Air moves faster on the upper side , creating a pressure differential.
A common and wrong explanation. The pressure differential is created by the fact that the air is being pushed into the lower side of the wing. It's much simpler than that anyway. The wing forces the air downward, so the plane must be forced up.
Overall you are correct that the plane receives an upward force due to the air it interacts with, and that the air receives an equal amount of force downward. In level flight the vertical force components must equal zero (or the plane falls/rises).
But equally, if the plane is forced up, the air must be forced down. Cause and effect are not obvious from a force diagram.
Note: The author is not entirely serious. It's part of a series called Mystifications: A short series of semi-satirical pop science articles, called "Here's why we don't understand". The science presented is mostly accurate. The first article was "we don’t understand electricity" and now it's "we don’t understand flight". You'll find the articles more enjoyable if you think of it as a thought experiment about the dep…
In this case I took it to be poking some fun at the two conflicting 'intuitive' explanations for a wing producing lift: one being that air strikes the bottom of the wing as it moves forward, pushing upward on it, and the other being that air moves faster under the flat underside of the wing than over the curved upper side, causing a pressure differential. Of course reality is more complex than either simple answer, a…
The sad thing is, "the air hitting bottom of wing > top where bottom is determined in reference to the side of the aircraft least distant from the Earth's surface assuming an experiment in Earth's atmosphere" is really the most concise and relevant explanation given all of the factors at work. At least until we start encountering significantly more dense atmospheres that mysteriously do not sink under realistic conditions and start trying to fly planes through them. You fly because you're a flat thing skipping off what essentially becomes a more dense surface underneath you than above you. If you didn't, you wouldn't be flying. You'd be falling. And yes, here's a crap ton of math, try not to think about it too hard.
Rocketry is heavier than air flight. I submit we discovered it before lighter than air flight. I will hazard that I do have a nice understanding of how it works. I learned it from media like this: https://youtu.be/X4iMeKif488 I do think you’re dead wrong!
The common connotation of "heavier-than-air flight" and "lighter-than-air flight" is that air is the medium in which the flight takes place, and that air is essential for the flight to happen. The science of aerodynamics is necessary for describing how such flight works.
That's not true for rockets. Rockets can fly in air, and a rocket's fins only work in air, but rockets don't have to use fins and rockets work fine in the vacuum of space. Because air is mostly irrelevant to rockets -- and rockets [in space at least] fly by principles that have nothing to do with aerodynamics -- rockets are not typically included in discussions of how "heavier-than-air flight" works.
Its complex...The example normally given is, the wing is shaped a little flat in the under side and curved on the top. So that would explain the flow as you mentioned. However when an airplane flies upside down, its not sucked into the ground ;-) It seems nobody really knows: "No One Can Explain Why Planes Stay in the Air" https://www.scientificamerican.com/article/no-one-can-explai... Edit: Added brief from article…
If an aircraft flies level upside down it will lose altitude towards the ground (as opposed to right side up wherein given adequate thrust it should keep its current altitude). In order to stay at a fixed altitude upside down you have to bring the nose of the aircraft up several degrees (increasing based on air speed).
Every aircraft has the wing set at an incident angle relative to the axis of the fuselage. Usually to generate enough deflection force for level (relative to the fuselage) flight at cruising speed.
Upside down flight requires you to basically inverse this deflection, but it isn't because of Bernoulli lift.
Its complex...The example normally given is, the wing is shaped a little flat in the under side and curved on the top. So that would explain the flow as you mentioned. However when an airplane flies upside down, its not sucked into the ground ;-) It seems nobody really knows: "No One Can Explain Why Planes Stay in the Air" https://www.scientificamerican.com/article/no-one-can-explai... Edit: Added brief from article…
It’s a common misunderstanding that the underside of a wing is flat and the top part curves. A paper airplane with thin flat wings still gets lift though there are several issues trying to scale this up. Similarly many aircraft will happily fly upside down. Wings need to support the weight of your aircraft while being light this means they need to be reasonably thick especially using the obvious choice of storing fue…
Kelly Johnson caused a stir in the engineering community when he came up with the F104 Starfighter, with it's thin and almost flat wings.
Because the pressure on the top is lower :) (this is half-serious: the whole problem with these explanations is that cause and effect for all of these variables is not straightforward: you can see from the navier-stokes equations they are all dependent on each other).
Kind of. Actually the real ‘cause’ in my understanding is 1) the curved geometry of the suction (upper) side of the aerofoil and 2) the fact that the flow remains attached to it. Everything else - you can actually approximate the curved surface to a circle and apply equations of circular motion to a parcel of air to satisfy yourself with why the flow is accelerating. And Newton’s 3rd law explains how lift is generate…
The devil is in that last detail. "Flow stays attached" is a description of the properties of the flow, not an explanation for what causes attached flow or why attached flow matters. It's semicircular reasoning to say that the plane gets lift because the flow stays attached... Attached flow and lift are correlated, but they may be two phenomena caused by the same underlying property.
Can confirm. I worked at Pratt & Whitney testing jet engines early in my career. At the time I read a similar article and spread it amongst my colleagues - the cognitive dissonance was palpable. As engineers we had been taught that lift was due to air above the wing traveling faster than air below the wing and thus creating lift by way of a pressure differential. The more accurate answer as seen in the article is tha…
I usually just answer Socratically: "So how can (some) planes fly upside-down?" whenever I encounter the Bernoulli-adherents.
Has someone taken an rc airplane and turned the wing upside down and flown it? It should be pretty easy to demonstrate.
Can confirm. I worked at Pratt & Whitney testing jet engines early in my career. At the time I read a similar article and spread it amongst my colleagues - the cognitive dissonance was palpable. As engineers we had been taught that lift was due to air above the wing traveling faster than air below the wing and thus creating lift by way of a pressure differential. The more accurate answer as seen in the article is tha…
I usually just answer Socratically: "So how can (some) planes fly upside-down?" whenever I encounter the Bernoulli-adherents.
Because there is not up or down for the wing when its cutting through a fluid. It is not that we have seen planes flying intercontinental flights upside down.
And those upside down events do not happen at 10 feet above ground. There is plenty of fluid (air) above and below the aircraft and power (fighters jet engines are the most powerful ones on aircrafts) to be able to correct any up-downward force with flaps (basically walls to air)
As a child I used to stick a school ruler out of the back window of the car and rotate it slightly to make it move upwards, like a plane's wing. Intuitively I felt that this happened because it was pushing some of the horizontal airflow downwards and the air was pushing back up on the ruler. Yet the books I read about aeroplanes referred to something called Bernoulli's principle which was pretty demoralising because…
I suspect, like many other things that didn’t make sense - the reason was that it wasn’t actually true. The Bernoulli effect explains that lift is due to the design of the wing such that the path above the wing is longer than the path below the wing. This coupled with the fact that due to the Bernoulli effect an air particle just above the wing would reach the back of the wing at the same time as an air particle just…
Isn't Bernoulli's principle only applicable when talking about the same flow? I've always found the "above path is longer than the lower path" explanation to be unintuitive because we're not talking about the same flow. They're separate flows.
It’s a common misunderstanding that the underside of a wing is flat and the top part curves. A paper airplane with thin flat wings still gets lift though there are several issues trying to scale this up. Similarly many aircraft will happily fly upside down. Wings need to support the weight of your aircraft while being light this means they need to be reasonably thick especially using the obvious choice of storing fue…
Kelly Johnson caused a stir in the engineering community when he came up with the F104 Starfighter, with it's thin and almost flat wings.