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  #1  
Old 08-02-2018, 01:33 PM
GEM930 GEM930 is offline
 
Join Date: Aug 2007
Location: Chico (KCIC) , CA
Posts: 259
Default GT Propeller Blades - help me understand CS operation!!

Ok, I thought I understood how a CS propeller works, but I guess I don't. I purchased new blades from GT Propeller in Italy and had them installed on my Hartzell hub. Alex at GT told me I would probably need to adjust my governor, so I was not surprised to only see 2400 on a high speed ground roll. My thought was that I would need to adjust the stop screw on the governor arm to allow more forward travel, but the propeller shop says the propeller should be at its fine pitch stops during the run up and the stops (not the governor) need to be adjusted on the hub. I work with several professional pilots and a couple A&Ps and everyone seem to have a different opinion about exactly how the propeller should be set up. I'm sooooo confused...... I'm obviously going to follow the prop shops directions, however, I am just trying to understand what is actually happening.
Anyone out there have a dumbed down explanation I might understand???
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  #2  
Old 08-02-2018, 01:57 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 5,264
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Think of the mechanical stops as a Ďback upí to the governor. If the governor fails you donít want to go to zero pitch (no thrust), but you also donít want the stops to limit full RPM on takeoff. So adjust the fine pitch stop so you just barely make red line RPM with a full power sea level run up, and the governor disconnected. The actual prop pitch should be in the prop manual, to get close with the engine off. Then adjust the governor to hold red line rpm when full forward in flight. You can test this in a high power run up by noting that you are at red line, but any aft movement of the prop control reduces rpm.
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  #3  
Old 08-02-2018, 02:13 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 1,603
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Iíll give it a go:
- The prop governor, if properly set for our type of props, will not be porting oil to the prop hub at high RPM (fine pitch). Fine pitch is set via the prop hub stop. In other words, if you lost all oil pressure the prop will go to fine pitch stop (high RPM).
- So assuming the prop hub is set up right, on takeoff roll the prop will be at fine pitch limit as set by the hub (2700 RPM) but will start to try to increase RPM as you gain airspeed. The governor will port oil to the hub at that point to have the prop take a bigger bite, thus holding RPM at 2700. This is a governor adjustment that should be set right about right as it comes out of the box.
- I can see how a prop governor not set up right could port oil to limit RPM to 2400, so worth checking. That is a simple screw sitting so easier than messing with the hub as the first step.

Of interest, Alex and Paulo Tonini just finished installing new custom blades for an RV-14A (first set of blades where a touch small). These are the blades they had on display at Oshkosh.

Carl
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Old 08-02-2018, 05:27 PM
GEM930 GEM930 is offline
 
Join Date: Aug 2007
Location: Chico (KCIC) , CA
Posts: 259
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Ok, but it thatís the case (the stops limiting the fine pitch to redline at sea level), would that not reduce your rpm on take off at higher density airports?
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  #5  
Old 08-02-2018, 07:36 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 5,264
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As the air density drops, the engine power and the drag both drop, approximately canceling out.
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