Elemental Rp1

The lightweight, road-legal sports car uses a carbon-fibre tub, turbocharged gasoline engine and sequential transmission

The core of the engine is the same, however, with the crank, pistons and valves untouched. But because of the changes introduced, the CO2 emission figures for the vehicle have still to be confirmed.
To keep the centre of gravity as low as possible in the Rp1, the engine is mated to a Hewland JFR six-speed sequential transmission in a mid-mounted, longitudinal layout which also contributes to better vehicle balance.
It is, perhaps, surprising that a sports car would have the option of an engine as small as 1-litre. But a comprehensive approach to reducing weight across the vehicle means that the three-cylinder engine has an estimated top speed only 22km/h slower than the larger unit.
The desire to take as much weight as possible out of the vehicle means that even the water pipes on the radiator are made from aluminium.
However, by far the most significant contribution to keeping the Rp1’s kerb weight down to 650kg is made by the 68kg, carbon-fibre, one-piece composite tub. “Initially it was a two-part composite structure that we bonded together, but it was time-consuming and cost a lot,” says Peter Kent, composites director. “Structurally it was fine, but we had to have a better solution than that as you could see a bond line on the finished component. We spent a lot of time developing a one-piece, and the secret was all in the tooling.”
The lightweight tub is built to FIA standards of strength and stiffness, and consists of carbon side pods and a dash panel with an integrated structural cross-beam.
Laser-cut, aluminium sandwich panels form the bulkhead and floor panels, while the subframes are tungsten-welded high-strength steel that carry the loads of the suspension and powertrain.
Much thought went into the decision to use specific materials in certain areas of the tub, says Begley. “Originally it was going to be an aluminium honeycomb structure, so more an LMP-type thing, and it evolved into the carbon/aluminium structure it is now.
“There is no point using carbon fibre throughout the whole vehicle – the bulkhead surfaces, for example – because it doesn’t bring any extra benefits. Maybe some areas could be replaced for carbon but you’re not going to save any weight and could actually take up a little more space,” he says.
In addition to its lightweight properties, the tub’s design gives the driver a Formula One-style ‘feet up’ seating position – something that was included on the first sketches of the car at the beginning of the project.
More than simply a gimmick, it maximises aerodynamics in the vehicle, as the front diffuser fits into the space created, while the angle of the rear bulkhead at 60° means the diffuser at the rear starts more centrally than normal.
Begley, whose final project at McLaren concerned aerodynamics, describes the result as effectively turning the underside of the car into a wing. The front diffuser sits behind a custom-made, marine plywood, front splitter that directs airflow as it hits the underside of the car, while a central flat floor panel creates a large, smooth surface.
The co-efficient of drag of 0.4 is not hugely impressive, but the downforce generated by the diffusers helps the tyres to grip the road. “Being so light obviously can cause a power-to-weight ratio issue, but generating the downforce that it does – even at motorway speeds – we have the effective weight on the tyres of a heavier car but the inertia is kept as that of a low-weight car,” says Begley.
To have a vehicle enter the fray that benefits from fresh engineering approaches and perspectives as the Rp1 does can only be a good thing for the industry.
It will be intriguing to see the car’s impact over the coming years.

tags: Elemental Rp1 High Performance
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