The drag coefficient (C_d, C_x or C_w, depending on the country) is a dimensionless quantity that describes a characteristic amount of aerodynamic drag caused by fluid flow, used in the drag equation. Two objects of the same frontal area moving at the same speed through a fluid will experience a drag force proportional to their C_d numbers. Coefficients for rough unstreamlined objects can be 1 or more, for smooth objects much less. In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement... Aerodynamics is a branch of fluid dynamics concerned with the study of gas flows, first analysed by George Cayley in the 1800s. ... A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... In physics, the drag equation gives the drag experienced by an object moving through a fluid. ...

    explanation of terms on drag equation page.

Flow around a plate, showing stagnation.

Usually A is the projected frontal area. For example, for a sphere A = πr², (i.e., not the surface area.) In physics, the drag equation gives the drag experienced by an object moving through a fluid. ... Image File history File links drawing by Meggar File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links drawing by Meggar File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

The drag equation is essentially a statement that, under certain conditions, the drag force on any object is approximately proportional to the square of its velocity through the fluid. The required conditions are that the Reynolds number of the flow around the object must be high enough to create a turbulent wake (larger velocities, larger objects, and lower viscosities make for larger Reynolds numbers), and that the object does not approach the speed of sound in the fluid. An object moving through a gas or liquid experiences a force in direction opposite to its motion. ... For other uses, see Force (disambiguation). ... This article is about velocity in physics. ... In fluid mechanics, the Reynolds number may be described as the ratio of inertial forces (vsρ) to viscous forces (μ/L) and, consequently, it quantifies the relative importance of these two types of forces for given flow conditions. ... Turbulent flow around an obstacle; the flow further away is laminar Laminar and turbulent water flow over the hull of a submarine Turbulence creating a vortex on an airplane wing In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by low-momentum diffusion, high momentum convection, and... A wake is the region of turbulence immediately to the rear of a solid body caused by the flow of air or water around the body. ... For other uses, see Viscosity (disambiguation). ...

At low Reynolds number, that is for small objects, low velocities or high viscosity fluids, the flow around the object is laminar, C_d is no longer constant but depends on velocity, and F_d is proportional to v instead of v². Laminar flow (bottom) and turbulent flow (top) over a submarine hull. ...

A C_d equal to 1 would be obtained in a case where all of the fluid approaching the object is brought to rest, building up stagnation pressure over the whole front surface. The top figure shows a flat plate with the fluid coming from the right and stopping at the plate. The graph to the left of it shows equal pressure across the surface. In a real flat plate the fluid must turn around the sides, and full stagnation pressure is found only at the center, dropping off toward the edges as in the lower figure and graph. The C_d of a real flat plate would be less than 1, except that there will be a negative pressure (relative to ambient) on the back surface. The overall C_d of a real square flat plate is often given as 1.17. Flow patterns and therefore C_d for some shapes can change with the Reynolds number and the roughness of the surfaces. Stagnation pressure is the pressure at a stagnation point in a fluid flow, where the kinetic energy is converted into pressure energy. ...

C_d in automobiles

Main article: Automobile drag coefficients

The drag coefficient is a common metric in automotive design, where designers strive to achieve a low coefficient. Minimizing drag is done to improve fuel efficiency at highway speeds, where aerodynamic effects represent a substantial fraction of the energy needed to keep the car moving. Indeed, aerodynamic drag increases with the square of speed. Aerodynamics are also of increasing concern to truck designers, where a lower drag coefficient translates directly into lower fuel costs. The drag coefficient is a common metric in automotive design, where designers strive to achieve a low coefficient. ... Designers at work in 1961. ... Fuel efficiency, in its basic sense, is the same as thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. ... For the Daft Punk song, see Aerodynamic (song). ... For other uses, see Truck (disambiguation). ...

About 60% of the power required to cruise at highway speeds is taken up overcoming air drag, and this increases very quickly at high speed. Therefore, a vehicle with substantially better aerodynamics will be much more fuel efficient. Additionally, because drag does increase with the square of speed, a somewhat lower speed can significantly improve fuel economy. This was the major reason for the United States adopting a nationwide 55 mile per hour speed limit during the early 1973 oil crisis as slower traffic would save scarce petroleum. 55 mph speed limit being erected in response to the National Maximum Speed Law. ... The 1973 oil crisis began in earnest on October 17, 1973, when the members of Organization of Arab Petroleum Exporting Countries (OAPEC, consisting of the Arab members of OPEC plus Egypt and Syria) announced, as a result of the ongoing Yom Kippur War, that they would no longer ship petroleum... Petro redirects here. ...

C_dA

While 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 is C_dA (or C_xA), a multiplication of the C_d value by the area.

