Trackplanners needed

Mitchell:
Since noone else has stepped forward yet, I'd like to offer my version for consideration.

Some comments first:
To come up with layout design elements for your layout, I looked at a topographic map of Mullan Pass and traced the RR from Helena to Blossburg trying to identify features you might want to model.

I made some notes about the elevation of the track at various points, but also elevations to either side of the track and where roads and rivers crossed the RR so I could incorporate them into the final plan.

I dropped the double track main early on in my design efforts for a few reasons:
1. to make the track plan reflect the Mullan Pass trackage through the mountains (even though you said the Mullan Pass was just an example of what you wanted);
2. a prototype single track main is cheaper to carve out of the mountain sides than a double;
3. a model single track main is easier to fit onto a shelf than a double;
4. double tracked helixes (either bowl-shaped spiral or cylindrical stacked) take up more space than single;
5. If you wanted the double main for continuous running, you could opt for the techno-magic of automatically reversing circuitry.

When deciding on track configurations, I wanted to preserve the east is right, west is left orientation through out the layout, rather than going west to the left on one level and west to the right on the other. Also, I tried to make the curves in the track plan match the curves in the topographic map.
1. The track west of Helena is mostly straight until the Narrows where it turns sharply west, so I put the Narrows in the corner of the room.
2. Austin has a curve to the right followed by the left curve through Iron Ridge and then Weed looks down the mountain toward Austin. Putting the bow around Austin and Weed also brought the siding closer to the front of the layout for easier reaching. Since there is no need to reach to Iron Ridge except to clean track, the tracks could go back as far as you want. I was going to put Weed at 50 inches but opted to use a helix to raise it higher above Austin.
3. I debated putting the Greenhorn Trestle directly across the aisle but decided against that because the bents would extend too low and you would be constantly inserting or removing the bridge and that would only increase risk of damage...so Greenhorn Trestle is in the corner (curving to the left, like the track near the bridge).
4. Skyline Trestle over Austin Creek is also curved to the left, so it fit in the other corner just before the Mullan Tunnel East Portal.

Minimum radius on the layout is 18 inches in staging, the helix, and the reversing loops; main line minumum is 19 inches. All the lines make it look like a complicated layout, but it is just a reverse loop to reverse loop single track main design that climbs through 3 levels.

The track plan:

The lowest level is at 44 inches and has a reversing loop and four 6-foot long tracks for the East Staging Yard. In the track plan, lower level track is shown in solid green lines, and the front of the lowest level shelf is indicated with a dashed green line. I opted for visible staging 4 inches below the main level rather than hiding it where maintanance, repair, and fiddling with cars would be impossible.
Some people don't like to do staging that way, others do...I'll try to post a pic of a similar spot on my layout so you can see what I have in mind.

The middle level is reached by a 1.5 loop helix. Points along the ROW: Helena Yard (elevation 48 inches), the Narrows (+48"), Austin (49"), and Iron Ridge (50"). Middle level tracks are indicated by a solid purple line, and the front of the middle shelf is shown in a dashed purple line. There is a 3-loop bowl shaped spiral helix that rises to Weed (elevation almost 57"). The tightest radius in the helix is 18" held for a fraction of the arc and the radius continually increases by 1.5 inches each loop.

The upper level is reached by exiting Weed into a 2 loop helix that rises to a removeable section that spans the entrance to the layout room. The narrowest point in the entrance aisle is about 20 inches wide:sad:, but the aisle opens immediately on either side of the choke-point. (FWIW, we can probably tweak the plan a little to get two or three more inches across that choke point, if you absolutely need it.:teeth At 63" elevation, the removeable section is almost high enough to be labelled a "nod-under" rather than a duck-under for anyone not afflicted with back problems.

The upper level is all at 65 inches and includes Greenhorn Trestle, Skyline, Skyline Trestle, the East Portal of the Mullan Tunnel, the West Staging Yard (which I labeled Blossburn/Elliston and which could extend all the way behind the helix to the doorway), and a reversing loop which could fit around the top/outside of the helix.

Except around the helixes, the lower level is 30 inches deep, the middle is 24 to 30 inches deep, and the upper level is 12 inches deep. I set the base elevation at 44 inches, but you could adjust that up or down to your own preference. Click on My Albums linked below for an example of a double deck layout...lower at 48 and upper at 65--note the 12 inch tall benches and step stools I use to bring the upper level to a functional height of 53 inches.

 

Mitchell:
You are certainly welcome! Thank YOU for the compliments.

The short answers:
1. 2%.
2. 2 scale miles (66 feet).
3. Yes.

The long answers:
1. Maximum grade is 2% in the helixes. Because of resistance through the continual curve, it is harder to pull long trains up a 2% helix than up a 2% straight track. The maximum grade in the visible portion of the layout is also 2%, but since track is straighter and the length of the grade is held for shorter distances before reaching level ground, there may not be as much drag on a long train as in a helix.

