The massive diameter prop on Defiant will have a massive roll torque input to the airframe. When a conventional helicopter loses tail rotor authority, the helicopter spins about its axis. Large gear reduction, large torque, transmitted through the ring gear to the airframe. Normally the only roll torque in a conventional helicopter is from the much lower torque from the engines. The Defiant has to have a substantial gear reduction from the engine to the prop. Large gear reduction, large torque. The AVX design was better.