In straight and level flight in order to increase forward speed:
Refer to figure.
Helicopter rotor thrust is the force generated by the rotation of the rotor blades, which lifts the helicopter off the ground and keeps it in the air.
The rotor blades are airfoils, similar to wings, that create lift when they move through the air. As the rotor blades rotate, they push air downwards, creating an upward force on the helicopter.
This upward force, or thrust, is what allows the helicopter to overcome gravity and remain airborne. The greater the speed of the rotor blades, the greater the thrust generated, allowing the helicopter to lift off the ground and move in any direction.A good way to understand the thrust required is to compare it with the power curve. The figure shows a significant amount of power (also rotor thrust) is required during hover and up to the point of translational lift is introduced during transition to forward flight. From the point of translational lift to the point of minimum power required speed (Vx) thereafter, as the speed increases the power required will increase as well as rotor thrust increasing.
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