X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 07 Apr 2010 13:41:00 -0400 Message-ID: X-Original-Return-Path: Received: from mail.skywerx.com ([206.123.212.134] verified) by logan.com (CommuniGate Pro SMTP 5.3.5) with ESMTPS id 4212979 for lml@lancaironline.net; Wed, 07 Apr 2010 10:14:35 -0400 Received-SPF: none receiver=logan.com; client-ip=206.123.212.134; envelope-from=aflyer@lazy8.net Received: from mail.skywerx.com (mail.skywerx.com [206.123.212.134]) by mail.skywerx.com (8.12.8/8.12.8) with ESMTP id o37EBkwH020361 for ; Wed, 7 Apr 2010 08:11:46 -0600 Received: from blueroom ([206.123.213.175] helo=blueroom) with IPv4:25 by mail.skywerx.com; 7 Apr 2010 08:11:46 -0600 From: "John Huft" X-Original-To: "'Lancair Mailing List'" References: In-Reply-To: Subject: RE: [LML] Re: fixes for S-TEC 50 alt hold X-Original-Date: Wed, 7 Apr 2010 08:13:55 -0600 X-Original-Message-ID: <033c01cad65c$8f895d80$ae9c1880$@net> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_033D_01CAD62A.44EEED80" X-Mailer: Microsoft Office Outlook 12.0 Thread-Index: AcrWWtRC0Ot+ZMmOQ5exBYpeWEjL9wAAH3Cw Content-Language: en-us X-Assp-ID: mail.skywerx.com (49506-05407) X-Assp-Version: 1.5.1.8(1.0.00) This is a multi-part message in MIME format. ------=_NextPart_000_033D_01CAD62A.44EEED80 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit The most important point to remember for autopilot altitude functions is that there be no "lag" in the static input. Any lag will cause porposing, and the STECs are especially sensitive to this problem. The STC'd install for STECs always include a dedicated static port. If you have too many instruments hooked up to a single static port (especially those pitot-static combined probes with the tiny holes) there will be lag as the pressure changes. This lag will cause classic oscillations in the control system math. One way to address this is to just open up the autopilot static input to cabin pressure, but it will (as has been noted) make it sensitive to vent and cabin heat changes, and also have different errors at various altitudes and airspeeds. The better way is to have a dedicated static port for the autopilot. John Huft RV Spy 2 years part-time spent writing code for TruTrak From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Sky2high@aol.com Sent: Wednesday, April 07, 2010 8:01 AM To: lml@lancaironline.net Subject: [LML] Re: fixes for S-TEC 50 alt hold Colyn, The important point to remember for those components that use static pressure data is that it be "quiet". No airflow burbles to upset what should be a solid reference point. Grayhawk In a message dated 4/7/2010 8:41:42 A.M. Central Daylight Time, colyncase@earthlink.net writes: one other comment on the static source: the a/p doesn't care how accurate the static source is, only that it changes with altitude. Therefore some people have found that (on spam cans) putting a dedicated static port in just for the pressure transducer works well. ...or you can just use the vents to fine tune your altitude.... ------=_NextPart_000_033D_01CAD62A.44EEED80 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

The most important point to remember for autopilot = altitude functions is that there be no “lag” in the static input. Any = lag will cause porposing, and the STECs are especially sensitive to this = problem. The STC’d install for STECs always include a dedicated static = port.

If you have too many instruments hooked up to a single = static port (especially those pitot-static combined probes with the tiny holes) = there will be lag as the pressure changes. This lag will cause classic = oscillations in the control system math.

One way to address this is to just open up the autopilot = static input to cabin pressure, but it will (as has been noted) make it = sensitive to vent and cabin heat changes, and also have different errors at various altitudes and airspeeds. The better way is to have a dedicated static = port for the autopilot.

John Huft

RV Spy

2 years part-time spent writing code for = TruTrak

From:= Lancair = Mailing List [mailto:lml@lancaironline.net] On Behalf Of = Sky2high@aol.com
Sent: Wednesday, April 07, 2010 8:01 AM
To: lml@lancaironline.net
Subject: [LML] Re: fixes for S-TEC 50 alt = hold

Colyn,

The important point to remember for those components that = use static pressure data is that it be "quiet". No airflow = burbles to upset what should be a solid reference point. =

Grayhawk

In a message dated 4/7/2010 8:41:42 A.M. Central Daylight = Time, colyncase@earthlink.net writes:

one other comment on the static source: the a/p doesn't care how accurate the static source is, only that it changes = with altitude. Therefore some people have found that (on spam = cans) putting a dedicated static port in just for the pressure transducer = works well.

...or you can just use the vents to fine tune your = altitude....

------=_NextPart_000_033D_01CAD62A.44EEED80--