Why do people say the top of the wing causes the plane to fly?
10-10-2008, 10:43 PM
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RE: [Deleted]
ORIGINAL: pimmnz
JohnW, what I was trying to say was that in the case of the rotating wings, there are all being held against motion, like the fan. The fan is 'lifting' but is not allow to move in the direction of lift, so it has a slipstream, and this is the downwash theorists proof of, downwash. I was trying to make the point that, without constraint the rotors would move in the direction of the lift, and the wash would disappear. In the case of the model airplane prop where the small section would have a likely stalling angle of around 7 degrees, most of the prop is stalled and it is only the tip 10~15% that is actually 'flying'. Naturally this creates huge drag and wash. When you release the aircraft, and the forward speed of the prop starts to reduce the effective AOA the prop sees, then it starts to unstall, drag decreases and the engine 'unloads'. That's why we set the things up a bit rich on the ground, cos they do unload in the air. Course, as the AOA decreases, so does lift (thrust), all the way to the point where the total airplane drag is the same as the lift available from the prop. As I alluded, with a small slippery airframe you can get to the point where the measured speed is greater than the 'pitch X rpm' would suggest, showing that at apparent AOA's of less than 0 a cambered section will still produce useable lift. Dunno what all this has to do with all this 'top of the wing' stuff, but I'm beginning to feel a bit like Dick H, all alone. But he is correct, lots of dearly held beliefs would be destroyed, if only we could see the stuff the damned things are flying through. But it is fun to kick against the myths, is it not?
Evan.
JohnW, what I was trying to say was that in the case of the rotating wings, there are all being held against motion, like the fan. The fan is 'lifting' but is not allow to move in the direction of lift, so it has a slipstream, and this is the downwash theorists proof of, downwash. I was trying to make the point that, without constraint the rotors would move in the direction of the lift, and the wash would disappear. In the case of the model airplane prop where the small section would have a likely stalling angle of around 7 degrees, most of the prop is stalled and it is only the tip 10~15% that is actually 'flying'. Naturally this creates huge drag and wash. When you release the aircraft, and the forward speed of the prop starts to reduce the effective AOA the prop sees, then it starts to unstall, drag decreases and the engine 'unloads'. That's why we set the things up a bit rich on the ground, cos they do unload in the air. Course, as the AOA decreases, so does lift (thrust), all the way to the point where the total airplane drag is the same as the lift available from the prop. As I alluded, with a small slippery airframe you can get to the point where the measured speed is greater than the 'pitch X rpm' would suggest, showing that at apparent AOA's of less than 0 a cambered section will still produce useable lift. Dunno what all this has to do with all this 'top of the wing' stuff, but I'm beginning to feel a bit like Dick H, all alone. But he is correct, lots of dearly held beliefs would be destroyed, if only we could see the stuff the damned things are flying through. But it is fun to kick against the myths, is it not?
Evan.
Ask any sailboat racer what happens when you are in the backwash of the sail of a boat that is somewhat ahead of you, you drop even farther behind unless you tack for "clean air". Once you tack for clean air, the lead boat will sometimes also tack to cover you and try to keep you in his dirty air and then you have to tack again and a classic America's Cup style tacking duel results.
10-10-2008, 11:18 PM
#427
RE: [Deleted]
Thanks, banktoturn. I guess any theory could be used to explain lift, it's just that some do have an empirical prediction, like Dan B, that actually very closely match the real world observations.
Evan.
Evan.
10-10-2008, 11:50 PM
#428
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RE: [Deleted]
Pimmnz, OK, thanks for the clarification. I now think I understand the concept you posted. If the fan were released, it would accelerate and eventually "screw" thru the air kind of like threading a bolt, i.e. no downwash. I'm not clear how that would work in a fluid. I'm thinking thru this, so as Reynolds increases, the air becomes more "solid" like and the wing acts more like it is being held up by a "solid" pillar of air, so we don't need the downwash? Is that the concept or have I gone way of course?
