Published: 16.12.08
Dossier Citius

Hammerhead on the test bed

After nearly two years of development and production, the day had arrived: the “Citius” bobsleigh went into the wind tunnel at the car manufacturer AUDI. The tests exceeded expectations. Now the next hurdle must be cleared: the ice track.

Simone Ulmer
ETH scientists and AUDI employees fix the Citius 2-man bob in the wind tunnel.
ETH scientists and AUDI employees fix the Citius 2-man bob in the wind tunnel. (large view)

The wind tunnel at the AUDI works in Ingolstadt resembles a high-security wing. The latest models are tested there under the strictest security and secrecy precautions. There are a few formalities and security barriers to go through and camera phones must be handed in before the doors open to one of Europe’s most modern wind tunnels. It is normally used to test cars in a headwind of up to 300 kilometres per hour. So it’s all the more exciting that a few chosen bobbers from the Swiss Bobsleigh Federation were allowed to use it to test the prototypes of the 4- and 2-man bobs for the 2009/2010 winter season. As a sponsor of the “CITIUS” bobsleigh construction project (see box), AUDI made the wind tunnel available for half a day to the bobsleigh developers and builders and to the athletes who are going to drive the bobs in 2009/2010.

“It’s draughty in there”

Last year’s 4-man bob was tested first in the early morning, followed by the Citius 4-man bob. The purpose of the comparison values is to show whether the new bobsleigh has less air resistance than the previous year’s model and thus could be faster. When we entered the wind tunnel, the athletes were just testing last year’s 2-man bob. The size and atmosphere of the wind tunnel are reminiscent of a gymnasium. Were it not for the big black funnel-shaped throats at the two longitudinal ends from which the wind blows and into which it returns, and the digital display panels on which the wind speed and other measured parameters light up, then it would very much feel as if you were in a sports hall.

The Swiss Bobsleigh Federation’s athletes, pilot Maya Bamert and her pusher Anne Dietrich, who have been a team since 2006 and won bronze at the 2008 European Championships in Cesana, Italy, had already finished testing last year’s 2-man bob and were happily warming themselves in the wind tunnel’s control room amongst computers, monitors and a snackbar. A large glass window separates the room from the wind tunnel. “It’s draughty in there”, commented Maya Bamert, glancing at the wind tunnel hall.

The Citius 4-man exceeds expectations

Up to now, the whole project team has had every reason to be in good spirits: the 4-man bob comparison values showed that the new bob has less air resistance than last year’s bob, and even exceeded expectations. How much faster the new bob is remains a secret for the time being, so as not to draw unwelcome interest from the competition.

Tension rises as the prototype 2-man Citius is installed in the wind tunnel. Its shape is reminiscent of a hammerhead shark and its bright yellow high-visibility colour heightens the impression of a dangerous object. The bob for the 2010 Olympics will also need drive to help the Swiss team achieve success. The bob’s name as well carries significance: Citius, the Latin word for “faster”.

The AUDI staff responsible for the wind tunnel trials – for whom testing a bobsleigh is also not something they do every day – and the ETH Zurich scientists bolt and fasten the bob until it is correctly positioned and firmly anchored to defy the imminent blasts of wind. Thomas Kern, a member of the ETH Zurich kinematics team, explains: “We were all slightly nervous as we prepared the bobs this morning and we had to improvise in some places, but it has all gone extremely well so far.”

Beyond 100 kilometres per hour, it gets a bit uncomfortable

In the meantime, Maya Bamert and Anne Dietrich are wearing their high-tech racing suits again and have put their helmets on. Sitting in the bob, they receive instructions through wireless headphones from the control room from Christian Reich, himself a successful bob driver in the Swiss Bobsleigh Federation and now a bobsleigh constructor. The wind tunnel’s blower is gradually run up to speed. The first measurements are made when it generates an air flow reaching sixty kilometres per hour and remaining in the wind tunnel is still bearable. The blower is not powered down again until a wind speed of 150 kilometres per hour is reached – corresponding approximately to the speed that can be reached on the Whistler Olympic bob track in Vancouver. However, at 100 kilometres per hour, it began to get unpleasant for the bystanders remaining in the wind tunnel, and, at 150 kilometres per hour, everyone except the drivers was on the sidelines in the area shielded from the wind or in the control room.

Fun at 150 kilometres per hour

During the tests, the athletes were instructed to adopt the correct, optimum sitting position which presents the smallest possible air resistance – just as in a real race. Only the pilot is allowed to lift her head far enough so she can only just see. Dietrich is completely crouched down behind Bamert and keeps her head tucked in. Lifting it could cost important seconds in a real race, with even hundredths of a second meaning the difference between victory and defeat in bobsleigh. Next, the athletes simulate just such a situation to see how severely a wrong movement or body posture increases the air resistance and slows the bob down. The forces acting on the bob along the X, Y and Z axes are measured during these tests, together with other factors such as air resistance and the uplift on the bob with its man.

After the women’s team, the same procedure is followed with the men, who have been enjoying success for several years now: Ivo Rüegg, the pilot and 2007 World Champion, and his pusher Cedric Grand, who took fourth place in the last Olympics. They obviously enjoy the part when the effects of incorrect behaviour are measured, so mischief-making is allowed for once: “muscleman” Grand stretches out his arm against the 150 kilometre per hour headwind as though it meant nothing. Rüegg limits himself to pushing his finger through a gap in the chassis.

The test makes it clear: progress is good as far as aerodynamics are concerned. The comparison with last year’s bobs showed that the Citius bobsleighs have less air resistance than their predecessors. Christian Reich explains that the women achieved better results than the men in the 2-man bob, but the 4-man achieved fundamentally better results in the tests. However, he said the exact comparison values would remain under lock and key for the time being.

This bobsleigh construction project is a whole new experience for Reich. “The production stages and developments that we previously carried out based on intuition and experience are instead now simulated on computers or developed and tested in laboratories.”

Testing on the bobsleigh track as the next hurdle

Although the aerodynamic behaviour of the new Citius chassis is better than that of last season’s bobs, one essential question remains to be resolved: will the bob also pass the ice track test? This will be answered by the test runs planned for this week. These will reveal whether the bob’s chassis and slip properties of its runners as well as its driving behaviour meet the expectations of the project team and athletes.

The prototype of the 2-man bobsleigh was shown to the public for the first time a couple of days after the wind tunnel trials. “ETH transfer” provided an opportunity to view Citius on a stand at the Swiss Innovation Forum in Basel. Christian Reich and other project team members were present to supply information about their “baby”. On a screen, a presentation supplemented with short video clip inserts also gave visitors an insight into part of the previous production processes.

The “CITIUS” project

The Swiss Bobsleigh Federation joined forces with around ten industry partners (sia Abrasives, Sika, Indrohag, Georg Kaufmann, Quadrant, Bucher, AUDI, Promec Estech, Ruag, V-Zug and Franz Marty) with the aim of building the winning bob for the 2010 Winter Olympics in Vancouver. This means that the “CITIUS” project launched for this purpose in 2007 has set itself lofty goals that will need to be achieved in a narrow time frame.

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