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Prop Governor

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romanupshaw

Joined: 27 Apr 2009
Posts: 3
Location: Mobile Alabama

Posted: Mon Apr 27, 2009 8:16 am Post subject: Prop Governor

Long time reader, rare poster but need some help.  I have bugged Carl and Jill with M14P Inc as well as Dennis enough so I thought I would give them a break.  Also thought there must surely be someone else out there who has had this problem before who could offer their experience/advice. This is on a Yak 52. The prop "seems" to cycle from fine to coarse perfectly on the ground during run-up. I say "seems" because maybe I am missing something??? Once airborne it refuses to cooperate. The lowest (coarsest) I can get it is 70% with the throttle pulled back to even idle. I did try one recommended test which was while in flight and stable at around 70 square, to quickly (but cautiously) push the prop lever full forward to see if it went toward red line.  It did. Linkage seems to be fine, and again, it cycles great on the ground. In the air it acts more like a fixed pitch prop except I can take it from the 70 mark to higher when I need to.  It's like the pressure isn't backing off to allow the counter weights to rotate the prop.?!  I don't know....which is why I write. Rich Hess also flew it recently and can attest to this.  I think it is fine to fly, just not very efficient but I don't fly much for efficiency anyway.  It's just starting to bug the crap out of me!  I should mention that I just had one blade replaced and both re-painted with new edges. Jill and Carl handled that for me too. (Though I am innocent this time, don't ask why a blade was replaced. Suffice it to say... I now have a stop sign up at the end of my runway)  Any input from this well experienced list would be greatly appreciated.



Roman Upshaw

Mobile Alabama

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NebraskaYak

Joined: 02 Sep 2008
Posts: 31
Location: Nebraska

Posted: Mon Apr 27, 2009 8:33 am Post subject: Re: Prop Governor

I had a very similar problem last year. In flight I could never get below 70%, but on the ground it checked good. Double check your blade angles. mine were both off a couple degrees. Once I got them set right, everything worked as advertised.

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mark.bitterlich(at)navy.m
Guest

Posted: Mon Apr 27, 2009 12:29 pm Post subject: Prop Governor

I am not totally sure of the problem.. .but as I understand it, you are

saying that in straight and level flight, if you pull the throttle to

IDLE (???) your engine RPM does not go below 70% ???  Really?  



And... 



1.  You have not adjusted or replaced the prop governor. 

2.  You did not have this problem until recently. 

3.  You just removed and replaced the prop blades.  



If this is correct... And ONLY if this is perfectly correct, then follow

the Tech Reps Rule.  Suspect ANY problem to be where humans last had

their hands involved.  In this case, check the blade angles on the prop

blades after they were re-installed into the prop hub.  



Also, it would be of interest to know what your RPM is in flight at full

power with the prop handle pushed all the way forward to the stop.. An

exact number.  If it seems like it is going to go over 100%, then of

course STOP and go not further. 



Mark Bitterlich

 



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romanupshaw

Joined: 27 Apr 2009
Posts: 3
Location: Mobile Alabama

Posted: Wed Apr 29, 2009 8:26 am Post subject: Re: Prop Governor

Sorry... been away a couple days.  Thanks for the feedback.  I will try the suggestions.  Mark, you do understand it correctly.  And remember, it cycles fine on the ground.  However, if I pull the throttle back to idle and really slow the speed down, the rpm will come back.  To what I don't know.  But in straight and level, pulling throttle back, it will not slow down UNTIL speed really bleeds off....like on landing.  This goes along with what I meant with it acting like a fixed prop.  Hope that's understandable.



 To answer your questions, pretty much all of them are "yes". I haven't touched the prop governor. I took the entire prop, hub and all, off and shipped it to Jill. I didn't personally replace the blades. The only thing I question is if I had a little of this prior to recently.  It has never come back to a GOOD solid cruise setting but, again, I don't cruise much if ever.  I know it used to come back to very low 60's.  It is MUCH worse now though and is very evident ... even annoying.  I agree with "where hands were last".  That's why I wanted to seek advice before I went fooling around with the governor or elsewhere.  



I know that on takeoff the power is right on 100%.  I don't have much room for "sightseeing" on my strip during takeoff but I know it doesn't go over 100%.  I will fly this afternoon again and keep both at FULL forward in flight and reply back with an exact reading on that.



Thanks to all who are offering suggestions!!

Roman Upshaw

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wlannon(at)persona.ca
Guest

Posted: Wed Apr 29, 2009 9:55 am Post subject: Prop Governor

I would suggest that you check the blade angles. This should be done using a 

propellor protractor by some one familiar with it's use.

It can be done using a modern level device but these are very subject to 

operator error since they are a level not a protractor and require 

calculation to establish the zero reference.



If the blade angle is set too low it will work just fine at high RPM because 

it is under control of the governor which, from your comments, appears to be 

doing it's job.When you move the RPM control to full coarse the governor 

pilot valve is at positive coarse pitch. You now have a coarse angle fixed 

pitch prop. But if the blade angle is set too low the RPM will be high.



Walt



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mark.bitterlich(at)navy.m
Guest

Posted: Wed Apr 29, 2009 12:47 pm Post subject: Prop Governor

Everyone agrees... Check the blade angle. 



