Structural Optimisation and Aeroelastic Tailoring of the BERP IV Demonstrator Blade

The AW101 BERP IV main rotor blade was designed using a combination of structural optimisation and aeroelastic tailoring techniques, which have been demonstrated by analysis, structural test, model rotor test and full-scale flight test. During the blade design, a detailed investigation of existing flight test measurements to characterise aircraft vibration and correlate prediction tools gave sufficient confidence to use structural optimisation to reduce fuselage vibration. The dynamic modelling of structurally-coupled composite beams was validated by static and dynamic testing of box beam sections, where predictions and test results showed excellent agreement with published data. The study of aeroelastic coupling effects on vibratory head loads is a complex task, so a fundamental understanding of the key mechanisms was gained through analytical formulations of the aeroelastic coupling terms using a modal approach. Wind tunnel testing of model rotor blades featuring structural optimisation and aeroelastic tailoring gave further confidence in the applicability to full-scale blades. Aeroelastic tailoring was subsequently employed in the BERP IV design to further enhance the optimised design and combat an anticipated increased in control loads caused by the optimised frequency placements and the nature of the aftswept tip. Detailed analysis of BERP IV flight test measurements has verified the beneficial mechanisms introduced through structural optimisation and aeroelastic tailoring.