Winglets

[Tony]

Most winglets I've seen point upward, but thinking about the physics of
the things, if they had to extend in only one direction wouldn't down
be better, and wouldn't a plate -- extending both up and down, be best
for sub sonic flight?

[Jose]

> if they had to extend in only one direction wouldn't down
> be better

Not on a crosswind landing. :)

Jose
--
Money: what you need when you run out of brains.
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[Matt Barrow]

"Tony" > wrote in message
oups.com...
> Most winglets I've seen point upward, but thinking about the physics of
> the things, if they had to extend in only one direction wouldn't down
> be better, and wouldn't a plate -- extending both up and down, be best
> for sub sonic flight?
>

Ground clearance, for one. As for your latter, that would be like a vortex
generator such as Bonanza wings have.

[OP]

On 12 Mar 2006 16:18:44 -0800, "Tony" > wrote:

>Most winglets I've seen point upward, but thinking about the physics of
>the things, if they had to extend in only one direction wouldn't down
>be better, and wouldn't a plate -- extending both up and down, be best
>for sub sonic flight?


According to something I read somewhere :-) either up or down
winglets (or tiplets if you prefer) accomplilsh the same thing with
the same efficiency... increase the effective wingspan of the
aircraft. Most commercial aircraft (Boeing, Airbus, etc.) turn them
up for ground clearance.

Don't know about tip plates.

Ron

[Tony]

It seems to me tip plates would remove wing tip effects completely:
airflow would be along the chord all the way to the plate. I'd expect
the tip vortex effects one often sees would no longer exist.

[Capt.Doug]

>"Tony" wrote in message
> It seems to me tip plates would remove wing tip effects completely:
> airflow would be along the chord all the way to the plate. I'd expect
> the tip vortex effects one often sees would no longer exist.

The plate would have to big enough to block most of the tip flow in order to
be effective. That would be a fairly large tip plate and may have other
consequences such as directional stability. I used to tow banners in
modified Super Cibs with tip fences. The fences were about about 4 inches
bigger than the chord profile and did very little in reality.

D.

[Dylan Smith]

On 2006-03-13, Tony > wrote:
> Most winglets I've seen point upward, but thinking about the physics of
> the things, if they had to extend in only one direction wouldn't down
> be better, and wouldn't a plate -- extending both up and down, be best
> for sub sonic flight?

Take a look at some models of Airbus - they have winglets that extend
both above and below the wingtip.

--
Dylan Smith, Port St Mary, Isle of Man
Flying: http://www.dylansmith.net
Oolite-Linux: an Elite tribute: http://oolite-linux.berlios.de
Frontier Elite Universe: http://www.alioth.net

[Michelle]

OP wrote:
> On 12 Mar 2006 16:18:44 -0800, "Tony" > wrote:
>
>
>>Most winglets I've seen point upward, but thinking about the physics of
>>the things, if they had to extend in only one direction wouldn't down
>>be better, and wouldn't a plate -- extending both up and down, be best
>>for sub sonic flight?
>
>
>
> According to something I read somewhere :-) either up or down
> winglets (or tiplets if you prefer) accomplilsh the same thing with
> the same efficiency... increase the effective wingspan of the
> aircraft. Most commercial aircraft (Boeing, Airbus, etc.) turn them
> up for ground clearance.
>
> Don't know about tip plates.
>
> Ron
>
Airbus has plates that go both up and down at the end......
Michelle

[Chris Wells]

I've seen a lot of discussion on this topic in radio-controlled plane groups, and I've been working out winglet design on the r/c planes I've built for years. I've also seen the results of tests done by laboratories. (on the internet somewhere, hunt & I'm sure you'll find them) I think it's pretty well established that upwards is better, though a small projection on the bottom seems to be a good thing.
The way the tip transitions into the winglet is probably just as important as the shape of the winglet itself. I've had several flying wings that flew well without winglets or any vertical surfaces at all, by shaping the tips. The stock wings, with squared-off tips, don't fly well at all without the winglets.
Of course, if someone can provide evidence of an advantage for downward-pointing tips (other than non-aeronautical reasons such as LG convenience, such as on the Quickie) I'd like to see it.

[OP]

On Mon, 13 Mar 2006 15:55:21 +0000, Chris Wells
> wrote:

>
>I've seen a lot of discussion on this topic in radio-controlled plane
>groups, and I've been working out winglet design on the r/c planes I've
>built for years. I've also seen the results of tests done by
>laboratories. (on the internet somewhere, hunt & I'm sure you'll find
>them) I think it's pretty well established that upwards is better,
>though a small projection on the bottom seems to be a good thing.
>The way the tip transitions into the winglet is probably just as
>important as the shape of the winglet itself. I've had several flying
>wings that flew well without winglets or any vertical surfaces at all,
>by shaping the tips. The stock wings, with squared-off tips, don't fly
>well at all without the winglets.
>Of course, if someone can provide evidence of an advantage for
>downward-pointing tips (other than non-aeronautical reasons such as LG
>convenience, such as on the Quickie) I'd like to see it.

Well, the XB-70 Valkyrie is the only example I can come up with at
the moment. Although the wing tips in this case were more for
increase lift, reduced drag and increased speed at sub-sonic and
supersonic speeds.

See: http://www.labiker.org/xb70.html#compression

Ron

[Capt.Doug]

>"Dylan Smith" wrote in message
> Take a look at some models of Airbus - they have winglets that extend
> both above and below the wingtip.

Toulouse is experimenting with new wingtips for the A-320 series. The
present tips make for a measly 2.7% fuel efficiency gain.

D.