Leading the Chase: Interview with BMW's Willi Rampf

With the 2007 season now over, BMW Sauber can rightly look back at the season as their best yet.

Even as the independent Sauber team their best result in the constructors' championship was fourth back in 2001, coincidentally with Nick Heidfeld as part of the team. This year, their results placed them second - or, more realistically, third in the constructors, if you discount McLaren's penalty.

Backing up the teams' performance was the drivers consistently finishing firmly behind the runaway leaders at Ferrari and McLaren, and clear of the opposition.

Sauber were always a solid team, bringing results with reasonable budgets. Their takeover by BMW in June 2005 led to increased resources and greater integration with the engine supply. The power train (engine gearbox and electronics) development went under one roof in Munich, leaving the chassis side at their base in Hinwil, Switzerland.

Already the factory boasted a state of the art wind tunnel and the teams' first CFD supercomputer, 'Albert'. This year started with the construction of an extension to the factory. Their second supercomputer (in preference to a second wind tunnel) had already been commissioned in December 2006.

Leading the chassis operation at Hinwil is Willi Rampf, a Sauber stalwart and one of the more underrated technical directors in F1. He took some time this week to speak to Autosport.com about a dramatic season and the impressive F1.07.

Design

While the process of investing in the team's facilities following the BMW takeover took place, the team raced the F1.06 through the 2006 season.

This car was identifiably a progression from the previous Sauber car of 2005. BMW's investment in the Swiss factory was evident with the increased running of the wind tunnel and Albert 2, the second CFD supercomputer.

I asked Rampf whether the changes were also apparent in other areas of the team.

"We have increased the manpower in all the engineering departments," he said. "In the design office, in simulation, in rig testing and the biggest part was definitely aerodynamic department."

In preparation for the 2007 season, the team was able to make greater use of more staff, funds and resources to plan the new car. This took the form of a series of CFD evaluations into various concepts around the car, the nose layout, the wings and the cooling system.

"We have done quite an extensive evaluation of the cooling system, because in the years before we were sometimes a bit tight on cooling," Rampf said.

"When we have to run more open than the design specification, you lose a lot on aerodynamic performance. For the F1.07 overall, the cooling was on target and even slightly better than expected."

These extra resources and the process of getting the basics right proved to be beneficial when the late change to a single tyre supply from Bridgestone was announced.

"We only received tyre data at the time when the car was already designed," Rampf explained. "So we had to consider this at a fairly early stage, doing some simulation and making some assumptions on what we could expect. Concept-wise we built a car, or developed a car, that was able to provide a wider range of weight distribution than a normal car.

"It needs to be flexible. The same also applies to the aero balance, which goes with the weight distribution."

While the aero and weight demands were critical, Rampf felt the changes to suspension geometry were less of an issue:

"On the mechanical side, I think that all cars are in a similar range of mechanical set-up. The cars are, say with regards to settings, flexible to cope with the requirements of the tyre when it comes roll stiffness and overall body stiffness."

Certainly the convergence of design across most teams sporting zero keel suspension and easily adjustable roll and pitch controls backs up his assertion that if the basic layout is right, then the detail of the set-up should be within the reach of most cars.

However, Rampf feels that the tyre deformation issue was one that was important for the teams to cope with. The shape of the Bridgestone tyre, both when static and when flexing during braking/cornering, is different to the Michelins.

"We did extensive testing and simulation to cope with the Bridgestone tyres, and this helped as well," he said.

This suggests that BMW Sauber are one of the teams that aim for a close interaction between the front wing endplate and the tyre, rather than trying to make the aerodynamics insensitive to tyre deformation, potentially at the cost of some performance.

This in turn means that BMW Sauber may be pushing the aerodynamics harder than some teams.

"That's one of the critical areas, and here simulation was quite useful," Rampf said. "With the help of CFD, it gives you an idea how sensitive the front end is, and then you can prepare the model to do the development work."

Although the aero shape of the tyres was something that could be researched off-track before pre-season testing, the tyre's physical characteristics were something that needed track time to understand - especially when the disparity between the front and rear tyres was discovered. Did this come as a surprise to the team?

"The thing was unexpected when you came from the Michelin tyre, but in the early testing we saw that this will be the case, that there's a strong front tyre," Rampf said. "Then we tried to prepare the mechanical set-ups accordingly, and the preseason testing was enough to find decent settings".

Again Rampf confirms that the aim to make a car with a flexible set-up window paid off.

"Also," he said, "the car having wider range of weight distribution than normal helped to be able to cope with this tyre."

The 2007 Bridgestones proved hard to balance. The front tyre gave immense grip but the rear tyre was much weaker, which made the front of the car very stable to the point of oversteer.

Getting a balance front-to-rear was one task, and helping the drivers cope with the different balance of grip was another. In this respect, Nick Heidfeld's smoother style worked well with the tyres, but the more aggressive turn-in style of Robert Kubica struggled.

"For Nick, it was not a big problem," Rampf said. "For Robert, it was more a problem at the start of the season, particularly with braking and turn-in because the front was very stable.

