university of florida thesis or dissertation formatting template
university of florida thesis or dissertation formatting template
university of florida thesis or dissertation formatting template
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Popular methods f<strong>or</strong> finding the solution to the flutter equations include the k-method and<br />
the p-k method 9 in which velocity-damping, V-g, diagrams and velocity-frequency diagrams are<br />
constructed from the roots <strong>of</strong> the eigenvalues solutions. 10<br />
Limit Cycle Oscillation<br />
LCO is a sustained, non-divergent, periodic motion experienced by aircraft with<br />
configurations which <strong>of</strong>ten include st<strong>or</strong>es. The external st<strong>or</strong>es consist <strong>of</strong> any object carried on the<br />
aircraft, such as a weapon, fuel tank, <strong>or</strong> pod. N<strong>or</strong>ton 11 provides an excellent overview <strong>of</strong> LCO <strong>of</strong><br />
fighter aircraft carrying external st<strong>or</strong>es and its sensitivity to the st<strong>or</strong>e carriage configuration and<br />
mass properties. The characteristics <strong>of</strong> LCO motion are a result <strong>of</strong> nonlinear effects that are<br />
difficult to model, and prediction <strong>of</strong> LCO likelihood is typically perf<strong>or</strong>med using linear flutter<br />
models. Flutter and LCO are related, and this association is due in part to the accuracy with<br />
which linear flutter models predict LCO frequencies and modal mechanisms. 7,12,13 However,<br />
flutter models do not accurately predict LCO onset speed and amplitude.<br />
There are two types <strong>of</strong> LCO, typical and non-typical. Typical LCO is characterized by the<br />
gradual onset <strong>of</strong> sustained limited amplitude wing oscillations where the oscillation amplitude<br />
progressively increases with increasing Mach number and dynamic pressure. 7,12,13 Non-typical<br />
LCO is characterized by the gradual onset <strong>of</strong> sustained limited amplitude wing oscillations where<br />
the oscillation amplitude does not progressively increase with increasing Mach number. These<br />
oscillations may only be present in a limited p<strong>or</strong>tion <strong>of</strong> the flight envelope.<br />
Flutter and LCO are known to occur on many fighter aircraft, such as the F-15, F-16, and<br />
F-18. Carriage <strong>of</strong> a missile on the outboard wing station <strong>of</strong> an F-15 leads to traditional flutter,<br />
theref<strong>or</strong>e this station is no longer used. The F-18 encounters a 5.6 Hz LCO mechanism f<strong>or</strong> most<br />
st<strong>or</strong>e configurations, so the developers devised an Active Aeroelastic Control device which is<br />
23
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