Feel the Force – Part 2
In the first part of “Feel the Force” I looked at the forces F1 drivers endure as part of their normal work; this second part looks at how track design affects g-force loads, a bit about human g-force deceleration experiments and continues with examples of the extreme g-loads drivers can face during a collision.
I for one have been critical in the past of some of the newer circuits to the F1 calendar, those designed by Herman Tilke, one of four FIA approved circuit designers. However it wasn’t until I started researching some background material for this article that I discovered just how difficult a task this could be.
Texas Motor Speedway CART series 2001
Back in April 2001, the American CART series Firestone Firehawk 600 was to make its debut at Texas Motor Speedway, a 24° banked oval circuit in Fort Worth, Texas. These cars could reach speeds in excess of 230 mph and in the process, exerted lateral 5g loads on the drivers.
But this was not the momentary lateral g that exists on cornering, it was a 5g load sustained over 18 seconds or two thirds of each lap. After qualification ended, twenty-one of the twenty-five drivers complained of feeling dizzy and disorientated, of inner ear problems and loss of peripheral vision. These symptoms were reported after completing ten or more laps. One of the drivers, Mauricio Guglemin claimed to have had a momentary blackout due to vertical g-LOC which led to him crashing.
After speaking to the drivers, the director of CART medical affairs contacted a specialist in the field of human tolerance to vertical g-load to enquire about minimising the effects of g and safety of the drivers. The director was advised that the maximum speed should be restricted to 225 mph to avoid the risk of g-LOC. With insufficient time to implement changes to the cars’ downforce and horsepower levels the race was cancelled, much to the annoyance of the 60,000 strong crowd. How did the circuit designers get it so wrong, there had been sterling work done on survivable g-forces in the late 40’s and early 50’s?
Human deceleration experiments
At one time it had been widely thought that the maximum g a body could withstand was around 18g, so there had seemed little point in making structural support to aircraft or vehicles beyond that limit. Those ideas changed due to the pioneering work of Colonel (Dr.) John Paul Stapp, a US Air Force flight surgeon. In 1947, armed with data from US Navy aircraft crashes during the Second World War, he and his team set about trying to find out why people had died in crashes that had seemed survivable. This initial analysis led Stapp to believe that it was not the impacts themselves that had caused the deaths, but rather that the seats, harnesses and cockpits that supported pilots had been contributing factors.
Stapp set out to show that the human body was more resilient than the 18g limit by looking at the effects of deceleration and protection from crash forces in voluntary human subjects. Their rocket sled “Gee Whiz” could achieve a maximum of 100g: the sleds’ 4-kN rockets powered the acceleration along a 2000 foot track followed by abrupt deceleration by means of an hydraulic braking system. Stapp himself endured forces of up to 46.2g; this video shows some of his experiments and the injuries he sustained.
As a result of Stapp’s work new seating requirements were made and better multi-point harnesses were developed. His pioneering work has impacted in many fields, not just aircraft design but also in safety measures employed in modern F1 cars, he showed that if properly secured the human body could cope with very large crash forces.
High g-load accidents involving formula one drivers
Anyone who witnessed Robert Kubica’s spectacular crash at the Canadian Grand Prix in 2007 will have seen the devastating forces than can be elicited during a high speed collision. Data collected from the black box recorder which the FIA demands is fitted to all F1 cars during testing, and race weekends revealed that he had sustained a momentary 75g at the peak of the collision.
It’s testament to the design of the monocoque, harness and other safety features that he survived the impact relatively unscathed.
But as spectacular as Kubica’s accident was, it was by no means the highest recorded g-force load endured by a driver; that record goes to David Purley after his accident at the pre-qualification session for the 1977 British GP.
It has been estimated that Purley endured split second g-forces of 179.8 when he decelerated from 108 mph to complete stop in a distance of 26 inches. Although Purley sustained multiple fractures he did recover and later raced again. To put the magnitude of these accidents into perspective it was estimated that the collision which killed Diana, Princess of Wales produced around 70g to her chest and 100 g to her head, she may even have survived if she had been wearing a seat belt.
The FIA are always looking at ways to reduce the risk to drivers and there are many features such as chicanes, gravel traps and those beautifully painted run off areas at circuits like Abu Dhabi and Sakhir which considerably reduce the speed of a collision with barriers after a run-off. For background reading there is a very nice article in the FIA Sports Automotive magazine highlighting Heikki Kovalainen’s 27g accident at the 2008 Spanish Grand Prix as told by Charlie Whiting, the FIA Safety Delegate. I’ll end with a quote from Professor Sid Watkins from 2008.
“We’ve been blessed really. ‘Although we’ve had some big accidents, nobody’s really got hurt since 1994.” -Professor Sid Watkins
A very interesting piece Saltire!
