Just heard from a freshly minted flight instructor that if your AOA is zero then your lift is also zero. Do physics no longer matter to airplanes or is this some sort of newfangled teaching revolution imposed by TC?
ahramin
Angle of Attack
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lmao
That is what this forum needs. More good quotes. But speaking of quotes, i am not going to say who wrote it but i am still laughing about a new word i learned today:
This one is going to keep me going all week. Can you just imagine someone in a serious argument saying that out of nowhere. I think i will use it. "No, i think we will probibally have a problem."
ahramin
That is what this forum needs. More good quotes. But speaking of quotes, i am not going to say who wrote it but i am still laughing about a new word i learned today:
Go ahead, say it out loud.probibally
This one is going to keep me going all week. Can you just imagine someone in a serious argument saying that out of nowhere. I think i will use it. "No, i think we will probibally have a problem."
ahramin
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Flying Low
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Snagmaster E
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Don't feel bad, I had a person say once, "well if you put compressed helium tanks in a plane it should make it lighter...".
It's almost as stupid as a girl I know who was on an on-ramp and since she couldn't find an opening she just drove the car into the ditch.
Darwin's theory of natural selection....
Love the "fuzzy Physics". If it was a symetrical airfoil I might believe that.
It's almost as stupid as a girl I know who was on an on-ramp and since she couldn't find an opening she just drove the car into the ditch.
Darwin's theory of natural selection....
Love the "fuzzy Physics". If it was a symetrical airfoil I might believe that.
Money, wish I had it...
Check out this web site at NASA: http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html
According to NASA "0" angle of attack equals "0" lift. fart
According to NASA "0" angle of attack equals "0" lift. fart
Pilots get higher, SCUBA Divers do it deeper!
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duplicate2
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Bingo. There is this thing called the "Coefficient of Lift" or Cl curve which has AOA on the x axis, and lift on the y-axis.
A symmetrical airfoil (such as a piece of plywood!) will produce zero lift with a zero AOA. However symmetrical airfoils are rarely used on aircraft, except perhaps for serious aerobatic types such as Extra, Sukhois, etc.
However, a flat-bottomed wing, with a cambered upper surface, will produce lift with a zero-degree AOA, through the magic of Bernoulli.
Then, there is angle of incidence. One could bolt a symmetrical airfoil one with an angle to the fuselage, so that you could fly with a level fuselage but with the wing at say 5 deg AOA.
Get out your old Flight Training Manual and look up the Coefficient of Lift curve, and see what lift is produced with a zero deg AOA.
It is truly scary what Transport Canada-certified flight instructors know (or don't know).
A symmetrical airfoil (such as a piece of plywood!) will produce zero lift with a zero AOA. However symmetrical airfoils are rarely used on aircraft, except perhaps for serious aerobatic types such as Extra, Sukhois, etc.
However, a flat-bottomed wing, with a cambered upper surface, will produce lift with a zero-degree AOA, through the magic of Bernoulli.
Then, there is angle of incidence. One could bolt a symmetrical airfoil one with an angle to the fuselage, so that you could fly with a level fuselage but with the wing at say 5 deg AOA.
Get out your old Flight Training Manual and look up the Coefficient of Lift curve, and see what lift is produced with a zero deg AOA.
It is truly scary what Transport Canada-certified flight instructors know (or don't know).
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Cat Driver
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Right Seat Captain
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Perhaps the instructor just didn't read up on his theory of flight. It has been my experience, that an instructor in training has lost much of the information they had learned getting their licences. Therefore they must review their material and learn it like the back of their hand. Although it is impossible to know everything, when asked a question they don't know, they say 'hold on!' and the go look it up. This is what I do.
There are some however, that when faced with a question they do not know, they try to figure it out in their head, which is someimes succssful, more often not, or they make up an answer that sounds best, hopingn they are right. I usually see this with non-critical questions, and therefore isn't too unsafe. But these instructors pick up a habit of making up this information, and fail to ever re-read any manuals.
I know that I am incapable of remembering everything. Even as I teach something over and over, I have a tendency to forget things. So I make sure to regularly read over my notes and refresh my memory.
