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 web53702.mail.re2.yahoo.com ([206.190.37.23] verified) by logan.com (CommuniGate Pro SMTP 5.2.3) with SMTP id 2979874 for lml@lancaironline.net; Sun, 22 Jun 2008 19:11:26 -0400 Received: (qmail 86569 invoked by uid 60001); 22 Jun 2008 23:11:25 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Received:X-Mailer:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type:Message-ID; b=SbgacqT5LSe+3HqfljdobJZmTmBDHbbYsuzjAtA2O0Gs8mbZlRYJfctdnqioY21VuJE4inHojZn1aDRIx6sPro9rPnxq4iYDQQQh48tMB7yao3EwFlffYZn5t7qO06lZxDP2e9MViHrPDfhf7z09QBriuYrbQ7qU19fcmGCbBNQ=; Received: from [66.32.25.196] by web53702.mail.re2.yahoo.com via HTTP; Sun, 22 Jun 2008 16:11:24 PDT X-Mailer: YahooMailWebService/0.7.199 X-Original-Date: Sun, 22 Jun 2008 16:11:24 -0700 (PDT) From: Kyrilian Dyer Reply-To: kyrilian_av@yahoo.com Subject: Re: [LML] IAS Error/ Trouble shooting tips? X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1374787220-1214176284=:86262" X-Original-Message-ID: <40745.86262.qm@web53702.mail.re2.yahoo.com> --0-1374787220-1214176284=:86262 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Larry, The pitot-static check only evaluates whether the instruments themselves fu= nction properly and whether there are leaks in the lines between the test g= ear and the instruments.=A0 Errors caused by the location of the pitot and = static probes on the aircraft and in the airflow can not be checked on the = ground.=A0 In TC'd light airplanes 14 CFR 23.1323 requires that the error b= e known and and not exceed 3% of calibrated airspeed or 5 knots, whichever = is greater (during certain phases of flight).=A0 The error, shown in the fo= rm of a plot or table of calibrated vs indicated airspeed is found in the P= OH of TC'd airplanes. As far as I know, this is yet another case where we experimental builders a= re left to our own devices to calibrate (or not) as we wish.=A0 This is one= prime reason to question the fantastic claims of high airspeed that some p= roud builders make. To calibrate, I'd suggest running some GPS legs and use the spreadsheet sho= wn on this page (http://www.ntps.edu/HTML/Downloads/) to determine true air= speed.=A0 You'll simply pick an airspeed and maintain altitude and heading = and read the GPS groundspeed.=A0 Then, holding the exact same airspeed, rep= eat at two significantly different headings and punch the numbers into the = spreadsheet.=A0 Don't forget to record pressure altitude and temperature.= =A0 Then, using the measured true airspeed (what comes out of the Excel spr= eadsheet) and the temperature and altitude, one can calculate calibrated ai= rspeed.=A0 The 'position error' is simply the difference between this calib= rated airspeed and the indicated airspeed read during the level flight poin= ts corrected for instrumentation error (as determined by the pitot-static c= hecks).=A0 This should be done for a few representative airspeeds in level = flight (100, 150, 180, etc) since the error isn't usually constant. If you need any help with this, lemme know. =A0Cheers, - Kyrilian --- On Sun, 6/22/08, Larry Henney wrote: From: Larry Henney Subject: [LML] IAS Error/ Trouble shooting tips? To: lml@lancaironline.net Date: Sunday, June 22, 2008, 10:37 AM =20 Gents, =A0 I flew formation=20 with a 320 today that had an IAS 20 kts above mine in welded wing.=A0 The= =20 weird part was that the a/c had an IFR pitot/static transponder cert less t= han a=20 month ago.=A0 Additionally, the internal static port was found to be loose= =20 and the shop reattached it and certified the installation.=A0 Meanwhile the= =20 airspeed indicator was sent out for check out and was yellow tagged with no= =20 problem found. =A0 What is wrong with=20 my buddies airspeed system?=A0 Inquiring minds need to=20 know. =A0 TIA for helping us=20 mitigate trouble shooting. =A0 Larry=20 Henney N360LH IAS within a couple=20 kts of a dozen other planes.=0A=0A=0A --0-1374787220-1214176284=:86262 Content-Type: text/html; charset=us-ascii
Larry,

The pitot-static check only evaluates whether the instruments themselves function properly and whether there are leaks in the lines between the test gear and the instruments.  Errors caused by the location of the pitot and static probes on the aircraft and in the airflow can not be checked on the ground.  In TC'd light airplanes 14 CFR 23.1323 requires that the error be known and and not exceed 3% of calibrated airspeed or 5 knots, whichever is greater (during certain phases of flight).  The error, shown in the form of a plot or table of calibrated vs indicated airspeed is found in the POH of TC'd airplanes.

As far as I know, this is yet another case where we experimental builders are left to our own devices to calibrate (or not) as we wish.  This is one prime reason to question the fantastic claims of high airspeed that some proud builders make.

To calibrate, I'd suggest running some GPS legs and use the spreadsheet shown on this page (http://www.ntps.edu/HTML/Downloads/) to determine true airspeed.  You'll simply pick an airspeed and maintain altitude and heading and read the GPS groundspeed.  Then, holding the exact same airspeed, repeat at two significantly different headings and punch the numbers into the spreadsheet.  Don't forget to record pressure altitude and temperature.  Then, using the measured true airspeed (what comes out of the Excel spreadsheet) and the temperature and altitude, one can calculate calibrated airspeed.  The 'position error' is simply the difference between this calibrated airspeed and the indicated airspeed read during the level flight points corrected for instrumentation error (as determined by the pitot-static checks).  This should be done for a few representative airspeeds in level flight (100, 150, 180, etc) since the error isn't usually constant.

If you need any help with this, lemme know.

 Cheers,
- Kyrilian

--- On Sun, 6/22/08, Larry Henney <LHenney@charter.net> wrote:
From: Larry Henney <LHenney@charter.net>
Subject: [LML] IAS Error/ Trouble shooting tips?
To: lml@lancaironline.net
Date: Sunday, June 22, 2008, 10:37 AM

Gents,
 
I flew formation with a 320 today that had an IAS 20 kts above mine in welded wing.  The weird part was that the a/c had an IFR pitot/static transponder cert less than a month ago.  Additionally, the internal static port was found to be loose and the shop reattached it and certified the installation.  Meanwhile the airspeed indicator was sent out for check out and was yellow tagged with no problem found.
 
What is wrong with my buddies airspeed system?  Inquiring minds need to know.
 
TIA for helping us mitigate trouble shooting.
 
Larry Henney
N360LH
IAS within a couple kts of a dozen other planes.

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