10-11-2008, 04:03 AM
#429
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RE: [Deleted]
ORIGINAL: banktoturn
That's not a theory from Aerodynamics. If you're referring to Bernoulli's equation, it only asserts that pressure decreases as velocity increases, along a streamline. It says nothing about 'longer'. The so-called 'equal transit time' nonsense has nothing to do with Bernoulli's equation, and is not taught in Aerodynamics. It seems to have arisen in various 'popular' explanations of lift. Indicting that nonsense does not prove that any bona fide theories from Aerodynamics are 'dead wrong'. Bernoulli's equation is not dead wrong. Net lift does indeed result from the pressure reduction that is explained, and accurately predicted, by Bernoulli's equation. If this isn't what you meant, you'll need to correct me.
banktoturn
ORIGINAL: dick Hanson
lift is due to air going faster over the top of the longer, curved foil.
Theres one -
ORIGINAL: banktoturn
Dick,
Can you give me an example of some theory that's dead wrong?
banktoturn
ORIGINAL: dick Hanson
Ok-
Theory is not a straight line authority tho -and some of it is dead wrong. The Wrighte Bros were supposedly the first heavier than air flyers - but shortly after- others around the world had far better craft going which were VERY different in concept. The reason
Simple
Technology begets more technology -exponentially.
Once the "cat is out of the bag" you get lots n lots of kittens.
The pusher -replaced by the tractor
the necessary(?) warped wings replaced by aileron plates etc..
My point is much of "how does it work" is obvious - once you look into it.
I know theorists who
A .can't fly and
B. I wouldn't want to fly in anything they had their mitts on. But- thankfully they are in the minority.
FWIWThe best one I ever knew just eeked out of high school but he had the concepts down cold.including the bestconstruction -which is a mystery to many.
Ok-
Theory is not a straight line authority tho -and some of it is dead wrong. The Wrighte Bros were supposedly the first heavier than air flyers - but shortly after- others around the world had far better craft going which were VERY different in concept. The reason
Simple
Technology begets more technology -exponentially.
Once the "cat is out of the bag" you get lots n lots of kittens.
The pusher -replaced by the tractor
the necessary(?) warped wings replaced by aileron plates etc..
My point is much of "how does it work" is obvious - once you look into it.
I know theorists who
A .can't fly and
B. I wouldn't want to fly in anything they had their mitts on. But- thankfully they are in the minority.
FWIWThe best one I ever knew just eeked out of high school but he had the concepts down cold.including the bestconstruction -which is a mystery to many.
Can you give me an example of some theory that's dead wrong?
banktoturn
Theres one -
banktoturn
Let me step in and offer a description of what was said. And indirectly, what was meant.
There was a request for an example of some theory that was wrong, and the example was offered.
" lift is due to air going faster over the top of the longer, curved foil." was presented as an example of some theory that is wrong.
The sentence is a good example of what most would consider to be a theory. Matter of fact, I think almost exactly that idea has been offered in these forums as the basic theory of lift by possibly hundreds of posters. They haven't all used the word, "longer", but that's a good example of semantics versus meaning. Let's move a couple of words and see how it sounds.
Lift is due to air going faster over the longer top of a curved airfoil.
I'd have to agree with both of you guys. The theory is wrong. And it's certainly one that is repeatedly offered as a basic aeronautical one.
10-11-2008, 04:16 AM
#430
Senior Member
RE: [Deleted]
BTW, let's have some fun with the theory so many embrace as the basic definition of lift: "Lift is due to air going faster over the top of a curved airfoil."
Airplanes with cambered airfoils fly unside down every day. How DO they do that?
Well, they do, so doesn't that disprove the theory?
Airplanes with cambered airfoils fly unside down every day. How DO they do that?
Well, they do, so doesn't that disprove the theory?
10-11-2008, 04:18 AM
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RE: [Deleted]
Rocketman, did you ever look up the past threads on lift here at RCU about 2 years ago? There was an 18 pager that went back and forth much like this thread. In the end I came to realize that the pressure variation and downwash flow are intimately tied together and are aspects of the same action. How else can you explain that at the same time you can show that the lift from the integrated pressure differences equals the same lift generated by the air mass in the downwash and they BOTH equal the total lift of the wing at the same time. You can't have the wing lifting twice at the same time so it would seem that both actions are actually the same action.
