4 ms·
tl;dr The wings are angled so that air is forced slightly downwards when it collides into the wing. This collision is sustained by engines which force the plane
by acchow 11y ago
tl;dr
The wings are angled so that air is forced slightly downwards when it collides into the wing. This collision is sustained by engines which force the plane into the air in front of it.
- cft 11y agoIf that was it, then the wings would have been symmetrical or flat. The angle of attack probably accounts for less than 10% of the lift.
- mhuffman 11y ago> As one can see, the popular explanation, which fixates on the shape of the wing, may satisfy many but it does not give one the tools to really understand flight. Well, apparently that is it! That also explains why planes don't slam into the ground when flying upside down.
- unavoidable 11y agoSource? The whole article basically argues against this view. What is your evidence to say AOA only contributes 10%?
- vlehto 11y agoThis is common misconception probably coming from level flight situation. Commercial aircraft wings are made for adequate lift in takeoff and minimal drag in level flight. Which encourages building wings that generate all necessary lift in level flight while being relatively "flush".
- cpncrunch 11y agoAerobatic wings are symmetrical. Lift is proportional to CL, which is related to angle of attack: https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/lift_formula.html https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/lift... Most non-aerobatic wings are asymmetrical because it produces lift at zero angle of attack, and also because it results in a lower stall speed. https://en.wikipedia.org/wiki/Camber_(aerodynamics) https://en.wikipedia.org/wiki/Camber_(aerodynamics)
- wysiwylwysiwyl 11y agoConsider how flaps are shaped. When extended they increase the angle of attack; not the ratio of air travel distance.
- burnte 11y agoThey actually do both, depending on their deployment.
- rrrrrraul 11y agoGenerally, when flaps and slats are extended, they increase the camber of the airfoil, increasing the Coefficient of Lift for the same AoA. Also, the air gaps introduced at the junctions between slats/flaps and the main wing re-energize the boundary layer on the top surface of the wing to retard flow separation on the upper surface (becomes a concern because of the increased camber).
- deleted 11y ago[deleted]
- bdamm 11y agotl;dr The wings pump air down from above, causing lift not through pressure effects but rather from the volume of displacement. (I got a little bit lost in the discussion of upwash. It seemed to me that the idea was upwash was less efficient at moving air than downwash, and therefore more air was moved down.)
- nether 11y agoPressure effects still take place. Pressure is just force divided by area. If a net force (lift) exists, then a pressure differential must exist per newton's third law. A flat plate at a positive alpha has both a pressure and speed differential across the upper/lower surfaces, see http://www.windsofkansas.com/AZ2Fig5.jpg http://www.windsofkansas.com/AZ2Fig5.jpg
- pif 11y agoJust one more bit: "Air has viscosity". Without naming viscosity, the explication doesn't hold. If the air didn't have any viscosity, like it is natural to imagine, planes could not fly.
- zby 11y agoNot really - if a wing moves through fluid without viscosity it still has to move the particles down.
- FiatLuxDave 11y agoThis is incorrect. A wing can impart momentum to air even in the absence of viscosity. However, the optimal wing shape is different. For an example of a wing that moves air "down" without viscosity, look at turbomolecular vacuum pumps: http://www.physics.rutgers.edu/ugrad/387/388s06/UHV_LEED/UHV_Pumps.pdf http://www.physics.rutgers.edu/ugrad/387/388s06/UHV_LEED/UHV...
- meagain20000 11y agoIs there such a thing as non-viscous fluid?
- mcguire 11y agoYes, one example is superfluid helium. https://en.wikipedia.org/wiki/Superfluid_helium-4 https://en.wikipedia.org/wiki/Superfluid_helium-4 Viscosity is weird. https://en.wikipedia.org/wiki/Non-Newtonian_fluido https://en.wikipedia.org/wiki/Non-Newtonian_fluido
- Gravityloss 11y agoThat's not correct, then the upper surface of the wing would not have effect on lift, when in fact it contributes over half of it.
- Retric 11y agoAll the low pressure above a wing does is reduce a downward force it does not provide lift. Drop a piece of paper and it drifts slowly. Drop a book and it falls fast. In your model the paper is supported by the air below and pulled up by the void behind it. However, if you put a piece of paper behind a book it sticks to it and is not pulled up. Thus, all lift comes from the bottom. Edit: You can do the same thing with a piece of paper on top of a wing. PS: The same is true if you pick up a piece of paper with a vacuum. Even if it seems like the suction is providing lift all the force is from outside air.
- JumpCrisscross 11y ago> All the low pressure above a wing does is reduce a downward force it does not provide lift. NASA explains why the "skipping stone" theory of lift is incorrect well [1]. In summary, the upper surface does generate lift. [1] https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html
- Retric 11y agoI did say the top of the wing reduced a downward force, unlike the skipping stone theory. But, that's not lift. Do you think individual air molecules are going to magically hold the top of the wing and pull? Now, you can use an inaccurate model of what's going on. And mathematically it looks like the top of a wing provides lift. But, physically that's not what is happening. PS: This is only an issue, because we think an aircraft as zero forces acting on it when it's sitting still on a runway. Instead of being under ~2100 pounds of force per square foot on all sides from air.
- Gravityloss 11y ago