What has less drag...

[rosco]

What would have less drag?


A...a wing with a high aspect ratio ie. 1000mm X 100mm (1000dmsquared)

B...a wing with a low apect ratio ie. 400mm X 250mm (1000dmsquared)

Both wings have the same thickness...
Both wings are very smooth...
Both wings are the same airfoil MH43

I ask this question, because I am interrested to know if the frontal area on a wing creates more drag than the cord depth
I know this is a silly question, but I find it hard to believe...


Sorry...question 2
Well then,why don't gliders use swept back wings to reduce frontal area?

cheers
rosco

[Brandano]

the higher the aspect ratio, the less the induced drag induced, all other aspects being equal. This at least until you reach ballistic regimes. As for the 2nd question, I assume you are talking about variable geometry wings? They would mean added weight, and complexity, and would require a complex mechanism to maintain pitch authority with the wing swept back. If anything you could have a wing folding back in two portions, like a bird wing, but then again you have a lot of complexity, draggy spots where the wing folds, and you'd have to carry with you something to actually move all that wing surface. Either an hydraulic or electric system with the batteries or reservoirs that this implies.... just not worth it. If you have to make a glider as complex as a plane, you might as well just make a plane :)

[vintage1]

The reason WHY are important. MOST of the wing drag once you have a decent smooth section, comes from the tips. Air flows down towards the tips underneath and spills over to make the spiralling vortices that you can see in misty weather on planes pulling G or just landing. Those vortices take energy to create, and that energy means drag.

Long thin wings have a lot more surface area per wingtip vortex. Seagulls have long thin wings and they are the top soarers. Raptors that have to work around trees and so on and need to manoeuvre faster, have multiple winglets at the tips.

[JetPlaneFlyer]

It really depends.
For a glider operating at it's optimum L/D or somewhere close then induced drag is a dominant factor and a high aspect ratio wing will produce less induced drag.. Thats why high performance gliders ahave long thin wings

Note: incuced drag is not directly to do with tip vortexes, it's due to the rearward inclination of the lift vector that the wing generates; so lift effectivly pulls the aircraft back.

At higher speeds induced drag is less critical and profile/friction drag begins to dominate, smaller shorter wings will then work better in these conditions. This is why high speed aircraft (even subsonic ones) have relatively smaller low aspect ratio wings, .

Steve

[Pinecone]

Hmm, then why do airliners have long wings? And why do some (Airbus) have winglets (which reduce wing tip vortices)?

Induced drag is a function of the coefficient of lift, so higher speed means flying at lower Cl, so less induced drag, but it is still factor.

And the lift vector is inclined due to the drag induced by making lift, the inclined vector is not the CAUSE of the lift. The ture vector due to lift is vertical, but due to the induced drag, the vector is inclined. And a major source of that drag is the wingtip vortices.

Swept wings don't reduce frontal area, they only effect the formation of shock waves when the speeds get high subsonic.

JetPlaneFlyer, which Aberdeen?

[Brandano]

induced drag is the amount of energy the plane puts into the air in order to produce lift. It's energy subtracted from the aircraft propulsion system, be it an engine or gravity. It does manifest in several forms, the most evident being the wingtip vortexes, but these are a byproduct rather than a cause. Same goes for the turbulence in the wake of a plane. Essentially, the energy that is left in the air after the plane has passed is energy wasted by the plane. Winglets on airliners are designed to recover part of this energy, and therefore reduce induced drag. Induced drag is that part of drag that can't be imputed to skin friction and cx alone, the drag that is generated as a consequence of producing lift.

[JetPlaneFlyer]

Hmm, then why do airliners have long wings? And why do some (Airbus) have winglets (which reduce wing tip vortices)?

Induced drag is a function of the coefficient of lift, so higher speed means flying at lower Cl, so less induced drag, but it is still factor.

And the lift vector is inclined due to the drag induced by making lift, the inclined vector is not the CAUSE of the lift. The ture vector due to lift is vertical, but due to the induced drag, the vector is inclined. And a major source of that drag is the wingtip vortices.

Swept wings don't reduce frontal area, they only effect the formation of shock waves when the speeds get high subsonic.

JetPlaneFlyer, which Aberdeen?
Aberdeen in Scotland... the original :D

The 'true' lift vector does indeed incline from the vertical, because lift is defined as the force that the wing produces perpendicular to the aiflow (not necassarilly vertically)...
Due to downwash the airflow over a wing is not horizontal, it's downward, if the airflow is downward then the lift vector (being perpendicular to the airflow) inclines backward and this is what generates induced drag.
High aspect ratio wings and anti-vortex tip devices act to reduce downwash, which therefore reduces induced drag.

