Date: 201706
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Sail Plane
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Final Approach; Landing
Airspace: Class G ZZZ
ATC / advisory: CTAF ZZZ
Second aircraft: Skyhawk 172/Cutlass 172
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Commercial
Human factors: Situational Awareness; Communication Breakdown
Anomaly: Conflict NMAC
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: While on a left base leg for landing on runway 23; a conflict arose between me and another aircraft. I was flying a Schweizer SGS 1-26 single seat glider. The other aircraft was a Cessna 172 engaged in dual instruction. Two other aircraft were factors in the conflict: a high wing aircraft operated by a skydiving operation based on the field; and the towplane that launched me.I took off from runway 23 for a pattern tow. The tow was to 1200 ft AGL on the downwind leg and was unremarkable. I released and continued straight ahead on the downwind leg while the towplane dove to the left and also continued on the downwind for 23. In hindsight; I realize I should've made a right 360 degree turn for spacing from the tow plane; but I didn't. As a result I was hypervigilant about maintaining visual separation from the towplane. Both the towplane and I announced our positions and intentions to land on CTAF.The towplane landed well ahead of me. I turned left to enter the base leg and announced my position on CTAF. At that time I heard the Cessna 172 announce that it was on a right base leg for 23. I began looking for the Cessna and saw a high wing aircraft passing off my right in the opposite direction. Believing that plane to be the Cessna; I stated on CTAF that I was 'just off your [the Cessna's] right wingtip.' That plane was; in fact; the jump plane; but I didn't realize this until after landing.I continued on my base leg and continued scanning visually for traffic. I soon saw the Cessna at my 2 o'clock and slightly above me; turning from right base to final quite close to me; and heard their announcement on CTAF. I executed an immediate; steep right 90 degree turn and announced the conflict on CTAF. The Cessna acknowledged my radio call and executed a go around. I turned back towards the runway and landed uneventfully. The pilot of the Cessna later told me that neither he nor his student ever saw me.After landing I realized that the airplane that had passed off my right had actually been the jump plane departing from runway 12; and that I hadn't heard the jump plane's takeoff announcement on CTAF. I presume I missed their takeoff announcement because I was so fixated on the towplane after release.In my opinion; factors leading to the near miss were: my failure to execute a separating turn upon release from the towplane; my subsequent fixation on the towplane's position causing me to miss the jump plane's takeoff announcement (and hence be unaware of their presence in the pattern); the jump plane's non-standard departure from a crossing runway; and the Cessna's use of a non-standard traffic pattern. (The preferred pattern for runway 23 is left.) Corrective actions were my steep right turn and the Cessna's go around.




Synopsis: Glider pilot reported a NMAC while practicing in the pattern.