Taylor Scott
When designing model railroad layouts, it is important to consider the incorporation of grades and curves. Curves in particular are intriguing as they are portions of circles, and the curvature is determined by the angle between two lines drawn from the circle's centre to points on its circumference 100 feet apart, rather than the radius. This design consideration is a crucial weapon in the battle against gravity and geography. An important aspect of railroad curves is their superelevation or banking, where the outer rail is raised higher than the inner one to counteract centrifugal force. The degree of superelevation, or cross-level, can vary depending on the desired speed of the trains traversing the curve, with higher speeds requiring greater superelevation. These design principles are not limited to model railroads but are also relevant to full-scale railroad engineering.
| Characteristics | Values |
|---|---|
| Purpose | To counteract centrifugal force as a train rounds a curve |
| Track Design | The outer rail is raised to a higher level than the inner one |
| Measurement | The difference in elevation between the two rails, called the "cross-level", is used to measure superelevation |
| Maximum Difference | On main lines, the maximum difference in "cross-level" can be up to 6 inches |
| Speed Considerations | A higher superelevation allows for faster speeds on curves, e.g., 95 mph on a 1-degree curve with a 6-inch difference |
| Maintenance | Reduced superelevation can cause excessive wear on the low rail, especially at slower speeds |
| Operational Considerations | Fast trains may require more banking than slower freight trains, and in some cases, the solution is to have the fast trains tilt |
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What You'll Learn
How to design model railroad grades and curves
When designing model railroad grades and curves, there are a few key considerations to keep in mind. Firstly, railroad tracks can be either ""tangent" (straight) or curved. Curves are portions of circles and are important to break the monotony of long straight tracks. The curvature of model railroad tracks is typically expressed as the angle between two lines drawn from the centre of the circle to two points on its circumference 100 feet apart, rather than in terms of radius. This angle is measured in degrees, minutes, and seconds.
The grade, or slope, of a railroad track is another important aspect. It is expressed as a percentage, calculated by dividing the rise in elevation by the length of the track. For example, a 1% grade means that for every 100 inches of track, the elevation rises by 1 inch. The maximum grade is determined by factors such as locomotive power, locomotive weight, and the number and weight of train cars. Steeper grades can cause difficulties for locomotives hauling long strings of cars, so it is generally recommended to keep grades below 2%.
When designing curves for model trains, it is important to consider the width of the space available. Longer trains may struggle with tighter curves, and turnouts should be avoided at the top or bottom of grades to prevent derailments. Additionally, vertical and horizontal clearances must be considered to ensure trains can safely pass under bridges and around curves without colliding with structures or trackside accessories.
To counteract centrifugal force on curves, the outer rail is typically raised higher than the inner rail, a feature known as "superelevation" or "banking". This helps trains maintain traction and stay on the tracks at higher speeds. The difference in elevation between the rails, known as the "cross-level", can be up to 6 inches on main lines, allowing for higher speeds on curves.
In summary, when designing model railroad grades and curves, it is important to consider factors such as track curvature, slope gradients, locomotive and train car capabilities, space constraints, clearances, and superelevation to ensure optimal performance, safety, and visual appeal.
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The importance of superelevation on curves
The benefits of superelevation are twofold: firstly, it mitigates the lateral forces exerted on the train, providing a more comfortable ride for passengers. Secondly, it helps distribute the load evenly across both rails, reducing excessive wear on the low rail, which can occur when trains traverse heavily superelevated curves at slow speeds. This wear can be detrimental to the reinstatement or speeding up of passenger services. Therefore, railroads must carefully consider the degree of superelevation based on expected train speeds.
The calculation of superelevation involves determining the equilibrium speed, where the centrifugal force is balanced by the cant (superelevation), resulting in no unbalanced radial acceleration. This equilibrium speed is influenced by factors such as the radius of the curve, cant deficiency or excess, and transition length. Additionally, the speed of slow-moving trains, such as goods trains, plays a role in determining the cant value.
Model railroad enthusiasts often seek to incorporate superelevation into their designs to enhance realism. This can be achieved through various methods, such as using cardstock shims, styrene strips, or balsa wood strips to raise the outer rail. By carefully implementing these techniques, modelers can create visually appealing and realistic representations of superelevated curves on their layouts.
In summary, superelevation on curves is of paramount importance in both full-scale and model railroads. It ensures the safe navigation of trains around curves, enhances ride comfort, and prolongs the lifespan of railroad infrastructure. By carefully calculating and implementing superelevation, railroads can optimize train speeds while minimizing wear and tear on the tracks, contributing to the overall efficiency and safety of rail transport.
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The use of tangent and curved tracks
Railroad tracks are either "'tangent'" (straight) or curved. Curves are portions of circles, but their curvature is not expressed in terms of radius. Instead, it is given as the angle between two lines drawn from the circle's centre to two points on its circumference 100 feet apart. For example, a 5-degree curve covers 5 degrees of a circle for each 100 feet of track. Curvature can be expressed in terms of the number of degrees traversed by 100 feet of track.
Track geometry is concerned with the properties and relations of points, lines, curves, and surfaces in the three-dimensional positioning of railroad tracks. The term is also applied to measurements used in the design, construction, and maintenance of tracks. Track geometry involves standards, speed limits, and other regulations in the areas of track gauge, alignment, elevation, curvature, and track surface.