There are some however, that when faced with a question they do not know, they try to figure it out in their head, which is someimes succssful, more often not, or they make up an answer that sounds best, hopingn they are right. I usually see this with non-critical questions, and therefore isn't too unsafe. But these instructors pick up a habit of making up this information, and fail to ever re-read any manuals.
I know that I am incapable of remembering everything. Even as I teach something over and over, I have a tendency to forget things. So I make sure to regularly read over my notes and refresh my memory.
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Flying Low
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As much fun (and often right) as it is to bash TC, why can't we just blame that instructor or his Class 1. There is no reason to get that wrong, and even worse is that his Class 1 didn't notice well in advance (like lesson 7). I'm working on my Class 4 right now and my instructor would have raked me over the coals if that came up (and he would have made sure it did). Yes, it is in the FIG.
Cheers.
Cheers.
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There has been much discussion about low lif works. The most comon attitude in the literature is that Beroulli's Theorm is not the best explanation. Bernoulli states that if you move a fluid through a restriction it will accelerate and the pressure within will be reduced, thus maintaining the total energy of the fluid.
Where is the other side of the restriction over a wing?
This theorm works well in a venturi.
The Coanda Effect is being addressed more frequently lately as a better explanation of why the air flows around the surface of the airfoil, and much is being said regarding Upwash and Downwash.
If Downwash is not greater than Upwash there is no lift. In another example of an airfoil simulator that I once tried they contend that if AOA is 0 there is no lift.
Obviously I have not done these experiments in a wind tunnel so I cannot speak from personal experience. I also cannot say with any degree of accuracy that in the several thousand hours I have flown that I have ever maintained level flight with a 0 degree AOA. My guess would be that I have not.
There is a lot written and a lot being said, but the old books that attribute the whole effect to Bernoulli are being seriously challenged.
If you visit the FoilSim Applet you will notice that , contrary to the old textbooks the air over the upper surface does not get to the trailing edge at the same time as the air under the wing, it gets there sooner.
Where is the other side of the restriction over a wing?
This theorm works well in a venturi.
The Coanda Effect is being addressed more frequently lately as a better explanation of why the air flows around the surface of the airfoil, and much is being said regarding Upwash and Downwash.
If Downwash is not greater than Upwash there is no lift. In another example of an airfoil simulator that I once tried they contend that if AOA is 0 there is no lift.
Obviously I have not done these experiments in a wind tunnel so I cannot speak from personal experience. I also cannot say with any degree of accuracy that in the several thousand hours I have flown that I have ever maintained level flight with a 0 degree AOA. My guess would be that I have not.
There is a lot written and a lot being said, but the old books that attribute the whole effect to Bernoulli are being seriously challenged.
If you visit the FoilSim Applet you will notice that , contrary to the old textbooks the air over the upper surface does not get to the trailing edge at the same time as the air under the wing, it gets there sooner.
Pilots get higher, SCUBA Divers do it deeper!
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Right Seat Captain
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The venturi effect does apply to a wing. The upper surface that restricts the flow, is the air above it. It can be proven by increasing the camber, and achieving the type of wing that can be found on a STOL aircraft.
It's always bugged me how groundschool instructors teach the Bob meets Margarite" at the back of the wing theory, as OW stated that it wasn't in the Foil Sim. The venturi effect causes an exponential increase in speed, thus getting the air at the beck of the wing much quicker than that on the bottom.
It's always bugged me how groundschool instructors teach the Bob meets Margarite" at the back of the wing theory, as OW stated that it wasn't in the Foil Sim. The venturi effect causes an exponential increase in speed, thus getting the air at the beck of the wing much quicker than that on the bottom.
Back in 2002, my flight theory teacher had our class do a research work with the following question, which is somewhat relevant to this thread:
"Find three popular theories on lift and state why each is incorrect"
I suggest you take a look at this page
http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
and this series
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html
"Find three popular theories on lift and state why each is incorrect"
I suggest you take a look at this page
http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
and this series
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html
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justplanecrazy
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So is Bernoulli's equation false then? The way I was demonstrated this phenomenon is by holding a piece of paper by the two corners closest you and let the trailing edge droop away from you. This mimics a shape close to the shape of an upper airfoil. If you blow over the top of the paper, the paper will lift. So why does the paper lift? I don't really get their reasoning behind lift other than the angle travelling through a liquid concept. With this concept, blowing over the paper shouldn't lift it, as the air isn't blowing up from below but sideways from above. Anyone else not a rocket scientist on here? Maybe I should get some sleep and try reading it again.
