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Analysis of Trunk Flutter in an Air Cushion Landing System

Report Number: AFFDL TR 79-3102
Author(s): Ashok B. Boghani; Roger B. Fish
Corporate Author: Foster-Miller Associates, Inc.
Laboratory: Air Force Flight Dynamics Laboratory
Date of Publication: 1979-08
Pages: 99
AD Number: ADA079008

Abstract:
This report deals with explaining the occurrence of flutter in the Air Cushion Landing System (ACLS) trunks and suggesting means of suppressing it. Observations of flutter in several ACLS trunks indicate that the flutter is caused by the interaction between the trunk membrane and the flow at the trunk bottom. The flow creates a negative stiffness effect at the bottom which, if larger than the positive stiffness due to the tension of the trunk, induces flutter. A computer simulation based on this model succeeds in predicting the flutter observed in the XC-8A tests. Suggestions on solving the flutter problem are based on either modifying the trunk or modifying the flow. Computer simulations of several suggestions indicate that: (1) Providing a minimum gap (2) Lowering the separation point (3) Changing the operating conditions show good promise in suppressing the flutter. Two other suggestions, not simulated, which also have good potential for flutter suppression are: (1) Incorporating circular trunk (2) Incorporating hybrid trunk.

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