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The 1000hp Sunbeam

The first car to exceed 200 mph

by Julian Edgar

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It’s the 29th of March, 1927.

The location is the long stretch of sand at Daytona Beach, Florida. The car, the like of which has never been seen before, is an ultra streamlined machine of imposing length – all 6 metres of it.

Under the skin there are two enormous engines, each a V12 of over 22 litres capacity. Power? Nearly 1000hp.

The man behind the large, thin-rimmed steering wheel is Major H O D Segrave.

And he is about to go faster than anyone has ever driven a car…

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The 1000hp Sunbeam – otherwise known as Mystery – was designed by Louis Coatalen, chief engineer of Sunbeam, a major car manufacturer in the United Kingdom. Detail design work and construction were left to Captain J S Irving – a name that was to be well associated with later Land Speed Record cars.

The new record contender aimed to achieve success through two main technical approaches – a lot of power achieved through the use of two engines, and low aerodynamic drag achieved through all-enveloping streamlining.

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The engines comprised Sunbeam Matabele aircraft engines.

The 12 cylinders were cast in blocks of three and arranged in a V angle with an included angle of 60 degrees. Bore was 122mm and stroke 160mm.

Each cylinder used four valves, operated by overhead camshafts, and each cylinder used two spark plugs. Four six-cylinder magnetos were used on each engine to provide ignition.

Carburetion was by two Claude-Hobson carbies positioned within the vee. Power output was 500hp at just 2000 rpm.

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The rear engine straddled the rear axle, while the front engine was placed just behind the front axle.

Each engine had its own radiator positioned ahead of it, and each engine was mounted in a subframe that in turn was mounted to the main chassis by three ball joints.

The engines were mounted back to back, with the small flywheels pointing towards the driver. A system of clutches allowed the front engine to be used to start the rear engine. To reduce the size of the frictional clutches and gearbox, engine speed was increased by 2.5 times to reduce the required torque handling. Following the 3-speed gearbox, the speed was reduced by further gearing before final drive was made to the rear wheels by two chains.

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During development, the car was placed on a custom axle dynamometer that used Heenan and Froude retarders. Contemporary accounts say that over 1000hp was measured by the dyno.

The chassis of the car used two longitudinal deep-channel girders, braced with channel section cross-members. The longitudinal chassis members were 35.5cm deep, spaced 108cm apart in the middle of the car but tapering in plan view at each end.

Given the large external dimensions, the wheelbase and track of the car were relatively small at 11 feet 9 inches (3.58 metres) and 5 feet 2 inches (1.57 metres), respectively.

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Half-elliptic springs and solid axles were used front and back, with the rear axle kinked downwards in its middle to avoid the engine above. Four-wheel mechanical Dewandre drum brakes were fitted and four Hartford friction dampers were used per axle.

The shape of the car was extraordinarily unusual. The top of the bodywork was only 117cm above the ground. The air intake for the front radiator was through a rectangular opening let into the otherwise curved front. Openings in the side of the bodywork provided air exits for the front radiator, while scoop inlets were used for the rear radiator and engine.

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The body shape was developed through the use of models tested in the Vickers aircraft wind tunnel at Weybridge. These tests indicated that on the full-size car, aerodynamic downforce at the front could reach 320kg while there would be 90kg of lift at the rear. (However, other sources suggest that the rear diffuser was designed to provide rear downforce – so these figures may have been reversed over time.)

It was estimated that at 200 mph, 355hp would be needed to overcome air resistance. (However, again there is confusion: a different contemporary source says 500hp.)

The body was made of aluminium. Complete with fluids, the car weighed 4 tons.

At the time, the car’s shape led to a rather irreverent nickname – the “Slug”.

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When the car reached Daytona, it had never been driven at high speed – there was no suitable test surface available in the UK.

A crown of 30,000 lined the dunes on Tuesday, March 29, 1927. At 9.30 am, Segrave started his first run, driving north into the wind. As with all Land Speed record breakers of the time, Segreve changed up the gears as he went – at 90mph changing into second, and at 135 mph into third.

Side winds pushed the car around and he knocked over some marker flags; the car was slow to respond to the steering inputs.

Reaching the end of the course, Segrave braked – but little happen. To slow sufficiently he had to steer into the sea, the shallow water achieving what the brakes had not.

On the return run the wind again blew the car around, but he was able to hold the car on course.

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The timing officials checked their calculations and then announced a new Land Speed Record: over the flying two-way mile, a speed of 203.792 mph. It was the first time anyone had exceeded 200 mph – 322 km/h.

And it had been no mean driving feat. Segrave commented later: “When 200 miles an hour becomes the normal speed of travelling, there will have to be a new design of braking system, new steering gear, and a different weight distribution. With the present equipment there is practically no control over the machine at that speed, or at least it answers so slowly as to make the controls almost worthless.”

Segrave’s record stood for only 11 months before it was beaten by Malcolm Campbell, again on Daytona Beach.

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