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Aerodynamic dragAerodynamic drag is the restraining force that acts on any moving body in the direction of the freestream flow. From the body's perspective (near-field approach), the drag comes from forces due to pressure distributions over the body surface, symbolized Dpr, and forces due to skin friction, which is a result of viscosity, denoted Df. Alternatively, calculated from the flowfield perspective (far-field approach), the drag force comes from three natural phenomena: shock waves, vortex sheet and viscosity.IntroductionThe pressure distribution over the body surface exerts normal forces which, summed and projected into the freestream direction, represent the drag force due to pressure Dpr. The nature of these normal forces combines shock wave effects, vortex system generation effects and wake viscous mechanisms all together.When the viscosity effect over the pressure distribution is considered separately, the remaining drag force is called pressure (or form) drag. In the absence of viscosity, the pressure forces on the vehicle cancel each other and, hence, the drag is zero. Pressure drag is the dominant component in the case of vehicles with regions of separated flow, in which the pressure recovery is fairly ineffective.The friction drag force, which is a tangential force on the aircraft surface, depends substantially on boundary layer configuration and viscosity. The calculated friction drag Df utilizes the x-projection of the viscous stress tensor evaluated on each discretized body surface.The sum of friction drag and pressure (form) drag is called viscous drag. This drag component takes into account the influence of viscosity. In a thermodynamic perspective, viscous effects represent irreversible phenomena and, therefore, they create entropy. The calculated viscous drag Dv use entropy changes to accurately predict the drag force.When the airplane produces lift, another drag component comes in. Induced drag, symbolized Di, comes about due to a modification on the pressure distribution due to the trailing vortex system that accompanies the lift production. Induced drag tends to be the most important component for airplanes during take-off or landing flight. Other drag component, namely wave drag, Dw, comes about from shock waves in transonic and supersonic flight speeds. The shock waves induce changes in the boundary layer and pressure distribution over the body surface. It is worth noting that not only viscous effects but also shock waves induce irreversible phenomena and, as a consequence, they can be measured through entropy changes along the domain as well. The figure below is a summary of the various aspects previously discussed.Automobile drag coefficientTatra T77 maquette by Paul Jaray, 1933The drag coefficient is a common metric in automotive design pertaining to aerodynamic effects. As aerodynamic drag increases as the square of speed, a low value is preferable to a high one. As about 60% of the power required to cruise at highway speeds is used to overcome aerodynamic effects, minimizing drag translates directly into improved fuel efficiency.For the same reason aerodynamics are of increasing concern to truck designers, where greater surface area presents substantial potential savings in fuel costs.Reducing dragReducing drag is also a factor in sports car design, where fuel efficiency is less of a factor, but where low drag helps a car achieve a high top speed. However, there are other important aspects of