I'm sure many of you are familiar with "rudder hardover", where an aeroplane's rudder deflects to an extreme position - full left or full right. Many of you will be aware that such an event, caused by a faulty Power Control Unit, was implicated in the loss of United Airlines Flight 585 and USAir Flight 427. A rudder hardover was also involved in an incident on Eastwind Airlines Flight 517 and the investigation into that incident unravelled the mysteries around the loss of the two aforementioned flights.
My question is about the effects of a rudder hardover on flight - and how it led to the two crashes. I'm interested in what happens, aerodynamically, after the rudder has moved to its extreme position and the sequence of events which follows. It's obvious to me that a rudder hardover must be an extremely destabilising event. But I'd like a more detailed explanation of precisely what happens. What effects does it cause? What happens to the affected aeroplane and why might it crash?