On 31/12/2018 01:04, Martin Gregorie wrote:
> On Sun, 30 Dec 2018 22:15:16 +0000, NY wrote:
>
>> 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?
>>
> None that I've noticed in altitude and very little or no rapid
> fluctuation on the ASI at altitude. Yes, on a windy day we fly finals
> faster than on a calm day (rule of thumb is 50kts plus half windspeed)
> but you're busy on finals in those conditions and monitoring the ASI
> amongst several items. I'll see changes that need reacting to NOW but
> AFAIK the ASI doesn't flicker. I don't watch it closely enough to see if
> it does so because I also need to be paying attention to a lot of other
> stuff such as approach angle, drift, sink, other gliders and anything
> moving on the airfield.
>
>> Presumably it's small enough that you can still see the average value.
>>
> There is no visible 'actual value', i.e. the ASI doesn't move appreciably
> during a glance though of course 2 seconds later it may be different as a
> gust passes. Hence no extra damping is needed: the ASI is displaying
> pressure in a tube facing into the airflow and gusts will not tend to
> change that much in relation to their effect on the glider's airspeed.
>
>
Fascinating.

My experience is flying aircraft at much lower heoghs and wingspans < 2
meters.

Gusts are quite slow things. Once clear of the boundary layer,
windspeeds do vary but over seconds. Not tenths of a second, That would
be heard as infrasound.  Like thunder etc.

Most full size pilots seem to not use ASI for final appriach as far as I
can tell - they adopt the techniques I discovered myself with models.
Keep the speed UP and fly into the ground. Dont glide in. That way there
is a bit of excess speed to allow for downdraughts or a wind lull. Once
on the ground, well, use the controls to STAY there and dump airspeed as
fast as possible...


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