

There are times in life that you simply kick yourself for not thinking of something that is now screamingly obvious. I suspect a number of people in sportscar racing, myself included feel that way today. When two Daytona Prototypes took off at high speed during testing at the Florida track, the initial response was one of shock. But once the dust had settled the root causes of the accidents seem obvious, and make you wonder “why did nobody think of this?” but perhaps it is only obvious once it has happened.

“We don’t design these cars to go backwards,” TUSC rules boss Scot Elkins said. “We got on the phone last night with all of the relevant aerodynamicists that have worked on the project from every aspect, from Ford to Pratt & Miller to Multimatic. We’ve got everybody on the horn and we’re looking through it and seeing where we’re going.

“It is an unintended consequence but I think anything that goes backwards at 180 mph has the potential for doing that. We don’t necessarily know that the diffuser is what caused that but we’re going through and doing some studies on that. We started last night.”

The cause of the two crashes during the test can be traced back to the 2014 update kits fitted to the DP rules cars. In simplified aerodynamic terms these consist of a new more powerful rear diffuser and an improved rear wing, along with some other changes this gives a 60% increase in downforce. In mechanical terms the engines have had a power hike giving them over 50bhp more to play with. The upshot of it is that the cars are quite simply quite a bit faster to allow them to live with the pace of the LMP2 designs being introduced into the prototype class next year.

So why did the cars fly? as I see it there are two or three reasons all of which are interconnected. The first of these is the tyres. Increasing a cars average speed over a lap, regardless of downforce, it will increase the demands on the tyre. If you increase downforce this too will increase the tyre loads and as speed increases so does the load on the tyres, a 60% increase in downforce is unavoidably a significant increase in tyre load. The increase in downforce was part of an attempt to increase the apex speed of the Daytona Prototypes (where the LMP2s are much faster) and reduce the top speed (where the LMP2s are much slower), the side effect of this is a hugely increased tyre load especially on the rears on Daytona’s very long high banked turns.

As far as I am aware the Continental tyres used on all of the cars use the same compounds and construction as the 2013 cars ran on, but are now being asked to withstand substantially more. This is not a new thing, cast your minds back to the United States Grand Prix in 2005 where the outside rear Michelin tyre was unable to withstand the loads through the low banking at Indianapolis. The bankings at Daytona are much higher increasing the load even more, and whilst a DP even with its downforce hike does not produce as much downforce as a F1 car it is significantly heavier.

So it seems likely that with increased tyre load you will get an increase in probability of tyre failures and in both of the testing accidents at Daytona the drivers reported punctures. Which brings me onto cause number two the aerodynamics. It seems to me that much of the additional downforce on the car is made at the rear of the car from the new diffuser and wing. I have not fully examined the update kits yet, and have not looked at any wind tunnel data but it seems to me that the aerodynamic centre of pressure on the car will probably have moved rearwards, creating a tendency towards front lift, this in itself is not a great issue as long as it is not too extreme and the teams will likely dial it out using ballast and setup.



As Yannick Dalmas illustrates perfectly at Road Atlanta when the aerodynamic forces (allied to the overall weight distribution) are too far rearward , in this case due to following another car closely the car can launch.

The combination of the two factors above, if a rear tyre fails at high speed it is by definition going to drop that corner of the car down and raise the opposite corner. With a rearward centre of pressure this can by itself be enough to launch the car skyward, as Anthony Davidson demonstrates below.



Finally the tyre failure or simple driver inadequacy can cause the car to spin, with the air hitting the side of the car it can essentially act as a wing with a curved top and a flat floor, causing the car to lift. As Stephane Ortelli demonstrates below.



In the wake of a spate of crashes Racecar Engineering conducted its own independent full scale wind tunnel testing using the Radical SR9 to investigate the causes of these accidents – the full findings were published in the December 2008 edition of the magazine – which can be read below.



But in short the reason for the flights is a simple matter of physics; a Daytona Prototype weighs around 1000kg and at Daytona they were running into the first corner at approximately 190mph. A Cessna 172 Skyhawk has a similar maximum takeoff weight.

When you total up the aerodynamic surface area of the Daytona Prototype it is not all that different to that of the Cessna, indeed it may even be larger. The Cessna takes off at under 100mph, so it is clear that if the yaw angle or pitch angle is such that the air gets under the car over a certain speed then a flight is likely.

So what can be done to stop Daytona Prototypes flying?

This will be the question taking up a lot of time at Daytona Beach and Concord, North Carolina right now and realistically with the Roar Before the 24 taking place in just over a month and a half the solutions are limited.



The ACO faced this problem with the Le Mans Prototypes some years ago as the clips above illustrate, and they embarked on a comprehensive programme of changes to the cars and indeed the track at Le Mans itself. A new floor was mandated with chamfered edges which prevented the air from getting under the car, when that alone was not found to be enough the more recent and more extreme measures of the large fin on the rear bodywork and air extractor holes were also mandated for LMP cars.

It would seem logical that elements like this should be mandated for Daytona Prototypes, but the reality is that the floor alone would render the cars uncompetitive against the LMP2 runners. Also the amount of time required to properly implement these parts is substantial, so in short there is almost certainly no time left for this. The same may be the case for NASCAR style roof flaps, which again would require extensive testing.

The tyres seem to be an issue, it remains to be seen if Continental is able to develop a new construction able to withstand the increased loadings of the DP’s in time for the Roar Before the 24 test or even in time for the Rolex 24. So it is certainly questionable whether the 2014 aerodynamic updates can be run at all with these tyres.

However it would be safe to run the Daytona Prototypes in 2013 specification, as the problem did not present itself in the many mile of running conducted with the DPG3 cars in that trim. This would leave the DP spec cars a long way off the pace however, but it seems to be the most likely solution unless the tyre issues can be resolved, but that would not resolve the aerodynamic issue.

One thing is certain it is a very interesting time in North American sportscar racing.