Re: Problem: Ground Speed Estimate with Volkslogger and WinPilot

[RamyYanetz]

I noticed the same problem with my winpilot/VL, although I don't think it has
anything to do with VL, since the ground speed is correct in the NAV box, but
incorrect only in the final glide display. I reported this problem to Jerry
last year, not sure if it was fixed in later releases.

Ramy

>Is anyone else seeing the WinPilot/Volkslogger problem I am seeing?
>
>Running WinPilot v3.019 Adv on an IPAQ 3635. GPS data is from a
>Volkslogger. The GPS signal is also fed to a Cambridge LNAV.
>
>Everything works fine except the WinPilot function to estimate task
>completion time based on ground speed. This function is found on the
>final glide display page (touching the chevrons on the left side of
>the map, then pressing the MC button to let finish time computation
>use the ground speed.
>
>The WinPilot estimate of ground speed shown is something like 18-20
>mph, instead of 50mph+ actual.
>
>My NMEA mask for the Volkslogger is
>- - X X X - - - -
>
>Inspection of the NEMA sentances my Volkslogger is putting out all
>look ok (short example below). GPGGA (fix data), GPRMC (speed data),
>and GPRMB (track data) are all present.
>
>Anyone else have this function working correctly with a Volkslogger
>feeding WinPilot?
>
>Bob
>
>==================== Example NEMA Stream ==============
>$PGCS,2,VL,175*30

[Bob Gibbons]

Ramy, good point, I did not check the Nav Box Ground Speed output. Per
your suggestion I just pulled up an old WinPilot log file and ran it
in playback mode. Sure enough, just as you say, the Nav box ground
speed is correct and the final glide page ground speed is wrong. The
finish time estimate matches the erroneous ground speed.

>I reported this problem to Jerry
>last year, not sure if it was fixed in later releases.

Interesting, I reported this to Jerry last week. His response was that
he had never heard of this problem before.

I'll fire him off another note with your Nav box example He should be
able to check it quickly himself with a WinPilot log file.

Thanks for the reply.

Bob


On 26 Aug 2003 02:56:29 GMT, (RamyYanetz) wrote:

>I noticed the same problem with my winpilot/VL, although I don't think it has
>anything to do with VL, since the ground speed is correct in the NAV box, but
>incorrect only in the final glide display. I reported this problem to Jerry
>last year, not sure if it was fixed in later releases.
>
>Ramy
>
..... Rest of post removed .....

[chris]

Is the ground speed supposed to be the current speed OR the average
achieved groundspeed for the leg or last 30 minutes?

The second will be a lot lower than the first if you spend time
thermaling.

The ETA could be based on either of these.

Chris

[Andrew Warbrick]

No, ground speed is supposed to be GPS ground speed,
'Avg Leg' is supposed to be achieved ground speed for
the leg (which appears to work properly). Unfortunately,
if it worked, ground speed would be the best option
for final glides in wave where you can be covering
100km or more at a fairly constant speed in a straight
line. The ETA can also be based on macready speed,
the average for the whole task or a manually entered
speed.

BTW, the problem is with Winpilot, not the Volkslogger
because the same happens to me using a Colibri, I guess
a unit conversion factor gets applied wrongly somewhere.

I have a feeling the same, incorrect, ground speed
might be being applied to the calculation of L/D in
the nav box, the value is frequently less than I would
expect when flying in good or still air and also less
than the value a quick mental calculation gives (ie.
cruising for a minute at a fixed airspeed and dividing
the airspeed by the average sink rate).

At 12:48 26 August 2003, Chris wrote:
>Is the ground speed supposed to be the current speed
>OR the average
>achieved groundspeed for the leg or last 30 minutes?
>
>The second will be a lot lower than the first if you
>spend time
>thermaling.
>
>The ETA could be based on either of these.
>
>Chris
>