1. 1 Reduced Transients at Wake Vortex Passage Wake Vortex Flight Control Laws robert.hillgren@saab.se presented at Meeting No. 98 SAE Aerospace Control and Guidance System Committee Williamsburg, VA October 11-13 2006

2. 2 Scope Background Simulation Model Open Loop Simulations Wake Vortex Detection Turbulence measure Reduction of Transients at Wake Vortex Passage Batch Simulations Flight Test Conclusions

3. 3 Background Gripen Wake Vortex Control Laws development. 1990’s. At evaluation of Gripen’s characteristics in wake vortices there were no wake vortex model. Flight tests were performed. Literature survey, Russian connections, initial model work… 1999 Aircraft lost in the lake of Vänern 2000 Development of complete wake vortex model as a prototype. Simulator demonstration. 2003 Spin incident after wake vortex passage at air combat training. 2004 Additional model development. Flight control laws change concept. 2005-2006 Implementation and flight test of Flight Control change.

4. 4 Wake vortex effect on aircraft and control system The entire aircraft is affected by the pressure field generated by the vortices. This creates forces and moments acting on the aircraft. The Flight Control System uses information from external (air stream) sensors as AoA and AoS vanes. The vortices create disturbances on the vanes. This information is used to control the control surfaces. McGowan

5. 5 Simulation Model

6. 6 The entire aircraft is affected by the pressure field generated by the vortices. This creates forces and moments acting on the aircraft. The Flight Control System uses information from external (air stream) sensors Wing body

7. 7 Open Loop Simulations Open Loop Simulation of wake vortex passage with a/c 39.107 made on a/c recording data. Detection signal (blue) ALFAF (red) ALFACV (black) Normal flying air to air aim Wake vortex High AoA Recovery ALFACV ALFAF Detection signal

8. 8 The Flight Control System angle of attack feedback signals Position correction Right AoA vane ALFACV Low pass filter Estimation of AoA dot nznz q ,, p,  High pass- filter t ALFAF Left AoA vane A blending of two different AoA signals are normally used in the Flight Control System as feedback signals.

9. 9 Wake Vortex Detection in the FCS | ALFACV-ALFAF | Filtering VORSET > VORLIMU and not VORSET < VORLIML VORSET VORSW Set Reset Delayed 5s ACVBPSW (ALFACV Bypass Switch) & VOROK Detection

10. 10 Turbulence Measuring Low pass filtering VORSET VORTURB 20 10 VORLIMU VORLIML + + + + K Limiter +30 0 Turbulence measure Turbulence measuring is used to adjust the limit for activation of wake vortex FCL. Flexible limit for activation. |ALFACV-ALFAF| Filtering Flexible limit for reset.

11. 11 Batch Simulations 12000 simulations at each envelope point. The 12000 simulations have different relative attitude between the two aircraft and passes at different positions in the wake vortices cross plane. All simulations are performed at or close to the maximum angle of attack. Vortex Cross Plane Relative start positions between vortex and aircraft at one specific envelope point.

12. 12 Reduction of Transients at Wake Vortex Passage

13. 13 Statistics from Simulations Altitudenznz nznz MNo. of departures (out of 12000)  > 35 deg Reduction Generating a/c Following a/c Previous FCS New FCS 1 km5g4g0.333304885% 6 km7g 0.6577631360% Two examples

14. 14 Flight Test The maneuvers were performed at turn in the horizontal plane and the vertical plane. Three different maneuvers: 1.Outside in through the vortices, 2.Inside out through the vortices, 3.Lateral passage of the vortices. G: Generating aircraft. B: Following aircraft.

15. 15 Symmetrical Passage

16. 16 Passage Outside Wing Tip G:\linje\TDAF\OH-material\Videoklipp\WVTR_0002.wmv

17. 17 From Flight Test Type 1 maneuvers Type 2 maneuvers Flying in C130 propwash

18. 18 AAR Flight test B707 C130

19. 19 Conclusions A system that successfully reduces transients at passage of wake vortices has been implemented in the FCS. The number of dangerous flight cases is reduced significantly. The wake vortex model and the aircraft characteristics at passage are verified in flight test.