Do winglets produce thrust?

[Bob Salvo]

Anyone?
Bob

[Keith W]

"Bob Salvo" > wrote in message
...
> Anyone?
> Bob
That's against the laws of thermodynamics. If you can make a passive device
produce thrust you should rule the world with your new perpetual motion
machine! At best it reduces losses.

Keith

[Eric Greenwell]

Keith W wrote:

> "Bob Salvo" > wrote in message
> ...
>
>>Anyone?
>>Bob
>
> That's against the laws of thermodynamics. If you can make a passive device
> produce thrust you should rule the world with your new perpetual motion
> machine! At best it reduces losses.

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.

--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

[cddb]

Don't think so.
Gravity provides the thrust. Quite noticeably when fuselage
is pointed vertically. None at all when fuselage/wing is horizontal.




In article >, Eric Greenwell
> wrote:
>Keith W wrote:
>
>> "Bob Salvo" > wrote in message
>> ...
>>
>>>Anyone?
>>>Bob
>>
>> That's against the laws of thermodynamics. If you can make a passive device
>> produce thrust you should rule the world with your new perpetual motion
>> machine! At best it reduces losses.
>
>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.
>

[Keith W]

"Eric Greenwell" > wrote in message
...
> Keith W wrote:
>
> > "Bob Salvo" > wrote in message
> > ...
> >
> >>Anyone?
> >>Bob
> >
> > That's against the laws of thermodynamics. If you can make a passive
device
> > produce thrust you should rule the world with your new perpetual motion
> > machine! At best it reduces losses.
>
> 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.
>
> --
> -----
> Replace "SPAM" with "charter" to email me directly
>
> Eric Greenwell
> Washington State
> USA

Yep - I was thinking of thrust as a primary force rather than that due to
'tobogganing' (ie a change of supporting force forward of the vertical).
Away I go to the sackcloth and ashes 8-).

As to whether the US should rule the world - I will duck out of that to
prevent a repetition of the reams of vehement verbiage which has already
filled the bit stream 8-))

Keith

[BTIZ]

I don't think it was that "US" rules the world.. but more the line that.. he
who masters the air above us.. (glider pilots) .. rule the world..

BT

"Keith W" > wrote in message
...
>
> "Eric Greenwell" > wrote in message
> ...
> > Keith W wrote:
> >
> > > "Bob Salvo" > wrote in message
> > > ...
> > >
> > >>Anyone?
> > >>Bob
> > >
> > > That's against the laws of thermodynamics. If you can make a passive
> device
> > > produce thrust you should rule the world with your new perpetual
motion
> > > machine! At best it reduces losses.
> >
> > 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.
> >
> > --
> > -----
> > Replace "SPAM" with "charter" to email me directly
> >
> > Eric Greenwell
> > Washington State
> > USA
>
> Yep - I was thinking of thrust as a primary force rather than that due to
> 'tobogganing' (ie a change of supporting force forward of the vertical).
> Away I go to the sackcloth and ashes 8-).
>
> As to whether the US should rule the world - I will duck out of that to
> prevent a repetition of the reams of vehement verbiage which has already
> filled the bit stream 8-))
>
> Keith
>
>

[Scott Correa]

Winglets produce lift, with a vector. The vector direction
can be perpendicular to the winglet surface, fwd or aft.
That is dependant on how it is shaped and mounted.
A lift vector facing the nose (fwd) being called thrust
might be a mishmash of terms, but it happens.
I usually think of thrust as a motive force acting on the vehicle.
Winglet vectors are recovery of lost energy by reshaping flow
to our advantage. Good idea, yes, thrust...... probably not
a really good description of what is happening........

Scott.

[Denis Flament]

Bob Salvo wrote:

> Anyone?
> Bob

Yes

--
Denis
Private replies: remove "moncourrielest" from my e-mail address
Pour me répondre utiliser l'adresse courriel figurant après
moncourrielest" dans mon adresse courriel...

[Denis Flament]

Keith W wrote:

> That's against the laws of thermodynamics.

No.

Provided the thrust of the winglets is not higher than the drag of the
other part of the glider, that's not (and of course the winglet thrust
is only a few % of the glider drag)


--
Denis
Private replies: remove "moncourrielest" from my e-mail address
Pour me répondre utiliser l'adresse courriel figurant après
moncourrielest" dans mon adresse courriel...

[Andy Blackburn]

Not thrust in the same way as a propulsion system,
but winglets generally do produce a lift vector that
has a spanwise and a chordwise component. Since the
flowfield at the wingtip is angled inward, the winglet
has an incidence angle that is slightly outward-facing
-- while still producing a positive angle of attack
(look at your winglets from straight ahead to see that
this is true). This means that the 'lift' produced
by the winglet is directed mostly inwards towards the
fuselage, but also forwards.

