There are a number of factors that govern the maximum speed of a helicopter. 6.- Available engine power Summary 1. Drag In aerodynamics, drag is the force opposing thrust . Parasite drag Parasite drag is the drag forces created by the components that protrude into the airflow around the helicopter. Because this drag is opposing thrust it is reducing the amount of thrust available to make the helicopter fly faster.
Parasite drag includes the landing gear, antennas, cowlings, doors, etc.
The shape of the fuselage will also produce parasite drag. On later helicopters where the manufacturer has attempted to raise the speed of the helicopter, the landing gear is retractable to reduce the amount of parasite drag produced. Generally, for a given structure, the amount of parasite drag is proportional to the speed that the structure is passing through the air and therefore parasite drag is a limiting factor to airspeed. Profile drag Profile drag is the drag produced by the action of the rotor blades being forced into the oncoming airflow. In general terms the greater the camber, the greater the profile drag.