The aerospace world

A researcher at Northwestern University's McCormick School of Engineering and Applied Science (Evanston, Illinois) has developed an X‐ray device that is believed to be the first practical means of detecting corrosion hidden beneath the surface of an aircraft's body. When the “virtual core drill” is positioned against the side of an aircraft, a computer screen shows an image of the layers of metal under the surface of the skin. If one or more of those layers are corroded, the amount of corrosion will be recorded on the screen, to an accuracy of 1/1.000 of an inch. The virtual core drill or, more technically, a Compton backscatter depth profilometer, was invented by Larry Lawson, research scientist at the McCormick School's Centre for Quality Engineering and Failure Prevention. The device sends con‐trolled X‐ray beams through the plane's body and detects those X‐rays that are deflected back at an angle near 90° from each layer. Today, whenever corrosion is detected on aircraft, the section must be dismantled, the layers pulled apart, and a micrometer used to measure the thickness. If the corrosion represents more than 10 per cent. the part must be replaced. The virtual core drill can eliminate the downtime and the damage that occurs when aircraft have to be torn apart for inspection. The new device includes a 200lb scan head, which is attached to the plane using feet shaped like suction cups while supported by a flexible boom mounted on a vehicle resembling a fork‐lift truck. The vehicle moves the scan head up and down the aircraft. The drill is equipped with the most sensitive detector known, the sodium iodide scintillator. The drill provides the same kind of information, layer by layer, as would be provided by cutting a plug out of the aircraft with a core drill, except that the aircraft is undamaged. Radiation exposure also is minimal.