Design Development: Riversimple Rasa

19 December 2016 | by Lem Bingley

In February 2016 new British startup Riversimple revealed its Rasa prototype, a hydrogen-powered, carbon-fiber car designed to pioneer not just fuel cell propulsion but an entirely new business model.

Rather than selling or leasing its vehicles, Riversimple aims to offer its cars like mobile phones – with a fixed-term contract for hardware plus a rate for usage. Monthly fees will include insurance, servicing, repairs, parts, tires and even the cost of fuel.

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“The fixed-price element will fall as the car gets older,” explains company founder Hugo Spowers. “Even for a secondhand owner, costs are entirely predictable. You’re never going to be hit with a surprise bill because something’s broken.”

Riversimple hopes these arrangements will give each Rasa a working life of at least 15 years, spanning multiple contracts and several different users. The car has also been designed for easy recycling at the end of its life, yielding greater than normal value from recovered materials.

Riversimple Rasa Rear Three Quarters High Res

The company’s novel business model is intended to make hydrogen fuel cells viable as a direct competitor to internal combustion, as pockets of potential users spring up around the first hydrogen filling stations. Riversimple has developed an extremely lightweight vehicle (around 580kg) that requires only a small fuel cell stack, curtailing what would otherwise have been a prohibitive technology cost. Low mass also helps the Rasa to run for about 300 miles between fill-ups.

“Our commercial viability hugely depends on weight,” says Spowers. “That’s what drove us to a two-seater. If you have a 2+2 you’re going to have a higher gross vehicle weight, so you need a stronger body, bigger motor, larger fuel cell. Everything spirals upwards faster than the price we can charge.”

120216 Riversimple

These requirements also led to carbon fiber construction, while Riversimple’s responsibility for running costs has driven an intense quest for efficiency. With fixed fees, every penny saved in operational costs adds a penny to the bottom line.

Spowers hopes this approach will enable a virtuous circle that has so far eluded the automotive sector. “At the moment if you make cars, there’s no incentive to prioritize efficiency,” he says, “Because customers will discount future savings almost to the point of zero.”

Exterior

Design director Chris Reitz joined Riversimple in 2010, shortly after quitting his role as Alfa Romeo design director to focus on his family’s business. Early in his career he worked on the VW Lupo 3L and Audi A2, a pair of highly efficient cars that saw weaker than expected sales. When work on the Rasa began in late 2013 he was keen not to repeat that experience.

“The car has to be attractive, even if it does things very well in comparison to other cars in aerodynamics or in being lightweight,” Reitz asserts. “That doesn’t mean it has to be expensive, but it must be something you’d like to be seen with.”

While overall length at 3.7m is city-car short, a long and low shape was needed for clean aerodynamics. Reitz says the first Porsche, the 1938 Type 64 Berlin-Rome car, was a key inspiration: “The early streamlined cars, the influence from aeroplanes and the cockpits of planes in the 1930s inspired us.”

Porsche Type 64

Initial brainstorming led to a wide variety of different proposals.  “We had cars that were extremely futuristic or wacky looking,” Reitz says. “But we decided to go more on the elegant, classical approach because longevity is very important to Riversimple. If we do something very fashionable it will age very quickly.”

Around ten initial proposals were cut down to a shortlist of three. “From there we had three full-size models made to appreciate the size, and also the size impression because the car should not look too flimsy,” Reitz says. The Rasa is a small, light car but the intent was to emphasise its strength. “It has to look strong enough that it won’t just fold up like a paper model in an accident,” he observes.

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Milled clay models were reworked manually, scanned and run through CFD software to assess aerodynamics. A lot of tweaking was done but the software results were so good they seemed hard to believe, Reitz recalls. The models went into the wind tunnel at MIRA in the UK to verify the calculations. “It was a very big positive surprise,” he adds.

Unusually, the Rasa’s teardrop shape has been optimized for modest speeds – below 70km/h – whereas behavior above 80km/h is normally the chief concern, Reitz says. “The belly of the Rasa is very high off the ground and there is plenty of draft going under the car,” he adds. “For high-performance cars this is something you don’t want, because you would start lifting off.”

Riversimple Interior Door Opened Warehousecrop

Dihedral doors were chosen not to add drama but to ease access to the cabin. “We are below 1.3 metres and we have expectations that the car will not just be used by young, agile people,” Reitz notes. That means taking part of the roof away, to avoid the need to stoop under a low cant rail.

“The doors also allow the sill to be wrapped in tight against the seat,” adds Spowers. “That makes your leg throw as small as possible, which is the key issue when standing up from a low seat.”

Interior

Riversimple’s focus on efficiency had a great influence over the Rasa’s cabin. “We had just 44 kilos to trim the whole interior – seats, door trim, dashboard, carpets, whatever you have inside,” Reitz says, adding that a single seat in a luxury vehicle like a Bentley would typically account for 90% of this mass.

Riversimple built several full-size interior models to explore what they might leave out. “We had one proposal where we eliminated almost all the dashboard, so you felt like you were in a helicopter,” he recalls. “The space impression was incredible but everybody felt the same thing – it did not communicate any safety.”

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A wide range of trim materials were evaluated for weight, durability and the potential for refurbishment between customers. Achieving multiple outcomes from single components was also vital.

Rasa’s floor covering, a natural rubber used inside Japanese Bullet trains, is typical. “It is extremely durable but can be manufactured with air pockets inside. It becomes the damping material we need for sound insulation, and it’s very good in vibration. It also gives us coloring options,” says Reitz.

The body’s carbon structure is revealed throughout the cabin, partly through necessity. “We can’t do a typical A-post cover because that’s weight we’d prefer to put into seat comfort,” Reitz says.

Exposing the structure throws up further challenges. “Carbon becomes very beautiful when you lacquer it, but lacquer adds weight and on top of that it’s extremely expensive,” Reitz notes. As a result, not all visible carbon will get the same finish: “It’s challenging but we believe if it’s done honestly it’s acceptable.”

The prototype Rasa’s interior has been upholstered in artificial suede made from recycled polypropylene bottles. The textile is automotive grade, UV resistant and fire resistant, Reitz says. “And on top of that it’s very light,” he adds.

Riversimple Rasa Interior High Res 1

The meager mass allowance has not stretched to air conditioning, perhaps explaining why air vents are “on the hidden side,” according to Reitz. The uncluttered dash that results emphasizes the central touchscreen.

The dashboard also offers some unusual storage options. “There’s a frame underneath allowing you to hang things,” Reitz says. “You can go shopping and attach them to the dashboard, so they’re not flying around.”

Front airbags are another missing feature, though there will be curtain bags for side impact protection. Spowers says the Rasa’s unique layout provides “much more crushable structure than a normal car”, removing the need for extra cushioning in frontal impacts.

Conclusion

Riversimple’s business model and the unusual design decisions that flow from it are due to be tested shortly, when prototype Rasas begin trials with potential customers. Those early adopters will sample one of the lightest vehicles put on the road since the bubble cars of the 1950s and 60s.