Why we don’t understand heavier-than-air flight • Hacker News Board

Re: Why we don’t understand heavier-than-air flight

#111

Post by zazen » Sat, Jun 26, 2021, 6:09 PM UTC

afterburner wrote: post #108

zazen wrote: post #97

Earlier quoted context omitted.

> If you are asserting that the angle of attack does not affect the lift, you are wrong. I am certainly not asserting that, and I'm baffled how you could have formed the impression that I was. You appeared to be attempting to rebut an argument in favour of the significance of angle of attack. We have another pointless internet misunderstanding on our hands.

I am replying to this: "I usually just answer Socratically: "So how can (some) planes fly upside-down?" whenever I encounter the Bernoulli-adherents." Which is a lazy and garbled gotcha attempt.

It is a lazy gotcha attempt. It is a lazy attempt at gotcha-ing someone who believes angle of attack ISN'T important. Unless you think a plane flying upside-down is somehow evidence AGAINST the importance of angle-of-attack?

Again: this entire pointless misunderstanding has arisen because you didn't see - apparently STILL HAVEN'T SEEN - which side of the debate the comment you replied to is arguing for.

Re: Why we don’t understand heavier-than-air flight

#112

Post by jjk166 » Sat, Jun 26, 2021, 6:12 PM UTC

stensonb wrote: post #53

Would be curious to get a physicist's explanation of how the Coanda effect relates: https://en.m.wikipedia.org/wiki/Coand%C4%83_effect

The Coanda effect is not directly related to lift but it is why airfoils have that distinctive shape. Because of the coanda effect, the air will follow the curves of both surfaces of the wing, and the two flows will recombine at the rear. This allows the flow to be pointed in a different direction after passing across the ring. This change in direction induces rotation of the air. This rotation is the true source of lift.

Re: Why we don’t understand heavier-than-air flight

#113

Post by laurent92 » Sat, Jun 26, 2021, 6:19 PM UTC

salawat wrote: post #69

laurent92 wrote: post #64

Earlier quoted context omitted.

> I learned multiple times. Everytime I understood less of it. Isn’t that how to spot seniority? The junior says “I know ReactJS and SpringBoot!” The senior says: “I don’t know much…” Unrelated, but that reminds me how my Masters Degree teachers touted the importance of their subject in their introduction course, all explaining the Ariane V explosion from a completely different angle: - The measurements professor: “A…

>They were all right. Or rather, they were all wrong: Everyone knows Ariane V exploded because the officer pushed a red button ;) ...and this is why learning the value of drawing the boundaries and selecting stop points in the analysis of complex topics, and the employment of humor is a powerful rhetorical tool. This is why you composition is the most important topic this semester! Sorry... Couldn't resist. Also, wha…

> Also, what school teaches QA These days?

Interesting question! INSA Lyon in France, but that was in 2005, you could mock that the Old Continent does a lot of V-Cycle waterfall projects and had missed the Agile turn of 2001.

BUT learning how processes help is, instead, a very important step to judge what exactly we give up with Agile.

The irony is I went on creating software for requirements, and I can testify that all of the hardware industry does QA more diligently than ever!

Re: Why we don’t understand heavier-than-air flight

#114

Post by [deleted] » Sat, Jun 26, 2021, 6:20 PM UTC

Anarch157a wrote: post #75

Retric wrote: post #48

Earlier quoted context omitted.

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.

[deleted]

Re: Why we don’t understand heavier-than-air flight

#115

Post by drwiggly » Sat, Jun 26, 2021, 6:20 PM UTC

adtac wrote: post #79

lowkey wrote: post #68

Earlier quoted context omitted.

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.

Is it possible to think of.. the roundness on the front disrupting the airflow over the top causing air to become turbulent and less dense on the top. Where as the air flow under the wing high higher relative density and the wing will rise to the less dense position?

Re: Why we don’t understand heavier-than-air flight

#116

Post by jjk166 » Sat, Jun 26, 2021, 6:34 PM UTC

Lift is the result of induced rotation of the fluid. Both the higher speed of airflow over one side of a cambered airfoil (bernoulli) and the redirection of the airflow (newton) are results of this, not causes. This is also why you get wingtip vortices, why flettner rotors work, why curveballs curve, and many other such readily observable phenomena. This has been well understood for over a century.

Re: Why we don’t understand heavier-than-air flight

#117

Post by defaultname » Sat, Jun 26, 2021, 6:38 PM UTC

jjk166 wrote: post #101

defaultname wrote: post #74

Earlier quoted context omitted.

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.

Wings can and generally do have zero degree angle of attack lift.

The 747 wing is at a 2° incidence angle relative to the body, which allows the body to be level with the direction of travel at cruising altitude/speed. An Airbus A320 has an incidence angle of about 5° at the body, twisting to -0.5° at the tip (many aircraft have such complex wings, but the aggregate is an important incidence angle). Every Cessna has a significant incidence angle.

The overwhelming majority of aircraft have an incidence angle relative to the body for the reason stated. So rather by "typically", could you name a single aircraft that doesn't have such an incidence angle? An SR-71?

As to "0 degrees angle of attack lift", such lift is close to negligible. Maybe you mean the body of the aircraft is zero degrees, but then we loop back to the core point again.

Re: Why we don’t understand heavier-than-air flight

#118

Post by robotresearcher » Sat, Jun 26, 2021, 6:40 PM UTC

graderjs wrote: post #27

Isn'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…

A defining characteristic of a plane is that it is not continuously falling. Falling can’t really be the explanation, since they don’t.

Re: Why we don’t understand heavier-than-air flight

#119

Post by mbrameld » Sat, Jun 26, 2021, 6:44 PM UTC

jjk166 wrote: post #101

defaultname wrote: post #74

Earlier quoted context omitted.

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.

Wings can and generally do have zero degree angle of attack lift.

Wings, at least on small civil aircraft, generally DO have a positive angle of incidence where angle of incidence is defined as the relative angle between the chord line of the wing and the longitudinal axis of the fuselage.

Re: Why we don’t understand heavier-than-air flight

#120

Post by jjk166 » Sat, Jun 26, 2021, 6:45 PM UTC

AstralStorm wrote: post #20

NickNameNick wrote: post #12

Earlier 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…

It does move faster. This can be readily observed in wind tunnel tests, and is a source of many issues once you get into transonic flight when the airflow can reach supersonic speeds while the plane in subsonic. Flat wings must be inclined to cause the air on the top side to move faster. The vortices cause air to move at different rates.