In the last two days there have been two high speed accidents at Indianapolis, involving cars using the Chevy speedway kits. Both Helio Castraneves and Josef Newgarden hit the wall at turn one and flipped their cars. Firestone have since spoken out over Josef's incident citing a cut in the tyre which deflated it ahead of the accident. However, Helio's accident remains a source of some mystery, the footage I have seen suggests he was struggling to rebalance the car as he entered the turn. We must remember that these speedway aero kits are new for 2015 and will undoubtedly force the teams and drivers to think differently.
I immediately questioned Chevy's endplate-less rear wing configuration when I saw the render, as it will clearly cut drag but what about the requirement of downforce? The underfloor is a carry over from the original DW12 design and so everything has been designed to complement it and compliment it must. The relationship between the rear wing and floor is often forgotten about but it's symbiotic, both in terms of drag and downforce. I suspect without the endplates the rear wing 'stalls' at a certain speed (ie the boundary layer on the surface is so large the flow detaches) ordinarily the endplates would control this 'stall' retaining its connection to the under floors airflow structure, keeping a semblance of downforce. When changing direction there is a fraction of time that passes as the car decelerates for which the airflow needs to 're-attach', stability can become a massive issue if it doesn't happen quickly enough. Paramount to this is ride height, with any change disturbing the consistency of downforce that is generated by the underfloor and rear wing. Therefore, I wonder in the moments leading to Helio's accident did the car lose downforce sufficiently to start the chain of events that led to the car ending up on its roof?
At the end of the day practice is for finding these sort of limits and with the kits being so new the teams will be pushing the envelope, to find the perfect setup.
The other thing that has irked me about the incident is a piece that I read about why the flip happened after the accident, especially as the information is a little light on facts but comes from a source from 'within' the sport: http://www.racer.com/more/viewpoints/item/116730-pruett-why-helio-castroneves-car-flipped
Pruett claims that ordinarily the floor 'functions like an inverted wing' creating downforce, what he fails to explain is that a racecar is in 'ground effect' when it generates downforce, meaning the relationship between the cars tunnels and the ground needs to stay relatively stable for the given speed. He goes onto make the following statement:
"Turn an Indy car around at 200mph and feed that air backward through the underwing, and it will behave like a normal airplane wing and generate lift. With enough air speed, and pressure build-up in the tunnels--which Castroneves obviously achieved, lift turns into liftoff".
I get the whole "dumbing down" of technical content, it's my niche... and although it makes for easy reading I'm sorry but in my opinion it isn't wholly accurate, the lift in my opinion came from another source of aerodynamic complication we have seen far too often in the past, in LMP racing (see below) and is the reason their fenders now have cut outs in the top.
You may argue that the Indy wheels are exposed on the top, however, they weren't designed to work at extreme yaw angles, perhaps that's why we see this as the car goes sideways (yes that is air between the tyre or tire for my American friends and the track):
Granted being in reverse led to a stall in the floor tunnels but for me the lift came as a consequence of the bumper pod design. Racecars aren't meant to work at such extreme yaw angles and at that speed and certainly not in reverse. Accidents will happen and you can't mitigate for every circumstance, I think the most important question is what led to the corrections that Helio had to make? Here's the video for you to draw your own conclusions....@liamthenry @ScarbsF1 things were already in motion when Helio tried to correct things. pic.twitter.com/vXw1UxPMXe— Matt Somerfield (@SomersF1) May 14, 2015