I don't know what lift coefficients winglets fly at,
but I suspect the actual magnitude of the 'thrust'
is very small.

9B

At 19:54 28 November 2003, Bob Salvo wrote:
>Anyone?
>Bob
>

[LittleJohn]

On Fri, 28 Nov 2003 21:36:17 +0000, cddb wrote:

> Don't think so.
> Gravity provides the thrust. Quite noticeably when fuselage
> is pointed vertically. None at all when fuselage/wing is horizontal.

Look at it from another point of view. If all forces are balanced and
winglets are added, drag is reduced. Then velocity increases until the
thrust/drag forces are equalized. The result of increased velocity is
additional lift. The horizontal component of the lift vector is thrust,
which increases as lift increases. Ergo, winglets produce thrust. ;>)

LittleJohn
Madison, AL

[Eggs]

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

[Bruce Hoult]

In article >,
(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

[Eric Greenwell]

Bruce Hoult wrote:
> In article >,
> (Bob Salvo) wrote:
>
>>Anyone?
>>Bob
>
>
> Winglets reduce induced drag by effectively making the wingspan longer.

Perhaps in the past, but maybe not anymore: 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.

--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

[Bruce Hoult]

In article >,
Eric Greenwell > wrote:

> > Winglets reduce induced drag by effectively making the wingspan longer.
>
> Perhaps in the past, but maybe not anymore: 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

[Paul Repacholi]

Bruce Hoult > writes:

> 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.

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

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

I wonder what class rules the 744 design has in mind :)

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

[Chris OCallaghan]

The winglet holder in my Cobra trailer comes with a bungee cord to
keep the winglets in place. I have noted that whenever I leave the
bungee off, the winglets wind up in all imaginable places inside the
trailer. Thus, I would conclude, that they do indeed produce thrust.

(Bob Salvo) wrote in message >...
> Anyone?
> Bob

[Bob Kuykendall]

Earlier, Paul Repacholi > wrote:

> I wonder what class rules the 744 design has in mind :)

It has to fit between established jetways at established airports.
That and the inboard bending moment contstraints mentioned earlier.

Bob K.

[Eric Greenwell]

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.

--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

[Bruce Hoult]

In article >,
Paul Repacholi > wrote:

> Bruce Hoult > writes:
>
> > 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.
>
> 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.


> > If it wasn't for class rules limiting winspan I don't think anyone
> > would have winglets.
>
> I wonder what class rules the 744 design has in mind :)

Terminal gates.

I don't know what excuse bizjets or small turboprops such as the Beech
1900 have. Possibly fashion.

-- Bruce

[Eric Greenwell]

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

[Nyal Williams]

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 anymore: 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!

[soarski]

>
> 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

[Jack]

> 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

[Duane Eisenbeiss]

"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

[Eric Greenwell]

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.

--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

[Bob Salvo]

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


Bob

[wsburhen]

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.

[Nyal Williams]

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
>

[Keith W]

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
> >
>
>
>

[K.P. Termaat]

"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

[tango4]

"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

[John Galloway]

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

[Eric Greenwell]

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

[John Galloway]

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.
>
>--
>-----
>Replace 'SPAM' with 'charter' to email me directly
>
>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

[LittleJohn]

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

[Eric Greenwell]

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

[Jon Meyer]

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.

[Bernhard Reinhardt]

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

[Libelle Driver]

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.

[Scott Correa]

"Todd Pattist" > wrote in message
> This is an interesting winter-we-can't-fly debate. The wing
> on a glider in steady motion through the air produces a
> total aerodynamic force. That total aerodynamic force is
> exactly vertical and exactly equal to the gravitational
> force. By convention, we resolve this total aerodynamic
> force into two components called lift and drag. The lift
> component is always perpendicular to the flight path, and
> the drag component is always parallel to it. By the usual
> convention, "thrust" is either parallel to the flight path,
> or is the non-aerodynamic force produced by an engine of
> some sort. Thus, "lift" cannot produce "thrust." Either
> the lift is perpendicular to the path, while thrust is
> parallel, or it's an aerodynamic force and is excluded. For
> a glider with winglets attached, when you are talking about
> the total lift and drag forces, winglets cannot produce any
> "thrust" by the definitions.

