Lichten Runner-up Paper: Aeroelastic Stability of a Hingeless Hub Tiltrotor at High Speeds

A 4.75-ft diameter dynamically scaled advanced hingeless hub swept-tip tiltrotor was tested up to unprecedented speeds of 200 knots. This paper describes its design, wind tunnel test, data, and comprehensive analysis predictions. The data consists of beam, chord, and torsion mode damping of the wing-pylon at a loosely Froude scaled RPM of 1050 extracted via the moving-block method. Three systematic parametric variations are studied; hingeless versus gimballed, hingeless versus gimbal-locked, and straight versus swept tip blades. In house comprehensive analysis, UMARC-II, was used to predict the data. The key conclusions were that the hingeless hub increases stability in the chord mode to more than twice that of a gimballed hub. The stability of the torsion mode increased when the hingeless hub was equipped with swept tip blades. The chord damping is slightly higher than the gimbal-locked hub. The beam mode remains unaffected. Comprehensive analysis is able to predict the beam mode but not quite the chord and torsion modes. Thus, the test provides data for validation as well as insights into the aeroelastic stability of hingeless hub tiltrotors.