Final answer:
A fixed pitch propeller has a non-adjustable blade angle, while a controllable pitch propeller's blade angle can be altered for efficiency and performance. Helicopters often employ a tail propeller or counter-rotating blades to maintain stability, complying with Newton's third law.
Step-by-step explanation:
The difference between a fixed pitch propeller and a controllable pitch propeller is that in a fixed pitch propeller, the blade angle cannot be adjusted whereas in a controllable pitch propeller, the blade angle is adjustable. This adjustment allows for improved efficiency and performance in various flight conditions. Fixed pitch propellers are not solely used in helicopters and controllable pitch propellers are not always three-bladed. The design of a fixed pitch propeller does not inherently provide better climb performance than a controllable pitch propeller.
Helicopters with a single set of lifting blades use a tail propeller to counteract the torque effect of the main rotor, ensuring that the helicopter body does not rotate in the opposite direction, following Newton's third law. With two sets of lifting blades rotating in opposite directions, helicopters do not require a tail propeller because the counter-rotating blades cancel out the torque effects on the helicopter's body, providing stability and better control.