Fabrication, Testing, and 3-D Comprehensive Analysis of Swept Tip Tiltrotor Blades

This paper covers the design, fabrication, testing, and modeling of a family of Froude-scale tiltrotor blades. They are designed with the objective of gaining a fundamental understanding of the impact of a swept-tip on tiltrotor whirl flutter. The goal of this paper is to describe the development the blades needed for this purpose. The rotor is three bladed with a diameter of 4.75 feet. The blades have a VR-7 profile, chord of 3.15 inches, and linear twist of-37° per span. The swept-tip blades have a sweep of 20° starting at 80% R. The blade properties are loosely based on the XV-15 design. A CATIA and Cubit based high-fidelity 3-D finite element model is developed. It accurately represents the fabricated blade and is analyzed with X3D. Experiments in a vacuum chamber were carried out to prove the structural integrity of the blades. Measured frequencies and strains were validated with X3D predictions proving the fidelity of the 3-D model. Thus, even though the wind tunnel facilities were closed due to COVID-19, hover and forward flight calculations for the blade stress could be performed numerically, using the high-fidelity 3-D structural model. The results prove the blades have sufficient structural integrity and stress margins to allow for wind tunnel testing.