***EDIT*** i missed the point about airliners having high A/R wings. As ponted out a couple of posts below it's because they have very high wing loading so (despite flying fast) they operate at high Cl and therefore generate a lot of induced drag.

induced drag is the amount of energy the plane puts into the air in order to produce lift.

No...An infinite wing or a wing operating in a wind tunnel where the tips are sealed by the tunnel sides has no induced drag... Also a wing operating in ground effect had 'almost' no induced drag... So it's not true to say that induced drag is a natural byproduct of lift.. It's actually a byproduct of downwash.

[HugePanic]

Hmm, then why do airliners have long wings?

There are some reasons:

-you have to be able to start/land at relatiely low airspeeds! Clmax is limited somewhere, so you need wing surface to get the right amount of lift
-you need room for fuel!!!
- .....
(and many more reasons)

[mnowell129]

The wingtip vortices produce extra downwash behind the wing. This induced downwash effectively raises the angle of attack of the wing, tilting the net lift vector backwards. The drag component of this vector is induced drag. It's been stated but I'll reiterate, infinite length wings or wings in wind tunnels make lift and have no induced drag, so it is in error to say that induced drag is a lift by product.
It does take energy to make those vortices, but it's probably safer to say that the energy lost in induced drag from the wing shows up as rotational energy in the vortices. It's not the production of the vortices that creates the drag, its the effect the vortices have on the wings downwash that create the additional drag. However for there to be an energy loss from the wing in the form of drag, that energy has to be transferred somewhere, and that somewhere is in the air left behind in the form of rotating and moving air particles.
Airliners are pretty heavily loaded so they are flying at a high enough Cl that induced drag is an issue, so winglets and wingtip extensions save enough gas that they are worth doing.

[Jurgen Heilig]

There are some reasons:

-you have to be able to start/land at relatiely low airspeeds! Clmax is limited somewhere, so you need wing surface to get the right amount of lift
-you need room for fuel!!!
- .....
(and many more reasons)

Well, remember the original question? The wing area is identical, the only difference is the aspect ratio.

The lower aspect ratio wing flys at a higher Reynolds number, but the higher aspect ratio wing has less induced drag. A short aspect ratio wing of identical area can usually be build lighter.

Assuming both wings using the same wing section, the lower aspect wing has 2.5 times more wing volume.

:) Jürgen

[Jurgen Heilig]

What would have less drag?

A...a wing with a high aspect ratio ie. 1000mm X 100mm (1000dmsquared)

B...a wing with a low apect ratio ie. 400mm X 250mm (1000dmsquared)

Both wings have the same thickness...
Both wings are very smooth...
Both wings are the same airfoil MH43

I ask this question, because I am interrested to know if the frontal area on a wing creates more drag than the cord depth
I know this is a silly question, but I find it hard to believe...


Sorry...question 2
Well then,why don't gliders use swept back wings to reduce frontal area?

cheers
rosco

Hi rosco,

you missed an important factor: speed. At low speeds and high Cl, induced drag dominates over profile drag, i.e. the high aspect ratio is usually better.

Cl figures/diagrams are based on wing area and sweeping usually has very little effect on the wing area. Swept wings have their own problems to deal with. ;)

:) Jürgen

[richard hanson]

wings on airplanes are all compromises and the structural requirements dictate much of the envolved shape
If structual requirements meant nothing -- what would the shape of the ideal wing be?
Each time I ask this --I get evasive answers -few free thinkers out there.

[eflightray]

Wow!, and all this time I've been designing wings just so that they fit in the car.

You live and learn, well at least I live, I think. :D

[HugePanic]

Well, remember the original question? The wing area is identical, the only difference is the aspect ratio.

servus jürgen,

you are right, wing area is identical.

my answer now is:
an airliners wing is the best compromise that can be build economicaly to meet the requirements.
they are a compromise in all aspects.

[richard hanson]

In model airplanes - many times the question arises "which is best airfoil for my 1/5 scale model of --(Example ) P51-

The right answer is -the one you can build strong enough , light as possible
It is assumed by many modelers , that the airfoil will make or break the performance of the model - when in fact -the weight is of far more importance.

[JetPlaneFlyer]

If structual requirements meant nothing -- what would the shape of the ideal wing be?
Excluding structural and practical factors the ideal wing, in terms of efficiency, would be one infinitely long and infinitely light :rolleyes: ... If you can’t quite achieve that then it's time to make compromises ;)

[Jurgen Heilig]

...
If structual requirements meant nothing -- what would the shape of the ideal wing be? ...


There still wouldn't be one ideal shape for all purposes. Why do you think there are all those additional things like flaps, slats, winglets etc. ?