aerodynamics that affect cars designed for high speed, including racing cars. Notably, it is important to minimize lift, hence increasing downforce, to avoid the car becoming airborne. Increasing the downforce pushes the car down onto the race track—allowing higher cornering speed. It is also important to maximize aerodynamic stability: some racing cars have tested well at particular "attack angles", yet performed catastrophically, i.e. flipping over, when hitting a bump or experiencing turbulence from other vehicles (most notably the Mercedes-Benz CLR). For best cornering and racing performance, as required in Formula One cars, downforce and stability are crucial and these cars must attempt to maximize downforce and maintain stability while attempting to minimize the overall Cd value.Typical drag coefficientsThe average modern automobile achieves a drag coefficient of between 0.30 and 0.35. SUVs, with their typically boxy shapes and larger frontal area, typically achieve a Cd of 0.35–0.45. A very gently inclined windshield gives a lower drag coefficient but has safety disadvantages, including reduced driver visibility. Certain cars can achieve figures of 0.25–0.30, although sometimes designers deliberately increase drag to reduce lift.Some examples of Cd follow. Figures given are generally for the basic model. Some "high performance" models may actually have higher drag, due to wider tires and extra spoilers.Production carsCdAutomobileYear0.7 to 1.1typical values for a Formula One car ( HYPERLINK "" \o "Downforce" downforce settings change for each circuit)0.74Legends car0.7Caterham Seven0.65 to 0.75Lotus Seven1957–19720.6 +a typical truck0.57Hummer H220030.54Mercedes Benz G-Class0.51Citro?n 2CV19480.48Volkswagen Beetle (original design)[1][2]19380.48Rover Mini19980.48Volkswagen Cabriolet (Rabbit Convertible)[3]1979–19930.47Lancia Aprilia19370.46Ford Mustang (coupe)19790.45Range Rover Classic19900.45Dodge Viper RT/1019960.44Ford Mustang (fastback)19790.44Peugeot 30519780.44Peugeot 50419680.44Toyota Truck19900.43TVR 3000S1978-790.425Duple 425 coach(named for its low Cd by coach standards)19850.42Lamborghini Countach19740.42Triumph Spitfire Mk IV19710.42Plymouth Duster19940.41Smart Roadster20030.41Volvo 740 (sedan)19820.405Subaru Forester1997-2002[4]0.40Ford Escape Hybrid20050.40Nissan Skyline GT-R R3219890.40Chevrolet Astro1995-2005[5]0.39Ford Aerostar1995[6]0.39Honda Odyssey[disambiguation needed]1994-980.39Chevrolet Tahoe20060.39Dodge Durango20040.39Ford Escort 5 Door1981-1984[7]0.39Triumph Spitfire19640.385Nissan 280ZX19780.38Smart Roadster Coupé20030.38Smart ForTwo19980.38Lexus GX20030.38Mazda Miata19890.38Subaru Forester2009[8]0.38VW NewBeetle[9]without wing or spoiler 0.39[10]20030.374Ford Capri Mk III19780.372Ferrari F5019960.37BMW Z3 M coupe19990.37Jaguar XJ (X300/X308)0.37Renault Twingo0.37Volkswagen Tiguan20080.36Alfa Romeo 331983[11]0.36Cadillac Escalade hybrid20080.36Cadillac Fleetwood19960.36Volkswagen Jetta1985-1992[12]0.36Citro?n CX (named after the term for Cd)19740.36Citro?n DS19550.36Chrysler Sebring19960.36Ferrari Testarossa19860.36Ford Escort1997-2002[13]0.36Ford Mustang19990.36Honda Civic2001–20050.36Opel GT19690.36Subaru Impreza WRX[14]20100.36Saturn SW1996-2001[13]0.36Toyota Celica Convertible1994-1999[15]0.355NSU Ro 8019670.35Aston Martin Vanquish20040.35BMW Z4 M coupe20060.35BMW M3 Convertible20050.35Dodge Viper GTS19960.35Honda Del Sol1992–1997[13]0.35Jaguar XKR20050.35Lexus GX20100.35Lexus RX2003–20090.35MINI Cooper20080.35Nissan Cube20090.35Renault Clio (Mk 