Wingtip Vortex: Heavy, Clean, Slow - Why?

emove (AJW) writes:


You get the strongest wingtip vortices when an aircraft is flying heavy,
clean and slow. But why?

Not so sure about dirty v clean, but at low speeds clean isn't very effecient
at generating lift. That means larger angles of attack, more air displaced,
maybe a bigger vortex.

From http://av8n.com/how/htm/airfoils.html#sec-wake-vortices:

You would think that...flaps extended would be the absolute worst, but that
is not quite true. The flaps do increase the circulation-producing
capability of the wing, but they do not extend over the full
span. Therefore a part of the circulation is shed where the flaps end, and
another part is shed at the wingtips. If you fly into the wake of another
plane, two medium-strength vortices will cause you less grief than a single
full-strength vortex. Therefore, you should expect that the threat from
wake vortices is greatest behind an airplane that is heavy, slow, and
unflapped.

d.

Dan Girellini wrote:
From http://av8n.com/how/htm/airfoils.html#sec-wake-vortices:

You would think that...flaps extended would be the absolute worst, but
that
is not quite true. The flaps do increase the circulation-producing
capability of the wing, but they do not extend over the full
span. Therefore a part of the circulation is shed where the flaps end,
and
another part is shed at the wingtips. If you fly into the wake of
another
plane, two medium-strength vortices will cause you less grief than a
single
full-strength vortex. Therefore, you should expect that the threat
from
wake vortices is greatest behind an airplane that is heavy, slow, and
unflapped.

Yeah. Go tell Denker to fly behind a flapped 757 on an approach.

http://www.aopa.org/asf/asfarticles/sp9810.html
http://www.aopa.org/asf/asfarticles/sp9403.html

Hilton