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speed for the particular configuration is the critical point associated with the known
aeroelastically-sensitive mode. It is considered to be directly comparable to the lowest airspeed
at which self-sustained oscillations are encountered in flight. The velocity-sensitivity of a mode
is indicated by the slope of the modal damping curve, where steep slopes indicate rapid decreases
in stabilizing damping with increased velocity.
In classical analysis, a Mach number and density are specified for the aerodynamic
solution, and then the damping and frequency variations with respect to velocity are determined
based on the applied aerodynamic forces for the specified Mach number and density. Several
Mach number and density combinations can be examined to determine the critical conditions for
a given analysis configuration. A downside of this approach is that it usually does not result in
the computed instability speed being consistent with the Mach number and altitude specified,
thus resulting in non-matched condition analyses. Even though the aerodynamic and flutter
solution velocities from these analyses are not consistent, valuable insight into modal stability
characteristics can be obtained for large numbers of configurations for a relatively small
computational cost.
LCO Flight Testing
For each store configuration on the F-16, thousands of permutations of a specific
configuration are analyzed via flutter analysis and reduced to the most critical configurations.
These are reduced further based on previous flight test results of similar configurations (usually
determined via mass properties) and the flutter engineer’s judgment. However, each new
configuration still requires many flight tests in order to ascertain the true flutter/LCO
characteristics.
Since LCO is so strongly related to, and usually precedes, an apparent classical flutter
response, all testing is conducted as if catastrophic flutter is imminent. 7 Denegri 23 provides a
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