Chichester Miles Consultants
Company: AutodeskCustomer: Chichester Miles ConsultantsSubmitted by: The WhiteOaks ConsultancyIn the skies over Wisconsin late last year, buzzed a unique aeroplane – the only jet powered four-seater light aircraft in the world. It was one of the daily highlights of the annual OshKosh Air show – the world’s annual fair for experimental and homebuilt light aircraft. Called the Leopard 002, the plane is a British innovation – the brainchild of Ian Chichester-Miles – a veteran designer of jet aircraft who spent all his working life in the British aviation industry, retiring as head of research at British Aerospace Hatfield over twenty years ago.It is sleek, luxurious, sexy and, for those with deep pockets, irresistible. Half way through the show, chief engineer Ian Townsend, said that if it was in production today, they could have sold 25 planes at $1.
35 million each. Known colloquially as the “Flying Ferrari”, the production version of the 500 mile/hour four seater will be able to travel for 1500 nautical miles at up to 45,000 ft when launched early next century.The Leopard’s fascination for light aircraft buffs extends beyond its jet propulsion, however, as it is one of the few aircraft in the world that has been designed, and run through initial flight simulation trials, entirely on computers. This aircraft never saw; a wind tunnel, its first experience of air moving over the wings being on the maiden flight.
Ian Chichester Miles, who began his working life at the Hatfield plant of De Havilland in 1946, quickly realised the potential of jet engines in smaller aircraft. When he retired in the late 1970s, he believed that aviation technology would allow the design and manufacture of an affordable, jet-powered “personal aircraft”. In 1982, he began a project to provide what he calls “proof of concept”. He was responsible for the design and build of Leopard 001 which first flew in 1988 – and displayed at Farnborough in 1990 – using British jet engines from Noel Penny Turbines. But these engines were not powerful enough to realise his vision of a 500 mile an hour aircraft, and his campaign suffered a setback when Noel Penny went out of business. He is still waiting for a production version of a gas turbine of the right size, weight and cost to make his vision a reality.
However, during his BAe days, he had got to know very well Sam Williams – in Chichester Miles words “the leading US expert in small jet engines” – and in the early 1990s persuaded him to supply him some larger turbo fan engines for the Leopard 002.During the 1980s, the world’s light aircraft industry had suffered a severe depression due primarily to costly product liability legislation and in the early 1990s the US Government and NASA decided to take steps to resurrect it. The first step was to cut the term of the product liability insurance that manufacturers were being forced to take out to 15 years (rather than the 40 years that had become the norm and had demolished the business case for building light aircraft). But the second – most crucial for Chichester Miles – was to instigate an R;D programme to harness the latest materials, instrumentation, propulsion and computer technology so that manufacturers could produce better light planes at affordable prices.Under the General Aviation Program (GAP), NASA commissioned the Williams Corporation to design and built a compact turbofan engine designated FJX-2 that would power “personal aircraft”.
The turbines at present used in the Leopard 002 are interim engines from Williams, delivering 700 pounds of thrust each. Leopard 002 first flew in April 1997, and currently achieves about 250 knots at 25,000 feet. Demonstration versions of the new FJX-2 engine are scheduled for 2000 with production turbines possibly due about two years later.From 1990, Chichester Miles and his small team, Chichester Miles Consultants (CMC) – based at Old Sarum airfield near Salisbury – were proceeding with the detailed design and specification of the airframe, the controls and the instrumentation of the Leopard 002. Initially they worked with the original airframe of the Leopard 001, created by traditional means using paper and pencils. But they soon realised that to manage the difficult task of developing a world-beating, advanced aircraft on a limited budget they needed to use high technology tools.
For example, as the Leopard 001 was simply a proof of concept aircraft it had basic controls, rudimentary fuel and avionics systems and lacked such essentials for a production plane as cabin pressurisation and air-conditioning. It was, as chief engineer Ian Townsend puts it equipped with “just enough to fly. It would not have been given a commercial airworthiness certificate”.So while the external shape of 001 was perfect, and has been retained, the airframe was structurally inadequate to carry the extra weight of additional controls and systems required in a production version. To do that detailed redesign CMC realised they needed a CAD/CAM system and went in search of something that would suit them. After a three-month search – which included visits to the CAD/CAM show in Birmingham and consultations with numerous suppliers – they came to the conclusion, says Townsend, that they must acquire a “turnkey” system, in other words getting hardware, software and support from a single organisation.
