How can planes take off even though they are so heavy? Your question of the month in May (2014) Henry, 7 years old Planes are huge and very, very heavy. But how can they still fly? First look at the four forces that affect a plane: air resistance, weight, lift and thrust.In simple terms you could say that the air flows around the plane. Because of the upward-curving wings the air above flows past faster than below. A suction force is then created: the plane is practically sucked upwards. The air on the shorter underside of the wing then flows slower because there is no resistance. Pressure is then created: together this creates what is called lift. As soon as the lift is stronger than the weight pulling the plane down, the plane takes off.The plane also needs to travel at a certain speed as well. The thrust from the jet engines provides that. It makes the plane move forward despite the air resistance. If you hold your hand out of the car window you can feel these forces yourself. You can only feel how the air makes your hand 'fly' if you hold your hand diagonally to the wind. If you hold your hand straight and flat out of the window almost nothing happens.