>Yes, positive, in relation to ambient.  There is positive pressure inside
>the fuselage since air going past the fuselage is at negative pressure.

I don't think this is true.  Or maybe you're just explaining it in the wrong
terms.  In fact, the pressure inside the fuselage is BELOW the ambient
static pressure.  The fuselage cannot "pressurize itself" just because
there's an airflow over its surface.

The reason that your canopy is bowing outward is that there is an acting
pressure LOWER than ambient static on the outer surface due to the airflow,
not because of a pressure HIGHER than ambient static inside the fuselage.
The pressure inside the fuselage starts out AT the total, or static,
pressure prior to takeoff.  Once in motion, the pressure fuselage gradually
starts DROPPING due to the negative pressure (from the airflow) acting
outside the fuselage.

Try this example of the same effect:  go down the highway in your car.  Open
the window halfway.  The pressure inside the car DROPS because the trapped
static (total) pressure inside the car tries to escape to equalize the
negative pressure flow going past the window.  So, the actual pressure
inside the car (or fuselage) will actually be LOWER than the static ambient
pressure.

--Andrew



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