Polar Analysis from flight logs?

We all know what the manufacturer's polars look like, but what about our
individual planes. Has anyone done any work to develop a program that
would look at some flight logs and determine what a particular glider's
actual polar is? At one point Ball was making a vario system that would
determine the aircraft's polar over time just by flying.

For someone who already had some algorithms for computing wind from
ground track drift during thermals could take this info and then be able
to back figure from GPS ground speed what the IAS was during a
particular phase of the flight. By isolating longer sections of cruise
flight at varios airspeeds it should be do-able. Question is, has it
been done.

Mark

extra "hot" in the address to delay the spammers...

Mark,

How do you propose to isolate the impact of vertical air motion? For
instance, I can fly the ridge at 100Kts and maintain altitude (same for wave
or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
publish the L/D of my LS8 from the average of my flights for a season:
"LS8, with a measured L/D of 800:1..."

Cheers,
Erik


"Mark Zivley" wrote in message
m...
We all know what the manufacturer's polars look like, but what about our
individual planes. Has anyone done any work to develop a program that
would look at some flight logs and determine what a particular glider's
actual polar is? At one point Ball was making a vario system that would
determine the aircraft's polar over time just by flying.

For someone who already had some algorithms for computing wind from
ground track drift during thermals could take this info and then be able
to back figure from GPS ground speed what the IAS was during a
particular phase of the flight. By isolating longer sections of cruise
flight at varios airspeeds it should be do-able. Question is, has it
been done.

Mark

extra "hot" in the address to delay the spammers...

Obviously ridge flight would not be conducive, nor wave, but put enough
data together from cruises during thermal flights and I bet something
could be put together.

Papa3 wrote:

Mark,

How do you propose to isolate the impact of vertical air motion? For
instance, I can fly the ridge at 100Kts and maintain altitude (same for wave
or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
publish the L/D of my LS8 from the average of my flights for a season:
"LS8, with a measured L/D of 800:1..."

Cheers,
Erik


"Mark Zivley" wrote in message
m...

We all know what the manufacturer's polars look like, but what about our
individual planes. Has anyone done any work to develop a program that
would look at some flight logs and determine what a particular glider's
actual polar is? At one point Ball was making a vario system that would
determine the aircraft's polar over time just by flying.

For someone who already had some algorithms for computing wind from
ground track drift during thermals could take this info and then be able
to back figure from GPS ground speed what the IAS was during a
particular phase of the flight. By isolating longer sections of cruise
flight at varios airspeeds it should be do-able. Question is, has it
been done.

Mark

extra "hot" in the address to delay the spammers...

Mark Zivley wrote:

Obviously ridge flight would not be conducive, nor wave, but put enough
data together from cruises during thermal flights and I bet something
could be put together.


No it couldn't for exactly the same reasons ridge and wave don't work. In
typical thermal conditions air is going up and down all over the place.
Skilled pilots tend to fly in the good bits and ignore the bad bits.

Even if you could measure vertical and horizontal airspeed components,
"cruising" is likely to involve frequent speed changes, accelerations and
decelerations.



Papa3 wrote:

Mark,

How do you propose to isolate the impact of vertical air motion? For
instance, I can fly the ridge at 100Kts and maintain altitude (same for
wave
or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
publish the L/D of my LS8 from the average of my flights for a season:
"LS8, with a measured L/D of 800:1..."

Cheers,
Erik

Mark,

My first post came across as a bit glib - apologize for that. But, I
actually put a little thought into that subject recently while writing some
batch analysis specs for GPS log files. The problem is that a good glider
pilot will not encounter random vertical motions - even in cruise flight.
He/she will stack the deck in his favor, seeking out cloud streets or
connecting the best looking individual Cu. Thus, you can't just average
out the L/D over time on specific segments (e.g. cruise flight). What you
can do is deterimine which pilot does the best job of achieving highest L/D
on a given day. Several of the popular flight analysis programs do this
already.

