Abstract: Single engine aircrafts, spot light, seaplanes, ultra-light planes, gyro-planes, power parachutes, trikes, airship etc commonly use fixed pitch low efficiency propellers that generate unbalancing torque. Pilots need to make offset turning to anti-torque. The subject novel anti torque coaxial counter rotation Bi-Prop Rotor fill out the empty of such variable and reversible thrust anti-torque propulsion device. The Bi-Prop Rotor comprises an on axis driving compact unobvious gear box; 2 sets multiple blades prop-rotors with variable pitch push rods and bearing-plate assemblies, co-axial tandem mounted at both sides of the gear box; a set sliding bridge mechanism that synchronized the tandem prop-rotors blade pitch turning; and a driving pulley chain or bell driving system. When engine power up the driving pulley, the primary prop-rotor mounted with the pulley rotates, and drives the gear box.