Formula for lift: Question
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Daniel is precise, and correct.
The problem with explaining lift as a Bernuilli effect is that it is completely un-intuitive. Regardless of how you slice it, lift is produced when the wing makes a bunch of air go down, which makes the force to fly up.
I tell folks to imagine that they were at the bottom of a 15 foot swimming pool, and a 10 lb weight is tied to their feet. If they scoop water with their hands and work hard enough, they can scoop enough water and throw it downward to make them rise. Scoop fast enough and hard enough, and they get to the surface, stop and they sink back down. That is exactly how a helicopter does it. Push enough air down and your aircraft rises.
They call it an air "plane" because it planes on the air, for pete's sake, and delta pressures really don't say a thing.
deeper, you can say that because something is labeled a "theory", it is not really known, but that really quite incorrect. It is also the argument made by lunkheads in the US who think that evolution is "only a theory" and that the earth was created 4000 years ago by magic!
The problem with explaining lift as a Bernuilli effect is that it is completely un-intuitive. Regardless of how you slice it, lift is produced when the wing makes a bunch of air go down, which makes the force to fly up.
I tell folks to imagine that they were at the bottom of a 15 foot swimming pool, and a 10 lb weight is tied to their feet. If they scoop water with their hands and work hard enough, they can scoop enough water and throw it downward to make them rise. Scoop fast enough and hard enough, and they get to the surface, stop and they sink back down. That is exactly how a helicopter does it. Push enough air down and your aircraft rises.
They call it an air "plane" because it planes on the air, for pete's sake, and delta pressures really don't say a thing.
deeper, you can say that because something is labeled a "theory", it is not really known, but that really quite incorrect. It is also the argument made by lunkheads in the US who think that evolution is "only a theory" and that the earth was created 4000 years ago by magic!
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I won't disagree with what you said, Deemar, but having the precise definitions about what the author in the NASA article (I don't have it) says could clarify things for us.
I have heard the theories broken down to Bernoulli being the portion of lift due to the difference in pressure and the remainder being due to the deflection of the free stream. You can describe the latter with coanda effect if you wish.
The point is, most of the descriptions of Bernoulli's theory don't discuss what happens to the air aft of the trailing edge, which as Nick points out is the lift that we can comprehend easily, and it is the majority of the contribution of the total lift according to the spectral NASA report on "incorrect theories".
If we only look at the deflection of the airflow, or more precisely the change in momentum of that airflow, then we miss the small contribution to lift due to the pressure differences.
So without seeing the NASA report, I can understand why someone may look at the theories in such a way as one being a small contribution and another being the most significant.
In the end, it doesn't matter too much to the average pilot. I disagree that line pilots don't need to know the lift equation. Understanding what your aircraft is going to do when conditions change is important, and I believe the lift equation is a good teaching tool to help us develop some anticipation. How you derive it doesn't matter too much because the formula that we use works well enough for the majority.
Matthew.
I have heard the theories broken down to Bernoulli being the portion of lift due to the difference in pressure and the remainder being due to the deflection of the free stream. You can describe the latter with coanda effect if you wish.
The point is, most of the descriptions of Bernoulli's theory don't discuss what happens to the air aft of the trailing edge, which as Nick points out is the lift that we can comprehend easily, and it is the majority of the contribution of the total lift according to the spectral NASA report on "incorrect theories".
If we only look at the deflection of the airflow, or more precisely the change in momentum of that airflow, then we miss the small contribution to lift due to the pressure differences.
So without seeing the NASA report, I can understand why someone may look at the theories in such a way as one being a small contribution and another being the most significant.
In the end, it doesn't matter too much to the average pilot. I disagree that line pilots don't need to know the lift equation. Understanding what your aircraft is going to do when conditions change is important, and I believe the lift equation is a good teaching tool to help us develop some anticipation. How you derive it doesn't matter too much because the formula that we use works well enough for the majority.
Matthew.
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That would be 6,000 years, as opposed to 4.5 billions of years ago by magic!
But back to the topic at hand...
I've found the dicscussion very useful and knowing a little more about it can only help, in my view.
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i4iq,
It never fails to amaze me that those of us (and you, perhaps) who make a living in a very scientific endevor, where the physics of flight - the very topic we are discussing - is part and parcel of our occupation can just divorce a selected scientific fact when demanded by their religion. Precisely where is the line drawn between 1/2rho V squared and creationist theory? I cannot see how a fundamental religious belief can so vastly replace one section of the scientific firmament without leaving gaping holes!
