"Doug Haluza" writes:

I have tried using a $10,000 carrier phase GPS receiver with 0.1m
precision (post-processed) for glide testing. The GPS data was so
precise, you could clearly see the antenna move a few cm when the
wing was raised for takeoff. Even when flying in the calmest
conditions, with no discernable airmass movement, the vertical
motions are significant.

In analysing the data, I could not precisely fit a straight line to
the data points from 1-2 min glides at constant airspeed, even after
correcting for slight airspeed variations using total
energy. Johnson does not have this problem because he only has two
data points, one at the beginning and one at the end of each
glide. When you have about a hundred data points, one every second,
you can really see the problem. You need a lot more data points to
average out the noise.

Based on this, I doubt that you could get useful data from a less
precise GPS, with a slower sampling interval, in uncontrolled
conditions. There is just too much noise to get useful results
without an impossibly huge data set.

You do not have a problem with lots of data, that's just more compute.
You will probably need another unit so you can do DGPS or RTK post
processing of the data. More data, at a faster rate is in fact simpler.
You do not have to worry about boundary conditions if your sample rate
is WAY over the responce of the airframe.

What you need to do is develop a set of Kalman filter parameters, to
fit your data, then extract the polar from them.

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
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