An Examination Of Helicopter Rotor Load Calculations

The structural response of three full-scale helicopter rotors has been examined. Airloads predicted by CAMRAD were compared by harmonics with test measurements. Flapwise bending moments were calculated from the CAMRAD airloads using three methods: force integration, curvature, and a finite-difference method. The force-integration and curvature moments were calculated with the CAMRAD program itself; however, the finite-difference method was calculated externally by a forced response program, Blade Response to Aerodynamic Loading (BRAL). The BRAL analysis with measured airloads was shown to agree well with slrain-gauge measurements on the CH-34 rotor in a wind tunnel. The CAMRAD/force-integration bending moments were shown to accumulate error as the integration progressed from tip to root. The CAMRAD/curvature moments agreed well with the finite-difference moments over most of the blade; however, at regions of rapidly changing stiffness the agreement was poor. When applied to the BRAL solulion, force integration was shown to give excellent results, provided the integration had a small step size. Shear forces calculated by CAMRAD and BRAL showed fair agreement.