Pass or Fail "Grades"


waredbear

waredbear

Member
Have you ever topped a mountain road and started down and see the warning sign of "3% grade for next 3 miles"? This might be something new for those of you in Florida or Kansas. ;) (I was born and raised in FL, whose highest point is Britton Hill at 345 feet, so I can get away with that statement.) Anyway...I had a guy explain that to me this way. For every 100 feet horizontally (level) you will travel 3 feet down. Or on a 2% grade it will be 2 feet down for every 100 feet traveled. I find it easy to translate that into model railroad lingo this way. A 1% grade (either up or down) will be broken down as 1 inch (up or down) for every 100 inches of travel...or 1/2 inch for every 50 inches of travel...or 1/4 inch incline for every 25 inches of travel...or 1/8" rise in the track for every 12.5 inches of travel. So you want a 2% decline from that mountain top. That means you can only go 2" down for every 100" of track. Or 1" for every 50" of track or 1/2" decline for every 25" or 1/4" of downward slope for every 12.5 inches of track laid.

So you need to raise your track 3" at 2% to clear a lower track. You will need 150" or 12.5 feet of track to maintain a constant 2% incline. Anything less than 12.5 feet increases the grade.

I expect some of you reading this are scratching your head and wondering why I made this post. The reason is simple. I just read another post where somebody was explaining to somebody else the idea of a smooth, reasonable grade. I've spent the last several days reading posts here and this idea seems to get explained every so often. I saw a picture of a layout where the "grade" looked more like a ramp in a parking garage then a smooth transitional railroad grade. I don't think the modeler understands this "grade" equation. To me it is simple when you break it down like this instead of just saying you can't go over 3%.

I hope I haven't stepped on anybodies toes, I didn't mean to if I did. I'm just trying to help where I can.

Reid
 
I use a simple rule, PERCENT, the word cent derives from the Latin word "centum" meaning hundred, so 3 perCENT is 3" per 100", or fractions of, 0.3" per 10", 0.03" per 1" etc

Simple calc for clearances is "vertical distance divided by grade" grade is 2%/100, so if you need 3" of clearance, 3"/0.02=150"

The problem with the ramping effect is that modelers sometime have no transition to their grade. The train travels along at 0% then BAM 3%! I work in Civil Engineering and when designing road grades, if you have even a simple 1% downgrade and immediately have an upgrade of 1%, you need a vertical curve between them, in typical in-city designs that equates to a vertical curve length in metres matching the design speed. (ie 50km/h speed = 50m...differs on highways, usually longer)

So when a model railroad goes up 3% to clear a road/track then down 3% to 0" again, it looks terrible.

But what kind of room do you have? That is the question. Ideally you want to ease into the 3% for 2' to 3' at grades increasing from 0% to 3% over 3' and up to your 3" height and ease back down to 0% over 3' or so. Then reverse that theory on the other side of your obstacle. So you've added an extra 6' to the upside and 6' to the downside, effectively doubling the length you need but eliminate the ramping effect.

Or you can hide your transitions behind building flats...:D
 
What gets a lot of model railroaders in trouble is not so much the grade itself, but the transition into and out of the grade. If the track goes from flat to 2% virtually instantaneously, the problems will be huge. The resulting vertical movement of the couplers will cause them them to un-mate, and since the solution is to effectively lengthen the grade overall, it isn't an easy fix. Grade changes, just like curves, need easements.

don't ask how i know.....
 
kenw, good point on easement. with proper easement even the most extreme grades can be made reliable enough.

waredbear said:
I saw a picture of a layout where the "grade" looked more like a ramp in a parking garage then a smooth transitional railroad grade. I don't think the modeler understands this "grade" equation. To me it is simple when you break it down like this instead of just saying you can't go over 3%.
Click to expand...
well i reply since i have extreme grades on my layout. equation i understand however while you decided to keep grade constant at 3%, i had to find a grade to match my constant length as limited by my room.
you decided on minimum 3% and don't want to go over, up to you and very good for you that you have the room. but saying "you can't go over 3%" the only reply i can give you is "you can go over 3%".
 
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Well the CPR has some grades exceeding 4% in British Columbia, so yes you can go over 3. Talk about special train handling rules!
I know of model RR's with up to 5 percent grades, a little steep for my liking but they still work.
Another cool thing about grades is that they are all the same no matter what scale you model, from Z all the way to the prototype.
And yes unless you have an easment or transition going into or coming out of a grade, good luck with those big ol' autoracks!

One more thought on roads... I've driven trucks on 15% and steeper grades. All you can do is crawl up to the crest and hang on (hopefully) down the other side!
 