2)2002[16]0.35SSC Ultimate Aero2007–present0.35Tesla Roadster[17]20080.35Toyota MR-219980.35Toyota Sequoia20070.35Toyota Previa1991-1997[18][19]0.35Volvo 940 (sedan)19900.348Toyota Celica Supra (Mk 2)1982[20]0.342Toyota Celica (Liftback Model)19820.34Subaru Impreza WRX (4 Door)2009[21]0.34Aston Martin DB920040.34Chevrolet Caprice19940.34Chevrolet Tahoe hybrid20080.34Chevrolet C6 Corvette Z062005–present0.34Ferrari F4019870.34Ferrari 360 Modena19990.34Ferrari F430 F120040.34Ford Sierra19820.34Ford Puma19970.34Geo Metro (Hatchback)1995-1997[13]0.34Honda Prelude19880.34Mercedes-Benz SL (Roof Down)20010.34Nissan Altima1993-1997[22]0.34Peugeot 10619910.34Saturn SL21991-1995[23]0.34Subaru Legacy Wagon1993-1999[24]0.34Toyota Supra (with factory 3 piece turbo wing)1989–19900.34Toyota Corolla (Wagon)1993-1997[25]0.338Chevrolet Camaro19950.33Alfa Romeo Giulia (saloon)1962[26]0.33Audi A320060.33Acura Integra1993-2001[27]0.33Citro?n SM19700.33Honda Civic Hatchback1988-1991[13]0.33Dodge Charger20060.33Ford Crown Victoria19920.33Ford Fusion2010[28]0.33Ford Escort ZX21998-2003[29]0.33Honda Accord Sedan20020.33Lamborghini Murcielago20010.33Lexus RX20100.33Mazda RX-7 FC3C19870.33Nissan 200SX Coupe1995-1998[30]0.33Peugeot 20619980.33Peugeot 30919860.33Renault Modus20040.33Subaru Impreza WRX STi20040.33Saturn SL21999[31]0.33Toyota Corolla1993-1997[13]0.33Toyota Supra (without wing)1989–19900.329Chevrolet Corsica1989-2006[32]0.324Cobalt SS Supercharged20050.321Toyota Matrix2003-2008[33]0.32Volkswagen Golf Mk319910.32AMC Pacer1975–19800.32Ferrari California20080.32Buick Riviera19950.32BMW M3 Coupe20050.32Dodge Avenger19950.32Ford Taurus1992-1995[34]0.32Geo Metro (Sedan)1995-1997[13]0.32Honda Accord (Coupe)20020.32Honda NSX19900.32Honda Civic (Coupe)1992-1995[13]0.32Honda Civic (Hatchback DX)1996-2000[35]0.32Honda Civic (Sedan EX)1996-2000[36]0.32Mazdaspeed320070.32McLaren F119920.32Mercedes-Benz 190E 2.5-16/2.3-160.32Nissan Altima1998-2001[37]0.32Nissan 240SX Coupe1995-1998[38]0.32Nissan 300ZX19890.32Nissan Maxima19970.32Porsche 997 GT22008–present0.32Peugeot 40619950.32Peugeot 80619940.32Scion xB20080.32Suzuki Swift19910.32Toyota Celica19940.32Toyota Celica2000-2005[39]0.32Toyota Supra (N/A with wing and turbo models)19930.32Toyota Supra (with factory turbo wing)1987–19880.32Toyota Tercel Sedan1995-2000[40]0.32Volkswagen GTI Mk V20060.32Volvo V502004Production cars (continued)CdAutomobileYear0.315Saturn SL11996-1999[41]0.31Audi A4 B519950.31BMW 7-series20090.31Buick Park Avenue19960.31Cadillac CTS-V20050.31Cadillac CTS20040.31Citro?n AX19860.31Citro?n GS19700.31Eagle Vision19950.31Fiat Coupé1995[42]0.31Ford Falcon19950.31Ford Thunderbird1989-1997[43]0.304Ford Probe1988-1992[44]0.31Holden Commodore19980.31Honda Civic (Sedan)20060.31Honda Civic (Hatchback)1992-1995[13]0.31Infiniti G37 (Coupe)2008-present[45]0.31Kia Rio (Sedan)2001[46]0.310Lamborghini Diablo19900.31Lexus LFA(wing retracted)20100.31Mazda RX-7 FC3S19860.31Mazda RX-7 FD R1(R2)19930.31Mazda RX-820040.31Mazda MX-61992–19970.31Nissan Tiida / Versa20040.31Peugeot 30720010.31Porsche 997 Turbo/GT320060.31Renault 2519840.31Saab Sonett III19700.31Saturn SC220010.31Scion xA20040.31Toyota Avalon1995–20000.31Toyota Corolla1998-2002[47]0.32Toyota Paseo1995-1999[48]0.31Toyota RAV420060.31Toyota Supra (N/A; without factory wing)19930.31Volkswagen GTI Mk IV19970.31Volvo S40 2nd generation20030.30Audi 10019830.30Alfa Romeo 164 Sedan1988[49]0.30Ford Taurus1996-1999[50][51]0.30Honda Accord Sedan2003, 2005–20070.30Honda NSX20020.30Honda CRX DX/Si[52]19880.30Honda