Birotary Engine – The Antivibration Property

Following the installation of the Birotary engine into an airplane, we observed a notably smoother operation compared to the commonly used Rotax 912 engine in similar aircraft. Our test pilot was impressed with the engine’s calm and smooth operation, which did not transmit vibrations to the airplane’s chassis. It’s worth noting that the Birotary engine incorporates the same torsion damper as the Rotax 912, indicating that the reduced vibrations are not due to the damper. The superior antivibration characteristic of the Birotary engine is attributed to its design.

Initially, it is necessary to identify the main sources of vibration. There are two primary sources: the movement of parts and the torque fluctuations induced by the combustion cycle. These issues are thoroughly discussed in our second project. In the Birotary engine, the first source of vibration is addressed by the tri-star arrangement of three cylinders with a single bent crankshaft, along with pistons of identical size and weight, allowing for excellent balance. The second source of vibration is significantly diminished by the birotary concept, which governs the movement of engine parts.

The vibrations in question arise from the tilting moment caused by inertial forces. As the engine block rotates in the opposite direction to the crankshaft, the accelerations of the engine block and crankshaft are nearly equal in magnitude but opposite in direction, which substantially reduces the tilting moment.

Furthermore, this design approach also helps minimize the gyroscopic moment of the entire powerplant unit. The rotation of the engine block also increases the total inertial mass, which positively affects the smooth operation of the powerplant unit.