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 |
|
|
|
|
|
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 |
|
|
|
|
|
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 |