Many thanks for the answers. I actually started my roll from the same point as the heavy a/c, not an intermediate point. Also, for clarity, the reason i was running out of tarmac was because I was heading left at about 30 degrees off the centreline. There was plently runway left in front of me. Just not so much to the side. Once i was airborne, there was no turbulence to remark about. Very strange and worrying at the time!