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

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

#61

Post by twirligigue » Sat, Jun 26, 2021, 3:20 PM UTC

lowkey wrote: post #56

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…

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 couldn't understand it.

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

#62

Post by HPsquared » Sat, Jun 26, 2021, 3:21 PM UTC

handrous wrote: post #57

k__ wrote: post #52

Earlier quoted context omitted.

Reminds me of learning what electricity is. I learned it multiple times. In middle school, in high school, in university, on youtube explained by a quantum physicist. Everytime I understood less of it.

I once read a book called "There Are No Electrons". I'm not sure I'd recommend it, but its approach was interesting: the author reasons that unless you're in grad school studying physics (and perhaps even then), everything you've been taught about electricity is a lie anyway, so the author attempts to present a framework of easier to understand lies intended to make the reader able to better reason about and predict…

For everyone other than the aforementioned physics grad student, it's a lie. For the physics grad student, it's a mystery.

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

#63

Post by [deleted] » Sat, Jun 26, 2021, 3:22 PM UTC

anvandare wrote: post #60

lowkey wrote: post #56

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.

[deleted]

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

#64

Post by laurent92 » Sat, Jun 26, 2021, 3:36 PM UTC

k__ wrote: post #52

garmaine wrote: post #16

Earlier quoted context omitted.

We understand flight perfectly well. Although the common explanations are often BS.

Reminds me of learning what electricity is. I learned it multiple times. In middle school, in high school, in university, on youtube explained by a quantum physicist. Everytime I understood less of it.

> 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: “Ariane V crashed because engineers tripped themselves into different imperial/metric units, this is why Measurements & Precision is the most important topic!”

- The programming teacher: “They fit a long inside an integer and it looped to negative, which inverted the trajectory of Ariane V and triggered its destruction, this is why learning C properly is the core of your teaching this year.”

- The quality assurance teacher: “They didn’t check the contract of the component! This is why QA is the most important when creating big systems!”

- The management teacher: “It’s the story of two teams who designed two components with different assumptions, one team worked in imperial units and they didn’t communicate clearly about assumptions, that’s why management is the one topic you should really work on.”

They were all right. Or rather, they were all wrong: Everyone knows Ariane V exploded because the officer pushed a red button ;)

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

#65

Post by scarier » Sat, Jun 26, 2021, 3:37 PM UTC

GuB-42 wrote: post #43

oolonthegreat wrote: post #31

I didn't understand what we don't understand about hta flight but maybe that's just me.

- Most of the popular explanations are misleading, the others are incomplete. - The real answer is so hard to compute that there is a million dollar prize attached to it. - Today, we design planes using approximations and trial-and-error. It works well because we are very experienced in designing planes, sometimes at the cost of many lives, but it is not exactly a "first principles" approach.

I mean, you can get deep into epistemology and argue that it's impossible for anyone to truly know anything, and tautologically all of engineering requires approximation in some way, but our modern understanding of aerodynamics is absolutely a "first principles" approach (the principles being conservation of mass and momentum in a viscous fluid), even if there are still some aspects of trial-and-error on the aircraft hardware level. Despite the open mathematical problem of the existence and smoothness of Navier-Stokes that you mentioned, the equations are a fantastic tool that have enabled us to make startlingly accurate calculations of lift, drag, stability, and performance, despite our inability to do direct numerical simulation at the Kolmogorov scale on usefully-sized things.

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

#66

Post by S_A_P » Sat, Jun 26, 2021, 3:46 PM UTC

tempestn wrote: post #3

bcaa7f3a8bbc wrote: post #2

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…

As others have said it’s not really the shape of the wing that matters. Some shapes work better but I’ve always thought of it as more of a fluid density problem. As you increase speed the wing is in contact with a larger mass of air which at some critical point becomes large enough to support the weight of the aircraft. After you hit that speed then you are just manipulating the air flow to steer the craft. Holding your hand out of the window at highway speeds really makes it feel more intuitive to me. Of course I could also be completely wrong here.

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

#67

Post by tdy721 » Sat, Jun 26, 2021, 3:47 PM UTC

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!

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

#68

Post by lowkey » Sat, Jun 26, 2021, 3:49 PM UTC

twirligigue wrote: post #61

lowkey wrote: post #56

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…

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 below, and that since the upper particle would therefore have to travel faster than the lower particle the pressure differential would cause lift.

The problem is the theory doesn’t hold up under testing because it isn’t true.

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

#69

Post by salawat » Sat, Jun 26, 2021, 3:50 PM UTC

laurent92 wrote: post #64

k__ wrote: post #52

Earlier quoted context omitted.

Reminds me of learning what electricity is. I learned it multiple times. In middle school, in high school, in university, on youtube explained by a quantum physicist. Everytime I understood less of it.

> 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, what school teaches QA These days?

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

#70

Post by beckingz » Sat, Jun 26, 2021, 4:01 PM UTC

HPsquared wrote: post #62

handrous wrote: post #57

Earlier quoted context omitted.

I once read a book called "There Are No Electrons". I'm not sure I'd recommend it, but its approach was interesting: the author reasons that unless you're in grad school studying physics (and perhaps even then), everything you've been taught about electricity is a lie anyway, so the author attempts to present a framework of easier to understand lies intended to make the reader able to better reason about and predict…

For everyone other than the aforementioned physics grad student, it's a lie. For the physics grad student, it's a mystery.

Turns out, the world is really really complicated.

So it's better to say that our models are simplified, not lies.