Hingeless Helicopter Rotor Response with Nonuniform Inflow and Elastic Blade Bending

A generalized harmonic balance theory for the steady-state, linear, response characteristics of a hingeless rotor in forward flight is presented and evaluated with the aid of recent experimental data. Comparisons of several approximate representations for the rotor blade revealed that the simple rigid hinged blade is inadequate except at very low advance ratios, or high flap frequencies. For typical values of flap frequency the first two elastic flap bending modes are required for accurate response predictions. Simplified models of the nonuniform induced inflow were derived, using momentum arid vbrtex theory, and found to be the most important factor in improving correlation with the data. An empirical inflow model was developed from the experimental data by obtaining an inverse solution of the present theory. This inflow model was found to be in reasonable agreement with the simple inflow theories for low advance ratios but revealed large unexpected variations in the induced inflow of the rotor for advance ratios near 0.8. a B b c CT d Cm e epc El J [L] m [M] [N] n p r, R U v'i v0 w