Single-engine planes do not roll in the opposite direction of the propeller because they rely on a different mechanism for stability and control compared to helicopters.
In a single-engine airplane, the propeller generates thrust by pulling or pushing the aircraft forward. The aircraft's stability and control are primarily achieved through the use of control surfaces such as ailerons, elevators, and a rudder. These control surfaces allow the pilot to control the plane's roll (rotation around the longitudinal axis), pitch (rotation around the lateral axis), and yaw (rotation around the vertical axis).
When the engine is running and the propeller is generating thrust, the torque produced by the engine tends to rotate the aircraft in the opposite direction of the propeller's rotation. However, this torque effect is counteracted by the design of the aircraft. The wings of the plane are built with a slight upward angle, known as dihedral, which helps stabilize the aircraft in flight. The dihedral angle creates a natural rolling tendency that counteracts the torque effect, keeping the plane level.
Additionally, the control surfaces of the aircraft, particularly the ailerons, allow the pilot to actively control and counteract any rolling tendency caused by the torque effect. By adjusting the ailerons, the pilot can generate a differential lift on the wings, causing the aircraft to roll in the desired direction independently of the propeller's rotation.
In helicopters, the situation is different. Helicopters use a tail rotor to counteract the torque generated by the main rotor. Without a tail rotor, helicopters would indeed tend to rotate in the opposite direction of the main rotor's rotation due to the torque effect. To eliminate the need for a tail rotor, some helicopters use alternative mechanisms such as a NOTAR (No Tail Rotor) system or a coaxial rotor system, which provide counter-torque without a separate tail rotor.
In summary, single-engine airplanes rely on dihedral angles and control surfaces to counteract the torque effect and maintain stability, while helicopters without a tail rotor require alternative mechanisms to counteract the torque and prevent unwanted rotation.