Search   Memberlist   Usergroups
 Page 1 of 2 [18 Posts] View previous topic :: View next topic Goto page:  1, 2 Next
Author Message
Robert Clark
science forum Guru Wannabe

Joined: 30 Apr 2005
Posts: 129

Posted: Thu Jul 20, 2006 4:03 pm    Post subject: Re: Using lift to reduce hypersonic drag.

A question sometimes asked is that if you have a large fan on a
sailboat blowing forward into the sails would that propel the boat
forward? The usual answer given is no because the fan blowing air
forward would produce momentum propelling the boat backwards. This
would swamp the effect of an effective wind acting on the sails.
But suppose instead you had the fan blowing rearward into the sails?
In this case the momentum would propel the boat forward. Furthermore by
using the method of tacking into the wind, the wind blowing into the
sails could produce a force with a forward component as well. Then the
acceleration forward should be higher than that produced by the
momentum flow of the fan alone. The speed could also be higher than the
speed of the air created by the fan.
Extrapolating this to the case of the hypersonic vehicle. If you had
the thrust directed rearwards to flow over a vertical "sail" attached
to the vehicle, though not over the attached "keel", then in fact you
could generate more thrust than that produced by the engines alone and
the speed of the vehicle could also exceed the speed of the exhaust.

Bob Clark

Robert Clark wrote:
BlagooBlanaa
science forum beginner

Joined: 05 Mar 2006
Posts: 15

 Posted: Wed Jul 19, 2006 2:30 am    Post subject: Re: Using lift to reduce hypersonic drag. the differential equation describing neutron kinetics in a reactor is exactly the same as the differential equation describing the buckling of a beam so if you do a study of nuclear engineering you will encounter the terms geometric buckling and material buckling i have designed nuclear reactors, and written simulations for them m'kay?
Tom Sanderson

Joined: 22 Dec 2005
Posts: 55

Posted: Tue Jul 18, 2006 8:59 pm    Post subject: Re: Using lift to reduce hypersonic drag.

"Robert Clark" <rgregoryclark@yahoo.com> wrote
 Quote: You could cook the rest of the wing such that you've got a wierd flow over the winglet and you could get a net forward force component on the winglet...basically, you could alter the local wind enough that the winglet was "pulling" forward on the rest of the wing. However, in order to do so, you'd have to be causing an opposite force on the rest of the wing. Since no airfoil can convert airflow to lift with 100% efficiency, the amount of force to gain from the winglet will always be less than the amount you lost on the rest of the wing. So what is your suggestion on what the result of this experiment would be?

There is no winglet you could add to a wing which would cause a net forward
force between the wing and the mount.

 Quote: Would there be a forward component to the net force on the winglet?

There can be, if you tweak the wing properly. It will be more than
counteracted by the backward force such a tweak induces on the wing.

 Quote: I argue that the effect of this is to pull the wing forward more than if the winglet was not there.

You're treating the problem as if the wing without the winglets just loses
the force from the winglet. The presence of the winglet alters the airflow
over the entire wing...it doesn't really make sense to talk about isolated
winglet/wing forces because you can't separate them.

A good winglet will reduce drag in the overall assembly. You can screw with
the wing such that the winglet actually generates a forward force, but
you'll induce so much drag on the wing that the overall effect will be worse
than the wing with a properly done winglet (which does not contribute a
forward force). Either scenario could have less drag than a wing without
winglets.

 Quote: If a rope tugs on rock the rock is tugging back on the rope. That doesn't change the fact that the rock moves forward.

Although true, it's not relevant to the forces on wings. Whatever's tugging
on the rock has to be tugging on something else. An aircraft has no
externally applied forces on the thust axis during level flight.

Tom.
Robert Clark
science forum Guru Wannabe

Joined: 30 Apr 2005
Posts: 129

Posted: Tue Jul 18, 2006 4:00 pm    Post subject: Re: Using lift to reduce hypersonic drag.

Tom Sanderson wrote:
 Quote: "Robert Clark" wrote: We are agreed that the drag reduction effect can occur from breaking up the vortices Also lift reduction...if you actually broke the vortices on a real aircraft wing, you'd have no lift. but any vertical plate could do that And does. Even a straight vertical plate lowers induced drag on the wing. They key is whether it reduces it enough to offset the weight of the plate. 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. No, it won't. The only thing that matters is the net force on the aircraft. You could cook the rest of the wing such that you've got a wierd flow over the winglet and you could get a net forward force component on the winglet...basically, you could alter the local wind enough that the winglet was "pulling" forward on the rest of the wing. However, in order to do so, you'd have to be causing an opposite force on the rest of the wing. Since no airfoil can convert airflow to lift with 100% efficiency, the amount of force to gain from the winglet will always be less than the amount you lost on the rest of the wing. Tom.

So what is your suggestion on what the result of this experiment would
be?
Would there be a forward component to the net force on the winglet?
I argue that the effect of this is to pull the wing forward more than
if the winglet was not there.
If a rope tugs on rock the rock is tugging back on the rope. That
doesn't change the fact that the rock moves forward.

Bob Clark
Tom Sanderson

Joined: 22 Dec 2005
Posts: 55

Posted: Tue Jul 18, 2006 2:41 pm    Post subject: Re: Using lift to reduce hypersonic drag.

"Robert Clark" <rgregoryclark@yahoo.com> wrote:
 Quote: We are agreed that the drag reduction effect can occur from breaking up the vortices

Also lift reduction...if you actually broke the vortices on a real aircraft
wing, you'd have no lift.

