I understand that the wing of the plane creates downforce, lifting the plane into the air, so how do planes fly upside-down? Wouldn’t the wings start pushing the plane down into the ground once flipped?
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The airfoil thing is a lie propagated by people who want to sound smart. You can fly upside down or right side up with a flat wing. Just keep the angle of attack positive.
When a plane is flying level, the wings are actually tilted up – the leading edge is higher than the trailing edge. This is how the plane is built. So, if you fly upside down, the wings would tilt down, and if you didn’t do anything, the wings would indeed start pushing you to the ground.
However, if you adjust the orientation of the plane while it is upside down, it is possible to get the wings angled so that once again the leading edge of the wing is higher than the trailing edge. If you do that, the wing will once again start lifting the plane, even though it is upside down.
The force created by a flat moving object pushing against the air, doesn’t care if it is “upside down”
Not wings themselves generate uplift, the wings cutting trough the air and creating high pressure on one side, low pressure on the other do.
Side doesn’t matter, the direction of the plane doesn’t matter.
If a plane flipped upside down, the “top” of the wing is thet is pushing against the air.
Angle of Attack, using the wing to defect the air in a manner that makes the aircraft to go where you want.
I mean, there’s the whole high speed/low speed of air causing lift and all that, but my understanding is that it quite a small part of it. The AoA is like 90%+ of ‘lift’.
A lot of it is due to angle of attack, from what I understand
If you have a situation like → where the arrow is wind and the line is the wing, you can imagine that the air will hit it and go down. If the air goes down, the wing goes up, so you generate lift
This is only true up to a certain point when the air separates from the wing above it, but that’s not relevant now
In real planes, the wing isn’t just a straight line because there are other effects that can generate lift, so it can be more efficient. With that said, if you fly upside-down and give yourself enough angle of attack, you can overpower the lift from the shape of the wing and generate lift upside-down. It’s more difficult to fly like that for many reasons, but it’s possible on some planes for a short time
It’s like nobody knows how planes fly, yet they still do…
This (https://www.youtube.com/watch?v=edLnZgF9mUg&t=2663s&ab_channel=MITOpenCourseWare) aggressively says that IT’S NOT due to Bernoulli’s principal and that it’s a false theory, but then this (https://www.youtube.com/watch?v=E3i_XHlVCeU&t=616s&ab_channel=TheEfficientEngineer) contradicts it…
Angle of attack (or angle to the wind) is important to create lift. Think about how a kite works. You can flip a kite upside down and itll work the same.
Any surface with a reasonably sharp trailing edge can generate lift with a positive angle of attack. The sharp trailing edge is important because it causes the flow to separate cleanly (the Kutta Condition). There will be a range of angles of attack from somewhat positive to somewhat negative where it will work well, and the lift increases/decreases (including being negative) with angle of attack. If that range is exceeded, the flow will separate from the suction surface (the one that has low pressure) leading to stall.
for a straight section with no camber, at zero incidence it will produce zero lift, and positive lift at positive incidence, and negative lift at negative incidence. This kind of neutral symmetrical section is useful for things like the vertical stabilizer.
If the airfoil section has camber (curvature so the wing bows upwards from leading to trailing edge), it will be biased towards producing positive lift at zero incidence, but if the incidence is sufficiently legation, it will still have a regime of producing negative lift at sufficiently negative angles of attack (meaning positive lift for an inverted aircraft). It will be less efficient (more drag) and have less range (ie the lift can increase with angle of attack less before stall), but it is sufficient to allow a plane to fly inverted.
There are three guys keeping an aircraft in the air (and two of them rides on the back on the first one):
* Newton. The wing has an angle of attack. Basically, it’s tilted, so it pushes the air downwards. Newton has the law of action and reaction. Air is pushed down, so the wing is pushed up. You can look at simple model aircraft, which has a flat wing profile, for a clean example of this.
* Bernoulli. The wing has a profile which is longer on the top side, which means the same amount of air needs to be spread over a larger area, so lower pressure. Air is sucked down. In pops Newton and says “Something is going down, something must go up!” and that’s the wing going up.
* Coanda. The wing has a curved profile. A flow tends to follow a curved surface (try the back side of a spoon under a water faucet). This means that the air will follow the top side of the wing downwards. Once again, Newton stomps in and proclaims “Air is going down, wing must go up!”.
All these effects work together, and depending on what you are doing (speed, attitude, height, wingload and so on), there will be more or less of each of them.
So, enough basics, back to flying up side down:
Bernoulli isn’t much use here, but if the plane lifts its nose a bit more (relative the horizon), the wing will have a higher angle of attack. In this situation, Newton and Coanda steps in and saves the day, because their principles will still push air downwards, and thus moving the wing upwards.
Bernoulli isn’t completely out, though. When you change the angle of attack like this, the leading edge point of the wing moves a little bit (hard to put in words, but if you look at a wing profile and tilt it, you’ll see it), so that it cuts the air stream a bit more evently. It doesn’t really make much lift, but it helps reduce the downforce the Bernoulli effect would otherwise create.
Some aerobatic planes have a symmetric wing profile, and, of course, that works equally well in either orientation. It isn’t as effective, but they aren’t built for efficiency, they are build for agility in all orientations.
The shape of the wing, the dynamic pressure on the wing which is determined by velocity and air density (where velocity plays a bigger role), the surface area of the wing and the angle of attack create lift.
Jets have high velocity thrusts and computer controlled control surfaces that can dynamically alter wing surface profiles, angle of attacks as well as thruster directions to sustain flight even when inverted.
Air hits wing, air directed under wing gets pushed down, wing gets lift.
Air above wing creates a low pressure zone, can creature turbulence and eddies that add to drag.
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