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Meeting	ACGS Committee Meeting 94 - Reno - November 2004
Agenda Location	5 SUBCOMMITTEE E – Flight and Propulsion Control Systems 5.2 F/A-18E/F Lateral PIO and Resulting Control Law Changes
Title	F/A-18E/F Lateral PIO and Resulting Control Law Changes
Presenter	Shawn Donley and Ron DeMand
Affiliation	NAVAIR and Boeing, respectively
Available Downloads*	presentation video
	Downloads are available to members who are logged in and either Active* or attended this meeting.
Abstract	During the second sea trials of the F/A-18E/F in March 1999, a single instance of a lateral pilot induced oscillation (PIO) was experienced on short final to the carrier. The trigger event appeared to be unexpected crosswind conditions. Post flight data analysis showed this to be a classic Category II rate saturation PIO, with the ailerons at their software and hardware rate limits, and the differential stabilators at their software rate limits. Attempts to duplicate the PIO in a fixed base simulator and during land-based flight testing were unsuccessful. To mitigate the PIO potential, the aileron and stabilator software rate and position limiters were replaced with a phase compensated rate and position limiter algorithm. This algorithm is an adaptation of an approach patented by the US Navy in 1989. The benefits and characteristics of the phase compensated rate limiter were presented. Embedding the actuator command position limit within the phase compensated rate limiter provides significant advantages over a phase compensated rate limiter alone.