Jeremy Furtek wrote:
> I think that the subtle and challenging part of doing this (accurately) is
> measuring static pressure. The presence of the aircraft influences the flow
> field. For full size aircraft I think that they expend some effort to find a
> position on the aircraft that will give an accurate reading for static
> pressure under a representative set of operating conditions.
>
> A wind tunnel test ($$$) of an aircraft may include placing pressure taps
> along the model along the centerline. If you plot the pressure coefficient
> (comparing measured pressure to the static pressure measured well upstream
> or far away from the aircraft) along the axis of the aircraft, good
> locations for the static pressure tap would be places where this value is
> zero.
>
> For a flying model, to determine the static pressure, I think that they may
> sometimes drag an instrumented object far behind the aircraft, and compare
> that to the taps on the aircraft.
>
> For an R/C, you could do something similar. Another alternative would be to
> determine the best location computationally, a la CFD.

The easiest way to get a static port on a model airplane is to not use a port.
Most model airplanes aren't anywhere close to airtight, but aren't open to the
wind either. In general the air pressure inside the airframe is close enough to
the ideal static pressure. Of course, this assumption breaks down if the
pressure sensor is too close to a "crack" (wing attach point, gear doors,
firewall...). And most importantly, you need to calibrate the sensor. Some
syringes (w/o needles) and fuel tubing can be very handy for that.

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