What is lift and drag coefficients ?

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    Lift coefficient: Lift coefficient is equal to the lift produced divided by dynamic pressure times wing area or surface area. We can determine the value of lift from the wind tunnel test by setting the velocity of air, density, and measuring the area of the wing surface. This value of the lift can be used to determine the lift coefficient. Lift can be then predicted by different sets of velocity, density, and area conditions by using the equation. Lift Coefficient also contains the effect of air viscosity and compressibility. For low Mach numbers compressibility effects, are negligible. However, compressibility effects increase with an increase in Mach number. Viscosity and compressibility effects should be the same between the measured case and predicted case. For viscosity Reynolds number of experimental real case should be close.   

    Drag coefficient: Drag coefficient of a surface is equal to the drag divided by the dynamic pressure times the area. Like lift coefficient drag coefficient can also be determined by wind tunnel by setting the value of viscosity, density, and area. After obtaining the drag coefficient drag can be predicted by setting different values of velocity, density, and area using the drag equation. Like the lift coefficient, the drag coefficient is also affected by viscosity and compressibility. Therefore, these two effects should be the same for the measurement and predicted cases. Mach number should be matched for a higher Mach number as the compressibility effect increases. With an increase in Mach number. At a supersonic speed, shock waves are also produced which are accountable for wave drag in the drag coefficient. For viscosity effects, the Reynolds number should be close to experimental and real measurements. For an aircraft, induced drag is also to be considered. The total coefficient of drag for an aircraft is equal to the sum of the drag coefficient at zero lift and induced drag coefficient.

    Answered on 3rd August 2020.
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