Re: "Twisters" (Wingtip vortices)

From: J.R. Ridgely (seven@mechsys2.me.berkeley.edu-DeleteThis)
Date: Thu Jul 01 1999 - 23:59:47 PDT


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Date: Fri, 02 Jul 1999 06:59:47 +0000
From: "J.R. Ridgely" <seven@mechsys2.me.berkeley.edu-DeleteThis>
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Subject: Re: "Twisters" (Wingtip vortices)
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> One of the things Ken Poulton added to the list of impacts of the SFO
> Airport exansion was:
>
> > Occasional violent turbulence (small 40+ knot "twisters") at water
> >level.
>
> I have witnessed these several times at Coyote and not everyone even
> believes me when I tell them. Basically, the twister just leaves the airport
> area and works it's [sic] way downwind -- a swirl of blasting winds, probably
> 40-50 mph, maybe more.

They should believe it...I would expect more than 50 mph when the vortices are
generated, decreasing as they dissipate, but that's just a guess with no
supporting evidence.

> A friend of mine flies 747's, and claims that vortex generated by each
> wing can knock down wind surfers.

Heck, they can knock down small airplanes (see below).

> It is a little like bowling, only a
> lot more fun.

Except that by the time the vortices reach the windsurfers a mile or two
away, the plane should be taxiing up to the terminal...

> My guess is these vortex's (vortices?) are generated from the wing tips
> of large planes, and I'm pretty sure they are a well documented hazard.
> Any small plane pilot should be able to give more information.

Tip vortices from large aircraft are indeed a well documented hazard. Every
small plane pilot learns how to avoid them; they can easily cause loss of
control and a crash of a smaller aircraft. In one pilot training movie, we
were shown video of a small plane flown into the wake of a C-5 at landing
speed (at a safely high altitude, as a demonstration). The small plane was
flipped completely over. Given what it can do to a 2500 pound airplane, the
vortex could reasonably be considered a significant safety issue for a 250
pound windsurfer.

                                                                           JR



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