Sender: <marv@lancaironline.net>
To:  lml@lancaironline.net
Date: Mon, 05 Nov 2012 11:39:09 -0500
Message-ID: <redirect-5862836@logan.com>
Received-SPF: pass
 receiver=logan.com; client-ip=204.186.29.65; envelope-from=liegner@ptd.net
From: jeffrey liegner <liegner@ptd.net>
Subject: Re: Performance Data Walter Engine (and properly calibrated OAT Sensor)
In-Reply-To: <deffaae4-03a6-4bc9-b58c-9089c80df7e9@mb7.mailnet.ptd.net>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0

I've been reading everyone's postings about True Airspeed (TAS) and I have to ask: are you absolutely certain that your OAT probe is accurately reading the outside air temperature?  

Without proper EFIS calibration, or due thermal (engine) contamination and also air compressibility, an OAT that reports higher than the real temperature will produce an erroneously calculated TAS that is remarkably higher than actual.  

This will also throw off the wind speed/direction calculations derived from TAS vs Ground Speed (GS) which is presented on your EFIS.  As an added footnote, a PIREP using erroneous OAT and report on Winds that is fundamentally incorrect is a disservice to other pilots who might rely on your report for their decision making.

I recently went through some self-study on this subject, and have recalibrated my Chelton's "Temperature Recovery" to more accurately read the OAT (based on recent NOAA soundings at altitude), and thus to more accurately present winds and TAS.  The change in OAT/TAS/Winds is notable, and like many men, I discovered my TAS was not as ample as I previously thought.

This recalibration is only applicable at the same power settings in level flight, so OAT in climb does not equal descent.

Based on my personal experience, I am now very suspicious when I read high TAS, particularly at lower power settings in the flight levels. 

Jeff L
LIVP