X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 22 Jun 2008 21:51:17 -0400 Message-ID: X-Original-Return-Path: Received: from smtp1.av-mx.com ([137.118.16.57] verified) by logan.com (CommuniGate Pro SMTP 5.2.3) with ESMTP id 2979387 for lml@lancaironline.net; Sun, 22 Jun 2008 12:24:58 -0400 Received-SPF: pass receiver=logan.com; client-ip=137.118.16.57; envelope-from=pinetownd@volcano.net Received: from DennisDell (65-166-100-250.dsl.volcano.net [65.166.100.250]) (Authenticated sender: pinetownd@volcano.net) by smtp1.av-mx.com (Postfix) with ESMTP id A284B29046A for ; Sun, 22 Jun 2008 12:24:18 -0400 (EDT) X-Original-Message-ID: <1C6ED955A93541229CA03DB2A0026280@DennisDell> From: "Dennis Johnson" X-Original-To: "Lancair Mailing List" Subject: IAS Error X-Original-Date: Sun, 22 Jun 2008 09:23:46 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00D6_01C8D449.AC5A7690" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.5512 This is a multi-part message in MIME format. ------=_NextPart_000_00D6_01C8D449.AC5A7690 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Hi Larry, I'd recommend everyone calibrate their airspeed indicator. It's easy = and fun and a great excuse to get some test pilot flying time. Once = you've done it, you won't need to guess how accurate your IAS is. =20 I used the "four course GPS" method from the following web site: http://www.reacomp.com/true_airspeed/ You need GPS and a somewhat accurate outside air temperature sensor. = (Using the Chelton procedure for measuring the compressibility effect on = temperature, my OAT at cruise speed is 4=B0F higher than ambient due to = "friction" heating. But the conversion from TAS to IAS isn't terribly = sensitive to changes in OAT readings.) I picked a day with relatively calm winds and smooth air and used the = autopilot to fly the four courses. I logged the IAS, TAS, ground speed, = altitude, altimeter setting, and OAT for each course. Back on the = ground, I input the info into the web site's calculator. I ran the = calculator four times, once each with the following courses: 1. north, east, south 2. east, south, west 3. south, west, north 4. west, north, east That gives TAS. To convert to IAS, I used the following web site: http://www.paragonair.com/public/aircraft/calc_TAS.html Enter the data and iterate with different IAS until the solved TAS = equals the amount from the previous step. That is your actual IAS = (well, I suppose it's actually calibrated, or maybe even equivalent, = airspeed, but for this purpose, it's okay to call it IAS). It turns out my IAS was reading low, probably because I body-worked my = Legacy's static ports flush with the fuselage. Legacies with accurate = IAS have static ports that are proud of the surface by 1/32" or so. = Modifying my static ports is on my to do list. Until then, I enjoy a = tail wind almost everywhere I fly! Dennis Johnson Legacy, 140 hours ------=_NextPart_000_00D6_01C8D449.AC5A7690 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable

Hi Larry,

I'd recommend everyone calibrate their airspeed indicator. = It's easy=20 and fun and a great excuse to get some test pilot flying time. = Once you've=20 done it, you won't need to guess how accurate your IAS is.

I used the "four course GPS" method from the following web = site:

http://www.reacomp.com/tru= e_airspeed/

You need GPS and a somewhat accurate outside air temperature = sensor. =20 (Using the Chelton procedure for measuring the compressibility effect on = temperature, my OAT at cruise speed is 4=B0F higher than ambient due to = "friction"=20 heating. But the conversion from TAS to IAS isn't terribly = sensitive to=20 changes in OAT readings.)

I picked a day with relatively calm winds and smooth air and used = the=20 autopilot to fly the four courses. I logged the IAS, TAS, ground = speed,=20 altitude, altimeter setting, and OAT for each course. Back on the = ground,=20 I input the info into the web site's calculator. I ran the = calculator four=20 times, once each with the following courses:

1. north, east, south

2. east, south, west

3. south, west, north

4. west, north, east

That gives TAS. To convert to IAS, I used the following web=20 site:

http://w= ww.paragonair.com/public/aircraft/calc_TAS.html

Enter the data and iterate with different IAS until the solved TAS = equals=20 the amount from the previous step. That is your actual IAS (well, = I=20 suppose it's actually calibrated, or maybe even equivalent, airspeed, = but for=20 this purpose, it's okay to call it IAS).

It turns out my IAS was reading low, probably because I body-worked = my=20 Legacy's static ports flush with the fuselage. Legacies with = accurate IAS=20 have static ports that are proud of the surface by 1/32" or so. = Modifying=20 my static ports is on my to do list. Until then, I enjoy a tail = wind=20 almost everywhere I fly!

Dennis Johnson

Legacy, 140 hours

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