

Jun 18, 2011, 05:30 PM  
Toronto Canada
Joined Dec 2002
5,329 Posts


Jun 18, 2011, 06:05 PM  

Of course!
My setting is far from perfect, it can be improved... any remark is helpful! ImagesView all Images in thread

Jun 18, 2011, 06:43 PM  
USA, ME, Ellsworth
Joined May 2008
16,320 Posts

"..Originally posted by a contributor in 2003..."
Right! You're not trying to distance yourself from that effort by any chance, are you? Jack 
Latest blog entry: Motor Rewinding & Modification...


Jun 18, 2011, 07:25 PM  
USA, ME, Ellsworth
Joined May 2008
16,320 Posts

OK, I can visualize that.
I wonder if you can get an air start on a fuelie that way, and if so how much speed it takes? I got to see a Reeve Aleutian Airways crew do an air start on one motor of a DC4 out on Shemya Island in the Aleutians in 1965. Then I got on the plane and flew away to Adak on it. I always sort of wondered why they made the passengers get off for the air start if it was safe enough to board an airplane with one engine running. Yomgui (or Martyn) if you guys can tell us what the definitions of the variables like "Cf" and "Ct" are in the spreadsheet and graphs it would be interesting. This is pretty much over my head but I am fascinated by the the data and the potential value in it. Of post a link to a sort of propellers 101 lecture... Thanks, Jack 
Latest blog entry: Motor Rewinding & Modification...


Jun 18, 2011, 07:52 PM  
Toronto Canada
Joined Dec 2002
5,329 Posts

The Thrust(Ct) and Power(Cp) coefficients are dimensionless coefficients which allow you to determine propeller thrust and absorbed power if you know the RPM, Pitch and Diameter and the air density (rho).
The coefficients in the TR237 Technical Report are determined using Imperial units (Pounds Thrust  Horsepower). http://hdl.handle.net/2060/19930091305 From the Advance graphs, the Thrust and Power may be determined for any airspeed. On the Advance Curves, the Xaxis may be considered airspeed. The Yaxis gives the value of the coefficients for that airspeed. On the Xaxis the Pitch Speed (RPM X Pitch) is equal to an Advance equal to the Pitch/Diameter ratio. A prop with a P/D ratio of 0.8 has a Pitch Speed (RPM X Pitch) with an Advance of 0.8. The Zero Thrust Speed is equal to the Pitch Speed Advance + 0.2. For a prop with a P/D ratio of 0.8, the Zero Thrust Speed occurs at an Advance of 1.0. 
Jun 18, 2011, 07:55 PM  

This explain Cp, Ct and V/nD... :
http://www.mhaerotools.de/airfoils/index.htm Things are not so easy unfortunately, Cp and Ct increase with rpm. This numbers are useful to predict prop's behavior. 
Jun 18, 2011, 08:50 PM  
USA, ME, Ellsworth
Joined May 2008
16,320 Posts

Martyn, yomgui, et. al.,
Thanks for the help and links. There is some interest there but the math is just too intensive for me. I'm still getting a lot of value out of the way Robert Goble has the prop data at FlyBrushless.com. That is about the level of interest and practicality I enjoy. As a last question, knowing that each different testing setup can change the results a little, if you turn a given prop at a specific RPM with a number of different motors, wouldn't the thrust produced be about the same for every motor? jrb, I like the "hang in there baby!" testing setup, that is one I have used myself. Jack 
Latest blog entry: Motor Rewinding & Modification...


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