Aerodynamic Loading on the Blades of a Helicopter Rotor in Steady Translational Flight

Abstract

<p>One of the most important and complex problems in the design of helicopters is the estimation of aerodynamic loading on the blades of the lifting rotor in steady translation flight. It is essential for the designer to have a fairly good knowledge of this blade loading, especially its harmonic content. Such information is necessary in order to successfully evaluate and solve problems such as: the structural integrity of the rotor hub and the blades; the oscillatory forces in the control systems; and the vibrations of the entire aircraft. Many analytical and computational methods have been developed to predict the blade loading in forward flight. These methods invariably demand a knowledge of the rotor wake details and the sectional airfoil data. The trailing wake of the rotor is extremely complex and it has not yet been possible to include in the analysis all its details. Nor has it yet been possible to obtain the sectional airfoil data in a manner which is compatible with the unsteady three dimensional and compressible aerodynamic environment of the rotating blades. We are presenting, in this thesis, a new technique to calculate the blade loading in forward flight. The proposed technique does not require a knowledge of the rotor wake or the sectional airfoil data. We have used our proposed model to calculate the blade loading for a full scale NASA model rotor at an advance ratio of 0.29. Our results compare very well with those obtained experimentally by NASA. In fact, our results show better agreement with the experimental results that those obtained by using currently available computational models for rotor blade loading in forward flight.</p>