Do winglets produce thrust?

Bruce Hoult wrote:

But the spar does not have to deal with the extra lift on a *long*
moment arm. Well not all of it anyway.


Hmm ... well a deliberately non-lifting horizontal section at the tip
would reduce induced drag as well.

This could be done for one angle of attack, but I don't see how it could
be done for the usual range a glider uses. A winglet has the same angle
of attack, independent of the wing.
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Eric Greenwell
Washington State
USA

At 07:54 29 November 2003, Bruce Hoult wrote:
In article ,
Eric Greenwell wrote:

Winglets reduce induced drag by effectively making
the wingspan longer.

Perhaps in the past, but maybe not anymo from page
104 of the
Fundamentals of Sailplane Design...

'Subsequently, it has been shown that good results
may be obtained with
relatively small winglets. In contrast to early winglets,
which were
essentially upward wing extensions, recent winglet
designs are optimized
to diffuse the vortex rollup at the wingtip, thus
reducing its strength.
There is also evidence that the velocity field induced
by the winglets
can improve airfoil aerodynamics in the vicinity of
the wing tip by
prolonging laminar flow and delaying separation.'

But the question is, would similar-shaped horizontal
extensions to the
wing have the same effect? What about multiple small
span 'winglets'
off the end of the wing? Birds do that. The modern
winglets look a lot
like a single tip-feather.

-- Bruce


Oh, Golly-gee! In one hundred years we've gone from
bi-planes to bi-winglets!

In my country, our gliders move forward because the wing produces
thrust, and our sailboats move over the water because the sail produces
thrust. Whether we should rule the world is causing much controversy.


PLEASE....Readers of the World! This is not in our textbooks! Did
someone in the USA write the above???

Wings produce Lift!! A by product of lift is drag! Winglets do also
produce lift, and therefore drag. Possibly less than the wing? But
you canot call it thrust!.......

This sounds like I am in the middle of some ski instructors!

Skiing is great in Aspen!

Think Snow!

The Redtail Hawk

From: Paul Repacholi
Date: Sat, 29 Nov 2003 18:49:16 +0800

Bruce Hoult writes:

If it wasn't for class rules limiting wingspan I don't think anyone
would have winglets.

I wonder what class rules the 744 design has in mind


Those rules which limit gate space at airport terminals.



--
Jack

"Heavier-than-air flying machines are impossible."
-- Lord Kelvin, President, Royal Society, 1895

"Bob Salvo" wrote in message
...
Anyone?
Bob

Do winglets produce thrust? (CAN winglets produce thrust?)
All non-believers should read the NACA report by Whitcome, the inventor of
winglets. Winglets are an airfoil and therefore produce lift. If the cord
of the winglet is oriented properly, the lift vector will be angled slightly
forward, hence the use of the term "thrust". Since the angle of attack of
the winglet is influenced by the lift coefficient of the main wing, a
significant amount of "thrust" is only produced at a very narrow range of
angle of attack (aircraft speed). A significant amount of "thrust" is
defined as when the forward component of lift of the winglet is greater than
the drag of the winglet. Since sailplanes are flying at either a slow speed
of near stall or very fast speed, the concept would not seem to be of much
use for sailplanes.

The winglets used on sailplanes seem to use an airfoil which has a large low
drag bucket and are designed more to diminish wing tip vortices. This
results in lower sailplane drag, sometimes better aileron control, and
perhaps at some angle of attack of the main wing some "thrust".

Duane

soarski wrote:
In my country, our gliders move forward because the wing produces
thrust, and our sailboats move over the water because the sail produces
thrust. Whether we should rule the world is causing much controversy.



PLEASE....Readers of the World! This is not in our textbooks! Did
someone in the USA write the above???

Wings produce Lift!! A by product of lift is drag! Winglets do also
produce lift, and therefore drag. Possibly less than the wing? But
you canot call it thrust!.......

"Thrust", for the winglet question and my remarks about gliders and
sailboats, was used to mean "force in the direction of motion".
Apparently, that was an unusual use of the word for some people.

Here's an expanded expanation:

Gravity is pulling straight down, and so can not propel the glider
forward; drag is pulling the glider back, and so can not propel the
glider forward. So, what is left to counteract the drag? Lift, produced
by the wings. This forward force comes from the lift, which is not
vertical, but tipped forward a bit. Look at any diagram showing the
forces on a glider, and you will see how the lift, drag, and gravity
forces accomplish this.

It is not common to call this force moving the glider forward (without
it, drag would bring it to stop) "thrust", but the word is sometimes
used that way.

I still can't answer the original question about the winglets, though.

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Eric Greenwell
Washington State
USA

If winglets produce thrust, at what angle of attack does its thrust/drag ratio
maximise?


Bob

With the production of levity such as this, winglets are certainly
adding (a) lift to dead of winter soaring in the northern hemisphere -
whether it's literally or figuratively! Bravo.

Now, I'm confused! An airfoil cannot produce thrust
-- only 'lift.' But if an airfoil has a reverse counterpart,
the two are joined at the center and rotated about
an axis in a vertical plane, they are then a propeller;
this produces 'thrust.' But if their pitch is differentially
variable and they rotate in a horizontal plane, they
are then helicopter blades; they produce 'lift.'
Why don't we just combine the two words in one concept
and call it 'thrift?'


At 20:36 29 November 2003, Bob Salvo wrote:
If winglets produce thrust, at what angle of attack
does its thrust/drag ratio
maximise?


Bob

Being a bit of a pedant, I have been trying to find whether the technical
definition of 'thrust' fits here, as my aerodynamics is more than a bit
rusty. I cannot find any book on unpowered flight which shows more than
three forces - lift; drag; weight, and might at best resolve these
horizontally and vertically to label the 'horizontal component of lift'.
Looking at general definitions, I would think that the backward force on the
air below the wings could be defined as thrust, but the notional forward
reactive force on the aircraft resulting from this couldn't! 8-)

Keith

"Nyal Williams" wrote in message
...
Now, I'm confused! An airfoil cannot produce thrust
-- only 'lift.' But if an airfoil has a reverse counterpart,
the two are joined at the center and rotated about
an axis in a vertical plane, they are then a propeller;
this produces 'thrust.' But if their pitch is differentially
variable and they rotate in a horizontal plane, they
are then helicopter blades; they produce 'lift.'
Why don't we just combine the two words in one concept
and call it 'thrift?'


At 20:36 29 November 2003, Bob Salvo wrote:
If winglets produce thrust, at what angle of attack
does its thrust/drag ratio
maximise?


Bob