Ok! here goes, ya gotta have a lot of ele(45deg or more) then take it way up(were gonna do a inverted flatspin)cut to idle and start a dive straight down, and give full left ailerons when it gets spinning real good then give it full down elevator and full right rudder and it will start entering a flatspin but you have to give it some throttle and start going right on your ailerons untill you get a flat flatspin.

and a 5.5 or more CG will also help

good luck