A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering. / The use of advanced composite materials in helicopter rotor systems offers opportunities for improvements in aerodynamic geometry, performance, weight, damage tolerarice, maintenance and operating costs. Technical aspects of the design and analysis and the-practical aspects of the manufacture of a composite rotor system are discussed herein. The rotor system was compared to an existing conventional teetering rotor system, in order to establish the viability of the new composite rotor system, This rotor system reduced the number of components by 55% and the manufacturing time by half, due to the simplicity of the design and lay up procedure, thus making the system economically more viable. The mass was predicted to within 1% of that achieved in practice and gave a mass advantage of 50.5% over the conventional rotor. Static tests identified the failure modes and stress concentration points, while. the comparative hover tests showed the system to have ±20% less drag. [Abbreviated Abstract. Open document to view full version] / AC2017

This study presents a discrete adjoint-based aerodynamic optimization algorithm for helicopter rotor blades in hover and forward flight using a Non-Linear Frequency Domain approach. The goal is to introduce a Mach number variation into the Non-Linear Frequency Domain (NLFD) method and implement a novel approach to present a time-varying cost function through a multi-objective adjoint boundary condition. The research presents the complete formulation of the time dependent optimal design problem. The approach is firstly demonstrated for the redesign of a NACA 0007 and a NACA 23012 helicopter rotor blade section in forward flight. A three-dimensional inviscid Aerodynamic Shape Optimization (ASO) algorithm is then employed to validate and redesign the Caradonna and Tung experimental blade. The results in determining the optimum aerodynamic configurations require an objective function which minimizes the inviscid torque coefficient and maintains the desired thrust level at transonic conditions.

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The purpose of this research was to develop parametric Design-to-Cost models for selected major subsystems of certain helicopters. This was accomplished by analyzing the relationships between historical production costs and certain design parameters which are available during the preliminary design phase of the life cycle. Several potential contributions are identified in the areas of academia, government, and industry. Application of the cost models will provide estimates beneficial to the government and DoD by allowing derivation of realistic Design-to-Cost estimates. In addition, companies in the helicopter industry will benefit by using the models for two key purposes: (1) optimizing helicopter design through cost-effective tradeoffs, and (2) justifying a proposal estimate.

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With the advent of variable geometric wing surfaces providing noticeable performance improvements in fixed wing aircraft, a theoretical study of the performance advantages of variable geometry designs for rotary wing aircraft is presented. The analysis is developed in three sections, namely: 1) Theoretical justification of variable geometry through application of simple blade element equations; 2) A simplified design proposal to implement variable geometry in rotor systems; and 3) A numerical comparison of fixed and variable geometry performance statistics applied to specifications of an actual helicopter. / Master of Engineering

The concept of applying several disciplines to the design and optimization processes may not be new, but it does not currently seem to be widely accepted in industry. The reason for this might be the lack of well-known tools for realizing a complete multidisciplinary design and analysis of a product. This study aims to propose a method that enables engineers in some design disciplines to perform a fairly detailed analysis and optimization of a design using commercially available software as well as codes developed at Georgia Tech. The ultimate goal is when the system is set up properly, the CAD model of the design, including all subsystems, will be automatically updated as soon as a new part or assembly is added to the design; or it will be updated when an analysis and/or an optimization is performed and the geometry needs to be modified. Such a design process takes dramatically less time to complete; therefore, it should reduce development time and costs. The optimization method is demonstrated on an existing helicopter rotor originally designed in the 1960's. The rotor is already an effective design with novel features. However, application of the optimization principles together with high-speed computing resulted in an even better design. The objective function to be minimized is related to the vibrations of the rotor system under gusty wind conditions. The design parameters are all continuous variables. Optimization is performed in a number of steps. First, the most crucial design variables of the objective function are identified. With these variables, Latin Hypercube Sampling method is used to probe the design space of several local minima and maxima. After analysis of numerous samples, an optimum configuration of the design that is more stable than that of the initial design is reached. The process requires several software tools: CATIA as the CAD tool, ANSYS as the FEA tool, VABS for obtaining the cross-sectional structural properties, and DYMORE for the frequency and dynamic analysis of the rotor. MATLAB codes are also employed to generate input files and read output files of DYMORE. All these tools are connected using ModelCenter.