# Transistional curves???



## ATHEARNFAN (Oct 13, 2011)

hi new here, but can someone please explain what a transistional curve is? 
thanks in advance


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## NIMT (Jan 6, 2011)

It's a method softening of a curve to make it less harsh of a transition from strait to curve.


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## ATHEARNFAN (Oct 13, 2011)

NIMT said:


> It's a method softening of a curve to make it less harsh of a transition from strait to curve.



thanks,that's what i thought but today while visiting my club's modular layout i asked what exactly is the radius of the corner modules. i was told the outside track was 37" in the center but had transistions on both sides. now what struck me odd was what kind of HO engines or rolling stock would require any kind of softening for a 90 degree 37" radius???? it just did'nt make any sense to me.
thanks again.


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## NIMT (Jan 6, 2011)

Simple answer would be long and heavy ones!
It helps keep them from "clothes lining".


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## timlange3 (Jan 16, 2013)

All trains will do better with transitions or easements on any radius. Others will refer to it as the lurch factor, going from straight to curving. A good example we all know and experience is driving a car. All of the turn (curves) you make are transitions, going from straight to the curve by increasing the turn over time. In a car, you would not enjoy going from straight to having your steering wheel turned as it would be in the midpoint of the turn in an instant.

As an exaggerated example, start your turn with a 50" radius with a piece of flex track and gradually reduce the radius until you reach the midpoint of the turn or your minimum radius. I see a lot of practical examples starting at just 2"-3" more radius than desired and gradually reducing to what you want.

You should find that by using easements your minimum radius can be smaller but still have trains operate and 'look' okay.


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## mopac (Feb 24, 2011)

What would be a good length of transition?


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## ATHEARNFAN (Oct 13, 2011)

timlange3 said:


> All trains will do better with transitions or easements on any radius. Others will refer to it as the lurch factor, going from straight to curving. A good example we all know and experience is driving a car. All of the turn (curves) you make are transitions, going from straight to the curve by increasing the turn over time. In a car, you would not enjoy going from straight to having your steering wheel turned as it would be in the midpoint of the turn in an instant.
> 
> As an exaggerated example, start your turn with a 50" radius with a piece of flex track and gradually reduce the radius until you reach the midpoint of the turn or your minimum radius. I see a lot of practical examples starting at just 2"-3" more radius than desired and gradually reducing to what you want.
> 
> You should find that by using easements your minimum radius can be smaller but still have trains operate and 'look' okay.


2"-3" more looks to be about what the layout has as it is not very obvious, that is what threw me. 40" R on either end of a 37" R sounds good after all. thanks


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## timlange3 (Jan 16, 2013)

Mopac, I've heard several answers to this, I would think the best would be half way through the curve. Check out John Armstrong's book "Track Planning for Realistic Operation".


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## mopac (Feb 24, 2011)

Thanks Tim. So probably longer than I thought.

And then there is super elevation I want to look into.

Some layout curves just look better than others and I am sure transition
plays into that.


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## NumberOne (Sep 19, 2012)

And of course, there are good reasons to have vertical easements as well...

-Mark


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