X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 05 Jun 2008 09:32:05 -0400 Message-ID: X-Original-Return-Path: Received: from QMTA07.emeryville.ca.mail.comcast.net ([76.96.30.64] verified) by logan.com (CommuniGate Pro SMTP 5.2.3) with ESMTP id 2953437 for lml@lancaironline.net; Wed, 04 Jun 2008 14:51:58 -0400 Received-SPF: pass receiver=logan.com; client-ip=76.96.30.64; envelope-from=j.hafen@comcast.net Received: from OMTA06.emeryville.ca.mail.comcast.net ([76.96.30.51]) by QMTA07.emeryville.ca.mail.comcast.net with comcast id Zr0d1Z00T16AWCUA70LP00; Wed, 04 Jun 2008 18:51:02 +0000 Received: from [10.128.88.85] ([206.191.160.125]) by OMTA06.emeryville.ca.mail.comcast.net with comcast id Zuqk1Z00G2idoaN8S00000; Wed, 04 Jun 2008 18:51:00 +0000 X-Authority-Analysis: v=1.0 c=1 a=XyI06yiW-0z4GhbeZwAA:9 a=oE42nLHBLpDr0JqPxPAA:7 a=h6vjWaTaOrpesjZCKYgVJzlsT5wA:4 a=AQ7_5bujvoIA:10 a=EzXvWhQp4_cA:10 a=pQ5v7ofoLL0A:10 a=hm2zs9liTaIJgmrZXAAA:9 a=1wuS_keAv7a2H_YjdHsA:7 a=i7z_sNfhzKrExxYDThZfJ_uejtUA:4 a=Sz-0p1zU2dQA:10 User-Agent: Microsoft-Entourage/12.10.0.080409 X-Original-Date: Wed, 04 Jun 2008 11:50:44 -0700 Subject: Re: [LML] Re: Selecting an EFIS From: John Hafen X-Original-To: Lancair Mailing List X-Original-Message-ID: Thread-Topic: [LML] Re: Selecting an EFIS Thread-Index: AcjGc+SqtNCNuREupkSFeNKl18lHow== In-Reply-To: Mime-version: 1.0 Content-type: multipart/alternative; boundary="B_3295425060_458725" > This message is in MIME format. Since your mail reader does not understand this format, some or all of this message may not be legible. --B_3295425060_458725 Content-type: text/plain; charset="ISO-8859-1" Content-transfer-encoding: quoted-printable Are any of you aware of an independent, stand-alone, self powered attitude back-up system? I was looking at the Garmin 495. Its panel page shows heading, bank angle, and vertical speed. So I assume with a little concentration, that would allow a guy to approximate straight and level flight. But there is no =B3attitude indicator.=B2 Is there something out there better than the 495? John Hafen On 6/4/08 4:50 AM, "Chuck Jensen" wrote: > If I ever decide to fly in circles for a long time, I will be sure to buy= a > Chelton. > =20 > Chuck Jensen=20 >> =20 >> -----Original Message----- >> From: Lancair Mailing List [mailto:lml@lancaironline.net]On Behalf Of B= rent >> Regan >> Sent: Tuesday, June 03, 2008 7:32 PM >> To: lml@lancaironline.net >> Subject: [LML] Re: Selecting an EFIS >>=20 >> Rick writes: >>=20 >> "... some EFIS systems (especially the inexpensive ones) derive their >> attitude depiction data from GPS and pitot data. In other words, if you= lose >> GPS or your pitot (blockage, icing, etc.), your ATTITUDE depiction will >> become INACCURATE. The most startling thing that I found out dur= ing >> my research is that the FAA CERTIFIED, Chelton system does have the pro= blem >> of inaccurate attitude data with the lost of pitot input. Their manuals >> state that the attitude indication can be off as much as 2.5 degrees wh= en >> pitot data is not available....>>> >>=20 >>=20 >> 2.5 degrees ??!!??!! Horror of horrors! >>=20 >> Rick's post proves two things. One is that a little knowledge is a dang= erous >> thing. The other is that if you start with a conclusion you can find f= acts >> that "support" said conclusion. >>=20 >> Now for some real facts and reason. Most mechanical AH gyroscopic >> instruments rely on the gravity to determine which way is up. The influ= ence >> of this "gravity vector erection" is small compared to the forces that >> maintain the gyroscope "rigid in space". Imagine a pendulum hanging in= a >> jar of honey. If you roll the jar, the pendulum will point in a new >> direction for a while but will, over time, return to pointing straight = down. >> Likewise, if you roll into a coordinated turn with a mechanical gyro AH= and >> hold the turn for several minutes the AH will eventually show level fli= ght >> when you are still turning. Your inner ear also has this property, but = for >> different reasons. >>=20 >> When your are in a turn the centripetal force vector and the gravity fo= rce >> vector combine to create an apparent gravity vector, which is not verti= cal >> (with respect to the earth). >>=20 >> Mechanical gyro AHs, and apparently GRT, rely on the assumption that, o= n >> average, aircraft fly straight and level. >>=20 >> Now suppose you were a cleaver guy and you knew the velocity of the >> aircraft and the rate of turn (degrees per second) you could calculate = the >> centripetal force vector and then subtract that from the apparent gravi= ty >> vector to get the actual gravity vector. You would know which way is up >> regardless of how long you maintain the turn. Chelton uses a proprieta= ry >> algorithm to do this very thing and delivers the resulting superior >> performance. The other benefit of this is that the Chelton ADAHRS is t= he >> only low cost solid state AHRS that does not have a "kill maneuver" tha= t >> will cause significant attitude errors (e.g. low rate climbing turn). >>=20 >> Will the Chelton attitude accuracy degrade with loss of air data? Yes, = but >> in it's degraded state it still has better performance that its competi= tors >> over its entire operating range. Rick's assertion that his GRT AHRS is >> superior to the CFS ADAHRS because it does not have an air data "proble= m" is >> like saying a car without wheels is superior to a car with wheels becau= se it >> does not have a potential flat tire "problem". >>=20 >> The bottom line is that the Chelton system has undergone extensive >> certification testing and has proven its performance. All the other wan= nabes >> can claim to be "just as good or better" but until they prove it >> empirically you should not take the claims as fact. >>=20 >> Having spent the last 14 years designing, building and flying cockpit f= light >> information systems and having the experience of having thousands of th= ese >> systems deployed I can say that it is never a good idea to fly actual I= MC >> without mechanical backups and that most experimental EFIS systems only= work >> great when you don't need them, although many fail that test as well. >>=20 >> Regards >> Brent Regan >>=20 >>=20 >=20 --B_3295425060_458725 Content-type: text/html; charset="ISO-8859-1" Content-transfer-encoding: quoted-printable Re: [LML] Re: Selecting an EFIS
Are any of you aware of an independent, stand-alone, self powered attitude = back-up system?

