The Lure of the Mean Axes

[+] Author and Article Information
Leonard Meirovitch1

Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and  State University, MS 0219, Blacksburg, VA 24061lmeirovi@vt.edu

Ilhan Tuzcu

Department of Aerospace Engineering and Mechanics, The University of Alabama, Tuscaloosa, AL 35487-0280ituzcu@coe.eng.ua.edu


Author to whom correspondence should be addressed.

J. Appl. Mech 74(3), 497-504 (Apr 18, 2006) (8 pages) doi:10.1115/1.2338060 History: Received July 26, 2005; Accepted April 18, 2006

A variety of aerospace structures, such as missiles, spacecraft, aircraft, and helicopters, can be modeled as unrestrained flexible bodies. The state equations of motion of such systems tend to be quite involved. Because some of these formulations were carried out decades ago when computers were inadequate, the emphasis was on analytical solutions. This, in turn, prompted some investigators to simplify the formulations beyond all reasons, a practice continuing to this date. In particular, the concept of mean axes has often been used without regard to the negative implications. The allure of the mean axes lies in the fact that in some cases they can help decouple the system inertially. Whereas in the case of some space structures this may mean complete decoupling, in the case of missiles, aircraft, and helicopters the systems remain coupled through the aerodynamic forces. In fact, in the latter case the use of mean axes only complicates matters. With the development of powerful computers and software capable of producing numerical solutions to very complex problems, such as MATLAB and MATHEMATICA , there is no compelling reason to insist on closed-form solutions, particularly when undue simplifications can lead to erroneous results.

Copyright © 2007 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 1

Flexible body in space

Grahic Jump Location
Figure 2

Flexible helicopter




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