Polar Analysis from flight logs?

On Thu, 30 Dec 2004 02:46:15 GMT, wrote:

The Zander flight computer performs a constant L/D calculations throughout a
flight. The L/D is presented numerically on the screen. All you need to do
is note the L/D, flap setting and speed at any particular time.

.... and the EXACT airmass rise/fall.
This is where the task becomes impossible with current technology.


Bye
Andreas

At 15:30 30 December 2004, Andreas Maurer wrote:
On Thu, 30 Dec 2004 02:46:15 GMT, wrote:

The Zander flight computer performs a constant L/D
calculations throughout a
flight. The L/D is presented numerically on the screen.
All you need to do
is note the L/D, flap setting and speed at any particular
time.

.... and the EXACT airmass rise/fall.
This is where the task becomes impossible with current
technology.

Yup.

I don't believe it is possible to distinguish sailplane
vertical motion from the vertical motion of the airmass
with any of the current instruments, since both GPS
and barometric altimeters measure distance from the
earth's surface (in different ways obviously). Therefore
vertical motion measured from these instruments will
always be relative to the ground rather than relative
to the airmass.

If you had a test boom mounted AOA vane and a good
laser gyro, however....

9B

"Andreas Maurer" wrote in message
news
On Thu, 30 Dec 2004 02:46:15 GMT, wrote:

The Zander flight computer performs a constant L/D calculations
throughout a
flight. The L/D is presented numerically on the screen. All you need to
do
is note the L/D, flap setting and speed at any particular time.

... and the EXACT airmass rise/fall.
This is where the task becomes impossible with current technology.


Bye
Andreas



I found this laser sensor on the web:
http://www.navysbir.brtrc.com/succes...navsea_p3.html
Not many details.
Assuming it's accurate enough, one could be used to get the glider's
vertical speed through the airmass.
Now you have both horizontal and vertical velocity measurements relative to
the local airmass.
That should simplify the problem.

Also, it might give Bill Daniels his negative-lag variometer. (Thiotimoline
being in such short supply these days)

Unfortunately, the manufacturer's website is down for revamping. I haven't
emailed the contact address.

Tim Ward

"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.

Andy Blackburn writes:

There are two main challenges with using flight logs only:

1) There is no good source for IAS, so you have to try to estimate
it from GPS ground speed.

2) Typical soaring flights don't involve adequately calm vertical
airmass movement and probably not constant enough airspeed to trust
even long glides of many tens of miles.

You really need a different logger, that records raw GPS carrier phase,
plus static, pitot and temp. And Alpha vane would also be a big help.
Also you would want to run at 10 sample/sec or possible more.

If you go to this much trouble, you may as well ues 3 sets of GPS and
can then extract full position, attitude, and velocities as well.

--
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.

Tim Ward wrote:


I found this laser sensor on the web:
http://www.navysbir.brtrc.com/succes...navsea_p3.html
Not many details.
Assuming it's accurate enough, one could be used to get the glider's
vertical speed through the airmass.
Now you have both horizontal and vertical velocity measurements relative to
the local airmass.
That should simplify the problem.

A Google search turned up laser airspeed sensors that, in concept, could
be used to measure L/D directly from the glider. Some of them were good
for the low speeds we need to measure sink rates. So, have one pointing
forward, one pointing down, divide the forward speed by the sink rate,
and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
measurements are relative to the airmass.

Unfortunately, none of the units I saw seemed to be small, cheap, or
readily available, as their audience appeared to be military types or
rather expensive aircraft.


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

Eric Greenwell
Washington State
USA

OK, here we go: Could devices like this not also be used to detect thermals?
The description in the link below about how the laser "sees" minute dust
particles in the air seems to be well suited to thermals.

Happy New Year to all,
Lars Peder


--
Lars P. Hansen


"Eric Greenwell" wrote in message
...
Tim Ward wrote:


I found this laser sensor on the web:

http://www.navysbir.brtrc.com/succes...navsea_p3.html
Not many details.
Assuming it's accurate enough, one could be used to get the glider's
vertical speed through the airmass.
Now you have both horizontal and vertical velocity measurements relative
to
the local airmass.
That should simplify the problem.

A Google search turned up laser airspeed sensors that, in concept, could
be used to measure L/D directly from the glider. Some of them were good
for the low speeds we need to measure sink rates. So, have one pointing
forward, one pointing down, divide the forward speed by the sink rate,
and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
measurements are relative to the airmass.

Unfortunately, none of the units I saw seemed to be small, cheap, or
readily available, as their audience appeared to be military types or
rather expensive aircraft.


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

Eric Greenwell
Washington State
USA

"Lars P. Hansen" wrote in message
k...
OK, here we go: Could devices like this not also be used to detect
thermals?
The description in the link below about how the laser "sees" minute dust
particles in the air seems to be well suited to thermals.

Happy New Year to all,
Lars Peder

Probably. It also talks about the ability to show a 3-D representation of
the airmass movement around the aircraft. Since it's eye-safe, it probably
has a fairly short range.

This ties back to Bill Daniels' wish for a variometer with a negative
delay -- to be able to see what the airmass is doing a few seconds in front
of the glider.

It's unlikely that it's as inexpensive or will be as inexpensive as handheld
GPS, but if you were serious about performance measurement, it might be
able to pay for itself in a reduced number of tows to characterize a given
aircraft or configuration. So it might make sense for a university
department or a manufacturer. At least it's light enough and rugged enough
to consider mounting it on a sailplane.

Still, some of the civilian applications (shooting, sailboats) were in
more-or-less recreational areas, so perhaps they expect to be able to keep
the cost down.


Tim Ward



Lars P. Hansen


"Eric Greenwell" wrote in message
...
Tim Ward wrote:


I found this laser sensor on the web:


http://www.navysbir.brtrc.com/succes...navsea_p3.html
Not many details.
Assuming it's accurate enough, one could be used to get the glider's
vertical speed through the airmass.
Now you have both horizontal and vertical velocity measurements
relative
to
the local airmass.
That should simplify the problem.

A Google search turned up laser airspeed sensors that, in concept, could
be used to measure L/D directly from the glider. Some of them were good
for the low speeds we need to measure sink rates. So, have one pointing
forward, one pointing down, divide the forward speed by the sink rate,
and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
measurements are relative to the airmass.

Unfortunately, none of the units I saw seemed to be small, cheap, or
readily available, as their audience appeared to be military types or
rather expensive aircraft.


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

Eric Greenwell
Washington State
USA

On Thu, 30 Dec 2004 13:36:59 -0800, Eric Greenwell
wrote:

A Google search turned up laser airspeed sensors that, in concept, could
be used to measure L/D directly from the glider. Some of them were good
for the low speeds we need to measure sink rates. So, have one pointing
forward, one pointing down, divide the forward speed by the sink rate,
and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
measurements are relative to the airmass.

This is exactly what is accomplished by today's L/D calculators that
use GPS speed and barometrical measured height loss over a given time.






Bye
Andreas

Andy Blackburn wrote:

...since both GPS
and barometric altimeters measure distance from the
earth's surface (in different ways obviously). Therefore
vertical motion measured from these instruments will
always be relative to the ground rather than relative
to the airmass.

The way I see it, a barometric measurement will not be relative to the
ground at all: might even be related to the airmass, if only to a
pressure level.

Relating a barometric measurement to the ground is pretty arbitrary,
though I hear some folks are willing to do it down to 200' and 1/2
mile, on dark and stormy nights.

Some things you just have to take on faith.


--
Jack
----
"It is possible to fly without motors,
but not without knowledge and skill."
-- Wilbur Wright