0

Published by Martin Zustak 2013 Copyright © Martin Zustak 2013

All rights reserved. This book or any portion thereof may not be reproduced or used in any manner whatsoever without the express written permission of the publisher except for the use of brief quotations in a book review.

First published in Ireland in December 2013 Second edition, August 2014 (version 2.8)

ISBN 978-0-9575657-0-8

www.martinzustak.com twitter.com/mzustak

1

There is no end to the knowledge you can get or the understanding or the peace by going deeper and deeper.

Ayrton Senna

2 Preface

I never met but I was a fan. Since his untimely death on , 1994 at , every book imaginable has already been written about him, except for one. The subject of that missing book is contentious because it addresses the fundamental question of what caused Senna’s car to veer off the track at 300km/h on Lap 7 of the Grand Prix. Tamburello was conceived more than fifteen years ago as a private project to fulfil my own need for understanding. The original project had grown in fits and starts and lay dormant for over a decade until its resurrection when I was approached to publish again my old material on Imola ’94. What began as minor revision of a short article has metamorphosed into a book. I’m painfully aware of the fact that - for many understandable reasons - the cause of Ayrton Senna’s accident remains a sensitive subject, but I feel an obligation towards the wider world to share what I’ve discovered. Any inaccurate assumptions or misinterpretations of proprietary design specifications, measurement inaccuracies, errors and omissions are entirely mine.

Martin Zustak December 2013

3 Acknowledgements

My foremost thanks to the late Christopher Hilton, whose numerous books on Senna and motor sport have been a source of inspiration. I still fondly remember our phone conversations and the visit to his family home in Hearts, UK, back in the spring of 2000. In compiling this book I have drawn background and quoted from several published works. All the relevant credits are indicated in the text and referenced in the Bibliography. For permission to quote, I formally thank Helen Wilson of The Guardian newspaper, and Graham Cook of Haynes Publishing. My most grateful thanks to Paul-Henri Cahier, who supplied the cover photo; to Remi Humbert and Joachim Kutt of GurneyFlap.com, who kindly allowed me to reproduce the close-up shots of Williams’ 1994 car; to Giorgia Buselli, Darragh Colgan, Tycho Schenkeveld, Dalin Vyskovsky, and Martin Kyncl for their generous assistance; and to all those who willingly helped but did not wish to be named in the book. Thanks, also, to the many motor racing enthusiasts whose videos on YouTube have helped massively in research. I am especially indebted to Mark Clair, the founder of RaceRecall in Victoria, Australia, for allowing me to reproduce and annotate the Mustang 350GT accident sequence. I’m most grateful to Patrizia Coluccia, the friendly Press Officer at CINECA in , who kindly gave me permission to enhance the original CINECA material and videos. The book would not have been possible without her support. I owe a particular debt to Rini Ruitenschild, CEO of Hydroline Powersteering B.V. in the Netherlands, for his valuable comments and for putting me in touch with the incredible Tony Woodward, CEO of Woodward Machine Corporation in Casper, USA. Tony generously gave his time and expertise and dealt patiently with my questions about the ins and outs of . This book would have been hollow without him.

4 Fact file

AYRTON SENNA

1960 – Born on March 21 in Sao Paolo, Brazil, to Neyde and Milton da Silva.

1964 – Gets a go-kart from his father and inadvertently discovers a world which fulfils his inner needs for control and detail.

1979 – Go-karting race in Jesolo, Italy. Overtaken by his experienced teammate Terry Fullerton and finishes second. Back in the hotel, pushes Fullerton into the swimming pool.

1981 – , . Moves to single-seaters, winning two championships. Unexpectedly decides to quit at the end of the season and flies home to Brazil.

1982 – Returns to England, divorced and fully committed to being a professional racing driver.

1982 –Rejects an offer from of McLaren to race in the junior F3 category because the contract doesn’t guarantee him a future seat in F1.

1983 – Graduates to F3 on his own terms and wins the first nine races.

5 Fact file

AYRTON SENNA

1984 – Arrives to F1 with the midfield team. Makes his mark in the rain-soaked Grand Prix by finishing second to in the McLaren.

1985 – Estoril, . Scores his maiden F1 win in torrential rain in only his second race with , almost lapping the whole field in the process.

1986 – Jerez, Spain. Amazes the Lotus engineers by being able to recall the car’s speed and revs at every corner around the circuit. In qualifying, predicts his own time to a fraction of a second.

1986 – Detroit, USA. Skips the mandatory press conference after setting in qualifying in order to watch Brazil lose in the football World Cup against France. Wins the race the next day and waves the Brazilian flag on his .

1987 – Monza, Italy. Announces a deal with Ron Dennis to join McLaren alongside two-time World Champion Alain Prost. Stays for the next six seasons.

6 Fact file

AYRTON SENNA

1988 – Monte Carlo, Monaco. Fastest in qualifying by an astounding margin, 1.427s clear of teammate Alain Prost. Later confesses to having an out of body experience on the record lap. Crashes out of the race while in an unassailable lead and storms off straight into his nearby apartment.

1988 – Suzuka, Japan. Clinches his first World Championship by charging from fourteenth to first.

1989 – Monte Carlo, Monaco. Refuses to speak to Alain Prost following a controversial overtaking move on his teammate at the previous race at Imola, and Prost’s subsequent comments in the press.

1989 – Suzuka, Japan. Has to win to keep his title hopes alive. With six laps to go, overtakes Alain Prost for the lead at the but Prost turns into him and the two collide. Senna re-joins the race and goes on to win, only to be disqualified for missing the chicane and causing the collision.

1990 – Suzuka, Japan. Prost – now driving for - has to win to keep his title hopes alive. Senna takes justice into his own hands and deliberately crashes into Prost at the first corner to clinch his second World Championship.

1991 – Sao Paolo, Brazil. Maiden win on home soil despite being stuck in sixth gear and suffering unbearable muscle cramps in the last ten laps. Goes on to win the Championship for the third time at the end of the season.

7 Fact file

AYRTON SENNA

1992 – Spa, Belgium. First on the scene of Erik Comas’ 300km/h accident. Stops the car and rushes to help the briefly unconscious Frenchman. Attends to Comas and holds his head until the paramedics arrive.

1992 – Plays second fiddle to in the Championship as his McLaren is no match for the technologically superior Williams car.

1993 – Donington, England. Excels in the rain in the underpowered McLaren and delivers the most memorable opening lap in motor racing’s history by going from fifth at the start to first at the end of Lap 1.

1993 – Estoril, Portugal. Confirmed as Prost’s replacement at Williams for the following season.

1993 – Adelaide, Australia. Wins his 41st F1 race in his final outing for McLaren, and afterwards is invited by singer Tina Turner on stage for ‘Simply the Best.’

1994 – Asks sister Viviane to set up what would become the Ayrton Senna Foundation, which helps millions of underprivileged children in Brazil.

1994 – Imola, Italy. Crashes fatally while leading the San Marino Grand Prix.

1994 – Sao Paolo, Brazil. Laid to rest at Morumbi Cemetery on May 5. An estimated three million people attend his funeral procession.

8 information. Would he accept that the world of motor Prologue racing has shied away from trying to resolve the conundrum of his death, or would he insist on going through every , every telemetry trace, and Ayrton Senna has been dead for a generation, yet the every piece of information again until he was cause of his accident remains a mystery. The question convinced there was no new knowledge to be gained? is - does it matter? Curiosity is fundamental to the human condition, Common sense says let him rest in peace: and the surest way of attracting someone’s attention establishing the cause is a mission impossible. The to a problem is to tell them it’s not solvable. safety lessons have been learned and since the Gigabytes of data about the accident are scattered tragedy, F1 enjoyed its longest ever spell without a across cyberspace and in print but, at least outside fatality. Further analysis is not going to bring Senna the courtroom, they’ve never been brought together back or help his family, and the Italian legal system in a comprehensive fashion. This book is an attempt had its day in court but grudgingly conceded that to achieve that, and to do Senna’s legacy justice by racing cars are prototypes just like the space shuttles approaching the subject with single-mindedness and Challenger and Columbia: when people and attention to detail of which the late Brazilian would components are pushed to the limit, mistakes and hopefully approve. accidents are inevitable. On the other hand, Senna never gave up. Suzuka 1988, Suzuka 1989, Donington 1993, and Sao Paolo 1991 particularly spring to mind. He was also the ultimate perfectionist who left no stone unturned in his quest to understand the car and its behaviour on the track - often to the point of mentally exhausting his engineers – and it is a cruel twist of fate the last seconds of his life remain obscured by imperfect 9 the culture colder and much different from what he CHAPTER 1 had been used to. Having forced his arch-rival Alain Prost into retirement at the end of 1993 by joining The driver the Williams team, Senna now also lost his main target and source of professional motivation. He

appeared softer, as if he had lost his killer instinct. At the age of 34, Senna was at his peak as a racing The new Williams car proved troublesome and its driver. He was fit and in perfect health: the tests unpredictable handling and constantly shifting ruled out a blackout and confirmed that he hadn’t balance forced Senna to dig deep in order to squeeze taken any drugs or banned substances. According to competitive lap time out of it. He spun out of the first comments in the press, he went into the 1994 San race of the season in Brazil and was punted off in the Marino Grand Prix with a higher than usual heart first corner in Japan while his younger rival Michael rate, which was almost certainly an effect of his Schumacher driving for the Benetton team won both troubled frame of mind. races. Senna was heading to Imola for the San Senna had been working hard to setup his emerging Marino Grand Prix on the back of his worst ever start business empire, and due to the time zone difference to a championship: zero points against Schumacher’s between Europe and Brazil, he was often on the perfect twenty. phone late at night. He was in love with model After his retirement in Japan, Senna closely observed Adriane Galisteu, whom he’d been dating since the the behaviour of Schumacher’s car on the track and 1993 , but their relationship met became convinced that the Benetton exploited illegal with the disapproval of his family and Senna was traction control and launch control systems. He was under pressure to split with her. incensed that the battle was not fought on equal After six glorious years at McLaren, which yielded terms. He complained bitterly to several close friends three world championships, 35 wins and 46 pole during the fateful Imola weekend and, as stated by positions in 96 races, Senna was still going through former McLaren principal Ron Dennis, the prospect the induction process at Williams, where he found

10 of racing an illegal car was at the forefront of Senna’s years and sadness, doubt, premonition, and fear thoughts immediately before the start1. must have, at least temporarily, entered Senna’s mind. But the most plausible scenario is that once the And then there were the feelings of his own fragility lights turned green, Senna’s famous powers of and mortality, awakened by the death of fellow racing concentration prevailed and when he met his destiny driver during the second in the Tamburello corner he was fully focused on one qualifying session the day before. It was the first thing and one thing only – winning. fatality during a Grand Prix weekend in twelve

Figure 1 - Ayrton Senna minutes before the start of his last race (photo Paul-Henri Cahier). 11 CHAPTER 2 The FW16 ran on Goodyear tyres fitted to 13’’ wheel rims, 13’’ wide at the front and 15’’ wide at the rear. The car Like all high performance tyres, the Goodyears were sensitive to temperature fluctuations and even a slight change in the ambient temperature or a sudden cloud could result in a 1.5psi drop in tyre pressures8. Due to regulation changes mandated by the motor The 1994 San Marino Grand Prix took place on a sport federation FIA, the new Williams car - warm spring day in dry conditions, and at racing designated FW16 - was forced to shed most of the speeds Senna had no trouble keeping his tyres in the electronic gizmos that had made its predecessors so optimal temperature window in which they stay dominant, and initially it struggled to adapt to life properly inflated and provide the best possible grip. without , traction control, launch control, and ABS brakes. It featured pushrod Paradoxically, the aerodynamics were the FW16’s operated ‘passive’ suspension with double wishbones, Achilles heel despite ’s presence as a torsion spring at the front and a coil-spring at the chief designer. The team ran active suspension in the rear. The car was powered by a normally aspirated previous two years and developed the aerodynamics 3.5-litre Renault that revved to around it, so the new FIA regulations that stipulated 14,300rpm6 and produced around 790hp6. Senna had passive springs and dampers were a major setback. been driving number 02 since the beginning Shifts in aerodynamic balance on the passive car of the season. At Imola, he ran the same basic set-up were much more pronounced than on its active as teammate Damon Hill7 and he was fuelled to stop predecessor and the design team didn’t fully twice during the race. Senna’s main rival Michael compensate for that. The FW16 ended up being Schumacher planned three stops, which made his car hypersensitive to changes in ride height and lighter and potentially faster in the early stages of the aerodynamically unstable9. Also, the sidepods were race. too long85 and the front wing sat too close to the ground10. To address these aero issues, the team introduced a raft of modifications for Imola,

12

Figure 2 – Ayrton Senna at speed in his Williams FW16-Renault, Imola 1994 (photo Paul-Henri Cahier).

13 including a raised front wing, slightly taller front just one. The whole steering assembly – nine wing end-plates, reshaped cockpit, and a revised components in total – went to production after . March 10, 1994, and took the different departments within Williams two to three days to make. The During the pre-season testing of the new Williams, it assembly was inspected to ensure it had been quickly dawned on Senna that the car’s ergonomics produced as per design specification and it also had Nigel Mansell’s DNA written all over it - the underwent quality checks before being assigned a monocoque was an evolution of the highly successful part number and stored in the warehouse. Three new FW14B model that Mansell won the world title with columns were then shipped to Brazil for the first in 1992. Senna preferred to sit as low as possible in Grand Prix of the season and put not only on Senna’s the cockpit to have less turbulence around his head11; car but also on ’s and the spare12. and because he sat low the steering wheel needed to be positioned lower, too. He drove with his fingertips After Senna’s collision with during the and liked a big steering wheel with a thin rim, which second race in Japan at Aida - where Larini’s Ferrari offered the best grip for his small hands. The bigger T-boned the stranded Williams into retirement - the steering wheel (280mm in diameter as opposed to steering column was subjected to tests by penetrating Mansell’s customary 240mm) couldn’t be liquids in the Williams factory. No cracks were found accommodated because of the tightly packaged and the column was put back on the car for the San cockpit of the FW16, but at least the Williams Marino Grand Prix3. engineers agreed to alter the steering position. According to Williams, the steering column design The requested changes necessitated redesign as the involved a considerable amount of flexing and the old specification would have protruded to the area steering wheel (made of carbon fibre) would also forbidden by the FIA regulations and would have flex13. Three years after the accident, the engineers obstructed the driver’s timely exit from the cockpit in conducted a demonstration using one of the FW16s an accident. The column was cut in half and a on display in the team’s museum, with Senna’s machined piece was inserted in the middle so the replacement behind the wheel. design now consisted of three elements rather than In the video footage later made public by National

14 Geographic Channel in their TV documentary series The team couldn’t change any settings remotely by Seismic Seconds14, Coulthard is seen bending the issuing commands while the car was on the track. steering wheel by several centimetres both vertically The main data logging unit (the black box) collected a and horizontally. range of parameters about the state of the car’s vital Little information has surfaced about the power systems including dynamic behaviour and steering system since the accident. Williams drew on environmental variables such as g-forces. The their experience with active suspension and in 1994 content of the black box could be downloaded to a pioneered electrohydraulic power steering. The computer using a three-pin connector and a data system sensed strain momentarily existing in the card. Engine supplier Renault operated their own steering assembly and converted it to an electrical data logging unit - installed behind the cockpit - and signal, which was then suitably amplified and fed into Williams used its spare capacity to piggyback on a solenoid, which in turn operated a linear hydraulic some of the main unit’s telemetry channels. Data servo valve. In response to this signal, the valve’s from the previous lap was beamed every time the car ports controlled the hydraulic fluid flow to and from passed the pits, the memory banks then reset and the pistons in the steering rack and assisted the started recording data from the next lap. driver. Electronics on the FW16 were largely confined to the engine management system, semi-automatic gearbox (six forward gears and a reverse), cockpit dashboard, radio communication with the pits, electrohydraulic actuators, sensors, and car telemetry. Williams employed one-way telemetry, which meant that data from the different sensors installed around the car was collected and radio-transmitted in regular intervals to the team’s computers in the pits.

15 modifications were only carried out in time for the CHAPTER 3 1995 race as a result of Senna’s death. The track

The track at Imola had been used for F1 in the same configuration since 1981 when it hosted the inaugural San Marino Grand Prix. Over the years, four high- speed accidents similar to Senna’s took place in Tamburello, although not at exactly the same spot: (Williams) suffered concussion after a left rear tyre failure during qualifying for the 1987 San Marino Grand Prix, spinning twice before hitting the wall sideways; (Ferrari) was Figure 3 - , Autodromo Enzo e Dino Ferrari. knocked unconscious and received second-degree Darker circuit outline represents the eight strips of new burns in the 1989 race when his car burst into flames tarmac laid between the start-finish line and the exit of after the front wing had failed; Tamburello.

(Footwork) ended up with several stitches in his leg after a test shunt before the 1991 race when his front The track surface was old and bumpy, and to improve wing collapsed; and (Williams) the situation eight short strips of new tarmac had suffered concussion and minor lower spine injuries been laid after the 1993 race between the start-finish during a test crash before the 1992 race, which was line and the exit of Tamburello. Nonetheless, during caused by a right rear tyre failure. Despite all these the test two weeks prior to the 1994 race drivers still accidents (whose footage can be viewed on YouTube), complained about a small dip in the middle of the the corner remained a flat out left-hander and track, which created an unevenness of three to four

16 centimetres, and Senna personally alerted circuit FIA inspections two months prior to the race and director Giorgio Poggi. It wasn’t feasible to resurface then again on the Wednesday before the race. this section of the track so close to the race, but Poggi Nothing of concern was reported3. at least managed to get it smoothed out3. The repairs only slightly improved the situation and there still was a bump. According to former driver , there was only one line through Tamburello and the bump could not be avoided; the cars touched the ground and were unsettled, but the bump effect was normal and the driver just had to hold his line3,4. The run-off area on the outside of Tamburello consisted of a narrow strip of grass followed by concrete that extended to an unprotected wall. This limitation was dictated by nature as immediately beyond the perimeter wall ran the Santerno River and its course could not be easily altered. There was an angle between the track and the run-off: the average gradient of the track was 3.1 percent, whereas the average of the run-off area was only 2.1 percent5, which made braking on the concrete less effective. The wall was not protected by old tyres because at the time the FIA considered a concrete wall the safer option in corners where impacts were likely to occur at a shallow angle. The Imola circuit passed official

17 decided to deploy the safety car. The race would have CHAPTER 4 been stopped in similar circumstances in the past, but the safety car alternative was introduced in 1993 The race to avoid disruption to TV schedules and to spice up the often processional racing.

