Mailing List flyrotary@lancaironline.net Message #28796
From: David Carter <dcarter11@sbcglobal.net>
Subject: Re: [FlyRotary] Re: Props
Date: Tue, 27 Dec 2005 17:45:41 -0700
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Bob, I think something along the way stripped the .exe file from your e-mail - it substituted a short "text" file that said the .exe file had been deleted - if the file is needed, then have the sender send it as a .zip file.
 
I did a google search for this program and found all the links "broken" except for one that has the full set of DOS files in a zip file named PROP OPTIMIZER (tm) PROPELLER DESIGN PROGRAM Copyright 1993 Donald R. Bates  I unzipped just the readme file and got the file name and Bates' Calif business info - phone was disconnected.
 
For those of us who have "graduated" to WinXP (which handles DOS programs in a "figure it out yourself" mode - I run WordPerfect 6.0a for DOS in a "cmd" window with some batch file that I accidentally cobbled together and works) I'm not sure exactly how to run such a DOS program as this prop optimizer.
 
Have I found the program you are talking about?  If so, the link to download the zip file(s) is:
http://cd.textfiles.com/swheaven3/SCIENG/  and scroll down to PROP90.ZIP - has 19 files zipped in it.
(I Googled prop90.zip and the 3rd link was active)
 
Then I Googled prop20.zip and got Version 2.0 (the other was V1), downloaded from
"PROP OPTIMIZER (tm) is NOT a public domain program.  It is copyrighted by
Donald R. Bates dba Bates Engineering/Software."  (from VENDINFO.DIZ changed to a .txt file so it could be read.)
 
David Carter
----- Original Message -----
Sent: Tuesday, December 27, 2005 4:24 PM
Subject: [FlyRotary] Re: Props

Attached is a Prop Design program, which I found some time ago, that has the following explanation on its help page. You can play with the numbers to match your prop and see what speed you will get or you can plug in the variables and see what size prop you should have.  I hope you can receive the attached file.

 

 

 


From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Thursday, December 22, 2005 7:46 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Props

 

I really do not know, George.  I have known folks with aircraft speeds somewhat faster than the "screw" calculations would have predicted - perhaps this "lift" factor played a role.  Most figures I have seen puts efficient of prop around 80-85% mostly around 80.

 

Ed

----- Original Message -----

Sent: Thursday, December 22, 2005 4:45 AM

Subject: [FlyRotary] Re: Props

 

Thanks Ed,

I like to reduce things down to the simplest formula, provided one doesn't lose track of what's relevant.

So I guess I should look at this as 100 % theoretically efficient - whereas we may be looking at only 80 % efficiency ( in real terms), Do you agree with 80%?

However your saying that the lift may give more speed ( MPH, in real terms) - So are you suggesting that these two (variables) may balance out?

 

Or should we use a fudge factor, and that could be what?

 

I'm not looking for a finite answer, just close enough to be able to access the experts opinion, and we all know what an expert is - " A drip under pressure".

 

George (down under)

Yes, George.  If we assumed no slip in the prop then theoretically the formula will give you the pitch of the prop you would need to screw through the air and achieve your MPH at your RPM input.  This is based simply on the screw principal.  I am certainly not a prop expert, but I also believe that since the prop is  a spinning wing (airfoil), that there is a lift component  in the direction of flight which may result in more speed than the formula could account for.  

 

Your second equation can be reduced further from   (Inches/Minute)/(RPM) = (Inches/Minute)/(Revs/Minute) = inches/Rev

 

Ed A

 


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