Metric Instruments

I'll second the use of the B40 as a backup. I don't have a mechanical vario
at all. As a precaution, I change the B40 internal battery on the same
schedule as the one on the MH Oxygen system, wasteful perhaps, but
reassuring.

Ray Warshaw
1LK


"Bill Daniels" wrote in message
...

"Andreas Maurer" wrote in message
...

How many times have you praised yourself for having instruments on
board that do not need electricity to work properly?

I did that dozens of times - electricity is definitely not a reliable
thing in gliders.



Bye
Andreas

This amazes me. Electricity not reliable? I know this is "conventional
wisdom" but, I have never had an electronic device fail in flight but
many,
many mechanical instruments have failed me. In fact, even when an
electronic device seemed to fail, it was always a mechanical switch or
battery contact that failed and not the device itself. (Hint: Use the
best
electrical hardware money can buy.)

I sit here typing on an incredibly complex device called a Personal
Computer. The CPU alone has over 10 million transistors in it. If the PC
ever fails, the reason will almost certainly be the mechanical hard drive.
If the power grid fails to provide electricity, the UPS will keep it
running
long enough for a graceful shutdown.

In just the last month, we have had a mechanical altimeter fail. The only
way we knew was that it couldn't be set to local field elevation. We had
an
airspeed indicator fail to work at all. I had mechanical altimeter
suddenly
lose 2000 feet as it became unstuck. The Winter mechanical vario in one
glider spends most of the time stuck at +10 Kts. so we rely on the only
reliable one - the Cambridge L-Nav. (If I ask, "Why the mechanical
vario",
I hear, "For backup".) Mechanical instruments are neither rugged nor
reliable.

Mike Borgelt makes an excellent case for using his B40 with it's internal
9V
battery as a backup. Unlike the Winter, it has audio even while running
on
the internal battery.

As for readability, I don't think you will find a "three hand" altimeter
in
an airliner anymore. They have had drum-type digital displays since
sometime in the 1960's. Many studies have shown the digital readout is
harder to mis-read. Although, today these are likely to be just the
back-up
to the digital "glass cockpit".

Bill Daniels

Bill Daniels wrote:

snip

GPS provides highly accurate, although not ATC compliant, altitude.

I am afraid that the claim that GPS altitude is recorded "highly
accurately" in IGC files from IGC-approved GPS recorders, is
unfortunately not true.

The second part of the statment above IS true, that the GPS altitude
datum is not the same as the pressure altitude datum used worldwide in
aviation for altimeter settings for aircraft separation and for
controlled and restricted airspace.

In theory, due to the angle of cut of the lines-of-position from the
satellites, GPS altitude errors should be, on average, about 1.8 times
those for horizontal position or lat/long. Measurements over many
years by the IGC GNSS Flight Recorder Approval Committee (GFAC) show an
average lat/long error of 11.4 metres, taken from a moving vehicle at
surveyed points at about 51N 001W (Southern England, near Lasham
Gliding Centre). Going on this, an average GPS altitude error could be
expected as about 20.5 metres.

However, in a significant proportion of IGC-format flight data files,
there are significant anomalies in the GPS altitude figures that have
been recorded, in excess of the 20 metres mentioned above. Only today
I was commenting in another email on aspects of an IGC file from a
recent glider flight in the USA that had a 1500 foot overshoot in GPS
altitude (compared to the much more reliably recorded pressure
altitude) for reasons unknown.

The problem seems to be, particularly in low-cost GPS boards, that,
rather than processing a fix in three dimensions, it is processed
separately as lat/long and then separately as altitude. The algorithms
for lat/long and for altitude appear to be different, hence the regular
occurrence in IGC files or GPS altitude anomalies despite few lat/long
anomalies. Naturally, more attention seems to be paid by GPS board
manufacturers to lat/long rather than altitude.

In a survey made in year 2000 after the deliberate Selective
Availability error was removed from the GPS system by Presidential
Decree, no less than 27% of over 400 IGC flight data files analysed
from 7 countries in both hemispheres, had anomaliesof one sort or
another in the GPS altitude recorded in the file. From IGC files that
I have seen since, there is no reason to believe that this proportion
is much improved today. Just look at a large selection of IGC-format
flight data files and see for yourselves. In my database, I have
literally hundreds of IGC flight data files that show major anomalies
in recorded GPS altitude data. Fortunately, anomalies in lat/long data
in the same IGC files are very rare.

This is not an attack on the accuracy of the GPS system or even its
altitude recording capability. It is a reporting of results of GPS
altitude recording in IGC flight data files derived from a number of
low-cost GPS boards made by a number of different companies from
different parts of the world. I guess that in more expensive
"professional aviation standard" GPS boards, and in differential-GPS
systems with local beacons, the GPS altitude figures are more accurate
and with less anomalies. But such (expensive) systems do not apply to
the current 27 types of GNSS flight recorders that are IGC-approved
(from 11 manufacturers) and whose IGC-approval documents appear on the
IGC gliding/gnss web site:

http://www.fai.org/gliding/gnss/igc_approved_frs.pdf

Ian Strachan
Chairman IGC GNSS Flight Recorder Approval Committee

Hi,

Winter instruments are available with either 6 O'clock or 12 O'clock zero
for airspeed indicators and altimeters. 12 O'clock is standard.