:) Jürgen

[Jurgen Heilig]

In model airplanes - many times the question arises "which is best airfoil for my 1/5 scale model of --(Example ) P51-

The right answer is -the one you can build strong enough , light as possible
It is assumed by many modelers , that the airfoil will make or break the performance of the model - when in fact -the weight is of far more importance.

We are deviating from the subject a bit, but the wing section or airfoil can make a huge difference in flight performance and handling.

You would not like a freeflight wing section on a P-51, or an extremely sharp leading edge, or with the max. thickness at 20% or 80%.

Any good model can easily cope with some additional ballast, providing the design hasn't got flaws to begin with. It will have to fly a bit faster, but usually not by much, to stay airborne.

:) Jürgen

[richard hanson]

The original question(which would have less drag )-is about as vague.
The reason is that "less drag at what speed and size and under what kind of loading .
In the real world as you noted - there are no absolutes . a small model may fly better with a low aspect ratio wing --simply because the RN is very low and the wingloading is fairly high.
slats on a 1/5 scale P51?
the added weight would offset the very improbable benifit -as an example.
I like theory -it is nice but I have become a very staunch believer in experience as having most benifit - expecially in "model" sized craft.
What works for an ideal airfoil on a 10,000 lb 300mph cruise speed airframe at 20000ft may work on the "1/5"scale P51 -but not be any better than a Florsheim derived airfoil

[Jurgen Heilig]

...
slats on a 1/5 scale P51?
the added weight would offset the very improbable benifit -as an example.
...

I did not recommend adding slats to your 1:5 P-51. I said you would not be very happy with a hollow bottom freeflight airfoil or a very sharp leading edge or ...

:) Jürgen

[vintage1]

wings on airplanes are all compromises and the structural requirements dictate much of the envolved shape
If structual requirements meant nothing -- what would the shape of the ideal wing be?



Everyt time I see this question, I have to ask

Ideal for what purpose?

If you want to go a long way on minimum fuel or very high the longer and thinner the better. Its called an Albatros. Or a Boeing 747.

If you want to turn on a dime, the shorter and fatter the better.
Its called a Pitts special.

If you want to punch through a wide speed range and go supersonic, and still pull plenty of G, try the Eurofighter.

If you want vertical takeoff, try a rotor blade and build a helicopter.





Each time I ask this --I get evasive answers -few free thinkers out there.

Thats because you haven't asked a question that is answerable. Or unless we say 'the wings on Angels: God makes em so they must be perfect and ideal in every way'

[richard hanson]

Everyt time I see this question, I have to ask

Ideal for what purpose?

If you want to go a long way on minimum fuel or very high the longer and thinner the better. Its called an Albatros. Or a Boeing 747.

If you want to turn on a dime, the shorter and fatter the better.
Its called a Pitts special.

If you want to punch through a wide speed range and go supersonic, and still pull plenty of G, try the Eurofighter.

If you want vertical takeoff, try a rotor blade and build a helicopter.




Thats because you haven't asked a question that is answerable. Or unless we say 'the wings on Angels: God makes em so they must be perfect and ideal in every way'
Well there are a few laws which work:
if it is light enough - the airfoil does not matter
AND if it is too heavy -it still does not matter .

[rosco]

Hey thanks for the answers fella's. I knew that my original question would come back to a question like "what are you trying to achieve?"

My question is in regards to pylon racers...
Some of the factors would be
1.High wing loading
2.High speed running
3.low speed landing

Sounds like an airliner, doesn't it? (I'm sure that Mr Boeing hasn't got it wrong)

So the original inputs still remain...
Same wing area
Low aspect versus High aspect
Either aspect ratio wing has the same thickness

Maybe a better question would be...
For a Pylon racer (F5D style) application, why do we use high aspect ratio instead of low radio wings?

I hope I haven't wasted anyones time. Thanks for the answers...they are very informative.
cheers
rosco

[macboffin]

In model airplanes - many times the question arises "which is best airfoil for my 1/5 scale model of --(Example ) P51-

The right answer is -the one you can build strong enough , light as possible
It is assumed by many modelers , that the airfoil will make or break the performance of the model - when in fact -the weight is of far more importance. The lighter the airplane, the less wing needed to fly ; hence lower wing drag.But.....are we talking pattern ship, soaring glider, turbine powered due to "need for speed"? If the plane is quick enough and light enough, no need for wings at all, fly on fuselage generated lift,(like an airship) all you need then are tail feathers to steer!

[mnowell129]

For a Pylon racer (F5D style) application, why do we use high aspect ratio instead of low radio wings?

This is an easy one. Pylon racers spend a lot of time turning
at high G loadings. This is a high Cl condition, therefore a high induced drag condition. High aspect ratio reduces the induced drag in the turns, thus all other things being equal the high aspect ratio airplane will lose less speed in the turns.