Although the marshals worked hard to clear the Sixty-one laps of the 5,040km Imola circuit awaited track, the cars had to weave through the carnage on the drivers as they lined up in sombre mood for the four separate occasions. While most drivers chose the start of the 1994 San Marino Grand Prix. For the middle of the track or the relatively cleaner side by third race in succession, Ayrton Senna qualified his the pitwall, on Laps 2, 3, and 4, Senna drove on the Williams on pole position, with outside line where the chances of picking up some in the Benetton yet again alongside him. It was a debris were the highest. The slow pace of the Opel variation on one of life’s universal themes: the saloon used as safety car prevented Senna from established star resisting a challenge from the young generating enough heat into the tyres, and the tyre pretender. pressures on his Williams must have dropped When the lights turned green, Senna made a perfect considerably. getaway, leaving two thick layers of rubber and the On Lap 5, the safety car extinguishes its roof lights. other twenty-four competitors behind him. But Senna’s radio crackles with the voice of race engineer farther down the field, there was mayhem. JJ Lehto David Brown confirming the imminent restart. Senna (Benetton) in fifth stalled on the grid and was struck acknowledges the message; there are no complaints by the unsighted (Lotus). Wheels and about the car. He holds back while the Opel peels off bodywork were flying everywhere, injuring spectators into the pits, then floors the throttle and accelerates in the grandstands and littering the straight with hard onto the start finish straight, catching every sharp pieces of carbon-fibre. The stricken Lotus driver other than Schumacher napping. The timing ricocheted down the track, but somehow both Lehto screens update with fresh gaps at the start of Lap 6: and Lamy escaped unharmed and the race control Schumacher -0.556s in second, Gerhard Berger

18 (Ferrari) -2.586s in third, Damon Hill (Williams) to 0.675s over Schumacher. Deft flicks of the paddle -5.535s in fourth. It’s looking good. Get more heat under the steering wheel engage the semi-automatic into the tyres. Build a gap. Focus on the track ahead. gearbox into third, fourth, fifth, and sixth. He will not Ignore Schumacher in the mirrors. change the gear again. The Renault black box beams the latest set of data to the computers on the pitwall Senna clears the new tarmac past the control tower, and the telemetry clock resets to 0.00s. It is May 1, the skid-plates under his Williams producing a 1994, 14.17hrs, the beginning of Lap 7. shower of sparks on the first and third strips. He takes the tight inside line through Tamburello and At four seconds, Senna passes under the start lights the rear of the car kicks up five ominous plumes of gantry and sweeps past the control tower, its red and molten yellow sparks as he rides over the longest white colour scheme synonymous with his best years seventh strip. There is another flash on the exit of the at McLaren. He is now entering the parkland of eighth strip: the tyres are cold but he has navigated Imola, a solitary place where tall trees outnumber the Tamburello and rushes towards the Tosa hairpin, spectators and where the afternoon sun casts long past the scene of Roland Ratzenberger’s fatal shadows across the track. accident the day before. At four-and-a-half seconds, Senna flattens a piece of The technical section of Piratella, Acque Minerali, blue debris from Lehto’s Benetton2, which is still Variante Alta, and Rivazza is next, the corners lying in his path despite the extensive clean-up coming at the driver in quick succession. The operations. He lets the Williams drift towards the Williams handles surprisingly well considering that outer edge of the track in order to minimize tyre the tyres must be still getting up to temperature; scrub and straighten the upcoming Tamburello Senna’s hand movements are smooth and there is no corner. The skid-plates graze the tarmac on the first snap oversteer or understeer that would require dark strip, spewing sparks back at the pursuing significant correction with the steering. Schumacher. He threads his way through Variante Bassa and Between six and eight seconds, the picture from the Traguardo at the end of the lap and extends his lead on-board camera mounted above Senna’s left

19 shoulder gets briefly distorted as the car shudders tyres while cornering. Engine revs have been rising crossing the third strip of new tarmac. Behind gradually and now plateau at nearly 14,000rpm; the Senna’s back, the Renault black box goes impassively speed touches 307km/h. The longest seventh strip of about recording data arriving from the different new tarmac is about 60 metres away. sensors installed around the car. He is on the short Since 10.00s, the lateral force has been decreasing straight before Tamburello, the mouth of the corner gradually from 2.92G to 2.01G (at 10.80s), indicating beckoning and approaching at eighty metres per reduced turning left. Shortly before entering the second. seventh dark strip, however, Senna makes a At 8.22s, Senna has travelled 582 metres since correction towards the left (10.90s) and the lateral breaking the start-line timing beam, his foot full force starts climbing steeply until it reaches the down on the throttle, the car doing 302km/h. As he maximum recorded by the telemetry (3.52G at begins the initial turn-in to Tamburello, he places the 11.20s). left front wheel by the white inside kerb and the At 11.08s, Senna has travelled 825 metres from the lateral force builds gradually from 0.37G to 2.45G start line. His Williams flings back a flurry of sparks (at 9.30s). as he hits the surface change from old to new tarmac The Williams travels across the fifth dark strip of new and the first bump on strip seven. The on-board tarmac (9.56s), the skid-plates churning sparks both images are distorted and their quality is getting on the entry and exit. The floor of the car hits the progressively worse until 11.16s. The speed is up to ground – ‘bottoms out’ (revs jump to 14,204rpm at 309km/h and the car keeps turning left, so much so 9.68s) - and then the car recovers grip (revs drop to that by 11.16s it is facing the grass verge that 13,561rpm at 9.72s). Moments later, there are more separates the track from the Armco barrier on the sparks on the sixth strip (10.26s). inside of the corner. Senna’s foot is still full down on the throttle but the In the cockpit, Senna realises something has gone car has stopped accelerating because of aerodynamic wrong. There is no margin for error in Tamburello: drag imposed by the rear wing and the scrub of the he is travelling at 86 metres per second, yet a mere

20 100 metres separate him from a concrete wall. Does is at zero throttle after the throttle damper has done he have time to grasp instinctively what is happening its work. The revs dip below 13,000rpm and the rear to him? wheels lock up temporarily as they rotate notably slower than is the speed of the car (the difference is Assuming the reaction time of top F1 drivers is 17km/h). around one tenth of a second, 11.10s is the moment he decides to lift and at 11.20s he is already Now Senna has abandoned the curve, deviating some responding. For the first time on Lap 7, his right foot nine degrees from the normal racing line, and the is not on full throttle (99.4 percent), the engine revs lateral force keeps falling from the maximum drop by 350rpm to 13,445rpm (at 11.24s), and the car recorded by the telemetry to virtually zero. His begins to slow down. Simultaneously, the Williams helmet lunges forward and tilts slightly to the left, straightens its trajectory. which is confirmed by the angle of the Nacional banner and the visor in the rear-view mirror. There are two short flashes from the underbody which correspond to the remaining two bumps on During 11.50-11.68s, Senna is shifting his right foot strip seven, and the on-board images are distorted from the throttle to the brake pedal and hydraulic accordingly at 11.22s, 11.26s, and 11.28s. The pressure is still building in the braking system. In the Williams bottoms out on the third, biggest bump middle of this lull in driver input, he exits the seventh (revs spike to 14,077rpm at 11.26s); at this point, strip of new tarmac and the floor of the car generates however, the car is already out of control. It stays on another flash of sparks (11.58s). the track for another 65 metres, lasting less than one At 11.68s, he has covered 41 metres since he began to second. lift, and is about to enter the final eighth strip of new At 11.30s, Senna has covered 10 metres since he tarmac. No brake pedal telemetry exists, but the began to lift, and his speed reduces to 306km/h. He steep increase in deceleration (up to 4.7G by 12.08s) hesitates with the throttle for a couple of tenths of a and the rapid fall in engine revs (down to 10,200rpm second - the values oscillate around 50 percent until by 12.10s) reveal the onset of hard braking: from this 11.42s – and then completes the lift. At 11.50s, the car

21 moment on, Senna is trying to reduce the speed of lateral force (from -0.12G to 1G to 0.33G). Senna’s the inevitable impact. feet bounce about the footwell, which shows on the telemetry as a squirt of throttle (9 percent at 12.12s) He releases the brakes briefly during 11.74-11.76s, and modulation of the clutch. Simultaneously, the which is visible on the telemetry as a blip in engine almost stalls (revs drop dramatically from otherwise steeply increasing deceleration, and his 10,750rpm to 4,200rpm within just 0.24s). head is moving back towards the headrest. The on- board picture gets distorted and the rear of the At 12.46s, about 15 metres separate him from the Williams sparks again as it exits the eighth strip at wall. Senna exits the grass strip and enters the 11.98s. concrete run-off area. The car twitches from left to right (there is a 1.8G lateral jolt during 12.50-12.58s), In the eight-tenths of a second since he began to lift, but once it lands fully on the concrete, the tyres grip Senna has travelled 62 metres and has managed to again and the braking improves. Senna’s foot slow down from 310km/h to 260km/h. His head touching the throttle means the revs fluctuate but are moves forward again due to hard braking, which no longer falling (4,900-6,600rpm after 12.42s). stops only when he runs out of road and enters the grass (12.16s). The dynamic weight of the car shifts Two-tenths of a second to impact. Either accidentally forward onto the front axle, and the Williams is or intentionally, Senna tries one more desperate pulling gently right in the last three tenths of a attempt to steer away from the wall by pressing second on the track (the lateral force turns negative, harder on the throttle pedal (7 percent at 12.60s, then -0.15G). 18 percent at 12.80s) and by further modulating the clutch (up to 8.7mm). The car straightens (lateral At 12.16s, about 25 metres separate him from the force falls to 0.4G) and reduces its speed to an wall. Senna leaves the track and drops three wheels estimated 216km/h81. on the grass. The change in surface makes the braking less effective (deceleration drops to 1.5-3G). At 12.80s and 930 metres into Lap 7, the telemetry The car gets momentarily airborne and bounces from goes blank. Senna hits the unprotected concrete wall side to side, inducing jolts that produce spikes in the at a shallow angle of twenty-two degrees3,5 about

22 three metres past the ‘I Pilotissimi’ sign. He suffers serious head injuries and dies four hours later in the Maggiore Hospital in . When the first track marshals and doctors reach him, they notice the steering column dangling uprooted in the cockpit. To extricate the deeply unconscious driver from the wreck, they remove the steering wheel and leave it lying beside the cockpit with the upper section of the column and one of the cables still attached to it. But did the broken column trigger the accident, or did it only break on impact and had no role to play?

Figure 4 – Imola, Tamburello corner, Lap 7.

23 company. Crucially, both tapes end before Senna CHAPTER 5 veers off the track, leaving question marks over his Video footage last actions in the cockpit. In 1994, 20 out of 26 cars carried miniature on-board cameras but live feed was received only from four cars at a time. On Lap 6, three of the four were TV cameras captured the accident from three Senna’s Williams, Schumacher’s Benetton, and different angles but the footage is of relatively poor ’s McLaren. As Senna was leading and quality and doesn’t paint a complete picture as to facing a clear track, ten seconds before the accident what happened to Senna. Images from Schumacher’s the director decided to switch to the Tyrrell of Ukyo on-board camera are grainy, showing the Williams Katayama. There was a delay of several seconds heading for the wall and disappear out of sight as the because RAI had to be notified about the switch and Benetton successfully navigates the corner. The Katayama’s camera had to be activated3. stationary camera of Italian network RAI positioned past the exit of Tamburello catches the Williams By sheer coincidence, the switch to Katayama’s already out of control but, thanks to the curvature of Tyrrell took place exactly at the moment when the run-off area, it mercifully misses the full impact Senna’s Williams was about to leave the track. of the right hand side of the car against the wall; and However, the next frame on the tape is not an image the on-board tape from Senna’s car ends abruptly from Katayama’s car but 14 seconds of blurred 0.9s before the impact. pictures and grey lines. According to the testimony of FOCA TV personnel in court, the switcher pressed The on-board footage was first publicly broadcast on the wrong button and transferred to Berger’s Ferrari Brazilian channel TV Globo using a VHS quality tape instead. As Berger’s camera wasn’t activated, the tape ‘discovered’ by Brazilian journalist Roberto Cabrini. only contains interference until the right button was It ended 1.4s before the impact. Later, an additional pressed and footage from Katayama’s car appears17. 0.5s of footage appeared when a Betacam quality tape Very limited amateur footage of the race exists, but was supplied by ’s FOCA TV the images do not reveal anything new.

24 CHAPTER 6 presented in court as prosecution evidence18. You can watch the videos on CINECA’s website. Image processing CINECA also attempted to analyse Senna’s steering wheel movement. It used the yellow button on the left spike of the steering wheel and the serigraphed CINECA ANALYSIS letter ‘V’ (Figure 5) to determine the amount of flexing and steering lock applied. Shortly after the accident, the State Prosecutor in Italy contracted CINECA consortium to process all available TV footage and telemetry from Senna’s car. CINECA (Interuniversity Consortium of North Eastern Italy for Automatic Computing) is a large scientific computing centre for public and private research and is comprised of 13 universities. Their software engineers digitized the footage and synchronized images from Senna’s car with those from Schumacher’s and also from the stationary RAI camera on the exit of Tamburello. Former Ferrari chief designer then synchronized the digitized video stream with telemetry data from the Renault black box3. CINECA prepared three versions: composite footage from the different camera angles, on-board footage that incorporates the track and the surroundings, and on-board footage Figure 5 - Ayrton Senna’s steering wheel, Williams that zooms in on the cockpit. The end product was FW16/2-Renault, Imola 1994. It differs from the steering wheels seen on the car later in the season (drawn to scale based on CINECA’s website19).

25

Figure 6 - Cockpit of the Williams FW16-Renault. The Senna Exhibition, Autosport International ‘98.

26

The yellow button’s ‚normal‘ position is 83mm from As CINECA used the safety car period for the centre of the wheel (green arc in the videos), the establishing the baseline position of the yellow ‚normal‘ position of the ‘V’ is 55mm from the centre button, it could be argued that it only captured of the wheel (red arc in the videos). The two reference steering wheel behaviour at relatively low speeds points were triangulated with the rim of Senna‘s whereas Senna’s accident occurred at 310km/h on a cockpit and their baseline movement was established bumpy section of the track. To understand the by tracking steering wheel rotation during the safety behaviour it is therefore important to study not only car period when both objects describe regular arcs the accident itself but also the car’s handling under dictated by the laws of geometry. The actual position normal conditions in the first three races of the 1994 of the yellow button in the video sequence against the season. green arc reveals the relative movement of the Hours of publicly available footage from Eurosport, steering wheel between the safety car period and Lap BBC, RAI, TV Globo, TF1, RTL, FOCA TV, and Ayrton 7. Senna Online Channel20 yield twelve minutes of The cockpit is in the shade and the bumpy track images from Senna’s car. On-board footage exists surface creates interference, which makes the yellow from qualifying and race in Brazil, from qualifying button hard to distinguish in some frames. For the and the warm-up session in Japan, and also from the purpose of our analysis, the original CINECA Imola weekend: the lap from Friday morning practice sequence was deconstructed frame by frame and a during which Senna unexpectedly greeted his old yellow dot superimposed on the actual yellow button. nemesis Alain Prost, a couple of laps from Friday No yellow dot was added to frames where the exact qualifying, brief sequences from the Sunday morning position of the button is uncertain or where it is warm-up, four short stints at low speed behind the completely off the screen. The individual frames were safety car, last seven seconds of lap 5, complete lap 6, then merged into a new on-board sequence. and the tragic lap 7. Enhanced yellow button sequence, Lap 7 To analyse Senna’s steering inputs in those first three races, a white circle of low opacity was superimposed on the footage (Figure 7) in such a way that the edge

27 was determined by comparing the ‘virtual’ distance of the yellow button from the serigraphed ‘V’ on the screen with the actual distance in the real world (which is known – 44mm, Figure 5). The serigraphed ‘V’ does not appear on the footage from Brazil and for that reason the rivet below the ‘DATA’ button was used instead as the reference point (the actual distance is known as well - 53mm, Figure 5). Analysis of the season opener in Brazil (total footage duration 3min 20s) reveals two brief instances (0.2s each) where the yellow button deviates 4-5mm from the white circle of low opacity. The story is very Figure 7 - A white circle of low opacity was superimposed similar during the race weekend in Japan (2min 34s on twelve minutes of on-board footage from Senna’s car to of footage): there are four instances of flexing that track steering wheel movement. This demo image shows stay within 4–5mm. two examples of the yellow button flexing with deviations ‘x’ upwards and ‘y’ downwards (background image used At Imola, the footage from the Friday morning lap with CINECA’s permission). (1min 35s) shows two deviations (0.5s each) that peak at 6-8mm in Tamburello and on the exit of of the white circle tracks the movement of the two Piratella. Laps from Friday afternoon qualifying yellow buttons located on the spikes of Senna’s (58s in total) produce three deviations of 6-8mm on steering wheel. In addition, the white circle was also the exit of Tosa, Piratella and in Tamburello. triangulated with the rim of the cockpit. Footage from the Sunday morning warm-up (1min The footage was studied frame by frame and 20s) is in line with our observations so far and deviations from the white circle were measured on reveals two peaks at 6-8mm on the exit of Rivazza the computer screen and then converted to real (0.2s) and on the entry to Variante Bassa distances using a scaling factor. The scaling factor

28 (1s duration). There is no perceptible flexing during of race lap 5 at Imola show no or minor flexing race laps 2 - 5 (1min 7s) as Senna is going slowly (peaks reaching 6-8mm) regardless of speed or track behind the safety car and is weaving from side to side conditions, and support the reliability of CINECA’s in preparation for the imminent restart. In methodology. The same is also true of the limited conclusion, the twelve minutes of on-board footage footage available from Damon Hill’s sister car. from the beginning of the 1994 season until the end

ACCIDENT TIMELINE, YELLOW BUTTON MOVEMENT, LAP 7

8.20s: Senna gradually turns into Tamburello. The yellow button begins to descend at a 45 degree angle.

9.86s: Within 1.5 seconds, the yellow button deviates to the level of the serigraphed ‘V’ (the red arc), some 25-27mm from its customary position on the green arc.

10.74s: The yellow button stops dropping and hovers on the edge of the screen.

10.74-11.20s: The yellow button remains on the edge of the screen or just under it, but it is moving from right to left. It is during this period that Senna loses control.

11.22-11.30s: The yellow button jumps up just above the red arc, and then nearly reaches the original green arc position in a vertical upward movement.

11.32-11.42s: There is another vertical steering movement, this time in the opposite direction (downwards) – the yellow button goes from being nearly at the green arc to being completely off the screen at 11.44s.

11.44s: The yellow button drops below the edge of the screen.

11.52s: The yellow button reappears just above the edge of the screen and then is gone again.

11.74s: The yellow button reappears for an instant on the red arc level, but quickly moves down below the screen after 11.76s. It is not seen until the end of the footage at 11.84s.

29 BOTTOMING EFFECT the Sunday warm-up and also following the second start after Senna’s accident. Even at rest, the ride height of an F1 car at the rear is only a few centimetres, and at top speeds it is not The ride heights and tyre pressures at the time of the uncommon for the bottom of the car to literally accident aren’t known, but it is possible to deduce scrape the ground. The FW16’s underbody was their relative changes from the extent to which protected by skid-plates made of titanium, which Senna’s car bottomed and generated sparks from its generated spectacular showers of sparks every time titanium underbody. All things being equal, if the the chassis made contact with the ground. This tyres are cold their circumference is smaller, the ride phenomenon was widespread in the late ‘80s and heights are lower, the bottoming effect is stronger, early ‘90s, especially in the opening laps of the race and the car should generate a higher amount of when the cars were still on full tanks and also in sparks compared to another lap on which the tyres qualifying when teams tried to get away with the are already warmer. That assumes the driver hasn’t lowest possible ride height in order to maximize suffered a puncture or a suspension failure, that he downforce over a single lap (watch some great takes a similar racing line through the corner, and examples on YouTube from the Japanese GP 1987, that he doesn’t suddenly lift or brake (which pushes Belgium GP 1992, or Brazilian GP 1994). the front of the car to the ground and raises the rear). TV footage from the Imola weekend reveals that the All through Friday practice, qualifying, and Sunday cars were prone to bottoming at four different parts warm-up, Senna’s car was visibly touching the of the track (Figure 8): through Tamburello, past ground while riding over the eight dark strips of new Tosa towards Piratella, in the downhill section before tarmac laid between the start line and exit of the Acque Minerali chicane, and on top of the hill Tamburello (strips two and four were very narrow). approaching Rivazza. Most drivers were affected, The Williams consistently generated sparks on the including Senna’s teammate Damon Hill, Pierluigi exit of the fifth strip (sometimes also on the entry); Martini (Minardi), and the of Gerhard on the exit of the sixth strip (sometimes also on the Berger and Nicola Larini. Berger’s Ferrari entry); it produced five distinct showers of sparks on in particular bottomed heavily at Tamburello during

30 the longest, seventh strip (with sparks on the exit elevation changes between the old and new surface always being the strongest); and it usually cleared the whereas on strip seven there were not only elevation eight strip without visibly touching the ground. changes on entry and exit but also three bumps in between. It was strip seven where Senna lost control These observations imply that the bottoming on on Lap 7. strips one, three, six, and eight was caused by

Figure 8 - Four sections of the Imola circuit where the cars regularly experienced bottoming during the 1994 race weekend (yellow numbers 1-4).

