Machine Design

Smart paints measure pressure

Determining aerodynamic load distributions on aircraft wings or Indy race cars usually requireswind-tunnel testing, placing pressure sensors at various points on the test surface, then estimatingloads on areas between sensors. The accuracy of this method relies on the number of taps, usingcorrect interpolating procedures, and the surface complexity of the test object. A simpler, morequantitative method is to use pressure-sensitive paints from Innovative Scientific Solutions Inc.,Dayton, Ohio. It takes advantage of a phenomenon in which certain luminescent compounds are quenchedand their luminescence declines in the presence of oxygen. When the luminescent compounds are in anoxygen-permeable coating on an object, the level of quenching and, therefore, the level ofluminescence, is inversely proportional to the static pressure on the object surface.

To measuredynamic or static loads, technicians apply pressure-sensitive paint to a wing, illuminate it with alight containing frequencies that will excite the compounds in the paint, then use a CCD camera torecord luminescent light from the painted surface. The camera's output is processed to produce digitalmaps of pressure distributions on the painted area. Paints can also be formulated to show temperaturedistributions as well. So far, most work done with pressure-sensitive paints has been on aircraft, butautomotive companies and race teams are also getting interested.

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