THE study of aeroelasticity has been an important discipline since the advent of ight. In particular, one of the primary goals of aeroelastic analysis is to predict the ight conditions associated with the onset of an instability called utter. 1 The mechanism associated with this instability may be somewhat complex; however, there are often some basic characteristics associated with it. A common type of utter is characterizedby a phased coupling of modes in which damping for one mode decreasesas speed increases near the onset of the instability. The extreme case, called explosive utter, occurs when this decrease in damping occurs suddenly and dramatically.

revision received 29 September 2001; accepted for publication 5 October 2001. Copyright c 2001 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, US Code. The US Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0021-8669/02 $10.00 in correspondence with the CCC.¤ Research Engineer, MS 4840 D/RS; rick. lind@ dfrc. nasa. gov. Member AIAA.