31 CAR TRAJECTORY Two additional yellow lines define the momentary angle between Senna’s car and the inside kerb in The process of establishing Senna’s exact trajectory is Tamburello. The absolute values themselves are not challenging because the telemetry wasn’t recording that significant, but the relative change in the angle the actual position of the car (front and rear) relative from frame to frame is a good approximation of the to the track, and conclusions based on watching the actual change in the attitude of Senna’s car as it is TV footage provide only qualitative insight. negotiating the corner. One option is to reconstruct the trajectory by The first line is defined by three points on the car that measuring the relative movement of the car against form a straight line - the outer blue edge of the stationary objects in the background such as kerbs cockpit rim, the black point that fixes the windshield and advertisement hoardings. Senna’s Williams hit to the monocoque, and the bottom end of the the wall about three metres to the left of Agip’s antenna. The second line is defined as the line of best advertisement hoarding ‘I Pilotissimi,’ which makes fit that runs alongside the top edge of the kerb. it the perfect candidate for a reference point as that’s where the car is irrevocably heading to. Alas, even this approach has its limitations because frame distortion blurs the stationary objects and prevents highly accurate measurement. A vertical yellow line in Figure 9 tracks the leading edge of the ‘I Pilotissimi’ sign; its relative shift from frame to frame indicates change in the direction of travel (if the car keeps turning left, the sign continues moving right until it disappears from the screen). Car trajectory analysis

32

Figure 9 – Car trajectory analysis

33

Figure 10 - Direction of travel analysis based on the ‘I Pilotissimi’ sign. This graph expresses the position of the yellow vertical line as a percentage of the overall frame width. The measurement is taken from left to right (i.e. when the left edge of the ‘I Pilotissimi’ sign just comes into view, the result is 0%; when the left edge of the sign reaches the right end of the frame, the result is 100%). Blue data points denote values from race Lap 7, green points from a Friday qualifying lap, and red data points from the Friday morning practice lap during which Senna greeted Prost. The three laps are synchronized using timing and distance markers of Lap 7 (synchronization is necessary because the car travels through the same place on the circuit at slightly different times). 34

Figure 11 - Momentary angle between Senna’s car and the inside kerb in Tamburello. Change from lower to higher values means the car is heading more towards the inside kerb; change from higher to lower values means the car is moving away from the inside kerb. Blue data points denote values from race lap 7, green points from the Friday qualifying lap, and red points from the Friday morning practice lap. 35

ACCIDENT TIMELINE – CAR TRAJECTORY

10.52-10.74s: Until now, Senna has driven on a nearly identical racing line compared with his laps from Friday. From 10.52s, however, the car’s rate of direction change is lower, and the Williams runs slightly wide towards the middle of the track. The angle between the car and the kerb is decreasing as well.

10.76-10.90s: The car’s direction change is still less than during the Friday laps but Senna has recovered some of the ground, as indicated by the increased angle between the car and the kerb.

10.90-11.10s: The car’s rate of direction change is greater than usual and the Williams recovers to its regular trajectory (the blue, green, and red lines meet again in Figure 10).

11.10-11.18s: The car’s rate of direction change becomes even greater and it keeps increasing to the point where the Williams is visibly facing the inside of the corner (the blue line crosses over and above the green and red lines in Figure 10). The angle between the car and the kerb also increases considerably. It is during this period that Senna loses control.

11.18-11.26s: The rate of direction change is still slightly higher than during the Friday laps, but the car is straightening up and the angle between the car and the kerb is decreasing.

11.26-11.40s: The blue line flattens and stays horizontal, which means the car is heading dead-straight for the ‘I Pilotissimi’ sign. There is no perceptible direction change. The Williams has abandoned its regular trajectory (the green & red lines are now above the blue line). The angle between the car and the kerb keeps decreasing.

11.40-11.56s: The blue line is going down, which suggests the car is moving back towards the right end of the ‘I Pilotissimi’ sign and that the Williams is heading gently right.

11.56-11.70s: The car’s direction change is gently left – about half the rate required to navigate the corner at this point (the green and red lines keep going up at roughly double the rate of the blue line).

11.70-11.84s: Until the end of the on-board footage, the Williams is heading straight for the ‘I Pilotissimi’ sign.

36 LEFT FRONT TYRE ANGLE pointing straight – for instance when Senna is on the short straight before Tamburello. The relative Because the Williams black box was damaged in the changes in tyre shape against this reference frame crash, we’re in the dark with respect to the will show on the composite footage as white space (or correlation between Senna’s steering angle and the black outline) in those areas where the superimposed directional change of his front wheels. The closest images differ (Figure 13). This method helps validate suitable proxy is the incremental change in the angle tyre angle during 10.90-11.18s when the tyre rotation of the left front tyre relative to the monocoque, which left reaches its peak. can be measured manually frame by frame and then plotted in time sequence (Figure 14). Independent validation of tyre angle Angle of the left front tyre It’s even harder to quantify the directional changes of Senna’s left front tyre as his out of control Williams The accuracy of this method is limited: Tamburello skims across the run-off area. The quality of the TV required only a shallow steering lock to navigate the images is poor and the car turns into a smudge in the corner and the incremental tyre movement is quite critical moments before the impact. Still, shortly after small; the tyre undergoes deformation under the car lands on the concrete the tyre’s sidewall cornering and deceleration forces (although the right comes distinctly into view, suggesting the front wheel front carried the bulk of the lateral load in is turned right, and the sidewall appears to be facing Tamburello), and some of the key frames are skywards. Moments later, the tyre seems to wobble distorted by bumps, which hampers highly accurate right and left; nonetheless, the images are so blurred measurement. Thanks to the large number of data that this could be just a mirage. One observation can points, however, the method yields a higher-order be made though: at no point did Senna’s tyre keep trend that indicates whether the tyre is turning left, pointing left in an attempt to steer the car away from turning right, or aiming straight. the wall. It is also possible to analyse the rotation of the left Williams skims across the run-off area front tyre by superimposing the complete video sequence on one reference frame in which the tyre is

37

Figure 12 - The width of Senna’s left front tyre sidewall as a percentage of a control height measured from the top of the tyre. Wider tyre profile corresponds to a higher percentage in Figure 14 (left front wheel turning right), narrower tyre profile corresponds to a lower percentage (left front wheel turning left).

38 Figure 13 - Difference in the shape of the left front tyre (white space) relative to the reference frame.

39 Figure 14 - The width of Senna’s left front tyre measured as a percentage of the control height (Lap 7).

40

ACCIDENT TIMELINE - LEFT FRONT TYRE ANGLE

3.98-4.74s: The left front tyre is turning left (Senna drives under the gantry and past he control tower).

4.76-5.62s: Tyre is aiming straight (Senna lets the car drift to the outside).

5.64-6.22s: Tyre is turning right (Senna guides the car towards the edge of the track to minimize tyre scrub and to straighten the upcoming corner).

6.24-8.20s: Tyre is aiming straight (Senna is on the short straight and approaching Tamburello).

8.22-9.08s: Tyre is turning gently left (initial turn-in to Tamburello).

9.10-9.66s: Tyre is aiming straight.

9.68-10.48s: Tyre is turning left.

10.50-10.72s: Tyre is aiming straight (Senna’s Williams drifts slightly wide).

10.74-10.88s: Tyre flicks left.

10.90-11.18s: Tyre rotation left reaches its maximum, with three observable culminations around 10.94s, 11.06s and at 11.18s. It is during this period that Senna loses control.

11.20-11.26s: Tyre returns swiftly to the neutral position.

11.28-11.52s: Tyre is aiming slightly right.

11.54-11.66s: Tyre is aiming straight or slightly left.

11.68-11.80s: Tyre is turning imperceptibly right.

11.82-11.84s: Tyre is aiming straight.

41 The graphs used in our analysis are based on CHAPTER 7 telemetry values from Lap 7 and are derived from the computer synchronization prepared by CINECA in Car telemetry 1997. The numerical values end at 11.98s at the same time as Senna’s on-board tape, values from 12.00s until 12.80s are therefore extrapolated from CINECA’s original telemetry graphs (which run in the The Williams black box was damaged in the crash: of computer synchronization until the impact, Figure the twenty memory chips it contained, eighteen 17). would lose data once the power supply failed while two chips were able to retain data even in case of a All parameters except engine revs, throttle pedal, power failure. Only two chips were damaged, the two throttle valve position, gear, clutch and longitudinal being those two that were capable of storing data acceleration were read from the sensors every tenth after the power had gone15. of a second. Distance travelled by Senna’s car from the start line was also refreshed every tenth of a The Renault black box survived intact. Information second and the actual distance may not be completely from the incomplete Lap 7 was copied onto a floppy accurate in case of those parameters that were disk on the day of the crash, and the black box then refreshed more frequently. got erased during tests on an engine bench in , France, a few days later16. The computers in the pits No data was captured regarding suspension travel, had received and probably retained data from the ride heights, tyre pressures, temperatures within the previous six laps of the race as well, but those car, brakes, brake pedal position, steering angle, and telemetry traces have never been made public. downforce levels. Williams haven’t disclosed the exact definitions of the telemetry channels, either. Most of them are self- explanatory except for the steering data, which calls for very specific knowledge of the system’s design and operation.

42

Channel Freq Colour Definition Unit

TIME 0.02s Grey Time S SPACE 0.10s Cyan Distance M RODSP 0.10s Red Car speed km/h REARSP 0.10s Yellow Rear wheels speed km/h LATACC 0.10s Blue Lateral acceleration G LONACC 0.02s Green Longitudinal acceleration G N 0.01s White Engine revs RPM GEAR 0.01s Green Gear engaged # CLUTCH 0.01s Red Clutch position mm PEDAL1 0.02s Brown Pedal 1 position % PEDAL2 0.10s Blue Pedal 2 position % POTG 0.01s Yellow Butterfly position (L.H.S.) % POTD 0.05s Grey Butterfly position (R.H.S.) % STGPR 0.10s Green Steering pressure PSI STGSTN 0.10s Grey Steering strain N/m2 STGTGT 0.10s Blue Steering target PSI STGACT 0.10s Cyan Steering pressure difference PSI STGERR 0.20s Red Steering error Dec

Figure 15 - Telemetry parameters recorded by the Renault black box as presented by CINECA in 1997 (reproduced with CINECA’s permission).

43 Figure 16 - Computer synchronization showing telemetry values from the Renault black box (reproduced with CINECA’s permission).

44

Figure 17 - Telemetry graphs from the CINECA computer synchronization (reproduced with CINECA’s permission).

45

Figure 18 – RODSP. Actual speed of Senna’s car on the road.

46

Figure 19 – REARSP. Rotation of the rear wheels. If the speed of the rear wheels is higher than the car’s speed on the road, it indicates loss of traction (for example, wheelspin under acceleration, on bumps or kerbs). If the speed of rear wheels is lower than the car’s speed on the road, it indicates braking, wheels locking under braking, or recovery of grip after wheelspin.

47

Figure 20 - Speed difference between the car and the rear wheels, extrapolated from the telemetry as REARSP minus RODSP.

48

Figure 21 – Engine revolutions per minute . A sudden rise in RPM at constant throttle corresponds to the rear of the car losing traction or touching the ground (riding kerbs or hitting a bump). A drop in RPM at constant throttle indicates that the rear has regained traction and the tyres bite harder into the tarmac.

49

Figure 22 – LONACC. Acceleration and deceleration of Senna’s car in a straight line. Positive figures indicate that the car is speeding up (driver is on the throttle), negative values indicate that the car is slowing down (driver lifts or is braking).

50 Figure 23 – LATACC. Lateral acceleration or cornering force on the car when it’s not travelling in a straight line, commonly referred to as g-force. Positive values indicate turning left, negative values turning right.

51

Figure 24 – PEDAL1. Throttle pedal application, from 0 percent (no throttle) to 100 percent (full throttle). Pedal1 data was ready every 0.02s, unlike Pedal2, which was read only every 0.1s. Pedal2 is less accurate for the purpose of the analysis and can be ignored.

52 Figure 25 – POTD/POTG. Position of the butterfly valve (throttle plate)78 that regulates the amount of air flowing into the engine - and hence the power of the engine - based on throttle pedal input from the driver , from 0 percent (valve fully closed) to 100 percent (valve fully open). L.H.S. denotes measurement taken in the intake manifold on the left hand side, R.H.S. on the right hand side. POTG data was read every 0.1s. It is displayed on CINECA’s telemetry as a graph without numerical values. POTD data was read every 0.05s but otherwise it looks identical to POTG. 53

Figure 26 – CLUTCH. Clutch barrel position. The semi-automatic gearbox engaged the clutch automatically; the FW16 however had a clutch pedal in the cockpit (to the very left) that was used by the driver during the start and pitstops.

54 electrical commands and are fundamentally the same CHAPTER 8 as hydraulic power steering on your road car – Steering telemetry they’re just much more compact and responsive22-28. Back in 1994, however, Williams did not operate a purely mechanical system and in fact became the first F1 team to develop power steering that exploited The steering telemetry cannot be interpreted electrohydraulic servo valves. The valves direct the unambiguously without the original technical flow of hydraulic fluid based on electrical rather than specifications; unfortunately, the spectre of the mechanical signals. They were originally used in the manslaughter trial and potential jail sentences for aerospace industry and, by the late ‘80s, found their senior Williams personnel in the late ‘90s meant that way into F1 as actuators in active suspension when the team didn’t divulge information about how the supplier Moog entered the scene with series 30 and steering worked, and the facts that are in the public later series 50 valve29-30. Their use quickly spread to domain today have come indirectly from witnesses other areas of design until by 1993 every car would giving evidence during the trial or from reports, feature as many as ten valves controlling anything drawings, and photos leaked to the press. from the clutch, differential, gearbox and throttle Still, certain fundamental principles apply. Since the actuation, to the engine and ABS brakes27. The main FIA ban on electrohydraulically assisted steering in benefit of electrohydraulic servo valves is their the early ‘00s the majority of F1 teams have been incredible power density: they can handle the same using hydro-mechanical power steering valves. These loads as electric or pneumatic motors yet they are valves are either rotary or linear systems that direct faster, smaller and lighter in comparison – all the flow of hydraulic fluid based on mechanical qualities much desired in F1 regardless of cost. input. In the rotary system, for instance, this input However, before trying to interpret the steering comes from a small torsion bar that senses strain telemetry from Senna’s car, we need to explain how exerted on the steering column. The valves are this type of power steering works. While the passive in the sense that they do not respond to any remainder of this chapter is inevitably a little

55 technical, it helps in following the rest of the book or the combination of both), the length distortion of and doesn’t require any special knowledge. the tiny conductors in the patches causes a change in electrical resistance, which is then measured,

amplified, and converted into a suitable electrical ELECTROHYDRAULIC STEERING signal. This signal is fed into an electrohydraulic Electrohydraulic power steering assembly consists of servo valve (10) where it controls the opening of two several components (Figure 27). The steering column hydraulic ports (11) which direct the flow of fluid to (1) typically runs through a support strut and bushing the cylinders at each end of the steering rack. The (2), and connects at the lower end to the pinion (3). steering rack works as a double-acting hydraulic Pinion is a circular gear used to convert rotational cylinder and assists the driver to turn the front motion originating in the column into linear motion wheels. of the steering rack (4) by engaging the teeth on the The electrohydraulic valve is the heart of the power rack (5) and causing it to slide left or right. In designs steering system. It is quite a small device (about where the pinion engages the rack from above rather 65x40x40mm, 400g) typically made of stainless steel than underneath as would be normal for a car with and aluminium alloy30. It is a valve, and therefore it the rack ahead of the front wheels, the pinion is doesn’t control the hydraulic pressure – it controls attached to the steering rack through a reversing gear the direction and rate of the fluid flow. It must be (6). Without this extra gear to reverse the direction capable of supplying adequate volume of fluid so it the assembly would otherwise steer backwards. The can respond to the greatest demand coming from steering rack houses the rack teeth and a hydraulic either the steering or the wheels. The quicker the cylinder (7) with integral piston (8) at each end. driver turns the steering wheel, the more rapidly the The twisting force on the steering column is sensed valve’s control ports must fill and drain the hydraulic by one or more strain gauges (9), which are small cylinders in the steering rack in order to assist the electrified patches glued to the steering column31,32 or direction change of the front wheels. tie rods. When the column is put under strain (i.e. driver turns the wheel, the front wheels hit a bump,

56 Figure 27 - Schematic diagram illustrating the basic function of electrohydraulic power steering components: (1) column, (2) support strut with bushing, (3) pinion, (4) steering rack, (5) rack teeth, (6) reversing gear, (7) hydraulic cylinder, (8) piston, (9) strain gauges, (10) electrohydraulic servo valve, (11) servo valve’s hydraulic control ports C1 and C2.

57 Figure 28 - Schematic diagram of an electrohydraulic servo valve29. (1) Permanent magnet, (2) Flapper, (3) Armature, (4) Solenoid, (5) Left nozzle, (6) Right nozzle, (7) Sliding valve spool, (8) Cantilever spring.

58

Detailed technical description of the valve’s operation second control port (C1). Pressure rises within line C2 is beyond the scope of this book, but it can be found and exerts force against the piston in the steering in the literature28-29 and a simplified version will rack until it performs the desired power assist. At the suffice here (Figure 28). same time, fluid escapes from the other side of the steering rack via line C and flows to the return port In the electrical part of the valve, a flapper (2) is 1 (R). When steering in the opposite direction, the attached to armature (3) rotating in magnetic field. process is reversed: the spool slides left and line When twist is applied to the column by the driver and C exerts force against the piston while line is resisted by the wheels, or when twist is applied by 1 C exhausts fluid to the return port (R). the wheels and is resisted by the driver, the electrical 2 current circulating in the solenoid (4) changes and The greater the difference between steering effort deflects the flapper, which restricts fluid flow from and resistance of the wheels, the greater the degree of one nozzle (5) while accelerating the flow from twist which momentarily exists in the steering another (6). column. The more twist, the greater the movement of the valve spool and the higher the rate of fluid flow in As a result, intermediate pressure difference builds and out of control ports C and C , up to the between the two sides of a linear valve spool (7), 1 2 maximum available at the end of a steering stroke or causing it to slide left or right from the centred when the wheels hit an obstruction. position. The sliding of the spool also creates a restoring torque on the flapper via a cantilever spring When the car is not being steered, the valve spool (8). Once the restoring torque equals the torque remains in the centred position in which it fully generated by the current in the solenoid, the flapper covers ports PS and R, and the supply pressure fluid returns to its neutral position and the valve spool flows directly from the two nozzles to port R. Ports C1 stops at a point proportional to the electrical current. and C2 and the respective lines to the pistons in the steering rack are still filled with fluid, but C and C The movement of the spool right opens the supply 1 2 provide equal pressure to both sides of the steering pressure port (PS) to one control port (C2) while rack, the pistons don’t move, and no power assist simultaneously opening the return port (R) to the occurs.

59 The system is closed-centre, which means that it is steering ratio if both gears are of identical pitch. The pressurized all the time with constant pressure while latter offers a quicker steering ratio as more teeth on the valve selects only the direction. There is no the pinion means more rack travel per degree of dedicated hydraulic pump and the supply pressure steering wheel rotation; however, it is physically comes from the car’s main circuit that serves other more demanding on the driver and puts more stress hydraulic-based components as well. The pump is on the steering column. In Williams’ case, the 10 never in a relieved state like in a road car where the tooth pinion gear was usually fitted only for the valve not only selects the direction but also demands qualifying, but at Imola, apparently, Senna drove supply pressure from the pump (open-centre with it in the race as well. system). Williams opted for Moog E050 electrohydraulic servo valve with three strain gauges sensing strain in the steering system and with three sensors per cylinder WILLIAMS INSTALLATION in the steering rack measuring hydraulic pressures When it comes to the actual power steering assembly (three of each to ensure redundancy). The supply used by Williams on the FW16 model, it was similar pressure of its hydraulic circuit is unknown, but the to the generic version described in Figure 27. A rare Moog valves usually operated at up to 3,000psi30 and photo of the footwell33 shows the lower end of the the values recorded by the Renault black box are well steering column connecting to an aluminium case, within that range. We’re now ready to return to which protrudes through a cut-out in the frontal area Senna’s telemetry and take a closer look at the five of the chassis and integrates on the other side with steering traces STGPR, STGACT, STGTGT, STGERR, the steering rack34-35. The drawings released by and STGSTN. CINECA19 suggest that this aluminium case contained the pinion and reversing gear.