Odyssey[disambiguation needed]20050.30Hyundai Sonata20060.30Koenigsegg CCX20060.30Mitsubishi Eclipse20000.30Nissan 180SX19890.30Nissan 300ZX19830.30Nissan 350Z Coupe Base and Enthusiast models2003–20080.30Nissan 370Z Coupe(0.29 with sport package)2009[53]0.30Renault 19 16V19910.30Saab 9219470.30Toyota Sienna2003–20090.30Toyota Corolla2003-2008[54]0.295Ford Falcon19980.291Toyota Avalon20050.29Lexus CT 200h2011-present0.29Alfa Romeo 1551992[55]0.29BMW 1-Series (116i Sportshatch)20080.29Pontiac Firebird Trans Am(with optional W62 Aero Package and N89 Turbo Cast rims)19840.29BMW 8-Series1989-19990.29Chevrolet Corvette20050.29Chevrolet Corvette C5 Z0620020.29Daewoo Espero19900.29Dodge Charger Daytona19690.29Eagle Talon1990s0.29Ford Escape2010[56]0.29Ford Focus C-Max2003[57]0.29Honda Accord Hybrid2005, 20070.29Honda Accord Coupe2003, 2005–20070.29Honda CRX HF19880.29Infiniti G35 Sedan20080.29Lancia Dedra19900.29Lexus LS 40019900.29Lotus Elite19580.29Lotus Europa19660.29Mazda Millenia19950.29Mazda RX-7 FC3S Aero Package19860.29Mazda 320100.29Mazda RX-7 FD19930.29Mercedes-Benz SL (Roof Up)2001-present0.29Mercedes-Benz C-Class Sportscoupe20010.29Nissan 350Z Coupe Track and Grand Touring2007–20080.29Nissan Versa2007–20080.29Peugeot 3082007-present0.29Peugeot 4072004-20110.29Peugeot 6072000-20100.29Porsche Boxster2005-present0.29Subaru XT19850.29Subaru SVX19920.29Toyota Echo2000-2005[58][59]0.29Toyota Yards2006-20110.29Toyota Camry1996–20010.29Toyota Prius20010.29Volvo C7020000.288Chrysler Concorde1998–20010.286Chevrolet Corvette C620060.284Volkswagen Passat CC2008-present0.281Chevrolet Volt20100.28Audi A2 1.4 TDI20000.28Citro?n XM19890.28Citro?n C420040.28Lexus IS2006–present0.28Lexus LS40019980.28Mitsubishi Diamante19950.28Porsche 997 Carrera(with optional automatic spoiler, PDK transmission 0.30)20040.28Renault 25 TS19840.28Honda Civic Hybrid2003-2005[13]0.28Rumpler Tropfenwagen19210.28Saab 9-320030.28Toyota Camry / Lexus ES20010.28Opel Astra Coupe Turbo20030.28Hyundai Elantra20110.28Hyundai Sonata(0.25 for the Hybrid)20110.28Opel Omega A19860.27Nissan GTR20080.27Mazda 620090.27Audi A2 1.6 FSI20030.27Honda Civic Hybrid2006-0.27Hyundai Genesis20090.27Infiniti G35 Coupe(0.26 with "aero package")2003–20070.27Lexus GS20050.27Mazda6 (sedan and hatchback)[60]20080.27Mercedes-Benz W203 C-Class Sedan20010.27Nissan GT-R2007–20100.27Toyota Camry Hybrid20070.27Tucker Torpedo19480.27Tesla Model S20120.27Volkswagen Passat B5 (sedan)19970.27Mercedes-Benz S Class(0.268 with Sport Package)2000–20050.27Opel Insignia(0.26 in EcoFlex trim)2008–present0.26BMW E90 (0.26-0.30)2009[61]0.26Hotchkiss Gregoire[citation needed]19510.26Lexus LS 430(0.25 with air suspension)2001–20060.26Lexus LS 46020060.26Mercedes-Benz W221 S-Class2006-present0.26Mercedes-Benz E-Class2002-20090.26Nissan GT-R2010–present0.26Opel Calibra(8 valve version)19890.26Toyota Prius2004–20090.25Audi A2 1.2 TDI20010.25Honda Insight1999, 2003, 20050.25Toyota Prius20100.24Mercedes E 220 CDI Blue Efficiency European version only, other E-Class Coupe 0.28(0.25 sedan)(20090.212Tatra T77A1935[62][63] [64] [65]0.195General Motors EV11996I 0.170 II Chrysler Ghia Dart II 1955 I-Concept/experimental carsCdAutomobileYear0.39Porsche 91820100.27Avion[66]19860.26Alfa Romeo Disco Volante19520.25Dymaxion Car19330.25SmILE (an experimental car)19960.22Citro?n ECO 2000 Concept1981[67]0.22BMW Vision EfficientDynamics Concept20090.20Loremo Concept200620XX (Planned production)0.20Opel Eco Speedster Concept20030.19Alfa Romeo B.A.T. 7 Concept19540.19Dodge Intrepid