Polar Analysis from flight logs?

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

"Tim.Ward" wrote in message
oups.com...
Robert Ehrlich wrote:
"Lars P. Hansen" wrote:

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.


I don't buy the explanation they give in the cited url

(http://www.navysbir.brtrc.com/succes..._navsea_p3.htm
l)
They pretend the device measures the speed and direction of dust
particles
from the shift in the frequency of reflected light, this is well
known
as Doppler effect and can only give the radial component (toward or
away
from the sensor) of the speed, not its value and direction. For
thermals
we are interested in the speed component which is nearly
perpendicular
to the measured component, so this would be of little interest. Of
course
whith several such devices on the ground, all the 3 compenents of
airmass
speed could be measured, maybe this in the intended use of the device
as it
is advertised, but in a glider you don't have sufficient vertical
distance
for putting 2 devices which could provide an accurate value for the
vertical
component of the speed.

It does work, but they use a little different technique.
The Doppler is only measured on particles at the focal length of the
optics.
The assumption is that the airmass (at least locally) is all the same,
and that the Doppler measurement is taken far enough away so the
effects of the airplane on the airmass are negligible.
So you send out two beams -- say, one forward at 45 degrees, one aft at
45 degrees.
It turns out that if you sum the signals from the two beams, you get
the vertical component of velocity, and if you difference the two
signals, you get the horizontal component.
Since we're measuring frequency, we can get sum and difference
frequencies from a mixer, though I have no doubt it runs through a DSP
somewhere.

So you only need one sensor head (though it puts out multiple beams).

By sending out two more beams, to each side, you can also pick up
sideslip information.
The clever thing is that they're using components developed for the
communications field, which helps to keep costs down.

Tim Ward

Still illegal under the rules IIRC, unless there's been a quiet change.

Frank Whiteley

"Lars P. Hansen" wrote:

OK, here we go: Could devices like this not also be used to detect
thermals?

Robert Ehrlich wrote:
disbelief that the sensors could work as described

I wrote an explanation of how they can work snipped

"F.L. Whiteley" wrote in message
...

Still illegal under the rules IIRC, unless there's been a quiet change.

Frank Whiteley


When I first looked at this, I would have agreed with you. But as
described, it gives just gives airspeed along all three axes.
Now, if you added a forward looking pair of beams with a longer focal length
to see any differences between the extremely local airmass and the slightly
further away airmass, _that's_ probably against contest rules.

Tim Ward

When thermal detectors come, people will discover they love flying with
them. Contest rules will change or people will stop flying contests.
Just as with GPS.

John Cochrane

"Tim Ward" wrote in message
nk.net...
"Lars P. Hansen" wrote:

OK, here we go: Could devices like this not also be used to detect
thermals?

Robert Ehrlich wrote:
disbelief that the sensors could work as described

I wrote an explanation of how they can work snipped

"F.L. Whiteley" wrote in message
...

Still illegal under the rules IIRC, unless there's been a quiet change.

Frank Whiteley


When I first looked at this, I would have agreed with you. But as
described, it gives just gives airspeed along all three axes.
Now, if you added a forward looking pair of beams with a longer focal
length
to see any differences between the extremely local airmass and the
slightly
further away airmass, _that's_ probably against contest rules.

Tim Ward

Yep. That could open a slightly separate can of worms, or perhaps lead to a
rules change.

Nevertheless, an interesting topic.

Frank

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.


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

Eric Greenwell
Washington State
USA

Yes, and thinking about it a little more, you sell it as a safety
device.
The reference to the local airmass gives you your current angle of
attack.
That's a pretty good safety device right there.
The longer-distance reference gives you what your AOA will be in, say,
200 meters.
(assuming the inertially-referenced attitude doesn't change)
That's a wind-shear detector.
For a light airplane making an approach at 100 kts, that's about 4
seconds of warning.
Is that something that could be sold to IFR pilots?

Tim Ward

"Tim.Ward" wrote:

It does work, but they use a little different technique.
The Doppler is only measured on particles at the focal length of the
optics.
The assumption is that the airmass (at least locally) is all the same,
and that the Doppler measurement is taken far enough away so the
effects of the airplane on the airmass are negligible.
So you send out two beams -- say, one forward at 45 degrees, one aft at
45 degrees.
It turns out that if you sum the signals from the two beams, you get
the vertical component of velocity, and if you difference the two
signals, you get the horizontal component.
Since we're measuring frequency, we can get sum and difference
frequencies from a mixer, though I have no doubt it runs through a DSP
somewhere.

So you only need one sensor head (though it puts out multiple beams).

By sending out two more beams, to each side, you can also pick up
sideslip information.
The clever thing is that they're using components developed for the
communications field, which helps to keep costs down.

Tim Ward

With these two beams at 45 degrees, you don't get truly the vertical and
horizontal components, rather the components along the two bissectors
of both beams, you would think this is nearly the same thing as the direction
of the components are just changed by the pitch attitude of the glider,
which is a very small angle usually, but this is sufficient for changing
lift into sink or vice-versa.