In aerodynamics, the product of some reference area (such as cross-sectional area, total surface area, or similar) and the drag coefficient is called drag area. In 2003, Car and Driver adapted this metric and adopted it as a more intuitive way to compare the aerodynamic efficiency of various automobiles. Average full-size passenger cars have a drag area of roughly 8.5 ft² (.79 m²). Reported drag area ranges from the 1999 Honda Insight at 5.1 ft² (.47 m²) to the 2003 Hummer H2 at 26.3 ft² (2.44 m²). For the Daft Punk song, see Aerodynamic (song). ... In aerodynamics, the zero-lift drag coefficient is a dimensionless parameter which relates an aircrafts zero-lift drag force to its size, speed, and flying altitude. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... Cover of Car and Driver from age of psychedelic lettering Car and Driver is an American automotive enthusiast magazine. ... This article or section does not adequately cite its references or sources. ... The H2 SUV/SUT/Hydrogen is the second vehicle sold under the Hummer marque of General Motors. ...

More C_dA examples

This value is extremely useful as either the area or drag coefficient alone are not enough to be used in any equation. Sometimes it is not possible to get either value, but it might be possible to deduce it. For a skydiver example below, it is possible to deduce C_dA from the mass of the diver and equipment and terminal velocity. Skydiver C_dA examples are in both  ft² and m² units.
Kg redirects here. ... Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector), defined by distance in metres divided by time in seconds. ...

C_d examples

Cessna 172RG 1964 Cessna 172E 1965 Cessna F172G 1971 Cessna 172 The early Cessna 172 Skyhawks had no rear window and featured a square fin design, like this 1957 model 1977 Cessna 172XP 1977 Cessna 172M Cessna 172R Panel of C-GLFC The Cessna 172 Skyhawk is a four-seat... The Cessna 182, marketed under the name Skylane, is a four-seat, high performance, single-engine, light airplane. ... 1968 Cessna 310N The Cessna 310 was the first twin-engine aircraft design from Cessna to enter production after World War II. The 310 first flew on January 3, 1953 with deliveries starting in late 1954. ... The Learjet 24 is a six to eight seat (two crew and four to six passengers) twin-engined, high speed business jet. ... The Lockheed F-104 Starfighter was a single-engined, high-performance, supersonic interceptor aircraft that served with the United States Air Force (USAF) from 1958 until 1967. ... “F-4” redirects here. ... The Boeing 747, sometimes nicknamed the Jumbo Jet,[4][5] is a long-haul, widebody commercial airliner manufactured by Boeing in the United States. ... Description Role: Research Aircraft Crew: one, pilot Dimensions Length: 50. ... For other uses, see Bicycle (disambiguation). ... In fluid mechanics, the Reynolds number may be described as the ratio of inertial forces (vsρ) to viscous forces (μ/L) and, consequently, it quantifies the relative importance of these two types of forces for given flow conditions. ... This article or section does not adequately cite its references or sources. ... Cross-country skiing (skating style) in Einsiedeln, Switzerland. ... The Empire State Building is a 102-story Art Deco skyscraper in New York City, New York at the intersection of Fifth Avenue and West 34th Street. ... The Eiffel Tower (French: , ) is an iron tower built on the Champ de Mars beside the River Seine in Paris. ...

See also

• Automobile drag coefficients
• Automotive aerodynamics
• Drag (physics)
• Drag equation
• Drag crisis
• Lift coefficient
• Pitching moment

The drag coefficient is a common metric in automotive design, where designers strive to achieve a low coefficient. ... Automotive aerodynamics is the study of the aerodynamics of road vehicles. ... An object moving through a gas or liquid experiences a force in direction opposite to its motion. ... In physics, the drag equation gives the drag experienced by an object moving through a fluid. ... In fluid dynamics, drag crisis is a phenomenon in which drag coefficient drops off suddenly as Reynolds number increases. ... The lift coefficient (CL) is a number associated with a particular shape of an airfoil, and is incorporated in the lift equation to predict the lift force generated by a wing using this particular cross section. ... The pitching moment of an airfoil, in aerodynamics, is a moment produced by a vertical force applied at a distance forward or aft from the aerodynamic center of the airfoil, causing the aircraft to pitch up or down[1]. References ↑ Preston, Ray (2006). ...

References

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Image File history File links This is a lossless scalable vector image. ...

External links

• A. Filippone's Advanced Topics in Aerodynamics: Drag
• Danish Wind Industry Association: Aerodynamics of Wind Turbines: Drag
• Improving Aerodynamics to Boost Fuel Economy
• Tel Aviv University reduces drag on trucks by 10%
• Simple roll-down test for measuring Cd and Crr for cars and bikes
• Variation of drag coefficient with Reynolds number
• Drag of Blunt Bodies and Streamlined Bodies