I'd certainly be interested in any detailed ideas you might have.

P3

"Mark Zivley" wrote in message
m...
Obviously ridge flight would not be conducive, nor wave, but put enough
data together from cruises during thermal flights and I bet something
could be put together.

Papa3 wrote:

Mark,

How do you propose to isolate the impact of vertical air motion? For
instance, I can fly the ridge at 100Kts and maintain altitude (same for
wave
or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
publish the L/D of my LS8 from the average of my flights for a season:
"LS8, with a measured L/D of 800:1..."

Cheers,
Erik


"Mark Zivley" wrote in message
m...

We all know what the manufacturer's polars look like, but what about our
individual planes. Has anyone done any work to develop a program that
would look at some flight logs and determine what a particular glider's
actual polar is? At one point Ball was making a vario system that would
determine the aircraft's polar over time just by flying.

For someone who already had some algorithms for computing wind from
ground track drift during thermals could take this info and then be able
to back figure from GPS ground speed what the IAS was during a
particular phase of the flight. By isolating longer sections of cruise
flight at varios airspeeds it should be do-able. Question is, has it
been done.

Mark

extra "hot" in the address to delay the spammers...

On this topic of determining L/D from interthermal cruising, Dick
Johnson did a fascinating and underappreciated study in the late
1970's of airmass behavior between thermals. Dick flew in mostly blue
conditions and simply recoded his height loss versus distance covered
between thermals. Dick's results are reported in SOARING, June 1979.

Dick found that, on the average, the airmass between thermals has an
average sink rate related to the upgoing thermal strength. The
relationship Dick found was; the airmass sink is approximately 10% of
the lift strength.

I have always felt Dick's study explains why it is so difficult to fly
cross country (in a blue conditions) with a ship having an L/D less
than about 30:1. The probability of running into the next thermal
purely by chance becomes too low as the L/D drops.

For this discussion, I think Dick's study shows the inadvisability of
trying to deduce flight performance from interthermal measurements.

Bob

On Mon, 27 Dec 2004 20:43:41 GMT, "Papa3"
wrote:

Mark,

My first post came across as a bit glib - apologize for that. But, I
actually put a little thought into that subject recently while writing some
batch analysis specs for GPS log files. The problem is that a good glider
pilot will not encounter random vertical motions - even in cruise flight.
He/she will stack the deck in his favor, seeking out cloud streets or
connecting the best looking individual Cu. Thus, you can't just average
out the L/D over time on specific segments (e.g. cruise flight). What you
can do is deterimine which pilot does the best job of achieving highest L/D
on a given day. Several of the popular flight analysis programs do this
already.

I'd certainly be interested in any detailed ideas you might have.

P3

"Mark Zivley" wrote in message
om...
Obviously ridge flight would not be conducive, nor wave, but put enough
data together from cruises during thermal flights and I bet something
could be put together.

Papa3 wrote:

Mark,

How do you propose to isolate the impact of vertical air motion? For
instance, I can fly the ridge at 100Kts and maintain altitude (same for
wave
or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
publish the L/D of my LS8 from the average of my flights for a season:
"LS8, with a measured L/D of 800:1..."

Cheers,
Erik


"Mark Zivley" wrote in message
m...

We all know what the manufacturer's polars look like, but what about our
individual planes. Has anyone done any work to develop a program that
would look at some flight logs and determine what a particular glider's
actual polar is? At one point Ball was making a vario system that would
determine the aircraft's polar over time just by flying.

For someone who already had some algorithms for computing wind from
ground track drift during thermals could take this info and then be able
to back figure from GPS ground speed what the IAS was during a
particular phase of the flight. By isolating longer sections of cruise
flight at varios airspeeds it should be do-able. Question is, has it
been done.

Mark

extra "hot" in the address to delay the spammers...

Mark Zivley wrote:

We all know what the manufacturer's polars look like, but what about
our individual planes. Has anyone done any work to develop a program
that would look at some flight logs and determine what a particular
glider's actual polar is? At one point Ball was making a vario
system that would determine the aircraft's polar over time just by
flying.