Suppose you suddenly found a section in the bible that told you to shut down all engines at 10,000 feet, would you do it because of your belief? You are clearly a reasonable person, therefore I know the answer, and I am glad! Perhaps it is easier to argue against evolution because it doesn't seem to matter, we blindly follow this portion of religious fundamental belief because nobody dies if we are wrong.
I truly hope that professional pilots know where to draw the line between religion and the aviation procedures they follow, just as I know Doctors do when they use fundamental evolution as a means to develop new drugs and medical procedures, in spite of those who label things they don't understand as "theory" and therefore not valid.
It never fails to amaze me that those of us (and you, perhaps) who make a living in a very scientific endevor, where the physics of flight - the very topic we are discussing - is part and parcel of our occupation can just divorce a selected scientific fact when demanded by their religion. Precisely where is the line drawn between 1/2rho V squared and creationist theory? I cannot see how a fundamental religious belief can so vastly replace one section of the scientific firmament without leaving gaping holes!
Suppose you suddenly found a section in the bible that told you to shut down all engines at 10,000 feet, would you do it because of your belief? You are clearly a reasonable person, therefore I know the answer, and I am glad! Perhaps it is easier to argue against evolution because it doesn't seem to matter, we blindly follow this portion of religious fundamental belief because nobody dies if we are wrong.
I truly hope that professional pilots know where to draw the line between religion and the aviation procedures they follow, just as I know Doctors do when they use fundamental evolution as a means to develop new drugs and medical procedures, in spite of those who label things they don't understand as "theory" and therefore not valid.
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i4iq,
It never fails to amaze me that those of us (and you, perhaps) who make a living in a very scientific endevor, where the physics of flight - the very topic we are discussing - is part and parcel of our occupation can just divorce a selected scientific fact when demanded by their religion. .
It never fails to amaze me that those of us (and you, perhaps) who make a living in a very scientific endevor, where the physics of flight - the very topic we are discussing - is part and parcel of our occupation can just divorce a selected scientific fact when demanded by their religion. .
I dont think this is the right "forum" to be discussing this but I'd be happy to continue the discussion via PM...
Last edited by i4iq; 21st Dec 2006 at 20:48.
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Creationists?
I suggest most scientists pre-Darwin were creationists as there was no Evolution theory to believe in. So saying Newton was a creationist is like saying Adam and Eve didn't believe a 747 could fly.
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Hello Nick,
I wrote that to throw a spanner in the works.
I am a Newtons person myself, the old hand out the window of a speeding car does it for me, or any other ideas that get the point of helicopter aerodynamics across in an educational way.
So many of the younger pilots of today have little to no idea how these confangled machines work. This is in plain evidence by the posts that are put up.
Very frustrating at times when a basic aerodynamic question is put and so many off the planet reasons are put forward.
They fly, they fly the same way every time, fly one you can fly them all, (if you can start them),
I have enjoyed your posts for a long time because it gets told as it is. Yes I am an old person approaching the happy end of my career.
Performance you can add up and calculate but helicopter flight is still some thing that you understand in the back of you mind.
i4iq,
you know the old saying......... if God had really wanted us to fly he would have given us wings............
We got the helicopter instead.
Now bugger off with this religious crap.
I wrote that to throw a spanner in the works.
I am a Newtons person myself, the old hand out the window of a speeding car does it for me, or any other ideas that get the point of helicopter aerodynamics across in an educational way.
So many of the younger pilots of today have little to no idea how these confangled machines work. This is in plain evidence by the posts that are put up.
Very frustrating at times when a basic aerodynamic question is put and so many off the planet reasons are put forward.
They fly, they fly the same way every time, fly one you can fly them all, (if you can start them),
I have enjoyed your posts for a long time because it gets told as it is. Yes I am an old person approaching the happy end of my career.
Performance you can add up and calculate but helicopter flight is still some thing that you understand in the back of you mind.
i4iq,
you know the old saying......... if God had really wanted us to fly he would have given us wings............
We got the helicopter instead.
Now bugger off with this religious crap.
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It is illogical to asume that pre-Darwin, scientists would think something couldn't fly. Otherwise, why do experiments to understand new things? DaVinci was convinced!
But we digress!
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That's intelligent! And very brave of you!
I think its reasonable to extend a different viewpoint on a forum, particularly in response to the comment posted. It was intended to be tongue in cheek and as you will see, I had suggested a better place to continue the discussion.
