Do winglets produce thrust?

"soarski" schreef in bericht
om...

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.


In my country (Holland) students will be disqualified from their examination
when they make an "interesting" remark like this. Reducing induced drag is
what winglets do and gravity is the engine of our gliders.

Karel Termaat

"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

At 14:06 30 November 2003, K.P. Termaat wrote:

'Reducing induced drag is what winglets do and gravity
is the engine of our gliders.'


Hallelujah

John Galloway

K.P. Termaat wrote:
"soarski" schreef in bericht
om...

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.


In my country (Holland) students will be disqualified from their examination
when they make an "interesting" remark like this. Reducing induced drag is
what winglets do and gravity is the engine of our gliders.

And what produces the "thrust" that moves your sailboats? Gravity?

This may be a simple confusion over the word "thrust", which I used (as
did the original question) in the sense of "force in the direction of
motion". Both the glider and the sailboat are propelled in a forward
direction by lift from the wing or sail.

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Eric Greenwell
Washington State
USA

At 17:18 30 November 2003, Eric Greenwell wrote:

And what produces the 'thrust' that moves your sailboats?
Gravity?

This may be a simple confusion over the word 'thrust',
which I used (as
did the original question) in the sense of 'force in
the direction of
motion'. Both the glider and the sailboat are propelled
in a forward
direction by lift from the wing or sail.

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Eric Greenwell
Washington State
USA

Eric,

The 'thrust' for a sailboat comes from the wind.
No wind, no go. The 'thrust' for a glider is from
gravity. No gravity, no go. A good clue to this is
that sail boats have their wings built vertically and
gliders have theirs horizontal.

The observation that the airofoil (wing, sail or winglet)
of a non powered vehicle can have a forward pointing
component to its lift vector cannot seriously be argued
to represent thrust by anyone with any notion as to
cause and effect. Your definition of thrust (as applied
to a glider) as a 'force in the direction of motion'
is fundamentally flawed as the 'force' cannot exist
without an external source of power i.e gravity dragging
the glider downwards. The thrust for a glider is always
directed vertically downwards. Conveniently for us
there is a viscous medium between the glider and the
ground and clever design of the lift and drag aspects
of the glider shape allows a resolution of the lift
and drag vectors such that the glider slides forwards
as it falls. Winglets have a favourable reducing effect
on the overall drag at certain speeds by reducing the
induced drag.

In the case of a glider the thrust or force that powers
it only acts in the direction of flight when the glider
is pointing vertically downwards.

John Galloway

On Sat, 29 Nov 2003 11:32:36 -0800, Eric Greenwell wrote:

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.

Sheesh! So many words and so little knowledge... Here's how it works,
guys.

For any aircraft in balanced flight, there are four forces acting on it.
All forces except gravity act only along the chord or perpendicular to it.
Gravity not only produces a force in opposition to lift, but a resultant
vector force which can be either thrust or drag, depending on the angle of
the chord in respect to earth (gravity). in other words; Gravity is the
'engine' in a glider that produces thrust.

For those that don't understand vector force components (or flunked trig),
don't worry 'bout it. Simply believe they exist.

As for the winglets, they only reduce drag. At the point where the
airfoil ends, air rolls to the other side of the wing due to the pressure
difference. The rolling air produces a vortex that kinda acts like vacuum
cleaner hoses grabbing the trailing tips of the wings. The winglets
interfere with the creation of the vortex(s) thus reducing drag. Smaller
vortex (smaller vacuum cleaner) means better L/D (slicker ship).

LittleJohn
Madison, AL

John Galloway wrote:

The observation that the airofoil (wing, sail or winglet)
of a non powered vehicle can have a forward pointing
component to its lift vector cannot seriously be argued
to represent thrust by anyone with any notion as to
cause and effect.

We are becoming almost philosophical here, but I'll give it a go. I'm
not seriously arguing it is "thrust" as the term is typically used by
aeronautical engineers. Bob Salvo asked "Do winglets produce thrust?",
and most of us knew exactly what he was asking: "Do winglets produce a
force in the forward direction?".

I continued to use in that manner in what I hoped was a light-hearted
way to get people to think about what does move a glider through the air.

Your definition of thrust (as applied
to a glider) as a 'force in the direction of motion'
is fundamentally flawed as the 'force' cannot exist
without an external source of power i.e gravity dragging
the glider downwards.

I agree the force of gravity is needed. I don't agree it is "the" source
of power. See below.

The thrust for a glider is always
directed vertically downwards. Conveniently for us
there is a viscous medium between the glider and the
ground and clever design of the lift and drag aspects
of the glider shape allows a resolution of the lift
and drag vectors such that the glider slides forwards
as it falls.

What if the glider isn't falling, but moving at a constant altitude
while ridge or wave soaring? What powers it then? I think it's the wind,
like a sailboat.

We also get our power (it might be better to say "energy") from the
towplane, that first pulls us up, then from the thermals that let us
climb on our own.

Winglets have a favourable reducing effect
on the overall drag at certain speeds by reducing the
induced drag.

Agreed.

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Eric Greenwell
Washington State
USA

You could describe it as 'interfering with the formation
of the tip vortex and thereby reducing drag', but an
easier to understand explanation (and just as accurate)
is that of the Thrust component of the force vector
produced by the winglet. The crossflow component generated
by the tip vortex means that the angle of incidence
of the winglet relative to the flow is different to
that relative to the line of flight. If this angle
is large enough then the winglet itself will no longer
produce a force component opposing the direction of
travel, but will instead produce a small 'Thrust' component
in the direction of travel. The fact that the winglet
is in fact producing a force in the direction of travel
is why the term 'Thrust' is perfectly correct.
Its easier to explain using a diagram, and plenty of
textbooks have them if you really are that interested.
The important thing to remember is that because of
the influence of the tip vortex, the flow striking
the winglet is not travelling in the same direction
as the freestream velocity. Thats what makes it all
possible.

May be they reduce drag, but in my opinion they can=B4t produce thrust. A=
n
airfoil can produce nothing but lift and drag. A wing produces "thrust"
because it=B4s lift is partially directed "forward".
I=B4ve made two graphics, I think they are more clearly than my bad engli=
sh:

http://www.ich-habs-doch-gleich-gesagt.de/fluegel.gif
http://www.ich-habs-doch-gleich-gesagt.de/winglet.gif

The black vectors are the real airforces.

Bernhard

The glider is always sliding "downhill", the updrafts, thermals, ridge lift,
all just change the height of the hill. The wing just changes the slope of
the hill, a 1-26 has a steep slope and an ASH-25 has a shallow slope. We
are all sliding downhill when we soar.

What if the glider isn't falling, but moving at a constant altitude
while ridge or wave soaring? What powers it then? I think it's the wind,
like a sailboat.