According to one source83, the FW16 could accommodate either a 7 tooth or 10 tooth pinion gear, although this represents a radical change in the

60

Figure 29 - Steering rack on the Williams FW16B-Renault, which raced from the 1994. This photo was taken during a historic race meeting some years later, but the rack assembly is fundamentally the same as the one used by Senna in the first three races of the season (courtesy of Remi Humbert and Joachim Kutt, GurneyFlap.com).

61

Figure 30 - Frontal view of the steering rack assembly – sensors inside the hydraulic cylinders measured pressures at both ends of the rack, but only pressure on the left hand side was reported by the telemetry (STGPR). Pressure difference between the two cylinders was reported as STGACT (based on photos from the 1994 Brazilian and San Marino Grand Prix34-35).

62 POWER STEERING TELEMETRY Pressure in the left cylinder (STGPR) is linked to the pressure in the right cylinder (not shown on the STGPR (Steering pressure) is the hydraulic pressure original telemetry) via STGACT – Steering pressure measured inside the cylinder on the left hand side of difference. That is obvious once the two telemetry the steering rack as seen from the driver’s viewpoint. traces are plotted together on one graph (Figure 32). The pressure is lower or falling when the front wheels are turning left (the cylinder on the right provides the Hence STGACT is the pressure difference between desired power assist); the pressure is higher or rising the ‘turning’ side and the ‘exhausting’ side of the when the front wheels are turning right (the cylinder steering rack (Figures 27, 30), and it is defined as on the left provides the desired power assist). When STGPR (right cylinder) minus STGPR (left cylinder). the wheels are centred the pressures in both cylinders Zero to low values are expected with the steering in the steering rack are very similar (around 400psi). centred or unloaded; maximum values are expected In addition, transient pressure fluctuations can also at the end of a steering stroke or at highest load (i.e. be triggered by shocks propagating into the cylinders shocks) coming through the front wheels. Positive through the wheels. values indicate steering left (pressure against the The trends observed on the telemetry back this piston is higher in the right cylinder), negative values interpretation up: STGPR drops from 317psi to indicate steering right (pressure against the piston is 188psi as Senna begins to ease his car into higher in the left cylinder). Tamburello, and the pressure drops even lower to 164psi between 11.00-11.18s when the car’s trajectory turns sharply left. In comparison, STGPR is generally higher once the car has abandoned its normal trajectory and is heading for the ‘I Pilotissimi’ sign (around 400psi after 11.30s).

63

Figure 31 - Steering pressure STGPR in the cylinder on the left hand side of the steering rack.

64

Figure 32 - Correlation between Steering pressure and Steering pressure difference.

65

Figure 33 - Steering pressure difference.

66

Figure 34 - Steering pressure in the cylinder on the right hand side of the steering rack (not measured by the original telemetry), extrapolated from Steering pressure difference values.

67

ACCIDENT TIMELINE – STEERING PRESSURES

7.98-9.08s: Pressure difference across the steering rack is building gradually from 58psi to 764psi as Senna eases his car into Tamburello. Pressure in the cylinder on the left hand side (L.H.S.) drops slightly while most of the difference comes from pressure rising against the piston in the cylinder on the right hand side (R.H.S.). This corresponds to smooth turning & steering assist left. From 9.08s, however, the pressure difference trace switches into alternating peaks and valleys, which points to the rack being repeatedly loaded and unloaded.

9.10-9.48s: Valley One. Pressure difference drops by 40 percent (from 764psi to 435psi), chiefly as a result of the R.H.S. cylinder becoming unloaded, although it still continues to offer reduced steering assist left.

9.50-9.88s: Peak One comes shortly before Senna enters the fifth strip of new tarmac. Pressure difference doubles (from 435psi to 929psi) as the R.H.S. cylinder is reloaded either through increased steering effort left or through the surface change from old to new tarmac.

9.90-10.18s: Valley Two. The R.H.S. cylinder becomes unloaded again and pressure difference drops by 50 percent (from 929psi to 411psi). That said, sufficient difference exists to continue steering assist left.

10.20-10.38s: Peak Two. Pressure difference increases by 60 percent (from 411psi to 694psi) as the R.H.S. cylinder is loaded harder, probably because Senna takes a bite left with the steering or because the surface change on the sixth strip disturbs the right front wheel.

10.40-10.98s: Valley Three starts at 10.40s and is characterized by a lull period of low pressure difference (around 294psi) between 10.60s and 10.98s. There is a noticeable pressure increase in the L.H.S. cylinder (from 176psi to 247psi) and, at the same time, the pressure in the R.H.S. cylinder is at its lowest since Senna began turning into Tamburello (529psi). This indicates minimal turning effort left.

11.00-11.08s: Peak Three is the steepest increase in pressure difference recorded by the telemetry (from 294psi to 788psi). Pressure in the L.H.S. cylinder is the lowest recorded as well (164psi), suggesting a sharp turn left with the steering. At this point Senna hasn’t entered the seventh strip of new tarmac yet. 68

ACCIDENT TIMELINE – STEERING PRESSURES

11.10-11.28s: As Senna enters the dark surface of the seventh strip and rides over the three bumps, substantial pressure in the R.H.S. cylinder and the very low pressure in the L.H.S. cylinder remain, although the pressure difference begins to taper off (from 788psi to 623psi). This implies that, at least until the next readout at 11.20s, the front wheels keep turning left. It is during this time interval that Senna loses control.

11.30-11.68s: Pressure difference falls off the cliff, with pressures in the L.H.S. and R.H.S. cylinders all but equal (around 400psi). No steering assist occurs and the front wheels are pointing straight.

11.70-11.88s: Pressure difference rises imperceptibly to the level last seen when Senna started easing his car into Tamburello at 8.10s (223psi). This is a sign of tentative steering effort left, a shock from the road, or disturbance from the onset of hard braking reaching the cylinders via the front wheels.

11.90-12.38s: For half a second, pressure difference turns negative (-190psi) and for the first time the pressure in the L.H.S. cylinder is higher than that in the R.H.S. cylinder – in Senna’s final metres on the track, the front wheels are steering right.

12.40-12.48s: A huge transient spike (1,520psi). This is almost certainly provoked by a shock propagating through the steering system as the front wheels land hard on the concrete before the wall. As the pressure difference is positive, it indicates that the right front wheel received the shock or the wheels bounced left.

12.60-12.68s: Another huge transient spike (1,170psi) and another hit propagating from the road through the front wheels to the cylinders and steering rack. The pressure difference is again positive, indicating that the wheels bounced left.

12.70-12.80s: Third transient spike, this time in the opposite direction (-590psi). It implies the front wheels bounced right immediately before the impact.

69 The next trace, Steering target (STGTGT), is the Plotting Steering target values against Steering strain differential pressure between control ports C1 and C2 values (STGSTN) reveals a near-linear relationship of the electrohydraulic servo valve (Figure 35), between the two parameters (Figures 36 and 37), technically referred to as Load Pressure Drop. which would suggest that the power steering valve Steering target stays within ±250psi of Steering responded in an approximately linear fashion to the pressure difference values (STGACT), as could be strain exerted on the steering column. The data reasonably expected in conditions where the primary points don’t fall into a perfect line and are scattered source of pressure difference across the steering rack around the line of best fit. This could be due to either comes from the steering column rather than shocks measurement accuracy, the inherent characteristics from the road. of the valve, or some other factor.

Figure 35 - Steering target, defined as the differential

pressure between ports C1

and C2. The white arrows signify the fluid flow and valve dynamics when steering left.

70 The final power steering trace, Steering error spool position sensor used to monitor correct servo (STGERR), is hard to decipher without having access valve operation. The values are zero except for a to the original design specifications, but this single moment at 11.74s where the graph shows a telemetry channel probably relates to the integral vertical line.

Figure 36 - The relationship between Steering target (STGTGT) and Steering strain (STGSTN) is almost linear, with correlation coefficient of -0.92 (as opposed to -1.00 for a straight line). Three orange ‘outliers’ highlight the biggest deviations from the line of best fit at times 8.60s, 11.20s, and 11.30s.

71

Figure 37 - Correlation between Steering target and Steering strain.

72

Figure 38 - Steering target.

73

Figure 39 - Steering error.

74

ACCIDENT TIMELINE - STEERING TARGET

8.60s: The first ‘outlier’ where the relationship between Steering target and Steering strain deviates from the line of best fit. Considering the relatively low strain on the steering column, the target pressure is higher than expected. 10.70-10.98s: A decrease in Steering target (from 505psi to 294psi) corresponds to the spool in the servo valve sliding back towards the centred position and therefore to reduced steering assist left.

11.00-11.08s: The steepest increase in Steering target recorded on the telemetry (from 368psi to 764psi), suggesting a strong steering assist left immediately before Senna loses control.

11.20-11.30s: The second and third ‘outliers’ – considering the high strain in the steering column, pressure difference between the control ports of the servo valve is appreciably lower than expected. 11.30-12.80s: The Williams has abandoned its regular trajectory and is heading more or less straight for the ‘I Pilotissimi’ sign. Steering target pressure falls dramatically at 11.30s (to 175psi) and stays low until the impact (below the level required for the initial turn-in to Tamburello). 12.40-12.48s: Steering target remains minimal (under 100psi) while Steering pressure difference spikes (to 1,520psi). This confirms there is little fluid flow through the control ports of the valve and the pressure spike in the cylinders comes from the wheels rather than from the steering, otherwise Steering target would also have spiked. 12.60-12.68s: Steering target again stays minimal despite another Steering pressure difference spike. The reason is another shock propagating through the front wheels.

75 cannot be seen on any of the drawings19 or photos33, STEERING COLUMN TELEMETRY and it wasn’t until May 2014 that Adrian Newey The telemetry records Steering strain (STGSTN) in alluded to their exact position in an interview for units of torsional stress N/m2 (Newton per square auto motor und sport85: the sensors were located ‘in meter). When a column is subjected to torque or the struts of the front axle’, which most likely refers twisting, torsional stress is produced in the column, to the tie rods linking the front wheels to the steering with values ranging from zero in the column’s axis to rack because a strain gauge measuring the tension a maximum at the outside surface. In this context, and compression of a tie rod is the same as one STGSTN is the stress momentarily generated in the measuring torsional stress in a column. No strain steering column by the continuously varying gauges were found in the upper section of the opposition of inputs from the driver and the front steering column that broke off, and it is unclear wheels. whether the third gauge was in fact positioned at the The three strain gauges measuring torsional stress lower end of the column near the pinion or not (Figure 40).

Figure 40 - Strain gauges measuring torsional stress on the steering column 76

Figure 41 - Steering strain.

77

ACCIDENT TIMELINE - STEERING STRAIN

7.98-9.08s: Steering strain is building in the column as Senna starts easing his Williams into Tamburello, reaching -19.15N/m2 at 9.08s (from -4.79N/m2 at 7.98s).

9.10-9.68s: A period of relatively stable strain in the region of -16 to -17N/m2 that is a sign of steady turning left.

9.70-9.78s: In the middle of the fifth dark strip, strain drops from -17.95N/m2 to -11.97N/m2. This is consistent with the steering becoming lighter as the car hits an undulation and experiences transient oversteer. 9.80-9.98s: A sharp increase in Steering strain indicates the oversteer has gone and Senna continues steering effort left (-23.34N/m2).

10.00-10.48s: The steering is still loaded but the strain is gradually decreasing (from -23.34N/m2 to -14.96N/m2), which suggests lighter steering effort left. 10.50-10.58s: Another quick steering correction left (strain reaches -22.14N/m2).

10.60-10.78s: Sharp drop in Steering strain (from -22.14 to -10.17N/m2) as steering effort declines. This is similar to the drop experienced on the fifth dark strip, but this time the car is not on the new tarmac and the decrease is not caused by transient oversteer.

10.80-11.08s: The steepest increase in Steering strain recorded on the telemetry. It keeps rising from -10.17N/m2 at 10.78s up to -26.93N/m2 at 11.08s. This corresponds to a brusque steering effort (left) exerted by Senna immediately prior to losing control.

78

ACCIDENT TIMELINE - STEERING STRAIN

11.10-11.28s: There is sustained high Steering strain (between -25.13 and -26.33N/m2) in the critical period during which Senna loses control. There is no sudden drop in the strain that would signal that the steering got light on the first two bumps.

11.30-12.38s: From this point onwards, Steering strain falls to virtually zero (0.60N/m2) in a close to quadratic curve.

12.40-12.48s: There is a blip in Steering strain that mirrors the huge spike in Steering pressure difference. The value (-7.40N/m2) is low and equivalent to the strain exerted by Senna on the initial approach to Tamburello.

12.60-12.68s: Second blip in Steering strain (-4.20N/m2) that again mirrors the huge spike in Steering pressure difference.

79 control on a bump. When the original trial ended in CHAPTER 9 November 1997 (the proceedings are comprehensively covered on the S-Files website33), The cause the three track officials and Frank Williams were acquitted, but the case against Newey and Head dragged on until May 2005 and April 2007, 86 There are several reasons why Ayrton Senna’s respectively . In the end, the appeal court ruled that accident has never been satisfactorily explained. Adrian Newey was innocent of involuntary Every unnatural death in Italy warrants an manslaughter and the case against was 77 investigation and Senna’s was no exception. The dropped under a statute of limitations . police impounded the car at the circuit and the The trial meant years of stress and sleepless nights authorities denied Williams unreserved access to the for Newey and Head36, who build racing cars with the wreck in the belief that this could potentially intention to win races, not to get their drivers killed. compromise the integrity of court evidence. In fact, Losing one of the greatest drivers of all time in one of technical director Patrick Head was granted just two their designs must have been a ‘life sentence’ in itself, ten-minute visits3,95. Likewise, the Williams team had so the threat of a suspended jail term was seen by no incentive to publicly release the full technical many as wholly unnecessary. details because their primary motivation was to Finally, some of the vital information is either protect their staff. missing or did not exist in the first place: telemetry In February 1997, three Imola track officials and data from the damaged Williams black box (Laps 1 to three senior Williams figures – team owner Frank 7); telemetry data from Renault’s black box (Laps 1 to Williams, technical director and shareholder Patrick 6 and the first eight seconds of Lap 7); tyre pressures Head, and chief designer Adrian Newey – were and tyre temperatures; on-board footage through charged with involuntary manslaughter. The Tamburello from Schumacher’s camera on Lap 6; prosecution alleged that the steering column design and the missing 0.9s of on-board footage from was to blame; the defence maintained that Senna lost Senna’s car until the impact from Lap 7.

80 Over the past twenty years, the different protagonists failure, tyre failure, aerodynamic instability, and have voiced contradicting opinions about the cause of steering column failure. Senna’s accident: Patrick Head hasn’t pointed the finger squarely at the aerodynamics but every now and then has re-emphasized that the steering worked until the car hit the wall; David Coulthard, who has never discussed his role in the steering wheel flexing demonstration, believes the steering column broke on impact87; Adrian Newey, now at Red Bull, openly admitted in May 2011 that the design of the steering column was very poor36 but otherwise he remains non-committal on the cause of the accident (steering failure94, aerodynamics94, tyre failure36); Damon Hill is convinced that Senna made a driver error, pushing too hard too soon in a difficult car37,84,92 ; while Frank Williams has maintained silence since the end of the trial. The cause may never be confirmed beyond reasonable doubt, but that doesn’t automatically mean that no further insights are possible. In the second part of this book, we’re going to build on the information presented in the first and take a fresh look at five hypotheses generally accepted as plausible explanations of what happened to Senna on Lap 7 of the 1994 San Marino Grand Prix. The five hypotheses are: suspension failure, power steering

81 the bumps and on the undulations between the old CHAPTER 10 and new surface (for comparison, watch ’s left rear suspension failure during the Suspension failure 2003 ).

According to Patrick Head21,38 the downforce generated at 300km/h was about 2,000kg plus HYPOTHESIS 640kg to account for the car, driver, and fuel. In a The accident was caused by a non-catastrophic long left hander like Tamburello, about 65 percent of suspension failure, which impaired the car’s handling this weight would be on the right hand side, where a but didn’t cause the suspension to collapse outright. suspension failure would most likely have occurred. Under the load of at least 1,700kg it would have

pitched the Williams sharply left or into a spin. EVIDENCE Intriguingly, though, later that year at Silverstone In the aftermath of the accident, unconfirmed reports Senna’s teammate Damon Hill suffered a front talked about a long score mark on the concrete area suspension failure where the upper suspension before the wall apparently caused by a piece of mounts were both pushed up and out of the chassis suspension38, but otherwise there is little to support a purely due to high load, causing the car to porpoise load-bearing suspension failure. badly (see YouTube). Williams blamed a manufacturing fault rather than component failure Had the rear suspension collapsed outright, the but, in principle, Senna could have suffered the same substantial aerodynamic loads acting on the car in a problem: the dynamics of his accident are consistent corner like Tamburello would have slammed the with a right front suspension failure (compare with chassis hard against the ground in the area where the Kimi Raikkonen’s crash at the Nurburgring in 2005), suspension failed, which would have resulted in some and photos93 showing the upper right front sparks from the underbody as the car ran off the suspension arm of Senna’s car apparently pulled out road. But the only sparks visible are those induced on

82 from the mount rather than snapped give this hypothesis some credibility.

A non-catastrophic suspension failure in a component such as damper or spring is a possibility, but it would have been difficult to detect if the component got destroyed in the crash, and it’s been so long since the accident that no new evidence can be extracted from the wreck. The mangled Williams FW16/2 was returned back to the team in April 2002, and although some sources maintain that it remains safely locked in a place known to only a few insiders39,40, the car - minus its engine, which was returned to Renault - was in fact cut up to sheets of carbon fibre and set alight in Frank Williams’ back garden95.

83 flow interruptions. The hydraulic circuit remained CHAPTER 11 intact until Senna hit the wall. Electronics can cause problems if the system decides to reboot while at Power steering failure speed but, based on the telemetry, that didn’t happen on Senna’s car.”

Had the telemetry recorded abnormalities in steering HYPOTHESIS pressures, the most likely cause would have been a A mechanical failure or electronics glitch in the burst pressure line or fitting, or blown piston seal in power steering system. the steering rack. As Woodward points out, however, none of them would have been catastrophic: “There

was little power steering [in a corner like EVIDENCE Tamburello], and if that failed Senna would have been able to continue. A sudden pressure loss would Williams first equipped its cars with power steering just double the force required to steer. I think his in 199412 and it is reasonable to expect that the new reaction would be different.” electrohydraulic system was still relatively unproven three races into the season. It is therefore logical that There is no indication that Senna suffered a power after Senna’s accident teammate Damon Hill was told steering failure, and Williams deactivated the system on the grid before the second start to switch it off. on Hill’s sister car as a precautionary measure rather than in response to a serious issue they noticed on Tony Woodward, CEO of Woodward Machine Senna’s car. Corporation in Casper, USA, brings more than thirty years’ experience in hydraulic power steering (do not confuse him with Gary Woodward, who was responsible for mechanical components on Senna’s car in 1994). According to Woodward, “the telemetry traces show no sudden drop in steering pressures or

84 Lower pressure in one of the tyres was the most likely CHAPTER 12 culprit. The tyre either failed to warm-up at the same rate as the other three tyres because of a cracked Tyre failure sidewall, a phenomenon that tyre supplier Goodyear reportedly experienced with several teams during the

Imola ‘94 weekend41, or Senna suffered a slow HYPOTHESIS puncture when he drove through the debris on the main straight during the safety car period. Both The accident was caused by a cracked tyre sidewall or scenarios would have had a similar effect on the car. slow puncture that wasn’t visible to the naked eye but was serious enough to disrupt the car’s handling. It is unlikely he would have felt the debris, especially if it was a flat or squashable piece. F1 steering is more

direct compared to a road car, but there is so much EVIDENCE activity going through the steering wheel that it would have gone unnoticed against the background A broken wheel rim forced Senna out of the San of other feedback. It is also not certain that Senna Marino race four years earlier; nonetheless, no hard actually drove over the debris, it could have just evidence exists to support a rim failure or debris in made contact with the front wing or the underbody the rim and it would have been difficult to detect, and then flipped at the rear wheel42. especially on the right hand side where the car smashed against the wall. In principle, the slow puncture or cracked sidewall could have affected any of the four tyres, but Slow motion replay of the out of control Williams considering the dynamics of the accident and Senna’s broadcast on BBC reveals porpoising which is initial twitch left before straightening the car, the consistent with a tyre problem - the car isn’t problem must have been triggered by the right rear bouncing up and down because it is braking on the or, which is less likely, by the right front. This means bumpy track, but because two of its four wheels are that the blue debris from Lehto’s Benetton that no longer in proper contact with the ground.

