4 ms·

> Why would pressure (Bernoulli out of Euler) propagate supersonically while momentum (Newton) does so subsonically? I'm sorry, I didn't understand the questio

> Why would pressure (Bernoulli out of Euler) propagate supersonically while momentum (Newton) does so subsonically? I'm sorry, I didn't understand the question. But in supersonic flight, with a flat plate, you don't have any rotation in the game, as illustrated here [0]. And yet you will be producing a lot of lift. [0] https://image.slideserve.com/251762/supersonic-flow-over-flat-plates-at-angle-of-attack-n.jpg https://image.slideserve.com/251762/supersonic-flow-over-fla... > But the very wrong answer is pressure alone. No, it really is the pressure alone. And viscous drag, if you want to be pedantic. Those are the only forces at play, the rest is only a side effect of those forces.

JumpCrisscross 2y ago
> you don't have any rotation in the game, as illustrated here The arrows literally moved down! > it really is the pressure alone NASA, pilots and aerospace engineers would disagree with you. But yes, you can construct a working model of flight with just pressure. Same way you can make a Copernican model match our observations of how the stars and planets move.
- fransje26 2y ago
  > The arrows literally moved down! On the top part, you've got a supersonic free-stream deflected with an expansion fan to a supersonic parallel flow over a plate, deflected back and slowed-down to free-stream conditions through an oblique shock. The only thing the upper-surface "sees" is a parallel, supersonic flow. On the lower part, you've got a supersonic free-stream deflected to a lower-speed supersonic flow through an oblique shock, creating a parallel supersonic flow over the lower surface of the plate, deflected back and re-accelerated to free-stream conditions through an expansion fan. The only thing the lower surface "sees" is a parallel, supersonic flow. Now, unless you can come up with a force component emanating either from the oblique shocks or from the expansion fans and contributing to the lift vector, it fair to say that the flow deflection is not directly what is causing lift on the angled plate.

JumpCrisscross 2y ago

> you don't have any rotation in the game, as illustrated here The arrows literally moved down! > it really is the pressure alone NASA, pilots and aerospace engineers would disagree with you. But yes, you can construct a working model of flight with just pressure. Same way you can make a Copernican model match our observations of how the stars and planets move.

fransje26 2y ago
> The arrows literally moved down! On the top part, you've got a supersonic free-stream deflected with an expansion fan to a supersonic parallel flow over a plate, deflected back and slowed-down to free-stream conditions through an oblique shock. The only thing the upper-surface "sees" is a parallel, supersonic flow. On the lower part, you've got a supersonic free-stream deflected to a lower-speed supersonic flow through an oblique shock, creating a parallel supersonic flow over the lower surface of the plate, deflected back and re-accelerated to free-stream conditions through an expansion fan. The only thing the lower surface "sees" is a parallel, supersonic flow. Now, unless you can come up with a force component emanating either from the oblique shocks or from the expansion fans and contributing to the lift vector, it fair to say that the flow deflection is not directly what is causing lift on the angled plate.