I have question for all of you concerning a grade that I am contemplating on my model railroad. Now the area that I am modeling (P&W Sub on the B&O Railroad) had a tough hill to crest heading out of Etna all the way to Bakerstown, PA. Now I don’t have the exact number in front of me right now but I know the hill ran a 1-2% and maybe a litle steeper all the way between those two towns. Now watching trains over that hill when I was younger it was a real battle and the always had a couple helpers shoving on the rear to get this train over the hill.
A little more background is that this trackage has a ton of curves on it and there are times it almost doubles back on itself.
What I am trying to figure out is based on the room I have and what I want to fit in it I would need about a 3.5% grade for this hill and it is no where near as windy on my railroad as in the prototype. Would my 3.5% be excessive or would it scale about right considering they prototype was around 2% in places and very windy so that would add to the “percentage” of the grade. So would my straighter 3.5% be about equivalent to the prototypes 2% with all the curves?
I do know that I want to use helpers on the grade just like the prototype was forced to do.
I know curves do “add to the grade” but I think no matter what 3.5% is going to be steep in looks and on the trains. You could eyeball it by laying out some flex track on a 2x4 and have it at 3.5% and test it out with your trains you plan to run. It would be bad to layout all the track only to find out your trains cannot climb it .
3.5% would be a mistake. Get a couple 1x4’s and some flex track. Raise the 1x4’s up with books or boxes to form a 3.5% grade. If you are using 1 eight foot 1x4, raise one end 3.5 inches, if you are using two raise the first one 3.5" and the second 7". Put a train on the grade try to start it.
Due to the physics of an HO model train vs real trains not being quite the same. Never the less, it depends on how much you want to pull up a grade and how many engines you would need.
I had a garage layout with a 2.5% grade and a train with 2 powered loco’s (Atlas GP9’s) would begin to slip if there were about 20 cars in the train. But that totally depends on the loco’s, cars, weight of cars and how free rolling the wheels are.
You can calculate grade with a simple Grade= Rise over run math formula. Say you want a 2% grade and you have a 10 foot section of track. 10 ft = 120 inches. 120 x 0.02 = 2.4 inches of rise from start to finish of the 10 foot grade (by way of example).
Curves do not add to grade in the same way as grade, and is not easily predicable. Grade is a measure of rise over run or linear track lenght vs elevation from point A to point B on the track centerline. What curves do add is some resistance due to flanges so in that sense, engines may need some additional tractive effort to overcome both the drag of the grade + the drag effect of the curves.
The the OP was looking for effects does a curve have to equal an increase in grade to give him the effect of a struggles the prototype locos had climbing the curvy hill
I gathered that much. However, due to so many variables, I don’t think there is going to be a clear answer to that. Plastic wheels, metal wheels, how free rolling are they?, weight of rolling stock, super elevation?, even code of the rail, all can affect this.
As I stated in an earlier email, there will be some “drag effect” but without a heck of a lot of controlled experimentation will there be enough inforamtion to find any direct correlation for a degree of curvature to a grade. Just think about the permutations required for all the common radii of curvature and then to find an equivelent measurement to % grade. Probably it would have to be a “draw bar” pull in tension using a gauge. Unless somenone has performed these measurements and graphed it, I doubt this information would be available. It may even vary when you combine curvature with grade and be a completely non-linear relationship.
One very good reference I used to rely on for track design is John Armstrong’s Track Planning for Realistic Operation. John approved this issue from a mechanical engineer perspective and discusses grades etc and effect on HO models. I’m not sure what else is out there which discusses this from a perspective which users a measurable and calculable system.
Probably the best thing to do is design in a modest degree of grade and go with it. Modest in a Model Railroad is probably about 2%. You can get away with steeper grades, maybe up to 3% and that might come closer to what is wanted to be simulated.
Curves do indeed add to the effective grade by creating additional friction, which must be compensated for. This has been known to the hobby for decades and to real-life railroaders for much longer.
I’ve edited my earlier comment to clarify what I meant and eliminate an unnecessary argument. Curves do not dd to grade in the strict sense of mass vs gravity so the correlation is not direct. Thus it is not a simple formula.
If this has been known in the hobby for decades … has it been quantified? If no one can quantify it this, there probably won’t be an easy answer to the original post.
For HO scale, the rule-of-thumb resistance factor for a curve is 32" divided by the radius in inches. Thus, a 24" radius has the resistance equivalent of a 1.3% grade. This assumes the curve is at least as long as the train. If the curve is shorter, the resistance is proportionately lower. So, if the 24" curve is half as long as the train, the resistance would be something like a 0.65% grade.
Nobody said it was simple. But that doesn’t mean that the effect does not exist.
“Mass vs. gravity” does not determine the effect of grade in any case – drawbar weight vs. horsepower, rolling resistance and friction are among the key components. The effects of grade are already not “a simple formula”.
So an effect exists only if it has been quantified? That’s an unusual position to take.