85 Senna flattened shortly after entering Lap 7 is a red deflated tyre whereas Senna according to the herring, because he drove over it with his left wheels. telemetry held the steering wheel centred. To understand what happens when a car suffers a Equally, there are uncanny similarities between tyre failure it helps to study high speed accidents Senna’s accident and ’s exit from the where the exact cause is known. Two relevant cases in 2011: Vettel suffers a right include ’s crash at the Nurburgring in rear puncture while on full throttle in the fast left 2007 (right front tyre failure in a fast left hand hander Turn 2. His Red Bull turns sharply left - corner) and Sebastian Vettel’s retirement from the distinctly pointing towards the Armco barrier on the Abu Dhabi Grand Prix in 2011 (right rear tyre failure inside of the corner exactly like Senna’s Williams - in a fast left hand corner). and then straightens up momentarily before the tyre deflates and the car spins off. In Hamilton’s case, the right front tyre delaminates as he is pointing his McLaren at the apex of Turn 8 at The right rear tyre failure hypothesis has a lot going an estimated 260km/h. Slow motion analysis reveals for it, including the backing of former Williams chief that just before the tyre thread peels off the wheel designer Adrian Newey who in an extensive interview rim, the car’s rate of turning left increases for a split for The Guardian36 in May 2011 admitted that “if I second in a fashion not dissimilar from Senna’s, was pushed into picking out a single most likely cause although the effect is not as pronounced. The that [right rear puncture] would be it.” McLaren then darts right and continues more or less Newey is of the opinion that Senna’s car bottomed straight towards the tyre barrier. It does not wobble much harder on Lap 7 than on Lap 6, which seems or spin because the rear tyres still maintain good counter-intuitive considering that the tyres should traction while Hamilton is not making any major have come up to their operating temperature by then. steering movements and simply brakes hard - he On-board footage from Lap 6 through Tamburello – knows instantly he has a big problem. Again, his released in 2014 after 20 years in the FOCA archives reaction resembles Senna’s. One weakness in this thanks to Roberto Cabrini’s efforts82 –contradicts argument is the observation that Hamilton keeps a Newey’s view. The bottoming on Lap 6 is so hard the steady steering lock left to compensate for the

86 camera can’t cope with the violent shaking and some mechanical grip. Senna put on more steering records only a few usable frames during the six lock to navigate the final part of the corner just as the seconds it takes Senna to navigate the corner. By imbalance in tyre pressures kicked in and the car contrast, the picture from Lap 7 remains relatively turned sharply left (time interval 10.90-11.18s). This clean until 10.56s and only then does it get marks the beginning of the accident and it is well marginally distorted. The analysis of the bottoming documented on the telemetry as steep increase in effect discussed in the first part of the book also Steering strain, lateral g-force, and Steering pressure indicates that the tyre pressures did in fact improve difference. Moreover, it is also present in the graphs as the sparks coming off the rear of the Williams look comparing the car’s direction change relative to the ‘I much stronger on Lap 6. Pilotissimi’ sign, in the car’s angle against the kerb, and in the rotation of the left front tyre. When the engineers inspected the cars after the race, they discovered that the front skid-plates on Senna’s Senna tried to straighten the car by applying opposite car were heavily worn and in the footwell area were lock (11.20-11.26s) and by reducing throttle to 50 even pushed into the chassis, whilst Hill’s identically percent (11.20-11.44s). The drop in pressure on the set-up car was found almost intact7,95. That said, the right rear however meant that the car didn’t react to damage to the front skid-plates could have occurred his steering input in the usual and expected way and on Lap 6 rather than Lap 7, or once the car left the swung right. The situation wasn’t helped at 11.26s road. No other evidence points to harder bottoming when the Williams drove over the third and biggest on Lap 7. bump. Senna realised he was a passenger and went hard on the brakes (11.68-12.16s). If the right rear tyre failure hypothesis is correct, the slow puncture (or cracked sidewall) made Senna’s Apart from the question mark over the degree of right rear wheel to drop and the left front to lift bottoming experienced by Senna in his last seconds moments before the Williams entered the seventh on the track, four additional factors cast doubt on the strip of new tarmac in Tamburello. Most of the load rear tyre failure hypothesis: the fact that the car did had already been on the right front tyre, but now the not spin and that it retained full braking capability, difference became even bigger as the left front lost statements from Goodyear regarding Senna’s tyres

87 after the accident, and the unusual movement of the damage inflicted by the impact masked any traces of steering wheel. a minor defect in the right rear tyre. If the right rear tyre had failed, the handling and This brings us to the final point: the tyre failure traction on the rear axle would have got progressively hypothesis doesn’t elaborate on the movement of the worse. Senna would have been fighting the bouncing yellow button on the steering wheel during the last car like Vettel in Abu Dhabi - although in Vettel’s three seconds before the crash. A puncture alone case the tyre deflated abruptly – and this would have cannot account for the observed phenomenon shown as wilder steering movements on the on-board because in order to lower the apparent position of the footage and telemetry. Senna did not attempt to steering wheel by 25-27mm relative to a camera avoid hitting the wall by forcing the car into a spin, viewpoint fixed in space, the car would have had to either. Furthermore, the car’s braking ability would assume a severe pitch attitude in excess of its static have reduced if it had lost significant contact patch ride height. The hypothesis therefore implies that the with the ground. The data suggests this was not the flexing was normal. case – deceleration still peaks at a healthy 4.4-4.7G.

Immediately after the accident, Goodyear technicians inspected all four tyres and ruled out a tyre failure. According to a statement made by Barry Griffin, there was no tyre delamination and no sign of damage caused by a foreign object that could have led to deflation. Three tyres had cuts, but all were consistent with the impact rather than a puncture43. A former Goodyear employee told writer Christopher Hilton that there was never any suggestion of a slow puncture as it would have become visible at some stage3. Still, it remains a possibility that the severe

88 The oversteer pointed the Williams towards the CHAPTER 13 inside of the track (11.10-11.18s). One tenth of a second later (11.20s), Senna started applying Aerodynamic instability opposite lock and reduced throttle to 50 percent to stabilize the sliding car. With less acceleration

pushing the car forward, the rear grip recovered but HYPOTHESIS was now applied sideways as the car was still being corrected to the right. The very next moment The trigger for the accident was some external factor (11.26s), the car struck the third, biggest bump in that unexpectedly disturbed the car’s aerodynamics Tamburello. as Senna entered Tamburello; or, the inherent aerodynamic instability of the FW16 was exposed in The car bottomed out heavily at the front, with much the wrong place at the wrong time by a set of of the weight sitting on the suspension mounts unfavourable circumstances: the long period behind instead of the tyres. This provoked a sudden loss of the safety car, low tyre pressures at the restart, front downforce and heavy understeer, which in bumpy track surface in Tamburello, the FW16’s conjunction with the rear grip acting sideways aerodynamic weaknesses, and Senna’s unwillingness prompted the car to slap back and turn right, so to back off even in tricky conditions. much so that Senna’s head swung out of the cockpit (11.48s). On Lap 7 Senna entered Tamburello flat out, travelling much faster than Damon Hill in the sister Senna now found himself nine degrees off the racing Williams and using the tighter inside line which was line, but the change relative to the car’s axis was even quicker but bumpier. As he crossed the seventh dark greater due to the initial oversteer. He realised he strip of new tarmac (11.08s) and rode over the first couldn’t recover the situation and decided to keep the bump, the rear of the car bottomed and stepped out steering centred for optimal braking. He lifted (oversteer) due to the combination of low tyre completely at 11.50s and began a desperate attempt pressures, bumpy surface, and a sudden loss of to slow the car down at 11.68s7. downforce.

89 Figure 42 - Oversteer (left) means that the front of the car continues on the racing line (white) while the rear steps out because of a lack of rear grip induced by either wheelspin or loss of downforce. Understeer (right) means that the rear of the car sticks to the racing line while the front of the car suffers from a lack of grip and struggles to make the corner despite increased steering lock.

90

EVIDENCE When the race resumed with Lap 6, it is likely Senna wasn’t aware that Schumacher was planning three In the opinion of French TV reporter Jean-Louis refuelling stops to his two, and that he was trying to Moncet, who studied the view from Schumacher’s on- keep at bay a lighter car. He had zero points in the board camera, a small piece of debris was dangling championship and simply had to win the race. from underneath Senna’s car and upset its Making a break from his pursuers on the first lap had aerodynamics in Tamburello just enough for Senna always been his trademark and he wasn’t going to to lose control. The debris flew off the track back off now just because the car was a handful on immediately afterwards21,44. Beside the grainy TV cold tyres. footage, however, Moncet’s theory has little else to rely on. Aerodynamic instability, on the other hand, There is also every reason to believe that Senna was is the official hypothesis put forward by Williams well equipped to cope with low tyre temperatures. As during the manslaughter trial in the late ‘90s. Its he revealed in an interview for Autosport11 in early origins go back to the dark days and weeks following 1993, he had a secret system for warming up his tyres the tragedy when the engineers in the factory pored and the first lap after the restart backs this claim up: for hours over the telemetry data and video footage. on Lap 6, he managed to navigate Tamburello on cold tyres and clocked 1min 24.887s, which was a very The sequence of events began to unravel with the competitive lap time that remained the third fastest start line collision between Lehto and Lamy, which lap of the whole race. Only towards the end of the brought out the safety car and prevented Senna from race did Hill and Schumacher better his time. building a comfortable margin over Schumacher in Although we do not have precise information about the Benetton. The Opel saloon used in Imola as safety the state of Senna’s tyres going into Lap 7, the logical car was too slow for F1 speeds and by the end of Lap conclusion from the above must be that the ride 5 the tyre temperatures (ditto tyre pressures and ride heights had gone up as the tyres got warmer and as heights) dropped dramatically - perhaps by as much the car burned one more lap worth of fuel. That as 25 percent45 - leading to a 7psi tyre pressure loss95 assertion is reinforced by the severe distortion of on- and ride height drop of about 4-5mm14. board images from Lap 6 and by the amount of

91 sparks generated by the rear of the Williams in Hill has a point, but it was easier for him to lift and Tamburello: the sparks do not look as strong on Lap take it easy through Tamburello. He was running in a 7 as they do on Lap 6 (although the footage is taken distant fourth place and didn’t have to content with from Schumacher’s on-board camera rather than a Schumacher breathing down his neck. This was a stationary RAI TV). motor race, after all, and Senna’s ability to transcend the ordinary was what set him apart from his peers. A lot has been written about Senna’s state of mind going into the race but as explained earlier, in all The next best qualified person to voice an opinion is likelihood he was fully focused on one thing – Michael Schumacher, who had seen the accident winning. Few are better placed to comment on unfold before his eyes and it was an experience that Senna’s psyche than his last teammate Damon Hill. affected him profoundly. Schumacher noticed that on Hill remained tight-lipped about the accident until the lap prior to the accident Senna’s car touched the the tenth anniversary of Senna’s death, when he ground in Tamburello and appeared skittish, and that suddenly decided to speak out in a column headlined on the next lap, in Schumacher’s words, “he just lost ‘The harsh fact is that Ayrton made a mistake’, it.” published by The Times37 in April 2004. By contrast, former rival-turned-TV-commentator In the article Hill didn’t mince his words, arguing Martin Brundle years later (2011, 2014) noted46,88 that Senna’s fiercely competitive nature and desire to that the on-board footage from Lap 6 on cold tyres cultivate a ‘demigod’ image made him disregard the looks serene, with smooth steering inputs and no risks of taking Tamburello flat out in circumstances wild oversteer or understeer moments. Senna looks in which the sensible thing was to lift. Hill is the only fully in control, not like a driver pushing the limits. living person who knows what it felt like to drive the Although Senna had made plenty of mistakes in his Williams FW16 on May 1, 1994 through Tamburello career, many find it hard to believe that the trigger on cold tyres, and the memory is enough to convince for the accident wasn’t some kind of a mechanical him that Senna made a mistake. failure. Indeed, all previous crashes in Tamburello were caused by a technical problem. The same

92 opinion was voiced during the trial by rival F1 drivers same spot on the circuit. In addition to that, Senna Michele Alboreto and Pierluigi Martini, and designer spun out of the race in Brazil and then in Friday Adrian Reynard; and recently in the critically qualifying at Imola, while Hill spun again during the acclaimed movie Senna also by Alain Prost and race in Japan and also in qualifying at Imola. The McLaren chairman Ron Dennis1. Former McLaren spins happened in low speed corners and usually on Team Coordinator Jo Ramirez muses in his Memoirs the exit. The front wing was to blame: it sat too close of a Racing Man (Haynes Publishing 2005)47 that to the ground and once the car hit a bump exiting the “despite all the investigation, deliberations and corner, the front suddenly gripped and the driver lost conclusions over the years, I remain unconvinced the rear10. that the best racing driver in the world could make a The FW16 was also prone to severe underbody mistake at Tamburello.” stall9,85. The floor of a modern F1 car at the rear is If driver error came into the equation, it was an error designed to exploit the Venturi effect, which says that of judgment rather than a driving mistake. Senna air accelerates when passing through a constricted must have been convinced he could keep the FW16 channel while its pressure drops. This is dictated by under control on the bumps in Tamburello regardless the law of conservation of energy: the total energy of its iffy aerodynamics. After all, he had been doing within a fluid system must remain constant and if the exactly that lap after lap during the Imola weekend, potential energy (air pressure) is reduced by a up to and including race Lap 6. constricted channel, the kinetic energy of the fluid particles (air velocity) must increase accordingly so

that the total energy is conserved. In F1’s parlance, UNDERBODY STALL this constricting channel is called diffuser (Figure 43) As mentioned in the first part of the book, the FW16 and it is the diffuser that in certain circumstances was an aerodynamically troublesome car. Both Senna induces underbody stall. and Hill got caught out on several occasions in the Diffuser on the Williams FW15D-Renault first three races of the 1994 season, notably in Japan where, bizarrely, they both lost control at exactly the

93

Figure 43 - Diffuser channels at the rear of the Williams FW16B-Renault, which replaced the unloved FW16 from the German Grand Prix 1994 (photo courtesy of Remi Humbert and Joachim Kutt, GurneyFlap.com). Regulation changes introduced after Imola forced fundamental modifications and the diffuser raced by Senna at Imola was larger and looked different80 . 94

the ground (downforce) and makes it go faster around corners. The diffuser further increases downforce by sucking the air out from underneath the car48. The diffuser channels gradually increase in volume and provide space in which the faster air flowing underneath the car is allowed to slow down and expand49. The net result is a smooth transition from high to normal air velocity and from low to high air pressure that maximizes the downforce (Figure 44). The slope of the diffuser is very important and it must be designed to match closely the airflow velocities through the channels otherwise the air will separate from the diffuser’s roof and sides50. This Figure 44 - The diffuser (in red) creates an area of faster separation is known as underbody stall. flowing air at lower pressure between the underbody and Underbody stall differs from aerodynamic stall, the track (2). The different colours represent different which affects wings on aircraft and F1 cars alike airflow velocities, from the peak velocity where the flat bottom of the car transitions into the diffuser (violet, 4), (Figure 45). A wing is stalled once a certain angle of to gradually reducing velocities (5, 6, 7) until the air attack is exceeded, whereas diffuser’s angle of attack 49 stays almost constant and airflow separation takes reaches the ambient pressure (red, 8) . place when the air velocity through the channels

Diffuser speeds up the airflow underneath the whole drops enough for the air to detach from the diffuser’s car, creating an area of low air pressure due to the surfaces. Venturi effect (Figure 44). This low pressure causes That can happen if the car’s ride heights change pressure difference to build between the car’s abruptly (lifting, braking, acceleration). Under underbody and bodywork, which pushes the car to

95 braking, for instance, the front of the car dives down A sudden loss of downforce ensues and if the car is while the rear rises up, allowing more air in from the going round a corner the rear may step out and the sides. The air pressure underneath the car increases driver will experience oversteer. and the air velocity decreases to the point where the Tamburello was bumpy: there were three bumps on diffuser stalls. The diffuser can also stall on a bump the apex and if the driver went straight over them the because once the chassis hits the ground (bottoms car travelled a slightly shorter distance but it was out) the air flow underneath the car is significantly running on the ground and the aerodynamic loads reduced or completely blocked51.

Figure 45 - Aerodynamic stall explained - a wing generates downforce when the air flows smoothly and remains ‘attached’ to the upper and lower surfaces (left). The curvature of the wing bends the streamlines and deflects masses of air upwards, causing air compression and higher pressure at the upper surface. Correspondingly, with less air to fill the space at the lower surface the pressure drops and the whole wing is pushed down. Once a certain angle of attack is exceeded (right), however, the air becomes turbulent and air flow separation occurs. The wing ‘stalls’ and loses its downforce52.

96 were going through the chassis rather than the tyres. but it’s unclear whether the damage occurred on Lap The car was no longer sprung by the suspension and 6, Lap 7, or in the course of the accident. it was effectively steered by the skid-plates instead of There is a textbook example of bottoming that led to the rear wheels. During the Imola weekend, Senna oversteer on the fifth dark strip: the revs spike by warned Hill about the tight inside line as it made 400rpm to 14,204rpm as the chassis touches the their Williams feel unstable, whether out of genuine ground (9.68s) and then, as the tyres grip fully again, concern or because it gave him an additional fall down to 13,561rpm (9.72s). Simultaneously, the advantage over his less experienced teammate. Hill steering feels lighter (strain drops from -18 to accepted Senna’s advice and avoided the bumps by -12N/m2 at 9.70s) and subsequently recovers (strain driving in the middle of the track, especially on cold doubles from -12 to -22N/m2 at 9.80s). tyres and heavy fuel. It cost him a few metres but the car felt more predictable. Senna stuck to the bumpy The pattern observed in the critical period when tighter line. Senna loses control (11.10-11.18s) is somewhat different. First of all, the engine revs rise steadily in From the distortions visible on the on-board footage, an almost linear fashion until 11.10s (14,014rpm) and we can establish that Senna’s car hit undulations then plateau until 11.22s (13,800-13,900rpm). There during 11.08-11.16s (entry onto the seventh dark strip is no observable spike in revs that would indicate and the first bump), at 11.22s (second, minor bump), heavy contact of the chassis with the ground. Second, and 11.26s (third, biggest bump). This fits the unlike on the fifth dark strip, there is no decrease in aerodynamic instability theory well; nevertheless, it Steering strain that would signify that the steering doesn’t answer the key question whether the suddenly got light due to oversteer: between 10.80- undulations gave rise to just bottoming, or bottoming 11.08s the telemetry shows a steep increase in the that resulted in underbody stall and oversteer. strain on the column (from -10 to -26.9N/m2) Bottoming at Tamburello was the norm and Senna’s consistent with substantial steering effort left, and car invariably generated five distinct showers of the high load on the column doesn’t drop and is sparks on the seventh strip throughout the whole sustained until at least 11.20s (-26.3N/m2). weekend. The front skid-plates were heavily worn7,95,

97 Lateral g-force and speed of the rear wheels are The neat explanation also gets complicated by compatible with oversteer and aerodynamic Steering pressure difference (STGACT), which instability: g-force keeps increasing from 2G (10.80s) measured hydraulic pressure difference across the to 3.27G (11.10s) to the maximum recorded by the steering rack. The difference more than doubles in telemetry 3.52G (11.20s). Also, the Williams must period 11.00-11.08s (substantial turning left) and it have lost some traction on the undulations because stays high during 11.10-11.18s (continued turning and the rear wheels are rotating 4km/h faster than is the power assist left). Correspondingly, pressure in the speed of the car (11.10-11.18s). hydraulic cylinder on the left hand side of the steering rack (STGPR) is at the lowest level recorded The car’s direction change tells a similar story. Based on the telemetry. on the ‘I Pilotissimi’ reference point the car’s rate of turning left against the static background is greater The movement of the left front tyre casts further since 10.76s as the Williams nearly recovers to the doubt on the aerodynamic instability theory (Figures racing line taken on the two Friday laps used as 13 and 14). The tyre is pointing more or less straight comparison (blue line meets the red and green lines during 10.50-10.72s but then it starts turning in Figure 10). progressively left until a peak at 10.94s. As the Williams enters the seventh dark strip of new tarmac The rate of turning left then further increases in the the tyre flicks further left around 11.06s before it critical period 11.10-11.18s (the blue line overtakes reaches what appears to be the third peak at 11.18s the red and green lines) and the momentary angle just when Senna loses control. If the rear has stepped between the car’s reference axis and the inside kerb out due to underbody stall and the car is also shoots up (Figure 11). All these observations are oversteering, Senna is making the oversteer worse by symptoms of oversteer, although the brusque simultaneously turning in the direction of the slide. direction change seems to have been initiated before That is atypical because usually the front wheels do Senna entered the seventh strip of dark tarmac and not move while the rears break traction and start the bumps (around 10.90s). sliding.