[BMatthews]

Yep, you ain't gonna find a much more demanding and contrary set of requirements than with a pylon racer.

The G loading in the turns is huge. Someone once told me that they had calculated it out as somewhere around 20 to 25 G's for the single pylon smaller diameter turn if you're up around 180 mph or something like that. It's been more than a few years. Crunch some numbers for a typical turn radius and speed and it'll soon tell you if I'm way out or not.

Buty either way it's big time loading so the wing will be pulling some serious Cl numbers and at that point as high an aspect ratio as you can build and still keep it accurate and non flexy is the way to go. Any slight difference in profile drag while flying semi level will be more than made up for by the better efficiency in the turns.

[Bobber Bob]

Hi Rosco, and Folks...

Just two points...

In your first variable, you said "Same thickness", did you mean "same thickness', or SAME PERCENT OF THICKNESS ??

Another point to the general discussion following...

Whether the effect comes from the lift vector, or the downwash, or... A wing "lifts" in an upward and FOREWARD direction, otherwise autogyros, and helicopters in autorotation would not work.

The above is only true when the wing is generating lift, not when in a "0" lift condition. I became functionally aware of this, when I found out that it takes more energy from the wing swing servo, to sweep the wings back on my TomKats.

Bob Reynolds
. "ComeUpHere"

[Brandano]

...The drag component of this vector is induced drag. It's been stated but I'll reiterate, infinite length wings or wings in wind tunnels make lift and have no induced drag, so it is in error to say that induced drag is a lift by product...
Ok, I'll take this on your word. However, as far as I know, without resorting to theoretical infinite length wings, a wing that produces no lift also produces no induced drag.

[mnowell129]

However, as far as I know, without resorting to theoretical infinite length wings, a wing that produces no lift also produces no induced drag.
Not entirely true. Wings mounted to the walls of wind tunnels make lift and don't produce any induced drag. Also a shrouded propeller makes lift without any induced drag losses if the the tips are close enough to the shroud or if the shroud rotates in a housing that is flush.
I think its even possible to have the center section of a wing rigged to be making zero lift, with the tips making lift. Then the tip vortex would affect the downwash of the center section causing it to have induced drag even while producing no lift.
Induced drag is a result of making lift with a finite length wing, it does not happen every time there is lift. To say that induced drag is a byproduct of lift implies that it occurs every time there is lift, which it doesn't.

[mnowell129]

Whether the effect comes from the lift vector, or the downwash, or... A wing "lifts" in an upward and FOREWARD direction, otherwise autogyros, and helicopters in autorotation would not work.


This is false. Autorotation occurs because the blade velocity and rotor tilt combine to give an angle of attack such that the blade's net lift vector is tilted forward. But this is still tilted back with respect to the airfoil. In fact it is tilted back an angle that is equal to the L/D of the rotor blade.
On the web, there are many vector diagrams of rotor blades in autorotation that show this relationship.
This same rigging angles and angles of attack apply to gliders. Gliders go forward for the same reasons autorotation works.

[richard hanson]

Not entirely true. Wings mounted to the walls of wind tunnels make lift and don't produce any induced drag. Also a shrouded propeller makes lift without any induced drag losses if the the tips are close enough to the shroud or if the shroud rotates in a housing that is flush.
I think its even possible to have the center section of a wing rigged to be making zero lift, with the tips making lift. Then the tip vortex would affect the downwash of the center section causing it to have induced drag even while producing no lift.
Induced drag is a result of making lift with a finite length wing, it does not happen every time there is lift. To say that induced drag is a byproduct of lift implies that it occurs every time there is lift, which it doesn't.
This is a matter of semantics :
if there is lift --there is a pressure difference --- lower surfacehas a higher pressure than upper surface -
You don't get something good without something else happening
So -you could say -- Lift and drag are really one and the same - that is - the lower pressure above is dragging the surface upward

the finite wing stuf??? -real world is that a wing works due to pressure differences
the whole durn airframe maneuvers due to setting up differences in pressure .
Most of the explanations are just too "busy".
It is all quite simple- We are not into supersonic flight
Flight occurs anytime pressure is lower above - than below - be it a 747 or a bumble bee flapping n clappin along. how you get there makes no difference

[Jurgen Heilig]

This is a matter of semantics :
if there is lift --there is a pressure difference --- lower surfacehas a higher pressure than upper surface -
You don't get something good without something else happening
So -you could say -- Lift and drag are really one and the same - that is - the lower pressure above is dragging the surface upward

the finite wing stuf??? -real world is that a wing works due to pressure differences
the whole durn airframe maneuvers due to setting up differences in pressure .
Most of the explanations are just too "busy".
It is all quite simple- We are not into supersonic flight
Flight occurs anytime pressure is lower above - than below - be it a 747 or a bumble bee flapping n clappin along. how you get there makes no difference

Lift and drag are two different forces. You can have drag without lift, but no lift without drag. Extra lift usually causes extra drag.

