REFLECTOR: GPS outage, no big deal

[Tony Babb]

Somewhat off topic but....about 15 years ago I was on a British Airways 747
flight from Hong Kong to London. After several hours I went up to visit the
cockpit and the pilot showed me his triple inertial navigation system, it
displayed on one screen where each of the 3 systems thought we were - less
than a quarter mile apart - and also showed position from VOR, if I remember
correctly. He pressed a button and all 3 reset their positions, at the time
I could see Istanbul out of the cockpit window. 

Tony Babb
Velocity SEFG 62% done, 78% to go

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Mark Magee
Sent: Monday, December 03, 2012 4:47 AM
To: Velocity Aircraft Owners and Builders list
Cc: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: GPS outage, no big deal

On Dec 2, 2012, at 4:27 PM, Scott Derrick <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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