hi,
when you are making a plane how do you know what engine is needed?
e.g. the MDS 40 is for a 40 sized model (i think) how is this worked out?

also

what makes an engine 40 or 28 is it the speed they go, the cc they have?

how do i work out the engine needed for RC planes?

i have seen this
http://home.earthlink.net/~plasticwings/spadscale.html
it has guidelines, how where the guidelines worked out?
i would like to be able to calculate this myself.

thank you