REFLECTOR: Prop

[NMFlyer1 at aol.com]

Since I have a unique setup, I needed to adress the prop-tip speed as well. 
My high HP engine, lots of torque and the redrive complicated things. 

Since I had it.. I thought I would pass along the quick and easy formula to 
find tip speed for those that need it:  

Dia. of prop (in feet) x 3.14 x RPM of the prop. Divide that total by 88 = 
tip speed. 

For reference, speed of sound at sea level is 761 MPH. 

In my case, a max takeoff engine RPM would be 5000, which gives me 2940 Prop 
RPM. 

my 76" prop = 6.333' x 3.14 = 58463.722 over 88 = 664 MPH. 


To find the max RPM you can turn a prop (withought breaking the speed of 
sound): 

66,984 Divided by (the distance,in feet, your prop travels in 1 RPM) 

Ex: 66,984 over 18.84' (72" prop) = 3555 RPM Max. 

My case would be: 66984 over 19.896 = 3366 RPM Max prop speed (5722 eng RPM).

Hope it helps. 

Kurt 



In a message dated 12/16/2006 9:06:43 AM Mountain Standard Time, 
MMurp16900 at aol.com writes:
Subject Prop R.P.M.
The other consideration is prop diameter and tip speed.
If the tips go supersonic the prop will not be as efficient.
some racing planes have short diameter props for that reason.
Some aircraft have geared engines and the engine runs at a higher rpm and 
produces more power and the prop turns at munch lower rpm and higher pitch
Mack.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20061216/fe05facb/attachment.html