Equivalent Sand Roughness

Most methods for estimating friction and profile drag of lifting surfaces and fuselages apply only to 'smooth' surfaces. If a surface is 'rough', additional drag is created. The program determines the actual level of turbulent boundary layer friction drag of rough surfaces by utilizing the equivalent sand roughness factor, a reference length, and Figure 4.77 in Airplane Design Part VI .

Type of Surface

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Aerodynamically smooth

0.0

0.0

Polished metal or polished wood

0.00167- 0.00667

0.00051- 0.00203

Natural sheet metal

0.01333

0.00406

Smooth matte paint, carefully applied

0.02083

0.00635

Standard camouflage paint, average application

0.03333

0.01016

Camouflage paint, mass-production spray

0.1

0.03048

Dip-galvanized metal surface

0.5

0.15240

Natural surface of cast iron

0.83

0.25298

As a practical matter, use the information as follows:

Application Type

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Light aircraft with standard sheet metal manufacturing methods

0.01333

0.00406

Business jets and jet transports with sheet metal manufacturing methods, but polished surfaces

0.0050

0.00152

Aircraft made of composites and polished surfaces

0.00167

0.00051

Military aircraft with camouflage paint applied in the factory

0.02083

0.00635

Military aircraft with camouflage paint applied in the field

0.1

0.03048