A Physical Description of Flight, Revisited (2009) [pdf]
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A Physical Description of Flight, Revisited (2009) [pdf]
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Re: A Physical Description of Flight, Revisited (2009) [pdf]
#2I 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 indirectly produces its lift) needed to overcome the combined weight of the aircraft (wings/body/powerplant) generated by gravity.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#3This is really helpful for my ParaWing invention. I still need a lot of work / help on doing the math for the exact wing dimensions though; very intimidating. However, using some sound research and an innovative design technique I do know my path is sound versus conventional designs - more lift, less aggressive stall, and smaller dimensions are all pretty necessary for human-scale personal flight device.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#4Many 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://ljjensen.net/Maritimt/A%20Review%20of%20Modern%20Sail...
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#5Wow, 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.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#6Many 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…
I remember some video, probably a TED talk, about the mechanics of bikes and how hard they are to describe formally.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#7Wow, 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.
"[T]he shape of the wing affects the efficiency and stall characteristics of the wing but not the lift. That is left to the angle of attack and speed."
So no, the top of the wing is not pulling the wing upwards. The air beneath is "blowing" the wing upwards.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#8Wow, 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.
"[T]he shape of the wing affects the efficiency and stall characteristics of the wing but not the lift. That is left to the angle of attack and speed." So no, the top of the wing is not pulling the wing upwards. The air beneath is "blowing" the wing upwards.
It's really both. Figure 8 in the paper depicts this circulation theory of lift. The top and bottom surfaces interact via this phenomenon, though the top is more critical as the paper explains.
Also terms like "push" and "pull" really confuse the mechanics here. What matters is that a net upward force is being generated, with positive pressure acting on all sides of the airfoil. There is more pressure acting upon the lower surfaces than on the upper surfaces, but at every point the pressure is positive because it is surrounded by fluid (not in a vacuum). If you integrated the pressure acting on a lifting airfoil and computed the average direction, it would be pointed up.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#9Earlier quoted context omitted.
"[T]he shape of the wing affects the efficiency and stall characteristics of the wing but not the lift. That is left to the angle of attack and speed." So no, the top of the wing is not pulling the wing upwards. The air beneath is "blowing" the wing upwards.
It's really both. Figure 8 in the paper depicts this circulation theory of lift. The top and bottom surfaces interact via this phenomenon, though the top is more critical as the paper explains. Also terms like "push" and "pull" really confuse the mechanics here. What matters is that a net upward force is being generated, with positive pressure acting on all sides of the airfoil. There is more pressure acting upon the…
No.
The wing throws air down, causing lift. The action causes an equal and opposite reaction. Of course.
It also causes vortices and ground effect, which are explained perfectly and only by the wing throwing air downwards.
Re: A Physical Description of Flight, Revisited (2009) [pdf]
#10Earlier quoted context omitted.
"[T]he shape of the wing affects the efficiency and stall characteristics of the wing but not the lift. That is left to the angle of attack and speed." So no, the top of the wing is not pulling the wing upwards. The air beneath is "blowing" the wing upwards.
It's really both. Figure 8 in the paper depicts this circulation theory of lift. The top and bottom surfaces interact via this phenomenon, though the top is more critical as the paper explains. Also terms like "push" and "pull" really confuse the mechanics here. What matters is that a net upward force is being generated, with positive pressure acting on all sides of the airfoil. There is more pressure acting upon the…
Good point, if the top of the wing diverts air downward via reduced air pressure above the wing, then it would be the higher pressure air underneath (pushing) that creates the lift. Yeah, I can see how terms like "push" and "pull" get pretty confusing.