Snead1 wrote:

I need math help with a spreadsheet. I want to enter 1: Wind Direction 2:
Wind speed 3: Desired track of the glider 3: Speed made good by glider in
still air.

I want to solve for 1: Glider heading 2: Speed made good of glider along
desired track.

I would appreciate any help form anyone who might have been a little more
focused in math class than I.


Bill Snead
6W


Here is a simple little spreadsheet setup that models the situation. I
threw it together rather quickly, so use with care. It is iterative in that
you have to try a few values to get your answer. I didn't bother to work
out the complete algebraic/trigonometric solution. That's one of the neat
things about spreadsheets. You can keep things simple and try a few
different values until you get what you want.

This is most easily viewed as a vector problem. There are 3 vectors:

1) DV is your destination vector
2) WV is your wind vector
3) CV is your course vector (or air speed/direction)

The relationship is DV - WV = CV

Type the following in the indicated cells of your spreadsheet:

A1 vector
B1 mph
C1 heading(degrees)
D1 radians
E1 x
F1 y

A2 DV
B2 110
C2 50
D2 =radians(c2)
E2 =b2*cos(d2)
F2 =b2*sin(d2)

A3 WV
B3 30
C3 280
D3 =radians(c3+180)
E3 =b3*cos(d3)
F3 =b3*sin(d3)

A4 CV
B4 =sqrt(e4*e4+f4*f4)
C4 =degrees(asin(f4/b4))
D4 leave blank
E4 =e2-e3
F4 =f2-f3

You input the mph and heading for the DV and WV. The output is the CV. In
this case I have supplied some made up vectors of DV = 110 mph at 50 degrees
heading, a WV of 30 mph at 280 degrees heading (wind is blowing towards the
south-east). To arrive at your destination direction at 110 mph groundspeed
you must set a course of 35.8 degrees and travel 93.6 mph indicated
airspeed. If the CV airspeed isn't what you wanted, just change the DV
ground speed until it is.

Again, this isn't *exactly* what you asked for because you have to guess at
the speed made good to destination (DV) until the correct speed made good by
glider in still air (CV) is obtained. I could do it but it would take more
time. Besides, this is simple to enter and use. Someone has surely written
a spreadsheet to directly solve as you stated. Maybe someone will send it.
Meanwhile, this will work.

Regards,

-Doug