Helix? Bi-Lix?

[preceng]

Working on my new HO layout design. I have a 20'x7.5' loop layout (with aisle in middle) and a helix proposed for one of the corners to take trains to the below level staging area along the back wall. Due to the basic loop design I expect that 90% - 100% of the traffic will use the helix in the down grade direction, and use the No-Lix loop at the other end of the staging area to re-enter the main level. I have been reading a lot about the problems with the helix grade issues, particularly the effects of the 24" radius which adds about 1.3% effect to the planned 24" radius 2.5% grade helix. This effect will produce an equivalent grade of almost 4%.

Due to the design of my layout, I could "split" the helix into two halve sections along the 7.5 foot wide area with an approximately 3 feet of tangent between the two "half loops" if necessary. I should add that my maximum train length will be about 9 feet, which occupies about 75% of a 24" helix loop.

My questions are:

Since the primary route is downhill through the helix, am I worried about nothing?

Since the max train is 3/4 of the helix diameter, is it worth the extra fuss to design and use the half loop with tangent helix, since only 1/4 of the train would be on the tangent?

And lastly, what do you call the split helix design? The Bi-Lix?

[cuyama]

I'm probably just not understanding the situation, but why would you want to double the helix footprint and construction effort when instead you could just make the single helix a bit larger radius and thus ease the grade?

regards,

Byron
http://www.modelrail.us

[ereimer]

from anything i've ever read the problem with steep grades on a helix is dragging a train up the helix . if all trains are heading downgrade through the helix i don't see a problem . on the prototype the brakes might get to hot , but we don't have that problem

[taylorjj123]

In answer to your second question, I don't think the tanget will affect your grade all that much. I've been playing with a similar idea for the railroad I am designing and was quite suprised at how much real estate I had to give up with the tangent design to actually affect my grade.

[nfmisso]

Going downgrade on a curve, the curve makes the grade appear LESS steep, as it increases the drag on the train.

Going upgrade on a curve, the curve makes the grade appear MORE steep, as it increases the drag on the train.