Polar Analysis from flight logs?

Robert Ehrlich wrote:

After a bit thinking about that my conclusion is that the above
solution doesn't work. Even if the system I was talking about
is overdetermined, there is always an undetermination on the couple
vertical speed of airmass/sink speed of glider relatively to airmass,
any combination of both with the same sum satisfies in the same way
the equations, so no valuable information on the polar of the glider
can be obtained unless we add some information on the airmass, either
by some other data, or by some further modelling (e.g. assuming the
total vertical movement of the airmass is zero, which is not realistic,
or that it is some given percentage of the average lift, or anything we may
think about it)

Maybe the laser airspeed devices could be applied to flight testing, but
by having them on the ground instead of in the glider. Pointing up, they
could be used to determine how much the atmosphere is moving during a
conventional, Johnson-style, flight test. The data could then be
corrected with this measurement of the actual air mass movement.

It would take units designed for long range measurements (meteorological
instruments, likely), of course, not ones really designed for airspeed
indicators.

Or, perhaps the laser unit could be used to determine when the airmass
is steady enough to make flight testing worthwhile, even it if can't
measure the vertical velocity sufficiently accurately to make
corrections useful.


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Eric Greenwell
Washington State
USA

Eric Greenwell wrote:

Robert Ehrlich wrote:

After a bit thinking about that my conclusion is that the above
solution doesn't work. Even if the system I was talking about
is overdetermined, there is always an undetermination on the couple
vertical speed of airmass/sink speed of glider relatively to airmass,
any combination of both with the same sum satisfies in the same way
the equations, so no valuable information on the polar of the glider
can be obtained unless we add some information on the airmass, either
by some other data, or by some further modelling (e.g. assuming the
total vertical movement of the airmass is zero, which is not realistic,
or that it is some given percentage of the average lift, or anything we may
think about it)

Maybe the laser airspeed devices could be applied to flight testing, but
by having them on the ground instead of in the glider. Pointing up, they
could be used to determine how much the atmosphere is moving during a
conventional, Johnson-style, flight test. The data could then be
corrected with this measurement of the actual air mass movement.

It would take units designed for long range measurements (meteorological
instruments, likely), of course, not ones really designed for airspeed
indicators.

Or, perhaps the laser unit could be used to determine when the airmass
is steady enough to make flight testing worthwhile, even it if can't
measure the vertical velocity sufficiently accurately to make
corrections useful.


OK, but this is far from the original question. Making Johnson-style flight
tests is one thing, using flight logs for polar analysis in another one.
A flight log provides some information about the polar as long a we have
or can assume some information about the airmass. We have here a huge
quantity of data it would be intersting to use. We could get some information
not found in flight test, like how far various gliders of the same model
are from the tested one, how performance degrades with time, ...

Robert Ehrlich wrote:

Or, perhaps the laser unit could be used to determine when the airmass
is steady enough to make flight testing worthwhile, even it if can't
measure the vertical velocity sufficiently accurately to make
corrections useful.



OK, but this is far from the original question. Making Johnson-style flight
tests is one thing, using flight logs for polar analysis in another one.
A flight log provides some information about the polar as long a we have
or can assume some information about the airmass. We have here a huge
quantity of data it would be intersting to use. We could get some information
not found in flight test, like how far various gliders of the same model
are from the tested one, how performance degrades with time, ...

I think the thread drifted from the original question because no one
could think of how to account for the airmass movement in any useful
way, so people began thinking of what the next best thing might be. A
new proposal on how to achieve a polar from flight logs would bring the
thread back to the original subject, I think.

Here's another way that flight logs might used: Comparison flights using
GPS logs to determine the difference between gliders would be useful,
but that requires at least two gliders to fly together at the same
airspeed; again, useful, but as you point out, not an answer to the
original question.


