Terry wrote:
*****
By subtracting the 2 equations above you get

WS=(GS2^2-GS1^2-TAS2^2+TAS1^2)/(2(GS2COS(180-ABS(WD-TR2)-GS1COS(180-ABS(WD-TR1))

What I then did was calculate the ground speeds for 2 aircraft for a
known wind of 20 kts from 220 M

aircraft 1 aircraft 2
TAS 120 100
GS 111.7 91.4
TR 290 150

If I then use my above equation for WS after setting wind direction to
220, I get 20 kts as expected. However if I round off the GS to 112
and 91 kts the Wind speed changes from 20 to 9.5kts which suggests the
ground speeds have to be super accurate to get anywhere near the right
wind speed.. Given that also you are taking the TAS from a flight
plan, which will vary with density altitude and RPM setting etc.
suggests your objective is going to be rather difficult to achieve in
practice.

Hope this helps and good luck. If you come up with the solution I would
love to see it.
*****

Thanks for taking a crack at that, Terry. I hadn't considered that
such a small inaccuracy in aircraft speed could cause such an error.

Wouldn't the situation you describe above be a near worst case scenario
for error, i.e. only two aircraft and a nearly direct crosswind for
each? How would rounding those speeds affect the calculated wind speed
if the aircraft headings were 260 and 020? Isn't that a bit like
plotting position based upon two nearly same or reciprocal bearings,
rather than two that are near 90 degrees offset?

Also, since data will be available for many aircraft, we will probably
be able to calculate winds using at least five or six aircraft within
2000 feet of each other, sometimes many more.

This tool is basically meant to be a replay of a high altitude training
session, where the trainer can say "Okay, let's see what would have
happened if you had turned AAL460 fifteen left rather than descending
him." As it exists now, it is really cool, but a bit unrealistic. If
the winds are strong enough, a fifteen degree turn can easily add
twenty knots to a groundspeed. It is common for a new (or weak)
controller to turn an aircraft behind another, only to see that same
aircraft pick up a bunch of speed. The turn has nearly no effect on
separation, so they turn them some more. Within minutes, the turn is
fifty degrees and the controller is sucking up a seat cushion. Fun to
watch, but it would be nice to train that kind of stuff out of the
workforce. :-)

With even a close approximation of the winds, the realism is greatly
enhanced. Otherwise, the what-if's are reduced to a bland simulation
and utility is reduced.

Thanks again for your thoughtful reply.


Chad Speer
PP-ASEL, IA
ATCS, Kansas City ARTCC