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.
I have just quit my browser, and I forgot to look at the runway
numbers, but 700ft to go is a bit tight in my book. Runway numbers
normally indicate thousands of feet to go in the direction you are
facing.
Chris
p.s. nice photo by the way. cb
At 11:35 -0700 17/09/02, siddiq wrote:
<insert obligatory self taken ego booster>
http://users2.ev1.net/~wesiddiquis/siddiq/takeoff.jpg
condensation visible starting leading edge of wing to midway down
where it dissipates! there's the OM content: 200/4 wide open w/ 2x-a
tc slight crop on the right, superia 400, om1n, handheld at 1/60 or
1/125 (i'm getting good at handholding that sucker), JFK delta
terminal, late afternoon august 1 2000. BA747-4xx, lifting off with
another ~700 feet of runway left, looks like. for those in the know,
is
that normal run or was this lightly loaded (or the cool air helped
shorten the run)?
on approach, if you view from the side or the rear (plane heading
away from you) you can see vortices coming off the wingtips. it is
TOTALLY awesome. alas, i don't get to much aero photography since
there are no decent airports around, and the few times i had to go
to lax was post 11 sep with no access to any decent viewpoint..
http://www.airliners.net has the best collection. get yourself
somwhere with broadband, and spend hours looking thru the photos.
man that place is swEEET
--
<|_:-)_|>
C M I Barker
Cambridgeshire, Great Britain.
?
+44 (0)7092 251126
mailto:imagopus@xxxxxxxxxxxxxxxx
http://www.threeshoes.co.uk
... a nascent photo library.
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