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Date: Tue, 09 Oct 2007 19:08:28 -0400
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From: "Douglas Brunner" <douglasbrunner@earthlink.net>
References: <list-2377549@logan.com>
Subject: Re: [LML] Re: Backup DG equivalent
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I would like to second John's opinion on the Tru Trak ADI.
I had one ordered and paid for, but sent it back, paid the restocking
charge and got a standard attitude indicator for a higher price.

It was just the scenario that John mentions that made me do it.  The
Tru Trak will function much like an AI at higher speeds, but if you
are slow and close to stall the behavior of the ADI and the AI
will diverge.

Assume you are 10 kts above stall, nose high, and losing altitude.
The AI will show you nose high, the ADI will show you "nose low"
(I know this is not correct, but for someone like me, in an emergency
this is how I would probably interpret it).  It seems to me that with
the ADI I might be tempted to pull back and correct may altitude
loss - thus precipitating a stall.  With the AI, I would know to add
power and push.

I am sure that my misinterpretation of the ADI could be corrected with
lots of training and for some people the ADI may be what they want.
But for me (and people like me) I think it could be dangerous.

My 2 cents

----- Original Message ----- 
From: "John Barrett" <2thman@cablespeed.com>
To: <lml@lancaironline.net>
Sent: Tuesday, October 09, 2007 11:38 AM
Subject: [LML] Re: Backup DG equivalent


For the enlightenment of all vis a vis the Tru Trak ADI, I spoke with Lucas
of Tru Trak this afternoon.  First of all he told me the “pitch” indication,
as was mentioned before in this thread, is not pitch at all, but rather VSI.
Therefore if the aircraft is losing altitude, the indicator will be expected
to show accurate roll information, but will look as if the nose of the
aircraft is below horizontal when in fact you could be nose up.  I would
consider this to be  a very dangerous situation at any time I needed to use
the instrument.  Just consider the unpleasant event you could face when your
Cheltons or other MFD’s all crap out while you’re in IMC and there is lots
of turbulence.  First you have to reorient your scan to instruments that you
only use in practice, and then you have to overcome your well ingrained
training that says this thing that looks like an attitude indicator is NOT.
While your brain is assimilating this disparity between past learning and
reality, precious seconds are going by and the turbulence has caused your
aircraft attitude to change to any position other than wings level and nose
level – probably to be swinging past those desirable positions somewhat
erratically.

I think it’s a shame this very nice instrument has what I think is a fatal
flaw.  It’s too bad Tru Trak put an electronic roll gyro in this thing, but
didn’t think a pitch gyro was necessary.  I sincerely hope they’ll rethink
the concept and will correct this discrepancy.  I will look forward to
buying one to complement my Tru Trak autopilot if they do.

By the way, the heading indication is totally GPS dependent and does not
derive information from the gyro or gyros that would allow it to keep
providing heading data if GPS is lost.  That would be another improvement if
it could use GPS to stabilize and correct a gyro track, which would continue
to function albeit with less accuracy when the GPS is lost.

My 2 cents.

Regards,
John Barrett


As a backup direction indicator on my Legacy, which also has a
2-screen Chelton EFIS system, I'm using the 2-1/4" ADI from Tru-Trak.
It's a bit of an odd critter, but if you buy it with the GPS and backup
battery options, it does give a heading (track, actually) indication
that's completely independent of your plane's electrical system.  It
also provides pitch and bank info.  Hard to find equivalent info from
2-1/4" instruments without spending a fortune.

Jim Cameron
Legacy N132X


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