undefined | Better HN

0 pointsrawgabbit3y ago0 comments

There is a slight semantic difference. The poster suggested the plane compressed the air underneath. I believe he was trying to describe lift. Technically the plane is too small to compress the air. The plane’s wing does not compress the air it generates lift.

0 comments

morpheos1373y ago

I am sorry but I disagree. Air as a gas is a compressible fluid. You can compress air with your hand. I don't understand why this is hard to grasp.

Basically it comes down to what is "lift."

It is known winged planes can not fly in a vacuum.

Rather planes fly by some sort of reaction force between air molecules and the wing.

You seem to suggest the wing is pulled up from the top. How does that work? Do air molecules have little hooks that attach to the upper wing surface?

Obviously no.

So lift is just another name for the ordinary newtonian reaction force. It pushes from the bottom.

How is that possible? It is possible because there are more air molecules colliding with the bottom of the wing than with the top. I.e. pressure is higher beneath than above.

These collisions transfer kinetic energy from the compressed air to the wing.

rawgabbitOP3y ago

You cannot compress air with your hand. What you are doing is displacing it, moving it somewhere else.

What you described It is possible because there are more air molecules colliding with the bottom of the wing than with the top. I.e. pressure is higher beneath than above. These collisions transfer kinetic energy from the compressed air to the wing. -- when I was in school a long long time ago -- we called it LIFT.

We called it lift because at subsonic speeds, airplanes relied on Bernoulli's principle. At supersonic speeds, the shock wave created at the bow of the wing prevented laminar airflow meaning no LIFT. At supersonic speeds, the airplane flew due to the newtonian breakdown of airflow against the wing's undersurface. At supersonic speeds, airplanes are inherently unstable which meant they relied on computers to constantly correct their trajectory.

j / k navigate · click thread line to collapse