‘Right, look at this,’ said Backhouse pointing at the data relating to the torque sensor. Straker would not have been able to explain exactly what he was looking at, but he could see that one of the numbers was rising – and then increased dramatically.
‘That's a torque spike,’ Backhouse explained. ‘It's showing the force that Remy was applying to the steering wheel. And it fits, exactly, with the wheel suddenly becoming heavy.’
‘As she tried to heave it?’
‘Precisely.’
‘So did the hydraulics fail?’ Straker asked.
‘That's what we thought, until we saw this.’ Backhouse backed the film up by a few seconds, pressed the space bar again and let the film run on. ‘I want you to look here this time,’ he said holding his finger on the line of the graph. ‘This measures the overall hydraulic pressure across the entire car. As you can see,’ he said keeping his finger in place, ‘right the way through Remy's two attempts to turn the wheel – and then as the car leaves the circuit – the overall pressure in the hydraulic system never faltered. It stayed constant throughout.’
‘So it wasn’t a hydraulic failure, then?’
Backhouse tapped the space bar and, using the slider, returned the film to a point before the corner. ‘That's what we thought – until we saw this.’ Backhouse ran the film again in slow motion. ‘On this pass, I want you to watch these two sets of data – which show the state of the metering valve and the hydraulic valves in the pistons, which steer the front wheels.’
McMahon and Straker both leant in.
‘At the point where the torque sensor reading starts to rise,’ Backhouse explained, ‘we want to see that the two sets of hydraulic valves in the steering opened. That would be consistent with hydraulic assistance being asked for and then being applied to help with the turn. So, here is Remy turning the wheel,’ he said pointing out the torque spike again, ‘and look – there! – at the reading from the metering valve, it's working perfectly. But – there! – look at the valve in the steering pistons. It's completely closed – shut down to zero.’
‘Meaning?’
‘That there's suddenly no hydraulic assistance … at all.’
‘So the hydraulics did fail?’ offered McMahon.
‘Yes and no.’
‘Was the piston valve “misfiring”?’
Backhouse shook his head. ‘No, not exactly as … wait … there … do you see? The piston valve is not stuck. It's suddenly back to being fully open again – exactly where it remains for the rest of the crash. Which explains how Remy was able to steer when she was out on the gravel.’
‘So,’ offered Straker, ‘the overall hydraulic system was working 100 per cent, the torque sensor was 100 per cent, the metering valve was 100 per cent and the hydraulic valve on the steering pistons was 100 per cent – except for a fraction of a second at the moment she's trying to turn?’
‘But that's not all,’ he added. ‘You remember we spotted that hint of smoke from Remy's right-rear tyre?’
‘Which we thought could have been a patch of dirty track, her being on the outside of the circuit?’
Backhouse nodded and said: ‘Except it wasn’t anything to do with a dirty surface.’
The race engineer switched screens, showing a different view of Sabatino's approach to the corner; he’d reverted to the overhead shot. ‘I want you to look at the timeline, here, before we go back to look at the telemetry.’
‘Okay.’
Backhouse ran the tape. They watched for the wisp of blue smoke. ‘There,’ he said freezing the video, ‘can you see? The timecode shows that it happened at 22.61.44.’
‘Okay.’
Switching the images, Backhouse toggled back to the on-board footage above Sabatino's helmet, which still showed the data overlaid in numbers, graphs and columns. ‘Okay, we’ll now run this forward,’ he said as the footage moved and the timecode clicked on. ‘There,’ he said, tapping the space bar, ‘I’ve stopped it at 22.60.01 – so just before we see the puff of smoke, yes?’
Straker and McMahon nodded.
‘Look at this,’ said Backhouse as he pointed to another block of data. ‘This is another valve reading, this time for the differential. I’ll explain that in a minute. Watch this, though,’ he said as he tapped the space bar to move the film on in ultra-slow motion. ‘22.61.20 – the valve half opens. Also, please note Remy's hands – that she makes no attempt to touch this dial here on the face of the steering wheel. Then, at 22.66.44 – look – the valve reading shoots up.’
‘Meaning what?’ asked McMahon.
‘That, once again, while the overall hydraulic pressure across the whole car remained constant, the differential valve went from half opened to fully opened. Meaning it had been activated hard.’
‘And the significance of the differential?’ Straker asked.
Backhouse paused the footage. ‘Okay,’ he said, ‘I need you to think about a car on a circle.’
‘Okay.’
‘While on a circle, the wheels on either end of any axle will want to travel at different speeds – the outer one wanting to run faster than the inner one.’
‘Because it's got further to go?’ offered McMahon.
‘Exactly. Now imagine trying to deliver power to the drive wheels in a corner, when they are each going at different speeds? The power delivery from the engine needs to be asymmetric, delivering a different level of power to the different drive wheels, depending on the specific circle each one is on, yes? On most cars, this is delivered using a set of angled gears – a differential – or a mini-gearbox, if you like, built into the middle of the rear axle. Still with me? Good.
‘Sometimes, though, this can allow all the power to go to just one drive wheel – think of how one wheel can spin when your car gets stuck in the mud? We want to prevent that – and we do so by a device that enables us to lock the differential, sometimes referred to as a diff-lock.
‘But … joining the wheels together can then produce another complication – and that relates to the readiness of an axle to turn. If an axle is fixed, like on a go-kart, there is always a conflict between the wheels on either end of it through a corner as they are both forced to turn at the same speed; this effect dramatically inhibits the whole axle from turning. We certainly do not want that effect on a Formula One car; and so, rather than have a diff-lock that's either straight on or straight off, we put a clutch in the middle of it, which can be varied by the driver using a dial on the steering wheel. This enables us to adjust the joining and unjoining of the rear axle all the time – into, through and out of corners. We call this facility a limited-slip differential; and it, too, is operated by hydraulics.’
‘So what happened here – to Remy?’ asked Straker.
‘As I showed you a moment ago,’ Backhouse replied, ‘Remy's differential clutch had been half activated into that corner.’
‘Because she had started to turn?’
