Formula for estimating speed using RPM and Prop Pitch??

[Darin Jordan]

Is there a good formula out there to give rough speed estimates for a given RPM and Prop, considering prop slip, etc.?

The one I found was:

RPM/1000 * Pitch(inches) * .95 * (1-Slip %) = Speed in MPH

I think this was derived for airplane props, however. Not sure what the .95 represents, and I added in the slip part. I think the .95 is partially derived from the conversion of inches and minutes to Miles per Hour???

[Brushless55]

how bought this about 1/2 way down the page?

http://www.offshoreelectrics.com/conversion.htm

[Darin Jordan]

how bought this about 1/2 way down the page?
http://www.offshoreelectrics.com/conversion.htm

Wow... never saw that page before. Thanks.

Would like to see the actual math involved for this if someone has it. And YES, I'm being lazy right now in not sitting down and figuring out the conversions myself...

[martin]

Go to Mark Sholunds site Props4u & click on props chart & you simply enter the info you mention. Depending on what you want to know ie speed, revs, pitch it will give you the answer on what one you want. Their are five boxes revs,gear,pitch,slip,& speed, You put any 4 in & it gives you the fifth one. Martin.

[FE Wannabe]

Formula

Darin,

Try using this as a formula:

Total Pitch in mm* Loaded RPM * (1-%slip)/26775 = MPH

Where slip is 15% - Rigger/20% - Hydro/23% - Cat/25% - Mono

The 26775 is the constant (forgot how it was calculated) used for metric and time conversion.

It appears to be in the ball park of OSE's calculator, less than 1 mph difference and about a tenth off of Sholund's calculator.

Brad