Boeing has deployed a high-tech paint that measures pressure on wind-tunnel models

BY WILLIAM COLE

It looks like paint you'd find in a hardware store. But it has properties that are helping Boeing aircraft designers to estimate closely the performance of airplanes in actual flight.

Pressure-sensitive paint - a high-tech coating that allows surface pressures on wind-tunnel models to generate colorful images on a digital video screen - is proving valuable in the testing of the latest Boeing products.

"The process complements the conventional experimental and computational methods that aircraft designers have available to them," says Pressure Sensitive Paint program manager Mike Benne. "It increases the knowledge they have about a vehicle in flight and is a valuable addition to their toolbox. It's a good example of how Phantom Works has found and deployed an idea that has the potential to reduce the cycle time and cost of wind tunnel testing while improving the quality of the results and the performance of the ultimate design."

The technology has found wide acceptance within Boeing for current and future commercial and military products. Pressure Sensitive Paint has been used on the Joint Direct Attack Munition, the F-15E, the High Speed Civil Transport and the X-32 programs. The Phantom Works' pressure-sensitive paint team recently demonstrated the process to the Sonic Cruiser program. The Ford Motor Co. is even using it to test cars and vans.

When Pressure Sensitive Paint is used in wind tunnel testing, digital cameras record the brightness of the painted surface, and a computer calculates the distribution of surface pressure based on the brightness. The pressure over most of the surface of the model can be examined on an interactive, three-dimensional color-coded display. Color-coded images may also be printed, and the numerical pressure data used to compute forces and various aerodynamic coefficients.

The conventional method of obtaining surface pressure is to drill a very small hole, called a pressure tap, into the model surface and connect the hole to a remote pressure transducer by a tube routed inside the model. A conventional "pressure model" contains hundreds, even thousands, of pressure taps. Pressure sensitive paint generally reduces the number of taps that must be hand crafted and connected individually in the model. Some taps are still used to calibrate the measured surface pressure.

Pressure taps are difficult to use in thin wing sections, highly curved areas, or on vehicle control surfaces. Pressure-sensitive paint, on the other hand, offers the potential for continuous measurement over all types of surfaces.