Using lift to reduce hypersonic drag.

If you do a google search on "winglets", "thrust", and "vortices" and
you'll see that one interpretation of how they work is that they create
additional thrust. To be precise, these explanations note that the
direction of flow of air in vortices around the wing tips when they
flow over the winglets produces a lift force in the *forward*
direction. This is in fact how they were first invented. Now since the
winglets could not produce this force without a propulsion method
driving the vehicle forward you can also describe their effect as
reducing the overall drag.

It is well known among sailors that the *magnitude* of the boat
velocity can exceed the *magnitude* of the wind velocity when tacking
into the wind. This is discussed in the web page I cited, "The physics
of sailing." This method of tacking into the wind also works with ice
sailing where the runners pushing sideways against the ice is what
causes a force on the boat with a forward component that allows the ice
boat to move at an angle into the wind. With ice boats the speeds can
exceed more than 70 mph when tacking into the wind, much higher than
the wind speed.

I am suggesting taking advantage of the fact that with the hypersonic
shockwave you have two fluids of very different densities moving with
respect to each other. That is what happens with a shock wave attached
to the vehicle.

It is known that placing vertical airfoils at the top and bottom of a
hypersonic vehicle can *reduce* the overall drag eventhough each of
these produces an additional shockwave. These are known as "star
bodies." This is discussed at the bottom of this page:

Waverider Design.
http://www.aerospaceweb.org/design/w...averider.shtml

Here's a reference:

Performance Study of a Power Law Starbody
John W. Sabean; Mark J. Lewis; David Mee; Allan Paull
Journal of Spacecraft and Rockets 1999
0022-4650 vol.36 no.5 (646-652)
http://pdf.aiaa.org/jaPreview/JSR/1999/PVJAIMP3496.pdf [abstract]

The authors though don't appear to be suggesting that these two
vertical foils operating in concert can produce additional forward
lift.


Bob Clark



wrote:
Robert Clark wrote:
The idea was to use the lift force to increase the forward velocity of
the craft.

Nope. You've misunderstood it totally. Thrust propels the aircraft,
lift keeps it airborne under normal circumstances. This is inverse
lift . I suppose you could say you use lift to maintain altitude
against centripetal force. The lift doesn't increase speed in any way.
In fact staying in the air induces drag and then there's drag induce
lift. Negative lift in this case allows you to operate at higher
speeds than you might, even though the these losses are present. Lift
doesn't contribute to your thrust at all.

However, I have been informed by email that since lift is
always perpindicular to the velocity it can not be used to increase the
forward speed.

The person who informed you was right. You are totally confused about
what's going on.

Nevertheless the idea of having the craft travel in a
circle could still work by using the lift force to counteract the large
acceleration implied by the formula a = v^2/r.

You are even more confused than you were a second ago! But so close!

Forget about what you're thinking and think this.

The circle you're travelling in is a great circle route around the
surface of the Earth. If you complete an orbit your r = 6,366,198
meters, and your centripetal acceleration at 11,000 m/sec is 19.64
m/s/s - double that of gravity. An object constrained to travel at
this radius at this speed would experience 2 gees of force directed
away from the center of rotation. Now, if that center of rotation
happens to be the center of the earth, then, 1 gravity pulls them back
toward the center, leaving one gravity directed away from the center.
So, someone sitting in the aircraft would have the aircraft 'lift'
pulling holding it at its altitude, and the persons sititing inside
would be seated looking out the window, feeling nothing unusual, except
the Earth would be ABOVE their heads, and the sky below.

However, there may be a way to use aerodynamic forces to increase the
forward speed.

No, aerodynamic forces will always slow an aircraft. That's the nature
of aerodynamic forces. If you want to add energy to the flow somehow,
that would be called thrust, and it involves the expenditure of energy.

The phenomenon of "tacking into the wind" in sailing
allows a sail boat to actually have a forward velocity component that
goes *into* the wind.

