PLT OF C208 DEPARTING CVO FAILED TO TURN NORTH ON COURSE PRIOR TO CONTACT WITH CASCADE DEP CTL. DELAYED TURN DUE TO INBOUND AND DEP TRAFFIC FOR OTHER RWYS.

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I WAS OPERATING A CESSNA CARAVAN FROM CORVALIS; OR. THE FLT WAS FILED UNDER IFR AND INITIALLY PROCEEDED N FROM CVO ON V-23. I OBTAINED A CLRNC FROM CASCADE DEP WHILE ON THE GND IN CORVALIS AND ADVISED THEM I WOULD BE DEPARTING ON RWY 17. WHILE OBTAINING THE CLRNC I OBSERVED AN ACFT PREPARING TO DEPART ON RWY 27; AND ALSO HEARD (ON CTAF) AN ACFT INBOUND FROM THE SE INTENDING A L DOWNWIND ENTRY FOR RWY 27. CASCADE CLRED ME 'AS FILED' AND TOLD ME TO RPT AIRBORNE. I WAITED FOR THE ACFT TO DEPART ON RWY 27 AND THEN ANNOUNCED ON CTAF THAT I WOULD BE DEPARTING RWY 17. AFTER DEP I NOTIFIED CASCADE DEP AND THEY ADVISED ME OF TFC INBOUND TO CORVALIS AS WELL AS THE TFC THAT HAD JUST DEPARTED. I ADVISED CASCADE THAT I HAD THE TFC IN SIGHT. SINCE THE INBOUND ACFT WAS ABOUT TO TURN DOWNWIND FOR RWY 27; I CONTINUED SBOUND ON A 170 DEG HDG UNTIL WELL CLR OF THAT TFC; AT WHICH POINT I QUERIED CASCADE APCH TO CONFIRM THAT I WAS CLRED TO TURN ON COURSE. AS I WAS APPROX 4-5 MI S OF CVO AT THIS POINT CASCADE QUESTIONED WHY I HAD NOT ALREADY TURNED ON COURSE. I RESPONDED THAT I HAD CONTINUED S TO MAKE SURE I WAS WELL CLR OF THE TFC INTO AND OUT OF CORVALIS. I THEN TURNED ON COURSE AND THE FLT WAS COMPLETED WITHOUT INCIDENT. I BRING UP THIS INCIDENT BECAUSE OF THE CONFUSION ON MY PART AND ON THAT OF THE CTLR (CASCADE DEP). EVIDENTLY CASCADE EXPECTED ME TO TURN SOONER THAN I DID; AND IN HINDSIGHT; I REALIZE I SHOULD HAVE ADVISED ATC THAT I WAS CONTINUING S TO BE CLR OF THE TFC THAT THEY POINTED OUT. AS I WOULD NOT HAVE TURNED ON COURSE SOONER THAN I DID IN ORDER TO AVOID THE TFC; AND SINCE I WAS NOT THAT FAR FROM THE DEP ARPT; I DID NOT CONSIDER MY FLT PATH TO BE UNUSUAL FOR A DEP FROM RWY 17. I WAS MISTAKEN; HOWEVER; TO ASSUME THAT ATC WOULD EXPECT ME TO GIVE THE TFC PATTERN WIDE BERTH. IN THE FUTURE; I CAN SEE I WILL NEED TO BE MORE VIGILANT IN INFORMING ATC ANY TIME MY FLT PATH MAY NEED TO DEVIATE EVEN A SMALL AMOUNT FROM MY EXPECTED AND CLRED RTE.