Chichester-Miles Leopard — A small aircraft but a huge challenge

Dwarfed by their museum neighbours, the surviving pair of Chichester-Miles Leopard jets need no viewing platforms; to examine each aircraft, you simply peer over it. The tiny twin-jet is a saga of endeavour, trial but finally, disappointment.

The Leopard was created by Ian Chichester-Miles, ex-de Havilland, Hawker Siddeley and a former chief research engineer at British Aerospace Hatfield; he founded Chichester-Miles Consultants Ltd (CMC) in January 1978. The new company was based near Hatfield at Welwyn, its mission to develop an economical high-performance miniature business jet. With planned cruising of around 435kts, CMC’s project aimed to completely surpass piston-engined private aircraft, and achieve a speed, altitude and range comparable with the HS.125-class bizjet. For Ian Chichester-Miles, the Leopard would be a flying Ferrari, small, sporty and elegant. He felt its operating costs per mile would be no more than those of a four-seat piston-engined light aircraft.

Design

Design of the privately funded aircraft began in January 1981 and 13 months later a full-size mock-up emerged. During June 1982, under contract to CMC, Leopard prototype construction was begun by Designability Ltd of Dilton Marsh, Wiltshire, a partnership between David Kent, consultant designer/ engineer on the Edgley Optica and Nash Petrel, and Brian Cunnington, a former Lotus designer who became responsible for much interior detail. CMC acquired further premises, at Old Sarum airfield near Salisbury.

As far as possible, the prototype Leopard would be similar to the production version, though it was acknowledged the mature jet’s all-up weight would be greater: At that stage choice of powerplant was undecided, though CMC had opened discussions with Noel Penny Turbines Ltd of Coventry, a growing player in small jet engines. That summer a target production price per aircraft was quoted of around £270,000.

The first Leopard, construction number 001 and registered G-BKRL, was presented to the public on static display at the 1986 SBAC Show, having recently undergone vibration tests at the Cranfield Institute of Technology. The aircraft was certainly eye-catching, a rakish mid-wing four-seater white overall picked out with a blue-and-red cheat line.

Technology

Combining supercritical and laminar flow technology, the Leopard’s swept-back wing was developed by the Aircraft Research Association at Bedford, who provided the computational fluid dynamics capacity and high-speed wind tunnel essential to the programme. A two-spar structure, the wing embodied sweep of 25% at quarter-chord and was mostly of glass-fibre reinforced polymer: with local carbon fibre reinforcement. Thickness/chord ratio at the root was 14%, decreasing to 11% at the tip.

Full-span electrically-operated carbon fibre trailing-edge flaps were fitted, with deflections of +/- 45° for air-braking and high drag landing. No ailerons were installed. The swept tail featured an all-moving fin providing yaw control, together with two low-set independently moveable tailplane sections on steel axles, operated collectively for pitch control and differentially for roll. All flying controls were manual. The tricycle undercarriage was electrically-operated, its main members inward-retracting and of impressively wide track; the twin-wheeled nosewheel retracted forwards.

The Leopard’s fuselage was arranged in three sections. A hinged, unpressurised nose cone contained avionics and the retracted nosewheel, while the cabin’s semi-reclining seats accommodated four in two pairs. The cabin was split roughly along the horizontal datum, its upper section formed by an electrically-operated upward-opening canopy, hinged at the windscreen leading-edge and secured by multiple latches. G-BKRL’s cabin was unpressurised, but plans were laid for the inclusion of pressurisation in subsequent examples. Aft was a baggage bay with fuel tanks below amounting to 75 gallons, and equipment bays aft again. Fuselage structure was monocoque, chiefly of GFRP with carbon fibre reinforcement at the fore and aft cabin bulkheads, engine pod attachments and tailplane axle points.

Applying Power

The first Leopard was powered by two 330lb/thrust Noel Penny Turbines NPT30I-3A turbojets installed in light alloy nacelles. Fuselage-mounted well aft of the cabin, the jets were isolated by stainless steel firewalls. But delays in the new engines’ appearance contributed to the long period between unveiling the Leopard mock-up in mid-1982 and G-BKRL’s first flight.

During that time too, various other changes emerged. CMC revised the undercarriage, drafting their own stronger and more compact oleo-pneumatic main landing-gear Preparations were made to fit improved avionics, together with wing and tailplane leading-edge de-icing. Meanwhile, the company’s market analysis had suggested initial sales of about 100 aircraft a year; particularly in the United States, at a 1986 target price of $500,000.

By the end of that year; the Leopard’s engines were being bench-checked and calibrated by Noel Penny, but weren’t dispatched to CMC until well into 1987. During the autumn, G-BKRL began highspeed taxiing trials at Cranfield aerodrome in the hands of Angus McVitie, the Institute of Technology’s chief test pilot. A minor problem with the nosewheel steering was resolved and Designability carried out flutter trials.

But in January 1988 the engines were removed and returned to Coventry for refurbishment, while though they were ground-cleared, modifications were deemed necessary before the Civil Aviation Authority would allow the Leopard to take to the air.

