No, the weight and balance of the aircraft has to be calculated very carefully to make sure that it can be "trimmed" to fly straight and level. If the nose pitches up in what is called an "abnormal attitude" it will dirupt the flow of air over the wings and cause what is called a "stall", that is, the plane will stop flying and start falling. If the pilot can't push the nose over because all the weight has shifted to the rear then the plane will crash.
Mandi