Jose writes:

What happens when, in a car, you go from second gear to fifth gear?
Unless you are going fast enough for fifth gear to be appropriate, the
car will lug, and slow down. The point of car gearing is to keep the
engine at its most efficient RPM range. While this is an extreme case,
something similar happens with an airplane engine - if you lower the
RPM, the pitch will become coarser (all other things being equal) and
the engine will have a harder time (do more work) for each revolution.
Each revolution pulls you through more air.

So ultimately why do you change the prop adjustment? At full power,
slowing the RPM just slows the aircraft down. So does reducing the
throttle. Why would I slow the RPM rather than reduce the throttle?

--
Transpose mxsmanic and gmail to reach me by e-mail.