(this is not a profile of a plane, but cross section of a wing.)
Above is the picture of the profile of your typical airplane’s wing. In this picture, plane is moving from left to right, and air from right to left. Because plane is moving forward at a constant speed, hence air is moving backward at a constant speed, both above and below the wing. But because of the clever profile of the wing, air at top surface of teh wing needs to cover longer distance to reach the back tip, but because lower and upper air reaches the back tip at the same time, air at upper surface needs to travel faster than the lower surface. This creates a negative pressure on the top surface and top surface gets sucked up, which lifts the plane in the air.
Now, during a flight, when plane hits turbulent air (usually happen when cold air hist warm air, or air masses of two different speeds hit each other), the air flow above and below the wing get disturbed, the wing loses the negative pressure, and the plane drops down few feet. The drop is literally few feet in most of the cases (around 5-10 feet). Its not dangerous to plane in anyway. Higher stresses it the airplane structure during a hard lading than a few feet drop that we call turbulence.
Why cant air above and below wing travel at same speed. So air on top of wing reaches tip slightly later than air at bottom? Then delta P would be zero between bottom and top.
If you and me have to run from point a to point b, and expected to start and finish at the same time, but I am running on a straight path, while you have to run following a curved path, then you are traveling more distance than I do. For you to reach point b at the same time as me, you have to run faster. Air on the top surface has to speed up as it's following a longer path.
More speed (velocity) in fluids mean less pressure. On a side note, less pressure means lower temperature. That is why when you blow air from your mouth on a spoon full of hot soup, air speeds up, pressure goes down, temperature goes down too, and soup cools down.
Coming back to the wings, top air is moving faster, so exerting lower pressure on the top surface. Bottom surface has higher pressure. Delta P is negative (only because pressure is conventionally taken positive when acting vertically downward, but in this case it's acting vertically upward), which lifts the plane.
Hadn't thought abt why blowing on hot surface can have cooling effect PV/T is constant.
I got the concept that high velocity means loser pressure. Bernoullis eqn. My question why should air at top reach back tip at same time? Why cant it go at SAME speed. And reach Ba k tip slightly later. Why does it HAVE to reach Ba k tip at same time as bottom air?
Lets assume that red bottom line and top curved green line are equal in length. If air is flowing at the same speed, then by the time lower air would reach the wing rear tip (end of red line), top mass of air would reach the end of green line only. By that logic, for a given mass of air flowing above and below the wing, there would be no air where the orange circle is. Because that is unacceptable to the mother nature (law of conservation of mass), top air speeds up to fill that gap.
Another explanation is in the profile of the wing itself. Top surface pushes the air upward, but there are more layers of air on top of that pushed air, which means that the pushed layer of top air is now passing through a narrow channel (squeezed between the top surface of wing and layers of air above it). Whenever you try to make the same mass of fluid flow through a narrow channel, it speeds up. Remember your garden hose when you were watering your lawn? For you to make the stream of water reach greater distance, you would squeeze the rubber hose tip, and make the water jet out of that narrow opening at a greater speed.
Hmm, I have to rethink what I said about P, V and T. According to PV/T = K, when V increases, P goes down, but T goes up. T is nothing but Kinetic Energy of particles. K.E. increases with velocity, so T increases too. That is why water temp at the top of the water fall is less than the bottom of the water fall. Stupid me. Thanks for pointing that out :k:
In my earlier example (post number 4), I was thinking more from the point of view of how a can of compressed air works. When you press the nozzle, air comes out, that immediately cools down the can (less pressure, low temp). Our refrigerator also works on the same principle. Hmmm, my mind is going crazy right now. I will solve this contradiction. It cannot be that difficult.
Note that in pv/t constant v kiss volume not velocity.
So we blow air. Its velocity increases. So pressure decreases.assume V the volume is constant, decrease in p accompanied by decrease in T. I was agreeing with ur original conclusion, which I hadn't thought abt
In my earlier example (post number 4), I was thinking more from the point of view of how a can of compressed air works. When you press the nozzle, air comes out, that immediately cools down the can (less pressure, low temp). Our refrigerator also works on the same principle. Hmmm, my mind is going crazy right now. I will solve this contradiction. It cannot be that difficult.
You git it. This is what I was agreeing with earlier. Lower P so lower T.
i had the worst turbulent flight of my life in a place i never expected. two days ago i flew from Allahabad to Delhi and the entire 100 minute flight was marred with extreme turbulence. i was flying in ATR-72 aircraft, a turbo prop. mind you i've experienced the notorious turbulence over Newfoundland.
