5Z wrote:

On Dec 27, 1:07 pm, Ian wrote:
One feature which both of these have is the ability to provide
airspeed data to a PDA which in turn can determine the wind vector by
comparing airspeed and GPS data - without having to stop and thermal. We
regularly fly ridges where knowledge of the wind speed and direction is
essential and flying 50 or 100 km without turning it the norm, so this
feature could be very attractive.

You also need a comapss sensor if you want to determine windspeed
without making any major course changes.

My SDI C4 manages to compute windspeed during a straight glide without a
compass as well as when circling in a thermal. In thermals it calculates
wind from the way the circles drift. In a straight line I think its
comparing GPS data with its pitot input: the wind speed seems consistent
between the two methods, but the calculated direction differs by 20
degrees or so with the straight line direction being less accurate.


The CAI 302, for example, computes wind by looking for a couple of
straight vectors that are different by some angle - perhaps 60-90
degrees. When on a long glide, I often find the vector wind is
different than the instantaneous headwind component as displayed by
GlideNav. To correct this, I change heading by 45 degrees, fly
straight for 10-15 seconds, then turn the other way 90 degrees and
again fly 10-15 seconds straight, then turn back to the original
course.

As I understand it, compass sensors are difficult and expensive to "get
right", so for now, most winds are derived this way.

The 302 provides airspeed and wind data to the PDA.

-Tom



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martin@ | Martin Gregorie
gregorie. | Essex, UK
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