Seems like rockets and bullets somehow don't count as being heavier-than-air flight. Maybe they should say we don't understand aerodynamic lift?
rockets and bullets don't fly. They [free]fall.
Rockets fly, although they use thrust rather than lift.
Why we don’t understand heavier-than-air flight
11–20 of 178 posts
Re: Why we don’t understand heavier-than-air flight
#12Earlier quoted context omitted.
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…
Air moves faster on the upper side , creating a pressure differential.
Why does the air move faster on the upper side of the wing?
It's not because there's a magic force that requires air particles parted be the leading edge to rejoin thier partner at the trailing edge.
The air particles on the upper surface reach the trailing edge much sooner than the ones under the wing.
Re: Why we don’t understand heavier-than-air flight
#13The continued assertion that "we don't understand heavier-than-air flight" is a weird one. The article even skates around this, saying (essentially) "well maybe we do understand it, but chaos theory!" If you're in the sky and you want to stay there, you have to counteract gravity. Heavier-than-air flight does this by pushing down on air. Want to stay in the sky? Push down on enough air, fast enough, and you will stay…
"We know how heavier-than-air flight works, but I want to be pedantic and nerd about some physics"
That title doesn't get quite as many clicks unfortunately.
Re: Why we don’t understand heavier-than-air flight
#14The continued assertion that "we don't understand heavier-than-air flight" is a weird one. The article even skates around this, saying (essentially) "well maybe we do understand it, but chaos theory!" If you're in the sky and you want to stay there, you have to counteract gravity. Heavier-than-air flight does this by pushing down on air. Want to stay in the sky? Push down on enough air, fast enough, and you will stay…
Knowing Newtonian physics doesn't mean we understand all things that move.
The point about "not understanding" flight is that, if we truly understood it, we could design the optimal aircraft from first principles before it ever entered a wind tunnel. Instead, we work based on incrementally improving tribal knowledge of what has worked in the past and try to make something similar to fit our desired flight envelope.
Compared to something like rocket science where the entire craft can be built on a computer and we'll know exactly how much cargo we can get to the moon without even turning a single screw, we don't understand flight.
Re: Why we don’t understand heavier-than-air flight
#15Note: 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…
When I was a teen I asked my dad who was an aerospace engineer. He said there is just more than one way to calculate the result.
Though I think it's more valid to think of the wing as imparting a downward momentum on the air flowing over it. Meaning it's really a reaction engine.
Re: Why we don’t understand heavier-than-air flight
#16Note: 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…
Hm, I was hoping this article would explain in what sense we don't understand flight, or in what sense people think we don't understand flight, but it didn't seem to answer that question...
We understand flight perfectly well.
Although the common explanations are often BS.
Re: Why we don’t understand heavier-than-air flight
#17Earlier quoted context omitted.
Air moves faster on the upper side , creating a pressure differential.
Why does the air move faster on the upper side of the wing? It's not because there's a magic force that requires air particles parted be the leading edge to rejoin thier partner at the trailing edge. The air particles on the upper surface reach the trailing edge much sooner than the ones under the wing.
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).
Re: Why we don’t understand heavier-than-air flight
#18Earlier quoted context omitted.
[flagged]
Though I don't know what idea he was referring to, tides can be pretty hard to predict accurately. Obviously nothing to do with God, but it's probably fair to say there are aspects of them we don't understand or at least can't simulate arbitrarily far into the future. "In an analysis of the tides in Venice Lagoon, at the head of the Adriatic Sea, where the tides seem to pick up because of near-resonancy of the basin,…
This was the video in question: https://m.youtube.com/watch?v=HABNe7_D22k?t=1m52s. It's not about predicting the exact movement of tides, he's arguing science fundamentally can't explain the regularity of tides...
Re: Why we don’t understand heavier-than-air flight
#19The continued assertion that "we don't understand heavier-than-air flight" is a weird one. The article even skates around this, saying (essentially) "well maybe we do understand it, but chaos theory!" If you're in the sky and you want to stay there, you have to counteract gravity. Heavier-than-air flight does this by pushing down on air. Want to stay in the sky? Push down on enough air, fast enough, and you will stay…
Knowing Newtonian physics doesn't mean we understand all things that move. The point about "not understanding" flight is that, if we truly understood it, we could design the optimal aircraft from first principles before it ever entered a wind tunnel. Instead, we work based on incrementally improving tribal knowledge of what has worked in the past and try to make something similar to fit our desired flight envelope. C…
I don’t think this is true. There are many physical ststems for which we know the underlying physics very well, but the equations can’t be simply solved, and numerical simulation is more costly than just building the damn thing and testing it. Wing lift under turbulent conditions is one of those things. So we use wind tunnels. Not because we don’t understand lift—we do—but because it’s just easier.
This is getting less and less true with each generation of supercomputers though.
EDIT: There is perhaps a better way of explaining it for this crowd though. To use numerical modeling to predict performance is to take a physical problem and turn it into a computational problem. And while engineers understand physical systems pretty damn well, us computer scientists have largely failed at the objective of making software systems with hard reliability guarantees. You can write a fluid dynamics simulation to test your new wing design, but how do you know that the simulation does what you think it does? Even if the code has been tested before, how do you know you're not now hitting some sort of edge case?
At the end of the day, you have to build the damn thing to test it. Numerical simulation are used more and more these days as the codes are refined, computers get more powerful, and engineers have more trust in their capabilities. But traditionally, and still a lot of the time, they build prototypes and test in wind tunnels because reality never fails to model physics accurately.
Re: Why we don’t understand heavier-than-air flight
#20Earlier quoted context omitted.
Air moves faster on the upper side , creating a pressure differential.
Why does the air move faster on the upper side of the wing? It's not because there's a magic force that requires air particles parted be the leading edge to rejoin thier partner at the trailing edge. The air particles on the upper surface reach the trailing edge much sooner than the ones under the wing.
Does not move faster either. Otherwise, a flat wing would not work, and they do.
Gravity or force creates the pressure differential. Wing pushes on air below it. (Why birds fly.) Additionally, for moving wing, edges create vortices that create local pressure differentials. (Why helicopters and planes and birds work better than floating pieces of paper.)
Wings work very similarly to performance ship hulls in this regard.