Good post Todd,
Isn't that what I said earlier??
Winglets produce lift, with a vector. The vector direction
can be perpendicular to the winglet surface, fwd or aft.
That is dependant on how it is shaped and mounted.
A lift vector facing the nose (fwd) being called thrust
might be a mishmash of terms, but it happens.
I usually think of thrust as a motive force acting on the vehicle.
Winglet vectors are recovery of lost energy by reshaping flow
to our advantage. Good idea, yes, thrust...... probably not
a really good description of what is happening........

Scott.

[tango4]

I'm amazed at the complete lack of understanding of the basic principles of
physics displayed by some posters in this thread. No wonder people can still
sell constant motion engines to investors!

Ian

[K.P. Termaat]

"Todd Pattist" > schreef in bericht
...
> This is an interesting winter-we-can't-fly debate. The wing
> on a glider in steady motion through the air produces a
> total aerodynamic force. That total aerodynamic force is
> exactly vertical and exactly equal to the gravitational
> force. By convention, we resolve this total aerodynamic
> force into two components called lift and drag. The lift
> component is always perpendicular to the flight path, and
> the drag component is always parallel to it. By the usual
> convention, "thrust" is either parallel to the flight path,
> or is the non-aerodynamic force produced by an engine of
> some sort. Thus, "lift" cannot produce "thrust." Either
> the lift is perpendicular to the path, while thrust is
> parallel, or it's an aerodynamic force and is excluded. For
> a glider with winglets attached, when you are talking about
> the total lift and drag forces, winglets cannot produce any
> "thrust" by the definitions.

You are exactly right Todd. The lift of the wing is perpendicular to the
flight path and the drag is pointing backwards parallel to the flightpath.
You may deduce these vectors from the total aerodynamic force acting on the
glider as you do. However I never state that this total force counteracts
the weight of the glider, which is true of course. I always tell my glider
friends that the lift counteracts the weight component perpendicular to the
flightpath while the drag is counteracted by the weightcomponent in the
direction of the flightpath. Four vectors in a sketch gliding forward on the
glidepath making an angle like 2 degrees with the horizon completes the
story. In fact back to earth all the time.

Karel
V-2cxT

[Eric Greenwell]

tango4 wrote:

> I'm amazed at the complete lack of understanding of the basic principles of
> physics displayed by some posters in this thread. No wonder people can still
> sell constant motion engines to investors!

Surely you don't mean Bernhard (my newsreader shows you replying to his
post)? His diagrams look correct.

--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

[Jon Meyer]

Bernhard's diagrams are spot on, but whether you call
it thrust or a reduction in drag is up to you. My Aeronautical
Engineering textbook uses both as alternative ways
of describing it. It all depends on how you choose
your frame of reference. The winglet produces a vorce
vector which consists of drag and lift, but when this
force vector is considered with the sailplane as the
frame of reference then its components could be considered
as a thrust force and a lateral force. I feel that
this is the easier way to describe the way they reduce
overall drag, but if you want to be pedantic........

[soarski]

"Libelle Driver" > wrote in message >...
> 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.




I can't believe you are so confused about Thrust and Lift? EG?

......For the libelle Driver: Normally an aircraft get's its thrust
from an engine, which pulls it's wings through the air and makes the
aircraft fly. Wings create lift! If your engine quitts, or you do not
have one, you will not necessarily quitt flying. You can glide! The
energy, thrust, is your altitude and gravity.

This is why we first NEED a towplane, in order to get altitude,
energy! then we can glide till we find lift! 3 kinds: Thermal, ridge
or Wave! Possibly one more..... When the lift is stronger than the
sinkrate (energy) we can soar, climb or fly streight, managing that
energy.

Did you forget that wave and ridge lift, IS lift also, air that is
moving UP just like thermals!?? Eric?

[Eric Greenwell]

soarski wrote:
> I can't believe you are so confused about Thrust and Lift? EG?

snip

> This is why we first NEED a towplane, in order to get altitude,
> energy! then we can glide till we find lift! 3 kinds: Thermal, ridge
> or Wave! Possibly one more..... When the lift is stronger than the
> sinkrate (energy) we can soar, climb or fly streight, managing that
> energy.

I think you are repeating my point: we don't get energy from gravity, we
just use gravity's field to store energy in the glider. When the glider
is sitting on the ground, it has no energy. As you point out, it gets
energy from first the towplane, then we release and get energy from
thermals or wind (ridge and wave).
>
> Did you forget that wave and ridge lift, IS lift also, air that is
> moving UP just like thermals!?? Eric?

We call them "lift", but they aren't aerodynamic lift like the lift from
a wing or winglets, which is what we've been discussing. The movement of
the airmass is really a separate issue from whether a wing or winglet
produces thrust. Except for dynamic soaring, the airmass motion is
simply superimposed on the aerodynamic motion of the glider through the air.