For someone who already had some algorithms for computing wind from
ground track drift during thermals could take this info and then be
able to back figure from GPS ground speed what the IAS was during a
particular phase of the flight. By isolating longer sections of
cruise flight at varios airspeeds it should be do-able. Question is,
has it been done.

I haven't heard of it being done, and I can't imagine how one would
compensate for air motion, both vertical and horizontal, just using the
GPS info. Both motions change with location, altitude, and time. Perhaps
if the flight record included the airspeed, like some varios can supply,
there would be some hope of doing it. I don't think you could count on
the vertical motion averaging to zero during the cruises, since we
typically adjust our path to include as much up air as possible.

You can get some good info using a flight recorder, but you have to do
it when the air is calm. If you are really interested, invest in a few
high tows and make the measurements. Take a look at this test done on a
DG 800:

http://groups.yahoo.com/group/ASA-NewsGroup/message/59

You don't have to be a group member to read the message.


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

Eric Greenwell
Washington State
USA

I have tried using a $10,000 carrier phase GPS receiver with 0.1m
precision (post-processed) for glide testing. The GPS data was so
precise, you could clearly see the antenna move a few cm when the wing
was raised for takeoff. Even when flying in the calmest conditions,
with no discernable airmass movement, the vertical motions are
significant.

In analysing the data, I could not precisely fit a straight line to the
data points from 1-2 min glides at constant airspeed, even after
correcting for slight airspeed variations using total energy. Johnson
does not have this problem because he only has two data points, one at
the beginning and one at the end of each glide. When you have about a
hundred data points, one every second, you can really see the problem.
You need a lot more data points to average out the noise.

Based on this, I doubt that you could get useful data from a less
precise GPS, with a slower sampling interval, in uncontrolled
conditions. There is just too much noise to get useful results without
an impossibly huge data set.

Eric Greenwell wrote:
Mark Zivley wrote:

We all know what the manufacturer's polars look like, but what
about
our individual planes. Has anyone done any work to develop a
program
that would look at some flight logs and determine what a particular
glider's actual polar is? At one point Ball was making a vario
system that would determine the aircraft's polar over time just by
flying.

For someone who already had some algorithms for computing wind from

ground track drift during thermals could take this info and then be
able to back figure from GPS ground speed what the IAS was during a

particular phase of the flight. By isolating longer sections of
cruise flight at varios airspeeds it should be do-able. Question
is,
has it been done.

I haven't heard of it being done, and I can't imagine how one would
compensate for air motion, both vertical and horizontal, just using
the
GPS info. Both motions change with location, altitude, and time.
Perhaps
if the flight record included the airspeed, like some varios can
supply,
there would be some hope of doing it. I don't think you could count
on
the vertical motion averaging to zero during the cruises, since we
typically adjust our path to include as much up air as possible.

You can get some good info using a flight recorder, but you have to
do
it when the air is calm. If you are really interested, invest in a
few
high tows and make the measurements. Take a look at this test done on
a
DG 800:

http://groups.yahoo.com/group/ASA-NewsGroup/message/59

You don't have to be a group member to read the message.


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

Eric Greenwell
Washington State
USA

"Doug Haluza" writes:

I have tried using a $10,000 carrier phase GPS receiver with 0.1m
precision (post-processed) for glide testing. The GPS data was so
precise, you could clearly see the antenna move a few cm when the
wing was raised for takeoff. Even when flying in the calmest
conditions, with no discernable airmass movement, the vertical
motions are significant.

In analysing the data, I could not precisely fit a straight line to
the data points from 1-2 min glides at constant airspeed, even after
correcting for slight airspeed variations using total
energy. Johnson does not have this problem because he only has two
data points, one at the beginning and one at the end of each
glide. When you have about a hundred data points, one every second,
you can really see the problem. You need a lot more data points to
average out the noise.

