TimRees
Topic Author
Posts: 298
Joined: Thu Aug 02, 2001 2:09 am

Calculating Wind Speed And Direction

Sat May 14, 2005 4:02 am

I'm puzzled as to how when ATC ask an aircraft the outside wind speed and direction they simply 'read it back'.

Is this a function of pitot tubes (wasn't mentioned in the thread on them I read) or is it the INS or something I'm not aware of. As you can guess, I'm not a pilot.
 
Goldenshield
Posts: 5005
Joined: Sun Jan 14, 2001 3:45 pm

RE: Calculating Wind Speed And Direction

Sat May 14, 2005 6:58 am

The GPS or INS takes and compares the following data:

Trajectory heading - actual heading
Actual airspeed - groundspeed

This will give you a simple wind. There are other factors taken into account as well for a more exact figure, such as altitude, OAT, etc.
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Pihero
Posts: 4196
Joined: Mon Jan 31, 2005 5:11 am

RE: Calculating Wind Speed And Direction

Sat May 14, 2005 9:13 am

Goldenshield,

Shouldn't it be :
"compares the following data :

heading - actual TRACK
TRUE airspeed - groundspeed " ?

Regards
Contrail designer
 
Goldenshield
Posts: 5005
Joined: Sun Jan 14, 2001 3:45 pm

RE: Calculating Wind Speed And Direction

Sat May 14, 2005 9:20 am

The heading part could be said either way, since you are correcting for drift, and, yes, true airspeed would be your actual indicated airspeed corrected for everything else, but I didn't want to get too in depth.

Basically, it's all triginometry in the end.
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saintsman
Posts: 2037
Joined: Fri Mar 15, 2002 12:34 am

RE: Calculating Wind Speed And Direction

Sat May 14, 2005 4:09 pm

If they simply read it back then the information is on a screen in front of them, already worked out by one of the navigational computers.

Actually, I bet most airline pilots would have to think hard about working those figures out! It would have been a long time since they had to do it themselves  Wink
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Calculating Wind Speed And Direction

Sat May 14, 2005 4:30 pm

Quoting Saintsman (Reply 4):
Actually, I bet most airline pilots would have to think hard about working those figures out! It would have been a long time since they had to do it themselves

Don't bet too much. There are some of us who had that drilled into our heads in the military. I can still remember having to determine wind at altitude with only DME, and wizz wheel. Funny thing is somethings you never forget. Or perhaps having to do an ICE T speed calculation?
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