Elmar Jaeger
BMW Carbon-fibre Advanced Development Team
Among the key figures in the HP4 Race’s chassis development is carbon-fibre specialist Elmar Jaeger.
Having worked to develop a carbon gearbox for the
Sauber team in Formula 1,
Jaeger moved to Munich when the firm was bought by BMW. “I started to get into series production of carbonfibre five or six years ago.
BMW is at the head of this technology with the i3 and i8, and here we use the same materials.”
The key advantage of BMW’s Resin Transfer Moulding process is the dramatic reduction in time and, therefore, cost as compared to traditional methods. “A hand-made carbon frame takes four or five days; with this process we have to do it in one or two hours,” says Jaeger. “We have people who put the sheets into the mould, which is done by robots with the i8, but the rest is automated. The complete frame is made in one piece, which is important for reliability.”
The expense of moulding machinery also has to be taken into account, but the cost of raw materials should not be a limiting factor. “Today we are more expensive than aluminium but we are not several times more expensive — that’s the difference between this and hand-made carbon,” says Jaeger. “The cost of raw material per kilogram is more expensive, but the performance is higher so you don’t need so much.”
An RTM-produced carbon frame’s weight reduction of between 30 and 40 per cent over aluminium is far from its only advantage. The technique allows very accurate prediction of a carbon component’s stiffness in different directions, which allows engineers to fine-tune performance very quickly and inexpensively.
“When we made our first carbon frame we calculated it, produced it and then measured the real stiffness on a test rig, and it was exactly the same as the calculation,” Jaeger says. “That’s the reason we can change the stiffness without trial and error. We can change the stiffness with the wall thickness, with the fibre directions and also with the profile. In terms of shape the HP4 Race frame is similar to the S1000RR frame but slightly thinner in profile.
“The other big advantage is the reliability of the whole cycle. With carbon it doesn’t matter if you use it 1,000 hours of 5,000 hours, it is always the same stiffness. It is also very strong — roughly as strong as steel. If you have a threemm plate in carbon it’s roughly as strong as a three-mm plate in steel.”
Will there be potential to change frame design dramatically, maybe move away from twin spars? “Absolutely. We are looking forward into the future and, of course, we have ideas also for other bikes. It’s too early, but it’s a good start. We also need to ensure that customers accept this new technology, and see that it is safe — if you do it right. BMW has a big knowledge about how to do it right and make it safe.”