How do aeroplanes fly upside down?

[Himal kharel]

When a aeroplane is flying due to its shape of aerofoil it gets lift. But it is common to see (as in stunt shows) that they can fly upside down too. When they do so they must experience a "downward" lift and start falling down. but they maintain a constant altitude.
How can they do it?

 

[elegysix]

I would guess the tail's elevators tilt the plane at an angle so that it doesn't fall as fast.

 

[rcgldr]

All that is needed to generate lift is some amount of forward speed and an angle of attack. Most stunt planes use symmetrical airfoils that have the same shape above and below. For normal (not upside down) flight, a cambered airfoil will produce the same amount of lift but with less drag than a similar symmetrical airfoil. A longer wingspan will also increase the ratio of lift to drag, but there are limitations to making long wings strong enough and the pratical aspect of trying to taxi (drive on the ground) or store an aircraft with a long wing span.

Here's a link to one of many web sites with information about wings:

http://www.avweb.com/news/airman/183261-1.html

This wik article has a reasonable animation of the air flow being diverted downwards by a wing:

http://en.wikipedia.org/wiki/Lift_(force)

 

[larrybud]

Also note that the cross section of aerobatic airplane wings are quite symmetrical.

 

[DaveC426913]

Read twice, post once...

Also note that the cross section of aerobatic airplane wings are quite symmetrical.

post #3:

Most stunt planes use symmetrical airfoils that have the same shape above and below.

 

[A.T.]

Here is a nice java applet from NASA, where you can try different profiles at different angles of attack. Just play around with the "Angle" silder, and you will see that you can produce lift in both directions (positive and negative):

http://www.grc.nasa.gov/WWW/k-12/airplane/foil3.html

 

[AlephZero]

The detailed shape of the wing has very little to do with generating lift. The basic causes of the lift are the viscosity of the air, the angle of attack, and the "sharp" trailing edge of the wing.

The detailed shape has a large effect on the amount of (unwanted) drag force generated by the wing, and the airspeed at which the wing "stalls" (i.e. the airflow pattern around the wing breaks down and the lift force becomes much smaller, but pretty much any shape of wing will "fly" if the engine has enough power to overcome the drag force and give the plane enough forward speed to prevent stalling.