In this final part, Steve Randle concludes his proposal for a latterday successor to the seminal Citroën DS.
Previously, we explored styling, power unit and drivetrain. Today, Steve Randle outlines his thoughts on body structure and vehicle dynamics.
Structure: “Aluminium and magnesium would dominate the vehicle. The recycling problem with composites – particularly thermosets – are a concern. While both Aluminium and magnesium alloys are expensive in the first instance, they are easy to recycle.”
Driven To Write: Given the problems inherent with using aluminium for the upper structure of the vehicle – the necessity for much stronger and thicker pillars/smaller openings – how would you see this being resolved? What areas of the structure would the use of magnesium benefit from?
Steve Randle: “Magnesium is good for seat frames, dash beams and so forth. With modern jointing techniques, a mixture of materials is no problem. Steel for door beams and pillars is a good solution. Castings are helpful where section nodes and hardpoints are required.”
Chassis: “I would retain the gas hydraulic approach for both practical and cultural reasons. The system should be configured to eliminate warp stiffness – this idea was successfully introduced in the McLaren 12C, though steel road springs were retained. Use of a completely gas hydraulic system would provide further ride benefits, as would pitch interconnection. The high speed damping valves now available would be useful in optimising ride composure. There is still an issue with any gas or air suspension in that the spring becomes stiffer with suspension velocity (the adiabatic / isothermal issue), but we would be running lower ride frequencies which will help.”
“We also have a few ideas we could apply to further improve matters here. I would also introduce more longitudinal compliance into the suspensions – having the frequency below wheel hop gives significant benefits. We’ve developed multi-link suspension systems that can deliver this while still giving the necessary elasto-kinematic properties. Finally, I would like to see a return to higher profile tyres. 17” wheels were declared some years back by Michelin to be the point beyond which there was little point in proceeding unless you need huge brakes or styling demanded it. I don’t believe anything has changed since then. We’ve also been involved with some interesting research work into adaptive camber controlled suspensions – this allows a narrower, lower drag tyre to be run without loss of grip. I’d like to investigate this further.”
DTW: Can you elaborate upon ‘warp stiffness’ and how it manifests itself?
SR: “Warp is when each axle is in roll, but they are in opposition. (like jacking up front right and rear left). A fully interconnected system where the four degrees of freedom are warp, heave (all wheels in phase), pitch (front & rear out of phase), and roll (left & right out of phase) would be an interesting approach.”
DTW: With wheel diameter limited to 17″, what about tyre aspect ratio? Would you advocate a taller sidewall than the 60-series which appears to be the most generous nowadays.
SR: “I think 60 profile tyres are a reasonable compromise. I’d seek to work with Michelin on this.”
DTW: Regarding Oleopneumatics, would you advocate a totally analogue system, the electronics-assisted version used in the latter-day cars, or a full electronically governed system?
SR: “Electronic control offers a greater range of possibilities and performance.”
DTW: I would assume braking would be handled by this oleopneumatic ‘ringmain’ as well. Is there any benefit to the driver in the original ‘solid’ brake, or would you apply an artificial travel as Citroën did latterly?
SR: “The road car brake pedal is an interesting combination of displacement and force control. Clearly, even the original Citroën brakes had a small amount of displacement. Racing drivers rely pretty much exclusively on force. I think a firm pedal with an appreciable amount of motion is preferable. Enough to remind you it’s a Citroën.”
DTW: Given that light weight is likely to be a key element of this vehicle, are there any merits in revisiting the idea of composite wheels – a la SM?
SR: “Carbon has its place, but I’m not sure it’s in a road wheel. I’ve seen some good looking solutions, but they’re not spectacularly light. They are however spectacularly expensive. Aluminium alloy wheels are typically design driven and are usually heavier than a steel wheel. Magnesium has been unfairly overlooked of late I think, as the corrosion issues have now been addressed.”
Steering: “We are developing an electric steering system which will provide manual steering levels of feedback with the potential for adaptive vehicle dynamic tuning. I’d like to see this in the car.”
DTW: What is your position on the subject of four-wheel steering?
SR: “There’s a lot we can achieve with front steer intervention, and with adaptive camber control. With both of those, rear steer becomes superfluous I feel.”
DTW: Have you reached a conclusion about the autonomy question?
SR: “Autonomy is coming, but I think it’s a yes or no answer. I have grave concerns about partial autonomy (throttle and brake only for instance), or expecting the driver to step in if things get tricky. I really feel that is asking for trouble. I believe that something needs to change significantly in the cockpit if the car has selectable driver and autonomy modes (steering wheel folded away, seat turned around or similar). You can’t risk the driver forgetting who is in control. If you’ve got used to an automatic, it’s easy to forget to dip the clutch of a manual as you come to a halt. That’s not a life-threatening oversight though.”
DTW: Given that the turbine idea has so much merit (and appears such an elegant solution), why is everyone blindly piling into batteries? Is it the path of least resistance?
SR: “Batteries are the bandwagon right now. They have their place as part of the solution – demand smoothing in particular. Energy density is still poor, as are their whole life cost and environmental impact. I would sooner carry as few as reasonably possible.”
As we draw our ruminations to a close, I ask Randle to reflect on such a vehicle’s likely reception with the motoring public. “Having successfully put off 90% of luxury car buyers, I intend that this car will be the firm favourite of those that remain. Far better that than everyone’s third or fourth favourite.”
We began this piece with LJK Setright so it’s appropriate we conclude with that great iconoclast, wordsmith, aesthete, critic and commentator, who summed up the original, the only Déesse in inimitable fashion. His words apply equally here I feel.
“No car had ever been cleverer. No car was ever braver. The DS should have inspired the world to embark on a new course of motor engineering, to accept and advance the new standards that Citroën had set. All it did was gratify the desires of 1.3 million people, to stimulate a lot of arguments, to expose a great deal of ignorance and to stand as a lasting reproach to the rest of the industry whenever we compared what they were making with what, on the evidence of the DS, they should have been making. If it achieved no more than that, it was not the fault of Citroën, it was the fault of everyone else.”
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