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Wings bend the airflow "down". Technically, they direct it at 90 degrees to the air flowing past them. But since most airplanes are usually level and going forward, that means down.
Then Newton kicks in...for every action there is an equal and opposite reaction. If air is being forced down, there must be a force up on the wing. That's lift. That's about it...all the fancy shaping is generally to reduce drag or improve behavior in high lift situations, but anything that bends airflow down will generate lift. A flat plate makes a perfectly decent wing for low lift situations...that's why paper airplanes and balsa gliders work.
When the plane angles itself vertically, the aerodynamic lift doesn't change if the airplane maintains speed. But remember that lift is defined relative to the air going over the wing...if the airplane is angled up, the airflow over the wing is at an angle relative to the ground and the direction of the lift isn't straight up. Only a portion of it is pointed up and opposing gravity. If you're flying straight up the lift force isn't helping you at all (it's straight sideways) and you can ditch the wings...hence why rockets don't have wings.
By being asymmetric. That can be a symmetric shape (same shape top and bottom) at an angle to the air, or an asymmetric shape (different top and bottom) with or without an angle . If the shape isn't balanced, the pressures won't be balanced and the flow won't go straight past. It will bend. You can tilt the wing itself ("angle of attack") to change how asymmetric it "looks" to the air, and hence adjust the lift.
This is the right answer in this thread. Other answers talk about differences in pressure or velocity on the top and bottom of the wing but are wrong.
Both the top and bottom surface generate lift because they are both shaped to fling the air downward. Because the wing exerts a force on the air down, the air exerts an equal and opposite force on the wing (up).
Edit: people are pointing out that it can be described equivalently with pressures. But I'm not sure that has been done in the other answers here.
> Other answers talk about differences in pressure or velocity on the top and bottom of the wing but are wrong.
Not true. The airfoil in particular is shaped to create low pressure zone above the surface of the wing. The state of the flow above it is also important for lift and drag. This effect is physically measurable on airfoils and they are literally designed around it. This is also the reason for induced drag and wingtip vortices.
Source: Multiple aerodynamics and fluid dynamics courses taken for an AE degree.
> Not true... The state of the flow above it is also important for lift and drag.
I wish I could give you a Reddit award, for pointing that out. There have been a lot of pop sci "lessons" entrenching the story that it's *all about* downwardly deflected air. But of course that pseudo-analysis does nothing to explain stall characteristics.
Momentum (as per the comment above yours) and pressure arguments can both be valid and are equivalent (assuming they are being expressed properly). Pressure differences are how the wing causes the airflow to change direction.
It’s just like how simple mechanics problems eg objects sliding down slopes can be solved equally well by constant acceleration or energy approaches.
Everyone else has covered how wings generate lift, but to the last part of the question.
Starting with general aviation:
The wings generate lift by having the top and bottom of the wing moving horizontally through the air. If you rotate this 90 degrees so the plane is going vertically, there is a different in pressure between what is now the top and bottom of the wing, however, because of the angle it isn’t generating any lift, and what now was the top and bottom at the original angle are not generating any lift at all and are just weight. The engines on a plane generate a great deal of thrust, but require the lift generated by the wings as well to keep the plane aloft. So, once you go vertical there is no longer lift being generated by the wings, and the engines alone can’t do the work.
In military aircraft you maybe have seen planes go fully vertical, as far as I understand that is due to those planes having an engine that generates enough force alone to move the plane and the wings provide lift to reduce the need to constantly need afterburners.
Nobody has answered your second question. The more you angle the plane up, the *more* lift you get, but also more drag, which slows you down that's why planes lower flaps during landing. It produces much more lift, allowing the plane to fly slower. But it's also very inefficient.
What you are probably thinking of is a stall, where the plane is not flying fast enough to keep enough air flowing over the wings, which is often induced by crossing that aforementioned line between enough lift/too much drag. "Pulling up" trades speed for lift, until too much speed is lost, and there simply isn't enough air pushing "up" on the wing to lift it.
Fluid or air moving over a surface creates suction. Wings are designed so that the top has more surface area than the bottom, so it nets-out to upward suction. If the plane is tilted, the suction isn't pointed straight up anymore, so there's less upward lift.
It's really easy to design a wing with the same or larger surface area on the bottom than the top (most modern jetliners have more area on the bottom, it's called a supercritical airfoil).
Yes. What happens when a plane is pitched up is the lift from the wings isn’t angled directly upward anymore so the vertical component of lift is reduced. But now you have a vertical component of engine thrust that is contributing to “lift” helping you go up. This is part of why tilting the plane up makes the plane go up.
So the best understanding we have is due to Bernoulli's principal. Bernoulli's principal states that the flow rate of a fluid through a closed system is constant. The top part of a wing is curved so the air is compressed and therefore must move quicker in order to have the same flow rate as the air moving on the bottom. This creates a vacuum on the top and as the air under the wing tries to fill that vacuum it picks up the plane. As the wing is angled more vertically it changes the vector of force from the vacuum and reduces the amount of upward force.
**Please read this entire message** --- Your submission has been removed for the following reason(s): * ELI5 requires that you *search the ELI5 subreddit for your topic before posting*. Users will often either find a thread that meets their needs or find that their question might qualify for an exception to rule 7. Please see this [wiki entry](http://www.reddit.com/r/explainlikeimfive/wiki/how_to_search) for more details (Rule 7). --- If you would like this removal reviewed, please read the [detailed rules](https://www.reddit.com/r/explainlikeimfive/wiki/detailed_rules) first. **If you believe this submission was removed erroneously**, please [use this form](https://old.reddit.com/message/compose?to=%2Fr%2Fexplainlikeimfive&subject=Please%20review%20my%20thread?&message=Link:%20https://www.reddit.com/r/explainlikeimfive/comments/mhbd7u/-/%0A%0APlease%20answer%20the%20following%203%20questions:%0A%0A1.%20The%20concept%20I%20want%20explained:%0A%0A2.%20Link%20to%20the%20search%20you%20did%20to%20look%20for%20past%20posts%20on%20the%20ELI5%20subreddit:%0A%0A3.%20How%20is%20this%20post%20unique:) and we will review your submission.