By the summer; its engines had been flight-cleared and a Permit to Fly was awaited.

Modifications

G-BKRL appeared at that year’s SBAC Show, on static again, but finally flew on December 12, 1988 from RAE Bedford; at the controls was Angus McVitie. During the flight, which lasted around 27 minutes, the undercarriage retraction cycle was proved; at that time the Leopard was limited to I30kts and a maximum altitude of 3,500ft.

Subsequently a new tailplane was fitted, incorporating a liquid anti-icing system on its leading-edge, prior to resumption of trials to develop airspeed, altitude and CofG envelopes. By early 1989 CMC was pricing production aircraft at around $650,000, an increase of $150,000 over the autumn 1986 target price. Funding for long-term development and manufacture, though, still wasn’t in place.

In July 1989 Flight magazine reported Slingsby Aviation would be supporting the Leopard programme. Tasks would include assistance with modifying the aircraft to production standard, refining its structure to save weight, and strengthening it ready for pressurisation, as well as work on adding an environmental control system and revising the undercarriage. More hopeful sales projections, quantities and dates appeared from CMC: again reported by Flight, a unit price was calculated of $700,000 equipped, assuming a market for 1,000 aircraft over ten years from 1995.

But in October 1991 the project took a severe blow: following a cash flow crisis Noel Penny Turbines went into receivership. By then around 50 hours’ flight-testing had been accomplished, but engine support for G-BKRL’s continued trials dried up. Chichester-Miles had always acknowledged that engines of the 300lb/thrust class were sufficient only for a first prototype; production aircraft, of greater weight, would need correspondingly increased power.

For the second Leopard, seen by CMC as a pre-production example, on which work had begun in 1989, new engines planned in principle became a necessity Accordingly aircraft c/n 002, registered G-BRNM, received two Williams International FJX-I turbofans of 700lb/ thrust; it also included other refinements. Structure was beefed up in numerous areas while CMC’s revised undercarriage was introduced. The cabin was pressurised, while provision was made for installation of two AlliedSignal Bendix/King electronic flight-instrumentation systems in a somewhat remodelled nose, and de-icing fitted.

High hopes

G-BRNM appeared statically at the 1996 SBAC Show; shortly afterwards CMC increased the Leopard’s production price to nearly $900,000 per aircraft. Continually the company sought investors for their programme, pitched by then at £25M including further development airframes. Plans were made to power later aircraft with the enhanced Williams FJX-2 engine, and fly that variant during 2000.

In the meantime, on April 9, 1997 G-BRNM’s first flight took place from Cranfield. Chris Chadwick became the programme’s test pilot, ex-Empire Test Pilots School and one-time chief test pilot on Edgley’s Optica, Despite the unusual arrangement of the flight surfaces he found handling very responsive and predictable, By January 1998 preliminary flight trials had been completed, the aircraft evaluated for handling and performance at speeds of around 260kt; during July G-BRNM appeared at Oshkosh, and in the autumn at Farnborough.

Early in 2000 the second Leopard was grounded to incorporate changes including improvements to its wing, and system modifications. That year too though, a grave problem emerged as once again supply of jets was denied CMC. Williams International signed an exclusive agreement to sell the production Leopard’s planned engine, the FJX-2, to Eclipse Aviation for its Eclipse 500 twin-jet. CMC quickly began searching for options, including possible use of a powerplant from Agilis Engines of Palm Beach, Florida.

Six-seater

But in March 2001 it was announced the company had tackled the problem in an unexpected way, Taking Williams International’s FJ33 turbofan, at 1,500lb/ thrust more than twice as powerful as the FJX-2, CMC drew up a six-seat variant of its aircraft which it named the Leopard Six, Ian Chichester-Miles explained to the aviation press that the company had concluded there was no alternative but to alter the Leopard design to fit the FJ33, which unlike its smaller brother hadn’t been earmarked elsewhere.

The Leopard Six was targeted to appear in 2004. Again a composite structure, it was 25% larger than the original Leopard, priced (initially) at $2.35 million per aircraft and accommodating four passengers in a small cabin, as well as pilot and co-pilot. Cruising speed would be 500 mph, range with full payload 2,000 miles. To fund the new programme through to certification, CMC announced it was seeking investment of $95 million. Work on the four-seater would continue, though on a piecemeal basis.

But by 2004, instead of yielding hardware, development of the Leopard Six had ceased; perhaps the odds had been loaded from the start. Chichester-Miles always found it a struggle to secure investment and while the company attracted some potential backers it appears that often, investors sought tough unattractive terms. Risk capital for the project, particularly in the economic climate of the day, remained stubbornly elusive.

CMC’s estimated timescales for a commercial return on the Leopard Six were at least four years even if all went well, and there were no guarantees, while their paper aeroplane faced growing competition. Additionally, establishing production, snaring launch customers and providing after-sales support — especially overseas — were always truly massive challenges. CMC soldiered on, but in June 2009 Ian Chichester-Miles died aged 83. Today both his Leopards survive, G-BRNM with Coventry’s Midland Air Museum, G-BKRL at Bournemouth wearing a vivid red scheme.

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