"We did a lot of fine-tuning on the engine braking and on the mechanical settings to make the handling characteristics better for Robert. He likes a car less sensitive to this manoeuvre".

Again, the car's conceptual flexibility reaped dividends, as the it did not differ physically between the drivers.

"The cars overall were very similar," Rampf agreed. "[The difference] was mainly the mechanical set-up."

2007 Season

If you can characterise an F1 car, the 2006 BMW Sauber, was better on low downforce/drag tracks. Thus, the car struggled with higher levels of downforce and at tracks which demanded more mechanical grip.

Comparing these traits to the F1.07 car that was so consistent throughout the season, it's clear Rampf and his technical team have made progress on the car's low-speed grip.

"I think on the mechanical side we have had some improvement," Rampf said. "But also we paid more attention on good downforce in conditions like yaw and steering, and this has been helping the low-speed corners more than the high-speed corners."

At the car's launch, Rampf said the its ability to create downforce at all attitudes was more important than simply creating more downforce through a more limited range of attitudes.

This reduction in sensitivity starts with the correct aims for aerodynamic performance, which are less of a drop-off in downforce when the car rolls, pitches, yaws or steers. Then, using CFD and the wind tunnel, find solutions that meet those targets. Its clear that BMW Sauber, like McLaren, have found a balance in finding enough downforce in all conditions.

Yet these improvements still left the team trailing behind the top two teams.

"I think on average it was about five-tenths," Rampf said. "We calculate in kilometres; one tenth per kilometre."

This is still quite a large amount of time to find over the winter for 2008, something Rampf agrees: "Yes. it's definitely a big gap."

Yet if the gap to the leaders was significant, so was the team's advantage over the rest of the field. With the team operating alone in the space between Ferrari/McLaren and the rest, their race strategy options were quite clear.

"We were not too worried about the cars behind us, we tried to fight the cars in front of us with strategy," Rampf explained.

"We were very close and tried to jump a car during qualifying, because we knew with the pace we had, we should finish in front of the cars behind us."

As a result, the team often ran light in the final qualifying session. This flattered the car's speed, but was an aggressive solution to beat one of the Ferraris or McLarens to the second row of the grid.

However when the ploy failed, the teams was left with little prospect of the lead four cars retiring. I asked if this was frustrating. "Yes, this is part of the game!" Rampf admitted lighthheartedly.

Aiding the team's ability to use strategy to their advantage was the development of an idling system for the engine, similar in concept to that used by McLaren and Ferrari.

"Yes, we thought it would be important to idle for three minutes or longer," Rampf admitted, adding that that the solution was not related to the cooling systems capacity. "It's more for the electronics."

Reliability

While the lead two teams posted few retirements, BMW Sauber had their fair share. In no way could the car be termed unreliable, but a weak spot was clearly the transmission.

BMW in Munich produced the team's first seamless-shift gearbox for the 2007 season. The unit first played up in pre-season testing, and led to four of the team's race retirements.

"We had some problems in pre-season testing, we sorted out most of the problems, but a few of them were coming back," Rampf said.

Usually in the hours after the race the team do not release details of what caused the retirement, often revealing nothing more than that the problem was linked to an area like the gearbox or hydraulics. So were these failures down to the new quick-shift, or within other areas of the gearbox/hydraulic packaging?

"Not packaging," Rampf confirmed. "I think it was more the gear shifting itself, with the quick-shift."

With the latest series of F1 gearboxes, the shift time is reduced to a negligible amount, as the engagement of the next gear is already partially complete. Only a slight lift to ease the load on the gears is required to fully engage the next gear.

In fact, it is possible to complete the shift even quicker by not lifting the throttle, as Rampf explains.

"To do it completely without a cut is quite a high risk," he said. "You have to take the load off. Overall, you have to have a very precise hydraulic system because everything goes within milliseconds; this is where you have to work most of the time to make a lot actuations synchronised very quickly."

Thus, any problem with the selector mechanism, dogs or hydraulics will prevent the shift working as it was designed. It was these issues that forced the retirements.

As well as the gearbox problems, the team did suffer one engine failure for Kubica at Spa in practice. To illustrate the team's pace this year, this was the only time the team qualified out of the ten.

Even then, Kubica actually took part in Q3, but his lap time to get fourth on the grid was hurt by a ten-place penalty for the final grid on Sunday. As one of the few engine failures for any team during the year it was a blow, but the pain was eased somewhat by the fact that it was apparently a random one-off. "It was a problem with a valve," Rampf simply said.

While the car generally made it to the finish, there was one retirement that caught everyone's attention. In Montreal after a restart, Kubica had one of the most enormous crashes seen at a modern Formula 1 race.

The car went off the track, launched over a kerb, clipped one wall and then dived down into a big impact with the main retaining wall at a speed of 230 km/h, whereupon it bounced off and rolled along the track before finally coming to a rest at the hairpin.

Although shaken, Kubica was uninjured and the car remained largely intact, with its safety devices doing their jobs. I asked Rampf what the team had learned from the crash.

