Examination of Helicopter Dynamic Response Using Dynamic Inflow Model

This paper concerned with the examination of on-axis and off-axis dynamic responses of helicopters using a dynamic induced velocity model for a main rotor. The model consisted a canonical Legendry polynomial and a trigonometric function with a time dependent coefficients and arbitrary harmonics. The main reason for this, was the compatibility of the Legendry polynomial with the potential acceleration function presented by Laplace PDE for a main rotor at incompressible flow condition in elliptical coordinate system. The Laplace equation was previously solved through the separation of variables with discontinuity of pressure over the rotor disc and cylindrical skewed wake below the rotor. The novel of the present research is the inflow dynamics with finite state wake that was efficiently adopted with the dynamic equations of single main rotor helicopters (rigid fuselage, elastic main rotor, horizontal and vertical tail) in the time domain. Therefore, the discretization of the wake inflow was avoided by the definition of finite inflow states. Furthermore, the possibility of air load computations is achieved through the state formulation and quasi steady aerodynamic implementation. Moreover, the singularity problem associated with the traditional inflow dynamics was avoided through the current inflow state. The obtained results showed that using dynamic inflow model with 28-state and 4- harmonics significantly improves the off-axis dynamic responses of single main rotor helicopters. Comparison of the obtained results with the flight-test data and with the other dynamic inflow models showed that both the off-axis and on-axis response of helicopters experience a fairy good improvements.