X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 12 Dec 2007 10:05:02 -0500 Message-ID: X-Original-Return-Path: Received: from web36605.mail.mud.yahoo.com ([209.191.85.22] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with SMTP id 2577387 for lml@lancaironline.net; Wed, 12 Dec 2007 01:58:40 -0500 Received-SPF: none receiver=logan.com; client-ip=209.191.85.22; envelope-from=wfhannahan@yahoo.com Received: (qmail 27258 invoked by uid 60001); 12 Dec 2007 06:58:00 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:Date:From:Subject:To:MIME-Version:Content-Type:Content-Transfer-Encoding:Message-ID; b=TRCKP+BQDwGz90sO0S8OuUlmkv/bgCHnU+AaZwsq7VLct+bWMo7EoHIe4NuES6APZ2FzNa/O54o8Ti+2Y3yHXG0EXFFBR+MMRvaZeRcWZOpyMYDr+3o1s+AEze8Ho+2Z8tbVVAx019Fs838zAu//7IoDww8D1ARTnylTHHR0SJY=; X-YMail-OSG: NNnSL4wVM1nOSoZztHJPrKUFJOdU.KPMHBlMTvkzXE0LX0_lsQvPGwHSwKr5BX0z92VBfY0Ijhf5V9OeB0DmoTpa2sWT76_x7pGSF6SVS1Ba_JQm.Ug- Received: from [71.208.37.93] by web36605.mail.mud.yahoo.com via HTTP; Tue, 11 Dec 2007 22:58:00 PST X-Original-Date: Tue, 11 Dec 2007 22:58:00 -0800 (PST) From: Bill Hannahan Subject: Computing TAS from GPS tracks X-Original-To: MAIL LANCAIR MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1506530051-1197442680=:26940" Content-Transfer-Encoding: 8bit X-Original-Message-ID: <865201.26940.qm@web36605.mail.mud.yahoo.com> --0-1506530051-1197442680=:26940 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Dave’s method is the simplest and most accurate method I know of. Pick a day with the big H in the sky when winds aloft are low. To find exact wind direction trim the plane for level flight in a shallow bank. Maintain a constant indicated airspeed and watch the groundspeed. It will go through a maximum or minimum as you pass through downwind or upwind. When you see a maximum or minimum write down the track and reverse bank. Keeping indicated airspeed the same, fly through the maximum or minimum again. Write down the track and split the difference to get the wind direction. Make a run upwind and downwind at the same altitude and average the two runs for TAS. Use a safety pilot to help look for traffic. Flying a triangle or box can introduce errors if you fly through a wind gradient. By flying through the same air in both directions you will get a very accurate result. A small variation between wind direction and track will have negligible effect. Or you can just find the wind direction and fly into the wind and then turn 180 and fly out of the wind and just average your groundspeeds. This is also TAS. But it’s tricky finding the wind direction. You need to line up your heading and your track to find it. My GRT in my Legacy was computing a TAS that is 5 knots too high for instance. GRT lets you calibrate this so now its more accurate! Dave T. Legacy RG Regards, Bill Hannahan wfhannahan@yahoo.com --------------------------------- Looking for last minute shopping deals? Find them fast with Yahoo! Search. --0-1506530051-1197442680=:26940 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: 8bit  
 
 
Dave’s method is the simplest and most accurate method I know of.
 
Pick a day with the big H in the sky when winds aloft are low. To find exact wind direction trim the plane for level flight in a shallow bank. Maintain a constant indicated airspeed and watch the groundspeed. It will go through a maximum or minimum as you pass through downwind or upwind.
 
When you see a maximum or minimum write down the track and reverse bank. Keeping indicated airspeed the same, fly through the maximum or minimum again. Write down the track and split the difference to get the wind direction.
 
Make a run upwind and downwind at the same altitude and average the two runs for TAS.
 
Use a safety pilot to help look for traffic.
 
 
Flying a triangle or box can introduce errors if you fly through a wind gradient.
 
By flying through the same air in both directions you will get a very accurate result. A small variation between wind direction and track will have negligible effect.

 
Or you can just find the wind direction and fly into the wind and then turn 180 and fly out of the wind and just average your groundspeeds.  This is also TAS.  But it’s tricky finding the wind direction.  You need to line up your heading and your track to find it.
 
My GRT in my Legacy was computing a TAS that is 5 knots too high for instance.  GRT lets you calibrate this so now its more accurate!
 
Dave T.
Legacy RG
 


Regards,
Bill Hannahan

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