98 A slow motion analysis of oversteering cars backs this track, he would have gone head-on into the Armco observation up: the random sample studied includes barrier on the inside of Tamburello. at Sepang 2008, in The car has now recovered full traction as there is Monaco 2008 and 2011, Kimi Raikkonen at Spa and minimal speed difference between the car and rear crashing into the back of in Monaco wheels. For the first time on Lap 7, Senna lifts 2008, Lewis Hamilton at Silverstone 2008 and in the (throttle goes down to 50 percent between 11.20- last corner in Valencia 2010, 11.26s) and the revs drop by 500rpm accordingly. He crashing out in Australia 2011, and Daniil Kvyat and must have decided to lift around 11.10s or earlier, Adrian Sutil in Monaco 2014. Unless the slide at the either in response to the oversteer or because he rear ‘overtook’ Senna’s increased steering input left, anticipated the car to get unsettled based on his it is likely his Williams turned sharply left not experience from Lap 6. Steering strain remains high because of oversteer alone but because the steering at 11.20s (-26.3N/m2) as he is about to apply opposite also pointed the car that way. lock, while the Steering pressure difference across the At 11.20s, Senna starts applying opposite lock to steering rack starts to drop drastically (STGACT goes correct the slide. That is not always the best response from 623psi at 11.20s to -12psi at 11.30s). to high-speed oversteer. On American ovals, where In the brief period between 11.20s and 11.26s, the left high-speed oversteer is common, drivers learn front wheel returns swiftly to the neutral position and quickly not to apply opposite lock because once the points straight, the angle between the car’s axis and car grips again the correction spits them the inside kerb returns to a level observed just before unceremoniously to the outside wall. Drivers instead the car entered the seventh dark strip, and the rate of steer into the slide so the car spins harmlessly down direction change against the ‘I Pilotissimi’ sign the track, avoiding a potentially massive accident7. reduces so that by 11.26s the car is heading straight Senna was conditioned by years of experience to for the sign. All of the above indicates the car is apply opposite lock in such circumstances and unlike responding instantaneously and that its direction on ovals, where there is plenty of room down the change doesn’t lag behind the rotation of the left front tyre.

99 By contrast, the slow motion analysis of oversteering the inside of Tamburello (like Wurz, Coulthard, or cars discussed earlier reveals a delay between the Perez did), or he would have experienced a major application of opposite lock and the subsequent ‘tank-slapping’ moment similar to McNish’s at correction in the car’s trajectory. The pendulum Suzuka. Instead, Senna’s car straightens within effect of the slide keeps the car oversteering in one 0.08s. direction even though the driver has already pointed There is a heavy bottoming moment at 11.26s (the the front wheels the other way, because the front third bump), which is visible on the telemetry as a tyres need some time to bite and regain sufficient 600rpm spike in revs (from 13,445rpm to 14,077rpm) grip in the new direction before they can correct the and as severe picture distortion on the on-board slide. footage. However, Senna is already out of control, This delay is even more dramatic in accidents in there is no oversteer, and the steering doesn’t go light which the driver loses the car on a bump (the rear (Steering strain remains relatively high at -18.5N/m2 bottoms out). Four confirmed examples in recent at 11.30s). times include Alex Wurz’s crash in Monaco 1998, According to the aerodynamic instability theory, the Allan McNish’s crash in Suzuka 2002, David Williams now understeers heavily at the front and the Coulthard’s crash in Monaco 2008, and Sergio rear grip is acting sideways, prompting the car to Perez’s crash in Monaco 2011. In all four instances, turn right. In terms of the car’s trajectory against the the direction change induced by the bottoming is so ‘I Pilotissimi’ reference point, the Williams initially forceful and so sudden that the drivers have no hope rushes straight for the sign (11.26-11.40s), then pulls of catching the slide despite the swift application of gently right (11.40-11.56s), then gently left (11.56- opposite lock, and the cars stay on the crash course 11.70s), and finally it heads straight for the sign until despite the fact that the front wheels are clearly the on-board video ends (11.70-11.84s). pointing the other way. This indirect evidence adds weight to the argument that had Senna lost the car The left front tyre follows a similar pattern: it turns purely as a result of bottoming on a bump, he would slightly right (11.28-11.52s), then straight or slightly have ended up crashing head-on into the Armco on left (11.54-11.66s), then slightly right or straight

100 (11.68-11.84s). Correspondingly, lateral g-force falls because ‘keeping the steering straight’ more often to virtually zero (11.30-11.58s), then pulls gently left than not involves a strain condition in the steering. (11.60-11.88s), and finally gently right (11.90-12.18s). What is puzzling is that unlike all the drivers studied In just over half a second, the strain on the steering in our oversteer analysis, Senna didn’t fight the car column drops to zero in a quadratic curve (11.30- and just kept the front wheels approximately straight. 11.90s) and Steering pressure difference across the He had a full second to take the corner, to react and steering rack also falls off the cliff to zero (11.30- to wrestle the car like the other drivers – apply 11.68s). There is a minor pressure difference (11.70- steering lock left, force the car into a tank-slapper or 11.88s) equivalent to the effort exerted by Senna into a spin. But he didn’t; either he chose not to or he when he was easing his car into Tamburello, and then wasn’t able to. the pressure difference becomes negative, implying The aerodynamic instability hypothesis is silent on that the wheels are turned slightly right (11.90- the movement of the yellow button on the steering 12.38s). wheel in the last three seconds before the crash other The above data confirms there is no or very little than saying that the flexing observed was normal as direction change after 11.26s, mainly because the demonstrated by David Coulthard in the team’s sharp direction change right was accomplished museum. The hypothesis would gain further strength during the brief correction period (11.20-11.26s). if it were able to reproduce the observed flexing Senna hesitates with the throttle (around 50 percent under a defined set of racing conditions, especially during 11.24-11.44s), then lifts completely (11.50s), because no such flexing exists in the twelve minutes and after switching his right foot to the brake pedal of on-board footage analysed from Brazil, Japan, and begins desperate braking (11.68-12.16s). Imola (see Chapter 6). The power steering and Steering strain telemetry correlates well with the hypothesis’ claim that from 11.26s on Senna kept the steering centred for optimal braking, although it would be next to impossible to distinguish that from any other condition of no input

101 column to such degree that the steering wheel began CHAPTER 14 falling into his lap. This caught him by surprise and Broken steering column momentarily upset his concentration. In the ‘partial failure’ version of the hypothesis, Senna could no longer steer the car with the usual precision as he tried to hang on to it at 300km/h. He HYPOTHESIS initiated a horizontal correction left with the steering The accident was caused by material fatigue in the at 10.74s just before he entered the seventh dark strip redesigned section of the steering column. The of new tarmac, probably to bring the car back to the column partially broke and felt ‘mushy’ but normal racing line from which he had started to continued transmitting sufficient torque for getting deviate after 10.10s, or because he finally noticed the the car round Tamburello (‘partial column failure’ unusual position of the steering wheel. As his version), or it broke off and stopped transmitting fingertips couldn’t feel the tyres through the steering torque even before Senna left the track (‘complete anymore, the wheels turned more than was necessary column failure’ version). and the direction change towards the inside of the corner continued unchecked until 11.18s. The tragic events were set in motion once the safety car peeled off into the pits and the race resumed with He began to lift at 11.20s but he must have made that Lap 6. The initially bumpy ride on cold tyres decision at 11.10s or earlier; in other words even accelerated fatigue in the steering column near the before he experienced the sudden twitch left. He bent support strut and a crack propagated through its the faltering steering column back up (11.20-11.30s), upper crescent (the crack may already have and the sharp vertical movement straightened the developed earlier during the weekend). Three car’s trajectory. The car received a massive jolt on the seconds before Senna crashed in Tamburello (8.20s third bump and Senna was now expecting the worst. into Lap 7), the fatigue extended far enough to impair He decided to keep the abnormally responding the steering. The combination of high downforce and steering straight although the partially severed Senna’s arms resisting lateral forces bent the steering column was still capable of handling enough steering

102 torque to get him round a long left hander like Tamburello53. The steering wheel oscillated up and down as Senna tried to keep it more or less straight. He lifted completely by 11.50s and then went hard on the brakes at 11.68s. The column broke off once the right front wheel hit the wall and bounced back against the cockpit54. In the ‘complete failure’ version of the hypothesis, the column broke off before Senna left the track. The severe flexing observed after 8.20s meant that the column became distorted beyond its rotating clearance in the bushing, and the distortion dragged Senna’s input enough to prompt the sudden twitch left. The column then seized in the bushing, which provided the resistance to complete the break and at the same time registered steering strain on the telemetry just as if the driver was resisting the front wheels.

103 STEERING COLUMN FATIGUE The machined part (red colour in Figure 46) was inserted into the original tube towards the steering As stated earlier, the steering column was altered at wheel but fit over the original tube where it went Senna’s behest before the start of the season and through the support strut. There were two regardless of the pros and cons of the new design, the circumferential welds (red triangles in Figure 46) – modification by default increased the number of one at the point where the machined part went inside possible failure modes because of the system’s the original tube, and the second just past the inherent complexity. support strut where the machined part fit over the The column assembly now measured 910mm and original tube. consisted of three elements rather than one: the The modification called for welding as the tubes used original tube (steel T45, diameter 22mm, wall were of different material and different diameter. All thickness 0.9mm), attached at the upper end to the publicly available drawings19 show the tube joints as steering wheel; a smaller tube (steel EN14, diameter fitting size-to-size while simply annotating the outer 18mm, wall thickness 1.2mm), fitted in the middle; diameter (OD) and wall thickness. When the and the original tube again (steel T45, diameter assembly is drawn strictly to the annotated 22mm, wall thickness 0.9mm), connected at the dimensions, however, it shows the dimensions lower end to the pinion and steering rack. cannot be accepted uncritically because the upper T45 and EN14 are compatible steel made of carbon joint has plenty of wobble room (Figure 47). One can manganese that conform to the Aerospace safely assume the splice part would not have been Specification laid down by British Standards (BS). machined for such a loose fit. T45 is commonly used in motorsport due to its high strength-to-weight ratio55 whereas EN14, used by Williams for the newly inserted piece of smaller diameter, has a medium tensile with excellent resistance to shock and its chemical composition makes it suitable for welding56.

104

Figure 46 - Steering column specification derived from three (contradictory) drawings used during the manslaughter trial and later released by CINECA on their website. Red colour represents modified material inserted before the start of the season. Blue colour represents the bushing and support strut. The orange line denotes the point where the column broke off.

105

Figure 47 - Detail of the steering column, drawn strictly to annotated dimensions. Orange line denotes the break.

Note the wobble room in the upper joint, which most likely existed only on paper (nominal dimensions).

Tony Woodward makes the following observation: The actual insertion invariably requires some hand

“It is likely the part sketches presented in court were work and it’s unlikely that the modified column gross approximations giving nominal dimensions would have been created entirely by computer- rather than actual dimensions. The part was surely controlled methods, which means the actual intended to fit the ID [inside diameter] of the tubing. dimensions were arrived at during fit-up and as such Tubing is manufactured oversize on the outer did not need documentation.” diameter and can vary somewhat in wall thickness. The quality and durability of the weld would have As a result, fitting machined pieces to it for welding is been heavily influenced by the welding procedure not predictable to the extent that they can be pre- employed, and any minor process non-adherence pr ogrammed on CNC machine tools with confidence. could have resulted in a somewhat embrittled weld in

106 the heat-affected zone. Even so, it is important to surface of the fatigue zone - the area of the initial emphasize that no issue was found with the weld slow crack propagation - exhibits a smooth rubbed itself – it was on the other side of the support strut and velvety appearance which extends from nine and nowhere near the break. o’clock position to about one o’clock at minimum (Figure 48). As part of the investigation conducted by the Italian authorities in 1995, the steering column underwent metallurgical analysis in Pratica di Mare, the Italian military aerospace laboratory, and also in one other independent laboratory. The analysis revealed a fatigue-related failure caused by a downward bending force. The fatigue occurred in the top semi-circular half of the modified section of the column and extended around its circumference. It was exactly at this point where the column broke off - at the reduction of diameter where the filleted corner of the modified section transitioned into the smaller straight diameter. All of the smaller diameter section stayed with the upper column. Both the prosecution and Williams agreed that sooner or later the column would have snapped; what they couldn’t agree on was the extent of the fatigue Figure 48 - Driver’s view of the cross section of the (40-60 percent prosecution figures, 21–40 percent modified steering column. Red colour denotes the Williams figures), and whether it weakened the minimum area of crack propagation (fatigue zone), 7,57 steering enough to hinder Senna’s ability to steer . black colour the area of final failure (instantaneous 33,81, 91 The fatigue is clearly visible in the photos and zone), grey colour the disputed area of fatigue. illustrations (Autosprint90, L’Automobile79): the Drawn to scale. 107

Conversely, the area of final failure (the rupture than the new element that fit over it. The stiffness of zone) where the column broke off is jagged and a shaft increases as the fourth power of its diameter brittled. The face of the fracture looks typical of a (for tubing one subtracts the inside diameter’s part that ruptured in stages. Higher resolution equivalent stiffness) and this property is not photos would reveal more about the forces involved – necessarily obvious at first glance. Tony Woodward whether they were predominantly torsional or in again: “Imagine the failure mode of a fishing rod if it bending, their magnitude, fluctuations, and the were tapered in the wrong direction, or had a estimated length of time from crack initiation to discontinuity like this column. The column protruded rupture58,59. quite a distance from its bearing point, and the bending load on a steering column is more than The modified section of the column had an people think. The localized stress concentration inadequate fillet radius and the crack propagated would just about guarantee Senna’s upper body from there3,60. There were also tool marks left on the would break it off there.” piece near where it fit over the original tube3,61,62. Unaware of the official report’s findings, Tony Although Williams accepted the results of the Woodward took one look at the drawings and the metallurgic analysis, they contested its interpretation photos of the broken column and observed that “the and disagreed that the accident was caused by the piece that broke had a stepped cross section. This is a broken column54. The team argued that the rupture textbook illustration of a sectional discontinuity zone was more consistent with a heavy impact creating a stress concentration. It begs the question brought on by the right front wheel hitting the wall how large and smooth (or small and rough) was the and then the side of the cockpit67. fillet radius in that corner, and did the crack The fatigue zone estimates vary from 21 to 60 percent propagate from a stress raiser such as a tool mark.” of the column’s circumference, but that in itself says The fatigue was most likely caused by a severe stress little about the likelihood of the column snapping concentration59,63-66 at the change in diameter because the size of the fatigue zone depends on how because the original part of the column extending heavily the part is stressed at the time of rupturing. from the support strut was disproportionally stiffer If a given material is highly overstressed, the fatigue

108 zone is very small compared with the rupture zone, if Senna’s steering column cracked near a fillet and the overstress is low the fatigue zone is much bigger near a tool mark. than the rupture zone58,68. What the 21–60 percent Forced to choose between the ‘partial failure’ and figure tells us is that Senna’s column was exposed to ‘complete failure’ hypotheses, most experts are medium to high overstress when it snapped. inclined to favour the former. Adrian Reynard, who Williams also reported that a fatigue failure would participated in the trial on behalf of Senna’s family, only have arisen after 350,000 stress cycles (a cycle is thinks the lower crescent of the column (the rupture one application of load on a component), but the zone) held out until the impact7. Aerospace engineer steering column had undergone a mere 27,000 cycles Augusto Suppo, called by the defence, testified that when inspected after the in the lower crescent of the column was strong enough Japan69. to get Senna round Tamburello72. Tony Woodward is of a similar opinion: “Unless the column twisted Stress tests are usually performed on servo-hydraulic apart, Senna would have retained rotational input. rigs using load that varies randomly in amplitude and Examination of the column would have revealed a frequency70,71 and the method assumes the material failure in torsion and there does not appear to have sample is entirely representative. The column raced been one. It looks like a tensile failure in bending by Senna bore a tool mark, whereas the column that with just a hint of torsion. I think it wasn’t broken all withstood 350,000 cycles on a test rig before failing the way through, and I would expect a low-carbon did not, and once a stress raiser in the form of a tool steel component of that diameter and wall thickness mark enters the picture, predictions about fatigue life in a partially severed condition to remain capable of become irrelevant53. More importantly, low cycle transmitting 25 inch-pounds of torque, or enough to fatigue can occur near stress concentration points retain practically full steering input as long as Senna such as holes and fillets63,71 and tool marks in the held the wheel so as to keep the column surface greatly accelerate the time to rupture because approximately straight. But once you lose it at that such microscopic discontinuities are natural starting speed you quickly run out of room to gather it back points (stress raisers) for the propagation of cracks64. up, steering or no steering.”

