Expansion tubes perform an important role in hypersonic flight research by providing a ground-based testing facility in which scale models can be tested at simulated flight conditions. High enthalpy and high velocity flow conditions are generated via an unsteady expansion process which accelerates test gas to hypersonic conditions. Unfortunately, due to the high velocities and low densities created by this expansion process, test times are shortened and very thick boundary layers develop, reducing the useable core flow. This restricts the size of the models that can be tested, as well as the ability to obtain sufficient or accurate experimental data.Previous studies have shown that a nozzle could be added to an expansion tube to not only expand the core flow diameter but also increase the test time. This included the successful implementation of a nozzle on the University of Queensland's X2 expansion tube [31]. In this thesis, a full-capture, contoured, shock-free nozzle has been designed for the X3 expansion tube. The X3 nozzle contour was scaled from the X2 nozzle contour and was originally 3.0075m long.CFD modelling of the X3 expansion tube with the nozzle attached was completed using a hybrid method coupling a one-dimensional and axisymmetric simulation in order to predict the flow conditions produced by the nozzle. Code package L1d [16] was utilised for the onedimensional analysis and MB_CNS [14], for the axisymmetric analysis. The core flow diameter was increased from 150mm to approximately 250mm and the test time increased by 70% to 1ms; confirming that the addition of a nozzle to the X3 expansion tube will expand the core flow and increase the test time. The nozzle was also examined in relation to its potential to be truncated and maintain its core flow diameter and test time. It was determined that the nozzle could be truncated to a length of 2.5m with no observed loss to the core flow size and test time achieved.The X3 nozzle is under construction. A fibre-wound composite construction technique is being utilised. This construction method was previously used by Jacobs in the fabrication of a nozzle for the T4 reflected shock tunnel [18] at the University of Queensland, although, has not been used for expansion tube nozzles. This technique has proved effective in providing a low-weight, reduced cost alternative to metals.The mandrel for the fibre-winding process was fabricated from high-density polyurethane foam in order to overcome issues of weight and surface instability experienced with other materials. This material had not been previously used for this application and proved very successful in this providing a rigid and stable surface that was suitable for machining as well as winding over.On installation of the nozzle on the facility, the testing of larger, more accurate models is possible. Test times will also be longer than previously observed, enabling the collection of more data, further improving the capacity to effectively model hypersonic flight conditions with this facility. This will benefit future ground based hypersonic flight research to beconducted in the X3 expansion tube facility. Overall, the work completed in this thesis has furthered the development of the X3 expansion tube and provided a foundation for greatly expanding the capabilities of this facility.