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Indeed, there are two issues that come up over and over again...grade and reach. It's a little easier for people to understand the concept of reach, since they know how far across a table they can reach to grab some food. :) I suspect I'm the guy that Reid refereed to when writing about grades, because I do it frequently. I too have some experience in civil engineering, having worked in project management with lots of engineers for a number of years. You get a great idea of grade and limitations when you're trying to design a temporary haul road to deliver a 125 ton transformer up 2,000 feet in less than three miles...plus haul the old one back down. :eek: Those were a matter of life and death. Thankfully, we don't reach that point in model railroading.

Almost no one gives any consideration to grade transition, which is as important as the grade itself. A relatively gentle grade of 1% will still have problems if you just go from zero elevation to 1% in about 4 inches of track. A 5% grade with well planned transitions will operate better than a 2% grade with no transition. I'd certainly rather see grades kept to 2% or less but grades up to 5% can work very well with good transitions and well laid track. It's so easy to consist locomotives with DCC , even steam locomotives, that it's just a matter of working out how many scale horsepower you need to haul so many scale tons over the grade. Coming down the other side is a lot more exciting than going up, since your train is basically out of control except for how well your engines can hold back that tonnage. Good motors, Back EMF, and cruise control on some DCC systems have made it a lot easier but a runaway train is still a possibility. The steeper the grade, the bigger the possibility.

I guess the message I keep trying to get across is actually calculate your grades while still in the planning state. Many times, there are ways to reduce the grade if you catch the issue early. It just makes my hair stand on end when I read that a modeler thinks "his grade will be about 3%" :mad: We wouldn't plan our track by saying we "think we need about 40 feet of track" and we shouldn't be that imprecise with grades either.
 
I read a lot about grades before building mine. When it comes to easement, well, I just don't have enough room. I needed to climb 6" in 8' on one side of my 8x12 layout and come down from the same height on the other side. That's a 3% grade. After building it, I tested it and with 2 locos and slow speeds, I had no problems pulling 12 properly weighted cars with steel wheels up the grade. as was noted, coming down was a lot more "fun". The solution here, at least for me, is reduced speed.

Most of us don't always have enough room to build an easement into a grade. To those who do, great. But I think that enough engines, proper weights of cars, good couplers, good track work and steel wheels will go a long way in making things run smoothly.
 
That reduced speed thing Bernie just noted is exactly what the real railroads have to contend with. No sitting back and watching them go!
I have a couple Atlas units that I got from a friend, I don't know what decoders he used in them, but you have to reduce the speed going down grade or they will speed up to the point where a long train will staert to push them faster than the wheels are turning. It doesn't happen with any other locos I have.
I just wrote that into my operations manual, just as the real thing does.
By the way, that steep grade in BC I mentioned earlier has some interesting rules. One being the amount of loaded cars you can descend the grade with. The more empties on the train the more loads you can bring down!
That has to do with braking related to weight.
 
The steeper the grade the more power needed to get up it.

The steeper the grade, the longer the transitions on each end so that couplers don't come apart, so that pilots and trip pins don't snag on the rails or ties, and so that the axles contributing to the tractive effort don't come off the rails.

The longer the transitions, the less run you have between them.

The less run between transitions, the steeper the grade if you still need the same change in elevation, particularly for clearances crossing over another track.

Depending on what you are modelling, and what you are running for equipment, transitions can be shortened somewhat, but steamers need transitions. Best to experiment to derive absolute minimums before you measure, cut, and solder flex track lengths. Mock it up first to demonstrate the feasibility of your assumptions.

-Crandell
 
On my new layout with grades and transitions, which was discussed quit heavily in my layout project. I'm actually really close to laying down the track for my crossover.

It was alot of work grinding and filing trenches into the 1" foam layer down to the plywood for the lower set of tracks, but it's looking pretty good. (sorry no camera right now to show everyone).

So with my 2" grade for the higher track I'm right at 2% including the transitions. So far so good, as soon as I get the track down temporarily I will do some extensive testing.

Alot of great input here on grades.
 
waredbear said:
Have you ever topped a mountain road and started down and see the warning sign of "3% grade for next 3 milesI've never seen signs for anything as minor as a 3% grade. Here in Colorado I've noticed them for 5%-11% grades. Coming down Floyd Hill there is one that warns "You are not down yet - 4 more miles of steep grades and sharp curves"

I saw a picture of a layout where the "grade" looked more like a ramp in a parking garage then a smooth transitional railroad grade. I don't think the modeler understands this "grade" equation. To me it is simple when you break it down like this instead of just saying you can't go over 3%.
Click to expand...
And then there is what they call the "ruling grade" vs "max grade". Two inches of a max grade of 3% isn't going to kill a train. Unlike a "ruling grade" of a long distance where the whole train could be in the grade at once. Where up and down hills are mixed the rear of the train could still be coming down the previous hill while the locos are going up the next. The combination of pushing and pulling make the effects of the "grade" less than they would be otherwise.

