The thing about a good argument is that it is not mere contradiction but a series of propositions which are designed to establish a reasonable position. The thing about a bad argument is that it contains assertions which when contradicted by evidence, is still asserted as though it were fact. It is the latter that I come across when people assert that the rear wing on the NASCAR Car of Tomorrow caused flips and blowovers. I think that this car is unjustly maligned and that the accusation made of its rear wing is misplaced.
The reason why the NASCAR Car of Tomorrow had a rear wing as opposed to the simple spoiler which had been in place since the mid 1980s, was itself in response to "the big one" which had become a feature in NASCAR racing. Cars travelling together at close proximity in very big packs, were beginning to have accidents of 20 cars in them. By keeping the rear of the car more grounded, it was hoped that the cars would track straighter and finally enter the world of modern motor racing. By adding end plate vanes to the rear of new rear wings, it was hoped that cars would track straighter and truer.
During 2007 and 2008 though, the accepted story that the rear wing was causing flips and apparently backed up by cars flipping and blowing over, ran away from the truth, and partway through the Car of Tomorrow's run, the rules were reverted back to an older style spoiler. The flips still happened but don't let the truth get in the way of a good story. This post is about arguing against the story with a series of propositions about why things work the way they do; instead of how they are imagined to be.
This is a tale of forces, of wings, and of air. Let's begin with the air.
Air is a physical substance which has weight. Air is a mixture of various gases, of mostly mostly nitrogen (78%), some oxygen (21%) and other gases such as water vapour, argon and carbon dioxide. All of these gases are made of various molecules of the gases in constant motion. Air pressure is created by these molecules moving around. Things that move create forces because things are made of stuff and stuff when accelerated, creates a force.
Things that fly, make use of those forces, either by moving through the air or by floating in it. Moving air is a swirly mass of forces which creates lift, which is itself a force, which lifts things like kites, balloons, birds, and aeroplanes. You can move air and make it do what you want it to do, with fins, blades, vanes, planes, et cetera et cetera et cetera.
An aeroplane as the name suggests, is a device which moves a thing through the air, with a series of planes which we call wings. A wing is just a fancy plane, which is used to control air moving over and under it. Aeroplane wings are shaped to make air move faster over the top of the wing. When air moves faster, the pressure of that particular air decreases. The pressure of the air on the top of a wing is less than the pressure on the bottom of the wing. Since practically the entirety of the physical world is about cancelling forces, an aeroplane wing wants to cancel the difference in air pressure on top of it and does this by trying to move upwards. This upwards movement is useful because the difference in air pressure creates a force on the wing that lifts the wing up into the air.
Physics is completely apathetic and agnostic when it comes to the orientation of wings in air; so if you turn a wing upside down, instead of lift being produced as a force to suck the wing upwards, downforce is produced to suck the wing downwards. The reason why wings are used on racecars and high-performance vehicles is because that downforce pulls the car downwards; which makes the tyres grip the road better. Since the only point of contact between a car and the ground is through its tyres, then having a wing pull the car into the ground is useful as it means that power is more efficiently transferred through the tyres into the road and also helps a car go through a corner better. Making a car go through a corner better means that when the corner straightens out, more power can be put to the road faster. The point of a racecar is to go around a track as quickly as possible.
However, if you turn that same wing backwards to the direction of travel because the car has spun, then you are no longer presenting the same shape of wing to air. Instead what is being oresented is a shape which because it was designed to face in the other direction, is now tilted upwards well beyond its stall angle, and where instead of the traailing edge having an attached layer of boundary air at higher pressure which creates downforce, that trailing side is now in turbulent air and is creating eddies.
Downforce is not a push force because air hits the front of the wing but rather, a pull force as the whole device is sucked downwards to try and cancel an area of lower pressure. When the wing faces backwards, there is a baffling push force trying to push the wing upwards but no pulling suck force which creates lift on the other side.