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Eric Greenwell
Washington State
USA

I think that a Cambridge 302 DDV has enough data in
its proprietary GPS sentence to be able to give you
the data you need. This is a cut and paste from the
manual:
----------------------
!w
The !w sentence is a proprietary format sentence that
contains air data and
instrument settings
The format is:
!W,1,2,3,4,5,6,7,8,9,10,11, 12,13*hhCRLF
1 Vector wind direction in degrees
2 Vector wind speed in 10ths of meters per second
3 Vector wind age in seconds
4 Component wind in 10ths of Meters per second + 500
(500 = 0, 495 = 0.5 m/s
tailwind)
5 True altitude in Meters + 1000
6 Instrument QNH setting
7 True airspeed in 100ths of Meters per second
8 Variometer reading in 10ths of knots + 200
9 Averager reading in 10ths of knots + 200
10 Relative variometer reading in 10ths of knots +
200
11 Instrument MacCready setting in 10ths of knots
12 Instrument Ballast setting
-------------------------------

Enough data here ?

John

John Ferguson wrote:
I think that a Cambridge 302 DDV has enough data in
its proprietary GPS sentence to be able to give you
the data you need. This is a cut and paste from the
manual:
-snip-

I recall from a conversation with Dave Ellis a few years ago, that the
302 can dump a lot of flight parameters at fairly high data rates over
the serial interface.

I don't know the details, but I beleive all one needs to do is connect
a terminal program, send the appropriate query, and the 302 starts
spilling its guts. A quick call to CAI might provide the answer.

I've often thought it would be cool if one could make a request of the
302 to produce a "super" IGC log with perhaps several records per
second containing airspeed, temperature and calculated windspeed. The
IGC spec allows for such data as comments or extra fields. It
certainly has the horsepower, and the results might provide some
interesting atmospheric information.

-Tom

John Ferguson wrote:
----------------------
!w
The !w sentence is a proprietary format sentence that
contains air data and
instrument settings
The format is:
!W,1,2,3,4,5,6,7,8,9,10,11, 12,13*hhCRLF
1 Vector wind direction in degrees
2 Vector wind speed in 10ths of meters per second
3 Vector wind age in seconds
4 Component wind in 10ths of Meters per second + 500
5 True altitude in Meters + 1000
6 Instrument QNH setting
7 True airspeed in 100ths of Meters per second
8 Variometer reading in 10ths of knots + 200
9 Averager reading in 10ths of knots + 200
10 Relative variometer reading in 10ths of knots + 200

11 Instrument MacCready setting in 10ths of knots
12 Instrument Ballast setting
-------------------------------

Enough data here ?

Not quite, it's missing indicated airspeed and temperature...

Marc

Can you get indicated airspeed from true airspeed and
add or subtract the vector or component wind.

I am presuming that the 302 is providing the data having
already been corrected for temp and alt.

Anyone from CAI have anything to add.

John

At 04:30 09 January 2005, Marc Ramsey wrote:
John Ferguson wrote:
----------------------
!w
The !w sentence is a proprietary format sentence that
contains air data and
instrument settings


Enough data here ?

Not quite, it's missing indicated airspeed and temperature...

Marc

John Ferguson wrote:
Can you get indicated airspeed from true airspeed and
add or subtract the vector or component wind.

No, you need temperature (which is also missing) and altitude to
calculate IAS from TAS.

I am presuming that the 302 is providing the data having
already been corrected for temp and alt.

The IAS and temperature data is available internal to the 302, but is
not reported by !w or any other usable sentence. The best one can do
(without additional input) is an approximation based on altitude, which
is not accurate enough for polar work.

Marc

Marc Ramsey wrote:


The IAS and temperature data is available internal to the 302, but is
not reported by !w or any other usable sentence. The best one can do
(without additional input) is an approximation based on altitude, which
is not accurate enough for polar work.

Hi Marc - the 302 can report the outside temperature with Log Mode 12
(page 4 in the data port manual), so IAS could be calculated.


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Eric Greenwell
Washington State
USA