Hugo
10-11-2008, 04:33 AM
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RE: [Deleted]
This post is in no way agressive. It is a very friendly one. It is asking a question to everyone, not one person in particular.
Guys, everyone,
I could have totally misunderstood here, but there seems to be some kind of resistence to having, or trying to find, a model of aerodynamics which fits reality. It's like, theories are worthless, because we have no idea if they're right.
This surprises me, and does make me sad. Having a model for how something works can give us deep insight into what's really happening. Think of all that science has achieved for us. It's all based on models and theories, which are tested against reality.
It would be very surprising if modern aerodynamic theory were 'dead wrong' considering the size of the A380, and the fact that it flew first time. It was not designed using a 'fingers in the stream' intuitive understanding of flight. It was designed using computer models of the behaviour of air, which are checked against wind tunnel tests. Clearly not everyone seems to share the same theory, and sadly there are still people going around teaching the dead wrong 'equal transit times' theory. But that doesn't make modern aerodynamic theory wrong.
Hugo
..................... edit .............................
Guys, everyone,
I could have totally misunderstood here, but there seems to be some kind of resistence to having, or trying to find, a model of aerodynamics which fits reality. It's like, theories are worthless, because we have no idea if they're right.
This surprises me, and does make me sad. Having a model for how something works can give us deep insight into what's really happening. Think of all that science has achieved for us. It's all based on models and theories, which are tested against reality.
It would be very surprising if modern aerodynamic theory were 'dead wrong' considering the size of the A380, and the fact that it flew first time. It was not designed using a 'fingers in the stream' intuitive understanding of flight. It was designed using computer models of the behaviour of air, which are checked against wind tunnel tests. Clearly not everyone seems to share the same theory, and sadly there are still people going around teaching the dead wrong 'equal transit times' theory. But that doesn't make modern aerodynamic theory wrong.
Hugo
..................... edit .............................
10-11-2008, 05:26 AM
#433
RE: [Deleted]
Don't panic-
Da Rocks clarification of my "dead wrong" was
"dead right".
My wording tho was ambiguous
It was exactly my point
Some theory is good some ain't.
Don't throw out the baby with the bathwater.
Bernoulli- good info
Coanda - good info
Newton- good inf.
Used incorrectly tho-
All bad info.
If one picks n chooses phrases - the intent of a comment goes sour -
I like to roll a theory around on my tongue and see if it really tastes right.
If it doesn't -I may "salt to taste".
Da Rocks clarification of my "dead wrong" was
"dead right".
My wording tho was ambiguous
It was exactly my point
Some theory is good some ain't.
Don't throw out the baby with the bathwater.
Bernoulli- good info
Coanda - good info
Newton- good inf.
Used incorrectly tho-
All bad info.
If one picks n chooses phrases - the intent of a comment goes sour -
I like to roll a theory around on my tongue and see if it really tastes right.
If it doesn't -I may "salt to taste".
10-11-2008, 06:03 AM
#434
RE: [Deleted]
JohnW, but you see, dear boy, the air IS a fluid. And thanks for getting the idea...you see, I have said all along I do not reject 'downwash', I just don't think that there is much of it going on, given the little bit of visual evidence that has been presented. I do agree that there is much we don't know, and I am pleased that if my small contribution has made one other mind question uncertain beliefs, then the quest for the real answer will one day be answered. I am not an aerodynamicist or mathematician, just a small person trying to fly model airplanes, but I do not like dogma masquerading as fact. We just need to be willing, keen, in fact, to change our minds when real evidence is presented, and accept the we could be completely wrong...
Evan.
Evan.
10-11-2008, 06:13 AM
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RE: [Deleted]
I have said all along I do not reject 'downwash', I just don't think that there is much of it going on
Hugo
10-11-2008, 06:36 AM
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RE: [Deleted]
Bernoulli- good info
Coanda - good info
Newton- good inf.
Used incorrectly tho-
All bad info.
