X-Virus-Scanned: clean according to Sophos on Logan.com From: Received: from omr-a010e.mx.aol.com ([204.29.186.54] verified) by logan.com (CommuniGate Pro SMTP 6.1.5) with ESMTPS id 8014914 for flyrotary@lancaironline.net; Thu, 24 Sep 2015 11:13:34 -0400 Received-SPF: pass receiver=logan.com; client-ip=204.29.186.54; envelope-from=ARGOLDMAN@aol.com Received: from mtaomg-mcb02.mx.aol.com (mtaomg-mcb02.mx.aol.com [172.26.50.176]) by omr-a010e.mx.aol.com (Outbound Mail Relay) with ESMTP id 5CE74380005A for ; Thu, 24 Sep 2015 11:12:59 -0400 (EDT) Received: from core-mxb004c.mail.aol.com (core-mxb004.mail.aol.com [172.29.192.141]) by mtaomg-mcb02.mx.aol.com (OMAG/Core Interface) with ESMTP id A05733800008F for ; Thu, 24 Sep 2015 11:12:57 -0400 (EDT) Full-name: ARGOLDMAN Message-ID: <18d10e.4c571e28.43356cf8@aol.com> Date: Thu, 24 Sep 2015 11:12:56 -0400 Subject: Re: [FlyRotary] OT: Calibrating altimeter and alt encoder To: flyrotary@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_18d10e.4c571e28.43356cf8_boundary" X-Mailer: Unknown sub 13 X-Originating-IP: [50.151.84.32] x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20150623; t=1443107579; bh=QgeYLH98XNk2nGErZt0E53ELDC5tmWt8ZmB5MExH6lI=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=xJNcNOSm+nsoQ4I+dfrtNQWxFf3sDYLqdwP8jbIs5kNOHSTG8C+m8smiPaOJKavAN QPzDVg498y37h94uc0lrx+BKwv1zlDWKERCqas/18z0g+7F5flmh/Zt07EiBJ1ARrg lt/IzlzM9WnBxRv5asWD2RQoV04divQx770d4Xac= x-aol-sid: 3039ac1a32b0560412f91ae1 --part1_18d10e.4c571e28.43356cf8_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Not sure that I understand completely, however the encoded altitude has nothing to do with your local setting. all encoders are calibrated to the same calibrations so that when ATC or whoever reads the reply all of the aircraft that they are looking at have the same altitude bias independent of errors in setting the kollsman window in the various aircraft. Since you have gone into the encoder, there is a possibility that the alterations that you have done may yield a constant error for ATC which is worse than not having an altitude report at all. You might want to have your encoder checked with proper instruments. Something that comes to mind is that since the encoder and the altimeter are both run from the static source, that there is a blockage, kink, water etc that may be influencing the readings. Good luck in your quest for vertical reading stability Rich In a message dated 9/24/2015 8:58:23 A.M. Central Daylight Time, flyrotary@lancaironline.net writes: Off topic, except it's in a 13B Van's RV-3 ;-) Again, after flying home from Sun'n'Fun, ATC saw me several hundred feet below what I saw on my altimeter. Last week I finally got around to removing all the screws that holds the fuselage top over the instruments. I hooked LEDs across the data lines that run from the altitude encoder to the transponder (gray code). (note that 1 is actually 0 volts -- active low). I checked METARs at nearby airports -- CTY, GNV... and I know my elevation exactly. That matched what my Dynon D10A and steam altimeter showed. I then spent several hours adjusting the high and low pots on the alt encoder until the codes changed within 10 to 20 feet of the 50 foot points when applying vacuum to the static system with a syringe. Can't get better that that, I though. Alas, after replacing the fuselage top and multitude of screws, yesterday I hopped over to Cross City (CTY) a mere 15 miles away. I had to set the altimeter to 0.03 or 0.04 below what their METAR reported in order to get altimeter to show their field elevation -- 42 feet. Basically shows 30 to 50 feet too high altitude if I set the Dynon to the reported pressure. All that work for nothing! Now I'm beginning to suspect that the pressures reported by the METARs are not all that precise. Checking METARS right now at nearby airports, they range from 29.98 to 30.02. Any suggestions on how to obtain an accurate air pressure reference? Finn -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html --part1_18d10e.4c571e28.43356cf8_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Not sure that I understand completely, however the encoded altitude= has=20 nothing to do with your local setting.
 
all encoders are calibrated to the same calibrations so that when ATC= or=20 whoever reads the reply all of the aircraft that they are looking at have= the=20 same altitude bias independent of errors in setting the kollsman window in= the=20 various aircraft.
 
Since you have gone into the encoder, there is a possibility that the= =20 alterations that you have done may yield a constant error for ATC which is= worse=20 than not having an altitude report at all. You might want to have your enc= oder=20 checked with proper instruments.
 
Something that comes to mind is that since the encoder and the altime= ter=20 are both run from the static source, that there is a blockage, kink, water= etc=20 that may be influencing the readings.
 
Good luck in your quest for vertical reading stability
 
Rich
 
In a message dated 9/24/2015 8:58:23 A.M. Central Daylight Time,=20 flyrotary@lancaironline.net writes:
Off=20 topic, except it's in a 13B Van's RV-3 ;-)

Again, after flying ho= me=20 from Sun'n'Fun, ATC saw me several hundred feet
below what I saw on= my=20 altimeter.

Last week I finally got around to removing all the scr= ews=20 that holds the
fuselage top over the instruments.

I hooked LE= Ds=20 across the data lines that run from the altitude encoder
to the=20 transponder (gray code).
(note that 1 is actually 0 volts -- active= =20 low).

I checked METARs at nearby airports -- CTY, GNV... and I kn= ow my=20
elevation exactly.
That matched what my Dynon D10A and steam alti= meter=20 showed.

I then spent several hours adjusting the high and low pot= s on=20 the alt
encoder until the codes changed within 10 to 20 feet of the= 50=20 foot
points when applying vacuum to the static system with a syringe= .=20 Can't
get better that that, I though.

Alas, after replacing= the=20 fuselage top and multitude of screws,
yesterday I hopped over to Cro= ss=20 City (CTY) a mere 15 miles away.  I had
to set the altimeter to= 0.03=20 or 0.04 below what their METAR reported in
order to get altimeter to= show=20 their field elevation -- 42 feet.
Basically shows 30 to 50 feet too= high=20 altitude if I set the Dynon to
the reported pressure. All that work= for=20 nothing!

Now I'm beginning to suspect that the pressures reported= by=20 the METARs
are not all that precise.
Checking METARS right now at= =20 nearby airports, they range from 29.98 to
30.02.

Any suggesti= ons on=20 how to obtain an accurate air pressure=20 reference?

Finn


--
Homepage: =20 http://www.flyrotary.com/
Archive and UnSub:  =20 http://mail.lancaironline.net:81/lists/flyrotary/List.html
--part1_18d10e.4c571e28.43356cf8_boundary--