Wow.....
If you wish to "split the difference" on a requisite separation of 4" in overhead clearance, you can make the underpass track descend for anywhere from 50-100" and then rise again to its previous level. The key for this splitting is that the overhead track must make up the deficit, which we hope will amount to, or total, 4" of overhead. This means, necessarily, that the higher level track must either climb by the same amount as the nether track descends at the preferred 2% grade, or already be at that level.
So, let's say you have that figure 8 and start at the apexes of the two lobes, opposite where the crossing is. You don't want a crossing...you want an overpass. So, pick one, but start at one lobe and begin an ascension, a positive grade, so that it rises about 2" by the time you get to the overpass. The point opposite, on the apex of the other lobe, must at the same time descend at the same rate. When you get to the overpass, the total accommodation in altitude with come to the needed 4". Then, the climbing track must commence to descend to meet up with 'itself' and the other must begin to climb for the same reason, and when they meet at their respective starting points they have a folded loop, figure 8, but with that oh-so-appealing overpass.
It should be obvious, then, that neither apex lobe point can be at flat rock bottom of the layout's lowest permissible level, our you'll need to do a lot of work to create a stable and supportive platform under the layout. No...you must start both lobe apex journeys at about 2-3" above what you may have intended. This might mean a 2.5" layer of foam that must be gouged down for the descending track, and then up the other side of the overpass. The other lobe starting point would have to use some kind of built-up structure, ramp, risers, to get up those needed 2". And so on...splitting the difference.
By not building it on a flat piece of plywood. The whole part of the trasitional train set figure 8 sits flat on the ground (rug, table, plywood, whatever you put it on). Instead of doing that, if you use some sort of benchwork, like l-girder with risers and cookie cutter roadbed, you put the whole thing on a grade. Now you have more distance on a grade, so you can use a less steep grade to obtain the same clearance.
At the expense, as I said, of any level areas for sidings and whatnot. But that's applying the concept to a minimal size layout. It can be extended to bigger layouts as well. Say you have a double deck around the walls layout. At one end, you have a 4 1/2 turn helix to connect the decks, which are both completely level. If yoou start climbing on the lower deck before you get to the helix, and climb an equal distance on the upper deck past the helix, you can get the same deck separation with a helix of fewer turns. Extend it to the extreme and you have a nolix - double deck layout with absolutely no helix at all.
Just gotta think below the plywood.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinker Right, no matter how you cut it, you are extending the run to reduce the grade. You cna do this in no extra space, considering again the figure 8 layout.
how can you extend the run in "no extra space"?
greg - Philadelphia & Reading / Reading
Right, no matter how you cut it, you are extending the run to reduce the grade. You cna do this in no extra space, considering again the figure 8 layout. Normally you have a track flat ont he baseboard. Then over 100 inches of track, it rises at 4% to give a 4" clearance. If the part that was flat ALSO was on a grade, now you have 200" at 2%, ot if you arbitrarily pick a point in the grade, you have 100" going UP at 2% and 100 inches going DOWN at 2%, either way, at the crossing point you still have 4" vertical, but there no longer are 4% grades anywhere. Or some split difference - change the 4% to a 3%, and make the part that goes below the 0 level use a 1% grade. You still get a total of 4" vertical, but now there are secontions with different grade.
Exactly, agreeing with Ray. One train going from the elevated station, past the ground level station, and down to the below level station, has dropped 4". If this is done in 100", you have a 4% grade. If the train travels 200" to do this, it is a 2% grade.
No smoke and mirrors involved, just math.
Mike.
My You Tube
rrinker Ok visualize it this way. Surface station sitting at 0" elevation, there are 2 tracks at this station. 100" away are 2 more stations, one 2" avobe the level of the main station, and one 2" below the level of the main station. What's the grade from the main station to the raised one? 2" over 100", 2%. What's the grade going down to the subway station? 2" over 100", 2%. Neither train ever negotiates more than 2%. Now go another 100" down the line, and have station 2 at the 0" level. 2% down from the elevated station, and 2% up from the subway station. Again, neither train has ever negotiated more than a 2% grade, yet in the middle they were 4" apart. Stick a balloon loop on either end, connecting the two tracks - a dogboone shape. Run just one train around the now continuous loop layout. It will go up a 2% grade, pass by the elevated station, descend a 2% grade, loop around station 2, descend a 2% grade to the subway station, then climb a 2% grade and loop around station 1. The train has changed elevation by 4" yet has never negotiated a grade more than 2%. --Randy
Ok visualize it this way. Surface station sitting at 0" elevation, there are 2 tracks at this station. 100" away are 2 more stations, one 2" avobe the level of the main station, and one 2" below the level of the main station. What's the grade from the main station to the raised one? 2" over 100", 2%. What's the grade going down to the subway station? 2" over 100", 2%. Neither train ever negotiates more than 2%. Now go another 100" down the line, and have station 2 at the 0" level. 2% down from the elevated station, and 2% up from the subway station. Again, neither train has ever negotiated more than a 2% grade, yet in the middle they were 4" apart.
