X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 02 Jan 2008 16:55:19 -0500 Message-ID: X-Original-Return-Path: Received: from mta16.adelphia.net ([68.168.78.211] verified) by logan.com (CommuniGate Pro SMTP 5.2c4) with ESMTP id 2627780 for lml@lancaironline.net; Wed, 02 Jan 2008 09:10:04 -0500 Received-SPF: pass receiver=logan.com; client-ip=68.168.78.211; envelope-from=glcasey@adelphia.net Received: from [75.82.218.90] by mta16.adelphia.net (InterMail vM.6.01.05.04 201-2131-123-105-20051025) with ESMTP id <20080102140922.CEUO7875.mta16.adelphia.net@[75.82.218.90]> for ; Wed, 2 Jan 2008 09:09:22 -0500 Mime-Version: 1.0 (Apple Message framework v752.2) In-Reply-To: References: Content-Type: multipart/alternative; boundary=Apple-Mail-1--215054929 X-Original-Message-Id: <775D1C51-2102-4E93-A6BE-532E2866190B@adelphia.net> From: Gary Casey Subject: Re: First dumb question of the year... X-Original-Date: Wed, 2 Jan 2008 06:09:20 -0800 X-Original-To: "Lancair Mailing List" X-Mailer: Apple Mail (2.752.2) --Apple-Mail-1--215054929 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed A pretty logical question actually. The gyro AI has small "pendulums" hanging from the side of the gyro cage and they sense gravity, deflecting an air jet to bring the gyro "upright" and keep it there. Their response is slow enough that during normal maneuvers they don't affect the attitude. That's also how it initially assumes an upright posture. The short answer is that the gyro isn't referenced to "space", but is referenced to gravity and therefore will follow the Earth's rotation. Presumably one could enter a shallow coordinated bank and keep it long enough for the gyro to eventually show a wings-level indication. I think. One of the failure modes is for the AI to gradually rotate in pitch or roll (I've had it happen) a full 360. This is usually caused by one of the pendulums getting stuck. Neither the yaw rate gyro or the heading indicator have these pendulums. If you have a really good heading gyro you might notice that the precession rate is different going north than when going south because of the effect you mention. A good question coming from an ES builder - after all, we don't have all those landing gear questions to ask :-) Gary Casey ES #157 > > From: "rtitsworth" > Date: January 1, 2008 12:49:33 PM PST > To: lml@lancaironline.net > Subject: First dumb question of the year... > > > > Happy new year, > > So, I was sitting around thinking silly thoughts (when I probably > should > have been building) and it occurred to me that gyroscopic instruments > essentially attempt to maintain a constant reference frame (in > space) from > which to measure changes in attitude, heading, etc. So, over time, > shouldn't the rotation of the earth cause the gyro to indicate a > change > (error) relative to earth's horizon. i.e. An attitude indicator in an > airplane sitting on the equator and facing west (or east) should > progressively pitch up (or down) at about 15 degrees per hour > (360deg/24hrs). That's a bunch. > > Likewise, the attitude indicator of a south (or north) facing > airplane on > the equator would indicate a roll at the same rate. Likewise, the > DG of an > stationary airplane sitting at the north (or south) pole would react > similarly. Likewise, at all other latitudes and orientations a mix > of the > above effects would seem to be at play. > > Hmmmm. Any insights? > > For BrentR, AHRS work differently (by measuring and integrating > changes in > accelerations over time???), but it seems they would ultimately be > subject > to the same effect? > > Rick Titsworth > --Apple-Mail-1--215054929 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1 A pretty logical question actually. =A0The gyro AI has small "pendulums" = hanging from the side of the gyro cage and they sense gravity, = deflecting an air jet to bring the gyro "upright" and keep it there. = =A0Their response is slow enough that during normal maneuvers they don't = affect the attitude. =A0That's also how it initially assumes an upright = posture. =A0The short answer is that the gyro isn't referenced to = "space", but is referenced to gravity and therefore will follow the = Earth's rotation. =A0Presumably one could enter a shallow coordinated = bank and keep it long enough for the gyro to eventually show a = wings-level indication. =A0I think. =A0One of the failure modes is for = the AI to gradually rotate in pitch or roll (I've had it happen) a full = 360. =A0This is usually caused by one of the pendulums getting stuck. = =A0Neither the yaw rate gyro or the heading indicator have these = pendulums. =A0If you have a really good heading gyro you might notice = that the precession rate is different going north than when going south = because of the effect you mention.

A good question coming = from an ES builder - after all, we don't have all those landing gear = questions to ask :-)

Gary Casey
ES = #157

From: "rtitsworth" <rtitsworth@mindspring.com>= ;
Date: January 1, 2008 12:49:33 PM = PST
To: lml@lancaironline.net
Subject: First dumb question of the = year...


Happy = new year,

So, I was sitting around thinking silly thoughts = (when I probably should
have been = building) and it occurred to me that gyroscopic instruments
essentially attempt to maintain a constant reference = frame (in space) from
which to measure changes in = attitude, heading, etc.=A0 = So, over time,
shouldn't the rotation of = the earth cause the gyro to indicate a change
(error) relative to earth's horizon.=A0 i.e. An attitude indicator in = an
airplane sitting on the equator and facing west = (or east) should
progressively pitch up (or down) = at about 15 degrees per hour
=A0 That's = a bunch.

Likewise, the attitude indicator of a south (or = north) facing airplane on
the equator = would indicate a roll at the same rate.=A0 Likewise, the DG of = an
stationary airplane sitting at the north (or = south) pole would react
=A0 Likewise, = at all other latitudes and orientations a mix of the
above effects would seem to be at play.

=A0 Any = insights?

For BrentR, AHRS work differently (by measuring and = integrating changes in
accelerations over = time???), but it seems they would ultimately be subject
to the same effect?

Rick = Titsworth