Does the figure, associated with Kubica’s crash, of 75g, take into account both, lateral, & tranverse g-loads? Slowflow(Quote)
Unfortunately I don’t know the answer to that,
I have been looking to see if I can find the official FIA report but no luck so far. The couple of links I found to it just said it had peaked at that value over a millisecond time frame. I’d assume it included both but maybe we need someone well versed in physics to answer that. saltire(Quote)
Given the nature of the accident, I believe it was a peak value in what ever direction it peaked at – a combination of both lateral and transverse (and probably vertical) components.
Dave Purley’s accident was the stuff of legends, but then so was he. He also survived a parachute failure by riding down on top of his comrade’s! Maverick(Quote)
What I thought was particularly unfortunate about the CART incident at Texas was that the rival Indy Car series was able to race at the circuit without any problems when it visited before the CART teams did. But while the Indy Cars didn’t get above 225mph, Paul Tracy’s best lap at the CART event was over 236mph. Not a huge difference in speed, but an important difference in terms of the g-force. And it was a massive blow for the championship. Keith Collantine(Quote)
That is fascinating about the human deceleration experiments. A great read again, Salti. Maverick(Quote)
Thanks Jackie. I’ll watch the video tomorrow, it seems that the Col. was very brave to put himself through those tests!
CART was rightly ridiculed for discovering the problem on Friday and not doing anything about it until well after qualifying on Saturday, and then not really acting until Sunday morning. Curiously in pre-season tests the cars were running at acceptable and safe speeds. Still, had they acted when speeds went that high on Friday they could have mandated lower boost pressure and more wing.
Although the IRL has raced successfully there for some time now there is still trepidation every year in the run up to that race – not for the g-forces but because cars end up in packs which lead to big accidents, and at those speeds you don’t want any accidents. Fearsome place. Pat W(Quote)
Speaking of deceleration, the HANS device has really helped drivers survive accidents of this type with only minor injuries, including Kubica – I have no idea how Purley managed to without one!
http://en.wikipedia.org/wiki/HANS_device Pat W(Quote)
Great article Jackie.
I think your sympathy for Tilke is misplaced though. He could still design far better circuits without endangering drivers. I think one of his biggest issues is that his circuits look like he has been paid a rate per corner. He often builds on flat ground which doesn’t help but if you look at the best flat tracks like Monza or Silverstone you find they have very few corners. Even including chicanes Monza has only 7 corners in about 3 miles where Valencia has 23-25 depending which track guide you read. Everyone knows the biggest problem F1 cars have is following another car round a corner so if you have a series of corners with no straights the problem is made worse. In effect the fewer corners the better. Steven Roy(Quote)
I think you’re right about that – it’s exemplified by the fact nobody knows how many corners Valencia has. The current fashion is to take every slight deviation from straight and give it a corner name. If Monza was built now, each kink in each chicane would have its own turn number. Istanbul’s Turn 8 would be Turn 8, 9 and 10 (and 11 by some counts). Now I don’t think that’s Tilke’s choice but it does show the mentality of these new circuit owners. It’s similar to this current obessession with running anti-clockwise in order to be different from the rest of the calendar (but exactly the same as all the new circuits!) Heck, Korea are even getting excited about being “the first course to actually be designed as a dual-structure from the beginning.” Err, no it’s not. By a long way. Maverick(Quote)
Great article Jackie, it’s very interesting that a high load for a short time is less damaging than a smaller load for a longer time.
The G loadings of David Purley’s accident are very interesting indeed. Stirling Moss’s career-ending crash in 1962 saw him stop from 60mph in 18 inches – slightly less than 2/3rds Purleys speed in slightly less than 2/3rds the distance. So perhaps Moss experienced a similar G load? Pitmonster(Quote)
Easy enough to calculate…
Purley:
26 in = 0.66 m
108 mph = 48.38 m/s
Therefore, average velocity = 48.38/2 = 24.14 m/s
Hence, time = 0.66/24.14 = 0.027 s
and deceleration = 48.28/0.027 = 1788.1 m/s/s
Acceleration due to gravity (g) = 9.8 ms/s/s
Therefore mean g-force sustained = 1788.1/9.8 = 182.5 g
Moss:
18 in = 0.46 m
60 mph = 26.82 m/s
Average velocity = 26.82/2 = 13.41 m/s
Time = 0.46/13.41 = 0.034 s
Deceleration = 26.82/0.034 = 788.8 m/s/s
Mean g-force = 788.8/9.8 = 80.5 g
So Moss experienced less than half of the g-loading that Purley went through. John C(Quote)
Excellent. Thanks for that John C.
It all makes sense now. str8guy(Quote)
Actually, I just spotted an error… my bad. Deceleration for Purley should have been 1791.9 m/s/s, and hence his g-loading was an average of 182.8 g. A small difference, I know, but it does explain where the 179 g figure quoted by Saltire comes from. Whoever calculated that number used the standard simplification that g = 10 m/s/s. Wow, but I’m feeling geeky today. John C(Quote)
Thanks to John for the explaning the calculation. I’m very interested in the topic but never knew how they did it. PS geeky is cool, what can seem like small differences can make a huge difference to a calculation
saltire(Quote)