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  #1  
Old 06-16-2016, 10:18 AM
Bayou Bert's Avatar
Bayou Bert Bayou Bert is offline
 
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Location: Prairieville, LA
Posts: 221
Default CS Propeller Agony Update

I guess it has been so long the thread I started with the same name
is gone.
Time for update and conclusion.
Below is graph of RPM of take off this morning, from start of roll to 1000'.
This is after changing crankshaft to one with the tube across the inside
with a slot cut in the center of the tube.


Below is graph of RPM of take off from start of roll for 30 seconds with the old crankshaft with only
a hole in crankshaft wall, no tube.


As you can see, no sag, no over speed to nothing. Just a nice steady RPM.
The only thing changed on the engine was the crank and new main bearings.
I put my MT governor back on for the first flight just to save labor if all
was good.
ALL IS GOOD!
Don Broussard (Cajunwings) and I made the flight. He put the prop
through a number of throttle changes, both up and down, the rpms showed
only slight deviations (30-40 rpm) and within seconds was back at set
rpm.
So, for constant speed operation, the crank has to have the cross tube.
No one we talked to could explain the physics of why, just that they had
never seen one work without the tube.
At this point I don't care, my engine, governor and prop are performing
as designed.
Thanks to all the people that helped, Aircraft Specialties, Hartzell and
Lycoming. Don for the rebuild and flying.
Now for a chance to just fly.
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Last edited by Bayou Bert : 06-16-2016 at 05:38 PM.
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  #2  
Old 06-16-2016, 10:21 AM
Mike S's Avatar
Mike S Mike S is online now
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Location: Dayton Airpark, NV A34
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Default

Old thread is still there.

http://www.vansairforce.com/communit...d.php?t=137088

The problem is that the forum software default is set to only display threads that have had activity in the last 30 days, and your prior thread was last updated 35 or so days ago.

At the bottom of each forum, you will find a menu "Display Options" to reset the time you can search through. Hopefully this is not one of those things restricted to mods/admin.
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Rv-10, N210LM.

Flying as of 12/4/2010

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Last edited by Mike S : 06-16-2016 at 10:28 AM.
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  #3  
Old 06-16-2016, 11:02 AM
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Steve Melton Steve Melton is offline
 
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Location: Cincinnati, OH
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Default

that was a lot of work. thanks for the info.
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  #4  
Old 06-16-2016, 01:57 PM
BillL BillL is offline
 
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Location: Central IL
Posts: 5,516
Default

Thanks for bring this full circle. The cross tube hole is in the center as that is where the air is. As the prop cycles the exiting oil will push the air out. Centrifugal force will keep the oil at the perimeter of the crank bore.
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RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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  #5  
Old 06-16-2016, 03:02 PM
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erich weaver erich weaver is offline
 
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Just curious, what caused the RPM deviation in the 2nd chart where it goes from 2780 to 2588 back to 2708?

erich
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  #6  
Old 06-17-2016, 07:57 AM
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airguy airguy is offline
 
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Quote:
Originally Posted by erich weaver View Post
Just curious, what caused the RPM deviation in the 2nd chart where it goes from 2780 to 2588 back to 2708?

erich
That looks pretty typical of a constant speed prop governor adjusting to the target RPM with a full power application. The blades stay on the low-pitch stop until the target RPM is reached, but the RPM increase rate is fairly high with wide open throttle, and the RPM overshoots a bit for half a second while the governor reacts.
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Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #7  
Old 06-17-2016, 04:18 PM
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Bob Kuykendall Bob Kuykendall is offline
 
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Location: Douglas Flat, CA
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Quote:
Originally Posted by erich weaver View Post
Just curious, what caused the RPM deviation in the 2nd chart where it goes from 2780 to 2588 back to 2708?
I think that glitch, and the other RPM instabilities, were caused by air trapped in the crank nose. That's the problem that the cross-tube fixes.
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