ESX Concept19950.19Mercedes-Benz Bionic Concept[68](based on the boxfish)20050.186Schl?r's G?ttinger Ei19390.186Volkswagen XL120110.168Daihatsu UFE-III Concept2005[69]0.16General Motors Precept Concept (5 seats)20000.16Edison2 Very Light Car, Automotive X Prize winner[70]20100.159Volkswagen 1-litre car Concept20022013 (Planned production)0.157Li-ion Motors Wave II, Automotive X Prize winner[71]20100.15Aptera 2 Series 2e2011 (Planned production)0.147JCB Dieselmax land speed record holder20060.146Urbee Production vehicle20100.14Fiat Turbina Concept19540.137Ford Probe V Concept19850.125Sunraycer, solar race car19870.12Reflex 1000, solar cycle1996[72]0.117Summers Brothers Goldenrod Bonneville race car19650.08Fortis Saxonia (Shell Eco-marathon) Concept20070.075PAC-Car II (Shell Eco-marathon) Concept20050.07Nuna, World Solar Challenge winner2001–2007Drag areaWhile designers pay attention to the overall shape of the automobile, they also bear in mind that reducing the frontal area of the shape helps reduce the drag. The combination of drag coefficient and area - drag area - is represented as CdA (or CxA), a multiplication of the Cd value by the area.The term drag area derives from aerodynamics, where it is the product of some reference area (such as cross-sectional area, total surface area, or similar) and the drag coefficient. In 2003, Car and Driver magazine adopted this metric as a more intuitive way to compare the aerodynamic efficiency of various automobiles.Average full-size passenger cars have a drag area of roughly 8.50 sq ft (0.790 m2). Reported drag areas range from the 1999 Honda Insight at 5.10 sq ft (0.474 m2) to the 2003 Hummer H2 at 26.3 sq ft (2.44 m2). The drag area of a bicycle is also in the range of 6.5–7.5 sq ft (0.60–0.70 m2).Automobile examples of CdACdAAutomobile model2.50 sq ft (0.232 m2)1986 Twike[75]2.69 sq ft (0.250 m2)2009 Loremo3.00 sq ft (0.279 m2)2011 Volkswagen XL13.95 sq ft (0.367 m2)1996 GM EV15.10 sq ft (0.474 m2)1999 Honda Insight5.40 sq ft (0.502 m2)1989 Opel Calibra5.71 sq ft (0.530 m2)1990 Honda CR-X Si5.74 sq ft (0.533 m2)2002 Acura NSX5.76 sq ft (0.535 m2)1968 Toyota 2000GT5.80 sq ft (0.539 m2)1986 Toyota MR25.81 sq ft (0.540 m2)1989 Mitsubishi Eclipse GSX5.86 sq ft (0.544 m2)2001 Audi A2 1.2 TDI 3L5.88 sq ft (0.546 m2)1990 Nissan 240SX / 200SX / 180SX5.92 sq ft (0.550 m2)1994 Porsche 911 Speedster5.95 sq ft (0.553 m2)1990 Mazda RX76.00 sq ft (0.557 m2)1992 Subaru SVX6.00 sq ft (0.557 m2)1970 Lamborghini Miura6.08 sq ft (0.565 m2)2008 Nissan GTR6.13 sq ft (0.569 m2)1991 Acura NSX6.17 sq ft (0.573 m2)1995 Lamborghini Diablo6.24 sq ft (0.580 m2)2004 Toyota Prius6.27 sq ft (0.583 m2)1986 Porsche 911 Carrera6.27 sq ft (0.583 m2)1992 Chevrolet Corvette6.35 sq ft (0.590 m2)1999 Lotus Elise6.37 sq ft (0.592 m2)2000 Vauxhall VX220 N/A6.40 sq ft (0.595 m2)1990 Lotus Esprit6.41 sq ft (0.596 m2)2003 Smart Roadster Coupé6.54 sq ft (0.608 m2)1991 Saturn Sports Coupe6.57 sq ft (0.610 m2)1985 Chevrolet Corvette6.63 sq ft (0.616 m2)2001 Audi A26.63 sq ft (0.616 m2)1989 Ford Thunderbird6.66 sq ft (0.619 m2)1996 Citro?n Saxo6.77 sq ft (0.629 m2)1995 BMW M36.79 sq ft (0.631 m2)1993 Toyota Corolla DX6.80 sq ft (0.632 m2)2007 BMW 335i Coupe6.81 sq ft (0.633 m2)1991 Subaru Legacy6.90 sq ft (0.641 m2)1993 Saturn Wagon6.93 sq ft (0.644 m2)1982 Delorean DMC-126.94 sq ft (0.645 m2)2003 Smart Roadster6.96 sq ft (0.647 m2)1988 Porsche 944 S6.96 sq ft (0.647 m2)1995 Chevrolet Lumina LS7.02 sq ft (0.652 m2)1992 BMW 325I7.04 sq ft (0.654 m2)1991 Honda Civic EX7.06 sq ft (0.656 