Thanks. The TeleMega reacquired shortly after boost and had 10 satellites at apogee. The GPS altitude trace looks good. The reason I ask it that the barometric altitude reads 9700 ft, but the GPS reported 10,240 ft. If that is accurate, it's my first flight above 10k (and a successful L3 to boot). I just want to know I have solid data to call it a 10k flight. Most of my flights have been with the TeleMetrum 1.2, and the GPS clearly doesn't get a good fix until well after apogee. My TeleMetrum 2.0 and TeleMega seem to work much better, with good fixes at apogee.
David On Mon, Jul 13, 2015 at 11:33 PM, Keith Packard <[email protected]> wrote: > Casey Barker <[email protected]> writes: > > > On the ascent, the barometric curve will be smooth and reasonably > accurate, > > save for the "Mach bumps" around the transsonic region, if you're going > > that fast. The GPS is likely to lose at least a few satellites in its fix > > at high speed, making GPS altitude inaccurate (or unreported) for most of > > the ascent. > > If the static ports are in clean air, then this is true. If the static > ports are too close to a transition, then all measurements above about > .8 mach are likely invalid > > GPS also will probably lose lock under high acceleration (about > 4g). Most of the time, it re-acquires within a few seconds of motor > burn-out and happily reports accurate altitudes from there through > apogee. Sometimes, it fails to re-acquire lock, and sometimes it reports > having lock but continues to report invalid altitude data. > > > However, once it slows down, and assuming the GPS maintains or regains > > lock, it will give you a more accurate absolute height at apogee. > > Barometers can only infer altitude from a standard model of the > atmosphere, > > so they're subject to pressure deviations, wind, etc. A GPS fix with at > > least 5 or so satellites will be quite accurate. > > Yup, within about 10m or so, independent of altitude, assuming it's > working correctly. It's easy to tell -- if it looks like a rocket > flight, it's working; if it's still reporting the pad altitude, it's not. > > -- > -keith > > _______________________________________________ > altusmetrum mailing list > [email protected] > http://lists.gag.com/mailman/listinfo/altusmetrum > >
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