pasir, Sikorsky is national Polish Hero, buried in Wawel cathedral, where all the kings are. Archives on him in the UK classified, yes. For 50 yrs longer, still. Famous mystery crash and Russians we always interested, because could be us :o), could be not at all.
For Stalin, though, Sikorsky was useful, as he declared war to the USSR, on behalf of Polish government in exile. And thus un-tied Stalin's hands in terms of thinking what to do with captured Polish officers. Sikorsky was a live proof USSR and Poland are officially in the state of war.