Kinda like the other CS Prop thread

[SkyHog]

The other CS prop thread got me thinking to something I noticed, but wasn't sure who to ask.

When simulating an failed engine, the Piper Arrow POH says to go prop full forward. I noticed, however, that by bringing the prop all the way back, my glide ratio improves dramatically - even to the point where I can feel the plane gliding further. Put the prop full forward again, and the descent steepens.

Am I noticing this incorrectly?

 

[bbchien]

The other CS prop thread got me thinking to something I noticed, but wasn't sure who to ask.

When simulating an failed engine, the Piper Arrow POH says to go prop full forward. I noticed, however, that by bringing the prop all the way back, my glide ratio improves dramatically - even to the point where I can feel the plane gliding further. Put the prop full forward again, and the descent steepens.

Am I noticing this incorrectly?

You are noting this correctly, Nick. The POH advises this because under most circumstances the propeller will windmill, driving the vacuum pump. But when you are doing, for example the practice hairpin reversal, power off, (provided you defeat the auto gear drop), the glide is SIGNIFICANTLY improved to from brick to encyclopedia. It does make a difference.

 

[LR-Jet]

As you and Bruce mentioned, bringing the prop back will increase your glide. However, it takes oil pressure to bring the prop to coarse pitch. If you have an engine failure you may not have any/enough oil pressure resulting in the prop going to fine pitch and excess drag.

Quinn
ATP, CFI-CFII-MEI

 

[charlie]

I once had the oil pump in a Mooney engine self destruct causing the prop to go to fine pitch. I did not want to ruin the engine by running it unnecessarily, and it was going to be tight making the shoreline with the prop windmilling in fine pitch, so I pulled the mixture and stopped the prop. The glide was at least as good as with the prop windmilling in course pitch. I also would have had the option of starting the engine and running it until it siezed if I needed to do that to save the airplane. As it happened the glide was so good I made it to an airport. I got the towers interest when I called in "Mooney glider"...... Charlie Melot Zephyr Aircraft Engines

 

[jdwatson]

That's one of my favorite "moves" on the precision power-off 180. If I'm coming up a little short, pull the prop and extend the glide. It's amazing the difference is on the 172RG.

 

[gismo]

You are noting this correctly, Nick. The POH advises this because under most circumstances the propeller will windmill, driving the vacuum pump. But when you are doing, for example the practice hairpin reversal, power off, (provided you defeat the auto gear drop), the glide is SIGNIFICANTLY improved to from brick to encyclopedia. It does make a difference.

And many times you don't necessarily need to stretch the glide so much as control it. The prop knob can be used as a "throttle" in reverse (pull to go forward faster/ descend less) to control your glide. If you do need the best glide performance available pull the blue knob out or stop the prop (more effective especially if you have a long ways to descend, but more difficult and you lose the vacuum pump).