Understanding Tractive Effort and Locomotive Speed under Bogie Removal

When discussing the performance of a train, the understanding of its tractive effort and the implications of removing bogies is crucial. If a train is running at a certain speed and its bogies are removed one by one, the locomotive's speed will be directly impacted. This article will break down the key concepts and explain the effects of such an operation.

Tractive Effort: The Core of Train Operation

Tractive effort is a measure of the force that a train's prime mover (such as an engine or motor) exerts on the tracks to pull the train. It is the key factor in determining how fast a train can travel and how much load it can pull. On most diesel-electric locomotives, the throttle does not control track speed directly. Instead, it regulates the engine's power output at specific rpm levels, which is what drives the digital multiple-unit (MU) control system. The engine governor maintains the engine speed to ensure that the tractive effort matches the demand.

Factors Affecting Train Speed

The speed at which a train travels is a result of a balance between the tractive effort and the train's resistance. Effective resistance includes factors such as aerodynamic drag, wheel friction, and the weight of the train. When a bogie is removed, the trains' resistance changes, and the train will find a new balancing speed. This new speed is achieved by the governor responding to the reduced load. The train may initially speed up but will eventually find a new equilibrium.

Theoretical vs. Real-World Scenario

The example given in the original question asks what happens if one bogie is removed one by one from a train running at 120 mil. In a controlled and theoretical environment, the train could theoretically speed up as each bogie is removed because the resistance decreases. However, in real-world scenarios, several factors might come into play, such as traction motor overspeed limits and the need to maintain operational safety.

For instance, if a train is running at 120 mil (or miles per hour) and a bogie is removed, the train's speed is likely to decrease rather than increase. The sudden change in the train's resistance means that the new balance must be quickly achieved. Traction motors have speed limits, and exceeding these limits could cause significant problems. Additionally, mechanical and electrical systems are designed with safety margins to prevent accidents.

Real-World Consequences: Derailment and Safety

The hypothetical scenario of removing bogies one by one raises significant practical concerns. In reality, if you were to remove a bogie while a train is in motion, the train would likely derail. The sudden reduction in the train's support structure, with no additional support from the removed bogie, could cause the train to overturn or go off the tracks.

Even if the mechanical systems were to some extent mitigated, the speed of the locomotive itself would be drastically reduced. In most cases, the locomotive would come to a complete stop due to safety measures. Disconnecting the air hoses and unlinking the carriage would trigger the automatic braking system, causing the train to slow down to a safe stop. Any attempt to continue would risk catastrophic failure.

To summarize, removing bogies from a train while in operation is a hazardous and impractical action. Whether it's a theoretical or practical scenario, the locomotive's speed is likely to decrease due to reduced support and increased resistance. Ensuring train safety and adhering to operational procedures is paramount in the railway industry.

Key Takeaways:

Tractive effort is the key to understanding train speeds. Removing bogies changes the train's resistance, affecting its speed. Theoretical scenarios must be balanced against real-world safety concerns. Locomotives and trains are engineered with safety margins to prevent accidents.