The skin friction and internal flow are treated like all other drag ratings. ( skin friction, internal flow and the drag from all wheels ( C D wheels)) such that equation (1) becomes: C D = The method adds the drag rating for only the first nine areas presented above, and the sum is put in equation (1): C D =īased on that work, equation (1) was modified such that the base factor (0.16) could be detailed. (p336-338), which gives a drag rating (the number under each figure) for shapes of different areas of a car body. The drag coefficient ( C D) can be estimated with a method presented in Handbook of Vehicle Design Analysis Drag coefficient is at the bottom of your screen. Navigation.C D = 0.347 C DA = 7.83 ft² C LA = 3.38 ft² Drag & lift coefficients For each category, select the most appropriate choice for your vehicle. Square of the lift coefficient, which is also based on the wing The drag coefficient in this equation uses the wingĪrea for the reference area. 7) (The outstandingĪerodynamic performance of the British Spitfire of World War II is partiallyĪttributable to its elliptic shaped wing which gave the aircraft a very lowĭrag coefficient Cd is equal to the drag coefficient at zero lift Cdo The efficiency factor (e) is equal to 1.0įor an elliptic distribution and is some value less than 1.0 for any The optimum (lowest) induced drag occurs for an elliptic distribution Long, slender, high aspect ratio wings have lower induced drag than Rectangular wing this reduces to the ratio of the span to the chord. (3.14159) times the aspect ratio AR times an The square of the lift coefficient Cl divided by the quantity: pi The induced drag coefficient Cdi is equal to Which changes the effective angle of attack along the wing and "induces"Ī drag on the wing. Because of pressureĭifferences above and below the wing, the air on the bottom of the wing isĭrawn onto the top near the wing tips. This additional source of drag is called theĪnd it is produced at the wing tips due to aircraft lift. Think of the drag coefficient as being composed of two main components a basicĭrag coefficient which includes the effects of skin friction and shape (form),Īnd an additional drag coefficient related to the lift of the aircraft. If we are considering an aircraft, we can The drag coefficient equation will apply to any object if we properly Problem and will predict an incorrect drag. Very different, we do not correctly model the physics of the real Of the viscous forces relative to the inertial forces. If the Reynolds number of theĮxperiment and flight are close, then we properly model the effects Recall that skin friction drag depends directly on the viscous In our discussions on the sources of drag, Reynolds number that expresses the ratio of inertial forces to The important matching parameter for viscosity is the It is even more important to match air viscosityĮffects. So it is completely incorrect to measure a dragĬoefficient at some low speed (say 200 mph) and apply that dragĬoefficient at twice the speed of sound (approximately 1,400 mph, The flow field and we must be sure to account for the wave drag in At supersonic speeds, shock waves will be present in Mach number is the ratio of the velocity to the Higher speeds, it becomes important to match Mach numbers between the Speeds (< 200 mph) the compressibility effects are negligible. Otherwise, the prediction will be inaccurate. To correctly use the dragĬoefficient, we must be sure that the viscosity and compressibilityĮffects are the same between our measured case and the predictedĬase. Object shape and inclination, but also the effects of air The drag coefficient contains not only the complex dependencies of (altitude), and area conditions using the drag equation. Predict the drag that will be produced under a different set of The reference area that is used to determine the coefficient. When reporting drag coefficient values, it is important to specify ) will affect theĪctual numerical value of the drag coefficient that is calculated. Through division we arrive at a value for the dragĪrea (wing area, frontal area, surface area. Tunnel) we can set the velocity, density, and area and measure This equation gives us a way to determine a value for the dragĬoefficient. Half the velocity V squared times the reference area A. Is equal to the drag D divided by the quantity: density r times Solve for the drag coefficient in terms of the other variables. Rearrangement of the drag equation where we The drag coefficient is a number that aerodynamicists use to modelĪll of the complex dependencies of drag on shape, inclination, and someįlow conditions.
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