Coanda - good info
Newton- good inf.
Used incorrectly tho-
All bad info.
Now, I have another question .............................edit................. ........................
I wanted to ask again about the lift/drag thing (sorry), and why you were so keen to not distinguish between them. I would like to give a couple of examples to illustrate why talking about lift and drag is very useful.
Why do we talk about walls, floor and ceiling, when they are all just surfaces which make up a room? Would be be reasonable to say that floors are ceilings?
Why do we talk about nose, eyes and mouth, when they are all just parts of the face? Would is be reasonable to say that the nose is the mouth?
Why do we talk about lift and drag, when they are all just parts of the aerodynamic force? Would is be reasonable to say that the drag is lift?
Imagine a world where we didn't have all of these different words. It would be terribly difficult to talk about rooms and faces, and ... aerodynamics.
Hugo
10-11-2008, 08:06 AM
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RE: [Deleted]
ORIGINAL: Rocketmagnet
I'm not sure what this means, but there is exactly as much downwash going on as is required for the plane to do what it's doing.
Hugo
I have said all along I do not reject 'downwash', I just don't think that there is much of it going on
Hugo
force = mass X acceleration
then
acceleration= force/mass
As mass approaches infinity, acceleration approaches zero with a given force.
It only takes so much force to support the plane and as the plane flys through more and more airmass per unit of time as it speeds up, there is less and less downwash velocity.
10-11-2008, 08:13 AM
#438
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RE: [Deleted]
We've got a couple of different things going on here.
One is a discussion of theoretical aerodynamics. Another is a discussion of the usefulness of theory to R/C modeling.
Some people are mistaking one for the other and it's causing confusion.
How about if we identify in each post which it is we're going to discuss? That is, unless someone wants to start a new thread about the usefulness of theory to model flying.
One is a discussion of theoretical aerodynamics. Another is a discussion of the usefulness of theory to R/C modeling.
Some people are mistaking one for the other and it's causing confusion.
How about if we identify in each post which it is we're going to discuss? That is, unless someone wants to start a new thread about the usefulness of theory to model flying.
10-12-2008, 08:38 AM
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RE: [Deleted]
ORIGINAL: da Rock
BTW, let's have some fun with the theory so many embrace as the basic definition of lift: "Lift is due to air going faster over the top of a curved airfoil."
Airplanes with cambered airfoils fly unside down every day. How DO they do that?
Well, they do, so doesn't that disprove the theory?
BTW, let's have some fun with the theory so many embrace as the basic definition of lift: "Lift is due to air going faster over the top of a curved airfoil."
Airplanes with cambered airfoils fly unside down every day. How DO they do that?
Well, they do, so doesn't that disprove the theory?
banktoturn
10-12-2008, 08:42 AM
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RE: [Deleted]
ORIGINAL: da Rock
If this isn't what you meant, you'll need to correct me.
Let me step in and offer a description of what was said. And indirectly, what was meant.
There was a request for an example of some theory that was wrong, and the example was offered.
" lift is due to air going faster over the top of the longer, curved foil." was presented as an example of some theory that is wrong.
The sentence is a good example of what most would consider to be a theory. Matter of fact, I think almost exactly that idea has been offered in these forums as the basic theory of lift by possibly hundreds of posters. They haven't all used the word, "longer", but that's a good example of semantics versus meaning. Let's move a couple of words and see how it sounds.
Lift is due to air going faster over the longer top of a curved airfoil.
I'd have to agree with both of you guys. The theory is wrong. And it's certainly one that is repeatedly offered as a basic aeronautical one.
ORIGINAL: banktoturn
That's not a theory from Aerodynamics. If you're referring to Bernoulli's equation, it only asserts that pressure decreases as velocity increases, along a streamline. It says nothing about 'longer'. The so-called 'equal transit time' nonsense has nothing to do with Bernoulli's equation, and is not taught in Aerodynamics. It seems to have arisen in various 'popular' explanations of lift. Indicting that nonsense does not prove that any bona fide theories from Aerodynamics are 'dead wrong'. Bernoulli's equation is not dead wrong. Net lift does indeed result from the pressure reduction that is explained, and accurately predicted, by Bernoulli's equation. If this isn't what you meant, you'll need to correct me.
banktoturn
ORIGINAL: dick Hanson
lift is due to air going faster over the top of the longer, curved foil.
