question on glide ratio functions in Garmin 96, 96C, 196 GPS

This post deals with less expensive portable GPS's
from Garmin.

Lead-in: I'm familiar with the current-glide-ratio
function on the Garmin Etrex Vista (which has a pressure
sensor). It's extremely responsive--too much so to
be of much use except in smooth conditions. In some
cases where the view of the satellites is very poor,
a peculiar 'bug' in the unit's design and/or software
manifests itself. (See www.aeroexperiments.org/GPSglide.shtml
for more on this). On the other hand, the 'glide ratio
to target' function is much more useable, because it's
inherently a much more stable value, not affected by
turbulence.

I assume that the 76S and 76CS have similar 'current
glide ratio' functions to the 'Vista'--very responsive,
maybe too much so for some users' tastes in rough air.


Main question: What I'm seeking now, is some user feedback
about the 'current glide ratio' function on Garmin
products that lack pressure sensors. I see that Legend
C (no sensor) now has this function. And I know the
96 and 96C and 196 have this function as well, and
they don't appear to have pressure sensors. In order
for this to work, I'm guessing that the satellite-derived
vertical speed data must be smoothed over at least
5 to 10 seconds, and therefore so must the 'current
glide ratio' function. Does this sound accurate to
folks who are familiar with these products? And is
this a good thing--does the more smoothed display work
better than a more responsive (less smoothed) display
would, in the opinion of people who are actually flying
with these units?

Also does the 'current glide ratio function' on these
products generally work pretty well most of the time
or are there noticeable glitches from time to time
due to errors in the satellite-derived altitude data,
non-optimal satellite availability, etc? Obviously,
altitude-related and vertical-speed-related data is
the first thing that's going to suffer whenever the
satellite reception and availability is less than ideal,
but an error of a few hundred feet in altitude wouldn't
neccessarily compromise the current-glide-ratio function
if that error was relatively constant over timescales
of several minutes.

Thanks for any feedback
Steve S.

Thanks for the notes Kirk, out of curiosity did your
tests include units like the 96, 96C, or 196 which
don't (to the best of my knowledge) incorporate a pressure
sensor? I'd be especially interested to hear feedback
re the current-glide-ratio functions of these particular
units. If anyone can compare the current-glide-ratio
functions on these units to the Vista or 76S that would
give me an even better point of reference because I
am familiar with these last 2 items.

Re glide-ratio-to-target: I like this function too.
For some of my (non-sailplane) soaring applications
a readout including a 'tenths' digit--which the Garmin
products lack-- would be extremely helpful, to help
the user judge whether the value is trending upward
or downwards. This is something you care a lot about
when the glide-ratio-to-target seems 'stuck' on a single-digit
value that is very close to your best estimate of the
the expected max performance of your aircraft given
the winds etc.

Steve


At 13:12 10 January 2006, wrote:
Steve,

I've toyed around with current L/D functions on various
Garmins and other glide computers, and never found
any of them to be of any use as they are much too sensitive.

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