Cheap GPS Loggers for FAI Badges - Status?

Paul Bart wrote:
I do not know about the conversion process required to convert geometric and
I assume the actual within the bounds of GPS error altitude, to pressure
altitude. However given the assertion that the pressure altitude can differ
by as much as 1000ft from the geometric altitude, does it imply that two
pressure altitudes can actually differ by 2000ft? Would it not provide
sufficient argument to switch to geometric altitude?

Yes, this is correct. You don't have to climb as high on a cold winter
day, as you would on a hot summer day, to obtain a specific pressure
altitude gain. But, I suspect some (maybe most?) would say that we have
always measured pressure altitude is this sport, and that we should
continue doing so...

Marc

"Marc Ramsey" wrote in message
. com...
Paul Bart wrote:
However given the assertion that the pressure altitude can differ
by as much as 1000ft from the geometric altitude, does it imply that two
pressure altitudes can actually differ by 2000ft? Would it not provide
sufficient argument to switch to geometric altitude?

Yes, this is correct. You don't have to climb as high on a cold winter
day, as you would on a hot summer day, to obtain a specific pressure
altitude gain. But, I suspect some (maybe most?) would say that we have
always measured pressure altitude is this sport, and that we should
continue doing so...

Marc

Hi Marc

Thanks for your reply. Given the budding status of my gliding career, this
is not likely to be an issue for me any time soon , however given that GPS
can *potentially* reduce an error, by up to 1000 ft it should be seriously
considered. I wonder if the resistance to change is mainly due to the high
average age of the gliding fraternity?

Paul

On Thu, 03 Jun 2004 13:52:29 GMT, "Paul Bart"
wrote:


"Marc Ramsey" wrote in message
.com...
Paul Bart wrote:
However given the assertion that the pressure altitude can differ
by as much as 1000ft from the geometric altitude, does it imply that two
pressure altitudes can actually differ by 2000ft? Would it not provide
sufficient argument to switch to geometric altitude?

Yes, this is correct. You don't have to climb as high on a cold winter
day, as you would on a hot summer day, to obtain a specific pressure
altitude gain. But, I suspect some (maybe most?) would say that we have
always measured pressure altitude is this sport, and that we should
continue doing so...

Marc

Hi Marc

Thanks for your reply. Given the budding status of my gliding career, this
is not likely to be an issue for me any time soon , however given that GPS
can *potentially* reduce an error, by up to 1000 ft it should be seriously
considered. I wonder if the resistance to change is mainly due to the high
average age of the gliding fraternity?


I have a strong suspicion that climbing to a pressure altitude should
present much the same difficulty regardless of which way it differs
from the geometric altitude, but climbing to a geometric altitude will
get easier as the pressure (and hence pressure altitude) rises.

Unless I'm much mistaken, this could be used as an argument for
retaining the pressure altitude for badges.

What have I missed or misunderstood here?

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Paul Bart wrote:
"Marc Ramsey" wrote in message
Yes, this is correct. You don't have to climb as high on a cold winter
day, as you would on a hot summer day, to obtain a specific pressure
altitude gain. But, I suspect some (maybe most?) would say that we have
always measured pressure altitude is this sport, and that we should
continue doing so...

Thanks for your reply. Given the budding status of my gliding career, this
is not likely to be an issue for me any time soon , however given that GPS
can *potentially* reduce an error, by up to 1000 ft it should be seriously
considered.

But, using GPS altitude only reduces the error if we were measuring
geometric altitude. Using GPS altitude under the present rules would
*increase* the error, because we are presently measuring pressure altitude.

I wonder if the resistance to change is mainly due to the high
average age of the gliding fraternity?

I'm not going to touch that one...

Marc

"Paul Bart" wrote in message news:x2Gvc.4102

however given that GPS
can *potentially* reduce an error, by up to 1000 ft it should be seriously
considered. I wonder if the resistance to change is mainly due to the high
average age of the gliding fraternity?

Paul


You seem to have missed the frequently stated point that the
difference is not an error. An error free measurement of pressure
altitude will not be equal to an error free gps (geometric) altitude
except under rare conditions.

Recognition of this fact may have something to do with age, but the
real issues are recognizing what is to be measured, why it is being
measured, and then determining whether it is reasonable to change to
measuring something else.


Andy

"Andy Durbin" wrote in message
om...
"Paul Bart" wrote in message news:x2Gvc.4102

however given that GPS
can *potentially* reduce an error, by up to 1000 ft it should be
seriously
considered. I wonder if the resistance to change is mainly due to the
high
average age of the gliding fraternity?

Paul


You seem to have missed the frequently stated point that the
difference is not an error. An error free measurement of pressure
altitude will not be equal to an error free gps (geometric) altitude
except under rare conditions.

No I did not. You are correct, I have incorrectly used the word error if
one considers it's meaning in a relation to the output of the measuring
device, however that was not my intention.


Recognition of this fact may have something to do with age, but the
real issues are recognizing what is to be measured,



Height above ground I would have thought. If I understand the preceding
discussion correctly, pressure altitude was used because there were no other
viable options, not because it was a good measure of height above ground.



why it is being measured,



To either establish benchmark, or to fulfill some requirements. For each of
these I would rather know the actual distance above ground, not a measure
that depends on prevailing meteorological conditions. Unless, of course,
you consider Martin's observation, that the effort to climb to a particular
pressure altitude takes about the same effort regardless of the geometric
altitude and also assuming that it is the effort that is important, rather
then the actual height above ground.



and then determining whether it is reasonable to change to
measuring something else.





Thank you for your observation.



Paul

"Paul Bart" wrote in message ...
Recognition of this fact may have something to do with age, but the
real issues are recognizing what is to be measured,



Height above ground I would have thought. If I understand the preceding
discussion correctly, pressure altitude was used because there were no other
viable options, not because it was a good measure of height above ground.



Without any effort I can identify 3 different measurements that are
curently derived from pressure based barographs and flight recorders.
They a

continuity of flight
altitude gained following a low point
absolute altitude achieved

Height above ground is not a parameter that is used for any badge,
award, or record as far as I know.

Please don't interpret my reply as being an objection to COTS GPS.

If ever there was an opportunity to change the world from pressure
altitude to GPS altitude it was when RVSM was introduced. But no,
many aircraft faced expensive air data system retrofits because the
system was too enrenched in barometric altimetry.

Andy