Multivariable design of a bank-to-turn autopilot for command guidance

The paper examines the feasibility of including an autopilot on board a bank-to-turn missile in an attempt to improve the missile turn co-ordination (i.e. eliminate the unwanted cross-coupling). To do so necessitates the introduction of rudder action and probably an on-board sensor for lateral acceleration. The potential benefits arising include improved guidance loop performance and also the fact that, once designed, the resulting autopilot can be readily used for either homing or CLOS guidance loops. A multivariable approach is adopted and the practicality of assuming that the roll rate is a constant at each design point is examined. A steady-state control law is designed for this fixed value. The full autopilot controller is then implemented by scheduling the resulting steady-state controllers. The paper compares two multivariable design methodologies, namely the frequency-domain characteristics locus method and the time domain linear quadratic optimal control method. The steady-state optimal controllers are analysed in the frequency domain to provide insight into their structure and to allow comparison with those designed by the characteristic locus method