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 smtp118.sbc.mail.sp1.yahoo.com ([69.147.64.91] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with SMTP id 2575743 for lml@lancaironline.net; Tue, 11 Dec 2007 03:40:13 -0500 Received-SPF: none receiver=logan.com; client-ip=69.147.64.91; envelope-from=elippse@sbcglobal.net Received: (qmail 70370 invoked from network); 11 Dec 2007 08:39:34 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=sbcglobal.net; h=Received:X-YMail-OSG:Message-ID:From:To:Subject:Date:MIME-Version:Content-Type:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=tp3alov1zGKhSC3wjUEtrDOBxne+1kwDFJDFez36nZfy0KqBeGCtIuB8/epyRJHKrJwV9Z7yQvBOm/d5r8pzC+jEGWVOKOX2gNJDCVImDnxC4LGCGQ3jgGR2J6IRoxLyrftMqXoBsgMnm+Li76D6Oo8oUUlrG/YHrLnIAyxuWz8= ; Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@75.15.114.199 with login) by smtp118.sbc.mail.sp1.yahoo.com with SMTP; 11 Dec 2007 08:39:33 -0000 X-YMail-OSG: 4F4un3gVM1k3ZgCD0YfzWlI8L.1XpSHDO0cMOONinu0kV1avTEV.pICzittnMcopXN3fNgi1XA-- X-Original-Message-ID: <000801c83bd1$6db03fd0$c7720f4b@Computerroom> From: "Paul Lipps" X-Original-To: "Marv Kaye" Subject: TAS from GPS X-Original-Date: Tue, 11 Dec 2007 00:40:01 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0005_01C83B8E.5DB02980" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 This is a multi-part message in MIME format. ------=_NextPart_000_0005_01C83B8E.5DB02980 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Without going into the math, to obtain TAS from two-way GPS = ground-speed runs, 1mph error will come from the following = wind-speed/directions for the listed TAS: 200 mph TAS, 20mph@/87deg.; = 250 mph TAS, 25mph@ 63 deg.: 300 mph TAS, 25 mph@ 78 deg. So don't sweat = the wind speed if the forecast is for less than 25 mph. Use the forecast = wind and direction and fly a GPS TRACK into and with the wind, then = average the ground-speed results. Don't forget to convert the forecast = wind direction, which is relative to true north, to magnetic north. = Nothing could be simpler! Here's something else. Note your altitude = reading on the ground, then fly a low pass down the runway and check the = altitude you get when flying at some estimated height. If it's not the = same, you've got an in-flight static error, which you can correct with a = slight obstruction ahead of the static port for an altitude error higher = than estimated or just behind the port for an altitude error lower than = estimated. About 1/32" obstruction will give about 5mph error at 200 mph. ------=_NextPart_000_0005_01C83B8E.5DB02980 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
Without going into the math, to obtain TAS = from =20 two-way GPS ground-speed runs, 1mph error will come from = the following=20 wind-speed/directions for the listed TAS: 200 mph TAS, = 20mph@/87deg.; 250=20 mph TAS, 25mph@ 63 deg.: 300 mph TAS, 25 mph@ 78 deg. So don't sweat the = wind=20 speed if the forecast is for less than 25 mph. Use the forecast wind and = direction and fly a GPS TRACK into = and=20 with the wind, then average the ground-speed results. Don't forget = to=20 convert the forecast wind direction, which is relative to true north, to = magnetic north. Nothing could be simpler! Here's something else. Note = your=20 altitude reading on the ground, then fly a low pass down the runway and = check=20 the altitude you get when flying at some estimated height. If it's not = the same,=20 you've got an in-flight static error, which you can correct with a = slight=20 obstruction ahead of the static port for an altitude error higher = than=20 estimated or just behind the port for an altitude error lower = than=20 estimated. About 1/32" obstruction will give about 5mph error at = 200=20 mph.
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