We have no effective screening methods to make sure pilots are sane.
— Dr. Herbert Haynes, Federal Aviation Authority.
— Dr. Herbert Haynes, Federal Aviation Authority.
Bernoulli's theorm is not false, but how we have for years applied it to the lift effect on an airfoil is questionable.
The piece of paper you refer to is an example of the Coanda Effect.
Try this: take a spoon (regular table spoon), hold it by the handle between your thumb and first finger so that you are holding the edges with the spoon end away from your hand. Turn on the water in a sink so it is flowing slowly but significantly (little pressure, just flow). Move the spoon into place so the water flows over the curved back of the spoon, and watch what happens.
NOTE: be sure that you are not holding the spoon too tight.
The piece of paper you refer to is an example of the Coanda Effect.
Try this: take a spoon (regular table spoon), hold it by the handle between your thumb and first finger so that you are holding the edges with the spoon end away from your hand. Turn on the water in a sink so it is flowing slowly but significantly (little pressure, just flow). Move the spoon into place so the water flows over the curved back of the spoon, and watch what happens.
NOTE: be sure that you are not holding the spoon too tight.
Pilots get higher, SCUBA Divers do it deeper!
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Right Seat Captain
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OW, you have the right principle, but your test with water and a spoon isn't completely acurate. spoon moves into the water because water is a polar substance, meaning each water molecule has a slight positive and negative side to it. Since most objects have a charge, either positive or negative, the water tends to stick to the surface of the charged object, and rotating the molecules to have opposite charges facing the object. The difference in poles causes attraction. Since the spoon has relatively similar mass to the water flowing, it moves into the water flow, as well, the water tends to stick to the surface and spread some. You can see this by sticking practically any object, regardless of shape into the edge of the water flow, and you'll the entire stream of water changes direction, from the charge pulling it to one side.
Now that I would have a tough time grasping. If I put a magnet on the faucet would that change it?
Does being drawn toward a speeding train when you are standing close also have to do with magnetic charges?
Do you wear a bimetal band on your wrist?
Does being drawn toward a speeding train when you are standing close also have to do with magnetic charges?
Do you wear a bimetal band on your wrist?
Pilots get higher, SCUBA Divers do it deeper!
Granted that the way flight instructors have been explaining bernoulli's theorem is bunk (minnie and micky molecule still makes me cringe) what do you expect? When you have people who did not pass grade 12 physics (or grade 13) explaining physical processes by analogy and then those people go on to explain it to their students, you are going to wind up with some pretty interesting concepts. Way too many people today do "proofs" and explanations by analogy.
If you want to understand lift, build a wind tunnel.
Anyone who does not believe that bernoulli's theorem plays a big part in lift generation needs to come racing with me and see that a curved airfoil can propell a 32 foot boat at seven knots. Upwind. It does this by chaning the speed of the air flowing over the sail. Increase the speed and the pressure decreases, pulling the boat forward and sideways. But sailors have much less trouble understanding this because you can see the telltales flapping and feel the increase in speed as you move your airfoil around and change its shape.
In addition there was a boat whose motive force came from a vertical rotating cylinder. The cylinder rotated clockwise for a port tack and counterclockwise for a starboard tack. This slowed down the air going past the back side of the cylinder and sped up the air going past the front side, moving the boat forward using no forces other than the pressure differences caused by the change in the wind speed.
Wings work by producing low pressure on the top of the wing. Again. Wings work by producing low pressure on the top of the wing. This is where the majority of the lift comes from. The rest (less than 20% of the total force) comes from the increase in pressure underneath the wing. First you need to understand this. Then we can get into esoteric discussions of how they do this.
They decrease the pressure by increasing the speed of the air. But how do they increase the speed of the air? This is where all these theories of lift are getting attacked. Somehow the proof by authority has come up with a fascinating series of explanations of how an airfoil speeds up the airflow.
