I crashed my blade MSR recently and started having this issue... it will lift and swirl in a small circle then take a huge backward right spiral to the ground. If I fight it I can keep it in the air but not fun. Trim will not stop it. I have done the following:
replaced blades, tail rotor - motor - rotor blade, replaced blade grips, replaced main gear, replaced main shaft, recalibrated... any other ideas?