Questions regarding the cause of the crash that sent Team Penske's Helio Castroneves flipping backwards through the air during practice for the Indy 500 have circulated since the No. 3 Chevy took flight at approximately 12:45 p.m. ET., and while the Brazilian's airborne maneuver was definitely spectacular to watch, the reason for the backflip is rather simple.

To start, the crash has nothing to do with aero kits. Rear blowovers like the one experienced by Castroneves have been happening for decades by cars with large underwings. It happened for the first time in the 1980s when underwings were introduced, and they will continue to happen in any form of motorsports where they’re used in high-speed vehicles.

And the aerodynamic safety changes incorporated by IndyCar for 2015 – the holes in the floor to reduce downforce, and the brand-new wicker that runs down the center of the tub – aren’t designed to prevent an Indy car from taking off by lifting at the rear.

The new-for-Indy center wicker.

The reason for the No. 3 lifting and flipping was due to the car’s aerodynamics working in the opposite direction they were designed to function. Castroneves entered Turn 1 on his first flying lap and lost control of the rear of the car. The three-time Indy 500 winner attempted to catch the car by turning into the slide--which initially worked – but it wiggled a second time and quickly swapped ends. The total time from pointing straight prior to the second wiggle and being completely backwards took just 1.08 seconds.

While accelerating forward, an Indy car generates significant amounts of downforce, and in Indy 500 trim, most of it comes from the wing-shaped floor. Chevy (and Honda) use relatively small front wings and tiny rear wings. The long, wide underwing is where most of the car’s downforce is generated, and with air flowing in from the front and out through the back, it functions like an inverted airplane wing and sucks the car to the ground

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.

Seen from below, the "holes" at the front of the floor and the curved underwing profiles.

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