How do you know when your turn is properly balanced?

The correct choice is grounded in understanding the principles of coordinated flight. When the turn is properly balanced, the ball in the inclinometer, which is a part of the turn coordinator instrument, will remain centered. This indicates that the forces acting on the aircraft are in balance, allowing for a coordinated turn without skidding or slipping.

In a balanced turn, the aircraft's centrifugal force is aligned with the vertical component of lift, indicating that the pilot is using the appropriate amount of aileron and rudder control inputs. If the ball drifts to one side, it signifies that the aircraft is not in a coordinated turn, perhaps indicating too much or too little rudder input.

Maintaining consistent airspeed, stable engine RPM, or a steady heading indicator can be helpful, but they do not specifically assess the coordination of the turn as the inclinometer does. Therefore, while these factors may contribute to the overall performance of the flight, the most reliable indicator of balance during a turn is indeed the position of the ball in the inclinometer.