Andreas Maurer wrote:
On Thu, 30 Dec 2004 13:36:59 -0800, Eric Greenwell
wrote:


A Google search turned up laser airspeed sensors that, in concept, could
be used to measure L/D directly from the glider. Some of them were good
for the low speeds we need to measure sink rates. So, have one pointing
forward, one pointing down, divide the forward speed by the sink rate,
and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
measurements are relative to the airmass.


This is exactly what is accomplished by today's L/D calculators that
use GPS speed and barometrical measured height loss over a given time.

GPS speed and pressure altitude are referenced to the earth, not the air
mass, so they would determine a different L/D than airmass referenced
instruments. In concept, a glider flying at constant speed through
rising and falling air would have a constant L/D according to the laser
airspeed sensors, but a widely varying one based on GPS speed and
pressure altitude.


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Eric Greenwell
Washington State
USA