Typically, 2% is considered an adequate grade for a model railroad. On logging RRs, modelers will often have steeper grades because they run shorter trains of maybe only 3 to 5 cars. If you plan on running trains that are longer, I would recommend you limit yourself to 2 or 2.25% grades even with helper service (although other N-scale modelers might have a different opinion about steepest grades on a layout like yours).

2. The visible main from the east end of Helena where the staging track comes out of the top of the helix all the way through Mullan Tunnel is about 66 feet--about 2 scale miles. I didn't count track in the helixes (2 scale miles) or staging and reverse loops (3/4 scale mile) as part of the modeled mainline.

3. I left the Helena area open so you could put in anything you wanted, including helper service. I would recommend an arrival departure track with one end by where the track comes out of staging, and the other end about 2 feet from where I labeled the Narrows. A yard lead could extend around the corner with most of it hidden behind the Narrows scenery. The topographic map showed classification tracks between the turntable and roundhouse near the back middle of the yard and the main at the front.

When modeling helper service in N-scale, especially on trains with long and light container cars, I strongly recommend you add your helper loco(s) at the front of the train. Setting helpers at the end of a train negotiating curves and grades will cause derailments, because, no matter how closely you think you've speed-matched your locos, there is bound to be enough difference to stretch or compress the cars enough to force a derailment.

Test this for yourself by coupling together the 2 or 3 locos that will pull the train and position them exactly one inch ahead of the loco(s) you will use as helpers. Using a single throttle, run them over 2 scale miles of track at correct speeds with all stops and starts that would normally occur in the run. Measure how far apart the couplers are now. The difference from exactly one inch is the amount of stretch or compression you will have occuring on your trains. Can your train accommodate that difference without derailing? Probably not.

It might be argued that DCC would let you adjust the speed of the pusher/helper as needed, but it takes LOTS of practice with the same locos over the same route to become proficient, and having cars of different weight the next trip will change your locos' performance.

 

Mitchell:
1. What are your hopes or preferences for the helix and the loops to staging in terms of
a. cylindrical stacked versus bowl-shaped helix,
b. inches of rise and fall,
c. grade within the helix, and
d. minimum/maximum radii?
2. Have you settled on how much separation you want between decks?
3. What do you think of visible staging? (If that part of your drawing IS to scale, then you've done a nice job of keeping the 3 levels from running above each other along that side of the layout...definitely great way to reduce construction and maintenance headaches.)

4. It looks like you are planning to install the trestle near Torrens Creek directly over the loops down to staging. There are 2 potential drawbacks to this location.
First, maintenance of the loops to staging may be difficult. The distance between the rail heads of the track on the trestle and the track from Charters Towers to the loop for staging will be fixed by your height gained in the 5 loop helix (plus perhaps 3 inches if you continue a strong grade from the trestle to the top of the helix down and from the bottom of the helix around the entire layout to Charters Towers). With the 12" radius 5-loop helix you may have a maximum of 10.5 inches between the critical railheads.

Assume the trestle is 1/3 as tall as it is long...about 4 inches from railhead to where the longest bents are secured into the scenery, probably on either side of the creek. Assume further, that the creek itself extends another inch below that at a point directly beneath the track. Will you be extending the scenery any farther forward from that point...because the creek may descend even closer to the lower level shelving if you do. This totals 5 inches so far, and we should assume perhaps another inch for a sturdy support under the bents and under the scenery shell that forms the creek. Grand total 6".

Cleaning track by hand will require at least 3 inches. Maintenance such as adjusting warping or kinking caused by changes in humidity or temperature will require more. If you have to replace the track for any reason, you will have a lot of aggravation, but cleaning, maintenance, and repair will probably all be do-able but inconvenient).

Second, designing a backdrop to hide the descending helix may be difficult. The fascia for the upper level must extend over the loop to staging but the farther forward it comes, the harder it will be to do maintenance of the looping tracks. The farther back it is, the easier it will be to see over the backdrop or view block between Charters Towers and the hidden looping tracks to staging.

As an alternative, please consider this:
a. shift the Torrens Creek siding and the Trestle farther around the layout--put the trestle almost into the corner and place the Torrens Creek siding running along the back wall from the corner almost to the next trestle, then disappearing momentarily before crossing the next trestle.
b. Make the upper track hug the wall from the corner to about 4 feet from the corner and then have it pass above the front part of the tracks looping to staging instead of the back. I think this will make it easier to hide the loops to staging with a permanent backdrop (running from about 9:00 to 5:00 on a clock centered in the loops), and then hide the top of the backdrop with the upper level fascia.

5. Is the yard trackage based on a particular location that you want to reproduce as accurately as possible, or are you comfortable moving the turntable and classification tracks to the back of the layout instead of the front?

6. How long will your trains be (cars plus locos so we can set adequate passing sidings and cars only for the classification tracks). Please offer dimensions in inches rather than number of cars due to variable car length.

 

15 cm = almost 6 inches.
Did you mean 15-20 mm? The rails on N scale track are 9mm apart, aren't they....Sorry, I'm not used to thinking in terms of metric measures.