I didn't understand what we don't understand about hta flight but maybe that's just me.
Why we don’t understand heavier-than-air flight
31–40 of 178 posts
Re: Why we don’t understand heavier-than-air flight
#32Earlier quoted context omitted.
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…
Almost nobody understands software then, by this definition.
Software is definitely still a craft, not engineering in the build-a-bridge sense.
So I would say, nobody really understands software, but many people have experience and total experience is growing. Via new languages, algorithms, patterns, etc.
The rapid experience advancement suggests there is a lot unknown and not understood.
Re: Why we don’t understand heavier-than-air flight
#33Isn't it because planes are continually falling (because gravity), and this leads to two things: 1) wings increase the surface area pushing down (gravity) on the air below, which pushes back (air pressure), and 2) as wings are falling toward ground (gravity), they create vortices above the wing, which lowers the pressure, increasing the push up effect of the air below, and at a certain speed, the vortices are stabili…
This is not how it works, no falling or positive angle of attack is required for an asymmetrical aerofoil. Imagine swinging a bucket of water over your head - the force your arm feels is similar to what the top surface of the wing feels.
Re: Why we don’t understand heavier-than-air flight
#34Earlier quoted context omitted.
Air moves faster on the upper side , creating a pressure differential.
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).
Re: Why we don’t understand heavier-than-air flight
#35The 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…
Not an expert or anything. Never studied aerodynamic or flight in depth.
As far as I understand, for helicopter to fly, it definitely has to have thrust to weight ratio greater than one. Flying things that have thrust to weight ratio > 0 are intuitive to me. They generate force and stay in the air indefinitely.
Planes obviously don't require that to fly. So, they're different type of beast. They somehow squeeze more from less, exploiting some nonlinearity in forces that air exhibit on wings. I can understand that too, but the nature of that phenomenon is not explained anywhere (other than in words: this is the formula. It is correct, trust us)
Re: Why we don’t understand heavier-than-air flight
#36Earlier quoted context omitted.
This is true of a symmetrical aerofoil (e.g. most helicopters) but not for an asymmetrical aerofoil (most fixed wing aircraft). It is true that a slightly positive angle of attack generates more lift than none (because the pressure/lower side starts making a contribution)
Correct. Still incomplete. Angle of attack causes a vortex at the trailing edge which has nothing to do with raw air speed and everything to do with fluid dynamics (which involves speed but is much more complex) Short version is that you created a hole (lower pressure area) in air which it now tries to fill. Air and gasses have finite limited velocity known as speed of sound, which is why you get these pressure diffe…
I’m not sure I fully agree. Do you not get this trailing edge vortex with an asymmetrical aerofoil at 0 angle of attack? (Just less strongly because less pressure difference between suction and pressure sides)
Re: Why we don’t understand heavier-than-air flight
#37I didn't understand what we don't understand about hta flight but maybe that's just me.
We don't know how to calculate turbulence, we can only predict it. It is the turbulence that create the uplift on a wing, so the author says we don't understand it.
Re: Why we don’t understand heavier-than-air flight
#38Isn't it because planes are continually falling (because gravity), and this leads to two things: 1) wings increase the surface area pushing down (gravity) on the air below, which pushes back (air pressure), and 2) as wings are falling toward ground (gravity), they create vortices above the wing, which lowers the pressure, increasing the push up effect of the air below, and at a certain speed, the vortices are stabili…
This is not how it works, no falling or positive angle of attack is required for an asymmetrical aerofoil. Imagine swinging a bucket of water over your head - the force your arm feels is similar to what the top surface of the wing feels.
Is that so? I thought that for asymmetric airfoil, zero angle of attack is by definition the angle where it creates no lift. So, tautologically, if it's creating lift a (positive) angle of attack is required.
Re: Why we don’t understand heavier-than-air flight
#39Earlier quoted context omitted.
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 rega…
For anyone who’s ever tried building a robotic bird, there is a lot more intricacy to how birds fly than just “pushing air”. A better article might have been, ‘we still don’t understand how certain species of bird fly so efficiently’
Re: Why we don’t understand heavier-than-air flight
#40The 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…
Not an expert or anything. Never studied aerodynamic or flight in depth. As far as I understand, for helicopter to fly, it definitely has to have thrust to weight ratio greater than one. Flying things that have thrust to weight ratio > 0 are intuitive to me. They generate force and stay in the air indefinitely. Planes obviously don't require that to fly. So, they're different type of beast. They somehow squeeze more…
It's the exact same principle for planes and helicopters.
If a plane isn't producing more lift than weight it will fall, just like a helicopter. Planes work by pushing a wing through the air, helicopters by spinning it. In both cases the wing has to push down enough air to keep the aircraft in flight.