Word hash. This is a trick with vector sums and relies on the relative
speed of wind and water. There are two fluids here moving relative to
one another. The boat takes advantage of both, with the keel operating
on the water and the sail operating in the air.

http://www.phys.unsw.edu.au/~jw/sailing.html

Indeed using this method the boat's speed can
actually exceed the wind speed. This page provides a good explanation:

The physics of sailing.
http://www.phys.unsw.edu.au/~jw/sailing.html

???

Tell me did you read this? I mean did you see the part about the keel?
You know that part in the water? Sheez.

An aircraft isn't floating in water. Its floating in air. I suppose
if you had two bodies of air moving at different speed relative to one
another you could take advantage of that difference to extract thrust
from it. But that's quite different than extracting thrust from
aerodynamic drag - which is not what I'm talking about.

So, you are proceeding from error to error each one building on the
next. lol.

The method is used with boats that have a keel that extends into the
water.

Yes. And there is no keel and no water in a free flying aircraft.

The basic idea is that if the boat is sailing at an angle to the
wind then the wind is pushing the boat at an angle. This causes the
keel to push on the water at an angle which means the water is
providing an equal and opposite force on the boat. Note now though this
force on the boat from the water does have a *forward* component. And
the sum total of the vector forces of the wind and the water on the
boat also has a forward component.

Look at the freakin' pictures - its a problem of vectors. You're not
sailing directly into the wind, you're sailing at an angle across the
wind, and taking advantage of how the vectors sum on the keel and the
sail to extract thrust from the difference.

This causes the boat to move at an angle into the wind. To arrive at a
course direction directly into the wind, the boat is made to move first
to the right of the wind and to the left of it alternatingly in zigzag
fashion.

The boat doesn't move directly into the wind, it moves at an angle
towards the wind, it has to tack - as you say, and while it can move
faster than the wind across the wind, it cannot move faster than the
wind into the wind. Check it out. Take the hypotenuse of the vector
triangle, and project it into the wind - its less than wind speed dude.

Could this idea be applied to hypersonic waveriders?

No.

At hypersonic
speeds, the density of the air within the shock wave is many times the
density of the ambient air, as water is many times the density of sea
level air.

Ever hear of the Hugoniot relations? They accurately describe
compressible supersonic flows. And they demonstrate that what you are
proposing to do is impossible in normally constitute fluids.

http://www.pma.caltech.edu/Courses/p...4/0416.2.K.pdf

Now there are exceptions to everything and in this case its if the
compressible flow detonates - then one of the assumptions is violated,
and you can produce thrust. But that's a totally different thing than
you're talking about - and ALL of this is a totally different thing
than what I talked about originally.

Then the idea would be to have a "keel" that extends into
the shockwave and a vertical airfoil (a "sail") that extends through
the shock layer into the surrounding low density air.
See the last image on this page:

The keel is creating the shockwave dude. Read that chaper I provided
and when you understand it, then come back and post. What you are
posting here is drivel.


Hypersonic Flow.
http://www.aerospaceweb.org/design/waverider/flow.shtml

You see the shock layer is close to the craft on the bottom of the
craft and extends further out at the top. Then the "keel" would extend
from the top in this case to remain within the shock layer, and the
airfoil "sail" would extend from the bottom into extend into the
ambient air.

Nope it don't work that way. Any object in the stream creates its own
shockwave. The angles and momentum transfer is such that it always
produces drag - for a normal fluid like air. Now, if you have an
explosive, that happens to release energy based on density, then you
might have something. But that's not a normal fluid. That's a fluid
that generates energy - a combustible mixture or something.


This page gives a formula for the stagnation pressure of the shock
layer at least initially:

STAGNATION PRESSURE
http://www.ae.utexas.edu/courses/ase...pres_temp.html


So? Read about how compressible flows work and then come back.

So at Mach 20 using a ratio of specific heats gamma of 1.4 for air,
the pressure increase would be by factor of 4783 of the pressure
initially in the shock layer over the pressure of the ambient air. This
is greater than for example the ratio of the ratio of the pressure of
the water on a keel than the pressure of the sea level air on a sail.
This pressure within the shock layer though would decrease as you get
further from the front of the vehicle so you would want the "keel" to
be close to the front.

