DESPITE A WX BRIEF DISCOURAGING VFR FLT THE NON-INSTRUMENT RATED PLT DEPARTED AT ABOUT 1330 CST. HIS STATED DEST WAS FT. WORTH, TX WHICH IS DUE NORTH. AFTER TAKEOFF IN VMC THE ACFT FLEW NE TOWARD AN UNKNOWN DEST. A WX STUDY INDICATED CONDITIONS ALONG THE TRACK OF FLT INCLUDED FOG, RAIN, AND THUNDERSTORMS. THE LAST PORTION OF THE FLT WAS IN THE VICINITY OF THUNDERSTORMS, HEAVY RAIN, SEVERE OR GREATER TURBULENCE, SEVERE ICING ABOVE 11,500 FT AND LOW LEVEL WIND SHEAR. RADAR PLOTS RECORDED THE ACFT GROUND TRACK AND SHOWED VERY ERRATIC AIRSPEED AND COURSE DURING APRX THE LAST 25 MIN OF FLT. 4 NEAR 180 DEG TURNS WERE MADE, ALT WAS UNKNOWN. IMPACT OCCURRED ON A WESTERLY HEADING IN ROCKY, HILLY TERRAIN GEAR AND FLAPS UP. THE DESCENT ANGLE WAS APRX VERTICAL IN AN APRX 20 DEG NOSE DOWN LEFT WING LEADING ATTITUDE. THE ELT DID NOT ACTIVATE; AIR SEARCH WAS UNSUCCESSFUL AND TERMINATED ON 12-3-84. THE WRECKAGE WAS FOUND BY A HELICOPTER ON 9-11-85 IN THE COMMERCIAL PINE TREE FOREST. INVEST REVEALED NO PRE-IMPACT MECHANICAL MALFUNCTIONS.