Cub flyer
Joined: 10 Sep 2006
Posts: 333
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| Posted: Fri Oct 26, 2007 8:47 pm Post subject: 130 noise rule |
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I was reading a AMA model magazine article on noise.
They had a rule of thumb for prop noise called the 130 rule.
Multiply the Prop diameter in inches by the RPM in thousands and see if the number is close to 130... If more then it will be loud. Less then quiet.
The magic number for full size airplanes would be different or maybe not.
For example.
Stinson V-77. 101 inches X 2300 RPM = 232,300 (very loud)
Piper J-3 72" X 2300 = 165,600 (quiet)
Piper tripacer 74"x 2700 199,800
X air 3300 X 60" 198,000
X air cruise prop 2850 x 60" = 171,000
Can we use a rule like this for SP airplanes when deciding on a propeller choice for experimentals or noise estimating. Simpler than calculating tip mach speed with temperature.
Warp drive has a automatic calculator but this was an interesting rough way of figuring.
How does this work out with the geared rotax types. I don't know the gear ratios or prop diameters to figure it out.
Try it for any propeller size. |
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