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Adventures in prop inertia, further

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jindoguy(at)gmail.com
Guest

Posted: Wed Dec 20, 2006 7:13 am Post subject: Adventures in prop inertia, further

Previously I published a list of props I tested per Rotax Service Information instruction SI 11 UL 91 E. I just chased down the 68" four blade Powerfin prop intended for the trike (officially refered to as Meadowlark from here after). I say chased down because UPS was trying to deliver it to an old address and the easiest way to get it was to go pick it up.  

Speaking of UPS, I show up fat dumb and happy with no tracking number on the day after their biggest day of the year which coincidentally was also the day the computer at the customer counter decided that black was the color of the day and took a hiatus. Five minutes after mumbling no to the question "do you have a tracking number?" I had my prop and was on my way out the door. Great job by Brown. 

This test also gives me some anecdotal evidence to give Larry C. an answer about the inertia of his two blade Warp Drive mounted on a "B" box. I think you're okay on the limit of the "B" box ( 3000 kg cm ). Here's why: 



Powerfin 68" 2 blade, 4 blade hub.

Wt. 6.88 lb  ( 3.12 kg ) 

Average time to 30 oscillations 157 sec

Inertia 2800 kg cm



Powerfin 68" 4 blade, 4 blade hub.

 Wt. 10.52 lb  ( 4.77 kg )

 Average time to 30 oscillations 183 sec

 Inertia 5800 kg cm



Here you can see the direct relationship between the mass of the propellor and the test results. Of course the only way to really know is to test the two blade Warp Drive, but I think some reasonable reassurance can be had inference. 

Hope this helps



Rick



 	  Quote: 	
		  [b]Like the weather, everyone talks about prop inertia. Okay, maybe it's only afew gearheads, but I got real interested after seeing the technique

demonstrated while doing the weight shift and powered parachute modules forthe repairman maintenance ticket. Having had plenty of time to think aboutit while driving back home from CA, I figured I had four props I could check

and see how it all fit together. So I gathered them altogether and built thesetup per Rotax Service Information instruction SI 11 UL 91 E, Availablefrom the Rotax owners site and paraphrased in the CPS catalog. So here are

the numbers for a 66" Ritz 2 blade wood prop, a 66" Warp Drive 3 bladestraight carbon fiber prop with CNC aluminum hub, an IVO 60" 3 bladecomposite prop with quick adjust hub, and a 48" 2 blade Tennessee Propellor

wood prop. Each prop was run 3 times and the times shown are the average ofthe three, although each prop's runs were all +/- 1 second. I'll go heaviestto lightest.Warp Drive 66" 3 blade CNC hub

Wt. 9 lb. 12 oz.Average time to 30 oscillations, 180 secondsInertia 5200 Kg cm^2IVO 60" 3 blade Quick adjust hubWt. 6 lb. 4 oz.Average time to 30 oscillations, 161 secondsInertia 2700Kg cm^2

Ritz 66 X 28 2 bladeWt 5 lb. 1 oz.Average time to 30 oscillations, 190 secondsInertia 3000 Kg cm^2TPI 48 X 34 2 bladeWt. 3 lb. 3 oz.Average time to 30 oscillations, 127 secondsInertia 1100Kg cm^2

So there you have it, you can definitely see the variance in inertia causedby length and mass. The Ritz is right at the top of the allowable range fora B gearbox, while the shorter, heavier  IVO is right near it and the TPI

shorty should represent no problem. The Warp drive is well within range ofthe C and E gearboxes but would be brutal on a B box.[/b] 	


-- 

Rick Girard

"Ya'll drop on in" 

takes on a whole new meaning

when you live at the airport.   [quote][b]

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lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Wed Dec 20, 2006 8:06 am Post subject: Adventures in prop inertia, further

[quote] ---

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jim

Joined: 03 Nov 2006
Posts: 107
Location: N. Idaho

Posted: Wed Dec 20, 2006 8:15 am Post subject: Adventures in prop inertia, further

Very interesting Rick.



