Proprotor Design Issues for High Speed Tiltrotors

This paper presents key findings from an analytical investigation carried out to identify technologies critical to the feasibility of advanced rotorcraft proprotors. The focus was on high speed tiltrotors, exhibiting both high cruise propulsive efficiency and helicopter-like hover efficiency, providing a low-risk design capability for advanced rotorcraft by the year 2000. It was concluded that 400 knot proprotors are feasible with existing aerodynamics and structure technology. Blade planform sweep would be needed for operation at and above 400 knots. Blade designs for operation below 380 knots should be possible without significant sweep. The results of the study also imply that thickness effects at the root are as much of a design issue as transonic effects at the tip. Hub configurations and interactional aerodynamic effects have a significant impact on the vibratory characteristics of high speed proprotors, and will require the use of carefully validated multi-disciplinary methods of analysis. Noise criteria will also have to be introduced as explicit design objectives in future tradeoff studies.