Question: I am in second class. How does a airplane stay up in the sky

Sinead Quirke answered on 6 Feb 2015:

Hi

An airplane stays up in the sky because there are 4 forces acting on it which are equal. Two of them are fighting up and down and 2 of them are fighting forward and back. When there is a draw between the 4 of them the airplane is flying.

The force pulling the plane down to the ground is gravity while the one pulling it up to the sky is lift. Then in the other direction the force pushing it forward is thrust while the force pulling it back is drag. When these forces are equal the plane stays up in the sky.

First think of up and down

The force pulling the airplane up is called lift. When air flows at speed over the wings of the airplane there is a difference in pressure between the top and bottom of the wing which lifts the wings up. The lift is generated as the airplane goes down the runway at speed. The force pulling the airplane down is gravity. These forces are always fighting against each other. For the plane to stay up there needs to be a draw between these 2.

Next think of forward and back. The force allowing the plane to move forward is called thrust. The engines on the airplane generate this and push the plane forward. The force pulling the airplane back is called drag. Think of walking along on a windy day and you are walking into the wind. Your heart is generating the thrust for you to walk forward while you are being dragged back by the wind pushing against you. Again these two forces are always fighting against each other. For the plane to stay up there needs to be a draw between them.