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Several months ago, there was good discussion on this newsgroup about
the TruTrak ADI attitude direction indicator and it's value as a backup
instrument. I gave mine a good workout today and want to share my
thoughts.
I installed a Chelton system in my Legacy and the small (2.25") TruTrak ADI
for backup. I also have steam gauges for backup airspeed and altitude and
a handheld GPS and handheld comm radio. Today I went up with a safety
pilot and tried out my backup instruments while wearing a "hood" with the
Chelton displays blanked out.
The ADI sort of acts like a conventional gyroscopic attitude indicator in
that it shows pitch and bank information. Instead of calibrations
in degrees nose up or down, its calibrations are in feet per minute
climb or descent. The roll information acts similar to the way a
conventional attitude indicator works, although it has only two bank calibration
marks.
This is a little hard to describe, so if you're not familiar with
it,here's a photo:
However, the photo shows the full size 3.125" ADI; the small one I have
does not have the slip/skid ball, has only two roll index marks, and
the climb/dive marks are labeled in feet per minute. I do not have mine
hooked up to a GPS yet, so mine does not show track. I might add
a GPS to it later, but the TruTrak autopilot displays heading, so
that's a low priority for me.
I was pleased at how easy it was to fly my Legacy under the hood with only
my backup instruments and a Garmin 196 handheld GPS. The ADI doesn't
respond exactly the way a conventional attitude indicator does, but I seemed to
quickly adjust to it. After a few minutes, I was interpreting the ADI's
input without thinking about it. The only thing that wasn't intuitive
was controlling a descent. The dive calibration marks don't "bank" when
the airplane rolls the way the climb calibration marks do. This is
hard to explain, but look at the photo from the link above. The blue part
of the display rotates as the airplane banks, but the brown part is
stationary. That's not a big deal, but sort of an oddity in a descending
turn that I'm sure I'll get used to with a little more practice. Also, the
dive calibrations are much closer together than the climb calibrations, which
makes them a little harder to interpret. But that's a pretty minor
complaint.
On the plus side, it costs a fraction of what a conventional attitude
indicator costs. It's also lighter weight and, if connected to a GPS,
provides track information that conventional attitude indicators don't.
On the minus side, it doesn't respond in exactly the same way as a
conventional attitude indicator, which might be an issue for some people.
It also uses similar electronic technology as the Chelton/Pinpoint and my
hunch is that any electronic attack on the system, such as from lightning, would
take out the ADI long before the Chelton/Pinpoint.
Which brings up the need to define what risk you want to protect
against. For me, I'm protecting against the risk that the Pinpoint, which
is the single point of information for GPS and attitude information, fails for
some reason internal to itself, such as a connector coming unplugged, etc.
I'm not protecting against a lightning strike or a total electrical
failure, which would also take out the ADI. I understand that other
people will choose different risks to protect against and will,
therefore, have different equipment requirements.
In conclusion, I'm happy with the TruTrak ADI and believe it will fill the
mission I have assigned it. And the Garmin 196 handheld GPS is
amazing, what a value! But that's for another post.
Dennis Johnson
Legacy, 125 hours
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