Seniors USA 2009 Start and Finish notes..... # 711 reporting

On Mar 18, 7:00*am, Darryl Ramm wrote:

It is my impression that many piltos with built in loggers like the
Cambridge 302 do not understand that the flight recorder is using
cockpit ambient pressure and not the static line-in on the rear of the
instrument (only used for airspeed calculations). This is a
requirement to prevent the pilot being able to connect to the static
line and tamperer with logged pressure altitude.

I'm aware of that but I see now that what I wrote may be ambiguous.
Perhaps this would have been better:

"loggers (which cannot have an external static connection) will read
lower than
an altimeter which has an external static connection. "


Andy

Perhaps the simple answer is to mount your colibri on the panel and use the
logged altitude reading as your reference for starts, airspace, and
finishes. You do however need to know the difference in feet +/- between
real QNH/QFE and QNE (1013.2). I write this on a sticky.

Jim


At 14:31 18 March 2009, Andy wrote:
On Mar 18, 7:00=A0am, Darryl Ramm wrote:

It is my impression that many piltos with built in loggers like the
Cambridge 302 do not understand that the flight recorder is using
cockpit ambient pressure and not the static line-in on the rear of the
instrument (only used for airspeed calculations). This is a
requirement to prevent the pilot being able to connect to the static
line and tamperer with logged pressure altitude.

I'm aware of that but I see now that what I wrote may be ambiguous.
Perhaps this would have been better:

"loggers (which cannot have an external static connection) will read
lower than
an altimeter which has an external static connection. "


Andy

On Mar 18, 11:15*am, Jim White wrote:
Perhaps the simple answer is to mount your colibri on the panel and use the
logged altitude reading as your reference for starts, airspace, and
finishes. You do however need to know the difference in feet +/- between
real QNH/QFE and QNE (1013.2). I write this on a sticky.

Jim

At 14:31 18 March 2009, Andy wrote:

On Mar 18, 7:00=A0am, Darryl Ramm *wrote:

It is my impression that many piltos with built in loggers like the
Cambridge 302 do not understand that the flight recorder is using
cockpit ambient pressure and not the static line-in on the rear of the
instrument (only used for airspeed calculations). This is a
requirement to prevent the pilot being able to connect to the static
line and tamperer with logged pressure altitude.

I'm aware of that but I see now that what I wrote may be ambiguous.
Perhaps this would have been better:

"loggers (which cannot have an external static connection) will read
lower than
an altimeter which has an external static connection. "

Andy

I have performed a number of tests on this subject and found that the
big variable is how the cockpit air is vented. On some gliders the
cockpit pressure will be negative and some will be positive. Closing
the vents will tend to drive cockpit pressure negative and therefore
raise the apparent altitude.

Brian Utley

On Mar 18, 7:31*am, Andy wrote:
On Mar 18, 7:00*am, Darryl Ramm wrote:

It is my impression that many piltos with built in loggers like the
Cambridge 302 do not understand that the flight recorder is using
cockpit ambient pressure and not the static line-in on the rear of the
instrument (only used for airspeed calculations). This is a
requirement to prevent the pilot being able to connect to the static
line and tamperer with logged pressure altitude.

I'm aware of that but I see now that what I wrote may be ambiguous.
Perhaps this would have been better:

"loggers (which cannot have an external static connection) will read
lower than
an altimeter which has an external static connection. "

Andy

Andy, I had the sense you did know this. My comment was really to the
overall thread. The near universal situation will be IGC logger with
ambient cockpit pressure (an IGC requirement) and an altimeter with
ships' static (a type certification/airworthiness requirement for many
(all?) gliders). In which case the warnings from the CD make perfect
sense.

A Cambridge 302 or other IGC flight recorder that displays pressure
altitude or a PDA with pressure altitude being displayed from a logger
is the thing to look at if close. But looking for traffic better be
more important. Doing a comparison between an altimeter and Cambridge
302 pressure altitude display at different speeds would be interesting
and something I want to do for other reasons (but related to ambient
cockpit pressure induced altitude errors).

Hopefully most pilots will understand many gliders will have three
static sources, the fuselage static lines (for altimeter and ASI),
static from a multi-function probe (usually for flight computers/
direct reading/digital varios) and ambient cockpit static (used by IGC
fight recorders). Pretty nice redundancy and isolation provided by all
that.

Darryl

Oh great, now we are down to fiddling with altimeters, closing/opening
cockpit vents, and staring at a variety of altitude readouts (I
personally watch both the mechanical altimeter, after tapping, and my
SN10 digital readout) while on short final glide.

I still think there is a better (safer, easier) way, just haven't
figured it out yet.

Kirk
66

On Mar 18, 9:33*am, "
wrote:
Oh great, now we are down to fiddling with altimeters, closing/opening
cockpit vents, and staring at a variety of altitude readouts (I
personally watch both the mechanical altimeter, after tapping, and my
SN10 digital readout) while on short final glide.

I still think there is a better (safer, easier) way, just haven't
figured it out yet.

Kirk
66

And the issue there is that most SN10s will be installed with the
static connected to the ship's static (that's what the manual says,
and is probably best for accurate wind calculations etc.) and AFAIK is
not able to display any pressure altitude delivered via NMEA from an
attached IGC flight recorder. So the SN10 is normally not sensing
cockpit ambient and unable to report what any attached IGC flight
recorder is sensing.

Hopefully the take away here is more allow a saftey margin and do soem
tests before hand rather than watch some stupid display while killing
yourself and others at a finish.