Theres one -
ORIGINAL: banktoturn
Dick,
Can you give me an example of some theory that's dead wrong?
banktoturn
ORIGINAL: dick Hanson
Ok-
Theory is not a straight line authority tho -and some of it is dead wrong. The Wrighte Bros were supposedly the first heavier than air flyers - but shortly after- others around the world had far better craft going which were VERY different in concept. The reason
Simple
Technology begets more technology -exponentially.
Once the "cat is out of the bag" you get lots n lots of kittens.
The pusher -replaced by the tractor
the necessary(?) warped wings replaced by aileron plates etc..
My point is much of "how does it work" is obvious - once you look into it.
I know theorists who
A .can't fly and
B. I wouldn't want to fly in anything they had their mitts on. But- thankfully they are in the minority.
FWIWThe best one I ever knew just eeked out of high school but he had the concepts down cold.including the bestconstruction -which is a mystery to many.
Ok-
Theory is not a straight line authority tho -and some of it is dead wrong. The Wrighte Bros were supposedly the first heavier than air flyers - but shortly after- others around the world had far better craft going which were VERY different in concept. The reason
Simple
Technology begets more technology -exponentially.
Once the "cat is out of the bag" you get lots n lots of kittens.
The pusher -replaced by the tractor
the necessary(?) warped wings replaced by aileron plates etc..
My point is much of "how does it work" is obvious - once you look into it.
I know theorists who
A .can't fly and
B. I wouldn't want to fly in anything they had their mitts on. But- thankfully they are in the minority.
FWIWThe best one I ever knew just eeked out of high school but he had the concepts down cold.including the bestconstruction -which is a mystery to many.
Can you give me an example of some theory that's dead wrong?
banktoturn
Theres one -
banktoturn
Let me step in and offer a description of what was said. And indirectly, what was meant.
There was a request for an example of some theory that was wrong, and the example was offered.
" lift is due to air going faster over the top of the longer, curved foil." was presented as an example of some theory that is wrong.
The sentence is a good example of what most would consider to be a theory. Matter of fact, I think almost exactly that idea has been offered in these forums as the basic theory of lift by possibly hundreds of posters. They haven't all used the word, "longer", but that's a good example of semantics versus meaning. Let's move a couple of words and see how it sounds.
Lift is due to air going faster over the longer top of a curved airfoil.
I'd have to agree with both of you guys. The theory is wrong. And it's certainly one that is repeatedly offered as a basic aeronautical one.
banktoturn
10-12-2008, 08:57 AM
#441
Senior Member
RE: [Deleted]
ORIGINAL: banktoturn
You don't need to say "curved" in your definition: "Lift is due to air going faster over the top of an airfoil" is a pretty good statement. The pressure drop caused by the higher velocity of the air above the wing. In inverted flight, the angle of attack is such that the air is moving faster on the bottom of the wing instead (relative to the wing, not gravity), and so the wing generates lift in this orientation. This doesn't disprove any theory.
banktoturn
ORIGINAL: da Rock
BTW, let's have some fun with the theory so many embrace as the basic definition of lift: "Lift is due to air going faster over the top of a curved airfoil."
Airplanes with cambered airfoils fly unside down every day. How DO they do that?
Well, they do, so doesn't that disprove the theory?
BTW, let's have some fun with the theory so many embrace as the basic definition of lift: "Lift is due to air going faster over the top of a curved airfoil."
Airplanes with cambered airfoils fly unside down every day. How DO they do that?
Well, they do, so doesn't that disprove the theory?
banktoturn
Wasn't trying to disprove any theory. I actually threw in "curved" in much the same way Dick threw in "longer" in his "theory that is wrong" answer.
The question was "How DO they do that?" and you gave a pretty good answer. kewl........
