CAD

December 2000

Notebook

Two wheels and fast turbulence

Mark Fletcher looks at how laser scanners have achieved "the impossible" to help the world of two-wheeled motorsport

A laser scanner has been used to "reverse engineer" a motorcycle plus rider to give one of the most stunning examples of Computational Fluid Dynamics Eureka has seen in years.

The analysis was carried out in an attempt to convince performance bike team bosses that CFD can play a major part in preparation for races and help them shave the necessary seconds off lap times using a process widely used by their four-wheeled peers.

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Motorcycle companies, for obvious reasons, are loath to give out full CAD drawings, this is one reason why Reynard Motorsports Advantage CFD Division had to come up with a different approach to getting reliable CAD data which could be used for aerodynamic analysis. The other problem to overcome was how do you accurately model a bike with the rider in position? The answer was 3D Scanners.

Approaches to motorcycle manufacturers achieved a mixed response. Dr Rob Lewis, at Advantage, CFD says: "We were surprised at the range of commitment to aerodynamic analysis among bike companies. Most recognised that it had some value, but few believed that it could win them races. We were determined to change their minds."

The first stumbling block to overcome was the Catch 22, where Advantage could not prove the benefits without the CAD data and the companies were not giving the CAD data. "To get the idea off the ground we needed to find a way of generating accurate, representative motorcycle geometry as quickly as possible," Lewis adds. "Fortunately 3D Scanners rode to the rescue.

"Although I know how accurate the ModelMaker software used by 3D scanners is, the priority for the job was to get a pretty good representation as quickly as possible. There would have been no point in scanning a bike on its own – the rider is very much part of the racing geometry."

Scanning the bike and rider, using the 3D scanner hardware, turned out to take less than a day. A workable CAD model was stitched together from a number of discrete scanning sessions and was then surface-meshed ready for CFD analysis.

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Bike angle and the dynamic positioning of the bike throughout a race were considered as major reasons why many manufacturers had not considered this approach – the sheer number of possible permutations would give most people a headache. "The flexibility of suspension and rider positions means that the geometry is constantly changing and a complete analysis would be impossible without CAD geometry and an in-depth knowledge of driver dynamics. Even with the limited number of configurations, we were able to estimate from our single scanning session, enough useful information could be gleaned to enable us to offer sensible advice," Lewis adds.

He is confident that, in time, CFD will become an important weapon in the arsenal of two-wheeled motor sport. "We have already been able to recommend design changes to bike companies and it is conceivable that the work we have been doing may even bring radical changes to the way motorbikes are designed. Without the help of 3D Scanners we would have struggled to crack the chicken-and-egg-situation of having no geometric data."

Design Pointers

It is possible to capture the geometry of a motorbike with the rider in position by 3D scanning

A full scan takes less than a day and enough information is collated to cater for bike dynamics

The system requires no initial CAD data

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