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Jack Wilhelmson

Propellers

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I have a wood propeller on my Cozy (0320 160 hp) that has the best all around performance of any prop I have ever had. Turns up 2300 on the ground. Starts turning 2500 after about 200 foot roll and takes off in less than 900 -1000 ft at 1600 lbs. Cruise is 175 knots at 2700 rpm at 8000 ft.At low altitude it will go faster and overspeed the engine slightly. Also this propeller is the smoothest and most vibration free of any prop I ever had, when balanced with a static knife edge balancer. Now, the plot thickens. I recently removed it for some minor refinish and decided to document the pitch angles, thickness and airfoil shapes at 3" stations along the prop blades. I found that one blade has approx. two degrees more pitch angle at the tip and at all stations toward the center down to about 18" from the hub. I used a electronic angle indicator with resolution down to .1 degrees. This is a large error because the pitch angle at the tips is approx 20 degrees avg. The error is so great that I find it hard to believe that is a mistake. Could it be that this is the secret of this props outstanding range of performance?

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Jack,

 

Sounds like a good prop. Normally, when the prop is not the same from blade to blade (and I assume your speaking of a two bladed propeller) in pitch angle, this causes uneven tracking and produces a vibration. Since your testing indicates smooth - I have to wonder about your equipment for measurement..... I know from looking at your products that you definitely know how to measure so, I am only asking you to look one more time make to sure something isn't interfering with your measurements.

 

I have no other reason for your success with this prop but might offer a guess. The wood on one blade is flexing more then the other?

 

I think I wood send it to Gary Hertzler and ask him to copy it!

 

Interesting condition

;)

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