Do winglets produce thrust?

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

"Nyal Williams" wrote in message
...
Why don't we just combine the two words in one concept
and call it 'thrift?'

Personally I'd prefer 'lust'


Ian

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.'

Well if that last statement is true then the earlier one
is false. Do propellers produce thrust?

--

FF

Fred the Red Shirt wrote:

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.'


Well if that last statement is true then the earlier one
is false. Do propellers produce thrust?

The first poster is confusing a wing and an airfoil. It's a _wing_ that
cannot produce thrust in the aerodynamic sense, by the definitions used.
A propeller can produce thrust. They both use airfoils.
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Eric Greenwell
Washington State
USA

At 18:54 05 December 2003, Todd Pattist wrote:
(Fred the Red Shirt) wrote:

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.'

Well if that last statement is true then the earlier
one
is false. Do propellers produce thrust?

Back to definitions again. 'Lift' is defined perpendicular
to the path of the airfoil through the air. 'Thrust'
is
typically parallel to that path. However, when we
have a
moving airfoil on an aircraft (rotating propeller),
there
are two 'paths' that are relevant. One is the path
of the
aircraft (this path defines the AOA of the wing), and
the
other is the spiral path of the rotating airfoil (this
path
defines the AOA of the prop blades). The propeller's
airfoil produces 'lift' perpendicular to the spiral
path.
It produces 'thrust' when considered relative to the
airplane's path.

IOW, at any instant, the prop is mostly moving at 90
degrees
to the path of the airplane. If it produced both lift
and
thrust relative to the same path, then the prop would
turn
itself :-)

Todd Pattist - 'WH' Ventus C
(Remove DONTSPAMME from address to email reply.)

Okay, it promises to be a long winter; I'll take my
tongue out of my cheek!

This has to be winter RAS debate bait, right Bob?

For those of you responding in the affirmative, park the nearest
winglet-equipped glider on the runway on a still day and measure the
"thrust" being produced by those puppies. Be careful not to stand in front
of the wing when you do it. wink

--=Curt=-

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

In article ,
ojunk (Bob Salvo) wrote:
Anyone?
Bob

Winglets reduce induced drag by effectively making the wingspan longer.

I've never seen anyone argue convincingly that a half a meter of
vertical wingspan does anything that couldn't be done equally well with
an extra half meter of normal wingspan. On the other hand winglets are
worse than span in that they don't produce lift in a useful direction,
and they are harder to make strong and rigid than ordinary span is.

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

-- Bruce

Bruce Hoult wrote:
In article ,
ojunk (Bob Salvo) wrote:

Anyone?
Bob


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."


I've never seen anyone argue convincingly that a half a meter of
vertical wingspan does anything that couldn't be done equally well with
an extra half meter of normal wingspan.

Winglets can improve roll rate, while longer tips tend to reduce it.

On the other hand winglets are
worse than span in that they don't produce lift in a useful direction,
and they are harder to make strong and rigid than ordinary span is.

The lift they produced is used to decrease drag, which is a useful
result, and the small ones used on the ASW 27, for example, look pretty
simple to make.


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

Much less likely, for sure.

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Eric Greenwell
Washington State
USA

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

Bruce Hoult wrote:


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.

Take a look at the winglet pages in the book. It doesn't sound like they
are doing the same thing they would be doing laying flat.

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Eric Greenwell
Washington State
USA