Lift R e s u l t a n t Thrust R e s u l t a n t Thrust Lift R e s u l $_{t}$a n t Drag RotorGLYPH<.notdef> Drag FuselageGLYPH<.notdef> Drag R e s u l $_{t}$a n t Weight Weight Figure 16-7. Unlike a helicopter in forward powered flight the resultant rotor force of a gyroplane acts in a rearward direction. thrust directly from the engine through a propeller. [Figure 16-7] The force produced by the gyroplane rotor may be divided into two components; rotor lift and rotor drag. The component of rotor force perpendicular to the flight path is rotor lift, and the component of rotor force parallel to the flight path is rotor drag. To derive the total aircraft drag reaction, you must also add the drag of the fuselage to that of the rotor. Rotor lift can most easily be visualized as the lift required to support the weight of the aircraft. When an airfoil produces lift, induced drag is produced. The most efficient angle of attack for a given airfoil pro- duces the most lift for the least drag. However, the air- foil of a rotor blade does not operate at this efficient angle throughout the many changes that occur in each revolution. Also, the rotor system must remain in the autorotative (low) pitch range to continue turning in order to generate lift.  Some gyroplanes use small wings for creating lift when operating at higher cruise speeds. The lift provided by the wings can either supplement or entirely replace rotor lift while creating much less induced drag. Total rotor drag is the summation of all the drag forces acting on the airfoil at each blade position. Each blade position contributes to the total drag according to the speed and angle of the airfoil at that position. As the rotor blades turn, rapid changes occur on the airfoils depending on position, rotor speed, and aircraft speed. A change in the angle of attack of the rotor disc can effect a rapid and substantial change in total rotor drag. Rotor drag can be divided into components of induced drag and profile drag. The induced drag is a product of lift, while the profile drag is a function of rotor r.p.m. Because induced drag is a result of the rotor providing lift, profile drag can be considered the drag of the rotor when it is not producing lift. To visualize profile drag, consider the drag that must be overcome to prerotate the rotor system to flight r.p.m. while the blades are producing no lift. This can be achieved with a rotor sys- tem having a symmetrical airfoil and a pitch change capability by setting the blades to a 0° angle of attack. A rotor system with an asymmetrical airfoil and a built in pitch angle, which includes most amateur-built teeter-head rotor systems, cannot be prerotated without having to overcome the induced drag created as well. Thrust in a gyroplane is defined as the component of total propeller force parallel to the relative wind. As with any force applied to an aircraft, thrust acts around the center of gravity. Based upon where the thrust is applied in relation to the aircraft center of gravity, a rel- atively small component may be perpendicular to the relative wind and can be considered to be additive to lift or weight. In flight, the fuselage of a gyroplane essentially acts as a plumb suspended from the rotor, and as such, it is ROTOR LIFT THRUST ROTOR DRAG 16-4