At 18:47 07 September 2010, PCool wrote:
That's correct, the HP310 (and 314, 316) has a "feature" you cannot
disable

in its embedded GPS: in order to filter out bad readings (that are highly

unlikely to happen anyway) it looks at what you are doing, trying to
"guess"
the correct position when you are turning fast and tight.
Sure, you may turn slow and in large circles.. but that's not good for
thermalling, it is good only in a car at a roundabout! (hehe).

This will result in bad wind calculation in the LK8000/XCSoar circling
wind
calculation engine. Which is in my opinion very accurate.
It is simply rejecting the "guessed" positions, thus not having enough
data
to process it won't compute the wind sometimes.

In my opinion, having an HP31X, the best solution is to get an RS232 USB

cable (custom for the HP) and connect it to an external instrument
feeding

both GPS position and barometric pressure (altitude). A Flarm will do it,

and send also traffic informations at the same time.
Using BlueTooth is an option, and the automatic fallback feature of LK on

dual rs232 feeds can be helpful when BT is dropped: in this case, the
internal gps is going to be used and flight can continue.
However, while choosing a BT GPS, it is important that it is both Slave
and
Master BT, which is not obvious.
Otherwise the connection cannot be established and resumed automatically
by
the HP.

FYI, many other (even cheap) PNAs can use the HP's serial cable. MIOs,
NILOX, and probably some navigon and virtually all PNAs declaring
external

TMC capability (because TMC is using serial rs232 TTL connection).
Also, we recently discovered that some cheap PNAs that were looking bad
under sunlight, were very good readable using.. polarized sunglasses! So,

the race to the "perfect" PNA is still open.

paolo


"Brad" ha scritto nel messaggio
...
On Sep 7, 11:06 am, Darryl Ramm wrote:
On Sep 7, 11:01 am, jb92563 wrote:





On Sep 7, 10:03 am, Andy wrote:

On Sep 7, 9:31 am, Brad wrote:

I have my HP-24 set up with the iPAQ 310 and it is running the
latest
LK8000 software, since the aircraft hasn't flown yet I am
curious
to
know if anyone out there is using this combination and what they

have
noticed regarding the wind calculation function (not the true
wind
feature).

If you are using the HP310 internal GPS you can expect the LK8000
circling wind calculation to produce an unreliable wind estimate
unless you thermal at a very low turn rate.

In small Arizona cores that require high bank angles my experience
is
that the internal GPS gets hoplessly confused and the wind
estimate
cannot work because it does not have good circling position data.

In smooth late afternoon thermals worked at low bank angles the
wind
estimate is in the same ball park as my 302 with Glide Nav II.

I don't think there is anything wrong with LK8000 wind calcs but
you
will need an external GPS with a fast update rate to give it a
chance
of producing a valid result.

Andy

I concur that the higher turn rate reduces the ability to get a good
wind direction fix.

It seems to me that the reason might be that the position fixes are
produced at a maximum rate of 1/sec under ideal conditions
and that just does not seem to be enough resolution when making
small
circles.

I wonder if there is a way to get more fixes or create your own
virtual fixes by projecting a position based on the turn rate and
average diameter to help out the wind calculator?

Ray

I think this has all been covered in the past.

It is not the update rate, it is the iPAQ 310 internal GPS doing
position extrapolation/smoothing based on past velocity - designed
for road navigation. This "feature" cannot be disabled in the
internal
GPS, technical folks have tried...

Use an external GPS and you'll be fine. Presumably an external
bluetooth will work, I've not tried it. This was one of the
limitations with the iPAQ 310 that many of the early purchasers,
including me, discovered to our annoyance.

Darryl

Thanks guys, I just talked to Paul Remde and bought an external GPS
unit that will plug right in to the PS-5a and send all the info to the
310.

I just got back from a mountain flying expedition and the wind info
was critical to my successful flights...............at least it seemed
to help me a lot and I will want the same features for the HP-24.

Darryl, yep......you're right..........this subject has come up often
and now for me I dropped the dime and have some resolution!

Brad



I'm surprised that Paolo didn't mention the other wind calculation
method in LK8000, TrueWind. This will calculate the wind in a straight
line.
The internal gps in the iPAQ31* series also gives odd results at times
other than circling. I've had a trace showing a winch launch finishing
700 metres to one side of the winch and 300 metres past it. I now use a BT
gps as the main device, and if for any reason that signal is lost (it never
has yet), LK will automatically switch to the internal gps. Pity the 31*
series is no longer made, it's the best display at a reasonable price
that I have come across.
Dave