Rotorcraft Flying Menu >Aerodynamics of Flight > Forward Flight

In or during forward flight, the tip-path plane is tilted for-ward, thus tilting the total lift-thrust force forward from the vertical. This resultant lift-thrust force can be resolved into two components—lift acting vertically upward and thrust acting horizontally in the direction of flight. In addition to lift and thrust, there is weight (the downward acting force) and drag (the rearward acting or retarding force of inertia and wind resistance). [Figure 3-11]

Figure 3-11. To transition into forward flight, some of the ver-tical thrust must be vectored horizontally. You initiate this by forward movement of the cyclic control.

In straight-and-level, unaccelerated forward flight, lift equals weight and thrust equals drag (straight-and-level flight is flight with a constant heading and at a constant altitude). If lift exceeds weight, the helicopter climbs; if lift is less than weight, the helicopter descends. If thrust exceeds drag, the helicopter speeds up; if thrust is less than drag, it slows down.

As the helicopter moves forward, it begins to lose alti-tude because of the lift that is lost as thrust is diverted forward. However, as the helicopter begins to acceler-ate,the rotor system becomes more efficient due to the increased airflow. The result is excess power over that which is required to hover. Continued acceleration causes an even larger increase in airflow through the rotor disc and more excess power.