"Dennis Lee Bieber"  wrote in message
news:g1751edssbc3h2lpgoh3qag0cl9gmjm97h@4ax.com...
> For ground speed, not air speed... Having a 200kt ground speed with a
> 100kt tail wind means an air speed of only 100kt.

Is there an electronic means of measuring airspeed, which doesn't involve
measuring air pressure as the plane flies forwards and subtracting the
current static air pressure, corrected for altitude?

>>My phone varies between about 20m and 5m radius of error for lateral
>>movement. Not sure how accurate it is for altitude. I sometimes find that
>>I
>
> I don't even know if any consumer level GPS is able to make use of dual
> frequency
> signals yet -- the precision signal is sent over two (or now, maybe four)
> frequencies, allowing the receiver to correct for ionospheric delays. C/A
> traditionally was sent on one frequency only.

Yes I was implying that if a consumer-grade GPS receiver can get position
information to +/- a few metres, then professional-grade equipment (which I
imagine aircraft would use) would be able to give more precise readings; I'm
surprised that any non-GPS equipment could be that accurate.

What is the typical +/- for air-pressure airspeed and altitude readings? How
much does ground-level air pressure vary from time to time or place to
place, and does it drop as altitude increases by a consistent formula? Are
such errors in altitude readings smaller than you'd get with consumer or
professional GPS?

I presume both airspeed and altitude gauges include a fairly long
time-constant in the needle damping to avoid gusts of wind causing apparent
fluctuations in speed and altitude.

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