Darryl

On Mar 18, 12:47*pm, Darryl Ramm wrote:
On Mar 18, 9:33*am, "
wrote:

Oh great, now we are down to fiddling with altimeters, closing/opening
cockpit vents, and staring at a variety of altitude readouts (I
personally watch both the mechanical altimeter, after tapping, and my
SN10 digital readout) while on short final glide.

I still think there is a better (safer, easier) way, just haven't
figured it out yet.

Kirk
66

And the issue there is that most SN10s will be installed with the
static connected to the ship's static (that's what the manual says,
and is probably best for accurate wind calculations etc.) and AFAIK is
not able to display any pressure altitude delivered via NMEA from an
attached IGC flight recorder. So the SN10 is normally not sensing
cockpit ambient and unable to report what any attached IGC flight
recorder is sensing.

Hopefully the take away here is more allow a saftey margin and do soem
tests before hand rather than watch some stupid display while killing
yourself and others at a finish.

Darryl

Maybe us cheap guys are doing better with this. My PDA is hooked up
to my logger and uses its output for altitude, so in theory I'm seeing
what's going into the logger file, no matter what static source is
being used for that (or GPS altitude for that matter). All I have to
do is
just fly the final glide numbers so I arrive above the required finish
altitude.

-- Matt

On Mar 18, 12:33*pm, "
wrote:
Oh great, now we are down to fiddling with altimeters, closing/opening
cockpit vents, and staring at a variety of altitude readouts (I
personally watch both the mechanical altimeter, after tapping, and my
SN10 digital readout) while on short final glide.

I still think there is a better (safer, easier) way, just haven't
figured it out yet.

Kirk
66

I say we put a big laser level on a ballon and tether it over the
airport. Like a omni-directional PAPI. If you see the red light, you
are too low :-)

Todd
3S

At 16:15 18 March 2009, Jim White wrote:
Perhaps the simple answer is to mount your colibri on the panel and use
the
logged altitude reading as your reference for starts, airspace, and
finishes. You do however need to know the difference in feet +/- between
real QNH/QFE and QNE (1013.2). I write this on a sticky.

Jim


At 14:31 18 March 2009, Andy wrote:
On Mar 18, 7:00=A0am, Darryl Ramm wrote:

It is my impression that many piltos with built in loggers like the
Cambridge 302 do not understand that the flight recorder is using
cockpit ambient pressure and not the static line-in on the rear of
the
instrument (only used for airspeed calculations). This is a
requirement to prevent the pilot being able to connect to the static
line and tamperer with logged pressure altitude.

I'm aware of that but I see now that what I wrote may be ambiguous.
Perhaps this would have been better:

"loggers (which cannot have an external static connection) will read
lower than
an altimeter which has an external static connection. "


Andy


Just to put the record straight, since AL4 (25 May 2001) Pitot Static MAY
be used. However some older designs may still be using Cockpit Static.

/*Quote

Pressure Altitude - In a GNSS FR, this is a five numeric group indicating
the pressure altitude in metres with respect the International Standard
Atmosphere (ISA) used in aviation, to a sea level datum of 1013.25 HPa.
The pressure recorded in the *.IGC file may either be "cockpit static"
(vented within the FR box), or use a tube connection to the pressure from
glider instrument system static tubing. If the pressure altitude signal
within the FR is used for other purposes such as cockpit instrument
readings which can be set to other datums such as
QNH or QFE, a one-way transmission system must be used from the sensor so
that the IGC file always records the required ISA to the 1013 sea level
datum irrespective of other settings used for flight instruments. The
permitted use of instrument-static is intended for a GNSS FR mounted in
the instrument panel. With such an installation, an OO as part of the
inspection of the FR installation must check the tubing and the pressure
connection to the FR to ensure that they will be out-of-reach of the
aircrew in flight. This is to prevent alteration to the IGC-file pressure
altitude record by any method. (AL4)

Unquote*/

Tim Newport-Peace >
Skype: specialist_systems
http://www.spsys.demon.co.uk/icom.htm

On Mar 18, 9:47*am, Darryl Ramm wrote:

And the issue there is that most SN10s will be installed with the
static connected to the ship's static (that's what the manual says,
and is probably best for accurate wind calculations etc.) and AFAIK is
not able to display any pressure altitude delivered via NMEA from an
attached IGC flight recorder. So the SN10 is normally not sensing
cockpit ambient and unable to report what any attached IGC flight
recorder is sensing.

Hopefully the take away here is more allow a saftey margin and do soem
tests before hand rather than watch some stupid display while killing
yourself and others at a finish.

Darryl

Ugh - now I have to go run experiments to see what generates the
lowest cockpit ambient pressure across different speeds and vent
configurations.

Since the official altitude for finishes is the logger baro altitude I
just fly that. I guess I could worry about the 100 feet or so of
pressure error - it's worth maybe 15-20 seconds in theory. If I were
going to reset my logger's altimeter I'd want to do it at the start of
my final glide, not the end. I suppose it would be okay for the CD to
call altimeter setting in addition to winds for finishers, but I'm not
sure it's worth the trouble.

Also, I don't recall whether my computer uses baro or GPS altitude for
calculating final glides, but it has never been so far off from the
logger baro readout that I can't just do what UH suggests in the last
mile or so - bleeding off speed to hold altitude as indicated by the
302 display, which is quite easy to scan.

The comments by UH, BB and others are REALLY important - staying on a
predictable track during the last part of final glide is a critical
safety practice. Thrashing around when you are low and fast is a
recipe for something really bad.

Also, an evil thought occurred to me - does Winscore check to see
whether you reset the logger altimeter between when you finish and
when you land? It strikes me you could finish really low then crank
the altimeter setting down 500 feet before you land. I'd guess someone
thought of that already and eliminated that opportunity for mischief.

9B