Under scrutiny -- Mercedes C291

Dr Hermann Hiereth, technical director of the Mercedes Sportscar World Championship programme, and car designer Leo Ress explain the background to the high-technology C291, the new "Silver Arrows" sports car.

Mercedes, Jaguar and Peugeot had spent two years preparing for their first confrontation in FISA's Sportscar World Championship, and their high-tech challengers met for the first time at Suzuka, Japan on April 7. At once the Mercedes C291, the Jaguar XJR-14 and the Peugeot 905 made the Porsche 962s, even the year-old Mercedes C11, look old, heavy and cumbersome, as indeed they must be with a weight penalty of 200-250 kilogrammes.

Sportscar racing, as the traditionalists know it, is now a thing of the past. The races are over and done with in 430 kilometres, little more than two hours' worth of Monza or Silverstone, and the term "two-seat Grand Prix cars" seems entirely apt.

The old-generation Group C cars were designed to win the 24-Hours of Le Mans, and then honed, adapted and modified to win "sprint" races as well -- the new breed is thoroughbred, nervous and twitchy, seemingly at the outer limits of control, and will need some persuasion to last around the clock when put on duty for 24 hours.

Perhaps the Mercedes C291 is an exception, though. Maybe it is next year's Le Mans winner, and if rumours are correct, the car to give the Stuttgart company its triumphant farewell to sportscar racing, and an entree to the world of Formula 1.

The C291 maintains a Silver Arrows tradition of being unorthodox in design, yet Dr Hermann Hiereth maintains that any attempt to be different, for the sake of it, would have led to compromise.

Mercedes' board of management gave the go-ahead for a new challenger in the 3.5-litre class in 1988, as soon as FISA announced that the new formula would be launched on January 1, 1991, and research started early in 1989. "The research took two months and involved 15 concepts" says Dr Hiereth. "Some were conventional and some were very advanced, and we formed a team of five to consider them."

The five were Dr Hiereth, his assistants Gert Withalm, Willy Mueller and Sigurd Heinmuller on powertrain development, and Leo Ress, who works for Peter Sauber in Switzerland as the overall car designer, with special responsibility for the chassis, suspension and aerodynamic bodywork.

"We made a notebook of the parameters we wanted to achieve" Dr Hiereth recalls. "The output of the engine (650 horsepower was our target), a certain weight (it had to be the minimum, 750 kg), a certain length, and the most important thing, the aerodynamic efficiency.

"We considered eight, ten and twelve cylinders, and what you see today is the result of the conclusions we reached...a 180-degree, 12-cylinder engine which gives us a very low centre of gravity, without any penalty concerning the aerodynamic efficiency."

The first engine built by Mercedes at 3.5 litre capacity was a V12, constructed from two experimental V6 engines which happened to be available in the company's research department. Drive was taken from the centre of the crankshaft, and the engines were of aluminium construction with four-valve cylinder heads.

"We started with an output of 530 to 540 horsepower, and realised that this is the base which anyone can achieve -- the problems begin when you get to around 600 horsepower, where we are at the moment."

Leo Ress confirms that a single, full-width venturi tunnel underneath the flat engine is more effective than two more conventional tunnels, one each side of a vee. "It was hard work to get the package balanced, because the flat engine allows a low centre of gravity but the gearbox makes it higher. We moved the gearbox a bit in the wind tunnel, and when we looked at the result we redesigned the gearbox!

"I had no experience of an undertray like this, and I was busy with the C11 when they made the initial studies. When we got to the wind tunnel we realised that many things would have to be changed, but in the end we reached a good compromise."

It was no easy matter developing the C291. There were a great many new-car problems when the car was tested at Paul Ricard and Jerez — indeed, a team is expected to meet these problems, and deal with them — to do with the oil circulation in the flat-12, and with the unusual 6-speed, transverse gearbox.

At Suzuka it immediately became apparent that the new Mercedes was off the pace of the Jaguars, though competitive with the Peugeot 905s, and this was underlined at Monza and Silverstone in the next six weeks. The Jaguars are around four seconds faster on an average lap, and up to 10 kph faster through speed traps. Such a difference is enormous and would cover a Formula 1 grid from pole man to back-marker.