The sailboat was a good example of how to do vector sums. That's it.
Could you do a vector sum of what's happening to the shock wave here?
Well, Chapter 16 will help you. You will find that you can't get
thrust this way - with air as the fluid that is.

The question, would the addition of these extra structures result in
just an increase in the overall drag of the vehicle?

Yes, definitely. Because they create their own shock waves If the
boat didn't have a keel, it couldn't tack into the wind. The shockwave
is part and parcel of the air that forms it.

As discussed on this page the addition of winglets to aircraft has a
similar effect of producing extra thrust, so reducing the overall drag:

How Things Work: Winglets.
"The airflow around winglets is complicated, and winglets have to be
carefully designed and tested for each aircraft. Cant, the angle to
which the winglet is bent from the vertical, and toe, the angle at
which the winglets' airfoils diverge from the relative wind direction,
determine the magnitude and orientation of the lift force generated by
the winglet itself. By adjusting these so that the lift force points
slightly forward, a designer can produce the equivalent of thrust. A
sailboat tacking sharply upwind creates a similar force with its sail
while the keel squeezes the boat forward like a pinched watermelon
seed."
http://www.airspacemag.com/ASM/Mag/I...1/AS/htww.html



Winglets do not produce thrust. They reduce drag by reducing wingtp
vortices. See, the wing causes a deflection of the air downward,
creating lift on the wing's surface. The air just outside the tip of
the wing isn't deflected. This causes a rotation of the air, and
increases drag slightly. A winglet at the tip of a wing, reduces this
vortical motoin, and thus reduces drag.

It would appear from Newton's second law you could not get more
forward acceleration than from the craft operating in vacuum under the
propulsion method used.

That is correct.

Nevertheless, effectively you get more forward
acceleration in air than without these extra structures because of the
overall drag reduction.

You made a logical error if you're connecting these two. You compared
an aircraft in vacuum to an aircraft in the air - and then switched to
say if you have more surface area you must get more drag. The shape of
the surface has an effect, and the total area involved is small while
the effect is large, since the vortice is concentrated in a small
volume around the aircraft;

http://www.nasa.gov/centers/dryden/p...04-15-DFRC.pdf



Just as importantly, the overall reduction in
drag would result in an increase in the lift to drag ratio.

Depends on the details. But generally speaking winglets on the
wingtips of aircraft are a good thing performance wise. They're not
producing thrust. They're not violating laws of physics.



Bob Clark


Bob you have proceeded from error to error and ended up in a bog. I
think I'll call you Bog Clark.



Robert Clark wrote:
wrote:
Orbital speed is where centripetal force equals gravity force and is
given by;

v = sqrt(GMe/r)

Which can be derived from the following three equations;

F = G*m*Me/r^2 - gravitational force
a = v^2/r - centripetal acceleration
F = ma - relating mass and acceleration

a = F/m = GMe/r^2 - gravitational acceleration
a = v^2/r - centripetal acceleration

Setting the two accelerations equal

v^2/r = GMe/r^2
v^2 = GMe/r
v = sqrt(GMe/r)

If we increase velocity by 41.4% we double the centripetal
acceleration, which means that if we were to fly an aircraft at Mach 33
we'd need wings to hold it in the atmosphere! Since wings lift
aircraft all the time against gravity, it seems reasonable to believe
that wings could hold an aircraft down. Everything would seem quite
normal to the occupants, except down would be up to them, and the lift
would be directed toward the Earth's center.

The vehicle if possible would be capable of circumnavigating the Earth
in 60 minutes - and delivering payloads to targets anywhere in 30
minutes or less.

Would such a craft be possible?

