PVT PLT OF A PIPER PA28-161 INADVERTENTLY ENTERED CLASS C AIRSPACE WITHOUT CONTACT WITH ATC.

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ON MAR/XA/99; AT APPROX XX45; I WAS ON A SHORT SIGHTSEEING TRIP WITH 1 PAX. AS I APCHED GRAND RAPIDS FROM THE W; MY PAX ASKED IF WE COULD FLY OVER THE DOWNTOWN AREA. I KNEW WE WERE NEAR THE CLASS C AIRSPACE BUT FOR SOME REASON I THOUGHT THE DOWNTOWN AREA WAS JUST OUTSIDE THE CLASS C AIRSPACE (I HAD NEVER FLOWN OVER THE DOWNTOWN AREA BEFORE). I MADE A QUICK LOOP OVER THE DOWNTOWN AREA WITHOUT GIVING IT MUCH THOUGHT THEN PROCEEDED ON A SW HDG. A WK LATER; I WAS STUDYING THE SECTIONAL FOR ANOTHER FLT AND I REALIZED I MAY HAVE VIOLATED THE ENTRY REQUIREMENTS FOR THE CLASS C AIRSPACE; SINCE THE DOWNTOWN AREA IS ACTUALLY WITHIN THE RADIUS OF THE CLASS C BOUNDARY AND I WAS NOT IN COM WITH GRAND RAPIDS APCH. I HONESTLY CANNOT REMEMBER EXACTLY WHAT ALT I WAS AT WHEN WE WERE OVER THE DOWNTOWN AREA BUT I THINK IT WAS BTWN 1800-2500 FT MSL. THE CLASS C AIRSPACE IN THIS AREA EXTENDS FROM 2000 FT TO 4800 FT MSL. IF I WAS ABOVE 2000 FT MSL; THEN I MAY HAVE VIOLATED THE CLASS C AIRSPACE FOR AS LONG AS 10 MINS OR SO. I DO NOT KNOW IF THIS SIT IS IMPORTANT ENOUGH TO RPT; BUT I TAKE PRIDE IN BEING A PROFICIENT; SAFE PLT AND IN FOLLOWING THE RULES. BECOMING A PLT IS POSSIBLY MY LIFE'S GREATEST ACHIEVEMENT BUT IT MEANS NOTHING TO ME IF I CAN'T DO IT WELL. THIS LAPSE IN JUDGEMENT IS ATYPICAL FOR ME AND I AM BOTHERED BY IT. I HOPE THIS RPT WILL SET THINGS RIGHT. ADDITIONAL FACTORS: THE CTLRS IN GRAND RAPIDS SEEM VERY HELPFUL AND PROFESSIONAL; BUT I AM SOMETIMES RELUCTANT TO CALL FOR FLT FOLLOWING WHEN I AM JUST SIGHTSEEING AND NOT FLYING TO A PARTICULAR DEST OR INBOUND FOR LNDG. THEY ARE QUITE BUSY AND I FIND IT SOMEWHAT CUMBERSOME TO EXPLAIN MY INTENTIONS. HAD I NOT BEEN RELUCTANT TO CALL THEM; I WOULD HAVE AVOIDED ANY POSSIBLE INADVERTENT AIRSPACE INCURSIONS.