I think he means the "Get You Out of Trouble" margin of power we add on as a matter of course.

For instance, the BUSA 1/6 "scale" models (Pup, Ne-17 and Morse) all had OS40 Fourstrokes in the Protoypes and probably flew fairly scale with this power plant. But a 6 - 7 Lb Bipe with only a 40? I would want at least a 50 in mine... Just for that little bit more oomph that might be required to get me up over the tope of that loop (realising that the Full Size would have had to dive into one to have enough momentum).

The reliability of todays engines is also welcome.

Cheers,

Hugh