So how does NASCAR test for coefficient of friction? Racecar Engineering is the worlds leading motorsport technology magazine. That's pretty much what they do: they drag an airplane tire around the track and measure how much force it takes. The trailing car suffers a reduction of downforce on its front tires, resulting in a loss of stability and handling coming out of turns. A much more common option is to replace the windshield wipers with lower profile wipers, or to only remove the windshield wiper on the passenger side of the vehicle, and even to fabricate a deflector to deflect the air up and over the wipers.[16]. However, the introduction of evocative coupes such as the Ford Mustang and Chevrolet Camaro meant fitting the production body style onto that sedan greenhouse proved challenging. An air dam is mounted underneath the front bumper to block air flow underneath the body. Although both methods can be accurate, nothing in the engineering world beats physical testing, where the true real world effects of the air passing over the car can be recorded to influence any design tweaks needed to the bodywork. [15], The effect that windshield wipers have on a vehicle's airflow varies between vehicles; however, they are often omitted from race vehicles and high efficiency concepts in order to maintain the smallest possible coefficient of drag. In motorsport, race car design is one big battle between low drag and downforce, with the happy-medium being active aerodynamics to decrease the induced drag from devices like large rear wings. Remember the example of measuring how much force it takes you to slide a file cabinet? With confidence in the CFD predictions and a need for more rear downforce, a multi-week CFD study began to refine the diffuser. Minimizing variables is always a good thing. This map was later used in wind tunnel testing at Windshear wind tunnel in Concord, North Carolina. These are all for normal tires, like the ones on your passenger car. In all cases, the reference area is the cross section orthogonal to the flow direction. Contoured deflectors, or tire spats, are often made as part of the front bumper in order to direct airflow around the tire without having any increase to the outward flow. However, achieving all that presented significant aesthetic challenges for manufacturers and NASCAR, since car designs not only had to be stretched at the rear, but also have different shapes on the left and right sides. Comparison of Aerodynamic Measurements on a Full-Scale NASCAR in Open and Closed Jet Test . If NASCAR makes measurements one year at Las Vegas with tire D1234 and the next year Goodyear bring tire D1235, how do you compare the two measurements? Do you know of any cars that have particularly low drag coefficients? Privacy Policy | Much like smooth wheel covers this modification reduces the drag of the vehicle by preventing any air from becoming trapped in the wheel well and assists in streamlining the body of the vehicle. In 2003, Car and Driver magazine adopted this metric as a more intuitive way to compare the aerodynamic efficiency of various automobiles. This offset generates rear side force, resulting in a restorative, positive yawing moment to the car. Source: Brad Bruno i This data was collected using a data acquisition system as well, and processed with a u0002u0004 u0001u0004 u0001 PC. The effects are especially beneficial on straightaways. Some of this was attributable to inadequate insulation and material changes in production, but a great deal was due to the ingestion of hot radiator air into the cockpit and inadequate evacuation of air from the cockpit. Terms & Conditions | drag area Finally, Goodyear constantly improves their tires. The Next Gen car is the first NASCAR vehicle to feature a full carbon fibre, aerodynamically-driven underbody. It also allows the car to correct itself when the driver oversteps the bounds of traction at the rear. A passenger car driving on the highway spends an estimated 60 percent of its energy overcoming air drag, a far greater percentage than tire friction and the energy needs of the drive train itself [source: Beauchamp]. This design can actually create too much airflow into the engine compartment, preventing it from warming up in a timely manner, and in such cases a grille block is used to increase engine performance and reduce vehicle drag simultaneously. But there are other forces involved too such as Newton's Law of Motion and centripetal force. This resulted in a laundry list of changes that were implemented at the Charlotte Roval test in mid-September, which included windscreen driver cooling ducts, slotted rear glass, a full right-side window, the elimination of left side NACA ducts into the cockpit, a NACA duct on the floor of the car and opening up the rear to evacuate the transaxle heat. on the actual NASCAR. A larger cross-sectional area increases drag because more air molecules have to be moved out of the way" [source: Leslie-Pelecky]. These issues had not arisen during single-vehicle testing, due to some seemingly minor design differences between the prototype vehicles and production. Overall, the path of development for the underwing was aggressive but successful, thanks to the strong correlation between CFD and the wind tunnel. {\displaystyle F={\tfrac {1}{2}}\times {\text{air density}}\times {\text{drag coefficient}}\times {\text{reference area}}\times {\text{speed}}^{2}} It was also decided to use a 14-point CFD ride height map, which included front and rear ride height, yaw and pitch sweeps to characterise as fully as possible the performance of the vehicle and any impact changes had. [23] A kammback is a truncated boattail. Reducing the balance required reversing this original development. Introducing a symmetric body eliminated the majority of these issues and presented a car that is a near spitting image of its street counterpart. Without grip aka friction there is no racing. Speaking of the tail, another key feature of NASCAR vehicles is the spoiler. Every issueprovidesunrivalled technical analysis ofeverything fromWorld Championship series including Formula 1, to grass roots racing. "Aerodynamics - Stock Car Aero Defined." "Passenger Car Aerodynamics." Aerodynamics is the study of how air moves -- especially how it interacts with solid, moving objects. PRO NOTE: This linear relationship doesnt hold for large downward forces. Passenger cars have become more shapely over the years as manufacturers discovered how streamlining can increase fuel efficiency, allowing a car to travel at the same speed using less horsepower. Studying downforce means paying attention to its opposing force, lift. Spoilers, front air dams and wings produce this effect. Racecar Engineering is the worlds leadingpublication for motorsport technology and engineering. Smooth wheel covers are hub caps with no holes in them for air to pass through. It has changed the culture and practice of car racing in ways some fans find infuriating. Right-side tires must deal with more force, so they are harder and dont wear as quickly. What worked in spring wont necessarily work in fall. A boattail can greatly reduce a vehicle's total drag. Early aero development focused on matching the evenly distributed downforce number. On the one hand, many drivers can remain competitive in a close race by piggybacking on the lead vehicle, taking advantage of the increased force and decreased engine strain. A stock Miata doesn't have a lot of drag, but it generates lift (positive Cl) while all the other body styles generate downforce (negative Cl). A speeding stock car pierces the air as it travels. While such application may be useful for racing, for most road vehicles this would produce minimal improvement in overall drag reduction. The deletion of parts on a vehicle is an easy way for designers and vehicle owners to reduce parasitic and frontal drag of the vehicle with little cost and effort. In the world of auto racing, it might be more important to augment the downward force the air exerts on the car's wheels. Most production sports cars and high efficiency vehicles come standard with many of these deletions in order to be competitive in the automotive and race market, while others choose to keep these drag-increasing aspects of the vehicle for their visual aspects, or to fit the typical uses of their customer base. This is a 3.48% decrease in the drag coefficient and a 0.12% decrease in the lift coefficient (or 0.12% increase in downforce).10 Jan 2018 Since underbody . Glad to see you are able to keep your sense of humor with everything going on! Another was at the rear of the car, where the production wheel tubs further closed off the rear of the boot (trunk) area, sealing in hot air from the transaxle cooler. Reported drag areas range from the 1999 Honda Insight at 5.1sqft (0.47m2) to the 2003 Hummer H2 at 26.5sqft (2.46m2). The application of new parts and concepts onto the vehicle design are easier to include when in the design stage of a vehicle, rather than in aftermarket (automotive) parts, however, the fabrication of these parts assists in the streamlining of the vehicle and can help greatly reduce the drag of the vehicle. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. In most racing vehicles this is eliminated by covering the entire underside of the vehicle in what is called an under tray. The drag coefficient is a common measure in automotive design as it pertains to aerodynamics. In a streamlined design the air flows around the vehicle rather than through; however, the grille of a vehicle redirects airflow from around the vehicle to through the vehicle, which then increases the drag. But this exterior feature could be knocked off the vehicle, resulting in a sudden loss of downforce and high probability of an accident [Source: Cislunar Aerospace]. Aerodynamics remains a vibrant and young field of engineering, with many innovations still to come down the road. The modern, curvaceous designs minimize the force that air creates against the car's motion, and the result is a sleeker, faster car. It keeps the pressure underneath the car down, preventing lift. Another factor in moving toward a symmetric body was the evolution of the NASCAR racing calendar. Because speed is, obviously, the main factor in NASCAR races, aerodynamics is a crucial element in stock car design. 