I hit a bump so hard in my KIS that I thought I'd hit another a/c it was that violent. It was a virtually calm wind summers day and I was flying just to the south of Stanstead CTA at about 1000ft agl and 140kts. Everything was reasonably smooth, apart from the typical small lumps associated with differntial heating.
Without warning there was an almighty thump that fisrt pushed me into my seat then tried to throw me out of it. My pax hit the roof and split his head open, I'd have done the same probably but I'm a bit of a short-ass so had further to travel and the belts kept me in. I did smack my legs on the instrument panel though.
At the time, I'd never experienced turbulence like it before in 8000hrs flying so thought I might have hit another a/c or something. On arrival at my destination I was that concerned I did a fly by of the tower to check that the undercarriage looked intact - it was.
I put it down to wake vortex from a departing 'heavy' from Stanstead. I've since discovered that wake vortex can descend several thousands of feet below a heavy aircraft.
JJ