I know that this might require some rudimentary thinking but in order for that wing to present itself backwards to the air in the direction of travel, it means that the whole car must have turned around immediately before it. This is where the real world makes liars out of people claiming that the wing caused the Car of Tomorrow to flip. Instead of that wing being the first thing to present itself to the air, the thing that presents itself is the whole side of the car and then underside of the car. The most dramatic examples of the underside of a car presenting itself to the air and causing a car to flip, happened at Le Mans when the Mercedes-Bens CLK prototypes flipped twice going down the Mulsanne Straight.
The Car of Tomorrow's rear wing was no bigger than about 6" x 75". This means that there is a nominal presentation area of 450 square inches. The underside of a NASCAR Cup Car is bigger than 135" x 78" or 10,350 square inches. This is an area a mere 23 times larger. Who is likely to win in a fight? An army of 450 or an army of 10,350? An 8 pound baby or a 184 pound boxer? There is no contest.
If you look at the statistics for the number of flips per year (fpy) then the real world yet again makes liars out of people claiming that the wing caused the Car of Tomorrow to flip.
It is possible to count every single flip and blowover in the entire history of NASCAR. I have only selected the first 73 years of data as the period of the so-called Gen-7 car is currently being run and is therefore incomplete. The Car of Tommorrow was Gen-5:
All flips:
Gen 1: 1948-1966 - 72 (3.78py)
Gen 2: 1967-1980 - 20 (1.53py)
Gen 3: 1981-1991 - 32 (2.90py)
Gen 4: 1992-2006 - 70 (5.00py)
Gen 5: 2007-2012 - 25 (4.16py)
Gen 6: 2012-2021 - 19 (1.90py)
If you drill down into that data for the flips and blowovers for the Car of Tomorrow we find two periods both with the rear wing and without it.
Gen 5: 2007-2012 - 25 (4.16py)
fpr w wing = 14/156 = 0.0897fpr
fpr w/o wing = 11/115 = 0.0956fpr
There was actually a weak tendency for cars to flip more after they changed the rear wing back to a spoiler.
If you really want to explore this further, then the Society of Automotive Engineers, ran models in water to experimentally address the issue at the time.
https://www.sae.org/publications/technical-papers/content/2011-01-1432/
There have been claims that the rear wing on the NASCAR Car of Tomorrow (COT) race car causes lift in the condition where the car spins during a crash and is traveling backwards down the track at high speed. When enough lift is generated, the race car can lose control and even become airborne. At least in part, to address this concern, a new rear spoiler was designed by NASCAR to replace the wing and prevent this dangerous condition. This paper looks at the flow characteristics of both the rear wing and the new spoiler using particle image velocimetry (PIV) to provide qualitative analysis as well as flow visualization. In particular, the interaction of these downforce devices with "roof flaps" (which are designed to prevent lift) is explored.
- Society of Automotive Engineers, Jan 2011.
The punchline of this technical paper was that it found no correlation between the Car of Tomorrow's rear wing and flips and blowovers and the SAE couldn't actually produce a flip or a blowover by running the models backwards into the flow as presented. The paper concluded that the cause was something else but made no experimental attempt to discover that cause.
Actually the very big data set suggests that the most massive spike in flips and blowovers happened not as a result of adopting the Car of Tomorrow's rear wing but before then, from season 2001 onwards. I think that the actual reason is likely a function of the beginning of "tandem drafting" which is actually cars locking bumpers and pushing each other. The data spike tells the story that the rates of flipping and blowovers, have more to do with how aggressive everyone is, rather than the cars themselves. When you have cars pushing each other, that is by far and a way a larger set of forces than the downforce at the rear of a car. Drivers pushing and punting each other, which seems to have become more acceptable after about 2001, I think is a far more likely and reasonable reason for flips and blowovers. 3000 pounds of car belting into each other and being used as bludgeons to bash each other with, is the far more reasonable reason.
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