TEN YEARS OF AEROSPATIALE EXPERIENCE WITH THE FENESTRON AND CONVENTIONAL TAIL ROTOR

Since the first flight with a fenestron rotor on a Gazelle helicopter in 1968, significant improvements have been made in the design of both fenestron and conventional types of tail rotors. On conventional tail rotors-new airfoils and high twist values have resulted in improvements in figures of merit from 0.5 to above 0.7. New technologies, such as cross-beam or Triflex type rotors, appear to be promising in terms of weight savings and reductions in cost and maintenance. On fenestron type rotors-improved aerodynamics due to optimization of airfoils and blade twist angles, together with revised shroud designs, has led to higher efficiencies. New external rotor fairing lines improve aircraft flying qualities about the yaw axis. The use of composite materials for the rotor and structure make the fenestron lighter and less costly. This paper reviews the state of the art relative to both concepts and assesses their advantages and disadvantages in terms of mission objectives and aircraft size.