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Abstract

Vibration is a continuing problem in helicopters. It can be particularly severe for the modern type of rotor head (hingeless rotor blade helicopters) in which the flap and lag hinges are replaced by flexible elements, unless a considerable effort is made at the design stage to keep it within reasonable limits. This type of helicopter is usually characterised by a relatively high peak to peak value of the hub non-rotating co-ordinate moments transmitted to the fuselage, e.g. on the pre-production Lynx helicopter. Part of the design process consists of manipulating the rotor (which is the major source of this vibration), by means of altering the blade structural and mass configuration, in order to minimise the overall vibration transmitted to the fuselage. Many of these adjustments are generally made on the basis of experience and intuition.

In this research project, the structural optimization technique is used to formalise the process with the desire to find the optimum configurations of the rotor blades (mass, flatwise stiffness and built-in twist distributions along the blade), in forward flight conditions, such that the oscillatory rolling and pitching moment is minimised. This problem is one of a general class which involves optimization by so-called "blade dynamic tailoring". It is a linear programming problem and the sequential unconstrained minimization technique (SUMT) which uses an algorithm based on the steepest descent method is utilised.

The results follow an orderly sequence leading to a substantial reduction in the oscillatory rolling and pitching moments peak values (up to 48.5% and 28.8% respectively) with small changes in the blade configuration. Therefore, optimum design of rotor blades provides substantial benefits with small penalties, so it is suggested that use of structural optimization as a design tool by industry could lead to improved rotors.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > T Technology (General) T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Department of Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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