COMMUTER FLC DEPARTS NON TWR ARPT VFR AND HAD CONFLICT WITH HELI DEPARTING.

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I WAS THE CAPT ON A FLT FROM BRL; IA; TO STL; MO. THIS ARPT IS UNCTLED AND OUR COMPANY OPERATES SCHEDULED PAX SVC HERE. ON TAXI OUT OF THE GATE; WE COMPLETED OUR TAXI CHKLIST AND CALLED ZAU FOR AN IFR CLRNC FOR TKOF. HE WAS UNABLE TO GIVE US AN IFR CLRNC BECAUSE A HELI (UH-47) WAS ON THE FIELD AND HAD THE IFR RELEASE FROM THAT ARPT. IT WAS VFR SO WE DECIDED TO TAKE OFF VFR; AND PICK UP THE IFR CLRNC IN THE AIR. WE ANNOUNCED WE WERE TAKING THE ACTIVE AND PROCEEDING SBOUND; AND I HAD VISUAL CONTACT ON THE HELI; WHO WAS MIDFIELD ON THE GRASS BESIDE THE RWY. HE ANNOUNCED HE WAS TAKING OFF AND THEN A L TURN AFTER TKOF. AS I ADVANCED THE PWR FOR TKOF HE BEGAN TO ROTATE AND PROCEEDED STRAIGHT AHEAD AND PARALLELED THE RWY. I HAD VISUAL CONTACT ON THE HELI THE WHOLE TIME; BUT AFTER ROTATION; I BANKED R AND QUICKLY PASSED THE HELI OFF TO HIS R SIDE; VFR. THERE WAS NEVER A CONFLICT OR DID I FEEL I WAS JEOPARDIZING SAFETY; BUT I OVERTOOK THE HELI QUICKLY AND FROM AN OBSERVER ON THE GND POINT OF VIEW; IT WOULD APPEAR THAT MY ACFT WAS CLOSE TO THE HELI. 2 THINGS THAT WOULD HAVE SOLVED THIS; IF THE HELI TURNED L AFTER ROTATION; AND I WOULD HAVE WAITED TO SEE HIS L TURN; BEFORE I ADVANCED THE PWR FOR TKOF.