Testing Capabilities for Evaluating Passive Coatings for Aircraft Drag Reduction

Riblets are an attractive method of reducing viscous drag on aircraft. However, the cost of applying and maintaining riblets is justified only if it is cost effective. Ease of riblet application and robustness of the riblets during flight and maintenance have been two obstacles to the adoption of riblets for drag reduction in the military and commercial fleets. Assuming these obstacles are addressed, optimization of riblet designs is needed so that the drag reduction is maximized. To optimize riblet designs, means of fabricating and testing new riblet designs are needed. We propose to develop means of testing riblets in a low-speed wind tunnel in order to evaluate different designs using a riblet assessment protocol (RAP). To enable this, we must first identify ways to fabricate riblet designs suitable for testing in low-speed wind tunnels and to develop means of measuring any drag reduction realized by these designs. Key to this effort is the development of an elastomeric balance capable of the milli-newton measurements required for measuring the decrease in drag realized by novel riblet designs. Using both this balance and scaled riblet test articles, we will demonstrate the measurements necessary to assess riblet designs through the riblet assessment protocol.