A spinning propeller will generate two reaction forces: one force perpendicular to the plane of rotation, known as thrust and one component in the plane of rotation, known as propeller torque. Propeller torque is the resistance to motion in the plane of rotation.
For a propeller to work and to provide thrust, the propeller torque must be overcome or be balanced by engine torque. Adding power causes the engine to rotate faster, increasing engine torque. As the engine rotates faster, the propeller also rotates faster, increasing propeller torque until the point where it comes into balance with engine torque and rpm stabilizes.
Functions Propeller Shaft-
The main function of propeller shaft is to connect two mechanical elements or component i.e. one is driving element and another is driven element. We can transmit torque/turning moment and power from one component to another which are apart at some distance. Propeller shaft in vehicle and ship just connects the main engine to the power drive which drives the vehicle or ship.
The main failure which is generally observed in propeller shaft is twisting moment due to excessive shear stress. By proper designing of shaft we can overcome this failure.