John Allen estimated the additional effective grade in the 1960s. His formula for HO was that the additional grade percentage caused by the curve was equal to 32/R, “R” being the radius of the curve. This figure was added to the actual grade to give the effective grade. Thus, for 24" Radius on a 2% grade, the effective grade would be 3.33%
But this was an empirical estimate and rule-of-thumb-only and may not take into account today’s typically longer railcars (which might increase the effect), modern model free-rolling trucks (which might decrease the effect), and other factors.
Having said that, Allen’s estimate does seem to be reasonably close to many observed results.
A project is underway now to measure and compare the effective grade created by curves of various radii in the model. This study will be published in the Layout Design SIG’s Layout Design Journal in 2012.
It’s not very nice putting words in someone elses mouth as you did above. For the original posters question to be easily answered, the effects need to be quantified, measureable and predictable so a design can be made.
That study sounds like it will do exactly that what the OP needs although for a lot of smaller layouts it may be overkill.
Well from what I am reading I think I am going to have to figure out a way to make it less of a grade.
As for some of the questions, I am modeling the mid 50’s with both plastic and brass steam locomotives and early diesels. I am going to be running all free rolling metal wheeled cars that are weighted appropriately.
I will also be running anywhere from a 8 to 20 car train depending on what it is for with my locals being the 8 car trains.
So now where can I get that left handed room extender?
The rule-of-thumb came from John Allen’s best guesses based on his experience. This was before the RP25 flange and the NMRA track and wheel gauge. Note that this is a non-linear formula, that I suspect has its origins in Allen’s photography work.
The actual added drag from a curve would be decidely non-linear with radius. At somewhere around 20" radius to 26" radius in HO, the RP25 wheelset has to start sliding instead of rolling - the 3 degree tread taper and flange fillet can no longer account for the difference in distance traveled. At whatever that point is - and it will vary with exact flange fillet and track gauge - overall drag will take a significant upward shot, and continue increasing at a much higher rate at smaller radii than at larger radii.
The way to come up with a reasonably valid formula would be collection of experimental data of drag on a variety of radii, and do some curve fitting from there.
Like you, the grade issue was a big issue in finalizing my design http://cs.trains.com/TRCCS/forums/t/191387.aspx. I have quite a bit of experience in model railroading but grades are an area I approach with trepidation, not from a conceptual perspective but from an operational perspective - I want my trains to look natural ascending and descending the grade and to have smooth transitions from 0 grade to incline.
I will leave you with this. I completed a highly detailed, fully sceniced model railroad that was based on a series of articles in Model Railroader. I was never happy with the layout, due to two factors:
grades that were too steep and
curves that had too tight a radius.
When I finally decided to start over I made a list of things that my layout had to have before I started to design. Here is part of the list:
keep grades to no more than 2 percent
keep curve radius to a minimum of 18"
leave plenty of room for smooth transitions to grades
no hidden trackage
no duck-unders
I know every model railroader has different goals and equipment lists, likes, dislikes, etc., but these items were at the top of my list, based on my experiences.
Well said. Sounds like a club (above) is working on such an exercise. Not exactly a recreational way to chill out! =P But then again, this could be “fun” for the engineering types!
CS NG,
Looks like a good list. Are we to assume you are an HO narrow gauager since you list minimum radii at 18-inches? And one good thing you pointed out and is easily over looked are the transitions. Just like curve easements are a part of curve design grade transitions are an important item in grade design.
I also agree, it’s better to err on the lower side of grade than higher side. I had 2.5 % in my garage layout but it did limit things. That was a smaller 16x19 foot layout with 28-inch curve minimums (HO) and train lengths at about 14 feet. It worked ok in that format.
riogrande5761, I model in HOn3, which I should have mentioned in my post. On the layout plan in my post I was able to keep minimum radius to 20"; with the vast majority greater than 22".
Grades on YOUR layout are what YOU want them to be. One of the things that you may want to do is first determine how long your average train is going to be. That also can be used to determine the length of any passing sidings that your trains are going to use. This should be done as “advance layout planning”.
Testing a grade with a train of average length goes a long way in determining how you wish to run, and your train lengths. The shorter your trains, the steeper the grade can be. Everyone talks about long trains, 20 cars or so. If you have the space to run long trains like that, you have the room for shallow grades. The smaller the layout, the more you have to compromise.
My layout is in a single car garage. My trains are 7 to 9 cars long, pulled mostly by single locomotives. I have determined that this is what “I” want on “MY” layout. If I tried to run a 20 car train, it would wrap half way around the room in some places and seem very un-scale like. I have a second level which is 25 inches above the first level. The grade to the top is between 4 and 5 percent. I double-head that grade with 9 cars and a caboose max. I HAVE to double-head it, or double the hill. I also have regular operating sessions, and the grades present a challenge that the operators have to plan for in their runs. Everyone enjoys it.
I’m not sure why you feel like you have to emphasize the it’s “My” layout and I’m going to do as “I” please, or “Its YOUR layout”, etc. Is that really necessary? Of course it is your layout, that goes without saying. No one can really force upon any of us how do enjoy our hobby so I’m baffled as to why people feel compelled to post these kinds of remarks. I think the original poster was just looking for advice and information and wasn’t being told how