Visually and with a stopwatch, an observer can tell that the C291's chassis is virtually the equal of Jaguar's but acceleration out of the corners is relatively slow, indicating a poor power-to-weight ratio. Peugeot's handling is obviously nervous and the drivers have difficulty putting down the power of the V10 engine, so for the time being the Jaguars have a clear advantage. The next test comes at the Nürburgring on August 18, when Mercedes and Peugeot fervently believe they will narrow the gap.

By the start of next season the Mercedes will be down to 750 kg and the power output will be at, or near the 650 horsepower mark. Progress was made in the first three races and the whole team was heartened by the second position at Silverstone (a result that enabled Sauber Mercedes to remain at the head of the Teams Championship). The objective, though, is to win races in 1992. . . . nothing less will be good enough.

The C291 raced at Suzuka weighed 790 kg and the engine was underpowered, so the areas of development are obvious. By the time the car had got to Silverstone it had shed 15 kg (the acrylic windscreen saved 5 kg and another 5 kg was pared from the transmission). Ress says that the next 15 kg will be more difficult, and Dr Hiereth concedes that the missing 50 horsepower may not be found before the end of the year.

Clearly this year's results won't match those of the past two championship winning seasons. The cost of innovative, complex design has been dear in terms of early results, and already Mercedes is beginning to regard the C291 as a machine that will mature.

"Maybe we started too complicated for the organisation we have" says Ress. "Walkinshaw is much more experienced in racing, more professional I would say, and he didn't need to develop the engine. Perhaps it would have been better for us to have a safe aim, to have the car running, because if you make your steps too big you always struggle, you never reach the goal."

Few designers would have considered a flat engine in the era of ground-effects, but the C291 clearly has superb handling in the high-speed corners. Schumacher and Wendlinger show breathtaking control in a car that runs rings round the old turbos, and at Monza Schumacher said that he had to brake at odd times to avoid running into the back of Fabi's Jaguar!

Despite the unusual configuration the car has considerably more downforce than the C11 (neither Dr Hiereth nor Ress would quote any figures), and the full-width venturi tunnel has the maximum permitted depth of 28 cms. Clearly the concept is sound.

The design of the engine is unusual with the fuel injection system alongside the cylinder heads, injecting between the twin plugs and four valve stems, and the exhaust ports on top. Drive for the transmission is above the centre-point of the crankshaft and that involves having a gearbox that's higher than the engine.

A monobloc construction is used (like that on the Porsche 962) with welded cylinder heads, a solution that gives the engine great strength and high thermal efficiency; these were extra advantages sought in the flat-engine configuration, Dr Hiereth confirms, not available in a vee engine. It seems likely that in time, the engine will develop 650 bhp at 14,000 rpm, compared with 13,000 rpm at Suzuka.

"The engine is overweight" says Dr Hiereth. "At Mercedes we can't have an engine that doesn't work, you see, so we had to build everything a bit bigger, or a bit stronger, to make sure that everything works from the beginning. We will reduce the weight, and increase the power step by step, but it will take time."

TAG Electronics, a McLaren subsidiary headed by Dr Udo Zucker, supplies the advanced engine management system which is unique to the C291. A comprehensive telemetric system is incorporated and Dr Zucker, recognised as the 'father' of the Motronic system while at Bosch, says that five million bits of information are transmitted per second...enough to occupy 1500 telephone lines at one time.

"At first," says Ress, "we had 16 kilos of measuring equipment on the engine. . . . imagine that! It takes one hour just to put tie-wraps around the lines. . . . it takes six hours to change the engine and another six to get it running! The objective is to be able to change an engine in three hours, but that's not going to be easy either."

The chassis and body were clearly the easy part of the design, comparatively speaking. Despite the similarity in appearance to the C11 Ress denies that the C291 is an evolution, although he adds with a laugh, "everything you do is an evolution of yourself, and I am a sports car designer."

The composite material monocoque easily passed FISA's mandatory crash test which involved loading the sledge to 900 kg and running into a block at 56 kph. The test, at Unterturkheim, was observed by FISA engineer Patrice Catalano. Then the body, which has an integral roll-over hoop in the roof, was voluntarily subjected to a massive 8.5 tonne crushing test, in which it yielded just 2.6 mm.

The body regained its shape when the weight was removed, and has been put through the test twice more without coming to harm. The drivers can sleep easy, knowing that the highest possible safety standards have been reached.

