jindoguy(at)gmail.com
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 Posted: Mon Nov 27, 2006 6:38 pm Post subject: Adventures in Prop Inertia |
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Like the weather, everyone talks about prop inertia. Okay, maybe it's only a few gearheads, but I got real interested after seeing the technique demonstrated while doing the weight shift and powered parachute modules for the repairman maintenance ticket. Having had plenty of time to think about it 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 the setup per Rotax Service Information instruction SI 11 UL 91 E, Available from 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 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 Propellor 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
--
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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