single pilot ifr trip tonight

David Megginson wrote in message ...
(Nathan Young) writes:

Your statements that the GPS lags dangerously are inaccurate (at least
wrt to the Garmin 295). The HSI updates quick enough to show heading
changes of a few degrees as long as the bank angle is kept under a
reasonable amount, say 10 degrees. Easy to do in smooth or light
turbulence.

The lag is time, not heading. How long does it take a heading change
to register? I've heard that it's at least a second on the 196, and
sometimes two seconds or more on the 295, but I don't own either.

It is probably a 1 or 2 sec update rate. That is often enough to
detect and display heading changes of a degree or two (as long as bank
angle is kept reasonable). The 'lag' is roughly equivalent to the
update rate. Ie, the GPS updates every second, and is showing you
position, heading, velocity derived from the t and t-1 epoch.

Most GPS engines are running faster than the display rate. GPS
engines from 5-10 years ago operated on 1 or 2 sec position updates.
Newer engines are more granular, with 5Hz operation being common.
That means the display data shown is typically derived from the
velocity/heading calculated from the time 1 and 1.2 seconds in the
past.

-Nathan

(Nathan Young) writes:

It is probably a 1 or 2 sec update rate. That is often enough to
detect and display heading changes of a degree or two (as long as bank
angle is kept reasonable). The 'lag' is roughly equivalent to the
update rate. Ie, the GPS updates every second, and is showing you
position, heading, velocity derived from the t and t-1 epoch.

The reason I'm skeptical is that the mag compass also works fine for
holding heading in smooth air with very shallow turns: it doesn't go
to hell in a handbasket until the air gets rough, precisely the same
time the update lag in a handheld GPS could potentially also make it
difficult to use. That's why I'm interested in hearing from people
who've used it successfully in rough air, preferably at night (where
there are fewer visual cues like shadows moving over the panel).

Note that I love GPS's -- so much so, that I collect GIS data just for
fun, and have even hacked a way to get DAFIF data into a Magellan 315
from Linux.


All the best,


David

David Megginson wrote:

The reason I'm skeptical is that the mag compass also works fine for
holding heading in smooth air with very shallow turns: it doesn't go
to hell in a handbasket until the air gets rough, precisely the same
time the update lag in a handheld GPS could potentially also make it
difficult to use. That's why I'm interested in hearing from people
who've used it successfully in rough air, preferably at night (where
there are fewer visual cues like shadows moving over the panel).

And that's why I'm looking for a device that acts - effectively - as a
backup AI.

I saw a couple of devices at the Expo. Both were "boxes" that plugged into
different "computers". One was a large box that plugged into what I think
was and Ipaq, and one was a small box that plugged into a "Cheeta" portable
MFD device.

I really liked the Cheeta, but I think it was the most expensive of the
solutions I saw.

Anyone have other thoughts about this?

What was the price of a panel-mounted electric AI? 4K? I wonder if I could
get the club to consider such an investment on our aircraft.

- Andrew

Nathan Young wrote:

Most GPS engines are running faster than the display rate. GPS
engines from 5-10 years ago operated on 1 or 2 sec position updates.
Newer engines are more granular, with 5Hz operation being common.
That means the display data shown is typically derived from the
velocity/heading calculated from the time 1 and 1.2 seconds in the
past.

What units have a 5Hz update? The only one I am aware of is the CNX80. I don't
know of any others better than 1 Hz... oh, maybe you meant 5 Hz intenally, with
a 1 Hz update of the display?

Dave
Remove SHIRT to reply directly.

Dave Butler wrote:
Nathan Young wrote:

Most GPS engines are running faster than the display rate. GPS
engines from 5-10 years ago operated on 1 or 2 sec position updates.
Newer engines are more granular, with 5Hz operation being common. That
means the display data shown is typically derived from the
velocity/heading calculated from the time 1 and 1.2 seconds in the
past.


What units have a 5Hz update? The only one I am aware of is the CNX80. I
don't know of any others better than 1 Hz... oh, maybe you meant 5 Hz
intenally, with a 1 Hz update of the display?

Oh, never mind. That's what you *said*. Sorry for the noise. Dave