Fuel imbalance is certainly one possible (and common) cause of a "wing heavy" condition to consider even though fuel balance is normally checked and corrected if neccesary, before takeoff. However, fuel balance is checked by referring to the fuel quantity indicators, which in some older aircraft at least, may be of questionable accuracy due to a number of age and maintenance related factors such as bio-contamination of the probes, corroded electrical connections and calibration drift in the fuel quantity signal conditioners. I have seen this quite a few times in my former life as a mechanic while troubleshooting fuel quantity indication problems. Balancing the guages may or may not balance the fuel load in each wing. One could transfer fuel until a level control wheel, level wings and centered ball can be achieved with all control forces trimmed out and accept the fuel quantity split as indication error. Zero sideslip angle and no deflected controls. This assumes that the inclinometers were properly centered while the aircraft was laterally levelled in the hangar.
Just as likely is the possibility that slight rigging assymitry of the flaps, slats or ailerons is the culprit. I have seen a new airplane delivered in rather poor rig right from the factory. (the delivery crew squawked it) Older airplanes have had flight control components adjusted, repaired, replaced or removed and re-installed any number of times. Each airplane is unique to some extent. These kind of rig-related errors are normally evidenced by an increased rolling moment with increased airspeed. Continnual corrections are required as airsppeed changes. Fuel imbalance induced rolling moment is more noticable (and critical) at lower speeds because of the greater control deflections needed to counter it.
Asymmetric thrust is (as Smokey mentioned) another possible cause of yaw-induced rolling moment. Easily compensated for with rudder and rudder trim.
My point in presenting all these observations is to illustrate the fact that we cannot make any assumption that the control rigging, fuel quantity indication or inclinometer ball are properly adjusted when correcting for a "wing heavy" condition. There are just too many variables beyond our control to make any unverified assumptions about these systems.
What we can do is stop any yaw with rudder, stop any roll with aileron and then follow any known flight manual procedures or recommendations.(as was suggested by Oldebloke) If a Boeing, then their procedure should be followed. Lacking of any official guidance, I would do the following if a "heavy wing"was noticed just after liftoff:
1) Stop roll with coordinated aileron/rudder if yaw is absent. Add more rudder input if aileron does not have immediate effect or yaw rate is detected. Correct yaw with rudder. Center the ball. (recommended for the airplane I currently fly) The gear should be in transit by now.
2) Once control is assured, trim away control forces, rudder first. Have the PNF trim if both hands are busy. Get away from the ground and get to a comfortable climb airspeed. After the airplane is trimmed and a safe altitude (400' min for my plane) and speed are reached, the cause of the problem may be investigated by the PNF and remedial action taken in coordination with the PF. Treat this problem like any other abnormal in that flying the airplane is the first priority. I don't prefer to fly around out of trim while investigating the problem and probably have a DP to fly. I'd rather fly it at least roughly trimmed. If fuel imbalance is found to be the culprit, I can re-trim as the fuel is transferred. I would wait until after the workload eased off to do this.
So the only differences of opinion I seem to have with Old Smokey's assessment is that I would trim BEFORE investigating so I can fly the airplane more precisely. And in the airplane I fly, they call for centering the ball rather than the control wheel. We do not have spoilers tied into the aileron control system. (one possible reason for Boeing's recommendation?) If the heavy wing is discovered in some other phase of flight, then I would guard the controls and maybe roll in some trim while George continued to fly and the other pilot looks for the cause. I recall that B-747 split S job over the Pacific! Normally, I would expect that we would monitor our fuel state more closely than that, but I wasn't there.
Thanks for your indulgence and I apologize for being unable to make my case in fewer words! I welcome any corrections or difference of opinion as I consider all exchange on this forum to be a learning experience.
Best regards,
Westhawk