Do a search on this subject on the forum “Search the Community” search engine. It is on the right hand side of the page This subject has come up on this site before. Also, here are references I found while doing a search on FSM:
http://cs.finescale.com/fsm/modeling_subjects/f/2/t/146401.aspx
http://www.aircraftresourcecenter.com/ISL/Prop_Blur/PropBlur.shtm
Lee
p.s. Make sure you have the props turning in the correct direction! [proplr]