10-12-2008, 09:38 AM
#442
Senior Member
RE: [Deleted]
ORIGINAL: banktoturn
The only part of that assertion that's wrong is the inclusion of the word "longer". Lift IS due to the pressure drop caused by the higher speed of air on top of the wing.
banktoturn
The only part of that assertion that's wrong is the inclusion of the word "longer". Lift IS due to the pressure drop caused by the higher speed of air on top of the wing.
banktoturn
Wanna talk about where lift comes from now?
10-12-2008, 09:54 AM
#443
RE: [Deleted]
I obviously have little interest in hashing the possible contributions of downwash etc., as for me , it has no practical use .
My interests are oriented in what I can use .
Lift and drag - yes -I understand what they are-
for me, knowing that lift is ALL about pressure differential - answers the question
Couple that and the observation that airflow ALWAYS takes the path of least resistance - always -
With these two generalities -I can sort out my needs for wing planform and airfoils.
I have not seen anyone comment about the "path of least resistance " - I can't be the only one who has noted that.
It is THE underlying reason for all the other studies of airflow.
Is this too obtuse?
My interests are oriented in what I can use .
Lift and drag - yes -I understand what they are-
for me, knowing that lift is ALL about pressure differential - answers the question
Couple that and the observation that airflow ALWAYS takes the path of least resistance - always -
With these two generalities -I can sort out my needs for wing planform and airfoils.
I have not seen anyone comment about the "path of least resistance " - I can't be the only one who has noted that.
It is THE underlying reason for all the other studies of airflow.
Is this too obtuse?
10-12-2008, 10:26 AM
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RE: [Deleted]
Wanna talk about where lift comes from now?
Perhaps I could suggest a definition (the same one I've already suggested). If anyone agrees or disagrees with it, it'd be useful to know. As far as I know, this is the standard engineering definition:
Drag: That part of the aerodynamic force which opposes the motion of the body.
Lift: That part of the aerodynamic force which is at right angles to drag.
The one thing I don't like about this definition is using the word 'lift' to talk about forces which may or may not oppose gravity.
Hugo
10-12-2008, 10:43 AM
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RE: [Deleted]
This post is on the subject of: "How is lift created".
I'd like to say something about this. I don't really see how it has any practical value in understanding airflow. I can think of several examples where it would lead me to the wrong answer, and I can't think of a single example where it would give me insight.
Example 1: Coanda effect. How could I possibly have predicted that following the curve would have been the path of least resistance? Considering surface friction, I would have thought the air would rather stay away from the surface!
Example 2: Air swirling in a vortex. Why on earth should round-and-round be the path of least resistance?
Example 3: Air being blown through two parallel tubes, one thin, the other fat. "path of least resistance" would suggest to me that all the air would choose to travel down the fat tube, whereas some air would go down the thin tube.
Example 4: Air blowing over an airfoil. Which has the least resistance, top or bottom? The air goes over both.
It also says nothing about inertia, buoyancy, speed of sound, the relationship between speed and pressure, relationship between speed/size/Reynolds number, existence of laminar and turbulent flow. In fact, all it seems to say to me is: "Air goes the way it goes".
Hugo
I have not seen anyone comment about the "path of least resistance " - I can't be the only one who has noted that.
It is THE underlying reason for all the other studies of airflow.
It is THE underlying reason for all the other studies of airflow.
Example 1: Coanda effect. How could I possibly have predicted that following the curve would have been the path of least resistance? Considering surface friction, I would have thought the air would rather stay away from the surface!
Example 2: Air swirling in a vortex. Why on earth should round-and-round be the path of least resistance?
Example 3: Air being blown through two parallel tubes, one thin, the other fat. "path of least resistance" would suggest to me that all the air would choose to travel down the fat tube, whereas some air would go down the thin tube.
Example 4: Air blowing over an airfoil. Which has the least resistance, top or bottom? The air goes over both.
It also says nothing about inertia, buoyancy, speed of sound, the relationship between speed and pressure, relationship between speed/size/Reynolds number, existence of laminar and turbulent flow. In fact, all it seems to say to me is: "Air goes the way it goes".
