McLean, who spent most of his professional career as an engineer at Boeing Commercial Airplanes, where he specialized in CFD code development, published his new ideas in the text Understanding Aerodynamics: Arguing from the Real Physics. Considering that the book runs to more than pages of fairly dense technical analysis, it is surprising to see that it includes a section 7.
I was never entirely happy with it. Where these clouds touch the airfoil they constitute the pressure difference that exerts lift on the airfoil. The wing pushes the air down, resulting in a downward turn of the airflow.
In addition, there is an area of high pressure below the wing and a region of low pressure above. It is as if those four components collectively bring themselves into existence, and sustain themselves, by simultaneous acts of mutual creation and causation.
There seems to be a hint of magic in this synergy. And what causes this mutual, reciprocal, dynamic interaction? McLean says no: If the wing were at rest, no part of this cluster of mutually reinforcing activity would exist.
But the fact that the wing is moving through the air, with each parcel affecting all of the others, brings these co-dependent elements into existence and sustains them throughout the flight. Soon after the publication of Understanding Aerodynamics , McLean realized that he had not fully accounted for all the elements of aerodynamic lift, because he did not explain convincingly what causes the pressures on the wing to change from ambient.
In particular, his new argument introduces a mutual interaction at the flow field level so that the nonuniform pressure field is a result of an applied force, the downward force exerted on the air by the airfoil.
There are reasons that it is difficult to produce a clear, simple and satisfactory account of aerodynamic lift. Some of the disputes regarding lift involve not the facts themselves but rather how those facts are to be interpreted, which may involve issues that are impossible to decide by experiment. Nevertheless, there are at this point only a few outstanding matters that require explanation.
Lift, as you will recall, is the result of the pressure differences between the top and bottom parts of an airfoil. We already have an acceptable explanation for what happens at the bottom part of an airfoil: the oncoming air pushes on the wing both vertically producing lift and horizontally producing drag.
The upward push exists in the form of higher pressure below the wing, and this higher pressure is a result of simple Newtonian action and reaction.
Things are quite different at the top of the wing, however. A region of lower pressure exists there that is also part of the aerodynamic lifting force.
We know from streamlines that the air above the wing adheres closely to the downward curvature of the airfoil. This is the physical mechanism which forces the parcels to move along the airfoil shape. A slight partial vacuum remains to maintain the parcels in a curved path. This drawing away or pulling down of those air parcels from their neighboring parcels above is what creates the area of lower pressure atop the wing. But another effect also accompanies this action: the higher airflow speed atop the wing.
But as always, when it comes to explaining lift on a nontechnical level, another expert will have another answer. But he is correct in everything else. The problem is that there is no quick and easy explanation. Drela himself concedes that his explanation is unsatisfactory in some ways.
So where does that leave us? In effect, right where we started: with John D. This article was originally published with the title "The Enigma of Aerodynamic Lift" in Scientific American , 2, February How Do Wings Work? Holger Babinsky in Physics Education , Vol. David Bloor. University of Chicago Press, Understanding Aerodynamics: Arguing from the Real Physics. Doug McLean. Wiley, You Will Never Understand Lift.
Peter Garrison in Flying ; June 4, Culick; July Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. In Brief On a strictly mathematical level, engineers know how to design planes that will stay aloft.
But equations don't explain why aerodynamic lift occurs. There are two competing theories that illuminate the forces and factors of lift. Both are incomplete explanations. Aerodynamicists have recently tried to close the gaps in understanding. Still, no consensus exists. Climate Change. Support science journalism. Knowledge awaits.
This friction can be reduced by constructing flight-bound objects with smooth materials. Do you love the sweeping look of winglets on a modern jet? That combats the action of lift. But in a widebody jet, the presence of a well-designed winglet—a wing on top of a wing—helps to push airflow towards the fuselage of the airplane. Weight, lift, thrust and friction are constantly pushing and pulling on one another, with the airplane in the middle. Applying aerodynamic principles to all aspects of flight is essential to advancing the scope of aviation.
Matthew A. Johnston has over 23 years of experience serving various roles in education and is currently serving as the President of California Aeronautical University. He is proud of his collaboration with airlines, aviation businesses and individual aviation professionals who are working with him to develop California Aeronautical University as a leader in educating aviation professionals.
It is with the essence of great levels of a heavenly order of intelligence to observe the great abilities of humans. Surely, the invention of the airplane was indeed created by superior minded men having the ability of the structure and design related to the science of great systems of aerodynamics. By: Hon. Desmond A. Planes are man made marvel.
It baffles me how the physics, aerodynamic flight laws keep the plane afloat in the air for a long time and being the safest method of transportation as well,enough respect to those intelligent wonderful human beings for coming up with such ideas. Save my name, email, and website in this browser for the next time I comment. Necessary cookies are absolutely essential for the website to function properly.
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The Four Forces of Aerodynamics You may be surprised to hear that aerodynamics applies to objects that never leave a runway at all. The Importance of Thrust in Aerodynamics The most spectacular illustration of thrust is a rocket launch. Aerodynamics in Action Weight, lift, thrust and friction are constantly pushing and pulling on one another, with the airplane in the middle. Matthew Johnston.
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