the fuselage taller too?
Now thats an interesting question! I would first determine the increased weight of the engine and fuel combination over the existing design and attempt to keep the wing loading the same. (Naturally there will be more wood/covering, heavier gear etc to consider too). Assuming you will be using the same airfoil, this will give you a number for the new span and chord. Then I would maintain the same ratio of stabilizer area etc to the new wing area as the old one. The stabilizer distance from the cg would be tough. I would probably multiply the old length times a ratio of the new wingspan over the old. Fuselage cross-section is irrelevant as long as it is strong enough to support the flight loads of the bigger plane. You can strengthen high stress areas with 1/16th ply for example.
I don't know what kind of plane you are considering or the difference in engine sizes. A high performance plane may have additional considerations like flutter, spar flex, etc.
What are the specifics of the project?