X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 27 Sep 2008 22:09:42 -0400 Message-ID: X-Original-Return-Path: Received: from blu0-omc3-s31.blu0.hotmail.com ([65.55.116.106] verified) by logan.com (CommuniGate Pro SMTP 5.2.8) with ESMTP id 3189688 for lml@lancaironline.net; Sat, 27 Sep 2008 18:21:29 -0400 Received-SPF: pass receiver=logan.com; client-ip=65.55.116.106; envelope-from=scottekeighan@sympatico.ca Received: from BLU0-SMTP9 ([65.55.116.73]) by blu0-omc3-s31.blu0.hotmail.com with Microsoft SMTPSVC(6.0.3790.3959); Sat, 27 Sep 2008 15:20:48 -0700 X-Originating-IP: [69.157.114.68] X-Originating-Email: [scottekeighan@sympatico.ca] X-Original-Message-ID: X-Original-Return-Path: scottekeighan@sympatico.ca Received: from your4dacd0ea75 ([69.157.114.68]) by BLU0-SMTP9.blu0.hotmail.com over TLS secured channel with Microsoft SMTPSVC(6.0.3790.2668); Sat, 27 Sep 2008 15:20:47 -0700 Reply-To: "Scott Keighan" From: "Scott Keighan" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: Legacy Static Port Fix X-Original-Date: Sat, 27 Sep 2008 18:20:27 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001B_01C920CD.B797E760" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3350 X-OriginalArrivalTime: 27 Sep 2008 22:20:48.0128 (UTC) FILETIME=[4AD16800:01C920EF] This is a multi-part message in MIME format. ------=_NextPart_000_001B_01C920CD.B797E760 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Another easy solution is to place a dab of clear silicone in front of = the static hole. This disturbs the boundry layer and can be trimed with a sharp knife til = the=20 correct airspeed is achieved. I've used this method on both of my planes and has worked perfectly. Scott Keighan LIV 75hrs=20 ----- Original Message -----=20 From: J H Webb=20 To: lml@lancaironline.net=20 Sent: Saturday, September 27, 2008 8:21 AM Subject: [LML] Re: Legacy Static Port Fix Dennis, Another nice side effect is to reduce the amount of water that gets = into the static system, when the airplane is overnighted out in the = rain. Jack Webb ----- Original Message ---- From: Dennis Johnson To: lml@lancaironline.net Sent: Friday, September 26, 2008 12:10:35 PM Subject: [LML] Legacy Static Port Fix As most of the Legacy pilots know, if the Legacy's static ports are = flush with the outside skin of the fuselage, the indicated airspeed will = most likely be erroneously low. I thought I was doing the right thing = by making mine flush when I installed them, but when I started flying, I = noticed that I almost always had a tailwind! Flying the four-way GPS = groundspeed check, my indicated airspeed was 13 knots too low. That = error was enough to make the Chelton computed winds meaningless.=20 Here's the link for the four-way GPS airspeed calculator: http://www.reacomp.com/true_airspeed/ I experimented with temporarily taping button head rivet heads over = the static ports, which seemed to solve the problem. A friend machined = some nice "buttons" that I bonded to the fuselage over the top of the = existing, flush, static ports. I flew the four-way GPS groundspeed = check this morning and my IAS is now three or four knots too high, which = is an error that's too small for me to chase down. I'm declaring it = fixed. The buttons are machined aluminum, 3/8" in diameter, with a convex = face that's .067" thick at the center, tapering down to a thin (but not = sharp) edge. The hole in the center is .063" in diameter. I painted = them the color of the fuselage and bonded them in place with = epoxy/micro/Cabo-Sil. The 3/8" diameter is much larger than it needs to = be, but that size was easy to machine and easy for me to bond in place. It appears there is a very thin boundary layer of disturbed (high = pressure) air along the fuselage skin at the location of the static = ports, which causes flush static ports to read erroneously high pressure = (and therefore low airspeed). The new buttons moved the static ports = far enough away from the fuselage skin that it is outside the disturbed = air. It surprised me that .067" is far enough to get outside the = boundary layer, but it works, so I guess it must be. =20 If you don't have a machinist friend, button head rivet heads, with = the shaft punched out, work fine. Double-sided clear Scotch tape will = hold them on for at least one test flight. Fly safe, Dennis Legacy, 198 hours ------=_NextPart_000_001B_01C920CD.B797E760 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Another easy solution is to place a dab = of clear=20 silicone in front of the static hole.
This disturbs the boundry layer and can = be trimed=20 with a sharp knife til the
correct airspeed is = achieved.
 
I've used this method on both of my = planes and has=20 worked perfectly.
 
Scott Keighan
LIV 75hrs 
----- Original Message -----
From:=20 J H = Webb=20
Sent: Saturday, September 27, = 2008 8:21=20 AM
Subject: [LML] Re: Legacy = Static Port=20 Fix

Dennis,

 

   Another nice side effect is to reduce the amount of = water that=20 gets into the static system, when the airplane is overnighted out = in the=20 rain.

 

Jack Webb



-----=20 Original Message ----
From: Dennis Johnson <pinetownd@volcano.net>
To= : lml@lancaironline.net
Sent: = Friday,=20 September 26, 2008 12:10:35 PM
Subject: [LML] Legacy Static Port=20 Fix

As most of the Legacy pilots know, if the Legacy's static ports = are flush=20 with the outside skin of the fuselage, the indicated airspeed will = most likely=20 be erroneously low.  I thought I was doing the right thing by = making mine=20 flush when I installed them, but when I started flying, I noticed that = I=20 almost always had a tailwind!  Flying the four-way GPS = groundspeed check,=20 my indicated airspeed was 13 knots too low.  That error was = enough to=20 make the Chelton computed winds meaningless.
 
Here's the link for the four-way GPS airspeed calculator:
 
I experimented with temporarily taping button head rivet heads = over the=20 static ports, which seemed to solve the problem.  A friend = machined=20 some nice "buttons" that I bonded to the fuselage over the top of = the=20 existing, flush, static ports.  I flew the four-way GPS = groundspeed check=20 this morning and my IAS is now three or four knots too high, which is = an error=20 that's too small for me to chase down.  I'm declaring it = fixed.
 
The buttons are machined aluminum, 3/8" in diameter, with a = convex=20 face that's .067" thick at the center, tapering down to a thin = (but not=20 sharp) edge.  The hole in the center is .063" in diameter.  = I=20 painted them the color of the fuselage and bonded them in = place with=20 epoxy/micro/Cabo-Sil.  The 3/8" diameter is much larger than it = needs to=20 be, but that size was easy to machine and easy for me to bond in = place.
 
It appears there is a very thin boundary layer of disturbed (high = pressure) air along the fuselage skin at the location of the static = ports,=20 which causes flush static ports to read erroneously high = pressure=20 (and therefore low airspeed).  The new buttons moved the static=20 ports far enough away from the fuselage skin that it is outside = the=20 disturbed air.  It surprised me that .067" is far enough to get = outside=20 the boundary layer, but it works, so I guess it must be.  =
 
If you don't have a machinist friend, button head rivet heads, = with the=20 shaft punched out, work fine.  Double-sided clear Scotch = tape will=20 hold them on for at least one test flight.
 
Fly safe,
Dennis
Legacy, 198 = hours

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