Zero-lift drag coefficient
Mathematically, zero-lift drag coefficient is defined as CD,0 = CD − CD,i, where CD is the total drag coefficient for a given power, speed, and altitude, and CD,i is the lift-induced drag coefficient at the same conditions. Thus, zero-lift drag coefficient is reflective of parasitic drag which makes it very useful in understanding how "clean" or streamlined an aircraft's aerodynamics are. For example, Sopwith Camel biplane of World War I festooned with wires, bracing struts, and fixed landing gear, had a zero-lift drag coefficient of approximately 0.0378, compared to 0.0161 for the streamlined P-51 Mustang of World War II which compares very favorably even with the best modern aircraft.
The zero-lift drag coefficient can be more easily conceptualized as the drag area (f) which is simply the product of zero-lift drag coefficient and aircraft's wing area ( where S is the wing area). Parasitic drag experienced by an aircraft with a given drag area is approximately equal to the drag of a flat square disk with the same area which is held perpendicular to the direction of flight. The Sopwith Camel has a drag area of 8.73 sq ft (0.811 m2), compared to 3.80 sq ft (0.353 m2) for the P-51. Both aircraft have a similar wing area, again reflecting the Mustang's superior aerodynamics in spite of much larger size. In another comparison with the Camel, a very large but streamlined aircraft such as the Lockheed Constellation has a considerably smaller zero-lift drag coefficient (0.0211 vs. 0.0378) in spite of having a much larger drag area (34.82 ft² vs. 8.73 ft²).
Furthermore, an aircraft's maximum speed is proportional to the cube root of the ratio of power to drag area, that is:
Estimating zero-lift drag
As noted earlier, CD,0 = CD − CD,i.
The total drag coefficient can be estimated as:
where η is the propulsive efficiency, P is engine power in horsepower, ρ0 sea-level air density in slugs/cubic foot, σ is the atmospheric density ratio for an altitude other than sea level, S is the aircraft's wing area in square feet, and V is the aircraft's speed in miles per hour. Substituting 0.002378 for ρ0, the equation is simplified to:
The induced drag coefficient can be estimated as:
Substituting for CL gives:
where W/S is the wing loading in lb/ft².
- ^ a b c d Loftin, LK, Jr.. "Quest for performance: The evolution of modern aircraft. NASA SP-468". http://www.hq.nasa.gov/pao/History/SP-468/cover.htm. Retrieved 2006-04-22.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Drag coefficient — In fluid dynamics, the drag coefficient (commonly denoted as: cd, cx or cw) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment such as air or water. It is used in the drag equation,… … Wikipedia
Lift-to-drag ratio — In aerodynamics, the lift to drag ratio, or L/D ratio ( ell over dee in the US, ell dee in the UK), is the amount of lift generated by a wing or vehicle, divided by the drag it creates by moving through the air. A higher or more favorable L/D… … Wikipedia
Drag (physics) — Shape and flow Form drag Skin friction 0% 100% 10% 90% … Wikipedia
Lift coefficient — The lift coefficient ( or ) is a dimensionless coefficient that relates the lift generated by a lifting body, the dynamic pressure of the fluid flow around the body, and a reference area associated with the body. A lifting body is a foil or a… … Wikipedia
Drag equation — In fluid dynamics, the drag equation is a practical formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid. The equation is attributed to Lord Rayleigh, who originally used L2 in place … Wikipedia
Lift (force) — For other uses, see Lift. Boeing 747 8F landing A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the … Wikipedia
Pressure coefficient — The pressure coefficient is a dimensionless number which describes the relative pressures throughout a flow field in fluid dynamics. The pressure coefficient is used in aerodynamics and hydrodynamics. Every point in a fluid flow field has its own … Wikipedia
Aerodynamic drag — Note This article is currently under renovation, and may, at times, appear disjoint. Please see the [http://en.wikipedia.org/wiki/Talk:Aerodynamic drag Discussion Page] . Introduction Aerodynamic drag refers to the retarding force on moving… … Wikipedia
Oswald efficiency number — The Oswald efficiency, similar to the span efficiency, is a correction factor that represents the change in drag with lift of a three dimensional wing or airplane, as compared with an ideal wing having the same aspect ratio and an elliptical lift … Wikipedia
F-104 Starfighter — infobox Aircraft name= F 104 Starfighter caption= A Fokker built, German owned F 104G in USAF markings in August 1979 type= Interceptor aircraft, fighter bomber national oigin = United States manufacturer= Lockheed designer= Clarence Kelly… … Wikipedia