The three main track types based on horizontal layout are tangent track (straight line), curved track, and track transition curve (also called a transition spiral or spiral). Transition spirals connect tangent and curved tracks. They are spiral-shaped lengths of railroad track that provide a gradual transition between sections with different profiles and radii, such as between straightaways and curves. This prevents undesirable sudden changes in lateral (centripetal) acceleration.
An important feature of a railroad curve is its "superelevation," or banking. To counteract centrifugal force as a train rounds a curve, the outer rail is raised higher than the inner one. This difference in elevation, called the "cross-level," is used to measure superelevation. On main lines, the maximum difference in cross-level between the two rails can be as much as 6 inches, allowing for speeds of up to 95 mph on a 1-degree curve or 45 mph on a 5-degree curve.
There are three types of curves: simple, compound, and reverse. A simple curve has the same radius throughout, while a compound curve comprises two or more simple curves with different radii but the same direction of curvature. A reverse curve, on the other hand, comprises two or more simple curves with opposite directions of curvature and is sometimes known as an "S" curve or serpentine curve.
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The impact of speed on curve banking
The speed of a train traversing a curve has a significant impact on the banking, or superelevation, required to ensure the train remains on the track. The rated speed, or balancing speed, of a curve is the velocity at which a vehicle will remain on its designated path, and it is influenced by the angle of incline and radius of curvature of the curve. A higher rated speed requires a greater degree of banking to counteract the increased centrifugal force acting on the train.
For example, on main lines, the maximum difference in elevation, or cross-level, between the outer and inner rails can be up to 6 inches, allowing for a superelevation suitable for speeds of up to 95 mph on a 1-degree curve. However, the same superelevation on a 5-degree curve would only accommodate a speed of 45 mph. Therefore, when designing railroad grades and curves, engineers must carefully consider the expected speeds of the trains and construct the track with an appropriate degree of banking to ensure safe passage.
The speed of trains also affects the wear and tear on railroad tracks. Trains travelling at relatively slow speeds on heavily superelevated curves can cause excessive wear on the low rail, prompting some railroads to reduce curve superelevation when passenger trains were discontinued. This reduction in superelevation, however, can hinder the reinstatement or speeding up of passenger service, as the tracks may no longer be suitable for higher speeds.
Additionally, the speed of trains can influence the design of banked curves in model railroads. While curvature in model layouts is typically not expressed in terms of radius, the principles of centrifugal force and friction still apply. Therefore, when designing curves for model railroads, hobbyists may consider the expected speeds of the model trains to ensure they remain on the track, especially when navigating tight turns or curves.
In summary, the impact of speed on curve banking is significant in the design of railroad tracks and model railroads. Higher speeds require greater degrees of banking to counteract centrifugal forces, and the speed of trains also influences wear and maintenance requirements. By carefully considering the expected speeds and constructing tracks with appropriate banking, railroads can ensure the safe passage of trains while also managing the wear and performance of the tracks over time.
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The role of centrifugal force on curves
When designing model railroad layouts, it is important to consider the effects of centrifugal force on curves. Curves on railroads are portions of circles, and the curvature is determined by the angle between two lines drawn from the centre of the circle to two points on its circumference that are 100 feet apart. This curvature plays a significant role in managing the impact of centrifugal force on trains traversing the curves.
Centrifugal force is a fictitious force experienced by passengers in a vehicle changing direction, such as when a car enters a curve. This force gives rise to the feeling of being pulled towards the direction opposite to the curve. In the case of a left-bending curve, passengers experience an apparent force pulling them to the right. This centrifugal force is necessary to explain the sudden acceleration towards the outside of the curve relative to the car.
On railroad curves, the outer rail is raised to a higher level than the inner rail, a feature known as "superelevation" or "banking." This design counteracts the centrifugal force as trains round the curve. The difference in elevation between the two rails, called the "cross-level," can be up to 6 inches on main lines. The amount of superelevation is crucial, as excessive superelevation at slow speeds can cause wear on the low rail, while insufficient superelevation may restrict train speed.
The concept of centrifugal force is also relevant in the design of railway vehicles. To manage the effects of centrifugal force on curved tracks, some trains are designed with tilting mechanisms. This tilting allows for higher superelevation, accommodating faster trains while ensuring slower trains remain stable. By incorporating tilt technology, railroads can optimize their operations for both fast and slow-moving trains.
In summary, the role of centrifugal force in curves on model railroads is significant. It influences the design of both the railroad layout and the trains themselves. By understanding and managing centrifugal force, model railroad enthusiasts can create realistic and functional layouts that mimic the challenges faced by real-world railroads.
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Frequently asked questions
Banked curves are portions of circles on a railroad track where the outer rail is raised to a higher level than the inner rail. This is done to counteract centrifugal force as a train rounds a curve.
Banked curves help trains stay on their tracks by counteracting centrifugal force. This force acts on trains as they round a curve and can cause them to tip over. By banking the curves, the train's momentum is shared, reducing the likelihood of derailment.
The degree of curve banking, or superelevation, is measured by the difference in elevation between the two rails, known as the "cross-level." On main lines, the maximum cross-level can be up to 6 inches, allowing for speeds of up to 95 mph on a 1-degree curve or 45 mph on a 5-degree curve.
Curve banking is more critical for faster trains than slower ones. If the superelevation is too high for the train's speed, it can cause excessive wear on the low rail. This has led some railroads to reduce curve superelevation, impacting the speed and efficiency of passenger service.