Furthermore, the discussion was one of science...
I think its reasonable to extend a different viewpoint on a forum, particularly in response to the comment posted. It was intended to be tongue in cheek and as you will see, I had suggested a better place to continue the discussion.
Furthermore, the discussion was one of science...
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i4iq,
Back to your original question,
Lucretius (d.55) probably knew the answer but didn't have any thing to write on. He was a very free thinker for his time. He caused quite an uproar in his village constantly running around flapping his arms and making wokka wokka noises. Irritated everyone.
Back to your original question,
Lucretius (d.55) probably knew the answer but didn't have any thing to write on. He was a very free thinker for his time. He caused quite an uproar in his village constantly running around flapping his arms and making wokka wokka noises. Irritated everyone.
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I have absolutely no idea of which you are speaking,
but systematically speaking from a diabolical point of view i find that your fundumental faculties are insufficiently sophisticated for me to associate an iota of credence to your head up XXXX, holier than thou, down the nose peering, obviously intelligent, (and want us to know it), but unfortunately misguided low level attack on us mere mortals.
Ask mummy to help you off the rocking horse and have a rum, and a merry christmas and a very very happy new year. All is forgiven.
P.S. Who said i was of the male gender.
but systematically speaking from a diabolical point of view i find that your fundumental faculties are insufficiently sophisticated for me to associate an iota of credence to your head up XXXX, holier than thou, down the nose peering, obviously intelligent, (and want us to know it), but unfortunately misguided low level attack on us mere mortals.
Ask mummy to help you off the rocking horse and have a rum, and a merry christmas and a very very happy new year. All is forgiven.
P.S. Who said i was of the male gender.
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Deeper
You read a lot into posts about science - and attack the individual rather than the reasoning!
Anyway, "man in the mirror" is a turn of phrase. My apologies to you for offending your sensibilities.
You read a lot into posts about science - and attack the individual rather than the reasoning!
Anyway, "man in the mirror" is a turn of phrase. My apologies to you for offending your sensibilities.
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Deemar said in post number 20 of this thread--
2) In order to deflect an airstream, you need to have a pressure gradient across the airstream. To deflect the airstream downwards the pressure above the airstream needs to be higher than the pressure below.
That seems to contradict the follow on statements that the wing creates a low pressure above and high pressure below.
How could a low pressure above a wing promote a mass flow down toward a high pressure area?
2) In order to deflect an airstream, you need to have a pressure gradient across the airstream. To deflect the airstream downwards the pressure above the airstream needs to be higher than the pressure below.
That seems to contradict the follow on statements that the wing creates a low pressure above and high pressure below.
How could a low pressure above a wing promote a mass flow down toward a high pressure area?
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What the Hell.
We can all choose to believe what we like, wings do lift, helicopters do fly and we exist. Why and how? I have my beliefs, you choose yours, I am not losing any sleep over worries about someone out there believing different theories to me.
You all just have a Great Christmas...if you believe in that!
You all just have a Great Christmas...if you believe in that!
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The point is, most of the descriptions of Bernoulli's theory don't discuss what happens to the air aft of the trailing edge, which as Nick points out is the lift that we can comprehend easily, and it is the majority of the contribution of the total lift according to the spectral NASA report on "incorrect theories".
It is also worth noting that there are incorrect explanations of some of these effects. One in particular is the theory that the air on top of an airfoil goes faster because it has a longer distance to travel and it needs to "keep pace" with its "brother" air particle that travels along the bottom of the airfoil.
If we only look at the deflection of the airflow, or more precisely the change in momentum of that airflow, then we miss the small contribution to lift due to the pressure differences.
So without seeing the NASA report, I can understand why someone may look at the theories in such a way as one being a small contribution and another being the most significant.
So without seeing the NASA report, I can understand why someone may look at the theories in such a way as one being a small contribution and another being the most significant.
In the end, it doesn't matter too much to the average pilot. I disagree that line pilots don't need to know the lift equation. Understanding what your aircraft is going to do when conditions change is important, and I believe the lift equation is a good teaching tool to help us develop some anticipation. How you derive it doesn't matter too much because the formula that we use works well enough for the majority.
I guess if I was able to convince everyone then that would be one less conversation to have when you're not flying.
In terms of understanding what the aircraft is going to do as conditions change, then you are right. An understanding of the lift formulas, along with the Cl and Cd curves is probably a good thing for a pilot to have.
Daniel (I hope you all had a good Christmas)