Yes. I speculated about this possibility for the use with beamed
propulsion:

From: Robert Clark
Date: Sat, Nov 19 2005 2:23 pm
Email: "Robert Clark"
Groups: sci.astro, sci.physics, sci.math
Subject: Math question for the trajectory of beamed propulsion.
http://groups.google.com/group/sci.a...a00732000ef7f7

This would also be applicable to the scenario where electrical power
for propulsion is transmitted though long cables:

From: Robert Clark
Date: Fri, May 27 2005 12:10 pm
Email: "Robert Clark"
Groups: sci.astro, sci.space.policy, sci.physics,
sci.electronics.design, sci.electronics.misc
Subject: Long cables to power "ioncraft" to orbit?
http://groups.google.com/group/sci.a...2b09463e87dde6

The problem is that though the height to orbit might be 100 km, the
horizontal distance travelled might be 2000 km in order to build up
sufficient speed for orbital velocity.
The proposals for beamed propulsion I've seen though do not use
lifting surfaces for the craft:

Riding Laser Beams to Space.
http://www.space.com/businesstechnol...on_000705.html

However, the lift to drag ratios at hypersonic speeds suggest we might
be able to increase the thrust and therefore the acceleration by
several times if the craft was designed for aerodynamic lift. See the
graph showing lift to drag ratio versus Mach number he

Waverider Design.
http://www.aerospaceweb.org/design/w...averider.shtml

With airplanes you have the thrust directed horizontally to overcome
the drag force against forward motion and the lift provides the force
to keep the airplane aloft. Since subsonic L/D ratios can be 15 to 1
and higher the thrust required from the engines is much less than the
actual weight of the plane.
However, with beamed propulsion a key problem is the dimunition of the
power with distance, which decreases with the square of the distance so
you want to keep the distance short. The idea then in this case using
aerodynamic lift would be to use the thrust produced by the beamed
propulsion to overcome gravity and drag and use the lift force to
provide the higher acceleration to reach orbital velocity in a shorter
distance. Essentially the craft would be pointed upwards so that the
wings/lifting surfaces provide the "lift" in the horizontal direction.
The graph on the "Waverider Design" page shows the L/D ratio can be
about 7 to 8 at hypersonic speeds. For instance if the beamed
propulsion provided a thrust of 1 g to counter gravity plus 4 g's
against drag for a total of 5 g's in the vertical direction, then the
horizontal acceleration could be as much as 8*4 = 32 g's.
Note though it would be important to keep the craft oriented so that
so that the velocity vector is always pointed through the forward
centerline of the craft. When lift and drag calculations are made it's
always in regard to the craft moving so the airstream is flowing more
or less parallel over the wings/lifting surfaces, according to angle of
attack. If instead the airstream was flowing perpindicular to the plane
of the wings the lift would be much less and drag would be much greater
so the L/D ratio would be severely reduced. The aerodynamic control
surfaces would be used to keep the craft properly oriented.
Estimates for beamed propulsion are about 1 megawatt of power to send
1 kilogram to orbit. If say such beamed propulsion provided thrust for
5 g's of acceleration then the lifting force could provide 32 g's, or a
factor of 6 more. So the distance required would be smaller by a factor
6. This means the power required would be smaller by a factor 6^2 = 36.
Then 36 times greater mass could be lifted for the same power. This is
dependent though on how much acceleration beamed propulsion could
provide. If it were 7 g's then the lifting acceleration would be 8*6 =
48 g's, about a factor of 7 more. Then the power required would be less
by 7^2 = 49, and 49 times greater mass could be lifted.
There are apparently megawatt class lasers already in operation:

Mid-Infrared Advanced Chemical Laser (MIRACL).
http://www.fas.org/spp/military/program/asat/miracl.htm

Let's say they are at the 10 megawatt stage now. Then this could
accelerate 10 kilos to orbit. Then with aerodynamic lift it could lift
perhaps 360 kilos to orbit, which is the size of a small sized
satellite.


Bob Clark

On 17 Jul 2006 16:50:29 -0700, in a place far, far away, "Robert
Clark" made the phosphor on my monitor glow
in such a way as to indicate that:

If you do a google search on "winglets", "thrust", and "vortices" and
you'll see that one interpretation of how they work is that they create
additional thrust.

No.

