A BAE4100 FLC BATTLES THE CONTROLS TO MAINTAIN CTL OF THE ACFT AFTER TKOF WHEN THE ACFT ATTEMPTS A HARD RIGHT TURN. POST FLT INSPECTION FOUND AN IMPROPERLY INSTALLED AILERON TRIM PUSH-PULL ROD THAT HAD BEEN INSTALLED BACKWARDS AT IAD; VA.

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AT THE TIME OF THE OCCURRENCE; I WAS HANDLING PLT ON THE TAKE OFF RUN. AS I ROTATED; I IMMEDIATELY FELT A TENDENCY OF THE ACFT TO ROLL TO THE RIGHT; TO COUNTERACT THIS; IT TOOK MY GREATER LEFT AILERON FORCE AND ALL LEFT TRIM TO KEEP THE ACFT IN A SOMEWHAT STABILIZED CLIMB. I IMMEDIATELY INFORMED THE CAPT OF THESE SERIOUS CONTROLLABILITY PROBLEMS AND AFTER COMPLETING THE AFTER TAKE OFF CHECKS WE EXCHANGED THE CONTROLS SO HE COULD ALSO FEEL WHAT THE PROBLEM WAS. HAVING ESTABLISHED THE SERIOUSNESS OF THE PROBLEM WE DECIDED TO DECLARE AN EMER AND RETURN TO LAND IN DULLES RWY 19L. I TOOK THE CTLS BACK AND LEVELED OFF AT 2000 FT. 160 KTS WITH FLAPS 9 DEGS; IN THAT CONFIGURATION THE ACFT WAS SOMEWHAT CONTROLLABLE. HOWEVER; GREAT FORCE TO THE LEFT ON THE YOKE WAS NECESSARY TO KEEP THE ACFT STRAIGHT AND LEVEL. WHILE I KEPT FLYING; THE CAPT CALLED COMPANY MAINT AND BRIEFED THE FLT ATTENDANT. AFTER THAT; THE CAPT DECIDED TO TAKE THE CONTROLS FOR LANDING. WE DID OUR LANDING CHECKS AND SAFELY LANDED THE AIRPLANE; ALTHOUGH IT TOOK BOTH OF US ON THE CONTROLS TO KEEP THE AIRPLANE ALIGNED WITH THE RWY ON FINAL. ONCE AT THE GATE; OUR MAINT TEAM DISCOVERED THAT THE PUSH PULL RODS TO THE AILERON TRIMS HAD AND BEEN INSTALLED BACKWARDS AND IT WOULD HAVE BEEN DIFFICULT FOR US (PLTS) TO NOTICE IT ON OUR STD WALK AROUND.