M20P PLT HAD LESS THAN LEGAL SEPARATION WITH AN RJ. THE PLT WAS ATTEMPTING TO FLY FORMATION WITH ANOTHER MOONEY AND MISTOOK THE RJ FOR THE MOONEY.

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I WAS ENRTE FROM I67 TO LUK AND HAD JUST LEVELED OFF BTWN 2800-2900 FT. I WAS AWARE THAT THE CVG; CLASS B FLOOR WAS 3000 FT. I THOUGHT THAT I SPOTTED MY FRIEND IN ANOTHER MOONEY AT MY 10-11 O'CLOCK POS AT MY SAME ALT. HE HAD TAKEN OFF FROM I67 RIGHT BEFORE ME AND WAS ENRTE TO LUK. WE HAD BEEN IN COM ON A CTAF; AND HE WAS ALSO LEVEL AT 2800 FT. HOWEVER; AS I GOT CLOSER TO THIS AIRPLANE; I REALIZED THAT THIS WAS NOT A MOONEY; BUT A COMMUTER REGIONAL JET. THERE WAS NO RELATIVE MOTION BTWN THE JET AND MYSELF. THE REGIONAL JET STARTED MAKING A R TURN TOWARDS ME AND APPEARED TO BE ON A COLLISION COURSE. I TOOK EVASIVE ACTION BY A CLBING R TURN TO 3200 FT. THE RJ APPEARED TO PASS BELOW ME BY 400-500 FT. I KNEW THAT I VIOLATED THE CLASS B AIRSPACE FOR APPROX 30-45 SECONDS; BUT I FELT IT WAS NECESSARY TO AVOID A POTENTIAL CONFLICT. AFTER THE RJ PASSED BELOW ME; I IMMEDIATELY EXITED THE CLASS B AND DSNDED TO 2500 FT. IF I DID NOT CLB; THE PROX OF THE JET WOULD HAVE BEEN MUCH CLOSER AND A POTENTIAL COLLISION MAY HAVE OCCURRED IN MY JUDGEMENT. I ONLY HAD SEVERAL SECONDS TO REACT WHEN THE JET TURNED TOWARDS ME. I WAS VFR AT THE TIME AND NOT IN CONTACT WITH ATC. TO PREVENT THIS FROM HAPPENING IN THE FUTURE; I WILL CONTACT CINCINNATI APCH EVEN IF VFR; IN AN AREA OF BUSY TFC. ALSO; CRUISING AT 2800 FT MAY HAVE BEEN TOO CLOSE TO THE FLOOR OF THE CLASS B (3000 FT) AND DIDN'T GIVE ME MUCH ROOM TO MANEUVER. 2500 FT PROBABLY WOULD HAVE BEEN A BETTER ALT WITH A 500 FT CUSHION INSTEAD OF 200 FT.