Less drag = less RPM ?
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Hmmm. How to answer your question. Very specifically, a better way to put that is:
EDIT:
Lower airspeed = less parasite drag
Lower airspeed = greater induced drag
Lower g-loading = less induced drag
If you want to relate that to energy retention is an entirely different matter requiring more physics understanding.
Simply put, comparing airplanes, the airplane with greater specific excess power (P
s) will retain energy better than the other.
P
s is determined by the complex interaction between thrust, drag, velocity, and weight for a given flight condition and as they change with time in flight.