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Massive Shadow DN4 wreck at Road America

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  • #16
    That's an insanely cool video. Thanks for sharing.
    Center Grove Trojans
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    Center Grove Jr. Trojans
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    • #17
      Originally posted by flatlander_48 View Post

      The other thing that happens is the air gets packed under the front wheel wells and that contributes to the lift. That’s why IMSA and WEC prototypes now are mandated to have the wheel wells vented. The static weight distribution is also a contributor...
      I could be completely wrong but I thought the fender holes were about sideways blowovers. Together with the "big honking fin".

      It did occur to me after my first post that I didn't address an important aspect. As the nose gains ground clearance, more air is hitting the bottom of the car at a high rate of speed. This air acts to lift the front of the car more, which allows more air to hit the bottom of the car, which in turn lifts it more... until the car flips.

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      • #18
        No, the fin acts to increase the silhouette from the side and would create a higher side force due to more area. The fin helps with straight line stability and reduces some of the turbulence as the air approaches the wing, thereby making the wing more effective.

        Here’s what MulsanneMike had to say on his site, mulsannescorner.com:

        Finally we get to the “moment”. Bringing all these issues, and a couple more, together to see why this occurred. Without the benefit of having witnessed all of the events, I can’t analyze the exacting specifics and will make some generalizations. In most cases it would appear that the CLR had leading traffic ahead of it. This certainly took downforce off the car’s nose. In most cases the CLR was experiencing an “attitude” change, it was either cresting a undulation in the track, running over a curb, something appeared to be changing the car’s disposition, if ever so slightly, leading to a sudden (if in itself insignificant) change in forces.

        So working forwards, downforce is reduced off the front of the car due to the turbulence coming off the leading car, the CLR’s pitch is changing due to terrain variations leading to additional downforce lost, the CLR is more pitch sensitive than most (due to those large overhangs and short wheelbase) and these issues lead to a larger than expected downforce change and the nose lifts as the low pressure being produced underneath the CLR approaches zero at the front and suddenly the lift created by the cockpit and top side bodywork begins to take effect lifting the nose even further. The rear wing is still working pretty well, firmly planting the rear wheels and providing a nice pivot point, the rear wheel centerline. As the nose lifts at the front, at the back of the car the rear diffuser, hanging way out past the rear wheel centerline, gets closer to the track and begins to generate even more downforce further accentuating the lift. By now the underside is exposed and the lift being generated by the cockpit, coupled with the face of the exposed underfloor, completely takes over and the car gets airborne in a rather dramatic fashion.


        Prior to what I copied, he talked about the car’s dimensions. The car had the shortest wheelbase and longest overhangs compared to its competition. Similarly the Shadow has a fair amount of front overhang and a big flat area underneath...

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        • #19
          Mulsanne Mike, saying the fin is for side-on blowovers:

          Yes, "honking great fins," as one put it, will unfortunately be adorning all the cars next year as the ACO's solution for reducing sudden high-speed yaw-induced blow overs. We understand this concept was developed 18 months ago and presented by Porsche to the FIA as a possible solution. We've also been told that when combined with the domed 20 mm skid (proposed by Wirth Research and adopted at the beginning of the 2009 seasons) the fin shows to be pretty effective. But ironically we're told that the fin itself generates a substantial over turning moment. But this over turning moment is offset by the fin's ability to kill the lift created by the leading side rear wheel arch when the car is suddenly yawed 90°. But more than one aerodynamicists has indicated that the fin also disrupt airflow to the rear wing in normal yaw moments (cornering, 0-5°), leading one to wonder if the solution was throughly thought out and sorted beyond a day or two in a full scale yaw tunnel? We're sure it has been, but we still would have hoped that the ACO would have commissioned an independent aerodynamics research study (similar to the Piper study that helped establish the 2004 LMP regulations related to yaw safety) to properly investigate the problem instead relying on what appears to be a grab bag of solutions put forth by various groups working separately."

          Elsewhere he points to Mike Rockefeller's crash at Le Mans as showing the effectiveness of the fin, keeping the car grounded.

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          • #20
            Originally posted by SteveK51 View Post
            Mulsanne Mike, saying the fin is for side-on blowovers:

            Yes, "honking great fins," as one put it, will unfortunately be adorning all the cars next year as the ACO's solution for reducing sudden high-speed yaw-induced blow overs. We understand this concept was developed 18 months ago and presented by Porsche to the FIA as a possible solution. We've also been told that when combined with the domed 20 mm skid (proposed by Wirth Research and adopted at the beginning of the 2009 seasons) the fin shows to be pretty effective. But ironically we're told that the fin itself generates a substantial over turning moment. But this over turning moment is offset by the fin's ability to kill the lift created by the leading side rear wheel arch when the car is suddenly yawed 90°. But more than one aerodynamicists has indicated that the fin also disrupt airflow to the rear wing in normal yaw moments (cornering, 0-5°), leading one to wonder if the solution was throughly thought out and sorted beyond a day or two in a full scale yaw tunnel? We're sure it has been, but we still would have hoped that the ACO would have commissioned an independent aerodynamics research study (similar to the Piper study that helped establish the 2004 LMP regulations related to yaw safety) to properly investigate the problem instead relying on what appears to be a grab bag of solutions put forth by various groups working separately."

            Elsewhere he points to Mike Rockefeller's crash at Le Mans as showing the effectiveness of the fin, keeping the car grounded.
            That’s a similar to what happens at the front when it begins to lift, but yaw is not involved, so the effect is working on both sides. NASCAR folks also discovered this many years ago. I don’t remember the specific reason, but someone took the wheel wells out of the front and it was discovered that it killed much, if not all, of the front end lift...

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