X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 28 Aug 2010 18:24:05 -0400 Message-ID: X-Original-Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.120] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4446986 for lml@lancaironline.net; Sat, 28 Aug 2010 14:28:58 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.120; envelope-from=super_chipmunk@roadrunner.com X-Original-Return-Path: X-Authority-Analysis: v=1.1 cv=GBv0B28wak1MsSRQKs6THzeQZLo5xx3+TKfhphPLS1Y= c=1 sm=0 a=zTXaGa_vW44A:10 a=I8zE26c0Y9d50tWaRzAbIg==:17 a=3oc9M9_CAAAA:8 a=Ia-xEzejAAAA:8 a=QAOKg3qtYodIoMQeoJsA:9 a=9M3KKtxSM1CgxK3KgVQA:7 a=uNvaBYtWHYv4fwZyI6oQcaTB4w4A:4 a=wPNLvfGTeEIA:10 a=U8Ie8EnqySEA:10 a=EzXvWhQp4_cA:10 a=7jo6E0DKNekvSV4bDg8A:9 a=L__G4qh0zGn76jv6eqAA:7 a=6g_d11BH1_rguSifx3i8XDSu6a0A:4 a=I8zE26c0Y9d50tWaRzAbIg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.65.190.246 Received: from [74.65.190.246] ([74.65.190.246:53231] helo=Laptop) by cdptpa-oedge03.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id 9A/A0-01206-845597C4; Sat, 28 Aug 2010 18:28:24 +0000 X-Original-Message-ID: <2B28C558CA564F21BA1CDFACAE674212@Laptop> From: "Bill Wade" X-Original-To: "Lancair Mailing List" References: In-Reply-To: Subject: Re: [LML] Re: Pitot System and AOA X-Original-Date: Sat, 28 Aug 2010 14:28:26 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0252_01CB46BD.46D4DE30" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Windows Mail 6.0.6002.18197 X-MIMEOLE: Produced By Microsoft MimeOLE V6.0.6002.18197 This is a multi-part message in MIME format. ------=_NextPart_000_0252_01CB46BD.46D4DE30 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Most jets I've seen have an array of pitots. I'm a lowly PP but I'd be = willing to bet they're connected to independent cockpit displays with = multiple redundancy. Why should jet jockeys have all the toys? I don't think there's any harm in a separate pitot system but I don't = think there would be a great advantage. It would add cost and weight = plus the dedicated AOA pitot would still be subject to blockage and = there could be a signifcant discrepancy between the two systems due to = position error. I bought an Advanced AOA, not yet installed- the AOA is = calibrated as part of the pitot/static system. Trying to switch between = two different pitot sources would probably result in an inaccurate = instrument that could be dangerously misleading. That's my take- it = would be best to ask the manufacturer. That being said, I'll take Grayhawk's comment further: if someone had = a glass panel I think it makes sense to connect the backup instruments = to an independent heated pitot and static system. The price doesn't have = to be crazy- pitots come up on Ebay fairly often and I've accumulated a = few good ones as spares. Another consideration is an alternate static system. I have one = installed- just a simple valve but it would save wear and tear on the = VSI (anyone keep a hammer handy?).=20 If the static port gets blocked with a glass cockpit display what = should be done? Is alternate static usually part of the install or do = you break the backup altimeter? That wouldn't help much in a pressurized = plane. I'd be careful about using GPS groundspeed as a proxy for airspeed. = Groundspeed is affected by wind direction and velocity but the GPS = doesn't know that. It just shows the result. -Bill Wade ----- Original Message -----=20 From: Sky2high@aol.com=20 To: lml@lancaironline.net=20 Sent: Friday, August 27, 2010 4:05 PM Subject: [LML] Re: Pitot System and AOA John, If you are going to be more comfortable with a backup pitot tube, why = not just plumb it to a second airspeed indicator? Will you have pitot = heat on both? The AOA system I use relies on 4 inputs - upper and lower wing = pressures, pitot and static. If I wanted an airspeed backup I would = install another heated pitot and a dedicated line to a separate AI in = order to keep it simple. Otherwise, I am just going to rely on known = power settings cross checked with GPS ground speed and how quickly the = clouds or trees are going by. Scott Krueger In a message dated 8/26/2010 8:06:05 P.M. Central Daylight Time, = JPKleber@aol.com writes: Greetings, I will have an AOA in my Legacy. =20 That said, I am concerned that if for some reason my pitot tube gets = blocked by something like an insect, bird, or other debris, my airspeed = indicator will probably be giving me an erroneous reading. =20 Would not this error also be reflected in the AOA? Therefore, would it not be a good idea to have the AOA on its own = pitot source? And could one tie both pitot tube together so that if one = was blocked, the other would continue to provide pitot pressure? Thank you in advance for your input. John Kleber ------=_NextPart_000_0252_01CB46BD.46D4DE30 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 Most jets I've seen = have an array=20 of pitots. I'm a lowly PP but I'd be willing to bet they're connected to = independent cockpit displays with multiple redundancy. Why should jet = jockeys=20 have all the toys?
 
