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WW 200RV Prop RPM Restriction?

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tlump51(at)sbcglobal.net
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Posted: Tue Feb 07, 2006 8:58 pm Post subject: WW 200RV Prop RPM Restriction?

I am considering purchasing a Whirlwind  200RV prop to replace my Hartzell on an IO360.  I am looking for a  weight reduction and elimination of the 2000 - 2250 RPM  restriction.  I talked to Whirlwind today and the rep mentioned  that the prop designer "recommends" avoiding 2250 - 2300 RPM and this  is identified in the owner's manual.  

  Those of you using this  prop, how are you handling this recommendation?

  

  Thanks

  

  Ted 

  Flying RV4

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gmcjetpilot(at)yahoo.com
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Posted: Wed Feb 08, 2006 5:19 am Post subject: WW 200RV Prop RPM Restriction?

It is a non issue.

   

  Here is how to fly with restriction.

   

  Since I have been flying HC-C2YK/F7666-4's with the same restriction I can tell you it is no big deal. Going thru it or momentarily dwelling in it is not a problem, even for metal props. It is continuous operation that's a problem.

   

  So for operation you just avoid that RPM range. Take off, climb and cruise should be well above 2300 rpm. If you want to cruise at 2300 RPM fine. In the pattern when you get it slowed down and go to high RPM, your RPM in the pattern should be around 1900 rpm to 2100 rpm. I don't think 2250 RPM is going to get in the way. 

   

   

  First to explain there is a little history that needs to be explained.  This should make you feel better.

   

  I hear good things about the RV 200RV, but you have to remember its a small company. When Hartzell did there extensive testing of their props on RV's using modified engines, electronic ignition and Hi Comp pistons a few years ago, they found stronger modes or more vibration modes to avoid. RPM restrictions are nothing new. The HC-C2YK/F7444 has a restriction on 180hp engines for many years going back to the 70's (like on the Piper Arrow with this engine/prop combo).

   

  When Hartzell said, wait there are differnt vibration modes, that are more severe with the stronger power pulse when EI, HC pistons are used, WW jumped on the bandwagon and copied or echoed Hartzells restrictions for electronic ignition and Hi Comp pistons. The posted on their web site that Hartzell gound XYZ so they where imposing the same restriction. I am sure at that point (about 2 years ago) they only where copying and had no actual data of their own. The kind of testing Hartzell does is very sophisticated, expensive and time consuming. (Note: There is a good reason for going with a big prop company.)

   

  No offense to WW but I suspect they still have not independently flight tested their props with strain gages. I could be wrong, but the restriction on Hratzells is due to theoretical metal fatigue life. Since the WW is composite it should not be fatigue critical.

   

  Flying in the restricted RPM region will not cause catastrophic problems, even for metal props, but from a theoretical total fatigue life calculation you are reducing the life, which originally was assumed for practical purpose to be almost infinite. Infinite is a very large finite number that is essentially for practical purposes forever. Remember we are talking low stress but lots and lots of cycles.

   

  You know the paper clip trick bend it enough it breaks. Well if you don't bend the clip at all or very little, it never breaks. Same with the prop. You keep the stress below a threshold the life goes up to 10 to the 99th power. Over a critical stress you do "fatigue damage". Fatigue damage is cumulative and adds up (miners rule).

   

  Therefore Hartzell limits blade life on highly modified engines (experimental aircraft) to some where around 8,000-10,000 flight hours even with RPM restrictions. They make some very conservative assumptions to get this number. Since that is a lot of flying, chances are the blades will need to be retired due wear before time. Also you have to remember there are huge factors of safety or margins of safety and conservatism on these numbers. In other words even at 8,000 hour Hartzell on a radical engine is still safe, may be for another 8,000 hours. If you don't have HC pistons and EI than the prop life is not an issue at all. It is essentially infinite. 

   

  WW is conservative, however its a mystery why a composite prop would have restricted RPM, at least from fatigue life standpoint, since composites are not subject to fatigue like metal. (I have a aerospace structural background).

   

  I got the feeling the WW was being conservative and coping what Hartzell was restricting. I think that is still the case. The  WW200RV should be better than a metal prop in vibration and fatigue,  so I also suspect the 2250-2300 RPM restriction is conservative. Their thinking is, hey it does not effect normal operation and since Hartzell suggest it, lets do the same. No doubt the power pulses are critical there for any prop and I guess they don't want to abuse their prop either.

   

  However when it comes to Props conservative is GOOD. The restriction is there for fatigue life on metal props. WHY WW has a restriction I don't know for sure. You would have to ask them. May be they did test it. Otherwise I think they are coping the Big Boy (Hartzell).

   

  So don't worry about it.

   

  Give use a report on your new prop.

   

  George

   

  From: Ted Lumpkin 

Subject: WW 200RV Prop RPM Restriction?






I am considering purchasing a Whirlwind 200RV prop to replace my Hartzell on

an IO360. I am looking for a weight reduction and elimination of the 2000 -

2250 RPM restriction. I talked to Whirlwind today and the rep mentioned that

the prop designer "recommends" avoiding 2250 - 2300 RPM and this is identified

in the owner's manual. 

Those of you using this prop, how are you handling this recommendation?



Thanks



Ted 

Flying RV4



			

---------------------------------

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alexpeterson(at)earthlink
Guest

Posted: Wed Feb 08, 2006 5:52 am Post subject: WW 200RV Prop RPM Restriction?

George,



Good post regarding the prop restrictions.  A couple additional thoughts:



Regarding fatigue life, what you said is true for alloys of steel, but not

for aluminum.  Even at low stresses, the fatigue life is not practically

infinite.  Aluminum and its alloys are somewhat unique in this regard.  I

haven't a clue what it would be for a prop, I suspect that there would be a

huge variation based upon usage and knick history.



Regarding the question of why an rpm limitation would be imposed on a

composite prop, I was under the impression that the Hartzell limitation was

somewhat based upon the crankshaft's interaction with the prop.  Others more

knowledgable can comment.



Alex Peterson

RV6-A N66AP 712 hours

Maple Grove, MN

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ronlee(at)pcisys.net
Guest

Posted: Wed Feb 08, 2006 7:46 am Post subject: WW 200RV Prop RPM Restriction?

At 09:50 PM 2/7/2006, you wrote:

 	  Quote: 	
		  



  I am considering purchasing a Whirlwind  200RV prop to replace my 

 Hartzell on an IO360.  I am looking for a  weight reduction and 

 elimination of the 2000 - 2250 RPM  restriction.  I talked to Whirlwind 

 today and the rep mentioned  that the prop designer "recommends" avoiding 

 2250 - 2300 RPM and this  is identified in the owner's manual.

   Those of you using this  prop, how are you handling this recommendation?




	


Supposedly MT makes a prop without an RPM restriction.



Ron Lee



Do not archive

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