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jindoguy(at)gmail.com
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 Posted: Thu Nov 01, 2007 7:23 am Post subject: Prop inertia, again |
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Since the old wives tale about the inertia of Warp Drive props has surfaced again, I am again publishing the data from the inertia tests I did last winter, The tests were performed per Rotax Service Information instruction SI 11 UL 91 E, available from the Rotax owners site and paraphrased in the CPS catalog.
Here are the numbers for a 66" Ritz 2 blade wood prop, a 66" Warp Drive 3 blade straight carbon fiber prop with CNC aluminum hub, an IVO 60" 3 blade composite prop with quick adjust hub, and a 48" 2 blade Tennessee Propeller wood prop. Each prop was run 3 times and the times shown are the average of the three, although each prop's runs were all +/- 1 second. I'll go heaviest to lightest.
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
So there you have it, you can definitely see the variance in inertia caused by length and mass. The Ritz is right at the top of the allowable range for a 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 of the C and E gearboxes but would be brutal on a B box.
Rick [quote][b]
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Thu Nov 01, 2007 8:18 am Post subject: Re: Prop inertia, again |
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| jindoguy(at)gmail.com wrote: | | Since the old wives tale about the inertia of Warp Drive props has surfaced again, I am again publishing the data from the inertia tests I did last winter, The tests were performed per Rotax Service Information instruction SI 11 UL 91 E, available from the Rotax owners site and paraphrased in the CPS catalog. |
Whoa, if these tests are accurate (and sounds like they are), I happily stand corrected. I don't remember too well but it seems I got the same no. of oscillations with my 62" IVO, but clearly my calculation came out messed up.....
I've always wondered how the boxes have stood up to years of use of these props anyway 
LS
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_________________
LS
Titan II SS |
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jindoguy(at)gmail.com
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| Posted: Thu Nov 01, 2007 10:12 am Post subject: Prop inertia, again |
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Lucien, Sorry, didn't mean to sound so strident, but over the years I've heard people claim this same thing about Warp Drive Props with no data to back it up. That was why I shivered my way through the tests last winter.
Ladies and gentleman, this test is almost ridiculously easy to do. There is no magic or mystery. The attached photo is of the plate on which I mounted the propellers. The slots in the end are where the 6 foot lengths of safety wire were placed. All told, it took less than 30 minutes to assemble, mount and level the test apparatus. Certainly not rocket science, although I do admit trying to track down the theory of the torsion pendulum to assemble a spreadsheet turned into an exercise in futility.
Fortunately that work was done by Rotax. All you have to supply is the weight of the prop and the time required to swing through 30 oscillations. The only trick to it, I found, was keeping any up and down movement out of the test. Once I got a good side to side swing, I started the stop watch, timed the first 30, then the next 30 and then 30 more oscillations. I also did the test by starting and stopping and starting again, just to make sure that what I learned in physics class about the frequency, speed and swing of a pendulum balancing out was true. Of course there is a small difference due to air resistance, but I couldn't find a meaningful difference in the variance of swing that I used.
It's coming on winter, some of us will lay up for the cold weather, others will be doing maintenance and some are still building. Why not setup the inertia test on your prop and publish the results here. I'll volunteer to assemble the data and publish a table from which some reasonable assumptions might be made by those in the process of considering a new prop purchase.
Rick
On 11/1/07, lucien <lstavenhagen(at)hotmail.com (lstavenhagen(at)hotmail.com)> wrote:[quote] --> Kolb-List message posted by: "lucien" <lstavenhagen(at)hotmail.com (lstavenhagen(at)hotmail.com)>
jindoguy(at)gmail.com wrote:
| Quote: | Since the old wives tale about the inertia of Warp Drive props has surfaced again, I am again publishing the data from the inertia tests I did last winter, The tests were performed per Rotax Service Information instruction SI 11 UL 91 E, available from the Rotax owners site and paraphrased in the CPS catalog.
|
Whoa, if these tests are accurate (and sounds like they are), I happily stand corrected. I don't remember too well but it seems I got the same no. of oscillations with my 62" IVO, but clearly my calculation came out messed up.....
I've always wondered how the boxes have stood up to years of use of these props anyway
LS
--------
LS
FS II
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