Hi Tim,
That's the first trick. The second is being able
to fly to a pressure at least 3% lower than the
current record. This is what appears anomalous
considering other the requirements of other airsports.
Geoff V
At 10:23 AM 14/09/2011, you wrote:
I'm not sure that a mistake and misinformation are quite the same.....
However I am happy to acknowledge that I am
human, and to support in full the rest of Mike's comments.
The trick to getting an altitude record at
present is to fly to a place where the pressure
is less than the last record. It doesn't matter much how high that is.
Cheers
Tim
tra dire e fare c'รจ mezzo il mare
On 13/09/2011 11:39, Mike Borgelt wrote:
In the interests of mis - information being quashed:
I was right about GPS vs Pressure altitude(PA).
Tim advised me he had GPS and Pressure Altitude
transposed in his spreadsheet. So his analysis
of flight records now agrees with the
theoretical analysis in my article and my
manual analysis of the IGC files that a few
very helpful people sent me. Thanks again guys.
As we fly gliders mostly in summer when it is
warmer than ISA, most of the time GPS altitude
is greater than PA. Not necessarily so in winter on wave flights.
If you find this isn't so it may be because you
have an early GPS receiver in the FR with some
heavy filtering (early Colibris in particular
or weird processing of GPS and PA) or your
pressure sensor in the FR is off significantly.
It also looks to me like the pressure altitude
is the anomaly in Geoff Vincent's Flarm. I'd need a few more files to be sure.
If you want to compare GPS and PA do remember
to take the offsets into account before takeoff
and after landing. In this case the FRs that
don't automatically start on movement or climb
are probably better. Pressure varies from day
to day and the pressure sensor in the FR is
fixed to 1013 Hpa reference pressure.
If you have an early Colibri don't attempt to
use the GPS altitude for final glide
calculations. Some other FRs seem to show gaps
in the GPS altitude record or in the case of
one recent FR design the GPS receiver seems to
be one optimised for 2D navigation and ground
vehicle dynamics with maybe some dead
reckoning of GPS altitude under some
circumstances . You can't really use that GPS
altitude for final glides either.
The CAI 302 traces seemed to be quite good with
only the odd gap(Garmin module), the EW
Microrecorder seems to have an excellent GPS
receiver and I would expect FLARM GPS data to
be very good also as the GPS module is one
where the user can set it for flight dynamics
and full time 3D navigation. Always assuming
you have a good antenna location with no
shielding by the airframe or your body.
This is one of the reasons we use our own GPS
module in the B500 and now B800 where we use
GPS altitude for final glides. We know how the GPS is set up.
The glider cares about geometric altitude for
how far it can glide, not PA. PA is a
requirement for airspace compliance. In my
experience given that the surface pressure will
change during the day and the errors inherent
in using cockpit statics as well as other
problems in electronic pressure sensing, GPS
altitude is superior to PA for final glides. Do
remember to give yourself a margin as your
glider may not really glide as well as assumed
in the polar in your electronic final glide
computer. In some B800 configurations you'll
get a real time display of how well it glides
against the assumed polar on every glide.
See the article on
<http://www.borgeltinstruments.com>www.borgeltinstruments.com
Mike
Borgelt Instruments - manufacturers of quality
soaring instruments since 1978 ABN: 75532924542
phone 0746 355784
fax 0746 358796
cellphones 0428 355784
0429 355784
email:
<mailto:[email protected]>[email protected]
website: <http://www.borgeltinstruments.com>www.borgeltinstruments.com
P.O.Box 4607 Toowoomba East, 4350
Queensland Australia
_______________________________________________
Aus-soaring mailing list
<mailto:[email protected]>[email protected]
To check or change subscription details, visit:
<http://lists.internode.on.net/mailman/listinfo/aus-soaring>http://lists.internode.on.net/mailman/listinfo/aus-soaring
_______________________________________________
Aus-soaring mailing list
[email protected]
To check or change subscription details, visit:
http://lists.internode.on.net/mailman/listinfo/aus-soaring
_______________________________________________
Aus-soaring mailing list
[email protected]
To check or change subscription details, visit:
http://lists.internode.on.net/mailman/listinfo/aus-soaring
