Mailing List flyrotary@lancaironline.net Message #3257
From: Ken Welter <rotary.coot@verizon.net>
Subject: Re: [FlyRotary] turbo math
Date: Tue, 23 Sep 2003 14:57:10 -0700
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Re: [FlyRotary] turbo math
 Them numbers are flat scary to my but I just read a chart on a Navaho that gave a temp of 350 degrees at 40 inches on a hot day, it didn't say what the temp was on a hot day.

 Ken welter




Greetings,
 
I did some searching around, and found the basic gas formulas at this page- 
http://www.pmel.org/HandBook/HBpage20.htm
 
For my measured temps:
 
MAP / temp F / RPM
18" / 105 / 3000
20" / 128 / 4225
30" / 167 / 5000
36" / 196 / 5500
40" / 214 / 5700
44" / 228 / 5800
 
It appears that at my 36" MAP boost level, I have the same air density that I would have at NA, on the same 90F ambient day. 
 
Unfortunately, this air density is only part of the problem.  I'm guessing that exhaust backpressure is as much, if not more of an issue.  This leaves me still thinking that I'll need 5-6 psi of boost to break even with a good NA engine, but I'm becoming more comfortable with those figures.  
 
Rusty (off to the hanger to see if I can find a place for Mr. intercooler) 
 

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