Good Soaring,

Paul Remde
Cumulus Soaring, Inc.
http://www.cumulus-soaring.com

"Stig Oye" wrote in message
...
No. I believe that it is an old German standard, but if you buy
PZL instruments you can specify it to either top or bottom.

http://www.pzl.com.pl/en/produkty/os...e/pw-12-a.html

BTW, these instruments are very high quality but somewhat heavy.
Highly recommended.

Regards Stig Oye

In article , Roy Bourgeois
says:

This may be a silly question - but are all metric altimeters
configured with 'Zero at 6 O'clock' as I saw in France?
I did not have trouble converting to meters/kilometers
but I did have trouble quickly reading the altimeter
with the zero at the bottom of the instrument face
(especially on the little 57mm instruments). Just
curious.

Roy

Bill Daniels wrote:
Does it strike some of the digerati here that expensive mechanical
altimeters with easily mis-read clock-like hands locked into either the
metric or US measurement systems are archaic?

I have both a mechanical and digital altimeter. When i want to check my
altitude, I tend to rely on the mechanical. Like a watch with hands, I
don'd read it as much as glance at it and I find that easier. YMMV.

Tony V.

"Stefan" wrote in message
...
Bill Daniels wrote:

This amazes me. Electricity not reliable? I know this is "conventional
wisdom" but, I have never had an electronic device fail in flight but
many,

I had the battery fail twice on me: During my first 300km flight and
during my second 300km flight. Which meant that I had done two
successful 300km flights without GPS and acoustic vario, but none of
them was logged. :-P

Stefan, buy a new battery. They are cheap these days. At least, much
cheaper than a failed 300Km attempt.

Bill Daniels

By my checking, WAAS enabled, dual antenna DGPS receiver boards are cheap -
on the order of $10US in OEM quantities. The specs say 1 meter RMS in Lat
Long and 6 meters RMS in altitude when a DGPS signal is available. Of
course, they probably aren't in approved loggers.

6 meters in altitude is a lot better than a barometric altimeter on a
non-standard atmospheric day.
I wouldn't want to change ATC's reliance on barometric altimeters. On a
hot day, they understate the real altitude, giving us western US guys
another 1000 or so feet to play in below the floor of Class A airspace.

I checked GPS altitude a couple of times by putting a hand held Garmin GPS
on a prime US Geodetic Survey marker. The marker said 10,346 feet. The GPS
said 10,350 feet + or - 70 feet. The + or - error estimate seemed pretty
pessimistic. Those are pretty typical numbers.

Bill Daniels

"Ian Strachan" wrote in message
ups.com...
Bill Daniels wrote:

snip

GPS provides highly accurate, although not ATC compliant, altitude.

I am afraid that the claim that GPS altitude is recorded "highly
accurately" in IGC files from IGC-approved GPS recorders, is
unfortunately not true.

The second part of the statment above IS true, that the GPS altitude
datum is not the same as the pressure altitude datum used worldwide in
aviation for altimeter settings for aircraft separation and for
controlled and restricted airspace.

In theory, due to the angle of cut of the lines-of-position from the
satellites, GPS altitude errors should be, on average, about 1.8 times
those for horizontal position or lat/long. Measurements over many
years by the IGC GNSS Flight Recorder Approval Committee (GFAC) show an
average lat/long error of 11.4 metres, taken from a moving vehicle at
surveyed points at about 51N 001W (Southern England, near Lasham
Gliding Centre). Going on this, an average GPS altitude error could be
expected as about 20.5 metres.

However, in a significant proportion of IGC-format flight data files,
there are significant anomalies in the GPS altitude figures that have
been recorded, in excess of the 20 metres mentioned above. Only today
I was commenting in another email on aspects of an IGC file from a
recent glider flight in the USA that had a 1500 foot overshoot in GPS
altitude (compared to the much more reliably recorded pressure
altitude) for reasons unknown.

The problem seems to be, particularly in low-cost GPS boards, that,
rather than processing a fix in three dimensions, it is processed
separately as lat/long and then separately as altitude. The algorithms
for lat/long and for altitude appear to be different, hence the regular
occurrence in IGC files or GPS altitude anomalies despite few lat/long
anomalies. Naturally, more attention seems to be paid by GPS board
manufacturers to lat/long rather than altitude.

In a survey made in year 2000 after the deliberate Selective
Availability error was removed from the GPS system by Presidential
Decree, no less than 27% of over 400 IGC flight data files analysed
from 7 countries in both hemispheres, had anomaliesof one sort or
another in the GPS altitude recorded in the file. From IGC files that
I have seen since, there is no reason to believe that this proportion
is much improved today. Just look at a large selection of IGC-format
flight data files and see for yourselves. In my database, I have
literally hundreds of IGC flight data files that show major anomalies
in recorded GPS altitude data. Fortunately, anomalies in lat/long data
in the same IGC files are very rare.

