Design, manufacture and testing of a multi-platform Mach scale composite rotor blade

The scope of this study includes the design, manufacture and experimental hover testing of baseline and improved Mach scale composite blades to prove the performance gains over the conventional aluminium blades of the target aircraft. This MEng thesis describes in detail the design, manufacture and performance testing of a multi-platform composite rotor blade to replace the existing aluminium blades on the Bell Kiowa OH-58A/C and Hiller UH-12E/L. The thesis concludes with a review of the certification and airworthiness requirements that must be addressed for the practical implementation of the new composite blade to service. A literature review is presented that comprehensively covers the major aspects of composite rotor blades within the context of this MEng project. Included is a historical background to the development and use of composite rotor blades in industry, as well as a review of the British Experimental Rotor Program which is widely considered to be the state-of-the-art in composite blades. A detailed review of composite blade design, Mach scaling, manufacture and experimental testing is also presented. The Mach scale composite blade design was performed using the numerical modelling and analysis tools developed as part of this research work. The tools cover hover and forward flight aerodynamics as well as blade structures and dynamics, and where feasible these models were validated against published data or experimental results. The improved Mach scale blade features advanced aerofoils, increased twist, and a tapered planform to improve hover efficiency while maintaining autorotation performance and the forward flight speed capability of the target aircraft. The structural and dynamic Mach scaling rules resulted in a detailed internal blade structure that subsequently demanded a complex blade manufacturing process, which was developed as part of this research work. The process selected was based on the In-Mould Pressing method which is widely used in industry for producing composite rotor blades. Blades can typically be manufactured in a two-step process whereby the spar is manufactured first and is then bonded to the afterbody, or a one-shot process where the entire blade is laid up and cured at once. The tooling requirements, process variables and quality assurance methods are examined. A whirl rig was designed and constructed for hover testing the baseline and improved Mach scale blades. The whirl rig was instrumented with a data acquisition system that was developed as part of this research work, to record lift, torque, grip loads, pitch link loads and local air density. The whirl rig was used to test the baseline and improved Mach scale blades from flat pitch to maximum thrust (approximately 120kg). The experimental results and theoretical predictions indicate that at the design point of 4000 ft and 35 o C, hovering OGE will require 4.9% and 9.5% less power when the improved composite blades are installed on the Kiowa OH-58A/C and Hiller UH-12L, respectively. Also, the unique lead-lag restraint system, developed within this MEng project, was tested and confirms the feasibility of a multi-platform composite blade solution for the target aircraft