--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

[tango4]

Nope not at all! ( Sorry Bernhard ) and that's why I cut out his posting

I just wanted to add to the tail of the 'discussion.'

Ian


"Eric Greenwell" > wrote in message
...
> tango4 wrote:
>
> > I'm amazed at the complete lack of understanding of the basic principles
of
> > physics displayed by some posters in this thread. No wonder people can
still
> > sell constant motion engines to investors!
>
> Surely you don't mean Bernhard (my newsreader shows you replying to his
> post)? His diagrams look correct.
>
> --
> -----
> Replace "SPAM" with "charter" to email me directly
>
> Eric Greenwell
> Washington State
> USA
>

[K.P. Termaat]

Correct Todd. Two vectors (weight and aerodynamic force) cancel each other
out so according to the first law of Newton
the glider maintains its direction and speed. But it is not obvious from
this model which force is pulling the glider forward. This was the basic
problem put up some days ago.
From the four vector model relative to the glidepath it is clear at first
sight that the component of the weight in the direction of the glidepath is
the force that pulls the glider forward.

As far as winglets are concerned one can say that when during flight
winglets are installed at the wingtips (a little difficult of course) the
total flowpattern of the wing, especially at the wingtip area is improved in
such a way that total drag is reduced. The glider will therefore accellerate
to a new somewhat higher velocity until the previous value of total drag is
achieved again. Therefore one can say that winglets have a "thrusting"
effect on the glider. However this is not a very sound way of reasoning. In
the same way one can say that "bugs" on the wing have a decellerating effect
on the glider. But the bugs are dead; the only thing they can still do is
spoil the nice laminar flow over the leading edge of the wing.. As a result
drag increases and the performance of the glider is reduced.
A sound statement I think is that winglets improve the general flow pattern
over the wing, especially at the wingtip area, thereby reducing induced drag
and therefore improving the performance (polar curve) of the glider.

Regards,

Karel
V-2cxT




"Todd Pattist" > schreef in bericht
...
> "K.P. Termaat" > wrote:
>
> >I never state that this total force counteracts
> >the weight of the glider, which is true of course. I always tell my
glider
> >friends that the lift counteracts the weight component perpendicular to
the
> >flightpath while the drag is counteracted by the weightcomponent in the
> >direction of the flightpath.
>
> And you do as almost everyone else does. In fact, that's why
> I made the point that the total force is simply a vector
> that exactly opposes gravity - it often comes as a surprise
> to someone trained in the conventional FAA
> four-balanced-forces model. That model is so prevalent that
> you almost never hear of the simpler two-forces description.
>
> Gravity points down, aerodynamic force points up.
> Everything is balanced and the glider maintains constant
> speed. Lift and drag are just two vector components of the
> total aerodynamic force that we've chosen for convenience.
> I'm not saying the four-forces model isn't good - it is, but
> there are times when it's useful to keep the basic
> definitions of lift and drag in the back of your mind.
>
> Todd Pattist - "WH" Ventus C
> (Remove DONTSPAMME from address to email reply.)

[Bernhard Reinhardt]

Jon Meyer wrote:

> 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.

Ok, so my diagram of the winglet isn?t ok, because the airflow has an
inbound direction. And so it?s possible that it?s lift can be divided
into a inbound component an a thrust-component. I think now I got it.
See also: http://www.ich-habs-doch-gleich-gesagt.de/winglet2.gif

Greetings

Bernhard

[Fred the Red Shirt]

Jon Meyer > wrote in message >...
> Bernhard's diagrams are spot on, but whether you call
> it thrust or a reduction in drag is up to you. My Aeronautical
> Engineering textbook uses both as alternative ways
> of describing it. It all depends on how you choose
> your frame of reference. The winglet produces a vorce
> vector which consists of drag and lift, but when this
> force vector is considered with the sailplane as the
> frame of reference then its components could be considered
> as a thrust force and a lateral force. I feel that
> this is the easier way to describe the way they reduce
> overall drag, but if you want to be pedantic........

If there is only drag and no thrust you'll eventually be
flying backwards, right?

Suppose you raise your glider up into the air under a balloon and
drop it. If the wings (nor anything else) generate only lift and
no thrust then you'll just move in the verticle direction only,
or hover.

If a wing can generate thrust then so can a winglet depending on
geometry, AOA etc. It will also generate drag and weight.

--

FF

[Fred the Red Shirt]

(cddb) wrote in message . net>...
> Don't think so.
> Gravity provides the thrust. Quite noticeably when fuselage
> is pointed vertically. None at all when fuselage/wing is horizontal.
>

Rather obviously if this were true the glider would only move in the
vertical direction, and not at all in the horizontal.

