On Wed, 19 Nov 2003 14:21:06 -0800, "Marc Ramsey"
wrote:

"Mike Borgelt" wrote...
We could also get real and eliminate the pressure sensor out of the
logger and start using geometric altitudes like the rest of aviation.

Which would make it really easy to fake a flight using a GPS simulator. The
change to geometric altitude will happen soon, at least above the mean
altitude of the tropopause (32K feet or so). I personally believe the
pressure sensor requirement should be eliminated for badge/diploma level
approval.

Marc


So you feed a pressure sensor to the computer controlling the GPS
pseudolites and it roughly matches with GPS altitudes with appropriate
corrections for reasonable guesses as to the mean temperature in the
atmosphere. Dead easy! And a trivial enhancement to your pseudolite
system. Given that some IFR aviation GPS systems already use pressure
altitude for GPS aiding it would not surprise me if test equipment
that can do all this isn't available off the shelf.

Why limit the change to geometric altitude to above 32K feet? Most
loggers are on cockpit static (an original adamantly insisted on
requirement by GFAC now changed I believe - why?). That is good for 50
to 100 feet of error, you get sea level pressure changes and huge
errors due to temperature in the atmosphere, let alone running the
pressure sensors at maybe -20 C or colder. The fully approved
Volkslogger only claims +/- 2hPa over temperature which is another
+/-100 feet at around 20,000. You are already over any reasonable GPS
error budget.

Mike Borgelt