1 Answer: Abyss lim The most successful design change was the rear deck lid modification which resulted in a drag coefficient of 0.472 and a lift coefficient of 0.816. After eight years of racing, though, it was time to update the look of NASCARs top series to more closely resemble their roadgoing counterparts, which too had evolved over that stretch. In the real world, road cars only really need to decrease drag force, especially in this age of fuel consumption obsession. Its much harder to slide, so it takes you 75 lbs of force to move it. Testament to all three of the manufacturer aero teams is they all passed their submission tests on the first attempt. Dividing the weight of the tire assembly by the force needed to pull it gives them the coefficient of friction. The drag coefficient is a unit-less value that denotes how much an object resists movement through a fluid such as water or air. A well-prepared student entering a world of possibility and excitement, with a proud group of invested parents standing behind it, wishing it every success. You hear number for stock-car tire coefficients of friction around 1.0 to 1.5. A large share of the drag on a NASCAR race car is due to the highly separated underbody flow (see Figure 6). If the coefficient of friction of our file cabinet on some surface is 1.5, it means you have to pull the 100-lb cabinet with 150-lbs of force to slide it. Youve measured the coefficient of friction. Either louvred or open designs were permitted, based on the styling desires of the OEM, which is apparent when comparing the different design paths of the three vehicles. The main purpose of a rear spoiler in a vehicle's design is to counteract lift, thereby increasing stability at higher speeds. Streamlining the body requires assumptions about the surrounding airspeed and characteristic use of the vehicle. 12h ago. 28 January 2009. Cookie Policy. In an effort to draw in higher energy air from the outside of the floor, the rear of the rocker boxes is ramped upward, and the diffuser outer tunnels feature a double hump design. This leads to various interpretations of what is acceptable, and often lengthy lists of revisions from NASCAR in terms of qualitative styling, as compared to the production vehicle. So its not like you can say that Bristol always needs x amount more friction in the upper lane. Please copy/paste the following text to properly cite this HowStuffWorks.com article: "How Stock Car Aerodynamics Work" To accommodate the maximum suspension droop, these outer tunnels then move back downwards before resuming an upward trajectory. The new MSN, Your customizable collection of the best in news, sports, entertainment, money, weather, travel, health, and lifestyle, combined with Outlook, Facebook . This relation also allows an estimation of the new top speed of a car with a tuned engine: Or the power required for a target top speed: Average full-size passenger cars have a drag area of roughly 8sqft (0.74m2). Stock cars circling oval tracks to the left are more likely to show their right face in a spin. One example was the use of Kevlar composites to form the seals between the exhaust and the cockpit, which appear to have resulted in greater conduction into the steel chassis of the car since no heat is dissipated from the composite surfaces. Lift is an aerodynamic force that acts perpendicular to the airflow around the body of the vehicle. With the bodies submitted and approved, work began on converting the bodies into composite components. Lets examine the coefficients of friction, , for tire rubber on various surfaces. = The following is a small part of the story of its development from an aerodynamic standpoint, as told by managing director of aerodynamics for NASCAR, Dr Eric Jacuzzi. NASCAR has given enormous concentration on aerodynamics in racing in which drivers rely solely on aerodynamic techniques in pursuit of podium finishes. After nearly nine months of private development testing, all three OEMs submitted their vehicles at the end of August 2021 for three grueling days at Aerodyn wind tunnel in Mooresville, North Carolina. On the lift-off safety front, NASCAR evaluated the vehicle in CFD before testing at the Automotive Center for Excellence (ACE) in Oshawa, Canada and the Chrysler Technical Centers Aero Acoustic wind tunnel in Auburn Hills, Michigan. The dark line is for a sphere with a smooth surface, while the lighter line is for the case of a rough surface. Theyre probably also reading the temperature of the track at each spot. Its a blunt instrument, but a historical element that completes the stock racecar look. "Going With the Flow." Its significance to the sport cannot be understated, and its promise has already yielded gains with increased team charter values and new team ownership entering. A front air dam is often used which extends from the very front of the vehicle down to the lowest part of the vehicle. It was decided to keep its kick line (the most forward edge) as far toward the centre of the car as possible. It was understood early in the process that the reduction of rear side force due to body symmetry would impact the useable aero balance, but initially it was a guessing game, although not entirely without value. This design reduces drag; however, it may cause the brakes to heat up more quickly because the covers prevent airflow around the brake system. As the car cuts a path through the air, some air molecules collide with the front bumper, producing resistance. Perhaps the greatest departure of the Next Gen (Gen 7) vehicle from the Gen 6 is the move to a coupe-like roof line, and the symmetry of the rear of the vehicle. Two cars drafting together can go 3 to 5 miles an hour faster than a solo car, and extra trailing cars add a little more speed, which is why the drivers spend so much time in single-file.