# change in grade



## kiwis (Jul 4, 2015)

my new lauout will have a change in elevation, i want to create a tunnel but also understand my grade should be less than 4%

how height should i leave for my tunnel entrance??

once i know this ill know how much room i need for my change in elevation


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## Bwells (Mar 30, 2014)

The height of your tunnel portal will remain the same no matter what the elevation is above your zero baseline. Lay the grade and track and add the portal wherever you chose. The portals have a certain size and are not related to grade.
PS can you go less than 4% as that is a little steep? Doable, but steep.


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## kiwis (Jul 4, 2015)

sorry that may not have been clear as im posting from my phone. 

my track concept is for my line to circle round back under itself, i want to insert a moulding/texturr (not sure the technical term) for my tunnel entrance. 

what height do i need for this? as that wil determine the radius of my circle


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## DonR (Oct 18, 2012)

Here are some guidelines for N 
Scale clearances, including tunnel portal vertical
height.

http://cs.trains.com/mrr/f/11/t/29777.aspx

I am confused, tho, as to how your tunnet vertical
clearance affects the radius of a curve.

Don


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## MtRR75 (Nov 27, 2013)

DonR said:


> I am confused, tho, as to how your tunnet vertical
> clearance affects the radius of a curve.
> 
> Don


It sounds like he wants to make a figure 8 (or part of one), with the train exiting the tunnel entrance, then climbing around to pass over the top of the tunnel portal. Is that right kiwis?


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## Bwells (Mar 30, 2014)

*grade*

I think I understand now. Since no one has replied, I will give it a try. I'm not real good at the metric measurement so the following will be in standard american. I see you are in Australia so I hope this won't be a problem. NMRA standards indicate 1 9/32" clearance so let's go 2". at 2% you need 50" of track to climb 1" so you need 100" for 2". Take that 100" track and make a circle. The diameter will be 100 divided by Pi (3.14) or 33" so you have an 18" radius. These are very rough numbers, ones that are close for planning. 4% grade requires 25" to climb 1". You need 50" to get to that 2" mark. Divide 50 by Pi and you get maybe 16" diameter so 8" radius. These are very rough numbers but they give you an idea of what you are looking at depending on your alotted space. Any where between 8 and 16 should do the trick, the bigger radius, the less the grade.
This does not account for the thickness of the subroadbed above or the fact that you are not making a complete circle but 3/4 of on with a couple intersecting tangent lines, or the calculation for theoretical grade as the rise will be on a curve. To me, this is beyond me so I ignore it.
I hope this helps and does not confuse.


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## traction fan (Oct 5, 2014)

*Grade and curveture*

Kiwis;

Bwells had good info in the last post. I'll try to add a bit. When a train is climbing a grade, and running through a curve, both the steepness of the grade and the tightness of the curve should be considered. Both add to the drag of the train and force the locomotive to work harder to pull it. Percent of grade works the same on any railroad from Z scale up to the "prototype"(real, full size railroad) It also works with any system of measurement, as long as you use the same system for all your measurements. It is simply the number of units,(say centimeters) of horizontal travel, used to raise the track a given amount of the same units, vertically.
For example if the track is 100cm.(1 Meter) long and climbs one cm. that's a one percent grade.
If the same 100cm track climbs two cm. it's two percent; Etc.
Generally it's wise to keep grades under 4%. 
As an N scaler, I would keep curve radius 36cm. or more. I had to increase my min. radius
from twelve inches(aprox31cm) to sixteen inches(aprox41cm) when one of my steam locos couldn't run reliably through the tighter radius curve. Speaking of tight curves, the eight inch(20.5cm.) radius that Bwells came up with,(remember he said that his figures were only rough estimates.) is a very tight curve indeed. While some N scale equipment can go around such a tight curve, other equipment flat out won't. Even train set curves(notoriously sharp), in N scale are usually nine and a half inch(23cm) radius.
Basically, the steeper the grade, and/or the tighter the curve,the more the evil forces of model railroading will try,and often succeed, in derailing your trains! Therefore it is wise to keep to conservative standards for both. 

Hope that answers your question

Traction Fan


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