"The safety devices on the car were working quite well," he said. "The HANS device, the headrest, the leg protection and the seat itself, all the systems were still in a very good shape, still intact and still in the correct place. This was a very positive sight.

"On the chassis strength, we are not saving weight and sacrificing the safety or the integrity of the chassis itself. Overall it pays to be on the safe side, not to be just on the edge of this curve."

One aspect of the crash was the first major impact ripped the nosecone off the front of the car and the front of the monocoque was subsequently damaged in the crash - Kubica's feet were visible though the damaged tub.

While this might at first be viewed as a failure in the car's safety structures, Rampf affirms that even this aided Kubica's survival.

"The nose came off because the impact was at a certain angle," he said. "For example, these mountings for the nose take loads of twelve ton,s and they're still not breaking.

"With a heavy impact from a certain angle they will break off, because the load is too high. The nose is an important part of the crash structure, and then the chassis is normally the next part taking away the energy.

"The front end of the chassis crashed - just on the front, which is good, because it collapsed before the drivers legs. The chassis in this area takes away a lot of the energy; it still acts like a crash structure on a much higher loading."

Its clear that F1 car safety has come along way in recent years. But judging from Rampf's attitude it's also clear that more work will go on to ensure the sports safety standards are continually improved.

Development

In some respects, any F1 car is an evolution of the car that went before it, but the F1.07 was clear step forwards from the F1.06.

The car older car's low nose was replaced by a more raised zero keel nose and anhedral [ED: downwardly-angled] front suspension. The shapely 2006 sidepods were altered for an even more undercut and swept back design, with newly relocated radiators.

However, it was the main aerodynamic appendages (wings and diffuser) that set the F1.07 apart from its forebear, and indeed, most of the rest of the grid.

At the back the influential diffuser was dominated by the low-placed and curved rear-impact structure. As with all of the 2007 cars aerodynamics, the solution at first appears to be counter-productive to good aerodynamics.

But the diligent CFD and tunnel testing carried out in Willem Toet's department produced parts that did perform better than they should have from visual examination.

The low-impact structure is at odds with the new regulations, specifying the size and height of the structure. Most teams ran the structure forwards in line with the higher rear tail light, however BMW's curved up from the central diffuser tunnel creating what appears to be a blockage in the flow through the tunnel.

Rampfs confirmed this was all by design: "The rear structure is quite low because on top of it is the lower wing element. With our aero concept of the rear, it was the most efficient way to design the rear end. This banana shape of the rear crash structure is more a consequence of it."

Thus, the apparent losses of the blockage in the diffuser are made up for in the position of the beam wing, permanently assisted by what Rampf calls the 'stinger wing', a small two-element winglet mounted above the crash structure.

Above both this stinger wing and the crash structure was a range of rear wings. Perhaps more so than other teams, BMW Sauber exploited complex shapes for their rear wings. What prompted such odd arrangements of curves across the rear wing?

"The shapes are normally the results of optimising or taking advantage of the flow behind the engine cover," Rampf explained.

"With the engine cover, the centre part takes away some of the flow. The airflow approaching the rear wing is far away from being clean airflow, so to use this airflow you end up with different shape of the tip and the central part."

These shapes also help the rear wing work when the car is at an angle to the airflow (yaw), when the engine cover creates an even greater interruption to the flow over the rear wing.

"This is always considered when you do the development of the rear wing, the yaw sensitivity of the wing," Rampf explained. "How they are shaped; it always optimised."

Rampf added that the hump-shaped fin on the spine of the engine cover helped the rear wing in yaw, unlike Toyota, whose fin only works to improve lateral stability.

Additionally, the Viking fins sprouting from the roll structure are there to aid the rear wing.

"They are helping the rear wing," Rampf confirmed. "They are flow devices, basically."

Correspondingly, at the front of the car, the front wing showed an imaginative and counter-intuitive design. Philosophically, BMW Sauber ran three types of the front wing - a conventional two-element wing, then the spit-flap wing and a more aggressive square profile wing.

The split-flap wing was an innovation, and one adopted by Renault later in the season. The centre section gained an extra slot gap due to the flap having a slot moulded into it.

Outwardly it was a simple innovation, making the hardest-working middle section effectively a three-element wing. But it was one which must have been hard to make work, particularly where the slot ended and the wing returned to being a normal two-element wing.

"This wing took quite some development time to optimise it," Rampf agreed. "CFD helps a lot here, to be sure we have attached flow, because the central part of the front wing is quite powerful. This slot-gap needs a lot of fine-tuning to get it working under all ride height conditions, under all flap angle conditions."

The aggressive front wing with the square jawed centre section was another success for the team. Although we have seen wings with angular drooped sections, they often create a lot of downforce, but with a lot of sensitivity as the wing has so much surface area close to the ground.

Rampf felt that the team's hard work had paid off in reducing this sensitivity:

"When we were optimising the profile, we got away with it. It looks very sensitive, that's correct. A similar wing five or six years ago would have created a highly pitch-sensitive car, but with the optimisation we can do now, we can take this behaviour away."

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