Chris Scott;
The graph was intended as a schematic illustration of the text in my post #9, i.e. assuming you make a plot of real data for a particular airplane. The curves represent an arbitrary 'parabolic drag polar' (*) and don't show how a real aircraft departs from that near the stall and at high speed. Another schematization is that each curve is for a fixed thrust-to-weight ratio, whereas the thrust of a real aircraft at either rated thrust/power or any fixed throttle setting (except, of course, for the 'glider') varies with airspeed.
If you will kindly keep that in mind, we can nevertheless draw a few tangents to the curves in my graph to illustrate the principle.
... you haven't drawn us a sample tangential line ...
The 'point of contact' of tangents drawn from the origin (x=0, y=0) i.e. for still air, is 100 m/s for all T/W, the 'minimum drag speed' (max L/D) or best-glide-angle speed (Wiki's Vx ?).
If you draw the tangent from (x=30, y=0) to the curve for T/W=0,2 you'll find the speed for max flight path angle relative to the ground for 30 m/s headwind at about 75 m/s air speed (45 m/s ground speed).
If you draw a tangent from the same point to the curve for T/W=0, you'll find the speed for minimum power-off glide angle in 30 m/s headwind at about 112 m/s airspeed.
Finally, as Bubbers and Capn Bloggs have observed, if headwind equals TAS then ground speed is zero and FPA is vertical.
Regards,
HN39
(*)Parabolic drag polar: cD = a + b*cL^2. The wing loading was chosen so that the speed for max L/D is 100 m/s.
P.S. As a point of interest, albeit off-thread, I rather liked the way this graph illustrates how and why the speed for max rate-of-climb increases with thrust-to-weight ratio, following discussion of that topic some time ago on another tech-log thread.