REFLECTOR: GPS outage, no big deal

Brett Ferrell reflector at velocityxl.com
Mon Dec 3 11:18:28 CST 2012


I have a 3 screen dual AHRS HX system with the RAIM GPS.



--

Brett Ferrell

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 <[1]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
[2]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 <[3]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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References

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2. mailto:reflector at velocityxl.com
3. mailto:scott at tnstaafl.net
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