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Re: [SFRC] Vortex reduction

My impression of wing-tip vortex control devices is that they work fine in
full scale service, and are usually tuned to a particular flight regime, such
as cruise where the drag reduction is helpful in saving fuel on transport
aircraft.  On sailplanes, the reduction could be helpful to the L/D.  But
these things are sensitive to speed and angle of attack.  When used at the
design AOA and speed, they are good, but the performance can change
drastically when opoerated at other flight conditions.  So there use in a
model might be more hinderance then help.

.........bc    (conk@xxxxxxxxxxxxx

Williamsburg, VA 23185

On Wed, 23 Jul 2003, Isaiah Cox wrote:

> I thought this clip, from Flight International, was cool. I know that
> some gliders use winglets... has anyone seen this in a model, and
> would it make a perceptible difference? It seems really cool. Does
> anyone have pictures?
> Isaiah
> Designer says wingtip-mounted device can perform far better than winglets
> A French invention designed to eliminate wingtip vortices could
> enable future aircraft designs to benefit from significantly lower
> lift-induced drag. French aeronautical teacher Christian Hugues
> claims his Minix device - a hollow cylindrical tube attached to an
> aircraft's wingtip - could reduce induced drag by 8%, while
> increasing lift by 5.4%.
> The tube, made of Kevlar and carbon composite, has spiral slits cut
> into its length. It works on the principle that the vortices
> generated at the wingtip will hit the wing at the same distance
> inboard of the tip as the wing's thickness. As the pressure exerted
> by the vortex on the wing surface increases, flow escapes through the
> slits and is dissipated into a linear flow through the open rear of
> the tube.
> Hugues obtained a French patent for his device in May following eight
> years of work, and says the design performs far better than
> conventional winglets. "While winglets can reduce vortex pressure
> around the wingtip, Minix can eliminate the vortex completely," he
> says.
> Hugues has tested his invention in a windtunnel and predicts an 8%
> induced drag reduction for a wing with an aspect ratio of eight at a
> Reynolds number of 7.5 x 106. He says the application is adaptable to
> all aerofoil shapes and sizes, including propeller and helicopter
> blades. More testing is needed to tailor the design to larger wings
> and for higher Reynolds number conditions, however.
> Hugues says that French aircraft racer Xavier Beck plans to use the
> Minix wingtip devices when he competes in the Reno, Nevada, air races
> next year, and he hopes to equip an 8m (26ft)-span model of the
> Airbus A380 that is due to fly in September. He says that French and
> US manufacturers have also expressed interest in using the device.
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