I was looking at the Garmin 495.  Its panel page shows heading, bank a= ngle, and vertical speed.  So I assume with a little concentration, tha= t would allow a guy to approximate straight and level flight.  But ther= e is no “attitude indicator.”

Is there something out there better than the 495?

John Hafen

On 6/4/08 4:50 AM, "Chuck Jensen" <cjensen@dts9000.com> wrote:

If I ever decide to fly in circles for a long time, I w= ill be sure to buy a Chelton.
Chuck Jensen

-----Original Message= -----
From: Lancair Mailing List  [mailto:lml@lancaironline.net]On Behalf Of Brent Regan
Sent:  Tuesday, June 03, 2008 7:32 PM
To:  lml@lancaironline.net<= BR> Subject: [LML] Re: Selecting an  EFIS

Rick writes:

"... some  = ;EFIS systems (especially the inexpensive ones) derive their attitude depict= ion  data from GPS and pitot data. In other words, if you lose GPS or y= our pitot  (blockage, icing, etc.), your ATTITUDE depiction will become= INACCURATE.  <snip> The most startling thing that I found out du= ring my research is  that the FAA CERTIFIED, Chelton system does have t= he problem of inaccurate  attitude data with the lost of pitot input. T= heir manuals state that the  attitude indication can be off as much as = 2.5 degrees when pitot data is not  available....>>>


2.5 degrees ??!!??!!  Horror of horrors!

Rick's post proves two things. One is that a little  knowledge is a da= ngerous thing. The other is that  if you start with a  conclusion = you can find facts that "support" said conclusion.

Now for  some real facts and reason. Most mechanical AH gyroscopic ins= truments rely on  the gravity to determine which way is up. The influen= ce of this "gravity  vector erection" is small compared to th= e forces that maintain the gyroscope  "rigid in space".  = ;Imagine a pendulum hanging in a jar of honey.  If  you roll the j= ar, the pendulum will point in a  new direction for a while  but w= ill, over time, return to pointing straight down. Likewise, if you roll &nbs= p;into a coordinated turn with a mechanical gyro AH and hold the turn for &n= bsp;several minutes the AH will eventually show level flight when you are st= ill  turning. Your inner ear also has this property, but for different =  reasons.

When your are in a turn the centripetal force vector and the  gravity = force vector combine to create an apparent gravity vector, which is  no= t vertical (with respect to the earth).

Mechanical gyro AHs, and  apparently GRT, rely on the assumption that,= on average, aircraft fly straight  and level.

Now suppose you were a cleaver guy and  you knew the  velocity of= the aircraft and the rate of turn (degrees per second) you could  calc= ulate the centripetal force vector and then subtract that from the  app= arent gravity vector to get the actual gravity vector. You would know which =  way is up regardless of how long you maintain the turn.  Chelton = uses a  proprietary algorithm to do this very thing and delivers the re= sulting  superior performance.  The other benefit of this is that = the Chelton  ADAHRS is the only low cost solid state AHRS that does not= have a "kill  maneuver" that will cause significant attitude= errors (e.g. low rate climbing  turn).

Will the Chelton attitude accuracy degrade with loss of air  data? Yes= , but in it's degraded state it still has better performance that its  = competitors over its entire operating range.  Rick's assertion that his=  GRT AHRS is superior to the CFS ADAHRS because it does not have an ai= r data  "problem" is like saying a car without wheels is supe= rior to a car with wheels  because it does not have a potential  f= lat  tire "problem".

The bottom line is that the  Chelton  system has undergone extens= ive certification testing and has  proven its performance. All the othe= r wannabes can claim to be "just as good  or better" but unti= l they prove it  empirically  you should not take  the claims= as fact.

Having spent the last 14 years designing, building  and flying cockpit= flight information systems and having the experience of  having thousa= nds of these systems deployed I can say that it is never a good  idea t= o fly actual IMC without mechanical backups and that most experimental  = ;EFIS systems only work great when you don't need them, although many fail t= hat  test as well.

Regards
Brent Regan



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