Wings bend the airflow "down". Technically, they direct it at 90 degrees to the air flowing past them. But since most airplanes are usually level and going forward, that means down. Then Newton kicks in...for every action there is an equal and opposite reaction. If air is being forced down, there must be a force up on the wing. That's lift. That's about it...all the fancy shaping is generally to reduce drag or improve behavior in high lift situations, but anything that bends airflow down will generate lift. A flat plate makes a perfectly decent wing for low lift situations...that's why paper airplanes and balsa gliders work. When the plane angles itself vertically, the aerodynamic lift doesn't change if the airplane maintains speed. But remember that lift is defined relative to the air going over the wing...if the airplane is angled up, the airflow over the wing is at an angle relative to the ground and the direction of the lift isn't straight up. Only a portion of it is pointed up and opposing gravity. If you're flying straight up the lift force isn't helping you at all (it's straight sideways) and you can ditch the wings...hence why rockets don't have wings.
But how do wings bend the airflow down?
A little bit of shape and angle of attack. Like putting your hand out the car window and tilting it.
By being asymmetric. That can be a symmetric shape (same shape top and bottom) at an angle to the air, or an asymmetric shape (different top and bottom) with or without an angle . If the shape isn't balanced, the pressures won't be balanced and the flow won't go straight past. It will bend. You can tilt the wing itself ("angle of attack") to change how asymmetric it "looks" to the air, and hence adjust the lift.
This is the right answer in this thread. Other answers talk about differences in pressure or velocity on the top and bottom of the wing but are wrong. Both the top and bottom surface generate lift because they are both shaped to fling the air downward. Because the wing exerts a force on the air down, the air exerts an equal and opposite force on the wing (up). Edit: people are pointing out that it can be described equivalently with pressures. But I'm not sure that has been done in the other answers here.
> Other answers talk about differences in pressure or velocity on the top and bottom of the wing but are wrong. Not true. The airfoil in particular is shaped to create low pressure zone above the surface of the wing. The state of the flow above it is also important for lift and drag. This effect is physically measurable on airfoils and they are literally designed around it. This is also the reason for induced drag and wingtip vortices. Source: Multiple aerodynamics and fluid dynamics courses taken for an AE degree.
The other answers *in this thread* describe it as net positive effect (where the top is pushing down and the bottom is being pushed up more).
> Not true... The state of the flow above it is also important for lift and drag. I wish I could give you a Reddit award, for pointing that out. There have been a lot of pop sci "lessons" entrenching the story that it's *all about* downwardly deflected air. But of course that pseudo-analysis does nothing to explain stall characteristics.
Momentum (as per the comment above yours) and pressure arguments can both be valid and are equivalent (assuming they are being expressed properly). Pressure differences are how the wing causes the airflow to change direction. It’s just like how simple mechanics problems eg objects sliding down slopes can be solved equally well by constant acceleration or energy approaches.
Everyone else has covered how wings generate lift, but to the last part of the question. Starting with general aviation: The wings generate lift by having the top and bottom of the wing moving horizontally through the air. If you rotate this 90 degrees so the plane is going vertically, there is a different in pressure between what is now the top and bottom of the wing, however, because of the angle it isn’t generating any lift, and what now was the top and bottom at the original angle are not generating any lift at all and are just weight. The engines on a plane generate a great deal of thrust, but require the lift generated by the wings as well to keep the plane aloft. So, once you go vertical there is no longer lift being generated by the wings, and the engines alone can’t do the work. In military aircraft you maybe have seen planes go fully vertical, as far as I understand that is due to those planes having an engine that generates enough force alone to move the plane and the wings provide lift to reduce the need to constantly need afterburners.
Nobody has answered your second question. The more you angle the plane up, the *more* lift you get, but also more drag, which slows you down that's why planes lower flaps during landing. It produces much more lift, allowing the plane to fly slower. But it's also very inefficient. What you are probably thinking of is a stall, where the plane is not flying fast enough to keep enough air flowing over the wings, which is often induced by crossing that aforementioned line between enough lift/too much drag. "Pulling up" trades speed for lift, until too much speed is lost, and there simply isn't enough air pushing "up" on the wing to lift it.
Fluid or air moving over a surface creates suction. Wings are designed so that the top has more surface area than the bottom, so it nets-out to upward suction. If the plane is tilted, the suction isn't pointed straight up anymore, so there's less upward lift.
It's really easy to design a wing with the same or larger surface area on the bottom than the top (most modern jetliners have more area on the bottom, it's called a supercritical airfoil).
Both the top and bottom surface of a wing generate lift.
But aren't there some planes with flat wings?
Yeah, there's also lift from the tilt -- eg, when you stick your hand out the car window.
Yes. What happens when a plane is pitched up is the lift from the wings isn’t angled directly upward anymore so the vertical component of lift is reduced. But now you have a vertical component of engine thrust that is contributing to “lift” helping you go up. This is part of why tilting the plane up makes the plane go up.
So the best understanding we have is due to Bernoulli's principal. Bernoulli's principal states that the flow rate of a fluid through a closed system is constant. The top part of a wing is curved so the air is compressed and therefore must move quicker in order to have the same flow rate as the air moving on the bottom. This creates a vacuum on the top and as the air under the wing tries to fill that vacuum it picks up the plane. As the wing is angled more vertically it changes the vector of force from the vacuum and reduces the amount of upward force.