I have a friend who's expressed some real interest in joining me in this madness. This evening he asked me a question I simply have no idea how to answer. Not sure if this is the best forum for this, mods plz move if it is not:

Friend wants to know if there is a 'formula' to allow one to compare a glow engine to an electric motor. E.G. a formula to calculate, say, lbs of thrust from a glow motor, and a seperate formula to do so for electric motors, such that we can compare the two in similar units.

For that matter, is there a simple 'rule of thumb', like, say, 'every X volts of electric motor are = Y inches of glow motor displacement'?

Obviously, I realize prop size, brushed vs brushless, several other factors would all come into play here...and we're not looking for a precise mathematical formula (though if one exists it would certainly be interesting to know), but just trying to get a good basic set of rules/guidelines by which one could say 'this electric motor will do about the same as this glow motor'.

TIA,