Flight is not limited to horizontal flight. In a dive or in a near vertical climb, the wing may produce zero lift, but that does not mean it has zero drag. ;)

:) Jürgen

[JetPlaneFlyer]

Most of the explanations are just too "busy".

Explanations of complex things do tend to be 'busy'. The human mind craves simple explanations to complex problems but they are rarely if ever correct.

Famous quote:
"For every complex problem, there is a solution that is simple, neat, and wrong."
H.L. Mencken (1880-1956)

[Flight Engineer]

Explanations of complex things do tend to be 'busy'. The human mind craves simple explanations to complex problems but they are rarely if ever correct.

Famous quote:
"For every complex problem, there is a solution that is simple, neat, and wrong."
H.L. Mencken (1880-1956)


And usually found in the modeling science forum.

F Engineer (1969-?)

[mnowell129]

Explanations of complex things do tend to be 'busy'. The human mind craves simple explanations to complex problems but they are rarely if ever correct.

Famous quote:
"For every complex problem, there is a solution that is simple, neat, and wrong."
H.L. Mencken (1880-1956)
And aerodynamics is one of the most counter-intuitive, non common sense disciplines.
To prove this point in undergraduate school we did an experiment where we drop a ping pong ball and a tennis ball that have been modified to be the same weight. Guess what? The tennis ball falls faster. This is completely counter intuitive. It's due to reynolds number and boundary layer effects and overrides the relative area differences that your common sense would lead you to believe would happen. The tennis ball roughness trips the boundary layer, making it go turbulent, thus it stays attached longer in the adverse pressure region on the back of the ball. This lowers the drag of the tennis ball to less than the ping pong ball with its laminar flow that due to low energy detaches early leaving a larger detached flow region, increasing it's drag.
You have to constantly fight your common sense in aerodynamics because it leads you down dead ends.
The coanda effect saucer, the Moller Sky Car, etc. All examples of where common sense fails you.

[richard hanson]

Lift and drag are two different forces. You can have drag without lift, but no lift without drag. Extra lift usually causes extra drag.

Flight is not limited to horizontal flight. In a dive or in a near vertical climb, the wing may produce zero lift, but that does not mean it has zero drag. ;)

:) Jürgen
again semantics - of course you can have drag with no lift - but you can never have lift with no drag
they are simply locked together like Yin and Yang -just acting differently
more lift is always more drag - but more drag is not necessarily more lift -as you said.
A vertical powerdive needs (wants) no lift and a vertical climb requires no lift except that provided by the power used .
I just get weary of the phrases and exotics of "lift being a product of air rolling downward etc..
When all is said n done ----
-The damn plane is being dragged (or pushed) along and when necessary - differential air pressures determine direction. These long discussions are fun apparantly for some - But I seldom see anyone cutting to the chase when some poor modeler asks ,"why does my model roll when I add elevator"-

[richard hanson]

And aerodynamics is one of the most counter-intuitive, non common sense disciplines.
To prove this point in undergraduate school we did an experiment where we drop a ping pong ball and a tennis ball that have been modified to be the same weight. Guess what? The tennis ball falls faster. This is completely counter intuitive. It's due to reynolds number and boundary layer effects and overrides the relative area differences that your common sense would lead you to believe would happen. The tennis ball roughness trips the boundary layer, making it go turbulent, thus it stays attached longer in the adverse pressure region on the back of the ball. This lowers the drag of the tennis ball to less than the ping pong ball with its laminar flow that due to low energy detaches early leaving a larger detached flow region, increasing it's drag.
You have to constantly fight your common sense in aerodynamics because it leads you down dead ends.
The coanda effect saucer, the Moller Sky Car, etc. All examples of where common sense fails you.
- I worked with fluidic switches in control circuits -another discipline which is "sorta like flying a plane - where air sticks to things -if conditions ar right .
But I still think our "mystery of flight" can be simply explained - when necessary
those who say Phooey - have never had to stand before a jury and explain a technical matter - you can do it if you really put your mind to it.
If you can't ----- YOU don't really understand it.

[mnowell129]

again semantics - of course you can have drag with no lift - but you can never have lift with no drag

I think you missed a critical point. I was not discussing all drag, just induced drag. This was at the root of this thread, that is given two wings with the same area, etc and the only thing being different being the platform, what's the difference?
For two wings with the same form and parasite drag, the only difference is the induced drag, which is directly related to the aspect ratio. Anything you put in an airflow is going to have some drag, form and skin friction drag. But induced drag occurs when there are finite wings. I'll stand by my statement, you can make lift without any induced drag.

