X-Virus-Scanned: clean according to Sophos on Logan.com From: "Tom Mann" Received: from mail.infosaic.com ([216.226.129.129] verified) by logan.com (CommuniGate Pro SMTP 6.1.5) with ESMTPS id 8014971 for flyrotary@lancaironline.net; Thu, 24 Sep 2015 11:42:48 -0400 Received-SPF: none receiver=logan.com; client-ip=216.226.129.129; envelope-from=tmann@n200lz.com Received: from DSS04 (v-209-134-133-68.ip.visi.com [209.134.133.68]) by mail.infosaic.com with SMTP (version=Tls cipher=Aes128 bits=128); Thu, 24 Sep 2015 11:50:14 -0400 Message-ID: <054E654BC37B46AA95C991921C839ADE@DSS04> Reply-To: "Tom Mann" To: "Rotary motors in aircraft" References: In-Reply-To: Subject: Re: [FlyRotary] Re: OT: Calibrating altimeter and alt encoder Date: Thu, 24 Sep 2015 10:42:04 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_01B4_01D0F6B5.A6CE0F20" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 16.4.3528.331 X-MimeOLE: Produced By Microsoft MimeOLE V16.4.3528.331 This is a multi-part message in MIME format. ------=_NextPart_000_01B4_01D0F6B5.A6CE0F20 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I believe you are correct Rich. That was my understanding was that the encoding altimeter for the = transponder is set to 29.92 (or standard pressure.) This is when you pull it out and have someone with the proper equipment = take a look at it. From: ARGOLDMAN=20 Sent: Thursday, September 24, 2015 10:12 AM To: Rotary motors in aircraft=20 Subject: [FlyRotary] Re: OT: Calibrating altimeter and alt encoder 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=20 below what I saw on my altimeter. Last week I finally got around to removing all the screws that holds = the=20 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=20 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=20 encoder until the codes changed within 10 to 20 feet of the 50 foot=20 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,=20 yesterday I hopped over to Cross City (CTY) a mere 15 miles away. I = had=20 to set the altimeter to 0.03 or 0.04 below what their METAR reported = in=20 order to get altimeter to show their field elevation -- 42 feet.=20 Basically shows 30 to 50 feet too high altitude if I set the Dynon to=20 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 ------=_NextPart_000_01B4_01D0F6B5.A6CE0F20 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
I believe you are correct Rich.
That was my understanding was that the encoding altimeter for the=20 transponder is set to 29.92 (or standard pressure.)
 
This is when you pull it out and have someone with the proper = equipment=20 take a look at it.
 
From: ARGOLDMAN
Sent: Thursday, September 24, 2015 10:12 AM
Subject: [FlyRotary] Re: OT: Calibrating altimeter and alt=20 encoder
 
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 = encoder=20 checked with proper instruments.
 
Something that comes to mind is that since the encoder and the = altimeter=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 = home=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 = screws=20 that holds the
fuselage top over the instruments.

I hooked = LEDs=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 = low).

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

I then spent several hours adjusting the high and low = pots 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 = Cross=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 = suggestions on=20 how to obtain an accurate air pressure=20 reference?

Finn


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