Stick a balloon loop on either end, connecting the two tracks - a dogboone shape. Run just one train around the now continuous loop layout. It will go up a 2% grade, pass by the elevated station, descend a 2% grade, loop around station 2, descend a 2% grade to the subway station, then climb a 2% grade and loop around station 1. The train has changed elevation by 4" yet has never negotiated a grade more than 2%.
In your example, to go between the two stations with 4" separation you have to go 200". That's how you get the 2% grade. If you only have 100" of track and need 4" of separation, you must have 4%. Can't overcome the math.
Ray
gregcwhat's the distance from 1) the surface station to the elevated station and 2) the surface station to the underground station.
100 inches between each station.
gregci assume there is a 4% grade between where the tracks cross over one another or to achieve the desired change in height.
No, none of the grades exceed 2%.
Exactly.
The depressed track becomes a longer distance because in the case of a single 4% grade, the other half of the track stays level. If instead of being level, it continues downgrade below the 0 point, you have extended the distance which has a grade in it, meaning you can reduce the grade for the identical vertical separation.
ok, you've doubled the distance from 100" to 200" to change height by 4".
maxmanOn the other hand, if the track to be crossed can be depressed below grade by 2 inches, then the track crossing over only has to go up 2 inches. We end up with the same 4 inch separation but the grade for each track is only 2%.
don't understand how "depressed" track ends up being a longer distance
maxmanSo the train starts from your surface station and travels to the elevated station on a 2% grade, which means that it has gone up 2 inches. Another train runs from the surface station to the underground station on a 2% grade, which means that it has gone down 2 inches. I think you'll agree that the two trains are now 4 inches difference in elevation, but they have each traveled only 100 inches to get there.
what's the distance from 1) the surface station to the elevated station and 2) the surface station to the underground station.
i assume there is a 4% grade between where the tracks cross over one another or to achieve the desired change in height.
davidmurray I used Woodland Scienics 4% inclines to go up 2 inches, short "Y" and switch back on the level, then up two more inches to an iron ore mine. !4 years later no derailments, no percieved engine damage. The trains are short, as it is a one stop switching branch, but it works, with no deliberate transitions, with ore cars, or box cars or gondola. Dave
I used Woodland Scienics 4% inclines to go up 2 inches, short "Y" and switch back on the level, then up two more inches to an iron ore mine. !4 years later no derailments, no percieved engine damage.
The trains are short, as it is a one stop switching branch, but it works, with no deliberate transitions, with ore cars, or box cars or gondola.
Dave
This is referenced a bit in the original post too. I don't think anybody ever said a 4% grade would cause derailments necessarily, or damage engines, or make them slide back down the grade. If your track is well laid it shouldn't be a problem. However, a 4% grade will reduce the number of cars an engine can pull significantly. I seem to recall reading that a 2% grade could reduce an engine's pulling power to like 40% of what it is on level track.
Think of your basic 'train set' figure 8 - some sets came with that track plan, all 18" radius curves, maybe 2 straight tracks for the center of the 8. Smaller than a 4x8. One part is completely level, the part that goes up and over is the only one that climbs, at a steep grade. If the next sectioon past the lowest pier didn;t stop at the table top and went lower - you'd have this effect. No extra space required. At, as I mentioned, the expense of having ANY track on the level, it would all be on a grade.
mbinsewi rrinker Starting at 0 level, go clockwise on a 2% grade going up. 100 inches later, you are 2" above the 0 point. Back to the starting point, run counter-clockwise for 100 inches, going down at 2%. 100 inches later, you are 2" below the 0 point. Total separation, 4". But you traveled a total of 200" to get that 4" seperation. Evidently, the OP doesn't have that much space. Mike.
rrinker
Starting at 0 level, go clockwise on a 2% grade going up. 100 inches later, you are 2" above the 0 point. Back to the starting point, run counter-clockwise for 100 inches, going down at 2%. 100 inches later, you are 2" below the 0 point. Total separation, 4".
But you traveled a total of 200" to get that 4" seperation. Evidently, the OP doesn't have that much space.
rrinkerStarting at 0 level, go clockwise on a 2% grade going up. 100 inches later, you are 2" above the 0 point. Back to the starting point, run counter-clockwise for 100 inches, going down at 2%. 100 inches later, you are 2" below the 0 point. Total separation, 4".
mbinsewi It sounds like it would make sense, But, if you start at the lowest on the "under" track, go around the loop to the top of the "over" track, wouldn't that total run be a 4% grade? Or am I missing something. Mike.
It sounds like it would make sense,
But, if you start at the lowest on the "under" track, go around the loop to the top of the "over" track, wouldn't that total run be a 4% grade?