To be precise, these explanations note that the
direction of flow of air in vortices around the wing tips when they
flow over the winglets produces a lift force in the *forward*
direction. This is in fact how they were first invented. Now since the
winglets could not produce this force without a propulsion method
driving the vehicle forward you can also describe their effect as
reducing the overall drag.

Yes, they reduce drag. They don't, in any way, increase thrust.

On 17 Jul 2006 17:41:18 -0700, in a place far, far away, "Robert
Clark" made the phosphor on my monitor glow
in such a way as to indicate that:

Rand Simberg wrote:
On 17 Jul 2006 16:50:29 -0700, in a place far, far away, "Robert
Clark" made the phosphor on my monitor glow
in such a way as to indicate that:

If you do a google search on "winglets", "thrust", and "vortices" and
you'll see that one interpretation of how they work is that they create
additional thrust.

No.

To be precise, these explanations note that the
direction of flow of air in vortices around the wing tips when they
flow over the winglets produces a lift force in the *forward*
direction. This is in fact how they were first invented. Now since the
winglets could not produce this force without a propulsion method
driving the vehicle forward you can also describe their effect as
reducing the overall drag.

Yes, they reduce drag. They don't, in any way, increase thrust.

How Things Work: Winglets

Nothing you posted refutes my statement.

"Robert Clark" wrote:

Rand Simberg wrote:
On 17 Jul 2006 16:50:29 -0700, in a place far, far away, "Robert
Clark" made the phosphor on my monitor glow
in such a way as to indicate that:

If you do a google search on "winglets", "thrust", and "vortices" and
you'll see that one interpretation of how they work is that they create
additional thrust.

No.

Agreed: no. They can be interpreted as recovering thrust from the
induced drag, but they don't create any. They create *lift*, and that
lift does act partially in the direction of travel, but the lift is
taken from the motion of the tip vortex, which robbed the vehicle of
some of its thrust in the first place.

How Things Work: Winglets
"The airflow around winglets is complicated, and winglets have to be
carefully designed and tested for each aircraft. Cant, the angle to
which the winglet is bent from the vertical, and toe, the angle at
which the winglets' airfoils diverge from the relative wind direction,
determine the magnitude and orientation of the lift force generated by
the winglet itself. By adjusting these so that the lift force points
slightly forward, a designer can produce the equivalent of thrust. A
sailboat tacking sharply upwind creates a similar force with its sail
while the keel squeezes the boat forward like a pinched watermelon
seed."
http://www.airspacemag.com/ASM/Mag/I...1/AS/htww.html

If you can wrap your head around that complicated airflow and follow it
from the right point of view, you can see that the apparent thrust from
a "toed" winglet is more simply understood as a targeted disruption of
the tip vortex and consequent reduced drag.

Of course, there are always people who don't want to make the effort to
see it from the point of view that simplifies things. For them, the
"forward lift = thrust" explanation is the easy way out. It adequately
describes the effect, but it completely obscures the mechanism.

Read the NASA paper I gave you a reference to originally. Winglets
don't operate like sails on a sail boat. They reduce wingtip vortices.
Period.

Read up on compressible flow that I gave you. It shows in detail how
compressible flow works, and why you can't produce thrust by sticking
things across shock waves (since doing so creates new shock waves!)
You *might* be able to create thrust with weird gas flows, as in
supersonic combustion - but that's not what you're talking about.

Quit talking and start listening - and maybe you'll understand.

wrote in message
ups.com...
Read the NASA paper I gave you a reference to originally. Winglets
don't operate like sails on a sail boat. They reduce wingtip vortices.
Period.

Read up on compressible flow that I gave you. It shows in detail how
compressible flow works, and why you can't produce thrust by sticking
things across shock waves (since doing so creates new shock waves!)

what you need to do is combust *in* the shock wave interface

You *might* be able to create thrust with weird gas flows, as in
supersonic combustion - but that's not what you're talking about.

Quit talking and start listening - and maybe you'll understand.

