polarbearjim
Chines or as we call them today leading edge root extensions (LERX) are extremely effective at increasing the directional stability of an aircraft once it has a significant angle of attack (say 10 deg or so) and the wing is on its way towards its stalling AoA.
To understand why this should be so look at this pic of the HP115 slender delta research aircraft.
This highly swept wing with a sharp leading edge presents the airflow with an impossible task to remain attached to the top surface of the wing at any serious AoA. Instead the airflow detaches at the leading edge of both wings and wraps up into a vortex forming (as it were) a pair of ice cream cones flying point first attached just behind the cockpit. It is important to remember that when viewed from behind the aircraft the left vortex is rotating clockwise and the right hand one anticlockwise.
The more you force such a system through the air (force is the right word as there is a lot of drag) and the more you increase the AoA the more energy your put into the two vortices and the lower the pressure is at their centres. (This is called vortex lift and such a wing does not stall in the way that a conventional one does at high AoA).
Returning to look up the backside of such a system it is clear that the top of each vortex is rotating TOWARDS the aircraft centre line and the combined action of the two vortices is to pour airflow down onto the aircraft centreline (this feeds the HP115 intake beautifully when first impressions might lead one to think it would be blanked at high AoA).
Finally (at last) the fin also benefits from this ‘negative blanking’ - hence the improvement in directional stability as the fin is immersed in a good high velocity flow at high AoA.
The F16, F18, MiG29 and Su27 (to mention but four) all use these vortices generated by their chines/LERXs ) to maintain directional stability at high AoA (think Cobra…).
Make sense?
JF