Monk Subdivision - Assessing the Grades

A week ago, I wrote a very long blog post about how I could improve the grade on the layout. Lots of numbers and even a spreadsheet. It explains how curves and grades compound together to create a horror show. I postponed its publication because some tests were performed in the last few days to better understand what was really happening. I discussed the matter with friends and people online... Most replies left me perplex, but others did confirm me that compensating curvature to get a constant effective grade was the way to go.

A 4-6-2 struggling with an effective 2.5% grade

The first test was very simple and served to determine the pulling power of my Bachmann 4-6-2 light Pacific on a straight grade. The goal was to find out the maximum grade permissible to haul a decent passenger consist made of one express boxcar and 5 heavyweight coaches. Using wood shims and a 8 feet long straight plank of pine, I built a temporary track. At 1.6% I didn't see any serious loss in power. Sure the train slowed down a little bit, but it wasn't struggling nor exaggerate. About the speed reduction you would expect in real life. 

Testing performance on a straight grade to get useful data

At 1.8%, it's still within acceptable limit if the train pulls 3 very free rolling coaches and a boxcar. At 2%, you break the proverbial camel's back and performance goes down the drain. Serious slowing down and wheel slippage. This is good information because it means the grade + curvature factor should never exceed 1.8%-2% to ensure smaller and lighter steam locomotives can perform adequately. Let's see the data for my layout.

First, eyes can trick you. When you look at a grade curving toward you, an optical illusion is created and it seems the incline is much steeper than it is. I was under the expression that my grade wasn't constant and that it was the chief cause of all my issues. Using a level and a ruler, several measurement were taken. When compiled, a constant 1.6% grade was obtained, which was in the ballpark of what I planned. It's also the Bachmann 4-6-2 theoretical limit to pull a decent consist. A conclusion imposed itself: I didn't take into account the curvature effect on the grade. Maybe I thought it was of little consequence when using 36" curves. Go figure out... When I designed a helix for the first version of this layout, I took it into account.

We know from John Allen and John Armstrong that the effective grade for a curve is Grade + 32/R, R being the curve radius. These results are a rule of thumb obtained by empirical means. They are not a scientific formula, but they give an excellent approximation when dealing with model railroad typical radii.

For Monk subdivision, the radius is 36" (32/36) thus we get an additional 0.9%... Everybody knows that 1% in railroading (the real thing) is a serious operation challenge that can warrant helpers or double heading. No different with model trains even if their pulling power isn't scalable. A mere 1.6% is thus bumped to 2.5%, which is starting to enter Woodland Scenics trainset territory... and for our poor Bachmann 4-6-2, it's far beyond the 2% threshold.

I seriously won't go further with math explanations has I'm terrible with numbers and several modellers have done much more valuable and serious work than me in that department. The layout goal isn't about doing feats of engineering, but rather getting decent and consistent results whatever the quality of locomotives. It's understandable that the current grade works well with quality diesel and steam locomotives. One could elect to only run these excellent models, but this isn't the reason why I designed that layout, otherwise, I would have made different choices. This layout is a display case for my entire collection, thus it must takes into account the poor runners too.

Diesels are versatile compared to steamers...

That leaves us with contemplating various solutions, but let's start by assessing the acceptable grade for curves. Let's say we want a ruling effective grade of 1.8%. It means 1.8% - 0.9% = 0.9%. We should thus try to build something that isn't over 1% in the yard.

The actual numbers are a rise of 1.5" for 8 feet.  The curve length is about 5 feet long thus an elevation of almost an inch at 1.6%. We must drop that a little bit. At a 0.9% grade, it means an elevation of about 1/2". Can it be done? Yes, if I spread the grade over a longer length.

Fast forward a few days and I've done exactly that. I dropped the riser in the yard and curves to get a 0.9% grade and extended the straight grade over the swing gate. Taking curvature into account, both sections now have an effective grade of approximately 1.7%. The Bachmann 4-6-2 can now easily pull a decent consist of one boxcar and 6 poorly rolling Athearn Blue Box heavyweight cars! Now, imagine if I succeed adding a little bit more weight into the boiler and making the car trucks free rolling! We've reached the point I wanted. I'm quite happy to have solved that issue even if it meant tearing down previous work and removing all the tracks that were already installed.

I also relearned a lesson. I wasted one week calculating things instead ot tweaking pieces of wood when the actual work took about 1 hour... Another proof overthink problems solves nothing. That said, I've learned a good share about pulling power, free rolling trucks, grades and operational challenges. These are aspects I never really faced seriously with other layouts in the past. As expected, this layout is not only a project, but a challenge to myself and my skills in model railroading.

On a side note, I found out track on fiberboard are noisy so a cork roadbed will be added to reduce noise transmission. Some tests shown me it was indeed the way to go. I guess trying to be cheap didn't pay off in the end.