Combust in the shock wave -

Yes, that's what I'm talking about some sort of air/fuel mix. Another
possibility is to wave the 'winglets' like flapping wings - which I
didn't think of but could work, maybe. But they the little buggers
have gotta move FAST! I'm not sure you could do it.

Another possibility is that you have a nearly supercritical fissile
material that goes critical in the shock wave - but we're talking BIG
**** here, a control sytem for a rocket with downtown Chicago as the
payload, burning the entire inventory of nuclear weapons material every
few hours, or if you really crank up pressure and temperature, you pass
the Lawson criterion in a fusile material! lol. But I'm damned if I'd
know how to build THAT! lol. Maybe a fusion assisted fission rocket.
lol.

That last might be useful in moving STARS around if you could do it!
lol. Directing the stellar winds coming off of stars. Self
replicating starships that spread across the universe would implement a
Kardeshev V civilization! lol. They would have this little trick in
their bag of tricks.

The solar wind goes through a shock somewhere between Earth orbit and
Heliopause.

If you had solar collectors held by in place by solar wind close in to
the solar surface, modulating that wind might move the sun around.
Folks back in the 70s and 80s talked about 'starlifting' - which might
be possible. This is might be a nuance in actually lifting stars.

Frank Tipler talked about the universal paradigm that all intelligence
has, which is to change the environment of the universe to extend life
as long as possible. This entails encompassing the entire universe and
changing the momentum of stars so that things collapse into the right
kind of shape so that we can process an infinite amount of information
over an infinite period of time. Damn you if you're wrong! lol. The
end of the universe would then be one big DOH! Which may explain the
popularity of Homer Simpson.

But if Tipler's right, then there are no Type V civlizations - and
we're the first.

Other folks think we don't see these advanced civilization. We think
their work is nature. The voids we see around us are evidence of their
existence - since they turned off the stars once they moved them, to
conserve resources for the long haul, and the bright regions are left
untouched for some cosmological reasons - and we think its natural, but
ask about the missing mass! lol.

Still others think we're already stuck in a VR model of the universe at
the end of time, a footnote in a infinitely complex program that never
stops - we're already in a matrix.

But I digress! lol.

as you know critical mass is accomplished by having the right
geometric buckling for any given material buckling

you could use standing acoustic waves in the bow shock to shape
species concentrations so that a self-sustaining critical mass
was acheived

i would not want to be in the exhaust plume however

Robert Clark wrote:
If you do a google search on "winglets", "thrust", and "vortices" and
you'll see that one interpretation of how they work is that they create
additional thrust. To be precise, these explanations note that the
direction of flow of air in vortices around the wing tips when they
flow over the winglets produces a lift force in the *forward*
direction. This is in fact how they were first invented. Now since the
winglets could not produce this force without a propulsion method
driving the vehicle forward you can also describe their effect as
reducing the overall drag.

It is well known among sailors that the *magnitude* of the boat
velocity can exceed the *magnitude* of the wind velocity when tacking
into the wind. This is discussed in the web page I cited, "The physics
of sailing." This method of tacking into the wind also works with ice
sailing where the runners pushing sideways against the ice is what
causes a force on the boat with a forward component that allows the ice
boat to move at an angle into the wind. With ice boats the speeds can
exceed more than 70 mph when tacking into the wind, much higher than
the wind speed.

I am suggesting taking advantage of the fact that with the hypersonic
shockwave you have two fluids of very different densities moving with
respect to each other. That is what happens with a shock wave attached
to the vehicle.

It is known that placing vertical airfoils at the top and bottom of a
hypersonic vehicle can *reduce* the overall drag eventhough each of
these produces an additional shockwave. These are known as "star
bodies." This is discussed at the bottom of this page:

Waverider Design.
http://www.aerospaceweb.org/design/w...averider.shtml

Here's a reference:

Performance Study of a Power Law Starbody
John W. Sabean; Mark J. Lewis; David Mee; Allan Paull
Journal of Spacecraft and Rockets 1999
0022-4650 vol.36 no.5 (646-652)
http://pdf.aiaa.org/jaPreview/JSR/1999/PVJAIMP3496.pdf [abstract]

The authors though don't appear to be suggesting that these two
vertical foils operating in concert can produce additional forward
lift.


