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Meeting	ACGS Committee Meeting 98 - Williamsburg - October 2006
Agenda Location	5 SUBCOMMITTEE A - AERONAUTIC AND SURFACE VEHICLES 5.3 Wake Vortex Flight Test Results
Title	Wake Vortex Flight Test Results
Presenter	Staffan Bogg
Affiliation	Saab Aircraft
Available Downloads*	presentation video1 video2
	Downloads are available to members who are logged in and either Active* or attended this meeting.
Abstract	During the 1990 evaluation of JAS 39 Gripen’s characteristics at wake vortex passages only flight test was used. This made it hard to cover all the possibilities of wake vortex passages. At 1999 a JAS 39 Gripen a/c was lost during combat training at low altitude encountering a wake vortex passage. This event started development of a complete wake vortex simulation model. During air combat training 2003 a Gripen a/c encountered a wake vortex passage, which resulted in a high AoA spin. The high AoA spin was recovered by the FCS high AoA automatic recovery control laws. This event resulted in further refinement of the wake vortex simulation model. The data from the spin incident could also be used to define a FCS change to solve the problem with wake vortex passages. The proposed FCS change was implemented in the JAS 39 Gripen FCS. The control system change was simple and effective. The wake vortex effect on the angle of attack vane signal, which is normally used by the FCS, caused an elevator/canard command that resulted in an angle of attack overshoot when maneuvering at maximum AoA. The new FCS change detects a wake vortex passage and switch to a complementary filtered AoA, which is used under the wake vortex passage, and the transient is significantly reduced. Extensive batch simulations with 12000 simulations at each envelope point were performed to verify the FCS change using the wake vortex simulation model. The FCS change was also extensively flight tested using information from the batch simulations. The FCS wake vortex control law change showed very good wake vortex passage characteristics with very small transients.