Polar Analysis from flight logs?

Robert Ehrlich wrote:

After this discussion we are far from the original question, i.e.
can we infer anything about the polar of a glider just from GPS
fligth logs of this glider?
... solution proposed ...

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)

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.


--
Change "netto" to "net" to email me directly

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.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Wouldn't it be sufficient if the other glider was calibrated?
mg
Eric Greenwell wrote:
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.

Wouldn't it be sufficient if the other glider was calibrated?
mg
Eric Greenwell wrote:
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.

Wouldn't it be sufficient if the other glider was calibrated?
mg
Eric Greenwell wrote:
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.

Mike I Green wrote:
Wouldn't it be sufficient if the other glider was calibrated?
mg

I'm not sure what you mean by sufficient, but in any case, using a
comparison sailplane (calibrated or not), was not what the original
poster had in mind.

The advantage of a using a calibrated sailplane for the comparison is
you could actually calculate a polar, rather than just a relative
performance curve. Perhaps that was what you meant?

Eric Greenwell wrote:


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.




--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA