## 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.

## Airspeed Conversions (CAS/EAS/TAS/Mach)

The AeroToolbox airspeed conversion tool allows you to quickly convert between Calibrated Airspeed (CAS), Equivalent Airspeed (EAS), True Airspeed (TAS) and Mach number (M). You need to specify the altitude at which you would like to perform the calculation as well as any one of the four airspeeds stated above. Use the sliders to select an input speed and whether to apply a temperature deviation offset from the standard atmospheric value. The model is based on the US Standard Atmosphere of 1976.

Further information about the various aeronautical airspeeds quoted as well as the equations used in the mathematical model are presented below the calculator.

## NACA 5 Series Airfoil Generator

The calculator below can be used to display and extract coordinates of any NACA 5-series airfoil. The chord can be varied and either a blunt or sharp leading selected. The most common NACA 5-series airfoils are available from the drop-down menu; or alternatively you can design your own.
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## NACA 4 Series Airfoil Generator

The calculator below can be used to plot and extract airfoil coordinates for any NACA 4-series airfoil. The chord can be varied and the trailing edge either made sharp or blunt. Use the “Show Coordinates” button to export the resulting coordinate points to a spreadsheet or text editor.

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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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## Lifting Surface Correction Factor

The calculation below provides an estimation of the lifting surface correction factor used when compiling an estimation of the zero lift drag produced by the wing. This is described in the tutorial on the Drag Polar. The graph shown below 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 correction factor based on the digitization of the graph and an interpolation between datapoints. The methodology is described below.
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