# how do planes stay in the air once they reach cruising altitude?

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I think I understand how airplane wings create lift when taking off, but I can’t wrap my head around how they stay in the air once they reach cruising altitude.

My understanding of how wings work during takeoff is: by changing the wing’s angle of attack, air molecules under the wing are deflected down, in turn creating lift on the wing. And air molecules that go over the wing are not met with that resistance from the wing, so they move faster than the molecules underneath, creating a pressure difference which also helps generate lift.

But when the airplane reaches cruising altitude, the wings seem pretty much horizontal, so it seems the angle of attack is not nearly as large as it was during takeoff. So at that point how do the wings generate enough lift to stay in the air?

Thank you

Edit: I’m studying mechanical engineering and have taken a fluid mechanics class so I have a little bit of background knowledge, but am still having a hard time understanding this

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The geometry is specifically chosen so that as the plane moves forward in steady and level flight, the pressure on the underside of the wing is higher than the pressure on top of the wing, resulting in enough upward lift to balance the weight of a fully-loaded aircraft.

You’re right in assuming angle of attack contributes heavily to lift. That’s how takeoff and landing works. But even in steady level flight the wings still produce lift.

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The angle of attack is close to zero but not quite. If you look at how a wing is mounted to the fusulage you will notice that the rear of the wing is much lower then the front of the wing when the fusulage is level. This means that in cruise the fusulage is level and people can walk around the cabin normally but the wings have a significant angle of attack to generate lift.

The idea about creating lift by deflecting air downwards remains exactly the same, just for steady level flight, just instead of creating enough lift to make the plane travel upwards it just needs enough lift to balance out with the plane’s weight.

The thrust and speed play a big part, on take off most jetliners take off with less speed than at cruise altitude. 130 knots vs nearly .7 or .8 mach at 30-40k feet. Flaps help achieve more lift at lower speeds, after reaching certain speeds flaps are raised because there’s enough speed & thrust to avoid stalling. If you simply try to look at this without the speed and thrust components you will be missing vital info related to what you wish to understand.