109 BOTTOMING EFFECT & OVERSTEER difference in speeds could represent just a minor loss of traction on the bumps and not necessarily a heavy Contrary to some of the theories discussed earlier, bottoming event accompanied by underbody stall. this hypothesis argues that Senna’s Williams didn’t bottom out heavily and didn’t oversteer because of Another argument against oversteer is the fact that underbody stall. Detailed arguments for and against Senna decided to lift even before his car turned are covered in the section dealing with aerodynamic sharply left (11.10s or earlier, if we consider 0.10s instability; a brief summary will suffice here to reaction time), and that he decided to stop the car demonstrate that the evidence for oversteer is rather than just lift and gather it up again. He had a inconclusive: bottoming at Tamburello was the norm full second to steer the car left in what was a shallow and Senna had no major issue with it throughout the corner, and he was already at the geometrical apex. weekend or on Lap 6; tyre pressures must have On-board footage from the Imola weekend shows markedly improved as he set the third fastest lap of him at this point of the circuit running the car wide the race on Lap 6; the on-board picture distortion is towards the outside of the track. As Mauro Forghieri much more pronounced on Lap 6; the sparks flying points out in the National Geographic documentary, from underneath the Williams don’t look as strong on the likely explanation for Senna’s decision to lift and Lap 7 as they do on Lap 6; there is no sudden spike start braking is that he’d realised there was and drop in revs, suggesting the car bottomed out something wrong with the car. and then recovered grip; there is no considerable During the trial7, Williams stated that the telemetry drop in steering strain signalling that the steering got isn’t compatible with a steering failure because Senna light; and the video analysis of oversteering cars would have decided to lift and brake around 11.36s indicates that the dynamics were different in Senna’s (0.10-0.15s after losing the steering) rather than at case. The on-board footage does become distorted 11.20s, and that he would not have hesitated with the and the rear wheels do rotate 4km/h (1.1m/s) faster throttle for another 0.20s. Not necessarily. The brief than is the speed of the car (11.10-11.18s), but this is hesitation looks on the telemetry more like an not abnormal in the context of values observed since uncontrolled stab on the throttle, and it coincides 7.98s, which range from -2km/h to +4km/h. The with the front of the car bottoming out on the third

110 bump: the shock could have disturbed Senna’s foot stopped being firmly restrained by the steering on the throttle pedal just enough to interrupt the lift. column. Likewise, it would have taken him until 11.36s to During 11.20-11.26s, the left front tyre returns swiftly react only if the steering column had snapped to its neutral position and the rate of direction without warning. In Senna’s case, however, the change against the ‘I Pilotissimi’ sign and the angle steering wheel began to flex at 8.20s and that gave between the car’s axis and the inside kerb reduce him at least three seconds to suspect something was accordingly. Again, the conclusion is that the car amiss and convinced him to stop the car. straightened its trajectory because the front wheels pointed it that way – either due to Senna’s correction with the imprecise (but still partially functional) TRAJECTORY & DIRECTION CHANGE steering, or because the front wheels centred back to Car trajectory and direction change were their neutral position once they were no longer comprehensively covered in the section on restrained by the steering column. There is little or aerodynamic instability; nonetheless, both fit the no observable direction change after 11.26s. steering failure hypothesis as well: the left front tyre Direction changes against the ‘I Pilotissimi’ sign after rotates left from 10.74s, it reaches the first peak at 10.52s (Figure 10) reveal an unusual pattern that 10.94s just before the car crosses the dark strip, and hints at the steering becoming imprecise: while the then it rotates left again at 11.06s and 11.18s. The two sample laps from Friday display gradual car’s rate of turning left increases from 10.76s and direction change as Senna keeps constant steering culminates at 11.18s, while the momentary angle lock to navigate Tamburello (the green and red lines between the car’s reference axis and the inside kerb follow a near-perfect straight line), the blue line from also goes up. The interpretation of these observations race lap 7 looks erratic and wayward in comparison. is that the car turned towards the inside of the corner There is less direction change (10.52-10.76s), then because the front wheels pointed it that way - either more (10.76-11.10s), and then significantly more due to loss of accurate steering input or because the (11.10-11.18s). wheels moved uncontrollably on the bumps once they

111 One of the arguments put forward by Williams driver during the 2008 Phillip Island Classic in against the steering failure theory has been the Australia (see video and Figure 49). evidence that Senna’s car didn’t leave the track on a Shelby Mustang GT350 steering failure tangent but instead straightened (turned right) after the initial twitch left. Adrian Newey made this point This unique footage was captured by Mark Clair, the on at least two separate occasions, back in 2000 for founder of RaceRecall, and it is reproduced here with Autosport10, and in May 2011 in the interview for his kind permission. RaceRecall specializes in on- The Guardian36. board video systems and for the race at Phillip Island it equipped the Mustang with three cameras mounted “The honest truth is that no one will ever know inside the car. The synchronized feed from the three exactly what happened. There's no doubt the steering different angles not only allows studying the column failed and the big question is whether it trajectory as the car is leaving the track, but it also failed in the accident or did it cause the accident? It pinpoints the exact moment when the steering fails. had fatigue cracks and would have failed at some point. There is no question that its design was very When the steering wheel detaches from the column, poor. However, all the evidence suggests the car did the Mustang doesn’t leave the track in a straight line: not go off the track as a result of steering column it actually keeps turning left, then it veers right, and failure. The telemetry we have, and the view from the only then does it plough straight on. The accident is a on-board cameras, show that what happened does textbook demonstration that Senna’s twitch left not fit with a steering column failure. The car didn’t (11.10-11.18s) and the subsequent turn right (11.20- go straight on as most people believe, it physically 11.28s) could have taken place under broken steering turned right.” column conditions. I have great respect for Adrian Newey’s genius and We can also plot direction change of the Mustang his towering achievements over the past thirty years, against a fixed point in the background, using as a but there is the possibility that a car veers right when reference the black and white pattern on the bridge it experiences a steering failure. A case in point is the that crosses the track (as we did with Senna’s car steering failure suffered by a Shelby Mustang GT350 position against the ‘I Pilotissimi’ sign, Figure 50).

112 Figure 49 – Top left: the exact moment when the steering wheel comes off the Mustang GT. The yellow line tracks the car’s direction change against the black and white pattern on the bridge towards which the Mustang is travelling, the orange line is ‘fixed’ to the bonnet.

Bottom left: three frames since the steering wheel has come off. Notice that the car is still turning left (the orange line ‘fixed’ to the bonnet has moved away from the yellow reference line).

Bottom right: seven frames since the steering wheel has come off. The car turns sharply right compared with the previous frame (the orange line ‘fixed’ to the bonnet moves back very close to the reference yellow line). Courtesy of Mark Clair, enhanced by author.

113 Figure 50 - Direction of travel based on the ‘I Pilotissimi’ sign (Williams FW16) and the pedestrian bridge (Mustang GT). The graph for Mustang GT is offset by 20 percent to bring the two lines closer together for easier comparison. The orange vertical line pinpoints the moment when the steering wheel comes off on the Mustang.

114

When the position change is tracked over time and damaged in the crash, which means the steering adjusted for the speed differential of the two cars, we angle applied by Senna during the accident cannot be get strikingly similar graphs. The Mustang accident determined. On top of that, Adrian Newey recently was clearly caused by a steering failure and its confirmed that in fact there was no position sensor85. dynamics can explain the directional changes of the Power steering pressures would be recorded Williams as well. regardless of the state of the steering column as long as the hydraulic circuit remained intact. All evidence points to that being the case – there is no STEERING TELEMETRY catastrophic drop in steering pressures and no flow Within a month of the accident, Williams produced a interruptions. The Mustang accident proves that even comprehensive technical report on the steering without steering, a car can still twitch left or right, telemetry that according to Patrick Head and for that reason the pressure in the steering rack demonstrated to the Italian authorities that steering cylinders (STGPR) doesn’t reveal whether the column data couldn’t be recorded with the wheel physically failed or not. What the STGPR trace does say is that separated from the column3,74. Because the report the pressure is at its lowest during the critical period was never published, it is unclear whether ‘steering when Senna loses control (a sign that the wheels are data’ represents steering angle applied on the turning firmly left), and that after 11.30s the pressure steering wheel, power steering pressures, steering stays around 400psi (wheels pointing more or less strain, or all of the parameters. straight) except for period 11.68-11.88s (wheels Steering angle is measured by a potentiometer that gently left, possibly due to the onset of hard braking). tracks either linear or angular movement. It can be This brings us to Steering pressure difference installed on the steering rack (linear), on the end of (STGACT), which measured the difference in the pinion (angular), or under the steering wheel pressures between the left and right hand side of the (angular). Tom Rubython in his book The Life of steering rack (Figure 33). Senna states21 that Williams deployed the last option and that the data was captured by the black box

115 Until 9.10s everything looks ordinary – Senna eases wheels are steering straight. This data is compatible his Williams into Tamburello at 7.98s and the with both versions of the broken column theory. pressure difference builds smoothly and gradually During 11.70-11.88s, the pressure difference raises from 58psi (the previous straight) to 764psi (steering momentarily to 223psi (equivalent to the initial slightly left). This is consistent with the constant smooth turn-in to Tamburello): if the ‘partial failure’ steering lock Senna habitually applied through theory is correct, the imprecise steering further Tamburello. Having said that, it would be easier to wobbled as Senna tried to stop the car; if the spot normal and abnormal trends on the telemetry if ‘complete failure’ theory is correct, this minor the data was available over a longer time span, i.e. at pressure difference came from the unrestrained front least from the beginning of Lap 7. wheels as they hit undulations or as they twitched From 9.10s, pressure difference across the steering under the onset of hard braking (which started rack begins to fluctuate. This can be seen on the around the same time at 11.68s). telemetry as a series of peaks and valleys (Figure 51) In the final quarter of a second on the track (11.90- that continue until 11.28s when Senna loses control. 12.14s) and then on the grass (12.16-12.38s), the The oscillations in pressure difference originated pressure difference actually turns negative (front either from steering input or road surface or from the wheels turning right). The remastered footage that combination of both, and they repeatedly loaded and appeared in the movie Senna1 bears that out – the unloaded the pistons inside the rack that assisted the left front wheel visibly turns right just as the left rear front wheels. If the primary source of these wheel drops on the grass. This gives weight to both fluctuations was steering input rather than bumps, it versions of the hypothesis because had Senna would indicate that Senna experienced imprecise retained full steering capability it’s unlikely he would steering from about two seconds before the crash. have turned towards the wall in the last moments on Pressure difference then falls to zero at 11.30s and the track. stays close to zero until 11.68s, which signals that in that period the steering rack is unloaded and the

116 Figure 51 - Peaks and valleys observed in Steering pressure difference (STGACT) two seconds before losing control (9.10-11.10s).

117

Two pressure difference spikes at 12.40s and 12.60s the target pressure would be zero or whatever most certainly weren’t prompted by driver input. Williams had under a no-load or residual load Tony Woodward expands on this: “the steepness of condition. these spikes is considerably more than I would expect The telemetry registers a steep increase in Steering from even the most panicked driver input, so my target during 11.00-11.08s, suggesting strong power conclusion is that they were oscillations produced by assist left immediately before Senna loses control. external impact on the wheels, thence on the STGTGT then begins to fall at 11.10s when the car hydraulic pistons within the steering rack, within a starts turning sharply left and it reaches what could sufficiently brief timespan as to not necessarily be interpreted as residual load condition at 11.30s involve the steering wheel. Such shocks can occur (175psi). At this point Senna is already a passenger independently of steering wheel input - it’s often and is heading more or less straight for the ‘I possible to hammer the steering hard enough to burst Pilotissimi’ sign. The target pressure stays low and something before the driver gets involved.” never recovers above 170psi. The final power steering trace is Steering target Then there are the three outliers where the steering (STGTGT, Figure 38), which measured pressure target pressure notably deviates from the expected difference across the control ports of the values. If the observed near-linear relationship electrohydraulic servo valve (Figure 35). Again, between Steering strain and Steering target holds STGTGT offers no proof that the steering column true, there should be an explanation why two out of suffered either partial or complete failure, but the the three outliers transpire at exactly the point when graph is consistent with both versions of the Senna pulls the steering wheel sharply up and loses hypothesis. control (11.20s and 11.30s). If the ‘partial failure’ hypothesis is correct, the target pressure in the servo valve after 11.30s would be minimal because Senna kept the steering approximately straight; if the ‘complete failure’ hypothesis is correct and the column broke off, then

118 The situation is more complex when it comes to abnormally responding steering column (‘partial analysing strain present in the steering column failure’ hypothesis), or by a column in the process of during the accident, because even the knowledge that seizing in the bushing (‘complete failure’ hypothesis). all three strain gauges were located below the break Equally, the release of the strain after 11.28s is is insufficient for determining which of the reconcilable with either letting go of the wheel competing theories is correct. (highly unlikely), returning the steering to its centred position (column intact or the ‘partial failure’ The sharp increase in Steering strain during 10.80- hypothesis), or with having the steering wheel 11.08s (from -10 to -26.9N/m2) could have been detached from a seized column (‘complete failure’ brought on either by brusque but regular steering hypothesis). input (column intact), or by a sudden bite of an

Figure 52 - Schematic diagram of the lower end of the steering column that remained in the bushing and connected to the pinion and steering rack.

119 If the steering column remained intact, the strain driver of the Mustang GT did by forcing it back in reported by the telemetry would be the actual strain where the modified piece changed in diameter. The present in the column during the accident. The same outer diameter of the modified piece (18mm) could applies if the column partially broke but continued technically fit in the inside diameter of the original transmitting enough torque to get Senna round column (20.4mm) provided that the deformation at Tamburello (‘partial failure’ hypothesis), and also if the filleted corner allowed it. But considering the the column held together but was so close to little time Senna had to react and the dimensions of rupturing that it stopped transmitting sufficient the parts involved, the chances of even partial success torque (imagine two sections of a snapped curtain are virtually zero. rail that haven’t twisted apart yet). All three scenarios Residual strain would also be recorded if there were are compatible with the observed Steering strain some resistance in the section of the column that values (Figure 41). remained in the bushing and connected to the pinion The final possibility is that the column physically (Figure 52). Strain would be generated from friction separated from its lower end (‘complete failure’ of this ‘amputated’ column getting partly stuck or hypothesis, Figure 52). Under normal circumstances, jammed in the bushing, especially if that part rattled no strain would be logged because the lower end of or had become ovaled in the course of rupturing. The the column attached to the pinion would rotate amputated end in the bushing looks slightly unrestrained. Although an electrical cable ran inside deformed in the photos33,91 although the resolution of the hollow tube of Senna’s column and stayed the images is too poor to be certain. The drag from connected until the impact (it was cut with pliers by even minor deformation such as this can be the driver of the medical car Mario Casoni) , it is significant and it could have provided enough difficult to imagine that a cable alone could generate resistance to seize the column in the bushing and measurable strain. read on the telemetry as steering strain. Still, it is possible to record strain with the top end of “It would be good to know what the rotating the column disconnected: in theory, Senna could clearance was in the bushing and what it was made have tried to reattach the broken column just like the of,' says Tony Woodward. “It’s black so my guess

120 would be DuPont Black Delrin, Celcon, or even black completely when Senna pulled the steering wheel up Nylon. Black Delrin is so slick it will run against steel (11.20-11.30s). Once deprived of driver input, the under water, and is rigid and accurately machinable. ‘amputated’ end of the column got jammed or rattled However, it is subject to thermal growth and, in my in the bushing and offered residual drag that experience [from NASCAR series], when used as a registered on the telemetry as gradually decreasing steering column bushing it needs about 0.125mm strain. clearance [to permit free rotation]. Therefore the It is the way Steering strain falls in the next second modified piece of Senna’s column running in it would (11.30-12.30s) that adds to the intrigue: the trace have had to be distorted by about that much, minus follows a quadratic curve (Figure 41), and when the any existing ovality. The expected ovality in that area square root of strain is plotted instead of the actual due to the variable contraction stress of the weld, if Steering strain, the trace turns almost into a straight the weld were performed manually, would be around line (Figure 53). This relationship hints at a natural 0.025 - 0.050mm.” process at work rather than human intervention, and So under such circumstances, the column could have if a meaningful physical property can be assigned to seized once it became distorted beyond the square root of strain, then that property was approximately 0.1mm. But without being able to falling all but linearly between 11.30s and 12.30s. measure that part of the column and the effective When Senna arrives on the grass (12.16s), the strain inside diameter of the bushing, we can’t know what momentarily turns positive (0.6N/m2). This signals happened. If, however, the piece of the column that the front wheels turned right on the surface running in the bushing still exists and is frozen in change, briefly exerting strain in the opposite place or nearly so, it would be a major coup for the direction against the residual resistance of the seized ‘complete failure’ version of the hypothesis. column. The unusual direction changes experienced by Senna during 10.74-11.30s are very similar to those of the Mustang GT driver. They could have been triggered by a column seizing in the bushing that broke off

121 Figure 53 - The square root of Steering strain is reducing almost linearly in Senna’s final second on the road (11.30-12.30s). The orange line represents the line of best fit.

122

There are two final blips in Steering strain at 12.40s video evidence indicates that Senna gripped the and 12.60s, with amplitudes even lower than the steering wheel until the impact. modest strain levels recorded during Senna’s initial The emotionally charged footage shown in the movie turn-in to Tamburello. They were induced by the Senna1 incorporates a remastered sequence taken bouncing front wheels as the car landed on the grass from the helicopter hovering over the scene of the and concrete before the wall because they coincide accident. The improved images allow to study, for the with the two massive spikes in Steering pressure first time, the grim reality inside the cockpit of the difference (STGACT). Williams before the arrival of the medical crew. Regardless of the state of the steering column, the Senna sits motionless except for a slight reflexive strain values could be low simply because the shocks head movement to one side. His right hand is from the bouncing wheels were so short in duration outstretched alongside his thigh and is clearly that they occurred independent of driver input. The identifiable by the white contours of his racing glove. strain could also be low because the condition of the But Senna’s left glove – a fuzzy patch of white and partially severed column further deteriorated after blue against the darker background of the cockpit – is the car’s hard landing on the grass and concrete (for still clutching the rim of the steering wheel, which comparison, watch ’s crash in Malaysia has been pulled out and is now resting in his lap. 2011), or because the drag of the ovaled column rotating in the bushing wasn’t able to offer more than just residual resistance against the bouncing wheels (‘complete failure’ hypothesis). Finally, low strain values would have been recorded if Senna had let go of the steering wheel and the front wheels had turned unrestrained. This may sound counter-intuitive, but racing drivers sometimes ‘brace for impact’ to avoid injuring their hands. Such a scenario can be ruled out, however, because recent

123 STEERING WHEEL FLEXING yellow button almost reaches the expected position as defined by the reference green arc on the CINECA The starting point for studying the behaviour of video (11.30s). Nonetheless, this correction is only Senna’s steering wheel in the seconds leading to the temporary and the button is immediately dropping accident is the CINECA analysis18 from 1997 again in vertical fashion (11.32-11.42s) until it discussed in Chapter 6. The other vital ingredient is disappears from the screen (11.44s). There is a the digitally remastered on-board footage from Laps glimpse of the button at 11.52s before its final 6 and 7 that recently appeared in the movie Senna1. appearance at the edge of the screen during 11.74- The painstaking work of the producers sheds new 11.76s. It is gone until the end of the footage (11.84s). light on the movement of the steering wheel, particularly in frames where the yellow button is not The enhanced cockpit zoom sequence, which is based clearly distinguishable on the earlier CINECA on the original CINECA analysis, affirms that the footage. steering is pulled downwards and forwards after 8.20s. The rim of the steering wheel - outlined by Nothing out of the ordinary happens as Senna blue dots where the dark contours of the rim are crosses the line to start Lap 7 and the yellow button discernible against the lighter background – clearly follows its customary trajectory. Then, 8.20s into the drops at 10.48s, at 10.74s, and then at 11.40s. lap and three seconds before Senna loses control at 310km/h in Tamburello, the steering wheel begins to Enhanced cockpit zoom sequence, Lap 7 drop steadily at a 45-degree angle, so much so that by The late Ferrari driver Michele Alboreto testified in 10.74s the button has descended to the edge of the court that the stress on the steering column at a screen some 25-27mm from its regular position. circuit like Imola would normally generate flexing in After 10.74s, the behaviour of the yellow button the order of two or three millimetres, not centimetres changes. It is no longer dropping and instead it is as seen on the footage, and that the flexing would moving horizontally from right to left until 11.20s just depend on the bending force inflicted by the arms of as Senna’s car suddenly twitches left. At 11.20s, the driver, the composition of the materials, and the Senna pulls the steering wheel sharply up and the

124 distance of the steering wheel from the support magnitude shown in the demonstration. Senna’s strut75. strive for perfection was legendary and he forced the designers to alter the steering wheel position before Williams’ answer to Alboreto’s assertion was the the start of the season just to get more feel and video showing David Coulthard sitting in an FW16 performance out of the car. Had he experienced car in the museum and replicating Senna’s steering similar flexing on regular basis in the previous races, wheel movements from the last three seconds before he would have demanded design modifications the crash. Williams didn’t disclose the methodology immediately. used in this demonstration, and it remains unclear how the demonstration was put together, which part In the closing trial statements on November 18, 1997, of the steering assembly was responsible for the Williams’ lawyers argued that the oscillations of the flexing observed, and under what circumstances yellow button cannot be relied upon due to optical would such flexing actually materialize on the race illusions because the on-board camera was not of track. The fact that the dashboard and steering fixed rigidity69. No part on a racing car is of fixed column on the video are hidden from view by white rigidity, but that doesn’t mean that, for instance, the space doesn’t help either. flexing of the front wing on Red Bull’s model RB6 from 2010 was just an optical illusion. The reality is From the other side of the pond, Tony Woodward that all publicly available on-board footage from offers the following perspective on the Williams Senna and Hill’s 1994 races shows no or just minor demonstration: “Until we introduced the SCA827 flexing, and the yellow button describes regular column (1.25’’ OD x 0.065’’ wall), many a US stock- circles that do not deviate considerably from the car racer would bend his 0.75’’ OD x 0.120’’ wall white circle of low opacity (Figure 7). steering column while climbing into the car, and then have to bend it back straight in order to drive. I’m not As we discussed in Chapter 6, there is literally no making this up.” flexing observable on the footage from Brazil despite the track’s notoriously bumpy and relatively high- Despite that, it is hard to believe that any F1 driver - speed nature (two brief instances, 4-5mm); there is let alone Senna - would accept flexing of the barely noticeable flexing on the footage from Japan

125 (four instances, 4–5mm); and several minor finish straight, his upward steering movement not deviations during Imola practice, qualifying, and circular but almost linear. There is one more jitter warm-up sessions (peaks at 6–8mm). The story is the (9mm) before Senna crosses the line and the button same in the race until 36 seconds into Lap 6. then settles on the white circle. But then something unusual happens, visible once a This evidence is significant for two reasons: first, it white circle of low opacity is superimposed on the on- suggests that the flexing progressively worsened over board footage of Lap 6. Only the overlay of steering the course of the first three races, and second, it movements can be published here; however, the reveals that substantial flexing arose not just once, original sequence on which the overlay is based but on several occasions in the last sixty seconds appeared in the official review of the 1994 season76 before the crash. Moreover, the flexing becomes and also features in the movie Senna1. visibly worse towards the end of Lap 6 after Rivazza corner. It strongly supports the assertion that at this Overlay of steering movements, Lap 6 stage Senna was already driving with a partially 36.54s after the restart on Lap 6, the yellow button severed steering column. on Senna’s steering wheel jitters substantially and The final deviation begins 8.20s into Lap 7 when the drops from the white circle on the exit of the fast left- yellow button strays by 25-27mm and never recovers hander Piratella. The peak deviation is twice as high to the level of the white circle. Three distinct phases as anything observed previously (15–16mm) and the are recognisable: the dropping of the button at a 45- angle of the deviation is approximately 40 degrees degree angle towards the centre of the steering wheel (Figure 54). (8.20-10.74s), the slight horizontal movement from 1:13.60min into Lap 6, the yellow button drops after right to left during which the car turns sharply left exiting Rivazza (10-11mm), it shoots up above the (11.74-11.20s), and then vertical oscillations up and white circle (8-9mm) shortly afterwards on the entry down once Senna loses control after 11.20s. to Variante Bassa, and then it falls again on the exit Overlay of steering movements, Lap 7 (11–12mm). It stays markedly below the white circle (10-11mm) as Senna turns right and enters the start-

126 In comparison, Senna’s (and Hill’s) on-board footage through Tamburello earlier during the Imola weekend looks very different and the yellow button barely moves because both Senna and Hill keep constant steering lock all the way round the corner. And even if Senna is holding the steering straight after 11.26s to achieve optimal braking, the yellow button should still remain visible and it should stay near the reference green arc because that’s how the button behaves under braking on all footage from the 1994 season.