Hugo
10-12-2008, 10:49 AM
#446
Senior Member
RE: [Deleted]
ORIGINAL: Rocketmagnet
There is very little use in us talking about it, if we are all talking a different language; if we do not all agree on a definition for lift and drag.
Wanna talk about where lift comes from now?
10-12-2008, 10:54 AM
#447
RE: [Deleted]
ORIGINAL: Rocketmagnet
This post is on the subject of: "How is lift created".
I'd like to say something about this. I don't really see how it has any practical value in understanding airflow. I can think of several examples where it would lead me to the wrong answer, and I can't think of a single example where it would give me insight.
Example 1: Coanda effect. How could I possibly have predicted that following the curve would have been the path of least resistance? Considering surface friction, I would have thought the air would rather stay away from the surface!
Example 2: Air swirling in a vortex. Why on earth should round-and-round be the path of least resistance?
Example 3: Air being blown through two parallel tubes, one thin, the other fat. "path of least resistance" would suggest to me that all the air would choose to travel down the fat tube, whereas some air would go down the thin tube.
Example 4: Air blowing over an airfoil. Which has the least resistance, top or bottom? The air goes over both.
It also says nothing about inertia, buoyancy, speed of sound, the relationship between speed and pressure, relationship between speed/size/Reynolds number, existence of laminar and turbulent flow. In fact, all it seems to say to me is: "Air goes the way it goes".
Hugo
This post is on the subject of: "How is lift created".
I have not seen anyone comment about the "path of least resistance " - I can't be the only one who has noted that.
It is THE underlying reason for all the other studies of airflow.
It is THE underlying reason for all the other studies of airflow.
Example 1: Coanda effect. How could I possibly have predicted that following the curve would have been the path of least resistance? Considering surface friction, I would have thought the air would rather stay away from the surface!
Example 2: Air swirling in a vortex. Why on earth should round-and-round be the path of least resistance?
Example 3: Air being blown through two parallel tubes, one thin, the other fat. "path of least resistance" would suggest to me that all the air would choose to travel down the fat tube, whereas some air would go down the thin tube.
Example 4: Air blowing over an airfoil. Which has the least resistance, top or bottom? The air goes over both.
It also says nothing about inertia, buoyancy, speed of sound, the relationship between speed and pressure, relationship between speed/size/Reynolds number, existence of laminar and turbulent flow. In fact, all it seems to say to me is: "Air goes the way it goes".
Hugo
ALL of the laws of physics conform perfectly with this secenaio.
Including the ones you mentioned
You forgot that I did not redefine AIR and the characteristics of AIR are such that it does -it must -it will ALWAYS take the path of least resistance
but then -liquids also do the same .
Iv'e been involved with fluidic control circuits -I have not forgotton about Coanda effect. That is the premise for these devices.
10-12-2008, 11:03 AM
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RE: [Deleted]
Jeez, I hope that actually isn't what you meant because the discussion on theory has been rooted on different choices of definition.
Honest, isn't it the goal of some of you guys to figure out which is the real definition?
Hugo
10-12-2008, 11:46 AM
#449
RE: [Deleted]
ORIGINAL: da Rock
We've got a couple of different things going on here.
One is a discussion of theoretical aerodynamics. Another is a discussion of the usefulness of theory to R/C modeling.
Some people are mistaking one for the other and it's causing confusion.
How about if we identify in each post which it is we're going to discuss? That is, unless someone wants to start a new thread about the usefulness of theory to model flying.
We've got a couple of different things going on here.
One is a discussion of theoretical aerodynamics. Another is a discussion of the usefulness of theory to R/C modeling.
Some people are mistaking one for the other and it's causing confusion.
How about if we identify in each post which it is we're going to discuss? That is, unless someone wants to start a new thread about the usefulness of theory to model flying.
I hope somebody interested in theoretical aerodynamics has read my post #408, and he has some explanation for my question.
10-12-2008, 12:03 PM
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RE: [Deleted]
lnewqban,
I assume this is the question you refer to?
Hugo
Why the mass of air above the airfoil is accelerated more than the mass below?
Hugo