Bob Clark



As I see it the basic Physics is the following. In general vortices
lead to drag. reducing vorticity will thereby reduce turbulent drag. If
you pump air from low pressure to high pressure you do work, where that
work goes is not clear and depends very much on circumstances. If you
pump air into a vortex it will incease the size of the vortex and
thereby create more drag. If you had an airplane with holes in the
airframe/piezoelectric material you could have reduced drag for most of
the flight and put energy into the vortices on landing giving the
effect of retro thrust.

If on the other hand you have continuous high pressure on the lower
wing anf low pressure on the upper wing (causing lift) and you pump gas
from the upper to the lower wing you will, in principle, get thrust.
Mind you have to be careful that in so doing you don't induce drag.
This in fact is the principle of swimming with flippers and the leg
movements of "crawl". You are moving your legs at right angles to the
fluid flow.

At super and hypersonic speeds one of the main characteristics is the
presence of shock waves. If you inject fuel into a shock wave it is
possible, in principle, to gain energy. There are of course a very
large number of ifs and buts. The shape of the trailing edge is
critical. In principle you could place rocket motors on the leading
edge and increase the specific impulse from what you would get in a
vacuum.

This is all however in principle, in principle. Years of research would
be needed to get any effective advantage. I think most people would
agree that a 2STO, completly recoverable was the best practical
solution at this stage.

Alan Anderson wrote:
"Robert Clark" wrote:

Rand Simberg wrote:
On 17 Jul 2006 16:50:29 -0700, in a place far, far away, "Robert
Clark" made the phosphor on my monitor glow
in such a way as to indicate that:

If you do a google search on "winglets", "thrust", and "vortices" and
you'll see that one interpretation of how they work is that they create
additional thrust.

No.

Agreed: no. They can be interpreted as recovering thrust from the
induced drag, but they don't create any. They create *lift*, and that
lift does act partially in the direction of travel, but the lift is
taken from the motion of the tip vortex, which robbed the vehicle of
some of its thrust in the first place.

How Things Work: Winglets
"The airflow around winglets is complicated, and winglets have to be
carefully designed and tested for each aircraft. Cant, the angle to
which the winglet is bent from the vertical, and toe, the angle at
which the winglets' airfoils diverge from the relative wind direction,
determine the magnitude and orientation of the lift force generated by
the winglet itself. By adjusting these so that the lift force points
slightly forward, a designer can produce the equivalent of thrust. A
sailboat tacking sharply upwind creates a similar force with its sail
while the keel squeezes the boat forward like a pinched watermelon
seed."
http://www.airspacemag.com/ASM/Mag/I...1/AS/htww.html

If you can wrap your head around that complicated airflow and follow it
from the right point of view, you can see that the apparent thrust from
a "toed" winglet is more simply understood as a targeted disruption of
the tip vortex and consequent reduced drag.

Of course, there are always people who don't want to make the effort to
see it from the point of view that simplifies things. For them, the
"forward lift = thrust" explanation is the easy way out. It adequately
describes the effect, but it completely obscures the mechanism.

Einstein said: "Things should be made as simple as possible -- but no
simpler."

We are agreed that the drag reduction effect can occur from breaking
up the vortices, but any vertical plate could do that. But if you
ignore the lift production effect then you are ignoring an important
facet in how they operate and furthermore this could limit further
insight in how to improve them.
It would be easy to see if a forward lift force is operating and thus
validate that this is an important *part* of the explanation of their
method of operation. Attach winglets to wings in a wind tunnel, but
attach them in a way using springs that allows them to move to shift
their position somewhat under applied forces. Then connect force meters
to the winglets to detect which direction the *net* force is operating.

If the *net* force on the winglets has some component pointing forward
despite the fact that the drag from the wind tunnel air flow tends to
move them backward, then this will confirm that the forward lift force
produced is an important part of their operation.


Bob Clark