Reduce RPM to "coast" in long descent?

In article ,
(Stuart Grant) wrote:

Answer to this question isn't in the flight manual for my '53 Cessna
180. Hope to get some expert advice.

I am planning a long flight Labor Day Weekend and calculate no wind
reserve based on my previous fuel burn rate of about 50 minutes. Book
says even more.
My last leg will be about 170 N mile and as much as 20 miles off the
coast of Georgia. Not in a rush. I want to save gas.

I expect to be descending from either 9,500 or 7,500 feet at about 200
feet per minute to a sea level landing. This will take about half an
hour. My economy cruise will be max 22.5" MP or WOT and 2200 RPM. Any
advantage to reducing the RPM to 2000 or lower during the long
descent? Does it save gas? Is it better to reduce MP and leave RPM at
2200? I know the prop acts like a brake a high RPM-fine pitch. Is low
RPM and coarse pitch-more like feathering when you are going downhill?

Thanks in advance -

You might save a small bit of fuel with lower RPM, depending on the MP.

As long as the engine is driving the prop I don't believe you will
notice any advantage to a lower RPM as far as "coasting" is concerned,
prop drag comes into play when the engine is no longer providing power.

Flying jump planes I use 2100 RPM and bottom of the green MP, but my
rate of descent is more like 3000-3500fpm due to the airspeed I use.

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

Dale wrote in message ...
In article ,
(Stuart Grant) wrote:
You might save a small bit of fuel with lower RPM, depending on the MP.

As long as the engine is driving the prop I don't believe you will
notice any advantage to a lower RPM as far as "coasting" is concerned,
prop drag comes into play when the engine is no longer providing power.

Usually that transition point is about 1500 RPM. Below that the air
tends to drive the prop.