Commercial aircraft exterior cleaning optimization

The time interval between aircraft exterior cleaning has traditionally been based upon experience and maintenance patterns rather than scientific reasoning. Therefore, the relationship between skin friction drag, aircraft exterior cleaning intervals, and fuel consumption has never been fully established or understood by airline operators. This work represents an attempt to investigate the effects of subtle changes in surface roughness on skin friction drag. Experiments were set up using several differently roughened surfaces. The results were analyzed and compared to a smooth reference surface which showed a clear correlation between skin friction drag with surface roughness. Surface roughness was reduced by approximately one-third as a result of aircraft washing in measurements taken from a sample of commercial aircraft. Using regression analysis of the surface measurements and relationships established in the experimentation, an optimum time interval between aircraft exterior cleaning was found. The optimum time frames recommended weighed the effects of the aerodynamic deterioration, due to surface roughness, against the costs involved in cleaning an aircraft. As a result a time interval between aircraft cleaning that maintains aerodynamic efficiency and cost practicality was achieved.