A really horrible thought though is that something might have gotten into

the hub when the blades were removed for any kind of repair and the hub is

now not ALLOWING the movement of the blades that it should.  I'd say that

this is highly unlikely and that the most probable cause is ... Blade angle.

But... If the blade angle checks out to be dead on, I'd be thinking of

checking to make sure the hub has "stop to stop" movement without

restrictions of any kind. Some FOD inside of that hub could conceivably

cause this.  Hope not.  And in fact, PROBABLY not.  But....   



Mark Bitterlich

 



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nc69666(at)aol.com
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Posted: Wed Apr 29, 2009 9:54 pm Post subject: Prop Governor

Roman, Gary in Las Vegas, I have had the same problem with my CJ, I have a M14-P, So just last week I checked the blade angles, by looking at the index marks on the hub, my blades were set at "0" on the hub markings so I loosened the blade clamps and reset the blade angles to 2 index marks coarser giving me a higher blade angle. Your Governer is working just fine, as it controls the high RPM, which it is doing at 100%.  The blade angles in the hub, and the counter weights is what controls the low RPM. When the blade angles are set too low of an angle in the hub, as the airspeed increases the counter weights will go to the high pitch stops trying to control the RPM, but when they reach the high pitch travel stops, then the propeller becomes in a sense a fixed pitch prop. and the RPM will increase as the airspeed increases.  I am getting 100% 0n take off, and at 160 MPH indicated below 4500 ft, I can get it to 64%, Manifold pressure setting 735 MM.&nbsp  ; At around 7000ft. I can hold about 67%.  I may set the angles ONE index coarser to see if I can get a bit slower RPM, but if you do, check the High Rpm on take off as I think that setting may be getting close to the limit for high pitch setting to still be able to get 100% on the off..

 Good Luck with the settings..  Let me knw how it works out for you...   Gary

 

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wlannon(at)persona.ca
Guest

Posted: Thu Apr 30, 2009 8:17 pm Post subject: Prop Governor

There appears to be some misconception regarding  propellor and governor operation and possibly some questionable practices being  carried out as a result.

  

 The prop. hub assy. (whether  Chinese,  Russian, Polish, etc.) are identical for operational considerations.   They are all nominal 15 deg. hubs which guarantee a minimum available pitch  range of 15degs. Both the Huosai and the M14P installations obtain a  15.5deg. range safely. Of course the blade angle settings for each are quite  different.  Obviously any change made to the fine pitch angle has  made the same change to the coarse pitch angle.

  

 The specified angles for the M14P installation are  14.5 deg. +/_ 10 Min (fine) and 30.0 deg. +/_ 20 Min (coarse) with the  maximum difference between blades not more than 10 Min.  These  angles have been determined by the aircraft & engine manufacturers as the  best compromise between take-off, cruise performance and margins of safety  in the event of pitch control failure or engine failure.

  

 The blade angle index mark set to "0" indicates the  blades are set to the correct angle.  However that cannot guarantee they  are within tolerance limits. 

 NOTE to Roman:  I should have advised you to  check this setting to determine if your blade angles are correctly  set.

  

 The governor (more accurately the CSU or constant  speed unit) consists of two units 1. a gear type oil pump that boosts engine oil  pressure to approx 230psi for propellor operation and  2. a   fly-weight governor that, with changing RPM,  positions a pilot valve  to control oil flow to and from the prop. pitch change unit. The CSU both  provides and controls the motive power (oil pressure) for moving the blades  toward fine pitch and CONTROLS the motive power (blade counterweight force)  moving the blades toward coarse pitch.  It does this by opening a single  oil gallery from the prop. either to governor oil pressure or to  drain.

 Therefore the propellor blade angle and  engine RPM are directly controlled by the governor, in both  directions, at the RPM selected by the pilot.

  

 There is one very important exception.  That  is when the RPM control is set to full minimum RPM.  In this position  the pilot valve is mechanically lifted and retained to fully open the  propellor gallery to drain. The governor is out of the picture, the  counterweights force the oil to drain and move the blades to coarse pitch.   This function is called POSITIVE coarse pitch and directly relates to the safety  considerations for the coarse pitch blade angle.

  

 In the event of engine failure you will want the  blades at the highest possible angle to reduce drag.  If the engine is  windmilling it will get there much sooner if you go to positive coarse. In this  case you want as coarse as possible - feathered would be nice!

 But, there is another failure mode to  consider.  

 Here is the scenario;

 You hear the engine RPM drop, the windshield is  covered in oil and, if you took the time to look, the manifold pressure is  up.  But you don't have time to look. Your immediate action must be RPM  control to positive coarse.  The prop.pitch change unit has  failed, governor oil pressure went to zero and the counterweights moved the  blades to coarse.  All the governor knows is that RPM has dropped  and it senses an underspeed condition which it is trying desperately  to correct by pumping all your engine oil overboard.

 Positive coarse pitch stops the bleeding and you  still have an engine that may get you to a safe landing albeit at greatly  reduced power.  In this case you want a coarse pitch angle as FINE as  possible to provide enough power without over boosting your engine.

  

 All the radial engines (using a single acting prop  & governor) I am familiar with use a propellor coarse pitch  setting that provides about 1400 RPM in the positive coarse position.   The M14P is no exception if set up as the manufacturer intended..

  

 Walt   

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