Their researches had revealed that many of the systems on offer could do far more than CMC actually required – a fact reflected in the price being asked, and that all too often the hardware and software would be supplied by different firms. But when they found that SSI Microsystems – in nearby Pewsey – was a distributor for Autodesk products they concluded this was the system for them. SSI’s Tony Sands recalls that the first thing they agreed upon was the need for a turnkey system so that CMC Ltd (Chichester Mile’s company) could deal just with them. Townsend adds that the closeness of SSI was also a benefit.So it was that in about 1991, CMC took delivery of a single “seat” of AutoCAD, release 11, running on a PC under Windows 3.11.
The drawings were scanned into the system and detailed design modifications, and ultimately final manufacturing drawings, were generated on the system. Final geometry was sent (on disk or by e-mail) to the aeronautical Research Association (ARA) at Bedford as the basis of final aerodynamic profiling and flow simulation and testing.Over the past few years, CMC has added extra seats (one running the full AutoCAD suite and two using the LT version – it means “light” but Townsend describes it tongue-in-cheek as “low tar”) and has also upgraded to release 12 (soon to be followed by release 14). About three years ago it bought the 3D solid hard surface modeller from Autodesk Mechanical Desktop, which Townsend says will fully come into use from now on as CMC begins detailed design of essential systems for the production aircraft such as air-conditioning.It must be appreciated that these design drawings include far more extensive data than the basic shape and major components of the final aircraft.
They include every detailed aspect of the final plane – from the complex retractable undercarriage (it is a tough job to stow away a mechanical linkage and its landing wheels in such a tiny aircraft’s wing or nose cone), through the “all-glass” cockpit (in other words using LCD screens to display every “instrument reading” from air speed and altitude to oil pressure and engine temperature on demand, or automatically in the event of a problem) right down to material specifications and screw sizes and threads.
The design data are held on disk as computer files that can be shipped to subcontractors for manufacture. For example, the “buck” (the name aircraft designers use for the former, or male mould, used to create the female mould in which complex composite structures are laid up) for the tail plane was designed on AutoCAD and the disks sent to a machining firm called Burwood. Using CNC, it machined the buck from solid African Mahogany, and it will be used again to produce tail plane mould whenever necessary.
Another fact is less obvious. This is that in such a novel, and tiny, aircraft such as the Leopard, off-the-shelf fuel, avionics or air-conditioning systems are of no use. As Townsend puts it, “They are too large, heavy and (often) inefficient. It might look as though we were re-inventing the wheel, but we really had no option”.In the end, although it began life on paper, the data for 002 were all held on the computer – with printouts being generated in engineering drawing form for review and checking of key details and elements of the final machine.
Today, while these data are being used on a continuous basis to modify and improve 002 following the extensive programme of flight and ground tests, Ian Chichester Miles and his colleagues chief engineer Ian Townsend and designer Dave Fisher are working away at 003, due to fly with the new Williams engines early next century.And this new – pre-production version – has been created entirely using Autodesk’s software suite. Although based closely on 002, the new aircraft is slightly longer, more spacious and has different window and windscreen profiles in addition to more sophisticated controls, systems and instrumentation.For example, Fisher is redesigning the main undercarriage to improve its efficiency and to reduce weight. He has drawn and specified every aspect of this complicated mechanical structure – from the hinged legs and the retraction mechanism to its linkages with the control lever and the bay door – on the Mechanical Desktop system.
It would have taken at twice as long to do it traditionally, perhaps longer, as the software allows him not only to design the mechanism but simulate in action to ensure it works.Of the Mechanical Desktop software, Fisher says that its provides almost as much functionality as much more complex software such as Dassault Catia, but at a fraction of the cost. And, echoes Townsend, Mechanical Desktop meshes seamlessly with finite element programs such as Algor, graphics packages such as 3D Studio’s animation software.As you’d expect in a Ferrari style personal jet, the Leopard will have all the creature comforts – except a toilet. And that is why the plane can fly 1500 miles on a tank of fuel – its what Ian Townsend describes as “bladder range”.
Even so, that means London to Milan or half way across America on a tank-full.
