High Impact

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The moment of impact as the car hits the safety cap at 110 km/h during the test.
The moment of impact as the car hits the safety cap at 110 km/h during the test.

How a simple combination of steel and sand could play a major role in improving competitor safety on closed-road rallies

We’re standing in a field in the northernmost reaches of Germany as a rally-spec Volkswagen is about to be thrust at 110 km/h into a specially constructed Armco barrier.

Using a pulley system, the driverless car is shot into the barrier with a dramatic explosion of metal, glass and plastic that is all over in less than two seconds.

The smashed car and buckled barrier do not leave much evidence of safety progress. But it is only when looking back on the slow-motion video of the crash, microsecond by microsecond, that it is clear that this mess is not only the remnants of a highly successful test, but could lead to the implementation of an extremely important addition to safety within rallying.

The test was necessary because rally events take place on public roads – often running in the opposite direction to regular traffic. Many of these highways feature Armco structures that are designed to prevent slow-moving traffic from leaving the road by using metal guards mounted on posts.

While this will protect everyday road users from falling into ditches, they have become a real danger to rally cars, which are at serious risk of the Armco piercing the car into the cockpit and injuring its occupants during a high-speed impact. It was this situation that severely injured Formula One race winner Robert Kubica at the Ronde di Andora rally in February 2011 and fatally wounded Welshman Gareth Roberts, co-driver to World Rally Championship driver Craig Breen, in a similar incident on the eighth stage of the 2012 Targa Florio rally.

In response to these accidents, the Global Institute for Motor Sport Safety, working on behalf of the FIA Institute which is funded by the FIA Foundation, is aiming to create a detachable device that is designed specifically to absorb the impact of a crash and, in turn, force an Armco barrier to buckle and bend rather than penetrate the car.

Safety Cap

In this test, the car is fired at the Armco installation at 110 km/h and considerable damage is immediately apparent. But the impact has crushed the front end of the car, rather than piercing it, thanks to the experimental barrier protection device. The 0.7 m diameter steel tube stands at just under one metre in height. It weighs 550 kg when filled with sand, which is necessary to increase its overall mass while keeping it deliberately simple and affordable for rally organisers.

Before the test, the cylinder is placed at the end of the Armco barrier ahead of the impending impact. When it makes contact, the front of the car drives the device into the end of the Armco, and the huge forces between the device and the Armco cause the barrier to fold upwards and away from the chassis without penetrating the car.

This also avoids any excessive acceleration to the passenger compartment. The violence of the crash leaves the scene unrecognisable, but the safety device has done its job. Had there been a real driver or co-driver inside the cockpit, the acceleration loads would have allowed them to avoid serious injury and walk away into the crisp winter air.

“There is a massive incompatibility between the front of passenger cars and Armco ends that are not protected,” explains Andy Mellor, research consultant to the Global Institute.

After Kubica’s accident there was an initial project to see what could be done with engineering to make the cars safer. But when the early stages of that research concluded that an unviable amount of protection would have to be integrated within the front of a car, the project switched focus to concentrate on fitting the required protection to the exposed ends of the barriers instead.

“The focus of the study was engineering a mechanism to get the Armco to buckle early enough so that the exposed end didn’t penetrate into the car that’s just hit it,” says Mellor.

To try and create the force needed to cause a barrier to buckle, while ensuring the excessively-high stresses to the front of the car were avoided, a load-spreading cap was designed before Mellor evolved the concept into a multi-function element – the cylinder – to slow a car. This provides load spreading onto the Armco end and hammers the sharp end of the barrier away from the cockpit.

Mellor explains: “We conducted a number of mathematical simulations to understand how the cylinder configuration could be optimised. The cylinder actually provides four distinct functions during the impact event. Firstly it acts as a momentum transfer device to significantly reduce the speed of the car before it reaches the Armco. The mass was chosen to maximise the reduction in speed over the short time duration of this initial interaction while ensuring safe acceleration levels for the occupants.

“Secondly, it acts as an energy-absorbing device to complement the crash structures engineered into the front of all modern passenger cars. Thirdly, it acts as a load-spreading device to prevent penetration through the front of the car. And finally it acts like a slide hammer to impart the kinetic energy accumulated during the momentum transfer phase directly into the Armco structure. This is what initiates the buckling process.”

The cylinder may be placed in front of any barrier with a letterbox-like slot matching the profile of the end of the barrier, thus ensuring it is fully encapsulated as the cylinder moves.

The results of the test showed that the cylinder slowed the car by 36 km/h, from 113 km/h to 77 km/h during the momentum transfer phase, thus reducing the kinetic energy by more than 50 per cent. “Which was exactly as you’d predict, based on the momentum-transfer calculations,” says Mellor.

Turning Point

There are over 50 major rallying events a year in the most fervent countries such as UK, Italy and France. So there are potentially thousands of corners that would benefit from the installation of this type of device. It was therefore vital that any potential safety solution was also cost-effective so there would be no barrier, be it literal or figurative, to their widespread use.

“At the start we understood that cost and logistics were major factors and we set a target of €100 for the installed product. Any more expensive it could become cost prohibitive,” says Mellor.

Every rally organiser could potentially need dozens of cylinders to protect the barriers on each stage of their event, so the study used commercially-available steel tubing that was built to the desired specifications to both slow the momentum of a car and force the Armco to buckle when the impact occurs.

Although the cylinder worked successfully in that it performed all four intended functions in a very controlled manner, there is still work to be done before it becomes a finished product. After the fourth phase, as the Armco buckled, the vertical motion was not sufficiently controlled by gravity alone and the resulting forces caused the cylinder to lift off the ground.

“It would be far more desirable to keep the cylinder on the ground and this might be a very simple fix,” says Mellor. “If we seal the lower end, possibly by welding a cap onto the bottom, then when car impacts and crushes the cylinder, some of the sand will be forced upwards out of the top of the cylinder, thus generating thrust downwards so it will inherently remain on the ground.”

This would reduce the risk of damaging the windscreen of a car during the final part of the impact, as the car’s speed is finally brought down to zero, and may also slightly improve the response during the first two phases of the event.

Once the redesign is complete, the solution would initially be available to all WRC events, after which it could be offered to the ASNs and National rally organisers. As Mellor says: “There’s potential to implement these devices in significant numbers.”

This article was originally published in the 14th edition of Auto magazine.