"Parasite drag of a Boeing 747 wing is only equivalent to that of a 1/2-inch cable of the same length."
That's. . . impressive.
A Physical Description of Flight, Revisited (2009) [pdf]
11–19 of 19 posts
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#12Many ask the simple question "what makes an airplane fly?" The answer one frequently gets is misleading and often just plain wrong. The exact same problem is found in sailing: "Popular concepts as to how sails generate lift, and how two sails interact with each other are discussed in light of modern aerodynamic research. Much of the old sail theory in the sailing references is shown to be wrong." [1] [1] http://ljjen…
> Many ask the simple question "what makes an airplane fly?"
I'm reminded of perhaps the most excellent 30 seconds in all of ground school instruction:
https://www.youtube.com/watch?v=CK1UGWw15lc
His joke aside, it illustrates an important point: there are a variety of ways to produce lift. For example, when one observes a jet overfly the runway during an airshow, holding its altitude while on its side, the engine is the source of the majority of its lift in that scenario.
(Edited for clarity.)
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#13Via our favorite search engine, I found this
http://www.aviation-history.com/theory/index-theory.html
OP PDF is link 2 ("Airfoils and Lift - Newton's Law"), but as text/html. The other links look very informative, if they're anywhere near the quality of the OP text, it will make for fascinating reading.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#14Wow, Great paper. The most interesting (and counter-intuitive) part for me was that the lift is generated by the top of the wing bending air downwards. In my head I always visualized lift as the bottom of the wing being pushed up, but this paper claims lift is really more like the top of the wing pulling upwards.
The lift is the sum of all the pressure vectors around every point on the wing. Since the pressure vectors are all normal to the wing surface, in order to have a net upwards vector, the pressure on the bottom surface has to be higher than that on the top.
I.e. air cannot "pull" anything anywhere.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#15I think the easiest explanation to a lay person involves the observation that all surfaces in a moving fluid (e.g. air) produce lift--whether a flat plate, rotating cylinder, or extending your hand outside a car window. Airfoils are merely highly optimized shapes to reduce the (often significant) drag the lift-producing bodies have. In an airplane, by reducing L/D enough you decrease the necessary power (which indire…
You mean increasing L/D?
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#16Wow, Great paper. The most interesting (and counter-intuitive) part for me was that the lift is generated by the top of the wing bending air downwards. In my head I always visualized lift as the bottom of the wing being pushed up, but this paper claims lift is really more like the top of the wing pulling upwards.
The lift is the sum of all the pressure vectors around every point on the wing. Since the pressure vectors are all normal to the wing surface, in order to have a net upwards vector, the pressure on the bottom surface has to be higher than that on the top. I.e. air cannot "pull" anything anywhere.
If I remember well: in normal condition the lift come 2/3 from the top of the wing and 1/3 from the bottom of wing.
So the depression above the wing is indeed "pulling up" the wing more than the surpression below the wing is pushing up the wing.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#17Many ask the simple question "what makes an airplane fly?" The answer one frequently gets is misleading and often just plain wrong. The exact same problem is found in sailing: "Popular concepts as to how sails generate lift, and how two sails interact with each other are discussed in light of modern aerodynamic research. Much of the old sail theory in the sailing references is shown to be wrong." [1] [1] http://ljjen…
> Many ask the simple question "what makes an airplane fly?" I'm reminded of perhaps the most excellent 30 seconds in all of ground school instruction: https://www.youtube.com/watch?v=CK1UGWw15lc His joke aside, it illustrates an important point: there are a variety of ways to produce lift. For example, when one observes a jet overfly the runway during an airshow, holding its altitude while on its side, the engine is…
Excellent resource and augment to the conversation here, thank you for posting! Totally love seeing the Harrier in that video - I saw one live at Oshkosh and WOW that thing was LOUD.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#18I think the easiest explanation to a lay person involves the observation that all surfaces in a moving fluid (e.g. air) produce lift--whether a flat plate, rotating cylinder, or extending your hand outside a car window. Airfoils are merely highly optimized shapes to reduce the (often significant) drag the lift-producing bodies have. In an airplane, by reducing L/D enough you decrease the necessary power (which indire…
You mean increasing L/D?
Yes, you're correct. Increase* L/D by decreasing drag.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#19Earlier quoted context omitted.
The lift is the sum of all the pressure vectors around every point on the wing. Since the pressure vectors are all normal to the wing surface, in order to have a net upwards vector, the pressure on the bottom surface has to be higher than that on the top. I.e. air cannot "pull" anything anywhere.
If I remember well: in normal condition the lift come 2/3 from the top of the wing and 1/3 from the bottom of wing. So the depression above the wing is indeed "pulling up" the wing more than the surpression below the wing is pushing up the wing.
No, a vacuum never "pulls". The pressure on the other side of the object pushes it.