 I don't think there's any harm in = a separate=20 pitot system but I don't think there would be a great advantage. It = would add=20 cost and weight plus the dedicated AOA pitot would still be subject = to=20 blockage and there could be a signifcant discrepancy between the two = systems due=20 to position error. I bought an Advanced AOA, not yet installed- the AOA = is=20 calibrated as part of the pitot/static system. Trying to switch=20 between two different pitot sources would probably result in = an=20 inaccurate instrument that could be dangerously misleading. That's my=20 take- it would be best to ask the manufacturer.
 
  That being said, I'll take = Grayhawk's=20 comment further: if someone had a glass panel I think it makes = sense=20 to connect the backup instruments to an independent heated pitot = and static=20 system. The price doesn't have to be crazy- pitots come up on Ebay = fairly=20 often and I've accumulated a few good ones as spares.
 
  Another consideration is an = alternate static=20 system. I have one installed- just a simple valve but it would save = wear=20 and tear on the VSI (anyone keep a hammer handy?).=20
 
  If the static port gets blocked = with a glass=20 cockpit display what should be done? Is alternate static usually part of = the=20 install or do you break the backup altimeter? That wouldn't help = much in a=20 pressurized plane.
 
  I'd be careful about = using GPS=20 groundspeed as a proxy for airspeed. Groundspeed is affected = by wind=20 direction and velocity but the GPS doesn't know that. It just shows = the=20 result.  -Bill Wade
----- Original Message -----
From:=20 Sky2high@aol.com=20
Sent: Friday, August 27, 2010 = 4:05=20 PM
Subject: [LML] Re: Pitot System = and=20 AOA

John,
 
If you are going to be more comfortable with a backup pitot tube, = why not=20 just plumb it to a second airspeed indicator?  Will you have = pitot heat=20 on both?
 
The AOA system I use relies on 4 inputs - upper and lower wing = pressures,=20 pitot and static.  If I wanted an airspeed backup I would install = another=20 heated pitot and a dedicated line to a separate AI in order to = keep it=20 simple.  Otherwise, I am just going to rely on known power = settings cross=20 checked with GPS ground speed and how quickly the clouds or trees are = going=20 by.
 
Scott Krueger
 
In a message dated 8/26/2010 8:06:05 P.M. Central Daylight Time,=20 JPKleber@aol.com writes:
Greetings,
 
I will have an AOA in my Legacy. 
 
That said, I am concerned that if for some reason my = pitot tube=20 gets blocked by something like an insect, bird, or other debris, my = airspeed=20 indicator will probably be giving me an erroneous reading. =20
 
Would not this error also be reflected in the=20 AOA?
 
Therefore, would it not be a good idea to have the AOA = on its=20 own pitot source?  And could one tie both pitot tube together = so that=20 if one was blocked, the other would continue to provide pitot=20 pressure?
 
Thank you in advance for your input.
 
John Kleber
 
=
 
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