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Old 4th Jun 2017, 21:38
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JammedStab
 
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Originally Posted by B2N2
If this wasn't covered during your training that's a little depressing.

At idle the engine is still running and developing some power.
Windmilling the airflow keeps the propeller rotating. This means rotating the crankshaft and moving the pistons up and down against the compression stroke.
That takes a lot of energy.

A constant speed prop does better if you pull it all the way back ( coarse) during a glide. You actually feel the airplane accelerating when you do this. Difference is a couple of hundred feet per minute in your rate of descent.
In all my various checkouts in different piston engine aircraft, no instructor or material has mentioned that there is a significant difference in glide distance until reading the Slingsby POH.

That being said, there appears to be a difference in opinion on the reasons why between yourself and Dave W. Which is correct?
Then again, according to Bookworm's post, based on a NACA study, there is little difference.
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