Based on this, I doubt that you could get useful data from a less
precise GPS, with a slower sampling interval, in uncontrolled
conditions. There is just too much noise to get useful results
without an impossibly huge data set.

You do not have a problem with lots of data, that's just more compute.
You will probably need another unit so you can do DGPS or RTK post
processing of the data. More data, at a faster rate is in fact simpler.
You do not have to worry about boundary conditions if your sample rate
is WAY over the responce of the airframe.

What you need to do is develop a set of Kalman filter parameters, to
fit your data, then extract the polar from them.

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

I asked Dick Johnson, why couldn't I fly in calm conditions
(morning) and hold a given airspeed (say 60 knots)
and a given heading (say west) for 10 minutes, then
reverse heading to east (to cancel out any wind) and
then analyze the GPS trace to determine my ships L/D
at 60 knots. We have an accurate distance covered and
fairly accurate altitude lost, so why can't we crunch
the numbers?
Dick said the GPS info wasn't accurate enough. I thought
it was a good idea, but I defer to the master.
JJ

At 03:00 28 December 2004, Bob Gibbons wrote:
On this topic of determining L/D from interthermal
cruising, Dick
Johnson did a fascinating and underappreciated study
in the late
1970's of airmass behavior between thermals. Dick flew
in mostly blue
conditions and simply recoded his height loss versus
distance covered
between thermals. Dick's results are reported in SOARING,
June 1979.

Dick found that, on the average, the airmass between
thermals has an
average sink rate related to the upgoing thermal strength.
The
relationship Dick found was; the airmass sink is approximately
10% of
the lift strength.

I have always felt Dick's study explains why it is
so difficult to fly
cross country (in a blue conditions) with a ship having
an L/D less
than about 30:1. The probability of running into the
next thermal
purely by chance becomes too low as the L/D drops.

For this discussion, I think Dick's study shows the
inadvisability of
trying to deduce flight performance from interthermal
measurements.

Bob

On Mon, 27 Dec 2004 20:43:41 GMT, 'Papa3'
wrote:

Mark,

My first post came across as a bit glib - apologize
for that. But, I
actually put a little thought into that subject recently
while writing some
batch analysis specs for GPS log files. The problem
is that a good glider
pilot will not encounter random vertical motions -
even in cruise flight.
He/she will stack the deck in his favor, seeking out
cloud streets or
connecting the best looking individual Cu. Thus,
you can't just average
out the L/D over time on specific segments (e.g. cruise
flight). What you
can do is deterimine which pilot does the best job
of achieving highest L/D
on a given day. Several of the popular flight analysis
programs do this
already.

I'd certainly be interested in any detailed ideas you
might have.

P3

'Mark Zivley' wrote in message
. com...
Obviously ridge flight would not be conducive, nor
wave, but put enough
data together from cruises during thermal flights
and I bet something
could be put together.

Papa3 wrote:

Mark,

How do you propose to isolate the impact of vertical
air motion? For
instance, I can fly the ridge at 100Kts and maintain
altitude (same for
wave
or cloudstreets). I'm sure Rolladen-Schneider (ahem,
DG) would love to
publish the L/D of my LS8 from the average of my
flights for a season:
'LS8, with a measured L/D of 800:1...'

Cheers,
Erik


'Mark Zivley' wrote in message
m...

We all know what the manufacturer's polars look like,
but what about our
individual planes. Has anyone done any work to develop
a program that
would look at some flight logs and determine what
a particular glider's
actual polar is? At one point Ball was making a vario
system that would
determine the aircraft's polar over time just by flying.

For someone who already had some algorithms for computing
wind from
ground track drift during thermals could take this
info and then be able
to back figure from GPS ground speed what the IAS
was during a
particular phase of the flight. By isolating longer
sections of cruise
flight at varios airspeeds it should be do-able.
Question is, has it
been done.

Mark

extra 'hot' in the address to delay the spammers...