Why does airspeed change when I adjust the prop?

The implication is that you can go faster in cruise
with coarse pitch (just as you can go faster in overdrive in a car
when cruising), but it doesn't seem to work that way.

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.

Jose
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He who laughs, lasts.
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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?

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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?

For better efficiency.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

"Mxsmanic" wrote in message
...

snip

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?


A fixed prop optimized for takeoff would overspeed the engine at cruise
speed. With variable pitch, the prop can be flat for take and higher pitch
for cruise.

Danny Deger