Are there any rules of thumb for matching an appropriate sized engine to a particular airframe, given it's weight, wingspan, and/or wing area?

Does anyone know of a chart showing the "typical thrust" you can expect from various "1/2A" engines (using the term 1/2A very loosely in this case)? What kind of thrust-to-weight ratio is typical on 1/2A sport aircraft?

If there aren't any rules of thumb, does anyone have a few examples of the thrust their engine generates and the weight/span/wing area of the model you fly it on?

I suppose standard procedure is to try one engine, and move up or down depending on how it performs, but it might be nice to be able to cut to the chase and use an educated guess for that first engine (particularly if one is new to 1/2A and won't have alternate engines lying around).

thanks,
Rick

HI RICK, This might be my favorite subject. I've always thought that one of the coolest things that a model can do is "thumb its' nose at gravity" and go straight up till you can't see it . A model can't be said to be able to "do it all" if it doesn't have unlimited vertical. It sure is good to have a beforehand idea of what we're playing with for thrust. I don't know what the breakoff point is where a model doesn't have enough thrust to accelerate straight up, but it has to somewhat less than 1 to 1.

I have measured .049 BABYBEEs at 9 ozs of thrust. An AME .061 checked in at 24 ozs. I think I got a best effort of 18 ozs from a BIG MIG .061. I haven't bench tested the .074 NORVEL, but it will take a couple of 16 oz models I have straight to JUPITER. I think a typical $60 sport .15 will go vert with 28 ozs.

As far as matching these engines to airframes [ and various wing loadings]goes, that is a matter of personal preference. Kit manufacturers want their planes to seem as versatile as possible so that is why you will see quite a wide range of recommended engine sizes listed. You also have to look at the airfoil when deciding which engine will suit the plane in question. I have a 40 oz plane with a lifting airfoil that flies nicely with a .15. It is very lively, it is actually a rulebook combat plane. It just doesn't have much vertical. Maybe I'm giving you too much info here... to answer your question as direct as I can, aim for 14 ozs for a .049 to .061 powered plane, and 16-18 ozs for a .074 powered plane, but if you want to go lighter, that's OK with me!