Aerodynamic Lift, Drag and Moment Coefficients

In the previous post we introduced the four fundamental forces acting on an aircraft during flight: Lift, Drag, Thrust and Weight and examined how they interact with one-another. We are now going to look more closely at the two aerodynamic forces Lift and Drag. We will look at the relationship between the two forces, study how they interact with one another, and learn how to non-dimensionalize the resulting forces. Let’s do this!

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Reynolds Number Calculator

The Reynolds number is an important dimensionless ratio used to predict whether a flow is laminar or turbulent and is defined as the ratio of inertial to viscous forces in a fluid. The calculator below can either be used in manual mode (density, viscosity or kinematic viscosity known); or alternatively use it in conjunction with the standard atmosphere calculator to quickly determine the Reynolds number in a standard atmosphere for any altitude and temperature combination.
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Turbulent Skin Friction Coefficient

The variation in turbulent flat plate skin friction coefficient with Reynolds number is calculated below. This is used when compiling an estimation of aircraft parasitic drag as described in the tutorial on the Drag Polar. The skin friction is graph originally published in USAF Stability and Control Datcom [1] and reproduced in Roskam Part VI Chapter 4.2 [2]. The calculator provides an estimation of the skin-friction coefficient based on a curve fit; the methodology is described below the graph.
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Wing to Fuselage Interference Factor

The calculation below provides an estimation of the interference factor between a wing and a fuselage. This is used when compiling an estimation of aircraft parasitic drag as described in the tutorial on the Drag Polar. The wing/fuselage interference graph was originally published in USAF Stability and Control Datcom [1] and reproduced in Roskam Part VI Chapter 4.2 [2]. The calculator provides an estimation of the skin-friction coefficient based on the digitization of the graph and an interpolation between datapoints; the methodology is described below the graph.
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