REFLECTOR: GPS outage, no big deal

Mon Dec 3 13:19:16 CST 2012

Mark,

The issue with MEM’s based accelerometers is accuracy…

A Ring laser gyroscope is likely what the 1MM+ systems had in them – notice that bias uncertainty could be better than 0.01 deg / hour.
http://en.wikipedia.org/wiki/Ring_laser_gyroscope

Some generic info on Accelerometers…
http://www.colibrys.com/files/pdf/products/30N-AHRS.B.05.11.pdf

.

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Mark Magee
Sent: Monday, December 03, 2012 11:37 AM
To: Velocity Aircraft Owners and Builders list
Cc: reflector at tvbf.org
Subject: Re: REFLECTOR: GPS outage, no big deal

Hi Brett,
From their data, two AHRS's in DR mode should have given you spot on accuracy once GPS was lost. As you said, I'd investigate the install. I'm hoping someone will give us a receiver that will take in multiple NDB's and with triangulation give us backup to the AHRS and GPS. I suppose that is what the next gen is: triangulating off any signal it can find and identify: cell, AM, FM, VOR, WIFI etc.

Mark B. Magee
Sent from IPhone 4S

On Dec 3, 2012, at 11:18 AM, Brett Ferrell <reflector at velocityxl.com<mailto:reflector at velocityxl.com>> wrote:
I have a 3 screen dual AHRS HX system with the RAIM GPS.

--
Brett Ferrell
reflector at velocityxl.com<mailto:reflector at velocityxl.com>

On Mon, Dec 3, 2012, at 09:23 AM, Mark Magee wrote:
Brett,
Do you have one AHRS's or two?

Mark B. Magee
Sent from IPhone 4S
On Dec 3, 2012, at 7:19 AM, Brett Ferrell <reflector at velocityxl.com<mailto:reflector at velocityxl.com>> wrote:
It does, and we did have a instance where GPS was unavailable (it was not NOTAMed, and I could not get GPS on my iPad either) where the GRT dropped into "dead reckoning" mode.  It was much better than nothing, but it did wander significantly from our true position over the course of 1/2 an hour or so.  That could be installation error, but it's a real data point.  Regardless, it was a lot better than no location data.

Brett
--
Brett Ferrell
reflector at velocityxl.com<mailto:reflector at velocityxl.com>

On Mon, Dec 3, 2012, at 07:46 AM, Mark Magee wrote:
On Dec 2, 2012, at 4:27 PM, Scott Derrick <scott at tnstaafl.net<mailto:scott at tnstaafl.net>> wrote:

Mark,
  I don't know what GR's INAV is, it's certainly not real Inertial Navigation!

As I understand it Grand Rapids, and hopefully others have -Electronic-
INAV: which is very accurate digital accelerometers on 3 axes that give
better accuracy than the old mechanical accelerometers coupled to
spinning gyros. Basically the AHRS that GR sells (I don't have one, and
won't sell you one) is a stand alone box that if told where on earth it
is, will calculate from 3 axis digital accelerometer data where on a 3D
plane you move to; no external reference. It does cross check to GPS. As
well you can install two of them for redundancy and they as we'll will
cross check each other.
GR sells this AHRS to the military and others for a wide array of
applications (hopefully not the Iranians!).
Basically you get better accuracy for around $2,500 USD as to what used
to cost the Navy 1MM each for the Submarine fleet. I knew the engineer at
NASA that owned the INAV package on the Space Shuttle fleet, he had a
team of 6? folks whose full time job was to maintain the 3 INAV boxes in
each Orbiter. This was mid 1980's, he said each box was 1MM USD's (x3 for
each bird). I had buddies that served on subs that had the same boxes,
they said they would submerge off Point Loma (San Diego) and be submerged
for 6 weeks. After 6 weeks of sub-surface maneuvering they would surface
and take a Celestial shot and would normally be within 100 feet or less
from where the INAV package said they were. That was 3MM USD's technology
and a dedicated team of technicians to maintain. We can now get better
data for around $2,500 USD's each. So buy two for cross checking and
redundancy and if Uncle Sam wants to jam my NAV (GPS), to Hell with him:

Damn The Torpedoes an Full Speed Ahead!

I don't have to have your GPS inputs! My precious little boxes have all
the data I need to get where I'm going, no external data required.

Jam my NAV signal? In flight?
I told you guys I am an activist on this.

Scott, it is -better- than what we used to term -real- INAV. For
fractions of a penny on the dollar.

Mark B. Magee
N34XL
Sent from IPhone 4S
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