RE: PropMakr program posted

From: John Kagan <john_kagan_at_hotmail.com>
Date: Wed, 7 Oct 2009 22:35:40 -0400

Hi Fred,
 
I plugged in some values that I think are accurate for my F1D. First, I
adjusted the lift and drag coefficients until the average climb angle was as
close to 0 as I could get. Then I played with the prop CL and CD, without
really knowing what I'm doing, until the cord matched what has empirically
worked for me.
 
I have no idea if any this is all correct, but here's what I came up with:
 
165 in2
1.8 g
0.716 0.14
5.8 ft-lb
1600 turns
2220 prop run
 
2 blades
19.5 dia 1 inner blade radius in.
0.55 CL 0.06 CD 0.1 Alpha
 
The resulting prop looks very much like the ones I'm using, except for some
variations in the pitch distribution.
 
I found that if I rotate the calculated blade -5 degrees, I get about 34
inches of pitch for about the middle 6 inches of the blade (coincidentally
what I'm using for a prop block), with the tip and root washing out about 5
degrees. I'm going to try that on my next prop and see how it does.


  _____

From: Fred or Judy Rash [mailto:frash_at_chartertn.net]
Sent: Wednesday, October 07, 2009 4:22 PM
To: Construction Indoor
Cc: Kagan John; drela_at_mit.edu
Subject: PropMakr program posted


Many years ago I tried to write a Larrabee-type prop design program and a
previous version appears in an old NFFS Sympo and later on Don Slusarczyk's
indoor site. Since my program needed work, it was not quickly re-posted onto
this forum.
 
About three years ago John Kagan's F1D in level flight was used as an
example for Prof Mark Drela of MIT and John to design a prop to compare to
John's actual prop. This thread gave some better Cl and Cd values for both
wing and prop blades than I knew about before. I have used everything that I
could from their discussion to help calibrate and improve my old program.
 
Downloading and extracting the posted, zipped file should give you a
readme.doc file and a compiled.exe file to run.
 
Please test and use if you can and give me any feedback that you will.
 
Thank you.
 
Fred Rash
Received on Wed Oct 07 2009 - 19:39:52 CEST