Or am I missing something.
No, it would be double the run length at half the grade.
If you start at the 0 point and only go up on one side (think your traditional figure 8 pier set), you have to use a 4% grade to get a 4" rise at 100 inches past the 0 point.
One track goes up, the other goes down, each at half the grade. The disadvantage is that neither track has any level space on it, they are both on grades.
average grade depends on the difference in height and distance.
don't see it. how can you "depress" the one track and still have the "same 4 inch separation"?
gregc maxman There may be alternatives to a 4% grade. For example if it is a figure 8 the over track can have a 2% up grade and the under track can have a 2% down grade. The separaton at the crossing point will be the same. huh?
maxman
There may be alternatives to a 4% grade. For example if it is a figure 8 the over track can have a 2% up grade and the under track can have a 2% down grade. The separaton at the crossing point will be the same.
huh?
maxmanThere may be alternatives to a 4% grade. For example if it is a figure 8 the over track can have a 2% up grade and the under track can have a 2% down grade. The separaton at the crossing point will be the same.
maxman I 100% agree with the comment made by Maxman. A good method many use when working with small layouts (4 by 8) is to split the difference. 2% up 2% down. That is why it's never a good idea to plan a layout around a flat table top unless you are modeling a yard or urban scene not requiring the need for grades. You simply set your zero elavation point at 2 inches or higher above the top of your surrounding bench work using risers. If working with the newer foam products such a woodland scenics, they make both a 2 or 4 inch (flat) riser that can be used to set your zero elavation track work, you then would lower or rise from that point using the 2% incline (up or down) to achive the desired separation. This is done by placing the inclince piece on top of the flat riser to go up, or just the incline in reverse to go down. Water Level Route maxman I didn't see anything about 4 X 8. So the question still stands. His plan probably requires it for some reason or another. Yes, but what reason? Is this a logging railroad, or a class 1? A figure 8 over and under? There may be alternatives to a 4% grade. For example if it is a figure 8 the over track can have a 2% up grade and the under track can have a 2% down grade. The separaton at the crossing point will be the same.
Water Level Route maxman I didn't see anything about 4 X 8. So the question still stands. His plan probably requires it for some reason or another.
His plan probably requires it for some reason or another.
Yes, but what reason? Is this a logging railroad, or a class 1?
A figure 8 over and under?
Have Fun.... Bob.
Carl: You're right about it not being a 401K but I hate wasting money. Hard to enjoy when have three young kids. They want to see the layout and I want to show them but trying to ensure it all looks ok.
I decied to not take chances and remove the 1" foam. The foam can get used elsewhere. While fun to have such an elevation change, I think the chances of potential issues out-weigh the enjoyment or desire to test the laws of physics. Thanks all for your help!
kasskabooseDid I waste all that time and money?
First off, this is a hobby, not a 401k. You need to look at all the money you put into the hobby, even on stuff you tear out, as money that was spent on entertainment.
Second, there no absolutes, no one size fits all. Everything is a tradeoff. You've already built it, it would be silly to tear it down before testing it.
FWIW, with an Athearn HO RTR SD45 I pulled 18 BLI 70-ton hoppers (granted, not very heavy cars) up a 5% grade. It is my opinion that a lot of these "rules" are rooted in old experiences with old equipment.
I have the right to remain silent. By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.
As others propose, I think running some trials with the actual equipment that you are planning to run makes the most sense.
Personally, I started building a layout that had 2.5% grades, compounded with 18" radius curves, and that proved too much for my steam engines (4-4-0 and 2-6-0) to run consistently. I found that I can run up 1.8% with reasonble length consists of about 5-6 cars. Per a calculation that originates by John Allen, you can calculate the additional drag in curves as 32/r, in my case 18", which results in a coefficient of 1.78, which then should be added as a percentage to the actual incline. This means that my incline in those curves is equivalent to roughly 3.6%. You should definitely consider assessing that aspect (from your post I do not see if you are in fact running a curve).
The second aspect someone mentioned is the length of transition, since abruptly going from 4% to flat would definitely cause unwanted uncouplings. E.g. before and after the actual inclines you are running, you would need to transition with lower inclines, making either the 4% even steeper in between, or would not get you to the height that you actually want to achieve (do you really need that height?).
Good luck with your construction.
Urs
maxman I didn't see anything about 4 X 8. So the question still stands.
I didn't see anything about 4 X 8. So the question still stands.
I have a curving (~25" radius) 3-1/2% grade on my layout. I run trains of roughly 8 cars plus caboose pulled by medium steam and early diesels. It's pretty much the limit of what my Bachmann 4-8-2 can pull up the hill. My Broadway 2-8-2's (have traction tires) or my Proto F-3's, however, can handle plenty more. I have tested that. It's a compromise I had to make and am happy I did. Mock it up with your intended consist and give it a shot. You might be pleasantly surprised.
Mike