m2)2004 Vauxhall VX220 Turbo7.10 sq ft (0.660 m2)1995 Saab 9007.14 sq ft (0.663 m2)1995 Subaru Legacy L7.20 sq ft (0.669 m2)1995 Nissan Maxima GLE7.34 sq ft (0.682 m2)2001 Honda Civic7.39 sq ft (0.687 m2)1994 Honda Accord EX7.48 sq ft (0.695 m2)1993 Chevrolet Camaro Z287.57 sq ft (0.703 m2)1992 Toyota Camry7.69 sq ft (0.714 m2)1994 Chrysler LHS7.72 sq ft (0.717 m2)1993 Subaru Impreza8.02 sq ft (0.745 m2)2005 Bugatti Veyron8.70 sq ft (0.808 m2)1990 Volvo 740 Turbo8.70 sq ft (0.808 m2)1992 Ford Crown Victoria8.71 sq ft (0.809 m2)1991 Buick LeSabre Limited9.54 sq ft (0.886 m2)1992 Chevrolet Caprice Wagon10.7 sq ft (0.99 m2)1992 Chevrolet Blazer11.6 sq ft (1.08 m2)2005 Ford Escape Hybrid11.7 sq ft (1.09 m2)1993 Jeep Grand Cherokee16.8 sq ft (1.56 m2)2006 Hummer H317.4 sq ft (1.62 m2)1995 Land Rover Discovery26.5 sq ft (2.46 m2)2003 Hummer H2Automotive aerodynamicsA truck with added bodywork on top of the cab to reduce drag.Automotive aerodynamics is the study of the aerodynamics of road vehicles. The main concerns of automotive aerodynamics are reducing drag (though drag by wide wheels is dominating most cars), reducing wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. For some classes of racing vehicles, it may also be important to produce desirable downwards aerodynamic forces to improve traction and thus cornering abilities.An aerodynamic automobile will integrate the wheel arcs and lights in its shape to have a small surface. It will be streamlined, for example it does not have sharp edges crossing the wind stream above the windshield and will feature a sort of tail called a fastback or Kammback or liftback. Note that the Aptera 2e, the Loremo, and the Volkswagen 1-litre car try to reduce the area of their back. It will have a flat and smooth floor to support the Venturi effect and produce desirable downwards aerodynamic forces. The air that rams into the engine bay, is used for cooling, combustion, and for passengers, then reaccelerated by a nozzle and then ejected under the floor. For mid and rear engines air is decelerated and pressurized in a diffuser, loses some pressure as it passes the engine bay, and fills the slipstream. These cars need a seal between the low pressure region around the wheels and the high pressure around the gearbox. They all have a closed engine bay floor. The suspension is either streamlined ( HYPERLINK "" \o "Aptera Typ-1" Aptera) or retracted. Door handles, the antenna, and roof rails can have a streamlined shape. The side mirror can only have a round fairing as a nose. Air flow through the wheel-bays is said to increase drag (German source) though race cars need it for brake cooling and a lot of cars emit the air from the radiator into the wheel bay.Automotive aerodynamics differs from aircraft aerodynamics in several ways. First, the characteristic shape of a road vehicle is much less streamlined compared to an aircraft. Second, the vehicle operates very close to the ground, rather than in free air. Third, the operating speeds are lower (and aerodynamic drag varies as the square of speed). Fourth, a ground vehicle has fewer degrees of freedom than an aircraft, and its motion is less affected by aerodynamic forces. Fifth, passenger and commercial ground vehicles have very specific design constraints such as their intended purpose, high safety standards (requiring, for example, more 'dead' structural space to act as crumple zones), and certain regulations. Roads are also much worse (smoothness, debris) than the average airstrip. Lastly, car