Re: detection of wind speed aloft

From:         jkkuchar@athena.mit.edu (James K. Kuchar)
Organization: Massachusetts Institute of Technology
Date:         15 Jun 95 14:25:30 
References:   1
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In article <airliners.1995.775@ohare.Chicago.COM>, Andy Tompson <andy@lll-winken.llnl.gov> writes:
|> I was recently on a cross country flight and was listening to the cockpit/ATC
|> communications, as I like to do (on UAL). There was some discussion about
|> finding good altitudes where the headwinds were low. I got to thinking how
|> headwinds can be measured from the plane. Now, I guess there are pitot tubes on
|> the plane that can be used to the wind speed relative to the plane. Do they
|> just subtract groundspeed to get the headwinds? If so, how do they measure the
|> groundspeed? Is there some type of correlation as a function of density,
|> temperature, and throttle setting (specific to the plane)? Is there some type
|> of differential measurement made with data from different parts of the airframe
|> to measure headwinds? Maybe this is all relatively simple, so maybe someone can
|> clear the air, as it were. Thanks in advance.

 Current aircraft constantly track their position using ground radio stations
and Inertial Measurement Systems. From this information, the aircraft can
calculate ground position, velocity, and ground track. Using data from the
pitot-static system, the true airspeed can be calculated. The wind direction
and speed can then be found using vector geometry. On "glass cockpit" aircraft,
an arrow is drawn on the Horizontal Situation Display that shows the wind
direction & speed, and the ground speed is also shown as a digital value. The
aircraft's ground track and heading are shown using separate symbols on the
display.

Jim Kuchar
jkkuchar@mit.edu