This is not an attack on the accuracy of the GPS system or even its
altitude recording capability. It is a reporting of results of GPS
altitude recording in IGC flight data files derived from a number of
low-cost GPS boards made by a number of different companies from
different parts of the world. I guess that in more expensive
"professional aviation standard" GPS boards, and in differential-GPS
systems with local beacons, the GPS altitude figures are more accurate
and with less anomalies. But such (expensive) systems do not apply to
the current 27 types of GNSS flight recorders that are IGC-approved
(from 11 manufacturers) and whose IGC-approval documents appear on the
IGC gliding/gnss web site:

http://www.fai.org/gliding/gnss/igc_approved_frs.pdf

Ian Strachan
Chairman IGC GNSS Flight Recorder Approval Committee

On Wed, 24 Aug 2005 15:17:23 -0600, "Bill Daniels"
wrote:


This amazes me. Electricity not reliable? I know this is "conventional
wisdom" but, I have never had an electronic device fail in flight but many,
many mechanical instruments have failed me.

Glad that you never had a problem.
I have lost count of the numbers where my clubs glider's batteries
were forgotten to charge after flight or ran out of energy because
they had reached their service life...

Not to mention more than a couple of GPS failures over the years...

Of course - there have been more than a couple of mechanical (Winter)
altimeter failures, too - but at least the altimeter didn't stop
working at all but only lost precision.


It's pretty impossible to convince me of the superiority of something
that needs to be charged as long as more than one owner is involved.
This includes a backup battery. vbg



Bye
Andreas

"Bill Daniels" wrote in message
...
Does it strike some of the digerati here that expensive mechanical
altimeters with easily mis-read clock-like hands locked into either the
metric or US measurement systems are archaic?

GPS provides highly accurate, although not ATC compliant, altitude.
Various
vendors provide electronic pressure altimeters with digital displays that
can be switched between meters and feet with the push of a button.
Digital
pressure altitude sensors drive the "glass cockpits" of new GA aircraft.

I seems to me that clock-like altimeters designed 70 years ago and
maintained by watchmakers must be nearing their well-deserved retirement.

Bill Daniels

Yeah, now if they can just make them so they don't need batteries.

Tim Ward

"Tim Ward" wrote in message
ink.net...

"Bill Daniels" wrote in message
...
Does it strike some of the digerati here that expensive mechanical
altimeters with easily mis-read clock-like hands locked into either the
metric or US measurement systems are archaic?

GPS provides highly accurate, although not ATC compliant, altitude.
Various
vendors provide electronic pressure altimeters with digital displays
that
can be switched between meters and feet with the push of a button.
Digital
pressure altitude sensors drive the "glass cockpits" of new GA aircraft.

I seems to me that clock-like altimeters designed 70 years ago and
maintained by watchmakers must be nearing their well-deserved
retirement.

Bill Daniels

Yeah, now if they can just make them so they don't need batteries.

Tim Ward


What's the big deal with batteries? IMHO, batteries are at worst a minor
inconvenience easily worth enduring for the benefits of the technology they
make possible.

Every portable gadget uses them. Most folks have a cell phone, PDA,
portable GPS, digital camera, maybe a camcorder and who knows what else.
Even your car, tug or winch won't start without a battery. They're cheap
and they work fine with a little TLC and regular replacement.

My glider uses a standard 7.5 AH 12V SLA that now sits on a shelf connected
to a charger that quietly maintains the charge. I know for sure that it
will work at least 10 hours and still show more than 12.5 volts while
transmitting. It has a three year "replace by" date written on it whereupon
I will plunk down $20 for another at "Batteries-R-Us" even if it still seems
OK. I don't trust old batteries.

Bill Daniels

Well, even if there is only one owner involved, I'm not going to rely on
electrically power instruments only. Never.

--
Bert Willing

ASW20 "TW"


"Andreas Maurer" a écrit dans le message de news:
...
On Wed, 24 Aug 2005 15:17:23 -0600, "Bill Daniels"
wrote:


This amazes me. Electricity not reliable? I know this is "conventional
wisdom" but, I have never had an electronic device fail in flight but
many,
many mechanical instruments have failed me.

Glad that you never had a problem.
I have lost count of the numbers where my clubs glider's batteries
were forgotten to charge after flight or ran out of energy because
they had reached their service life...

Not to mention more than a couple of GPS failures over the years...

Of course - there have been more than a couple of mechanical (Winter)
altimeter failures, too - but at least the altimeter didn't stop
working at all but only lost precision.


It's pretty impossible to convince me of the superiority of something
that needs to be charged as long as more than one owner is involved.
This includes a backup battery. vbg



Bye
Andreas