[Brandano]

... the only difference is the induced drag, which is directly related to the aspect ratio.
And if you allow me to add, wing loading (though the same area and weight perhaps were specified too?). I am not criticizing what you are saying, you are perfectly right, and I know it's obvious, but these things are sometimes overlooked. A higher wing loading means a higher AOA to maintain level flight at the same speed, therefore both more induced drag and "front area" drag. In the realm of model airplanes it might well be more convenient to have a lower AR, which allows to keep the weight of the structure down and allows a (relatively) thinner profile for the same structural strength and a slight advantage in reynolds numbers and wing loading.

[Jurgen Heilig]

again semantics - of course you can have drag with no lift - but you can never have lift with no drag
they are simply locked together like Yin and Yang -just acting differently
more lift is always more drag - but more drag is not necessarily more lift -as you said.
...

Sorry, but lift and drag are not locked together, they are just functions with certain interactions.

More lift does not always cause more drag. Those lift/drag curves can have quite some "bumps", i.e. areas where you have less drag for a given lift and areas where the drag increases while the lift may even decrease (high AOA).

:) Jürgen

[Jurgen Heilig]

...
But induced drag occurs when there are finite wings. I'll stand by my statement, you can make lift without any induced drag.

And as there will always be finite wings, there will always be induced drag in real life. ;)

:) Jürgen

[Brandano]

Jurgen, in that case we are talking about a ballistic regime, where the laminar flow has all but detached from the lifting surface. in the normal "flyable" range what Richard said holds true, at least for most common wing profiles. In any case, I am quite sure that you can't really have lift without some sort of induced drag creeping in. I mean drag that isn't caused by the surface friction of the air against the aerodynamic surface, or by the "suck back" effect of the turbolent flow detaching from the surface (there, I tried to fix the nomenclature a bit better). There is drag caused by the difference in pressure induced in the airflow. That energy is lost, and will be wasted by the air to reach a steady state again once away from the aerodynamic surface and no longer interacting with it.

[mnowell129]

And as there will always be finite wings, there will always be induced drag in real life. ;)

:) Jürgen
Still I disagree somewhat, a wing fixed to the ends of the windtunnel, or a turning vane in a duct doesn't have induced drag, just form and parasite drag. And a properly shrouded propeller does not have induced drag.

One sees a wing at some angle of attack to the flow and just intuitively you convince yourself that the lift vector is perpindicular to the chord line, therefore that's the induced drag, but it's just not so.

[richard hanson]

I rest my case ---
all lift and no drag?
neat trick

[mnowell129]

I rest my case ---
all lift and no drag?
neat trick
Rest all you want, you're not reading, no induced drag,
it still has form and skin drag.

[richard hanson]

Rest all you want, you're not reading, no induced drag,
it still has form and skin drag.
Try this :
can you make lift where there is no pressure differential?
Y/N?
It is simply a matter of words used .
No pressure differential= no lift. When we look at the airflow characteristics which made our fluidic valves function - we looked at flow and relative wall attachment
much the same as wings - well sorta - The so called Coanda effect was a biggie in these things

[JetPlaneFlyer]

I believe that everyone agrees that for 'real world' finite wings on conventional aircraft, flying in 'open air' then induced drag is unavoidable, no one is arguing this point.

What it is important to understand though is that induced drag is not a unavoidable 'price to be paid' for the generation of lift. It's not as someone stated earlier 'Yin and yang'. It is possible under certain conditions to generate lift without induced drag (e.g. a wind tunnel). Clearly some folk, at least at the start of this thread, did not understand this... If they do now then the thread has achieved something ;)

Steve

[richard hanson]

Lift and drag are two different forces. You can have drag without lift, but no lift without drag. :) Jürgen
eggzactly
and I said Yin and Yang.
wind tunnels - schmind tunnels --
You can't get something for nothing.

[JetPlaneFlyer]

eggzactly

Lets not confuse 'drag' with 'induced drag'... the first cant be avoided, the second can.

Steve

[richard hanson]

produced drag?

[richard hanson]

Yep, you ain't gonna find a much more demanding and contrary set of requirements than with a pylon racer.

The G loading in the turns is huge. Someone once told me that they had calculated it out as somewhere around 20 to 25 G's for the single pylon smaller diameter turn if you're up around 180 mph or something like that. It's been more than a few years. Crunch some numbers for a typical turn radius and speed and it'll soon tell you if I'm way out or not.

