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aadamson(at)highrf.com
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 Posted: Wed Aug 09, 2006 5:23 pm Post subject: EFIS - BMA or GRT? Op Tech |
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Easy to figure out if true... Unplug one or the other and see what happens.
Make sure you wait awhile after and then turn things thru their motions.
Most items that "self erect" after power loss do so via GPS aiding.
I suppose that terms needs to be mentioned as well. There is totally
separate, GPS aided, but still can function in a basic fashion if either
fail, then there it totally integrated. Luckily, I know of none of the
later. Most fall into the middle, but a few can function if one or the
other fail.
Even the G1000 is GPS aided btw, that's how they can "quick" erect in
flight. Its not a bad thing, it can be a good thing if done correctly.
Alan
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Tim(at)MyRV10.com
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| Posted: Wed Aug 09, 2006 8:55 pm Post subject: EFIS - BMA or GRT? Op Tech |
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I believe your spot on, Mike, with the link between the GPS
and some of these issues. I saw a graph recently of the
TAS, IAS, and GS logged by a 425, during a time when it went
nuts. The GPS readout was whacked, with spikes well above
any TAS and IAS value. The interesting thing was that the
unit did not throw an error bit that the GPS was unreliable,
and it apparently thought the GPS was fine. To the pilot,
the GPS was still locked on. So the unit didn't deal with
something right in regards to the GPS, either the signal, or
some calculation....but something hosed that 425, and it
was a "fixed" model. I've heard some interesting stories
regarding case design, and anodization and other things that
have caused some strange effects too.
Flying a Pinpoint today. Just got my production unit
this evening and should be flying it this weekend.
Had an engineering unit for the past few weeks. It's
looking like the people who get them will be pleasantly
surprised. It is very smooth in-flight.
Tim Olson
do not archive
Mike wrote:
[quote]
Tim,
Well written! I too fly behind the Chelton system and have worked with
the 420/425 and the problems that continue to plaque the unit. One of
the issue is the influence the GPS has over the gyro output. If you get
a map shift with the 420/425 due to a position error or reception error
you also get a gyro shift at the same time. This is not good in IMC.
The 425 had other problems with gyro initialization with low startup
voltage. This caused the unit to fail on initialization. Another
problem is a P-static ground feed back issue that has not been fully and
technically explained to me. The fixes for the units in question only
fix the later two issues, not the first issue. It is my opinion the
design philosophy to allow the GPS position to have influence over the
GYRO platform on the 420/425 unit is unacceptable and unworkable without
a redesign.
Mike Larkin
Lancair Legacy
TS-11 Iskra
Kitfox IV (All Flying!)
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