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Re: Formula Wanted



At 11:39 11/03/98 -0500, Jerald R. Malin wrote:

>Does anybody have the formula that will calculate the course you must
>fly and your ground speed if you know your true course, true air speed,
>wind direction and wind speed?

  Believe it or not, this is not a trivial problem. The wind triangle
problem involves three vectors. The wind vector is completely known,
that is you know the wind direction and its speed. The course vector
is only half known. You know its direction (your desired course),
but you don't know its magnitude (your ground speed which results from
the addition of the wind speed vector to your heading vector). In fact
this is one of the things you are trying to find. The third vector, the
heading vector is also only half known. You know the magnitude of it (the
airspeed you read from your airspeed indicator), but you don't know the
direction (the heading to fly such that when added to the wind results in
the desired course). This is the other thing we are trying to find. 
  There is in fact no analytic solution to this problem.

>I have some pilot calculators that do this calculation, but I would like

 The old E6-B circular slide rule flight computer (that some of us still use)
is an analog calculator for the wind problem that is quite simple and 
elegant in how it works. The newer electronic versions use an iterative
method to solve the problem. Basically they guess a heading, add the wind
to it and compare the resulting course with the desired course. By adjusting
the heading in a loop until the resulting course matches the desired course
it converges on a solution. There is no formula that you can simply plug
in the desired course and wind and get out a heading. 

>to do my own on a spread sheet, and would like the formula.

I don't know of any way to do an iterative solution to this problem
in a spreadsheet, but then again I don't know much about spreadsheets.

Good Luck!
Ron, wa4sir



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