Virtually refined: The engineering success story behind the 2012 Olympics

The design and manufacture of Great Britain's gold medal winning bike helped athletes in the last three Olympic Games win medals.

Everyone agrees that London 2012 was something special. Despite some pessimism leading up the Games the facilities, athletes and organisers came through with flying colours.

However, one criticism is that some of those involved in making it such a success, many of them engineering companies, were prevented from talking about their involvement. It was – many agree – a missed opportunity to showcase UK engineering expertise. Fortunately some of the stories can now be told.

One discipline that's been strong for the UK in recent years is cycling. Team GB has won gold medals in the last three Olympic Games, and continued success in between show this is no fluke.

The bike frames used by the now household names of Chris Hoy and Bradley Wiggins look every bit cutting edge. The sleek hollow monocoque frame melds together beautifully to cut through the air with a certain aerodynamic prowess. So, how did the cycling team end up with such an elegant and optimised design?

In fact the design was carried out by Dimitris Katsanis, a composites engineer and ex- cyclist. "I used to work for the Advanced Composites Group but when London was awarded the Olympics I decided to start my own company called Metron Advanced Equipment – a small engineering consultancy based in Nottingham – to concentrate on designing the bike frames for Team GB."

In December 2001 he was approached by British Cycling to produce the 'best bike in the world' for the 2004 Athens Olympics. After tentatively agreeing, he received funding from UK Sport and was asked to deliver the first 10 frames in time for the 2002 Common Wealth Games, just six month later.

The request followed the success of the cycling team at the 2000 Sydney Games where they won a gold, a silver and two Bronze medals. However, despite the success, there were some problems with equipment, delivery and quality.

"The commercial frames where not really strong enough to take the increasing power of the athletes," says Katsanis. "So we had to design a frame, do the stress analysis, make the tools, prototype, test and produce the bikes in a very short time."

The hard work paid off and within six months early versions of the bikes were racing. A few years on and the bikes helped bring home two gold, one silver and one bronze medal at the 2004 Athens Olympics. Further improvements followed and at the 2008 Beijing Olympics the bike helped the cycling team achieve a further eight gold, four silver and two bronze medals.

"After that we had the famous 2012 Olympic Games where we managed eight gold, two silver and two bronze medals," says Katsanis. "One thing to remember, there was only one rider per nation on track in 2012, where as in 2008 there were two. That is why the total number of medals appears to be better in 2008, but if you consider there were half the riders on the track in 2012, it is actually a much better result."

The requirements
It was Katsanis' ambition to design a frame that could be modified to make a number of variants. The frame, though designed originally for the pursuit event, could in fact be developed for a sprint rider and eventually even for road races.

"A lot of people will say aerodynamics, strength and stiffness are the most important factors when you're making a racing bike," says Katsanis. "No, number one is reliability. It has to take you to the finish line.

"The rider also has to be able to get the most out of the bike. People have gone in to wind tunnels to assess various aerodynamic positions and then designed a bike around that. But if you cannot ride it very well then it is not going to be competitive."

However, the major engineering trade offs when it comes to Olympic racing bikes are indeed aerodynamics, strength, stiffness and weight. The perfect balance must be made; over reliance on one variable reduces another and ultimately competitiveness.

Small production runs and short development times meant testing was limited and instead software tools were used to help understand the effects of the trade offs and give confidence to design decisions.

"We came up with software which simulates the whole race," explains Katsanis. "It includes the mass of the rider and the bike, the power the rider is producing, any aerodynamic effects and stress on the bike, the friction loses and rolling resistance on the tyres, chains, and bearings; we needed a tool to organise and prioritise all of that."

The team carried out a simulation of a 1km time trial and considered what would happen if the frame weight was reduced from 7.2kg to 7kg. Combined with the rider the total was about 100kg. Analysis showed that a 0.2% weight reduction (200g) resulted in a 0.024s improvement, equivalent to 0.29m over the 1000m race.

At this level of competitive cycling, tenths of a second are considered a lot and hundredth are still significant. At the 2002 Copenhagen Championship Chris Hoy used a new fork which was indeed 200g lighter. He went on to win the race by just 0.001s. These seemingly minute improvements can have a big effect in helping win championships and Olympic medals.

Simulation software such as Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) were extensively used as design tools in combination with 3D CAD. "Today this is quite common," says Katsanis, "but at the time many thought simulations should happen only at the end of the design process. But, we used it as a design tool."

As an example, FEA showed that the chain stays of the bike exhibited areas of high stress. However, by changing geometry and squaring the chain stays, areas of high stress and deflection were significantly reduced.

"These two chain stays (see page 13) weigh the same," says Katsanis. "I was not adding material, only manipulating the shape to see what effect it had. Without adding any weight we found significant improvement. After that there were a number of cases going forward and backwards from stress analysis to the geometry."

Material selection
The next stage was to develop the full composite laminate with each individual section of the bike potentially requiring a different layup. For example, each chain stay required a different layup due to the effect of the chain tension produced on one side.

"To narrow it down I looked at the combination of properties that gave high specific strength and stiffness at low weight," says Katsanis. "The critical properties for the vast majority of composite materials, however, is its compressive properties."

In the end, a high grade carbon fibre was used with a toughened epoxy resin. However, working out the appropriate properties and associated layup for each individual part of the bike was a challenge. To develop the laminate Metron made a simple model to represent different parts of the bike starting with all the tubes exactly the same. It then calculated the stresses and deflection each component would likely see. This was then used to develop the shape of the composite frame which has a bigger cross-sectional areas in places of higher stress and thinner sections in lower stress areas.

To assess the best orientation of the fibres, simulation software again acted as a guide. Using much the same approach, the geometry and orientation of the fibres was manipulated virtually to simulate the effect it had on stress build up in certain areas. As many components went straight from FEA to manufacturing to racing Katsanis confidence in simulation data was essential.

"In total there were 361 runs and various load cases," says Katsanis. "This led us to 139 different laminates that we used to optimise the frame in each individual area."

Finding improvement
By the time of Beijing in 2008 a MK2 frame had been designed that was set to be lighter, stiffer and more aerodynamic. It managed a 12% increase in stiffness and 200g weight reduction with 14% less material being used. Wind tunnel tests also showed that it delivered superior aerodynamic performance over the MK1.

The MK2 frame also had to cope with stronger and more powerful athletes. The original specification in 2002 quoted riders as producing 500Nm of torque. Before the 2012 Olympics physiology tests from some of the strongest athletes required the bike to cope with more than 700Nm.

"Fortunately, the original design allowed us to take more than was specified originally," says Katsanis. "But actually, in 2012 the frame design was identical to 2008 as we didn't manage to find anything that was significant enough to redesign. Some of the riders actually raced in 2012 with frames manufactured in 2008."

Since 2002 the Mk1 and Mk2 frames have achieved 58 gold medals, 33 silvers, and 22 bronze from three Olympic Games. So is there room for improvement?

"The worst mistake you can make as a designer is to say this is the best and it will never be surpassed," says Katsanis. "As a designer you have to stop at some point and send it to manufacturing. But at that moment you realise you can do it better. I would not be surprised if in the next bike there is a 10% improvement."

Author
Justin Cunningham

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