--

FF

[Fred the Red Shirt]

LittleJohn > wrote in message t>...
> On Fri, 28 Nov 2003 21:36:17 +0000, cddb wrote:
>
> > Don't think so.
> > Gravity provides the thrust. Quite noticeably when fuselage
> > is pointed vertically. None at all when fuselage/wing is horizontal.
>
> Look at it from another point of view. If all forces are balanced and
> winglets are added, drag is reduced. Then velocity increases until the
> thrust/drag forces are equalized. The result of increased velocity is
> additional lift. The horizontal component of the lift vector is thrust,
> which increases as lift increases. Ergo, winglets produce thrust. ;>)
>

Close. The horizontal component in the forward direction is thrust.
in a 90 degree bank the lift is also horizontal.

--

FF

[Fred the Red Shirt]

LittleJohn > wrote in message t>...
> On Sat, 29 Nov 2003 11:32:36 -0800, Eric Greenwell wrote:
>
>
> 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,

it can also produce a force in the same direction to, or perpendicular
to lift. 'lift' is the aerodynamic force perpendicular to the direction
of motion. It is the horizontal component of lift that turns a banking
aircraft, and a vertical, downward lift that allows an aircraft to
accelerate in a dive FASTER than the acceleration due to gravity as
when the old Hurricanes inverted to keep the fuel flowing into their
engines when chasing a diving Messerschmidt. If they dove without
inverting first, they'd be chasing that M. in a glider.

Weight is the only one of the four forces that is constant in direction
is an earth-centered frame of reference. The other three forces may
be oriented in any direction though not independently as drag must be
opposite to thrust and lift perpendicular to both. Of course these
defintions are arbitrary, but other equally arbitrary defintions are
less useful.

> Gravity is the
> 'engine' in a glider that produces thrust.

More like it is the 'fuel', the engine is the wing.

--

FF

[Fred the Red Shirt]

Eric Greenwell > wrote in message >...
> 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.

Not if you _define_ lift as perpendicular to the direction of motion...

--

FF

[Fred the Red Shirt]

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

[Eric Greenwell]

Fred the Red Shirt wrote:

> Eric Greenwell > wrote in message >...
>
>>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.
>
>
> Not if you _define_ lift as perpendicular to the direction of motion...

True, which was not my intention. What I meant was "horizontal motion",
as I said later ("propelled in a forward direction"), thinking as a
pilot might as he tries to get somewhere.

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Eric Greenwell
Washington State
USA

[Eric Greenwell]

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

[Nyal Williams]

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!

[Fred the Red Shirt]

Eric Greenwell > wrote in message >...
> soarski wrote:
> > I can't believe you are so confused about Thrust and Lift? EG?
>

Sometimes words have two (or more) meanings.

--

FF

[Ian Cant]

Let's go back to the beginning. The FAA likes to teach four =
balanced forces, lift exactly cancelling gravity [weight] and thrust =
exactly cancelling drag. Unstated or widely ignored assumptions are a =
powered aircraft, constant altitude, constant speed, stationary airmass. =
This does not normally apply to a glider !

Starting with your Cessna flying per FAA model, take away the =
engine's thrust. Now something has to give - you can fly slower at =
constant altitude as drag exerts a decelerating force on you; lift would =
be reduced as airspeed drops, so to maintain altitude you increase angle =
of attack [until you stall, then you will descend]. Or you can choose =
to hold airspeed and descend by nosing down a little; then both the lift =
and drag vectors are tilted relative to gravity, and two things happen - =
a component of your total lift will resolve in the 'forward' direction =
90 degrees from the gravity 'down' direction AND a component of your =
total drag will resolve in the 'up' direction. Only three primary =
forces [lift, drag weight], resolved and summed in four directions. You =
stabilize at a new flightpath angle, same speed, same angle of attack =
[because your nose down input changed both fuselage angle and flight =
path angle by equal amounts after transients wash out] and therefore =
same drag, constant descent rate. That's how a glider works, I believe. =
The vectors can be drawn EITHER in space coordinates [true up and down] =
OR flightpath coordinates but please don't mix 'em together.

Note that of your three primary forces, weight is always there but =
lift and drag only exist because you have airspeed to begin with. And =
you need altitude as well, otherwise you can't fly down your slope.

To get to this stabilized state in the first place, you must have =
airspeed and altitude. Bungees, winches, towplanes, ramps off clifftops =
all supply the initial energy to get this altitude/airspeed to start you =
off.

Now soaring, that's a different matter, and really starts when the =
airmass motion comes into play..

Ian