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New jet aircraft, designed and tested to the latest specifications, have suffered numerous structural failures of a type not previously encountered. These failures are concentrated in the flap, wing trailing-edge, empennage, and after fuselage areas. They have occurred both as sudden, large-scale skin failures and as progressive cracking during the service life of the airplane. Recent investigations have shown that these failures resulted from a previously unsuspected cause. Test programs by several aircraft companies have proved that jet-engine noise during ground run-up or take-off is the cause. More recent investigations have indicated that aerodynamic noise can produce failures in other areas or can add to the damage caused by engine noise. A proof test of an airplane surface is usually required because the present state of the art limits the amount of accurate analysis that can be used to design the surface for resistance to this sonic fatigue. Many methods have been used during the past few years to test for resistance to sonic fatigue. Each company has developed its own facility and there appears to be little or no correlation of results among facilities. References (1) through (6)2 describe some of these test facilities and methods. Most of the testing has been done to solve particular problems which existed at the time of the test, and very little design information has resulted.
Vreeland, Robert H.
Design Specialist, Douglas Aircraft Co., El Segundo, Calif.