On 15 Apr 2004 08:48:06 -0500, BJen
wrote:
Thanks for the info Paul. It helps. Let me try to
summarize, and anyone who wants to chime in on where I'm
wrong, or right, feel free:
All PDAs connected to a GPS know location, ground speed and
track from the GPS. That lets them calculate wind speed and
direction from circling algorithms. There are some
straight line wind calculation algorithms used by flight
computers, but that requires an airspeed input, and since my
flight computer won't output any airspeed info to a PDA, I'd
have to buy one that does.
With wind and location data, a PDA can calculate altitude
required for final glide, glide to emergency fields and
glide around a TP before going home in wind. Presumably
this would have to be displayed as "altitude required"
unless it know current altitude somehow.
If the PDA knows altitude from an input, it can display
which fields you can reach, and whether you are high or low
on final glide. GPS altitude is relatively poor, but is one
option for getting current altitude info to the PDA. I
suppose you could input it manually, but that doesn't sound
practical. The best is a pressure sensor, but that would
mean getting altitude info from either a flight computer
(same as the airspeed problem above) or a Flight Recorder
that outputs its pressure altitude. Does the Volkslogger
give pressure alt to the PDA? Reading between the lines on
the PDA summaries I think it does.
For vario functions, it looks like it would need access to
TE. That's only available from a vario or flight computer.
I suppose it could fake it with altitude info for non-TE or
pseudo TE using wind and ground speed info. Do any do this?
You may be over-complicating things. The following assumes you prefer
cheap toys to expensive ones.
A simple GPS + PDA system can handle all your navigation and glide
calculations independently of the rest of your instruments. Granted,
the GPS altitude is less accurate than position, but probably still
good enough for FG calculations given all the other uncertainties and
happenstances during the final glide.
All you really need on top of that is a simple audio vario such as a
B.40, Tasman, or even an ancient Cambridge Mk 4. These are all
stand-alone instruments, so no additional interconnection is needed.
For STF, it again needs TE from a vario or flight computer,
but I suppose it could fake it as above.
If you have room for a second vario, fit a mechanical unit with a
Macready ring.
A club mate uses exactly this type of rig for club class competition
in his ASW-19.
===============
Why I think this is a good way to go
-------------------------------------------
For the last two seasons I flew my club's Pegase 90 with a Garmin GPS
II+, Cambridge Mk 4 audio vario, Winter vario w/MaCready ring and EW
model D logger. The only additional thing I would have liked was some
sort of moving map display to show airspace restrictions, etc.
This season I was planned to buy a glider and intended to install an
iPAQ 3630 running XCsoar, Garmin GPS 2+, Tasman or B.40, Winter
mechanical and the EW logger. However, I bought an ASW-20 which turned
out to have an SDI C4 already installed. In addition I installed my
GPS II+ and my EW logger. I'd previously acquired an iPAQ 3630 and am
thinking (slowly) about where to fit it so as to add the moving map
capability, but am short of panel real estate: the only really
suitable space is occupied by my GPS II+.
=========
If you need anything more complex than the GPS+PDA and separate varios
be aware that there are interconnect issues. In particular, a lot of
glide computers require the turn points to be fed to them from the GPS
but many? all? PDA programs don't accept turnpoints from the GPS, so
immediately you're into double task entry. My immediate thought was to
bypass this by using a blind GPS and put the task into the PDA:
however, most of the free-standing PDA programs don't output the
route-related GPS sentences needed by the SDI glide computer.
If you use the simple set-up I outlined above you'll avoid this sort
of nonsense and can, if you want, install a blind GPS to feed the PDA.
This is a good idea because the GPS doesn't then take up panel space
(it can be invisible behind a panel-top compass) or need any inputs,
freeing up panel space for the PDA. The other way to avoid
connectivity problems is to go with a complete set of kit from the
likes of Borgelt or Cambridge but that's more expensive.
Anything else is likely to result in the sort of connectivity issues I
described.
HTH
Martin
--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :
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