Jan. 24, 2009 After the wind tunnel tests it was now the turn of the ice track, a big moment for those taking part in developing and building the Citius bobsleigh. The initial results were more than a relief.
It was two o’clock on Monday afternoon and the time had come: the Citius bobsleigh, a joint project between the Swiss Bobsleigh Federation, ETH Zurich and the industry, made its first run on the ice track. The start of the 1233 metre bobsleigh track at Igls, a suburb of Innsbruck in Austria, was a scene of industrious activity. Mechanics, students and doctoral students were all kept in suspense, as was Christian Reich, the pilot for the test runs.
Last year’s 2-man bob was already waiting at the start. Citius was still nowhere to be seen. The “baby” was not driven up until shortly before the start and remained covered by a tarpaulin, hidden from the inquisitive gaze of the bystanders. Now and then, a corner of the tarpaulin was lifted to attach a cable or take something out. The secret was finally unveiled shortly before two o’clock: Citius, with its bright yellow streamlined outer shell, was plastered inside with grey adhesive tape fastening the cables running throughout the bob. The cables led to small boxes that store the test run data; Christian Reich, the pilot, still remained in the background.
Serving the bob round the clock
Pascal Arnold, a doctoral student at the Institute of Mechanical Systems, and Benjamin Zoller, a doctoral student at the Institute of Fluid Dynamics of ETH Zurich, hurried back and forth with a laptop re-checking the bob and its measurement sensor equipment and fixing a camera to the pilot’s helmet, which was still lying on a table. Its task was to record the course of the run. At the same time, Martin Elsener from the D-MATL workshop of ETH Zurich together with other helpers prepared everything else needed for the start. During the past two weeks they had all worked flat out at the ETH Zurich Hönggerberg Campus to prepare the bob for the ice track. Often working more than sixteen hours a day, including at the weekend, they applied measurement sensors to the bob. Christoph Glocker, Professor at the Institute of Mechanical Systems of ETH Zurich and head of the Kinematics I team of the Citius project, explained that these had been positioned at the points where critical joints were located. For example sensors were installed at the flexible joints of the runners to follow their movements. Force sensors were also attached in especially highly stressed areas to measure the forces occurring. However, the participants were very reticent about the details of the test installations, not wanting to divulge too much to the competition.
The main aim of the test runs is to record the driving dynamics such as acceleration and rotation, as well as the aerodynamic properties. To do this, the scientists and technicians use a relatively simple method consisting of sticking wool threads to the bob, recording the behaviour of these threads on film during the race and analysing it afterwards.
Sixteen years of racing experience
When everything is ready, Christian Reich suddenly appears. He is a former bob driver for the Swiss Bobsleigh Federation who now builds bobs, playing a decisive part in the construction of Citius. He began his career with eight years as a brakeman and eight years as a pilot and has a reputation for driving with enormous precision, consistently and “damned well”. Glocker says, “When the data curves of the various test runs carried out with the old bob last year at St. Moritz were superimposed, they almost coincided.” Reich also looks relaxed, as you might expect: “When you’ve driven for so many years, you just know how to do it and this kind of thing no longer makes you nervous.” He estimates he has already that driven the Innsbruck track 200 to 300 times.
On the other hand, the ETH Zurich team doesn’t look quite as relaxed – after all, it is the first time they have built a bobsleigh. They are focused on the task in hand, say little and don’t let anything distract them. Then a voice through the loudspeakers announces the go-ahead for the start. Last year’s bob piloted by Gregor Baumann from the Swiss Bobsleigh Federation will start first. It acts as a reference bob and, at St. Moritz, has already run through the procedure now being undergone by Citius.
Momentum from a bungee rope
To achieve comparable starting conditions, a running start is not used. Instead the reference bob team sits in the vehicle and waits for Martin Elsener to give them a send-off with a stretched bungee rope. Then it’s Reich’s turn with Citius: the bungee rope is stretched by pulling the bobsleigh backwards. When it is let go, Citius starts to move. Everyone’s eyes are fixed on the panel which displays the time measurements. Right from the word ‘go’, the start time is better than that of the reference bob. However, the bob has still not experienced any particular stress or significant acceleration or strain in any of the curves. It rapidly disappears from view for those in the starting area and all that remains audible is the typical dull thundering noise of runners on ice retreating into the distance. Everyone stares expectantly as they follow the values on the display panel. Citius runs faster than its predecessor! But still no joyful roar, everyone just seems relieved. Christoph Glocker laughs and says, half joking and half serious, “It’s come down.”
Although the researchers, developers and constructors had, up to this point, assumed they had built a perfect bobsleigh, none could say with certainty how Citius would behave on the ice track.
Christian Reich also appears calm and relaxed when he comes back to the top with the HGV carrying the bob and its team. Project staff also return to the top with the HGV. At the finishing line, they have already written a log of the run based on Reich’s report, which is now discussed briefly with the team at the start. A certain satisfaction is noticeable in Reich’s terse, dry comments – that the bob drove well and his driving feel was no different to the bobs he had driven in the past. Almost with some surprise, he comments in passing that the driving behaviour of the chassis is unusually quiet. He has only one complaint: “The steering is not aggressive or direct enough.” However, he says this problem can be put right without much effort.
Unruffled to the last
In the meantime, Pascal Arnold downloads onto his laptop the data recorded by the sensors. After a total of three runs, in one of which – after a change of runners – the reference bob was faster, there are satisfied faces all round. Six more runs take place on each of the following two days. The data will be analysed carefully in Zurich. Only then will an idea be gained of what can be expected from Citius. Walter Caseri, Professor at the Polymers Institute, and Christoph Glocker, who together provide the scientific accompaniment for the program, appear satisfied for the time being: “It all looks quite reasonable.” However, no-one showed much emotion at the initial success, perhaps because they were exhausted by the hard work. But all were visibly more relaxed as everything was packed away quickly because a few had cold feet after two hours on the ice track.
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