ADVANCING TILTROTOR STATE-OF-THE-ART WITH VARIABLE DIAMETER ROTORS

Tiltrotor aircraft have a great potential for application to VTOL missions requiring high speed and long range. Presently available rotor systems for such aircraft, however, involve serious design compromises resulting from the greatly differing requirements of hover lift and cruise thrust. The rotors are too small in hover and much too large in cruise, leading to excessive disk loadings, performance limitations, and a number of other unfavorable attributes. A variable diameter rotor concept under development at Sikorsky Aircraft has the potential to reduce disk loadings to desirable values, to match the rotor to both hover and cruise requirements, and to provide significantly better Category A performance, greater operational flexibility, and superior growth capability. It also has the potential to reduce external and internal noise, to improve passenger comfort, and to increase the design cruise speed significantly where this is desired. The development of the required technology for the variable diameter rotor is well underway; this paper summarizes the system advantages and the status of the program.