okay let the debate begin...newton or bernoulli

[VNugget]

Bernouli: High pressure seeks a low pressure creating lift.

No, that's Newton's 2rd law. Bernoulli's principle is the inverse relationship of speed and static pressure.

The air on the top of the wing has to travel a longer distance to meet back up with the air at the bottom.

No, it doesn't.

 

[VNugget]

Well even though newton's " action reaction" is well known in physic. it is obvously bernoulli is the master of lift. Just take the upper surface of the wind (upper camber) overall area. it is definitely more than the lower camber.

... and?

 

[Super_Cub_2414P]

It states right in chap. 17 of the FAA Flight Training Handbook that most lift is the result of the airflow's downwash from ABOVE THE WING, Newton's law, and it further explains that without Bernoulli's principle that the downwash would not be possible.


"Herein lies the key to flight. The fact that most lift is the result of the airflow's downwash from above the wing, must be thoroughly understood in order to continue further in the study of flight. It is neither accurate nor does it serve a useful purpose, however, to assign specific values to the percentage of lift generated by the upper surface of an airfoil versus that generated by the lower surface. These are not constant values and will vary, not only with flight conditions, but with different wing designs."
http://www.faatest.com/books/FLT/Chapter17/AirfoilDesign.htm

"One must also bear in mind that associated with the lowered pressure is downwash; a downward backward flow from the top surface of the wing. As we have already seen from our previous discussion relative to the dynamic action of the air as it strikes the lower surface of the wing, the reaction of this downward backward flow results in an upward forward force on the wing. This same reaction applies to the flow of air over the top of the airfoil as well as to the bottom, and Newton's third law is again in the picture."
http://www.faatest.com/books/FLT/Chapter17/LowPressureAbove.htm

http://www.dauntless-soft.com/PRODUCTS/Freebies/Library/index-flighttraining.html

 

[flyifrvfr]

Bernouli: High pressure seeks a low pressure creating lift.

No, that's Newton's 2rd law. Bernoulli's principle is the inverse relationship of speed and static pressure.

The air on the top of the wing has to travel a longer distance to meet back up with the air at the bottom.

No, it doesn't.

I beg to differ. Since a wing is curved at the top, the air going over the top must travel a greater distance than the air at the bottom. I base this on the shortest distance between two points is a straight line. I may have missed the class when they changed that principle. The diagram shown is nice, but what it can't show you is that the air going above the wing is moving faster than the air at the bottom of the wing.

The reference to Bernouli is that he said that a high pressure and a low pressure are created from the difference in the speed of the air going over and under the wing.

 

[avbug]

While the curvature over the top of the wing means that a token molecule of "air" must travel a greater distance to reach the trailing edge of the wing, this has nothing to do with the airflow acceleration, or pressure loss.

Often as not, ignorant flight instructors try to explain lift by stipulating that two air molecules begin the journey around the wing at the leading edge. They postulate that the two molecules must reach the trailing edge at the same time. Therefore, they reason, the molecule that must move the farthest in that time must go the fastest. The faster the airflow, the lower the pressure and bingo! We have lift.

The problem is that the two molecules will never meet again, and no requirement exists for either one to arrive at the trailing edge, or any other point in space or time, at the same moment. The neophyte instructor's theory falls flat.

Yes, the distance along the curvature of the upper camber of the wing is greater (on a non symmetrical airfoil), but it is irrelevant with respect to the creation of lift, and downwash. Upper camber exists to form half of an inefficient venturi in concert with the free airstream, and it is this venturi effect which causes an increase in velocity over the wing. It is the acceleration of this airflow downward, along with acceleration (a change in speed and direction) imparted by the wing and angle of attack, that accounts for lift.

 

[uwochris]

With greater curvature, would there not be more downwash produced from the airflow as it flows down the wing from above? Avbug, is this what you are implying when you say "It is the acceleration of this airflow downward, along with acceleration (a change in speed and direction) imparted by the wing and angle of attack, that accounts for lift."

Anoter Q... what is the cause of the airflow being faster above the wing? Is it due to the curvature? We all know that how speed and pressure are related through Bernouilli, but I have not seen a good explanation as to WHY the airflow is faster above the wing than it is below it.

I never heard about the downwash from ABOVE the wing being a factor in the production of lift. I always associated the downwash with what was occuring below the wing (as the wing travels forward at a positive AOA, air will be forced downward as it contacts the lower surface of the wing, producing an upward force on the wing.)

Some seem to believe that lift is a result of the downwash. Others claim that downwash is the result of lift being produced. Any comments here, avbug? Is this a "what came first..." type statement, or is one statement more correct than the other?

I guess you must consider what is occuring ABOVE and BELOW the wing, and not try to isolate the two factors.

 

[avbug]

Again, there is no debate. One leads to the other. Air above the wing, air beneath the wing...an airplane displaces a mass of air equal in value to that which it lifts; downwash equals lift. Did the air result in being deflected downward by dynamic interaction with the lower surface of the wing, or was it accelerated by forces above the wing? Depending on the angle of attack, the relationships of any percentages that might improperly be applied are constantly changing...both contribute, and the only real measure of the lift is the downwash the wing produces.

Aerodynamic occurances above the wing are but one contributor to downwash. Airflow in downwash comes from both above and beneath the wing. There is no chicken, there is no egg. Just a lot of air. To ask what percentage of lift is created by reduced pressure above the wing is nonsensical; of it's own accord it's a very small percent (akin to the "suction" a baby applies to a bottle) for any given flight condition. What it does do, however, is assist in causing, creating, and sustaining downwash. It's not a matter of one or the other. One is the other.

 

[weekendwarrior]

The air on the top of the wing has to travel a longer distance to meet back up with the air at the bottom.

No, it doesn't.

Thanks, Vnugget. It makes me cringe when people get the "molecules have to meet up at the trailing edge" explanation. The molecules don't know they are disturbed, and don't have any desire or tendency to join one another again.

An examiner once mentioned another way to think of it. The air is not really flowing over the wing. The wing is flowing through the air. The shape of the wing inherently makes the "relative" wind move faster over the top. There really isn't airflow, it's wingflow through the air. One way to look at it anyway.

 

[Super_Cub_2414P]

I've provided the links to the FAA Flight Training Handbook below, lift is a result of downwash. Clear and simple right out of the FAA Flight Training Handbook.


It states right in chap. 17 of the FAA Flight Training Handbook that most lift is the result of the airflow's downwash from ABOVE THE WING, Newton's law, and it further explains that without Bernoulli's principle that the downwash would not be possible.


"Herein lies the key to flight. The fact that most lift is the result of the airflow's downwash from above the wing, must be thoroughly understood in order to continue further in the study of flight. It is neither accurate nor does it serve a useful purpose, however, to assign specific values to the percentage of lift generated by the upper surface of an airfoil versus that generated by the lower surface. These are not constant values and will vary, not only with flight conditions, but with different wing designs."
http://www.faatest.com/books/FLT/Ch...rfoilDesign.htm

"One must also bear in mind that associated with the lowered pressure is downwash; a downward backward flow from the top surface of the wing. As we have already seen from our previous discussion relative to the dynamic action of the air as it strikes the lower surface of the wing, the reaction of this downward backward flow results in an upward forward force on the wing. This same reaction applies to the flow of air over the top of the airfoil as well as to the bottom, and Newton's third law is again in the picture."
http://www.faatest.com/books/FLT/Ch...essureAbove.htm

http://www.dauntless-soft.com/PRODU...httraining.html

 

[ADF_Fixed]

Carb On

I just dont want to get too techinical. Cuz I may get CARBURATOR ICING