T o d d P a t t i s t wrote:
"Kublai" wrote:

I don't think testing against GPS makes sense at all, as the ASI will
surely work properly if indicating wrong ground speed at headwind - so
what information do you gain ?

This question is hard to understand, but GPS testing does
make sense. If the aircraft is flown at a constant ASI
indicated airspeed, and the GPS groundspeeds are recorded,
the calculator will give true airspeed. From that you can
determine if the ASI is off (with appropriate
altitude/installation error corrections).


I think his point is that flying into a headwind or with a
tailwind will give you the same true and indicated airspeed
but different groundspeeds as determined by GPS.

You could fly at constant indicated airspeed and
altitiude in a wide circle and note the headings at which
the groundspeed (GPS) is maximum and minimum. For a steady
wind, the true airspeed corresponding to that indicated
airspeed should be the average of the two.

The algorithim at the aformentioned webpage appears to do
something a bitmore sophisticated than that by numerically
solving for the wind.

--

FF