Normally the aircraft flies with the help of the four forces namely Weight, Lift, Thrust, Drag. Among these four forces, Weight is the force of gravity which acts in a downward direction and used to pull the aircraft down. To pull the aircraft down not only the weight force is used, it’s the composition of all the four forces. Drag is the force caused by the friction and it acts opposite to the motion of the aircraft. Thrust is the force which makes the aircraft to fly in the forward direction. Thrust is produced by the Engine. Lift is the force created by the difference in air pressure and it acts in the right angles to the direction of motion. This makes the aircraft to move upwards.
Thus the aircraft moves down with the combined action of the weight and the drag. Lift force is reduced and the weight is applied to make the aircraft move downwards while flying in motion. Weight of the plane effects is flight as it forces the body to move downwards with the gravitational force.