All generally correct, Chris, with one little exception. A spanwise flow
component exists on ALL wings of finite span. The magnitude and details are
influenced by the planform, "imperfections", sweep, loading, etc.
There are wingtip vortices here in Acer's photo - they are controlled by the
winglets, not eliminated. You just can't see them because the magnitude of
the pressure drop in the tip vortex cores, on this day, at this loading,
wasn't enough to cool the air to the dew point, though the pressure drop
across the wing was.
Gary Edwards - and that's enough Aero 101 for this list Gary Reese is
getting testy.
----- Original Message -----
From: "Chris Barker" <imagopus@xxxxxxxxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Cc: "siddiq" <iddibhai@xxxxxxx>
Sent: Wednesday, September 18, 2002 12:36 AM
Subject: Re: [OM] Totally OT: airplanes and humidity
Risky, this email, given we have an aero engineer in our midst ;-).
As the pilot rotates for takeoff (pitches up) he is doing it to
increase the angle of attack, and therefore the the lift, to get off
the ground. Increasing the lift is a function of reducing the
pressure across the top of the wing. Reduced pressure means reduced
temperature and reduced capacity for water vapour - so it condenses.
The shape you can see of the condensed vapour represents the pressure
pattern across the wing and indicates where the lift is being
generated. Imperfections in wing shape mean that that lift is
subject to spanwise flow (towards the tips) and the reaction between
low pressure over the wing and higher beneath cause the vortex on
each tip. The air in the vortices is low makes them visible when
conditions are right.
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