Buty either way it's big time loading so the wing will be pulling some serious Cl numbers and at that point as high an aspect ratio as you can build and still keep it accurate and non flexy is the way to go. Any slight difference in profile drag while flying semi level will be more than made up for by the better efficiency in the turns.
I gotta call you on this one -- how do you generate 25 gs on these things?
I will go along with 15 --maybe -but I would bet that the nice long skinny wings simply do a high speed stall and controlled recovery
If you were a bird flying above and watching closely - I bet the turn looks more like a race car "drifting" thru the turn
Some think that because the wing is stalled (sementics ) the plane is uncontrollable
I am one who thinks it can still be controlled - maybe not maneuvered but still under control. A g meter may answer this --
we fly stalled wings all the time (back to the friggen electrics)

[mnowell129]

produced drag?
No, induced drag.
Clearly what I've been writing and you've been reading
are two different things.

[Jurgen Heilig]

Still I disagree somewhat, a wing fixed to the ends of the windtunnel, or a turning vane in a duct doesn't have induced drag, just form and parasite drag. And a properly shrouded propeller does not have induced drag.
...

You will have induced drag there too.

You can write whole book chapters about "induced drag", but don't worry I am not going too. You may want to read "Mechanics of Flight" by A.C. Kermode - there is six pages about INDUCED DRAG - or just read wikipedia:

http://en.wikipedia.org/wiki/Induced_drag

:) Jürgen

[Jurgen Heilig]

eggzactly
and I said Yin and Yang.
wind tunnels - schmind tunnels --
You can't get something for nothing.

Sorry, but if this is your idea of a discussion, I am out here. It is just waisted time.

:) Jürgen

[richard hanson]

On that ------- I agree.

[mnowell129]

You will have induced drag there too.

No, you don't. Induced drag occurs with 3d flow, in wind tunnel the flow is 2D.
You may want to read "Mechanics of Flight" by A.C. Kermode - there is six pages about INDUCED DRAG - or just read wikipedia:

Thanks, but I studied this for a whole semester as an undergraduate aerodynamics student. My reference was my theoretical aerodynamics textbook.


http://en.wikipedia.org/wiki/Induced_drag

The first sentence in this reference says "a wing of finite span", just as I've already said. It further agrees with what I've been writing:
The equation for induced drag is
Cdi (coefficient of drag, induced) is = some stuff / (some stuff *AR)
So as the AR (aspect ratio) goes to a very large number the induced drag goes to 0. In a wind tunnel or shrouded prop situation the effective AR is infinity therefore the Cdi or induced drag is 0.
Keep believing what you want, but it is quite possible to have lift without induced drag.
And for me "the science has left the building" here, so I guess I will too.....

[richard hanson]

So a theoritical wing is what we need to be using?
I am stuck in a real world where these things don't exist.
Real world also says -- you need max power and minimum weight for best performance
The mechanics of holding all of this together is the REAL trick. The stress engineers are the real experts .

The final shaping is all compromise.

[Jurgen Heilig]

...
Thanks, but I studied this for a whole semester as an undergraduate aerodynamics student. My reference was my theoretical aerodynamics textbook.
...

Well, I have a Master's degree in Aeronautics, but even the so called "experts" can be wrong sometimes:

One of the great ironies of flight is that 100 years before the Wright brothers built the first airplane a French mathematician named D'Alembert calculated all the expected accelerations and predicted there would be no drag.

Unfortunately for us, D'Alembert was wrong. There is indeed a component of the reaction force parallel to the relative wind. This drag can be measured in a wind tunnel and affects us in flight. The difference between observed reality and D'Alembert’s calculations is referred to as D’Alembert’s Paradox.

Here is the link:

http://selair.selkirk.bc.ca/aerodynamics1/Drag/Page6.html

Ok, now I am really out of here. I am not into semantics. ;)

:) Jürgen

[JetPlaneFlyer]

Unfortunately for us, D'Alembert was wrong.

So are you denying that a infinite wing, or a wing in a wind tunnel with it's tips sealed, produce no induced drag?... Or are you agreeing?

[JetPlaneFlyer]

So a theoritical wing is what we need to be using?
I am stuck in a real world where these things don't exist.
Actually they do exist, it's not all theory... WIG (Wing In Ground-effect) aircraft rely on the virtual elimination of downwash and induced drag: http://en.wikipedia.org/wiki/Wing-In-Ground_effect_vehicle
http://en.wikipedia.org/wiki/Wing-In-Ground_effect_vehicle

[richard hanson]

Actually they do exist, it's not all theory... WIG (Wing In Ground-effect) aircraft rely on the virtual elimination of downwash and induced drag: http://en.wikipedia.org/wiki/Wing-In-Ground_effect_vehicle
http://en.wikipedia.org/wiki/Wing-In-Ground_effect_vehicle
They create more pressure under the apron than over the apron. Why make it all sound so complicated
nature is not complicated . just complex.

[JetPlaneFlyer]

They create more pressure under the apron than over the apron. Why make it all sound so complicated
nature is not complicated . just complex.

