A CESSNA C210 PLT DEPARTED OSU WITHOUT A CLRNC.

Narrative

ABOUT XA30 AT OSU; I RECEIVED ATIS AND GOT CLRNC FROM GND TO TAXI TO RWY 27L. I DID MY RUNUP AND FINAL CHKS. I TRIED TO CONTACT TWR ON RADIO #2 AND DID NOT GET A RESPONSE FROM TWR ON 118.8. I TRIED 4 OR 5 TIMES ON RADIO #2. I THEN WENT TO RADIO #1 AND TRIED TO CONTACT GND AGAIN. I TRIED TO CONTACT GND 2 OR 3 TIMES ON RADIO #1. I DID NOT GET A RESPONSE FROM GND. I THEN MADE A DANGEROUS ASSUMPTION. I ASSUMED THE TWR HAD CLOSED DOWN. I WENT BACK TO RADIO #2 AND ANNOUNCED THAT I WAS TAKING OFF ON RWY 27L AT OSU. MY ERROR WAS I WAS RUSHING TO GET GOING. I CHKED FOR TFC AND TOOK OFF. AFTER I WAS AIRBORNE AND ABOUT 10 MI FROM OSU; I HEARD TWR TRYING TO CONTACT ME. I ANSWERED THEIR CALL. THEY WERE BREAKING UP. THEY ASKED ME TO CALL THEM ON THE LANDLINE WHEN I LANDED. I DID SO. I SHOULD HAVE DONE A BETTER PREFLT BY LOOKING AT THE ARPT DIRECTORY AND I WOULD HAVE KNOWN THE TWR CLOSED AT XX00. I SHOULD HAVE TRIED TO CONTACT GND ON THE HAND MIKE. I ALSO SHOULD HAVE CHANGED FREQS ON BOTH RADIOS. I ALSO SHOULD HAVE GONE BACK TO ATIS TO SEE IF I COULD HEAR ATIS. INSTEAD OF TAKING OFF; I SHOULD HAVE TAXIED BACK TO THE RAMP AND CALLED THE TWR ON LANDLINE AND ASKED IF THEY WERE RECEIVING MY CALLS. I THEN COULD HAVE ASKED THEM FOR A CLRNC TO TAKE OFF ON THE LANDLINE. I SHOULD HAVE CHKED TWR FOR THE LIGHTS FOR TKOF AND TAXIING.