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  #11  
Old 11-29-2019, 05:35 PM
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airguy airguy is offline
 
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I cycle once on the first flight of the day for VFR ops. I cycle each takeoff for actual IMC departures. I'm not so much worried about cold oil in the hub as I am about catching a failing (or failed) component.
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  #12  
Old 11-29-2019, 06:34 PM
SHIPCHIEF SHIPCHIEF is offline
 
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I'm not convinced about the warm oil idea, the prop hub oil does not circulate, it only adds or subtracts a little oil to change the pitch a little bit during normal flight operations. The propeller hub oil temperature must certainly be very close to the ambient air temperature.
I have upgraded the blades on my Yak-55, which included removing the propeller pitch dome. Inside (after the expected liter of oil poured out) I found a ring of carbon crud. This is centrifugally deposited and lays next to the oil seal. Every hydraulic constant speed propeller must be like this.
The oil enters and departs the hub thru a tube in the center, so carbon deposited must be manually removed. The fewer times the prop is cycled, the fewer times carbon is deposited.
I cycle the prop twice before take-off because I want to know that it works.
I'll probably remove the piston dome on the next condition inspection to inspect the parts and clean the carbon out.
https://www.monoplaneforum.com/viewtopic.php?f=58&t=192
a link to the monoplane forum where I have a few pics of the prop blade upgrade and the carbon inside the prop pitch actuator.
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  #13  
Old 11-30-2019, 02:28 PM
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RV7A Flyer RV7A Flyer is offline
 
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What does the propeller manual from the manufacturer say?

The Hartzell manual gives instructions on prop checks during run-up in the Inspection and Check chapter, section 3, paragraph B.
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  #14  
Old 11-30-2019, 08:28 PM
Charles in SC Charles in SC is offline
 
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I read an article years ago about this. As I remember it one of the reasons for cycling the prop was to change the oil in the hub to prevent deposits from building up. If you want to check the operation of the governor it seems to me you would pull the prop control back some to the point where it doing some controlling and advance the throttle up to see if the rpms hold. Hope this makes sense.
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  #15  
Old 12-01-2019, 01:19 AM
salto salto is offline
 
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I only move my elevator two inches each way before take-off to make sure it works.. Hope this helps. 🙄
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  #16  
Old 12-01-2019, 10:40 AM
BillL BillL is offline
 
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Location: Central IL
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Default Not that it matters to your comment, but . . .

Quote:
Originally Posted by SHIPCHIEF View Post
I'm not convinced about the warm oil idea, the prop hub oil does not circulate, it only adds or subtracts a little oil to change the pitch a little bit during normal flight operations. The propeller hub oil temperature must certainly be very close to the ambient air temperature.
I have upgraded the blades on my Yak-55, which included removing the propeller pitch dome. Inside (after the expected liter of oil poured out) I found a ring of carbon crud. This is centrifugally deposited and lays next to the oil seal. Every hydraulic constant speed propeller must be like this.
The oil enters and departs the hub thru a tube in the center, so carbon deposited must be manually removed. The fewer times the prop is cycled, the fewer times carbon is deposited.
I cycle the prop twice before take-off because I want to know that it works.
I'll probably remove the piston dome on the next condition inspection to inspect the parts and clean the carbon out.
https://www.monoplaneforum.com/viewtopic.php?f=58&t=192
a link to the monoplane forum where I have a few pics of the prop blade upgrade and the carbon inside the prop pitch actuator.
Scott, typically the deposits are lead from the fuel that has made its way into the oil. It gets really hard from the centrifugal forces. Centrifugal oil filters do the same thing. They do collect carbon when applied to diesel engines with higher particulate (soot) production.

I suppose it could be carbon on a specific engine if the oil generates carbon particles from contact with high temperature interior surfaces. Not typical though.
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  #17  
Old 12-12-2019, 09:55 AM
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gmcjetpilot gmcjetpilot is offline
 
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Every constant speed prop Certified AC I know of (a few dozen both single and multi) AFM/POH all call for you to cycle the prop during run up...

With that said DON'T NOT DRAG RPM DOWN.... I pull the blue knob back and smoothly push forward almost before the Prop starts to react.... Sure once is OK. I get a drop of a few 100 RPM before it is going back to fine pitch/high RPM. You are checking function of the Prop control, governor not just getting oil into the prop. On that same note why check carb heat, ignition, flight controls, fuel pump? Why run up at all, kick the tires light the fire? This is a rhetorical question to make a point. Don't reinvent the wheel, check the Prop function. It does not hurt anything, just don't LUG the engine RPM down.
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Last edited by gmcjetpilot : 12-12-2019 at 09:59 AM.
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  #18  
Old 12-12-2019, 12:07 PM
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Low Pass Low Pass is offline
 
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It's necessary to get the system liquid full, and secondly to assure control effectiveness. Others I'm sure are much more nervy than me, but having the propeller surge when climbing out cured me early on of not cycling it before takeoff. And I never flew a government certified recip that didn't specify cycling the prop before takeoff.
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  #19  
Old 12-12-2019, 02:18 PM
219PB 219PB is offline
 
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I spoke to Hartzell about this a few months ago and they stated the reason to cycle the prop is to expel any air that might be present in the system. When the engine is shut down the oil drains back causing a slight negative pressure in the system and it is possible that air will come in through one of the seals.
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  #20  
Old 12-12-2019, 06:00 PM
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Walt Walt is offline
 
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Quote:
Originally Posted by Low Pass View Post
It's necessary to get the system liquid full, and secondly to assure control effectiveness. Others I'm sure are much more nervy than me, but having the propeller surge when climbing out cured me early on of not cycling it before takeoff. And I never flew a government certified recip that didn't specify cycling the prop before takeoff.
Surging is often caused by the low pitch stop not being adjusted correctly, the prop overspeeds while the gov attempts to catch it.
I hear this quite often on RV's when they take off.
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Last edited by Walt : 12-12-2019 at 06:05 PM.
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