That's how they produce lift... how they do it more efficiently that normel aircraft is by dispensing with induced drag.

[mnowell129]

So are you denying that a infinite wing, or a wing in a wind tunnel with it's tips sealed, produce no induced drag?... Or are you agreeing?
I'd like to hear the answer to this too.
The link provided is all about finite wings and doesn't apply to infinite spans or sealed end conditions like wind tunnels and shrouded props.
Also the accepted expression for Cdi has AR in the denominator therefore CDi goes to zero as AR goes to infinity. So the assertion here is that the accepted science is wrong..
I think what's being confused is the difference between form drag and induced drag. There is always form drag and parasite drag, but not always induced drag.

[richard hanson]

That's how they produce lift... how they do it more efficiently that normel aircraft is by dispensing with induced drag.
They what?

the things are made to run over grass -swamp whatever - and the REAL engineering is inhow to have more POWER and not increase weight
induced drag is hardly relevant The skirting design is important to eliminate losses ove irregular terrain-

[mnowell129]

They what?

the things are made to run over grass -swamp whatever - and the REAL engineering is inhow to have more POWER and not increase weight
induced drag is hardly relevant The skirting design is important to eliminate losses ove irregular terrain-
You're mixing up an aircraft in ground effect and a surface effect vehicle, other wise know as a hovercraft.
What jetplaneflyer is referring to is when an aircraft flies within 1/2 wingspan of the ground and experiences ground effect, the situation where the ground interferes with the production of the wingtip vortices and therefore greatly reduces the induced drag.
Most casual pilots refer to this as that "float" thing during landing.
This has nothing to do with SEV's or hovercraft that float on an engine produced air cushion that is contained within a skirt.

[JetPlaneFlyer]

They what?

the things are made to run over grass -swamp whatever - and the REAL engineering is inhow to have more POWER and not increase weight
induced drag is hardly relevant The skirting design is important to eliminate losses ove irregular terrain-

As mnowell said... you appear to be mixing WIG aircraft with hovercraft... two totally different things.

Here is a link I intended to put in my previous post which explains how real world WIG aircraft drastically reduce induced drag (not a 'skirt' to be seen ;) ):
http://www.aerospaceweb.org/question/aerodynamics/q0130.shtml

[richard hanson]

As mnowell said... you appear to be mixing WIG aircraft with hovercraft... two totally different things.

Here is a link I intended to put in my previous post which explains how real world WIG aircraft drastically reduce induced drag (not a 'skirt' to be seen ;) ):
http://www.aerospaceweb.org/question/aerodynamics/q0130.shtml
Yep-- I missed the seque to the skimmer craft.
these are extremely popular ( ever seen one?)
all of this stuff relies heavily on air trying to avoid compression.
Mama Nature takes the path of least resistance - so these only work well when either speed or area is increased - If you surfboard - or if you race boats you see the same forces at work .
OR if you run fast cars you see same stuff-- no mysteries about it - air does not like being compressed -and if you can capture it - you can ride on it --unless it has an escape path
Ditto for the Space Shuttle - these flying flatirons push a huge bubble of air as the make final contact. It is all is the same thing tho - create a pressure difference - and you move toward the lower pressure
Cars often flew on race tracks as pressure built under em .
Landing a large , low wing model or full scale - same effects .
So --how is trying to create "less drag " relevant here ?

[JetPlaneFlyer]

So --how is trying to create "less drag " relevant here ?
Because they create less drag by reducing induced drag. They are a practical real world example of an aircraft that produces lift while producing very little induced drag, or none if the tips skim the water...

WIG aircraft fly in the same way as any other aircraft, their wings work the same, they are nothing like a surfboard (or no more like a surfboard than a regular aircraft). Did you read the link I posted :confused:

I'm not sure what a 'skimmer' craft is (an Airboat maybe?) but I think your getting WIG aircraft mixed up with something else. WIG aircraft are not extremely popular, they are in fact quite scarce, unless you used to live on the shores of the Caspian Sea (look up Caspian Sea Monster).

This is perhaps getting a little off topic, I was just using WIG to illustrate that you can have lift without induced drag... if you want to talk more about WIG then maybe a new thread or PM?

[Jurgen Heilig]

So are you denying that a infinite wing, or a wing in a wind tunnel with it's tips sealed, produce no induced drag?... Or are you agreeing?

Even a wing in a 2-dimensional wind tunnel with the tips sealed may show induced drag. Only if it is a constant cord wing, with all the air flow parallel to the wind tunnel walls, you won't have induced drag, but you still will have unwanted drag effects where the wing meets the walls: Interference drag

http://aerodyn.org/Drag/idrag.html

:) Jürgen