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Why do rock solid 2% grades (gradients) set in Surveyor, and confirmed at exactly 2% with Get Gradient tool, show as 2.32% (and varying) in the in game HUD?
TRS19
Why do rock solid 2% grades (gradients) set in Surveyor, and confirmed at exactly 2% with Get Gradient tool, show as 2.32% (and varying) in the in game HUD?
The Surveyor setting is the average over a length between spline points - the HUD is displaying the instantaneous value. They won't be the same for several reasons, including curves and the grade of adjacent segments.
Not so ! A gradient whether it be on, a curve, or straight, is a ratio ... and a curve gradient %, is the same as a straight gradient %It is 2% between node points.
Gradient is the measure of run and rise - not the constant of the track.
In Australia we don't say 2%, we say 1:50, which means over a length of 50 units the track has risen 1 unit. This tends to be easier to explain a gradient than saying 2%. If we were to measure every individual unit of the 50 run you'd find it could be 1% in some areas and 3% in others.
Keep in mind that curves increase the effect of a gradient. A 2% gradient is only truly 2% if a perfectly straight line. Add a tight curve to that grade and 2% suddenly becomes 3.5-4.0%.
Not so ! A gradient whether it be on, a curve, or straight, is a ratio ... and a curve gradient %, is the same as a straight gradient %
So to not go over a 2% gradient I need to set gradients slightly less than 2%.
But if that is how the software works... that's how it works. I'm grateful to have the explanations and understanding now.
The train struggles in the 2nd test because there is an actual increase in train "resistance" is due to the added resistance of the curve. This effect happens on curves where there is no gradient - on level track with 0.0% grade. Since TS12 (maybe 10?) curve resistance has been include in Trainz. Typical estimate of the effect in real life is 0.8 x DoC lbf/ton, where DoC is the curve's degree of curvature and ton is 2000 lbf. For railroad curves in the US DoC is usually based on a 100 ft chord length. With a radius of R in ft, the DoC is approx. equal to 5730/R. The effect of curve resistance in Trainz appears to be in that general neighborhood.Read the first sentence of the last line again. I'm talking about the effect of the gradient, not the actual value. Test it for yourself. Run a train on a long straight track. Fix the throttle position and climb a grade. Now make the grade a continuous curve. The train will struggle compared to the first test.
The gradient is still 2%, but the effect on the train is greater.
Trainz track spline is a 3d curve that will be straight only if the straighten flag is set for it and not the for preceding and following section. In this case the track will have a constant grade between the 2 vertices. The preceding and following sections will have some 3d curvature (and varying grade in the vertical plane) based on their endpoint heights and straighten flags of the sections connected to them. Railroads actually design vertical curves into the track where changes in the grade take place with the constant grade set between the end points of those curves. We can do similar things in Trainz and I have but in examining a lot of routes in Trainz I can't say I've seen any that included this construction feature of real railroads.SailorDan
The gradient that the train actually experiences is the average over the length of the train. The engine might see more than 2%, the caboose less, but if they average out to 2% then that's what the train experiences. That's why you will often see instantaneous grades that exceed the allowed maximum. If the train is long enough, and the excess grade short enough, the average for the train is still within limits. And if the train isn't long enough then it's unlikely to be too heavy for that short-term excessive grade. So you actually have three grades to consider - the surveyor setting which is an average over spline points, the instantaneous readout from the HUD, and the average over the length of the train.
The train struggles in the second case because the changed curvature in the lateral plane changes the curvature in the vertical plane. There is no reason that this should happen - it just does.The train struggles in the 2nd test because there is an actual increase in train "resistance" is due to the added resistance of the curve.
Not necessarily. The gradient that the train actually experiences is the average over the length of the train. The engine might see more than 2%, the caboose less, but if they average out to 2% then that's what the train experiences. That's why you will often see instantaneous grades that exceed the allowed maximum. If the train is long enough, and the excess grade short enough, the average for the train is still within limits. And if the train isn't long enough then it's unlikely to be too heavy for that short-term excessive grade. So you actually have three grades to consider - the surveyor setting which is an average over spline points, the instantaneous readout from the HUD, and the average over the length of the train.