The first heavier-than-air flying machines had wings whose airfoil effect provided the force of lift, due to their curvature (convex in the downward direction) which allowed air to flow more slowly along the lower surface of the wing than along the upper surface of the wing, whose curvature forced the air to traverse a longer distance, creating a partial vacuum at the trailing edge of the wing which sucked the air on the top of the wing into itself at a speed greater than that of the air at the bottom of the wing. This made the air on the top of the wing less dense than the air at the bottom of the wing, which gives the lower face of the wing a platform of dense air to rest upon, as well as a partial vacuum applying to the upper surface of the wing sucking it upwards, as long as forward motion is maintained sufficient to maintain the necessary airflow. The wings were fixed to the fuselage, such that the only way to make the thing fly was to pull the whole aircraft, fuselage and all, through the air at a certain minimum speed. What pulled the aircraft through the air? A propeller, which was, itself, an airfoil, curved so as to attack the air at the proper angle for lift (or, in this case, due to the axis of application of it's force, propulsion) at each point along its length (recognizing the increasing velocity of a rigid revolving body as one moves further away from the axis of rotation). This gave some people the idea that one might liberate the fuselage from the wings, and use the propeller as the wing, by altering its axis of rotation to one perpendicular, rather than parallel, to the surface of the earth. This way, the wings move through the air without necessarily pulling the entire aircraft along with it, allowing the possibility of hovering flight. Of course, the rotary wings create tremendous mechanical torque, such that the rotor can choose to plow through the air, or to allow the air to resist it and expend the resultant built-up energy by spinning the helicopter fuselage beneath it in the direction opposite that of the rotor's rotation. This is why you need a tail stabilizer rotor: or twin tandem contra-rotating rotors: or twin side-by-side contra-rotating rotors: or twin coaxial contra-rotating rotors: *** I hope I helped!