4 ms·

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

progfix 5y ago
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.
- yiyus 5y ago
  > It is the turbulence that create the uplift on a wing You can have lift with laminar flow. In fact, the article includes an explanation of the usage of the Reynolds number to characterize laminar and turbulent flow and how the flow around plane wings is clearly laminar (called "smooth" in the article).
GuB-42 5y ago
- 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.
- scarier 5y ago
  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.
yarcob 5y ago
I have the same feeling. I think what people usually mean when they say that we don't understand flight is that there are no simple equations. A lot of physical problems have elegant solutions (eg. the shape of a hanging chain is roughly the cosh function). But there are no elegant equations that describe the profile of a wing, so it's a bit unsatisfying.

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.

yiyus 5y ago
> It is the turbulence that create the uplift on a wing You can have lift with laminar flow. In fact, the article includes an explanation of the usage of the Reynolds number to characterize laminar and turbulent flow and how the flow around plane wings is clearly laminar (called "smooth" in the article).

GuB-42 5y ago

- 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.

scarier 5y ago
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.

yarcob 5y ago

I have the same feeling. I think what people usually mean when they say that we don't understand flight is that there are no simple equations. A lot of physical problems have elegant solutions (eg. the shape of a hanging chain is roughly the cosh function). But there are no elegant equations that describe the profile of a wing, so it's a bit unsatisfying.