Ride the same roller coaster in the very front car of the train and then in the very last car. Very different ride experience. Same effects when the loco's top the hill but the rest of the train is still coming up.
Click to expand...
 
Selector said:
The steeper the grade the more power needed to get up it.

The steeper the grade, the longer the transitions on each end so that couplers don't come apart, so that pilots and trip pins don't snag on the rails or ties, and so that the axles contributing to the tractive effort don't come off the rails.

The longer the transitions, the less run you have between them.

The less run between transitions, the steeper the grade if you still need the same change in elevation, particularly for clearances crossing over another track.

Depending on what you are modelling, and what you are running for equipment, transitions can be shortened somewhat, but steamers need transitions. Best to experiment to derive absolute minimums before you measure, cut, and solder flex track lengths. Mock it up first to demonstrate the feasibility of your assumptions.

-Crandell
Click to expand...

One possible way to gain more run is to start the grade in the curve at each end of the straight grade. A 4'x8' layout that needs to climb 4-inches, with 18" radius curves at each end has less than 5 feet of straight (tangent) track. Trying to do that would result in a 6-2/3 percent grade. by starting the climb half-way through the curve at one end and ending halfway through the curve at the other, you can cut that to about 3-1/2 percent. (Go ahead, find my math errors! It's late!) The point is that by including the curves in the grade you can decrease the percent of incline. Of course, you'll pay a slight price in friction.

As far as overspeeding (runaways) on the downhill run, just slow the train down! On my old layout, I had a bunch of resistors wired in series with the downgrade feeder (DC). A rotary switch and several combinations of resistance allowed me to set the drop in voltage for several different engines. I'm in the process of building a new pike, and have a ruling grade of about 3-1/2 percent grade. I'm sticking with DC, but am not sure if I'll use this or not. With DCC and back EMF, etc., you ought to be able to control downgrades. Alternatively, you could get your 1/87th scale brakemen to apply the brakes! ;)

Green boards, all!
Trailrider
 
Trailrider, yes, you can begin the transitions on the curves, and I have that feature in my current layout. It can be done with some experience and experimentation with the engines needing to negotiate the entire grade. It is very difficult to do with snap track, such as EZ-Track, because those elements don't flex worth a darn, whereas flex track can be made to conform to the geometry necessary to both curve and climb at the same time, particularly a complex curve that has both azimuth and altitude increments in it. New people would have some challenging learning to do in order to achieve satisfactory results, but with patience and time, it would work for most of us.

-Crandell
 
good idea about not soldering your flex track yet! I'll use some snap track to experiment with. Bernie posted that he had to rise 6" in 8' and called it a 3% grade. Wouldn't it be more like 6%?
Also, does the scale you're working in make a difference? Traveling 8' and rising 6" in HO would look totally different in N, wouldn't it?
Norm
 
Percent of grade is percent of grade no matter if you are talking real, HO, or N. A 3% rise is 3' per 100' or 3" per 100". That is the way I see it.
 
Hi, Reid. Yes, I understand what you are saying, but wouldn't the appearance of a 3% grade look better in N scale, since the train is much smaller, and the scale distance traveled greater, than let's say, HO? Or would it be the reverse? It's confusing. I guess I'll have to mock it up & see how the train handles the grade.
Norm
 
while i was tuning my curved slope i found that transition is much more sencitive on the beginning of downhill grade. as the descent and curve started, the rail sort of went from underneath the front wheel and the car kept going straight derailing. solution was just a bit of bank - raising the outer rail so the flange can grab it better. now its working every time, even when a stray car or couple of them hurl downhill uncontrolled (runaway scenario)
the location where grade leveled out (from downhill to streight) this was not as critical in that respect
 
Actuallly, that's an interesting question about the apparent appearance of grades in different scales. There's no difference in the actual grade or effort required to make the grade in any scale, but N scale grades tend to look less steep than the same grade in HO, just because the bulk of the elements is smaller. I know when you get to G scale, a 3% grade really looks like a 3% grade. :) I think this smaller apparent grade lulls modelers in small scales to think the grade isn't so steep when they still need to calculate the actual grade to get it right.
 
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