writes:

This question is motivated by the recent discussion about deriving
polars from flight logs.

We know that GPS fixes have some amount of (absolute) error. What is
their accuracy relative to each other? In other words, when I'm
analyzing flight logs, how accurately can I calculate something like
sink rate using just the GPS fixes ("B" records)?

A standard logger is not much chop. You really need to record raw pseudo-range
data, and have a unit at a fixed place as well. Then with post processing
you can get to a few feet with good single frequency units, and to a hand
full of cm with a dual frequency one. I've heard mutterings of mm accuracy
with P-code over a few meters.

Get a reference on GPS surveying and look at the tollerence they quote.

I'm thinking about taking an early morning tow sometime this winter
when the pressure is high and the air is stable (at least vertically)
so I can calculate my actual polar, but I don't want to waste time and
money on this if the flight log isn't good enough. (And a few cockpit
notes of course -- IAS at various times, etc).



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