drivers are vastly under-trained compared to pilots, and usually will not drive to maximize efficiency.Automotive aerodynamics is studied using both computer modelling and wind tunnel testing. For the most accurate results from a wind tunnel test, the tunnel is sometimes equipped with a rolling road. This is a movable floor for the working section, which moves at the same speed as the air flow. This prevents a boundary layer forming on the floor of the working section and affecting the results. An example of such a rolling road wind tunnel is Wind Shear's Full Scale, Rolling Road, Automotive Wind Tunnel built in 2008 in Concord, North Carolina.Drag coefficientDrag coefficient (Cd) is a commonly published rating of a car's aerodynamic smoothness, related to the shape of the car. Multiplying Cd by the car's frontal area gives an index of total drag. The result is called drag area, and is listed below for several cars. The width and height of curvy cars lead to gross overestimation of frontal area. These numbers use the manufacturer's frontal area specifications from theMayfield Company Homepage.Some examples:Drag area ( Cd x Ft2)Year Automobile3.951996 GM EV15.101999 Honda Insight5.401989 Opel Calibra5.541980 Ferrari 308 GTB5.611993 Mazda RX-75.611993 McLaren F15.631991 Opel Calibra5.641990 Bugatti EB1105.711990 Honda CRX5.742002 Acura NSX5.761968 Toyota 2000GT5.881990 Nissan 240SX5.862001 Audi A2 1.2 TDI 3L5.921994 Porsche 911 Speedster5.951994 McLaren F16.001970 Lamborghini Miura S6.001992 Subaru SVX6.062003 Opel Astra Coupe Turbo6.082008 Nissan GTR6.131991 Acura NSX6.151989 Suzuki Swift GT6.171995 Lamborghini Diablo6.242004 Toyota Prius6.271986 Porsche 911 Carrera6.271992 Chevrolet Corvette6.351999 Lotus Elise6.771995 BMW M36.791993 Corolla DX6.811989 Subaru Legacy6.961988 Porsche 944 S7.021992 BMW 325I7.10Saab 9007.132007 SSC Ultimate Aero7.481993 Chevrolet Camaro Z287.571992 Toyota Camry8.701990 Volvo 740 Turbo8.711991 Buick LeSabre Limited9.541992 Chevy Caprice Wagon10.71992 Chevrolet S-10 Blazer11.631991 Jeep Cherokee13.101990 Range Rover Classic13.761994 Toyota T100 SR5 4x414.521994 Toyota Land Cruiser17.431992 Land Rover Discovery18.031992 Land Rover Defender 9018.061993 Hummer H120.241993 Land Rover Defender 11026.322006 Hummer H2Relationship to velocityThe frictional force of aerodynamic drag increases significantly with vehicle speed. As early as the 1920s engineers began to consider automobile shape in reducing aerodynamic drag at higher speeds. By the 1950s German and British automotive engineers were systematically analyzing the effects of automotive drag for the higher performance vehicles. By the late 1960s scientists also became aware of the significant increase in sound levels emitted by automobiles at high speed. These effects were understood to increase the intensity of sound levels for adjacent land uses at a non-linear rate. Soon highway engineers began to design roadways to consider the speed effects of aerodynamic drag produced sound levels, and automobile manufacturers considered the same factors in vehicle design. DownforceDownforce describes the downward pressure created by the aerodynamic characteristics of a car that allows it to travel faster through a corner by holding the car to the track or road surface. Some elements to increase vehicle downforce will also increase drag. It is very important to produce a good downward aerodynamic force because it affects the car’s speed and traction. ................
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