Why does an airplane can fly inverted?

WOW...TUOGH QUESTION...I NEVER FIGUERD THAT...I'LL THINK ABOUT THAT

When you fly inverted you are flying on angle of attack not lift. You have to feed in a lot of down elevator to keep the nose high enough to fly level. The wing is in fact working against you at that point since the lift generated by the wing is trying to pull you towards the ground.

When you're in the car stick your hand out of the window and tilt the front part of your hand upward. The wind tries to lift your hand up, you aren't generating lift it is just the angle of your hand in relation to the wind. That is angle of attack.

Yeah,in fact,there are even certain planes with certain wing shapes that you can't keep the plane nose level or up while flying inverted.

Well written WarHawk. You are right on.

WarHawk42 wrote:

When you fly inverted you are flying on angle of attack not lift. You have to feed in a lot of down elevator to keep the nose high enough to fly level. The wing is in fact working against you at that point since the lift generated by the wing is trying to pull you towards the ground.

When you're in the car stick your hand out of the window and tilt the front part of your hand upward. The wind tries to lift your hand up, you aren't generating lift it is just the angle of your hand in relation to the wind. That is angle of attack.

Yeap, that's also called Induced Drag.

Many of the things we learn in school are not right about lift. The bernoulli principle ( Lower and higher pressure) and the Newton explanation ( air bouncing on the bottom of the wing) are only partly right. In fact many airplanes are designed with the wings perfectly symmetrical. So where does the lift come from. The lift actually comes from the turning of the air over the wing. If you change direction or velocity of the air, you change its magnitude ( force). For way way more details, this is the site from NASA where I read all about this: http://travel.howstuffworks.com/framed.htm?parent=airplane.htm&url=http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html (and keep on going to next pages)
They even show you a Java applet to play with, to really prove you what's wrong with Bernoulli's and Newton's principles, and what is right with the turning of the air.

The fact that planes can fly upside down is the symmetrical wing shape. In a positive attitude, the air is "turned" downwards, while in a negative attitude the air is deflected upwards. Moreover, you don't need to have curved wings, airplane wings could just be flat and the airplane will fly (it is just that a little less lift is produced).

Anyways, I hope this helps.
Blake14

Actually a door would fly with enough power applied. With the symmetrical wing which in theory cancels the lift out since it is equal on both sides does fly on the combination of the applied power and the angle of attack (induced drag). The symmetrical wing is popular with stunt pilots since it will fly inverted equally well as it will upright.

Most planes are designed with a slight positive incidence built into the wing and with the power available fly on a combination of lift and angle of attack. At cruising speed that angle is very small. The reason you have to trim the nose up when you are making an approach is because the wing isn't developing as much lift as it does at cruising speed. You are relying on more angle angle of attack to make up for the loss in lift.