Body: Image is Everything... And More
The body of a racecar does more than make the car look like a car or act as a moving billboard for sponsors. The body affects how the car behaves at speed. The shape and material the body is made out of can either slow the car down or make it move through the air like a knife through hot butter.
On your everyday street car, the body serves several purposes. First and foremost, it’s a style statement. Some cars say “HEY! Look at me! I’m sleek and fancy and worth a lot of money, just like my driver,” while others say “There was absolutely no thought put into me, I’m just here to get paid.” The body also serves as part of the crash system (not a technical term, but the body is part of it). The body is designed such that, in the event of an accident, the energy goes into the car and around the driver, putting as little energy into the driver as possible. This is why when you get in a fender bender, you will most likely need a new front bumper. There are many traffic crashes where the car is completely destroyed – except for the cabin – and everyone walked away.
Look back to older-style cars like the 70’s, though, and you’ll see that those steel bodies didn’t suffer much damage, however the drivers and passengers didn’t get away so lucky. The stronger steel would mean the car was stronger and more resilient to dents and bumps, but the energy in crash has to go somewhere. In this case, the driver is where the energy went.
Fuel efficiency is the other main reason for the shape a car shell has. While the engine plays a large roll in fuel consumption, the efficiency at which the car moves through the air can help with fuel efficiency. Let’s compare a Dodge Challenger to a Honda Civic from the same year; for the sake of visualization, here’s what I’m looking at.
(Photos courtesy of Dodge and Honda. Both models are 2016)
Setting aside the gross differences in horsepower and price, look only at the shape of the car. The Challenger is like a soap box. Classic American muscle. No regard for aerodynamics, just raw power. And as such, the fuel economy sucks. It’s like driving a wall down the highway. Now look at the Honda. It’s more bubbly and flow-y (super technical terms, stop laughing), allowing the air to gracefully flow over it. Cleaner airflow = more efficient = better mpg.
Quick sidestep into physics for a moment. Air is a fluid, just like water or coffee or Monster or whatever else you use to get you going in the morning. So as the car moves through the air, the quality of the air flow is a huge factor in the efficiency of the car. Turbulent air causes drag and slows the car down. Same with lift (which can be both up and down). So that means the least amount of turbulent air flow and lift/downforce creates the least amount of drag. This is where the body comes in. The body channels the air around the car in a manner that produces the smoothest flow with the optimum amount of downforce (depending on the car’s requirements).
You’ll notice on racecars weird angles and wings and other various oddities that your normal car won’t have. This is to change the airflow around the car. Below are a few pictures of cars with super low drag coefficients. Notice how the body flows – the curves are smooth, the lines are tight, and the car just looks fast. The engineers behind these cars have whatever else is beyond Ph.D. in something probably related astrophysics and rocket science… Or something like that. They know their stuff.
Now let’s look at OR-15. The body is made of a carbon fiber nose cone, side panels, and side pods. Without these on there, you have an open chassis. A totally open car is not great for airflow, so we put a body on there. This also serves as a great place to put stickers. Each sticker is worth 5 horsepower. We have lots of stickers (Disclaimer: stickers don’t really add horsepower. Don’t believe anyone who says they do, they drive a stanced Civic). There is some rhyme and reason behind why we did what we did.
The nose is the first thing to go through the air, so you want to split the air as cleanly as possible. Ours isn’t the best thing out there, but it works. The side panels keep the air moving across the car. Without them, the air would go right back into the chassis, causing drag. The side pods direct air into the radiators. The shape of these is important because you want nice, clean flow through the radiator. Ideally, the flow should pull the air through and not be forced through. Imagine you have a vacuum hooked up to the back of the radiator. That’s what you’re going for.
Now, there are multiple ways of doing your body (stop it). You can have a body like ours that is a separate part from the chassis. You can also have what’s called a monocoque. I mentioned this in the chassis post a few weeks ago. A monocoque is where the body is a structural component, i.e. the body is the chassis. Per FSAE rules, the roll hoop and a few other parts must still be steel, but the rest of the chassis can be a monocoque. This a very expensive method and requires extra paperwork and testing, so most teams stay away from using this type of chassis/body. Below are pictures of other teams’ monocoques.
Aero packages can also be considered part of the body, since it’s a very visible component of the car and can have a huge effect on performance. Aero packages include the front wing, diffuser, and rear wing. To work effectively, you need all three, with a diffuser being most critical. A front wing directs the airflow over the tires, nose, etc. Starting with a smooth airflow is key. A diffuser sits under the car. While not easily visible, it does a fairly large portion of the work. I mentioned earlier that lift causes drag. As the car moves forward, air is shoved under the car at a slower speed than the air on top creating lift (this is how plane wings work). A diffuser attempts to channel the air so it gets out from the under the car quickly. Here’s one from a GT car.
Cool, right? These diffusers can work so well that the car is actually sucked down to the track. What’s the side effect? A super-fast car with minimum drag. Just be careful not to drop the car too low or you’ll be scraping the hell out of your very expensive underside.
Rear wings complete the aero package. Ranging from simple and elegant to outrageous and why-are-you-doing-that-to-your-poor-car-ness, some work and some are just for show. If you see it on a street car, probably just for show. If it’s on something like a racecar or high performance street car (Pagani, Koenigssegg, etc.), it’s there for a reason. Rear wings have seen some pretty cool advancements over the years, with the most recent being what’s called active aero.
Rear wings have gone from being a static trunk ornament to an active part of the car. F1 cars have been using them for the past 10 years as part of their Drag Reduction System (DRS). F1 rules say that a trailing car, when less than 1 second behind the leading car, can activate this system on certain parts of the track. When activated, the top section of the rear wing opens. While it may not seem like much, this can add anywhere from 10 to 20 or 30 mph to their top speed, enough to pass the car in front. When closed, an F1 aero package can produce nearly a hundred pounds of downforce, which is why F1 cars turn better at high speeds (opposite to what you would think, but yea. That’s how it works). Top Gear drove a Lotus F1 car. Click here to watch Jeremy Clarkson try to beat the Stig around the airport.
Some of your supercars now have active aero as well. The Pagani Hyura (“hu-why-ruh”) has four wings –two in front and two in back. At speed, these pop up slightly to keep the car on the road. When the car turns, the inside wings extend farther to bring the inside tires back down. So on a left-hand turn, the left wings would deploy. Under heavy braking, all the wings extend to dirty the airflow as much as possible (dirty airflow = drag = slow down faster). Bugatti Veyrons, Koenigsseggs, some Mercedes and Porsches, and the like all have active aero.
In FSAE, only a few teams run active aero, and it’s mainly for braking. At speed, the rear wing will open. Under heavy braking and below a certain speed, it’ll close. The mounting requirements for an active setup make the assembly slightly heavier than is ideal, so it’s a judgment call for the individual team.
Owls Racing did not run aero for several reasons. First and foremost, the car needs to be designed with an aero package in mind. You can’t just slap some wings and a diffuser on and call it a day. Flow simulations must be done, mounting styles and locations need to be determined, suspension geometry changes, and braking force goes through the roof. A lot of research goes into how these things look. Without it, the judges would hammer you for not doing the due diligence.
So there you have it. The shape of the car serves more than to just look pretty. On racecars, the biggest job the body does is direct airflow around the car to give it the cleanest flow possible. Aero packages are nice, however a lot of research and planning goes into building one that works well. How the car looks can be both functional and aesthetically pleasing. It’s all up to the engineers and artists behind the car.
