Thanks guys, this does help some. IH82, that link you provided tells me that the weight of the plane is the most important step in sizing the right engine to the plane. That is according to rcshowcase.

Tim22, I understand were your comming from when you say the mfg will state what size engine. However what if your scratch building and don't have that info either because the plans are very old and/or your the designer.

The things that I think play a role in sizing the engine to a plane are 1) weight 2) wingspan 3) wing area 4) style of flying. What % of those 4 factor into engine selection I really don't know (and I guess is what I want to learn). Just as an example a small gas engine can fly a large cub but if you take that engine off and stick it on a geebee that weighs the same it will never get off the ground. There has got to be a way to figure out "X weight + X wingspan + X wingarea + X flying style= (ballpark) gas engine cc size" . I may be 100% wrong in my approach to this.


Thank you NikolayTT some very usefull info in your post above. hehe I think I'm going to start telling people "Yeah I can fly it's everything else about airplanes I need to learn".