INST RATED SMA PLT; ON AN IFR FLT PLAN; LOSES SITUATIONAL AWARENESS; AS RESULT OF WHICH; WHEN CLRED DIRECT TO A VOR; (S)HE HEADS IN WRONG DIRECTION.

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I DEPARTED ISP ON AN INST FLT PLAN IN VMC. THERE WAS A STRONG NORTHERLY FLOW OVER THE HILLS BELOW CAUSING AT LEAST MODERATE TURB AT THE LOWER ALTS WHICH I WAS ASSIGNED EARLY IN THIS FLT. DEP IS RADAR VECTORS TO ASSIGNED RTE/FIX. MY FLT PLAN WAS TO TAKE ME WNW TO MY DEST (9G3) NEAR BUFFALO; NY; BUT I HAD BEEN VECTORED NBOUND AFTER TKOF. AFTER SOME PERIOD OF TIME AND SEVERAL VECTORS; I WAS TOLD TO FLY DIRECT CARMEL VOR (CMK). I HAD BEEN EXPECTING VECTORS; AND DIDN'T KNOW EXACTLY WHERE THAT VOR WAS; BUT I BELIEVED IT TO BE SW OF MY POS. I TURNED SWBOUND; SET THE AUTOPLT TO FOLLOW THE HEADING; AND TRIED TO CALL UP THE LOCATION IN THE (PANEL MOUNTED IFR CERTIFIED) GPS. TURB MADE IT DIFFICULT TO GET MY HAND ON THE UNIT; AND HANGING ONTO THE SCROLLING KNOB AND PUSHING THE PROPER BUTTONS WAS SLOW DUE TO THE TURB. I WAS HEADING WSWBOUND; IN THE DIRECTION WHERE I THOUGHT THE VOR WAS; WHILE I LOOKED FOR IT IN THE GPS; WHEN ATC CALLED ME AND ASKED ME ABOUT WHAT HEADING I WAS USING. I TOLD THEM; AND THEY SAID I WAS ON THE WRONG HEADING. I TOLD THEM I WAS HAVING DIFFICULTY GETTING THE DATA FROM THE GPS; BUT WAS WORKING ON IT AS WE SPOKE. THEY MAY HAVE GIVEN ME A MORE NORTHERLY VECTOR; OR I MAY HAVE FOUND THE CORRECT HEADING AT THIS POINT; BUT I RECALL HEADING TOWARD THE VOR ON ABOUT A 300 DEG OR 310 DEG HDG. THEY ASKED ME MY NEW HEADING; I TOLD THEM; AND ALL APPEARED WELL FOR THE REST OF THE FLT. SEVERAL THINGS IMPRESSED ME ABOUT THIS INCIDENT. FIRST; I HAD ASSUMED I'D BE GIVEN A VECTOR TO INTERCEPT MY FLT PLAN. IN RETROSPECT; THIS WAS CLRLY AN INCORRECT ASSUMPTION. SECOND; EVEN THOUGH THE AUTOPLT FLEW THE PLANE FLAWLESSLY IN THE TURB THAT AFTERNOON; IT WAS SURPRISINGLY DIFFICULT TO PUT MY HAND ON THE SMALL BUTTONS OF THE GPS (IT'S AN ALLIED SIGNAL KLN-90B). THIRD; I BELIEVE THE STRONG NORTHERLY AIRFLOW DECREASED MY GND SPD MORE THAN I REALIZED; AND THUS WHILE I FELT I SHOULD HAVE BEEN NE OF THE VOR; I IN FACT HAD NOT YET PASSED IT AND WAS STILL SE OF IT. LASTLY; I SHOULD HAVE KEPT THE VOR IN MY RNAV; OR IN MY #2 VOR RECEIVER; JUST IN CASE I GOT AN INSTRUCTION AS I DID. HAD I DONE THIS; I WOULD HAVE BEEN ABLE TO FLY DIRECTLY TO THE VOR WITHOUT DIFFICULTY. INSTEAD; I HAD THESE RADIOS SET UP FOR A RETURN TO THE DEP ARPT (IN CASE OF NEED) AND HAD NOT CHANGED THEM.