Robert Ehrlich wrote:

After a bit thinking about that my conclusion is that the above
solution doesn't work. Even if the system I was talking about
is overdetermined, there is always an undetermination on the couple
vertical speed of airmass/sink speed of glider relatively to airmass,
any combination of both with the same sum satisfies in the same way
the equations, so no valuable information on the polar of the glider
can be obtained unless we add some information on the airmass, either
by some other data, or by some further modelling (e.g. assuming the
total vertical movement of the airmass is zero, which is not realistic,
or that it is some given percentage of the average lift, or anything we may
think about it)

Maybe the laser airspeed devices could be applied to flight testing, but
by having them on the ground instead of in the glider. Pointing up, they
could be used to determine how much the atmosphere is moving during a
conventional, Johnson-style, flight test. The data could then be
corrected with this measurement of the actual air mass movement.

It would take units designed for long range measurements (meteorological
instruments, likely), of course, not ones really designed for airspeed
indicators.

Or, perhaps the laser unit could be used to determine when the airmass
is steady enough to make flight testing worthwhile, even it if can't
measure the vertical velocity sufficiently accurately to make
corrections useful.


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Eric Greenwell
Washington State
USA