First off there is the shape of the airfoil. This shape sticks into the air and the manner in which it sticks into the air determines its effect. The thicker the airfoil, the more effect. Secondly, there is the angle to the airflow. The greater the airflow, the more effect.
Personally i think this is as far as we need to take this with a student. As long as the above is understood it should be enough.
I do not think that ducking around the argument and stating that downwash produces lift is a good idea. Do you eat by excreting? Or do you excrete because you eat? You can see what excrement the downwash explanation is by asking how design an airfoil that produces more lift. Make it produce more downwash?
In addition there are two types of downwash. There is the downwash produced as a reaction to the amount of lift produced by the wings. There is also the downwash produced by wing tip vorticies. This downwash is of far larger magnitude than that resulting from lift. So before you say that lift is created by downwash, think about the fact that winglets increase lift and decrease downwash. Independently.
Jeez i just read through the above and man does it sound preachy. Sorry about that. I am not trying to lecture anyone here. I just thought that outlining the facts might be of some use.
ahramin
If you want to understand lift, build a wind tunnel.
Anyone who does not believe that bernoulli's theorem plays a big part in lift generation needs to come racing with me and see that a curved airfoil can propell a 32 foot boat at seven knots. Upwind. It does this by chaning the speed of the air flowing over the sail. Increase the speed and the pressure decreases, pulling the boat forward and sideways. But sailors have much less trouble understanding this because you can see the telltales flapping and feel the increase in speed as you move your airfoil around and change its shape.
In addition there was a boat whose motive force came from a vertical rotating cylinder. The cylinder rotated clockwise for a port tack and counterclockwise for a starboard tack. This slowed down the air going past the back side of the cylinder and sped up the air going past the front side, moving the boat forward using no forces other than the pressure differences caused by the change in the wind speed.
Wings work by producing low pressure on the top of the wing. Again. Wings work by producing low pressure on the top of the wing. This is where the majority of the lift comes from. The rest (less than 20% of the total force) comes from the increase in pressure underneath the wing. First you need to understand this. Then we can get into esoteric discussions of how they do this.
They decrease the pressure by increasing the speed of the air. But how do they increase the speed of the air? This is where all these theories of lift are getting attacked. Somehow the proof by authority has come up with a fascinating series of explanations of how an airfoil speeds up the airflow.
First off there is the shape of the airfoil. This shape sticks into the air and the manner in which it sticks into the air determines its effect. The thicker the airfoil, the more effect. Secondly, there is the angle to the airflow. The greater the airflow, the more effect.
Personally i think this is as far as we need to take this with a student. As long as the above is understood it should be enough.
I do not think that ducking around the argument and stating that downwash produces lift is a good idea. Do you eat by excreting? Or do you excrete because you eat? You can see what excrement the downwash explanation is by asking how design an airfoil that produces more lift. Make it produce more downwash?
In addition there are two types of downwash. There is the downwash produced as a reaction to the amount of lift produced by the wings. There is also the downwash produced by wing tip vorticies. This downwash is of far larger magnitude than that resulting from lift. So before you say that lift is created by downwash, think about the fact that winglets increase lift and decrease downwash. Independently.
Jeez i just read through the above and man does it sound preachy. Sorry about that. I am not trying to lecture anyone here. I just thought that outlining the facts might be of some use.
ahramin
If you are talking about Cousteau's Calypso II, it was much more than a rotating cylinder.
Neuton said that for every action there is an equal and oposite reaction. If there is no downwash there can be no lift. See again the NASA tests which were done in a wind tunnel with very sensitive instruments to measure results. I know that I can not produce this in my back yard, so I choose to believe the folks at NASA.
Neuton said that for every action there is an equal and oposite reaction. If there is no downwash there can be no lift. See again the NASA tests which were done in a wind tunnel with very sensitive instruments to measure results. I know that I can not produce this in my back yard, so I choose to believe the folks at NASA.
Pilots get higher, SCUBA Divers do it deeper!
The boat i was thinking of was before jack's time. I have never heard of the Calypso II. Have to try it on google now.
ahramin
I said that:OW wrote:If there is no downwash there can be no lift.
And if you are going to lecture on physics, learn to spell Newton.ahramin wrote:There is the downwash produced as a reaction to the amount of lift produced by the wings.
ahramin
