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Prop Feathering w/o aux pump

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Hello all herc operators, maintainers and lovers! Can someone kindly tell me that what would be the options of propeller feathering if essential AC is lost or the Prop Aux Pump becomes unserviceable. How much would the propeller be feathered through the condition lever, if at all?

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The "Manual feather valve" is mechanically actuated with the condition lever in feather. The valve ports fluid to drive the propeller "TOWARDS" feather but as the prop's rotation slows the pump output drops and the prop may not get all the way to feather. 

You can check operation on the ground by running the engine and pulling the Aux feather motor CBs and placing the condition lever to feather. Blade angle will increase towards feather and may get all the way to 92.5.

60 or 70 degrees while not fully feathered will reduce drag.


Your maintenance books should have a description of this operation.     


In addition to pulling the Aux feather motor CBs you need to pull the Feather and Airstart CB to fully check the manual feather valve. 

Pulling the CBs listed is for maintenance check ONLY.

You should NEVER do this in flight.

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I agree with NATOPS, once the engine shuts down, any fluid pressure from the still-spinning pumps will go directly to the increase-pitch side of the dome via the feather valve and feather actuating valve until the pumps can no longer supply 100 PSI. Then the blades stop changing pitch. Since the internal seals for each propeller are worn differently, it's difficult to nail down a specific degree when you transition through that pressure. Also, as you are flying, airflow is still trying to spin the propeller beyond what it would be during a ground run. I doubt you will get all the way to feather, but you should get far enough to make sure propeller drag isn't dangerous. Think of the propeller as an air brake which either absorbs or transmits airflow energy. If the airflow is inadequate to continue spinning the propeller, then the propeller resistance to airflow is naturally going to be low.

I am unfamiliar with the flight manuals, so purely from a maintenance standpoint I also want to emphasize that you will still have 28vdc attempting to actuate the propeller feather solenoid, so once the blades stop changing pitch, the propeller feathering circuit may still be energized, both overheating the circuit as well as sucking DC voltage if that bus is powered. Check your flight manual to see if you need to manually pull the feather override button up if the propeller blades stop changing pitch, but are not all the way in feather.

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On 09/04/2018 at 1:00 PM, Lkuest said:


The flight manual does say that if the prop feather solenoid valve buttons dnt pop out after the feathering; they should be manually pulled out. However, it doesnt explain the drain on 28 V ESS DC and that if the feather cycle is interrupted somewhere in the middle (prop stops increasing pitch to feather); you should pull the button out. So, your explanation enhanced our knowledge. I am thankful to both of you for the guidance.

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  • 4 weeks later...

Back in the late 90s a Ham Standard rep came down to Hurbie and taught us a class. He said that if you placed the condition lever to feather inflight and the Aux motor didn't work the blade angle MAY get high enough that the prop won't windmill. Of course that is depending on airspeed. My experience on the ground during emergency egress is that the props made it to the cuff which is approximately 45 -50 degrees(I think). Your mileage may vary.

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