Figure 54 - Steering wheel movements during the last 60 seconds before the crash. Grey arc denotes the regular trajectory of the yellow button, the white line represent the distance of the yellow button from the serigraphed ‘V’.

Top: deviation on the exit of Piratella corner towards Acque Minerali.

Bottom: deviation on the exit of the Variante Bassa towards Traguardo (this overlay is based on remastered on-board footage from Lap 6).

.

127

Tamburello wasn’t an acceleration or braking zone footage suggests that the lower crescent of the where strong forces could pull the steering column in column held together at least until 11.20s. While different directions under hard throttle or braking, or between 8.20s and 11.20s the yellow button either over the kerbs. So why would Senna exert effort drops steadily or moves across, once Senna pulls the strong enough to pull the steering down and right steering wheel sharply up during 11.20-11.30s the after 8.20s? button starts jumping up and down in a vertical line, indicating that the column may have sheared near According to the broken column hypothesis, the the support strut. fatigue crack in the upper crescent meant the weakened column could no longer withstand the There is video footage that demonstrates what the combined stress of high downforce, lateral g-force, accident may have looked like in this scenario. A and the bending force applied by Senna’s arms, and dragster driver suffers a column failure in a straight the steering dropped along the line of least line at an estimated 350km/h73. When observed in resistance. If a shaft develops a crack that extends slow motion, the dragster’s column wobbles left to from nine o’clock to one o’clock position33,79, it is right by several centimetres for about three seconds most susceptible to bending on the opposite side until it reaches the breaking point and shears between three o‘clock and seven o’clock (Figure 55). completely. The movement illustrates why Senna’s This explains why the steering wheel dropped steering wheel could drop by 25-27mm moments towards the bottom right hand corner of the cockpit before the crash and then oscillate up and down. at a 45-degree angle, and why the severe flexing observed on Lap 6 after Piratella, Rivazza, and Variante Bassa exhibits a similar pattern. Dragster driver suffers a column failure Although the flexing indicates a steering problem, it doesn’t clarify whether the column continued transmitting sufficient torque through the lower crescent or whether it broke off and was dangling in Senna’s hands. On closer inspection, the on-board

128 Figure 55 - Position of the yellow button at 10.74s on three different laps during the Imola weekend (timing based on race Lap 7). The orange dot sitting on the circle of low opacity marks the yellow button position at exactly the same part of the circuit on two Friday laps (morning practice and qualifying). The yellow dot is the actual button position on race Lap 7. 129 . At what point would Senna realise that the column something unusual towards the end of Lap 6, he may was rupturing? His reaction time, measured as the have decided to continue for another while – he was time elapsed since 8.20s when the steering wheel leading the race and was under massive pressure to started to drop towards the bottom right hand corner win. Diving into the pits for a precautionary check of the cockpit, is similar to that of the dragster driver was not an option. – about three seconds. Senna was famous for his ability to detect even the slightest changes in his car’s behaviour; in this instance, however, he would have The accident happened incredibly fast and therefore lacked a suitable reference point because he hadn’t it is hard to account for time lags or to separate cause experienced a steering failure behind the wheel of an from effect. Still, the movements of the yellow button F1 car before. This assertion is supported by the closely mirror those of Senna’s helmet and the frightening tale of former F1 driver David , helmet’s movements are in turn dictated by the laws who raced at Imola 1994 for the beleaguered of gravity as Senna stayed on partial throttle, lifted, team. Having witnessed his teammate Roland braked hard, or did nothing. Ratzenberger’s fatal crash on the Saturday, Brabham Steering and helmet synchronization, Lap 7 bravely decided to race on the Sunday, only to suffer a steering failure not long after Senna’s accident. The In period 11.24-11.40s – either intentionally or Simtek’s steering column detached completely from accidentally - Senna applies more or less 50 percent the steering rack on the short straight before the throttle. Correspondingly, no shifts in longitudinal Variante Bassa chicane, yet Brabham didn’t notice force act on the car or the driver’s body and the the problem until he tried to turn in at the end of the yellow button is visible after Senna has pulled the straight, and initially he suspected that he had lost steering up. He lifts completely between 11.42-11.50s the front wing89. and his helmet lunges forward. The yellow button drops and disappears from the screen, in sync with So it is by no means certain that Senna would have the movement of the helmet. diagnosed the severity of the situation accurately and immediately. And even if he had already felt

130 At 11.52s, the initial deceleration phase is complete and throttle is now zero. Senna’s helmet is moving back towards the headrest and his arms holding the steering wheel go up as well. The yellow button reappears accordingly at the bottom of the screen. Between 11.54-11.68s, Senna’s right foot switches to the brake pedal, his helmet is leaning slightly forward, and the yellow button dips below the edge of the screen again. Hard braking begins at 11.68s (longitudinal force is rising to 1.3G, to 1.8G, and then to 3.1G) and there is no sign of the yellow button. From 11.74 to 11.76s, Senna temporarily releases pressure on the brake pedal (longitudinal force is reduced from 3.1G to 2.3G) and his helmet moves back towards the headrest. This is exactly the moment when the yellow button makes its final brief appearance. The explanation is that as Senna’s head and body jolted forwards and backwards in response to the varying forces, his arms holding the steering wheel did likewise because they were no longer supported by the resistance of the steering column, which is under normal circumstances firmly anchored to the steering assembly.

131 wheel began to flex substantially only in the last sixty CHAPTER 15 seconds and never before that. The verdict The quest to solve the mystery of Senna’s death is no longer a mission impossible, but nor is it a mission accomplished. On balance, the evidence tips the scales in favour of a steering failure, although the There is no smoking gun, but also no underlying flaw only person who knows the whole truth took it with in the ‘partial column failure’ hypothesis. A great deal him to the grave. But at least Ayrton Senna can rest of disparate evidence points to Senna losing precision in peace knowing that the fundamental human desire and feel as he bent the faltering steering column, to go deeper and deeper in the search for which led to his Williams twitching left and right in understanding is alive and well. the critical moment. And because he retained some torque in the column, steering strain values were still recorded. There is intriguing evidence supporting the ‘complete column failure’ hypothesis as well; however, without knowing exactly how the power steering system worked, and without inspecting the amputated end of the steering column, it is not possible to complete the puzzle and make a definite judgment. The tyre failure and aerodynamic instability hypotheses look persuasive; nonetheless, the contradictory evidence is difficult to ignore, and some of the evidence can be explained via a more straightforward route - for instance, why the steering

132 Bibliography

1. Senna; movie by , Manish Pandey; ESPN/Working Title (2010) 2. F1 Racing; The Evidence They all Missed (April 1997) 3. Hilton, C.; As Time Goes By; Haynes Publishing (April 1999) 4. Auto Race; Jury told Senna’s car had problems (March 12, 1997) 5. S-Files; Senna could not have survived (July 9, 1997) ayrton-senna.com 6. All F1 Info; Renault engine technical specification allf1.info/engines/renault.php 7. Autosport; The Final Chapter (1999) 8. Hamilton, M.; Nicholson, J.; Pole position: Behind the Scenes of Williams-Renault F1; Motorbooks International (April 1996) 9. Motor Sport; Driven by Design; Adrian Newey Special (December 2012) 10. Autosport; Golden Years – Adrian Newey on his cars (December 12, 2000) 11. Autosport Legends – Ayrton Senna; Sitting with Senna (October 2011) 12. S-Files; Williams: Steering column was perfect (June 26, 1997) ayrton-senna.com

133 13. S-Files; Senna trial: Head and Newey silent (October 29, 1997) ayrton-senna.com 14. National Geographic Channel; Seismic Seconds – The Death of Ayrton Senna; A Darlow Smithson Production in association with Channel Four Television (2001) 15. S-Files; Senna not guilty (November 7, 1997) ayrton-senna.com 16. S-Files; Black boxes were scratched but intact (March 17, 1997) ayrton-senna.com 17. Motoring News; Video claims spark a new Senna row (May 21, 1997) 18. CINECA; Ayrton Senna Car Accident cineca.it/it/video/ayrton-senna-car-accident 19. CINECA; Image processing on Senna’s camera car video cineca.it/en/page/image-processing-sennas-camera-car-video 20. Ayrton Senna Online Channel; YouTube youtube.com/user/ayrtonsennaonline/ 21. Rubython, T.; The Life of Senna; BusinessF1 Books (May 2004) 22. Armstrong-Wilson, C.; Control under pressure; Racecar Engineering (November 2008) http://moog.com/news/articles/control-under-pressure/

134 23. Moog; E243 series miniature PAS valve; Technical Specification (2012) moog.com/literature/ICD/Datasheet_-_E243_Stard_PAS_Valve.pdf 24. Moog; E024 (LA series) Sub miniature servovalve, Technical Specification (2009) moog.com/literature/ICD/E024_(LA_Series)_datasheet_EUROPE.pdf 25. Design News; Miniature Servovalves Go to the Races (July 7, 2003) moog.com/literature/ICD/MiniatureServovalvesGototheRaces-dnarticle.pdf 26. Ideas & Applications; racers go with ultralight hydraulics (2006), Penton Media moog.com/literature/ICD/FormulaOne-hparticle.pdf 27. Jones, M. S; A Short History of Moog’s Involvement in Motorsport; Moving Your World, Issue 10 (1/2006) moog.com/literature/ICD/moogindustrialnewsletterissue10.pdf 28. Moog; Race Winning Motion control; Motorsport solutions; What Moves Your World (2008) moog.com/literature/ICD/Race_Winning_Motion_Control_-_Motorsport_Solutions.pdf 29. Moog; Type 30 Nozzle-Flapper Flow Control servo valves, Technical Specification mylesgroupcompanies.com/moog_pdfs/Moog%2030%20Series%20Catalog.pdf moog.com/literature/ICD/31_32seriesvalves.pdf 30. Moog; Series 50 valve; Technical Specification mylesgroupcompanies.com/moog_pdfs/moog_E0- LVDT_series_microvalves_with_spool_position_feedback.pdf

135 31. Sensorland.com; How They Work: The Strain Gauge sensorland.com/HowPage002.html 32. Wikipedia: Strain Gauge en.wikipedia.org/wiki/Strain_gauge 33. S-Files; Evidence from Italy ayrton-senna.com/s-files/evidence.html 34. Sutton Images; Image Ref: tmk0229ma22.jpg sutton-images.com 35. Giacon, M; Mitidieri, D; L’ultimo Ayrton; Giorgio Nada Editore (1996) 36. The Guardian; Ayrton Senna’s death ‘changed me physically’, says Adrian Newey (May 2011) guardian.co.uk/sport/2011/may/16/adrian-newey-ayrton-senna-death 37. The Times; D. Hill: The harsh fact is that Ayrton made a mistake (April 20, 2004) thetimes.co.uk/tto/sport/formulaone/article2333571.ece 38. The Face of A Champion; Sonopress with MicroPower (CD-ROM, 1995) 39. Autosport; News in Brief, (April 25, 2002) 40. F1 Racing; Rest in peace (May 2002) 41. F1 Technical; Newey on Imola 1994 discussion thread f1technical.net/forum/viewtopic.php?f=1&t=10054&start=60 42. Motoring News; New picture adds to Senna mystery (March 19, 1997)

136 43. Autosport; Why Did Senna Crash? (May 5, 1994) 44. S-Files; Don’t blame Senna (March 5, 1997) ayrton-senna.com 45. The Face of A Champion; Patrick Head – A Mechanical Failure?; Sonopress with MicroPower; (CD-ROM edition, 1995) 46. Autosport Legends – Ayrton Senna; Lest we forget that fateful day… (October 2011) 47. Ramirez, J.; Memoirs of a Racing Man; Haynes Publishing (September 2005) 48. Shell; Formula One Technology Explained – Diffusers shell.com/global/products-services/motorsport/ferrari/technical-partnership/f1- explained/diffusers.html 49. Racecar Engineering; Diffusers (April 2009) racecar-engineering.com/technology-explained/diffusers-engineering-basics-aerodynamics/ 50. McBeath, S; Murray, G; Competition Car Downforce, A Practical Guide; Haynes Group (1998) 51. Scuderia.net Forum; Diffuser Stall (February 2006) thescuderia.net/forums/showthread.php/13113-Diffuser-Stall 52. Babinsky, H; How wings really work; University of Cambridge; (Jan 25, 2012) cam.ac.uk/research/news/how-wings-really-work/ 53. Woodward, T.; Personal correspondence (October 2011) 54. Auto Race; Williams trial will be kept low key (February 18, 1997)

137 55. Aircraft Material UK, Data Sheet Carbon Manganese Steel T45 Tube aircraftmaterialsuk.com/data/alstst/T45.html 56. York Steel, Data Sheet EN14 Steel westyorkssteel.com/en14.html 57. Autosport; A sigh of relief (1997) 58. Sach, N.W.; Understanding the Surface Features of Fatigue Fractures: How They Describe the Failure Cause and the Failure History; Journal of Failure Analysis and Prevention, ASM International, Volume 5/2 (April 2005) asminternational.org/pdf/spotlights/jfap0502p011.pdf 59. Campbell, F.C.; Fatigue and Fracture: Understanding the Basics; ASM International (December 2012) 60. Martin Zustak; Personal correspondence (November 2012) 61. The Face of A Champion; Steering Column Patched; Sonopress with MicroPower (CD-ROM edition, 1995) 62. S-Files; Allegations to Answer… (January 7, 1997) ayrton-senna.com 63. Wikipedia; Stress Concentration en.wikipedia.org/wiki/Stress_concentration 64. Engineer Edge; Stress Concentration Fundamentals; (Jan 2013) engineersedge.com/material_science/stress_concentration_fundamentals_9902.htm

138 65. Noble, A.; Stress Concentration; Virginia Tech Materials Science and Engineering (April 1997) sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/anal/noble/stress_conc.html 66. Pilkey, W.D.; Pilke, D.F; Peterson’s Stress Concentration Factors, Third Edition; Wiley (January 2008) 67. S-Files; Williams engineers testify (July 4, 1997) ayrton-senna.com 68. Meyer, C.; Virginia Tech Materials Science and Engineering; Experimental Fatigue sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/exper/meyer/www/meyer.html (June 5, 1997) 69. S-Files; Defence: closing statements (November 19, 1997) ayrton-senna.com 70. Kelly, S. M.; Fatigue; Virginia Tech Materials Science and Engineering sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/anal/kelly/fatigue.html 71. Wikipedia; Fatigue (Material) en.wikipedia.org/wiki/Fatigue_(material) 72. Motoring News; Experts clash over the column (May 21, 1997) 73. CarsAndCrashes; Dragster Steering Wheel Off; YouTube youtube.com/watch?v=qlGZ5rr_v6A 74. Dever, P; The Auto Channel; Williams disavows responsibility for Senna’s fatal crash in 1994 (April 4, 1996)

139 75. S-Files; Alboreto: Senna knew of problem (September 16, 1997) ayrton-senna.com 76. 1994 FIA Review; Who Else But Schumacher!; Duke Marketing Ltd (FOCA 1994) 77. Autosport; Pit and Paddock…; Senna trial closed (June 2, 2005) 78. Wikipedia; Throttle en.wikipedia.org/wiki/Throttle 79. L’Automobile Magazine; Chronologie d’une catastrophe (May 1995) 80. Racing Day; F1 Renault Williams FW16 Rothmans of Ayrton Senna; YouTube; http://www.youtube.com/watch?v=QcFOgOTNMtg 81. Waack, W.; Veja; Remendo Fatal (May 3, 1995) http://veja.abril.com.br/acervodigital/home.aspx?edicao=1390&pg=1 82. Cabrini, R.; Conexao Reporter – Ayrton Senna e os 20 anos de sua morte (SBT 2014) 83. Autosprint; Chi Sa Parli by A. Antonini ( issue 21, May 24-30, 1994) 84. BBC Formula One Season Preview 2014; Ayrton Senna 20 years on (spring 2014) 85. auto motor und sport; Adrian Newey – Hatte mich mit dem Auto verrechnet (April 28, 2014) auto-motor-und-sport.de/formel-1/senna-zeitzeuge-adrian-newey-8-hatte-mich-mit-dem-auto- verrechnet-8313172.html

140 86. The Telegraph; Ayrton Senna: The inside story of the Formula One legend’s death at Imola (April 30, 2014) telegraph.co.uk/sport/motorsport/formulaone/10796725/ayrton-senna-death-inside-story-imola.html 87. BBC Sport; Ayrton Senna death: David Coulthard – I owe him my career (May 1, 2014); .com/sport/0/formula1/27190030 88. Autosport; The Imola grid looks back on a black weekend (May 1, 2014) 89. Autosport; Brabham: ‘I felt lucky I got out of there alive’ (May 1, 2014) 90. Autosprint; Senna, la vera storia dello sterzo rotto (April 30, 2014) autosprint.corrieredellosport.it/2014/04/30/senna-la-vera-storia-dello-sterzo-rotto/15070/ 91. OmniCorse; Ecco com’era il piantone rotto di Senna, caro Newey! (May 18, 2011) omnicorse.it/magazine/8946/f1-ecco-come-era-il-piantone-rotto-di-senna-caro-newey 92. F1 HD; The Last Team Mate (April 26, 2014) 93. Ayrton Senna Vive Blogspot; Fotos do acidente fatal de Ayrton Senna (May 1, 2013) ayrtonsennavive.blogspot.ie/2013/05/fotos-do-acidente-fatal-de-ayrton-senna.html 94. Rutten H; Sportclub Stars: Ayrton Senna; NDR.de TV programme (April 27, 2014) 95. Windsor, P; Senna: why?; F1 Racing, The Racer’s Edge YouTube channel (May 1, 2014)

141