Hello!
I am planning a new layout in HO, with a helix with two parallell tracks - one for traffic upwards, the other track for downwards traffic.
So to my question: What gives the best and most secure running: using the outer track for downwards or upwards traffic? For the record I plan for broad curves, using a grade of max 2%.
Olav,
I do think it really makes any difference. Our club has a 5 turn helix with 33"/36" radius curves, and about a steady 2% curve. The big thing is 'smooth' operation when decending the helix.
Jim Bernier
Modeling BNSF and Milwaukee Road in SW Wisconsin
Our club layout has a 5 turn helix that is four tracks across, two up and two down. It's basically a folded dogbone configuration that is double tracked or one loop inside the other. The helix is the "fold."
Applying a bit of simple geometry, using the outside track for the upward bound trains actually yields slightly less grade because the radius (and circumference) is a bit longer. Roll resistance caused by layout design comes from gravity (or grade) and the extra force required to pull the cars through a curve. A sharp curve has more resistance than a gentle curve or straightaway. It worked out that with our club's right hand running, the "up" is the outside tracks.
Since you didn't define "broad curves," our helix tracks are 36, 38.5, 41, 43.5 inch radius.
Because of the slightly broader radius of the outside track, it will have the gentler grade, obviously. The difference will be small, but if all else is equal, that might be the one to choose for uphill traffic.
But there are a lot of other overall layout design issues, such as the routing of the tracks at the top and bottom of the helix, the operational flexibility that might come from allowing both directions of travel on either track, whether the grade in the helix will be the ruling grade on the layout, etc. Those all need to be considered along with the difference in grades of the mulitple tracks in the helix.
ByronModel RR Blog
Layout Design GalleryLayout Design Special Interest Group
Completely off topic, Olav, but I see you're not too far from Drammen where my grandfather was born.
Hello
Thank you all for the answers, then I can go back to my think.tank again....
By broad curves I meant from 48" radius and up - I have a barn to play in...
And yes wistix: Drammen is about 34 miles (55 kilometers) from where I live, so you are an expert on Norwegian geography!
I'd have to agree with the others and say the outside track is best as the "up" track because of the grade advantage, beit ever so slight.
But there's one other factor that makes the outside the better choice, and nobody hit on it.
The outside track will resist stringing better. Stinging is more prevelent with longer trains, and the tighter the curve and higher the grade, the more pronounced it is. Having the train on the broadest curve available, with the easiest grade, will reduce the chances of this horrible thing happening. (Trust me, there aren't many more horrible sounds that can be heard in a hobby room then an entire train hitting the floor all at once!)