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?
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?
TRS19 98592: Win 10, ASUS B450M-A/CSM, GTX 1060-6 Windforce, 1TB EVO SSD
also a Mac install
If the spline before is flat (0%), then point between spline nodes is 2%. But if this gradient was perfectly linear it would cause a drastic gradient change at the node point. To eliminate this the gradient will gradually increase to reach the height between both node points that is equal to 2.0% overall.
The first third of your gradient will be less than 2.0%, sometimes event less than 1.0% if short distance. The middle is transitional and will vary greatly. The final third will be greater than 2.0% to make up for loss of height.
So are you saying that when I use the gradient tool in Surveyor, and set a Gradient of 2% from a spline to a spline, and another gradient of 2% to the next spline the gradient average isn't 2%? My splines show 2% for the entire grade from start to finish, highest point to lowest point. And HUD is all over the place from 1.99 to 2.35 for the actual "live" gradient point.
UPDATE: GOT IT - Just saw your post as soon as I posted this FirstSoloFlight... so the first and last are not linear... Thanks.
So to not go over a 2% gradient I need to set gradients slightly less than 2%.
Thanks to you both. I assumed 2% gave you 2%......
Last edited by 1611mac; February 10th, 2019 at 09:51 PM.
TRS19 98592: Win 10, ASUS B450M-A/CSM, GTX 1060-6 Windforce, 1TB EVO SSD
also a Mac install
If you go down the line for miles, applying a 2% gradient (without checking in back of you every 3 or 4 spline points) a gradient can become corrupted, especially if you miss a spline point ... so keep checking in back of you every 3 or 4 spline points, to make sure they are all 2%
On a double track, or quad track, just apply the gradients on the outside track, and eventually when the grade is set, apply those measured heights on adjacent tracks by measuring those spline point heights, as a inner track will be higher, as it is the shortest route
Last edited by cascaderailroad; February 10th, 2019 at 10:03 PM.
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 %
If you look on trackcharts, a grade is rarely a constant % numeral ... There are often rises and falls, and level sections on a real grade
Last edited by cascaderailroad; February 10th, 2019 at 10:12 PM.
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.
Chris Columbo: "The worlda', she isa' nota' flata'"
Also at the top and the bottom of a grade, the track actually swoops down, or flex's upward, bending like balsawood, or rubber
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.
Thanks for the added info cascaderailroad.. It can be quite frustrating learning. Especially considering how simple it is once you understand what is happening. The photo's given explain what I'm seeing I believe. I would have expected the software to figure in the beginning and ending transitions apart from the grade. IE: To me, If I ask for a 2% grade what I'm asking for is a MAXIMUM gradient of 2% between splines. To me, that is a "2% grade," not the average of gradient with transitions figured in. Just give me a max 2% by my entering 2%. What do I care what the average is with transitions included, etc etc. But if that is how the software works... that's how it works. I'm grateful to have the explanations and understanding now.
TRS19 98592: Win 10, ASUS B450M-A/CSM, GTX 1060-6 Windforce, 1TB EVO SSD
also a Mac install
Also whether it be a short section of track, or a long section of track, the % grade ratio is exactly the same amount of rise, for the same length of track
Last edited by cascaderailroad; February 10th, 2019 at 11:15 PM.
If I'm ever being particularly anal about grades there's two methods I use.
First is to just set the initial climb % at around 3/4 of the maximum of the intended grade. This works well if you're thinking ahead.
If due to testing difficulties you have to modify an existing line you add and remove spline points to achieve the desired outcome.
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.
% grade is measured by dividing the rise in the track by the length measured along the track including any curves. It is not measured using rise divided by just the straight distance between the 2 points unless there are no curves between those points.
Real railroads typically use compensated curves on grades where the grade is reduced thru the curve so the combined effect of the grade and curve are approximately the same as the uncompensated grade resistance. Since the grade resistance is 20 lbf/ton/percent grade, reducing the grade thru the curve by 0.04% x DoC reduces the total resistance by 0.8 x DoC lbf/ton which eliminates the effect of the curve.
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.
Railroads often set the tonnage allowed over a specific grade based on the anticipated speed the train will have when it reaches the grade and the minimum speed set for the grade. This allows the change in the train's momentum to haul a bit more tonnage over a grade than it normally could.
Bob Pearson
Last edited by RPearson; February 11th, 2019 at 06:23 AM. Reason: some edits for clarity
TRAINZ-UTC-TRS04-TRS06-TC1&2-TC3-TS09-TS10-TS12-TANE(KS-TEG)-TMR17
Member since 6-14-2002