One of the UK’s leading product design and development companies, Gemini Prototyping, has recently completed the construction of a unique 1/5th scale model of the Sabre hybrid air breathing rocket engine, which is being developed for use on the Skylon spaceplane. The project was unusual as it required a blend of traditional model making skills, allied to 3D CAD modelling and rapid prototyping processes, and had to be completed within just four weeks in order for the model to appear at the Farnborough International Airshow.
The Sabre engine is being developed by Reaction Engines and combines the features of both jet and rocket engines in a single power plant. This has been designed for use with the Skylon unpiloted and reusable single stage to orbit (SSTO) winged spaceplane, which is expected to provide low cost access to space, by delivering a payload of up to 12 tonnes into an equatorial low Earth orbit and then returning to earth using conventional runways. If required, the craft can then be readied for a return journey within hours, compared with several months that are required for current rocket assisted spacecraft.
Two Sabre engines will be fitted to Skylon, one on each wingtip, and operate by using a mixture of hydrogen and oxygen for fuel, both of which are stored in special tanks on-board. In practice, the engine will burn oxygen taken from the outside air at heights of up to 30km and at speeds up to Mach 5, and thereafter will draw oxygen from the on-board tanks to accelerate to orbital speeds at around Mach 25. Key to the effectiveness of the Sabre engines are extremely efficient, lightweight heat exchangers, which cool the incoming air to cryogenic temperatures before it is highly compressed and mixed with the hydrogen prior to combustion.
Simon Feast, Project Engineer at Reaction Engines, explains that, “Although our Sabre hybrid engine technology was originally produced for the Skylon project, we are now developing the concept further, for use in hypersonic passenger and commercial aircraft and wanted to showcase this at the recent Farnborough International Airshow. For various reasons, we had just a few weeks to commission and complete this project and therefore chose to work with Gemini Prototyping, selecting the company as they were both local to our head office in Abingdon and, more importantly, because they were able to offer all the services that we required in-house”.
Gemini Prototyping specialises in product design and development, with a full range of production facilities, including 3D CAD design and virtual prototyping, traditional model making, stereolithography (SLA), selective laser sintering (SLS), vacuum casting, injection and blow moulding, and CNC machining.
The company’s Director, Richard Pike, highlights the benefits that this brought to the Sabre project, “The tight timescale, plus the fact that Reaction Engines did not at that stage have detailed working drawings, meant that we had to create a 3D CAD virtual model, including all of the internal components and assemblies, before building each part, dry assembling to test fit and then finish, painting and final assembly. Additionally, as the size of the model, measuring over 3m in length, was far too large for us to use rapid prototyping systems we had to return to traditional model making techniques for the larger components, with the smaller parts being made using SLS and CNC machines.
The fact that we could do all of this in-house enabled us to meet the tight deadlines and to work closely with Reaction Engines; in particular, we were able to exchange ideas and drawings that helped to evolve existing component designs so that they could be produced in the most efficient manner possible.”
The engine nacelle was produced using traditional pattern making techniques, working in glass fibre, while smaller parts such as the compressor, pre-cooler, after-burner and pipework were manufactured by SLA and SLS or machined from aluminium, resin board and ABS, and then hand finished.
Simon Feast concludes, “The combination of traditional skills with the latest rapid prototyping and finishing technology is unusual these days, but allowed Gemini Prototyping to provide us with a superb model that was finished to the highest standards, on time and within budget. Indeed, the Sabre model was a terrific success at the Farnborough Airshow as it attracted a huge amount of interest, both for the engine technology involved and for the complexity, detail and quality of the finished model”.
For further information contact Richard Pike, Gemini Prototyping Ltd, Unit 20 Wornal Park, Menmarsh Rd, Worminghall, Bucks, HP18 9JX. Tel: 01844 339857. www.geminiprototyping.co.uk.
This information was written by 4CM.
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