Passive Venting for Alleviating Helicopter Tail-Boom Loads

The tail boom of a single-rotor helicopter is subjected to a complex flow field that includes the wakes of the main and tail rotors, the freestream, and the wake from the forward fuselage. Hovering and sideward flight present the operational regimes that are most critical with respect to adverse sideward and downward loads on the tail boom. These adverse loads necessitate additional engine power, thereby reducing payload, performance, and available yaw-control margins. In addition, nonlinear side-force gradients near conditions of boom stall can make precise yaw control very difficult for the pilot. The addition of strakes to the tail boom is one method that has been used to modify the flow field and reduce these adverse loads.