Greg Arnold wrote:
If the sensor is aiming straight down, at a glide angle of 40/1 the air
is going 40" aft for every 1" that it rises relative to the instrument.
If the sensor is aimed slightly aft (1/40, whatever that is in
degrees), the air won't be rising at all relative to the sensor. Right?

So isn't angle crucial?

OK, I'm persuaded! It now appears the sensor would need to be aimed up
or down rather accurately, or the at least the angle off vertical
measured accurately. Dang - that's harder. Perhaps the inertial system
would be a reasonable way to achieve this, or maybe differential GPS
system with antennas on the nose and tail.


Also, can the sensors measure speed when the air mostly is going
crossways in front of the sensor?

I think it depends on the sensor: some are optimized for speed in line
with the beam, some for speed perpendicular to the beam (cross wind
measurement, like for bullets). Perhaps there are ones that can read the
vector wind? I have no idea how much crossways speed the various sensors
can tolerate.

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Eric Greenwell
Washington State
USA