Message-ID: <05e601c378d8$3f74e3c0$292dbbd0@7n7z201>
From: "William" <wschertz@ispwest.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2575965@logan.com>
Subject: Re: [FlyRotary] Re: turbo wastegate requirements
Date: Thu, 11 Sep 2003 21:47:45 -0500
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What you are missing is that the atmospheric pressure is pressing on the 2
sq.in. valve in addition to the spring. So as you go up in altitude
atmospheric decreases, and the valve opens sooner.
Bill Schertz
----- Original Message -----
From: "Marvin Kaye" <marv@lancaironline.net>
>
> Since I'm nowhere near completion, this is one of those details that I've
yet
> to work out... all I know is this is the right way to do this job and how
I
> will attempt to setup my system.  It seems to me that if the popoff valve
is
> spring controlled, then it should be a simple thing to size and rate the
> spring to an absolute pressure.  Let's go through this little bit of
theory
> and you let me know where the holes are...
>
> Your recent post explained the relationship between MAP in inches of
mercury
> and PSI of boost, that being 1psi = about 2" MAP.  That says to me that at
36"
> MAP the deck pressure available is 18psi.  Imagine that the popoff valve
face
> has 2 square inches of surface area.  Opposing that 18psi would require 9
> pounds of spring pressure against the 2sqin popoff valve flapper or poppet
or
> whatever mechanical device is used to control the MAP inside the intake
> manifold.  Once the MAP reaches 36" (18psi) the pressure on both sides of
the
> valve flapper are the same... if the MAP goes higher it overpowers the
spring
> and forces the flapper door open, venting the excess pressure beyond
18PSI.
>  If you remember that the "A" in MAP stands for absolute, we are simply
> defining the amount of pressure available inside the manifold.  Since the
> spring rate is an absolute value that is unaffected by ambient pressure
and
> the area of the valve face is fixed, I can see no mechanical reason why
this
> shouldn't work. (This is essentially how the alternate intake air doors
work
> on most of the Lancair IV fleet... if the air filter clogs (ices up) and
> causes a bit of suction inside the air box, the little spring is
overpowered,
> the alt air door opens and allows the intake to breathe using the air
> available inside the cowling.)   It seems a simple problem in mechanics
and
> not one of plumbing, at least to me.  What am I missing?
>
>         <Marv>
>
>
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