 Quote: but any vertical plate could do that

And does. Even a straight vertical plate lowers induced drag on the wing.
They key is whether it reduces it enough to offset the weight of the plate.

 Quote: 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.

No, it won't. The only thing that matters is the net force on the aircraft.

You could cook the rest of the wing such that you've got a wierd flow over
the winglet and you could get a net forward force component on the
winglet...basically, you could alter the local wind enough that the winglet
was "pulling" forward on the rest of the wing. However, in order to do so,
you'd have to be causing an opposite force on the rest of the wing. Since
no airfoil can convert airflow to lift with 100% efficiency, the amount of
force to gain from the winglet will always be less than the amount you lost
on the rest of the wing.

Tom.
Robert Clark
science forum Guru Wannabe

Joined: 30 Apr 2005
Posts: 129

Posted: Tue Jul 18, 2006 2:00 pm    Post subject: Re: Using lift to reduce hypersonic drag.

William.Mook@gmail.com wrote:
 Quote: ... 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.

Reminds me of the famous Asimov story, "The Last Question":

The Last Question
By Isaac Asimov
http://infohost.nmt.edu/~mlindsey/asimov/question.htm

Bob Clark
William.Mook@gmail.com

Joined: 06 May 2006
Posts: 50

Posted: Tue Jul 18, 2006 1:43 pm    Post subject: Re: Using lift to reduce hypersonic drag.

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

I don't see how buckling has anything to do with it. So, I don't
understand your comment. From my worm's eye view of nuclear physics
classes I took in school, criticality is achieved when more neutrons
are generated in a given volume than are lost from the volume through
the surface. For a spherically symmetric implosion the integration is
easily performed. For other structures, as in a rocket exhaust, or
more complex structures, the integration would likely be done
numerically.

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

I don't see how this is possible.

 Quote: i would not want to be in the exhaust plume however

I agree, that would be bad.
Robert Clark
science forum Guru Wannabe

Joined: 30 Apr 2005
Posts: 129

Posted: Tue Jul 18, 2006 1:21 pm    Post subject: Re: Using lift to reduce hypersonic drag.

Alan Anderson wrote:
 Quote: "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/Index/2001/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
Ian Parker
science forum Guru Wannabe

Joined: 15 Jul 2005
Posts: 100

Posted: Tue Jul 18, 2006 10:13 am    Post subject: Re: Using lift to reduce hypersonic drag.

Robert Clark wrote:
 Quote: 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/waverider/waverider.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.
BlagooBlanaa
science forum beginner

Joined: 05 Mar 2006
Posts: 15

 Posted: Tue Jul 18, 2006 6:41 am    Post subject: Re: Using lift to reduce hypersonic drag. 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
William.Mook@gmail.com

Joined: 06 May 2006
Posts: 50

BlagooBlanaa
science forum beginner

Joined: 05 Mar 2006
Posts: 15

Posted: Tue Jul 18, 2006 2:50 am    Post subject: Re: Using lift to reduce hypersonic drag.

<William.Mook@gmail.com> wrote in message
 Quote: 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

 Quote: 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.
William.Mook@gmail.com

Joined: 06 May 2006
Posts: 50

 Posted: Tue Jul 18, 2006 2:13 am    Post subject: Re: Using lift to reduce hypersonic drag. 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.
Alan Anderson
science forum beginner

Joined: 31 Aug 2005
Posts: 3

Posted: Tue Jul 18, 2006 1:07 am    Post subject: Re: Using lift to reduce hypersonic drag.

"Robert Clark" <rgregoryclark@yahoo.com> wrote:

 Quote: 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.

 Quote: 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/Index/2001/AS/htww.html

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.
Rand Simberg
science forum beginner

Joined: 02 May 2005
Posts: 18

Posted: Tue Jul 18, 2006 12:46 am    Post subject: Re: Using lift to reduce hypersonic drag.

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

 Quote: 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.

 Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First
 Page 1 of 2 [18 Posts] Goto page:  1, 2 Next View previous topic :: View next topic
 The time now is Mon Mar 25, 2019 5:45 pm | All times are GMT
 Jump to: Select a forum-------------------Forum index|___Science and Technology    |___Math    |   |___Research    |   |___num-analysis    |   |___Symbolic    |   |___Combinatorics    |   |___Probability    |   |   |___Prediction    |   |       |   |___Undergraduate    |   |___Recreational    |       |___Physics    |   |___Research    |   |___New Theories    |   |___Acoustics    |   |___Electromagnetics    |   |___Strings    |   |___Particle    |   |___Fusion    |   |___Relativity    |       |___Chem    |   |___Analytical    |   |___Electrochem    |   |   |___Battery    |   |       |   |___Coatings    |       |___Engineering        |___Control        |___Mechanics        |___Chemical

 Topic Author Forum Replies Last Post Similar Topics Proposals for air breathing hypersonic craft. III Robert Clark Mechanics 5 Fri Jun 23, 2006 4:52 pm Proposals for air breathing hypersonic craft. II Robert Clark Mechanics 30 Sat Jun 17, 2006 6:43 pm Orbital drag & kinematic precession. brian a m stuckless num-analysis 0 Tue May 16, 2006 9:24 am Orbital drag & kinematic precession. brian a m stuckless Electromagnetics 0 Tue May 16, 2006 9:24 am Orbital drag & kinematic precession. brian a m stuckless Relativity 0 Tue May 16, 2006 9:23 am