twochi
Correct they are pipes to provide visualisation of the vortices from smoke cannisters fitted under the wing. Sorry I didn't have a pic of them working but essentially they produced two white filaments marking the centreline of the vortices.
BOAC
Yes with any sideslip (fom a gust say) the attachment points of the vortices would slide up and down the LE a tad which did not manifest itself as a yaw but as a dutch roll (which actually appeared as pure wing rock). Indeed in the 115 if you trimmed it out hands off in level flight and gave the rudder a tap you could sit back and watch the dutch roll diverge to about +/- 55-60 deg. You could not stop this with aileron (elevons actually) as it was difficult to get the phase right. The cure (instant) was to just poke the stick forward and get rid of the alpha which was of course the forcing function.
I used my experience of all this to get MiG to let me fly their 29 in 1990 in order to see how they had clearly mastered the nailing of the vortex attachment points and stopped them sliding about. Valery Menitsky their CTP explained that when he first flew the prototype it was a dog 'cos of this and it was fixed by a couple of small VGs at the base of the pitot which shed a couple of very small but very stable vortices that fed and located the main ones beautifully.
It is important to realise though that today's LERX are primarily used to increase Cl max through generating a degree of vortex lift and also reduce the dreaded spanwise flow that afflicts a simple swept wing. The directional help is a bonus that enables such vortex lift to be useable at silly AoAs
J