rpms and throttle ...

[tokenjo]

This was brought up in the 109 post ... is reducing rpms like feathering the prop ?  If I run out of gas and glide, should I reduce rpms to glide farther ? If so what other advantages / disadavantage to adjusting rpms?

tokenjo

[dtango]

This was brought up in the 109 post ... is reducing rpms like feathering the prop ?

 
This is as close as you're going to get to feathering.  For constant-speed props, prop pitch is automatically adjusted by the propeller governor.  The prop governor determines the prop pitch needed to maintain a set engine rpm.  The prop-governor manages engine rpm by adjusting pitch which increases or decreases the power required to turn the prop so that the engine (and the prop) rpm remain constant.  So why is this as close to feathering as we'll get in a single-engine fighter?  Read on below.

If I run out of gas and glide, should I reduce rpms to glide farther ? If so what other advantages / disadavantage to adjusting rpms?

Yes you should because it reduces prop drag and therefore maximizes your glide ratio.

With engine out / idle and the RPM set at high, the rotational speed of the prop is now only spun by the oncoming air and not the engine.  Because the rpm begins to get slower without the engine the prop governor tries to reduce the pitch of the blades which usually reduces the load to spin the prop so that it's easier to spin.  The prop governor does this to try and maintain an high rpm.  The trouble is in a windmilling situation because of the physics and relative wind striking the prop, decreasing prop pitch / angle actually increases the relative angle of attack of the prop.  This results in a whole heck of a lot of drag produced by the prop which greatly reduces your glide ratio.

Here are 3 other threads on the topic you might find interesting:
http://bbs.hitechcreations.com/smf/index.php/topic,202353.0.html

http://bbs.hitechcreations.com/smf/index.php/topic,220621.msg2656290.html#msg2656290

http://bbs.hitechcreations.com/smf/index.php/topic,209624.0.html

Tango, XO
412th FS Braunco Mustangs

[DoNKeY]

Reducing RPM's also allows you to get a greater range out of the fuel you have.  To get the best range, you'll need to adjust your manifold pressure along with your RPM settings.  Bring up your clipboard, and go to E6B.  There should be certain Manifold Pressure and RPM values for certain flight settings such as Military Power, Max Cruise, etc that give you the Manifold Pressure/RPM values for those settings.

donkey