"Martin Gregorie"  wrote in message
news:puv1da$27a$2@news.albasani.net...
>> 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.
>>
> No. Normally there's no damping. Its not needed in normal conditions. An
> ASI is an undamped pressure sensor that shows the pressure difference
> between the static vent and the pitot but is calibrated in knots rather
> than pressure units.
>
> An altimeter shows the undamped pressure at the static vent but is
> calibrated in feet or metres of altitude rather than pressure units .

So on a gusty day (ie air pressure fluctuates, even at a fixed position) how
much variation in displayed airspeed and height do you see? Presumably it's
small enough that you can still see the average value. That's why I
suggested that the speed/height meters may need long-time-constant damping
to perform any averaging - ie with a period longer than the typical cycle of
variation due to gusting.

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