Winglets

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?

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

Not on a crosswind landing.

Jose
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"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.

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

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.

"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.

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

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.

--
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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.

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