Counterrotating Flywheel for Single Engine Prop Planes: Myths and Facts

The idea of using a counterrotating flywheel to counteract engine torque in single engine prop planes has been a topic of debate among aviation enthusiasts and engineers. In this article, we will debunk the myths surrounding this concept and explore why simple solutions are often the best solution.

The Role of Aerodynamic Forces

Engine torque in a prop plane is primarily caused by aerodynamic forces acting on the rotating propeller blades. At a steady state RPM, the torque is due to these aerodynamic forces, which are highly predictable and manageable. The concept of using a flywheel to counteract this torque is based on an oversimplification of the physics involved. A flywheel, to be effective, would need to be extremely heavy and large, adding unnecessary weight and complexity to the plane.

When thrust is suddenly increased, the inertia of the propeller can produce forces that are independent of aerodynamic forces. This is when a flywheel might theoretically offer some benefit, but even then, the real-world benefits are minimal compared to the drawbacks. Other solutions, such as two-engine designs with counter-rotating propellers or contra-rotating propellers on a single shaft, are more effective and widely used in aviation.

WWI Pilots and Practical Examples

During World War I, single-engined fighter pilots often used a design trick to increase their roll rate in dogfights. They would either increase the throttle to add torque in the direction of the desired roll or use a “coupe” switch to cut the engine and cancel torque in the opposite direction. This is a practical example of how torque can be managed effectively without the need for a heavy flywheel.

To illustrate the point, consider a power drill held at arms length. When you pulse the trigger, you can feel the unbalanced torque of the rotor accelerating. Once the drill stabilizes, this torque dissipates. Similarly, in a prop plane, the torque from the engine stabilizes at a steady state, and the need for a flywheel to counteract this torque is negligible.

Why Simple Solutions Work Best

One of the primary arguments against using a flywheel is the increased weight and complexity it adds to the plane. A flywheel needs to be extremely heavy to match the torque, and it can only be effective if the propeller cannot change pitch. However, in a prop plane, the air drag can cause changes in pitch, making a flywheel an ineffective solution.

Instead of adding a heavy and complex flywheel, it is far more straightforward to counteract engine torque with aileron and rudder trim tabs. This method is simpler, lighter, and cheaper, and it provides adequate control over the plane's stability and maneuverability.

The key takeaway is that for light aircraft, it is better to keep everything as simple as possible. While advanced technologies like a counterrotating flywheel might seem appealing, they often come with significant trade-offs in terms of weight, maintenance, and cost. Opting for simpler, proven methods is usually the best approach for single-engine prop planes.

Conclusion

In conclusion, the idea of using a counterrotating flywheel to counteract engine torque in single engine prop planes is a myth. The physics behind the torque are well understood, and simple solutions like aerodynamic design, careful engine alignment, rudder trim, and counter-rotating propellers work more effectively and efficiently. For light aircraft, keeping the design simple is the key to achieving optimal performance and reliability.