So based on these data, can you estimate the max length 3-bladed QA IVO

prop that would be acceptable on a B box?



Thx,

Jim



 	  Quote: 	
		  

 Warp Drive 66" 3 blade CNC hub

 Wt. 9 lb. 12 oz.

 Average time to 30 oscillations, 180 seconds

 Inertia 5200 Kg cm^2

 IVO 60" 3 blade Quick adjust hub

 Wt. 6 lb. 4 oz.

 Average time to 30 oscillations, 161 seconds

 Inertia 2700Kg cm^2



 Ritz 66 X 28 2 blade

 Wt 5 lb. 1 oz.

 Average time to 30 oscillations, 190 seconds



 Inertia 3000 Kg cm^2



 TPI 48 X 34 2 blade

 Wt. 3 lb. 3 oz.

 Average time to 30 oscillations, 127 seconds

 Inertia 1100Kg cm^2



 --

 Rick Girard

 "Ya'll drop on in"

 takes on a whole new meaning

 when you live at the airport.

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_________________
Jim
N. Idaho

jindoguy(at)gmail.com
Guest

Posted: Wed Dec 20, 2006 10:54 am Post subject: Adventures in prop inertia, further

Jim, By rough estimate 64", based on nothing more than TLAR and a one sample statistic. Merry Christmas.



Rick



On 12/20/06, Jim Dunn < jim(at)tru-cast.com (jim(at)tru-cast.com)> wrote: 	  Quote: 	
		  --> Kolb-List message posted by: "Jim Dunn" < jim(at)tru-cast.com (jim(at)tru-cast.com)>



Very interesting Rick.



So based on these data, can you estimate the max length 3-bladed QA IVO

prop that would be acceptable on a B box?



Thx, 

Jim



 	  Quote: 	
		  

 Warp Drive 66" 3 blade CNC hub

 Wt. 9 lb. 12 oz.

 Average time to 30 oscillations, 180 seconds

 Inertia 5200 Kg cm^2

 IVO 60" 3 blade Quick adjust hub 

 Wt. 6 lb. 4 oz.

 Average time to 30 oscillations, 161 seconds

 Inertia 2700Kg cm^2



 Ritz 66 X 28 2 blade

 Wt 5 lb. 1 oz.

 Average time to 30 oscillations, 190 seconds

 >
	


 	  Quote: 	
		   Inertia 3000 Kg cm^2



 TPI 48 X 34 2 blade

 Wt. 3 lb. 3 oz.

 Average time to 30 oscillations, 127 seconds

 Inertia 1100Kg cm^2



 --

 Rick Girard

 "Ya'll drop on in" 


	


	


-- 

Rick Girard

"Ya'll drop on in"

takes on a whole new meaning

when you live at the airport.  [quote][b]

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Dennis.Kirby(at)kirtland.
Guest

Posted: Thu Dec 21, 2006 10:14 am Post subject: Adventures in prop inertia, further

Classification:  UNCLASSIFIED  

 

  

Richard Girard wrote: << Powerfin 68" … Inertia 2800 kg cm >>  

   

Rick –   

   

Thanks for the data on prop inertia.  

As we see from your post, Powerfin props have the lowest rotational inertias compared to most (all?) the other props.  This is one of their selling points – low inertia provides less stress on the engine & gearbox.  

   

However, this can also be a negative.  For example, I had used a Powerfin on the Verner engine that was originally installed in my Mark-III.  It was too light.  Result was insufficient “flywheel effect” for this engine, and it was not damping out the engine power pulses sufficiently, causing the prop redrive hub bolts to break.  

   

Dennis Kirby  

Mark-III, 912ul (now)  

New Mexico  

   

   

   

   

   

      

Classification:  UNCLASSIFIED   

 

  [quote][b]

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