Message-ID: <000b01bf082e$f89511a0$0200a8c0@Gnaf>
From: "Paul A. Nafziger" <naf@tminet.com>
To: <lancair.list@olsusa.com>
References: <19990926040139.AAA13213@truman.olsusa.com>
Subject: Re:Erring OAT's;  aileron trim tabs
Date: Sun, 26 Sep 1999 07:54:01 -0700
Mime-Version: 1.0

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> Erring OAT's.
> Same problem; different location.
>  Mine is mounted in the top wall of the carb box after the ram air inlet.
It
> always reads high.
> I cannot believe there is much heated air on the INSIDE of the carb air
box - at
> least not in flight. So I assume the bias is due to the sensor BODY being
too
> warm - being in the down flow of air which has just recently departed the
> cylinders and not yet escaped the cowling.

I believe you're seeing the temperature rise from ram recovery.  P=RT/D,
where P=pressure, R=the universal gas constant, and D=density.  If you take
a parcel of air and raise the pressure, the temperature will rise.  This
makes it pretty difficult to locate temperature sensors on aircraft.  The
big boys build probes that shade the sensor and keep pressure differences
from the free stream to a minimum.

The probe needs to be in the shade, but I suspect the pressure changes even
under the wing will affect the reading somewhat.  I think I'll try mine
under the fuselage about even with the static ports.

Naf

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