Much comment has been made about the full-width aerofoil at the front, like a double skin above the real nose, which forces air into the cooling ducts on both sides of the windscreen base. The first model, Ress explains, was a C11 nose with the radiator taken out, and the wind tunnel effectiveness persuaded him to develop the idea.

"Without the upper skin the front looked very ugly, and then we just glued a panel in. Everyone thought there was a radiator in there, but the wind tunnel results were good. We have good figures for cooling and downforce, and the rear downforce is good too, air over the wing."

At some stage the size of the twin water radiators had to be increased, and at that point the design grew a pair of 'ears' behind the door apertures, actually cold air boxes for the engine. It's a neat solution compared with the collector boxes on the roof of the Jaguar and the Peugeot, and is good for the flow of air over the wing.

It was Dr Hiereth who expressed satisfaction with the aerodynamic efficiency of the C291. "Our design allows better aerodynamic efficiency than two tunnels.

The effectiveness is defined as drag coefficient divided by downforce, and this gives you an aerodynamic efficiency factor.... or vice versa, if you like, downforce divided by drag coefficient. We are above the C11 by far, and that was considered to be an efficient car." Dr Hiereth declines to say how much stiffer the C291 may be, but offers that it is twice as stiff as the C9 model in 1989.

The suspensions are very different to those on the C11, which is interesting. In order to keep the rear tunnel clear and unobstructed the springs and shock absorbers are located inboard, transversely on top of the gearbox and operated by push-rods and levers; the gearbox itself is installed transversely and its operation is novel, on motorcycle principles with a push-pull lever (Michael Schumacher mentions that it takes 0.1s to change gear, against 0.2s in the C11).

Front suspension, moved inboard on the C11, goes outboard again in order to have a clean monocoque with no apertures; Ress was concerned to pass the frontal crash test with ease, another reason for the double-skinned nose. Also, it is far easier for the mechanics to maintain, with spring and damper changes taking only a few minutes. The C9's suspension was mounted on the lower wishbone, but the C291's is located on the chassis and operated by pull-rods.

Brakes, of course, are carbon from the Brembo company, and suppliers include Goodyear for tyres, Sachs for shock absorbers, TAG for electronics, Behr for radiators and Castrol for lubricants. Curiously, in the car prepared for Schumacher and Wendlinger, the dashboard is marked entirely in English, "the international language of motor racing," as Jochen Neerpasch explains.

Future developments include automatic, or semi-automatic operation of the gearbox, and active suspension. An active suspension system has already been developed on the C11 but the weight penalty, in the early stages, is some 40 kg, and that's out of the question for the C291 at the moment.

It is a Mercedes system similar to that in top-model passenger cars involving electronic control of springs and shock absorbers, not the Lotus patent system with hydraulic rams. "Michael Schumacher is a great fan of the active suspension, but he has to be patient for it," Dr Hiereth says with a smile.

Mercedes and Sauber have built a car with enormous potential, of that there is no doubt. In 1992 it may well prove to be the pace-setter, a machine in advance of its time, but Dr Hiereth and Leo Ress also acknowledge that the Jaguar will have progressed too by the start of the '92 season.

There was never any chance that they could repeat the domination of the Silver Arrows in 1954-55, a time when, as Stirling Moss says, "there would have been something wrong if they had not won all the races, such was their superiority," and the same might be said of their domination in 1989 and 1990. If Mercedes should decide to tackle Grand Prix racing, as many people suppose they will, all the hard lessons of the current programme will have to be analysed thoroughly -- MLC

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Key Features

Peter Sauber, team principal, is 47. He and Leo Ress designed the C8 in 1983/4 around the Mercedes-Benz V8, twin turbo engine. The C8 first appeared at the Le Mans qualifying in 1985, and looped at the end of the Mulsanne Straight. First race victory Nürburgring, August 1986. Mercedes gave official support in 1988, when AEG sponsorship replaced Kouros. The C9 became a 'Silver Arrow' in 1989, won world championships 1989 and 1990. The C291 engine and transmission are designed and built at Unterturkheim. Chassis build at Peter Sauber's headquarters in Hinwil, near Zurich. Wind tunnel at Unterturkheim.

Suzuka: retired with faulty fuel nozzle, fire follows first pit stop. Monza: retired first pit stop, broken starter ring (as in qualifying). Silverstone: finished in second position -- MLC