Active stabilization of surge was implemented on an Allied Signal LTS-101 axi-centrifugal gas producer, reducing the surging mass flow by 1%, for an operating range increase of 11%. Control was achieved using high response sensors in the inlet and diffuser throat, coupled to actuators that injected air near the diffuser throat. System identification and modeling indicate that a classical surge-type eigenmode and an eigenmode associated with engine duct acoustics dominate the engine’s input-output properties. The surge eigenmode’s stability determines the open-loop surge mass flow. A robust linear controller with three inputs and one output stabilized this eigenmode without destabilizing the acoustic mode. The controller facilitated a 1% reduction in surging mass flow at 95% N1 corrected; this increases the engine’s choke to surge stable operating range by 11%. This paper elucidates the measured unsteady pre-surge behavior of the engine, and outlines a systematic procedure for surge control law development.
Nonlinear regression with an intercept is investigated and a new nonlinear regression algorithm is developed. The application area considered is ballistic trajectory determination from battlefield radar measurements. Specifically, the geo-location of an enemy artillery piece is pursued. Careful modelling of the nonlinear measurement situation at hand and the inclusion of an intercept parameter in the nonlinear regression shows a considerable improvement over conventional iterative least squares estimation when nonlinearity is dominant. Moreover, the estimation performance does not degrade from standard iterative least squares (ILS) in cases where the nonlinearity is weak compared to the measurement noise in the equation error, provided that the data record is sufficiently long.
Indirect adaptive control for reconfigurable flight control is advocated. Specifically, online static system identification using a moving window/batch estimation is implemented. The ensuing linear regression is augmented with an intercept. The intercept parameter is included to address the effects of trim change associated with the occurrence of a control surface failure. Parameter estimate information is used to adjust the inner loop's control gains, and a command derived from the intercept estimate is fed forward to automatically retrim the aircraft. The tracking performance of this automatic retrimming method, which relies on system identification, surpasses the conventional approach of exclusively relying on integral action for retrimming. These adaptive and reconfigurable flight control concepts are illustrated in the context of a fighter aircraft's pitch plane dynamics. The novel adaptive and reconfigurable flight control system successfully handles a 50 per cent horizontal tail control surface loss.
Active stabilization of surge was implemented on an Allied Signal LTS-101 axicentrifugal gas producer, reducing the surging mass flow by 1 percent, for an operating range increase of 11 percent. Control was achieved using high-response sensors in the inlet and diffuser throat, coupled to actuators that injected air near the diffuser throat. System identification and modeling indicate that a classical surge-type eigenmode and an eigenmode associated with engine duct acoustics dominate the engine’s input–output properties. The surge eigenmode’s stability determines the open-loop surge mass flow. A robust linear controller with three inputs and one output stabilized this eigenmode without destabilizing the acoustic mode. The controller facilitated a 1 percent reduction in surging mass flow at 95 percent N1 corrected; this increases the engine’s choke to surge stable operating range by 11 percent. This paper elucidates the measured unsteady presurge behavior of the engine, and outlines a systematic procedure for surge control law development. [S0889-504X(00)01803-1]
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