PRIVATE PLT OF SMA ACFT ENCOUNTERED A NMAC WITH A GLIDER IN UNCTLED AIRSPACE IN VFR CONDITIONS.

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WHILE FLYING UNDER VFR AT CRUISE LEVEL 4500 FT MSL OVER THE VICINITY OF FITCHBURG; MA ARPT (FIT - UNCTLED); I SUDDENLY ENCOUNTERED A GLIDER AT MY 11:30 O'CLOCK; APPROX. 100 FT BELOW AND AHEAD. I WAS CONTINUALLY SCANNING FOR OTHER TFC AND LANDMARKS (USING PILOTAGE AND DEAD RECKONING) ENRTE FROM NASHUA; NH; ARPT (ASH) DIRECT TO WORCESTER; MA; ARPT (ORH); VIA A FLYOVER OF FIT ARPT. THE GLIDER APPARENTLY WAS RIDING A CONVECTIVE CURRENT BELOW MY FLT PATH AND ASCENDING QUICKLY. I WAS UNABLE TO SEE IT UNTIL IT ALMOST REACHED MY ALT AS ITS POS BELOW WAS BLOCKED BY MY COWLING AND CTL PANEL. WHEN IT 'POPPED' INTO VIEW JUST ABOVE AND SLIGHTLY TO THE L OF MY COWLING; IT WAS APPROX 100 FT AHEAD AND BELOW MY PATH. THE GLIDER PLT MAY HAVE SEEN ME ALSO AT THAT POINT AS IT SEEMED THAT HE BEGAN TO ARREST HIS RATE OF ASCENT. SINCE HE WAS IN A RISING PATH THAT I JUDGED WOULD TAKE HIM RIGHTWARD ACROSS MY FRONT; I DID NOT EXECUTE A RIGHTWARD EVASIVE MOVEMENT; BUT INSTEAD IMMEDIATELY GAVE FULL THROTTLE TO CLB OVER WHAT I JUDGED HIS 'BACK' PATH TO BE. A COLLISION WAS AVOIDED. CONTRIBUTING FACTORS/ADDITIONAL INFO: MY RTE FROM ASH TO FIT WAS INTENDED TO AVOID THE ONLY ARPT NEAR MY RTE THAT HAS PUBLISHED (NY SECTIONAL) GLIDER ACTIVITY. YET; THE ENCOUNTER OCCURRED APPROX 10 MI FROM THAT ARPT (PEPPERELL SPORTS CENTER) OVER THE FIT ARPT WHERE NO GLIDER ACTIVITY IS INDICATED ON THE SECTIONAL. OTHER PLTS IN THE AREA INFORMED ME AFTER THIS INCIDENT THAT SOMEONE WAS FLYING A GLIDER OUT OF FIT ARPT ON THE SAME WKEND AS THE ENCOUNTER. I MENTION THIS ONLY AS COINCIDENTAL; SINCE I DO NOT KNOW IF THE GLIDER AT FIT WAS THE SAME ONE THAT WAS ENCOUNTERED. THERE WAS NO NOTAM OR OTHER NOTICE OF GLIDER ACTIVITY IN THAT VICINITY. PERHAPS THE NY SECTIONAL SHOULD INDICATE GLIDER ACTIVITY IN THAT VICINITY.