From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [FlyRotary] Re: gauges
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Date: Wed, 19 Nov 2003 00:53:36 -0500
Message-ID: <web-2751010@logan.com>
In-Reply-To: <list-2750979@logan.com>
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>>>One of the main criteria for sizing
turbos is the pressure ratio between inlet and outlet, so being able to read
this directly from a gauge is useful to me.   I think Marvin and I will have
to agree to disagree on this.<<<      


I hate having to disagree <g>.  As you mentioned, knowing the pressure ratio 
is "One of the main criteria for sizing turbos..."  The thing I don't get is 
this.... once you've got it sized and installed, what the heck good does it do 
you to know the boost pressure?  There's going to come a point at some 
altitude that you've maxed out the turbo's operation, and even though the 
throttle is wide open the MAP is going to start to diminish... that's your 
critical altitude.  As long as the turbo was properly sized you can't push it 
into the surge zone because there isn't enough exhaust gas available, so boost 
just goes down.  So, my question is simply what good does knowing boost apart 
from MAP do you in a working system?  I can see having that extra data point 
for testing, just to insure that you're operating within the turbo's map and 
getting the kind of efficiency you want and have targeted.  Once that's 
accomplishedd, though, what's the point?  Also, I've never seen a boost gauge 
in any certified turboed airplane I've ever flown (at least none that I 
remember <G>), just MAP gauges.  Sorry if I'm being dense here, but I'm 
obviously missing something.  Help me out.

     <Marv>