Can an airplane in a thundercloud shake voilently?

Answer 1

Yes. This is basically why airplanes avoid areas of high turbulence. The greatest threat is that a turbulent movement of air will raise the plane's nose suddenly, causing a sudden dramatic increase in lift that can overstress the airframe. A pilot's first reaction to turbulence is to decrease airspeed to ensure that should the plane's nose rise suddenly, the plane would stall (lose lift due to air "peeling" off the wings) before the airframe would be overstressed.