In the prototype, it is impossible to superelevate the diverging route in a turnout until you get beyond the last long tie.
RWM
I believe you missed my point. If the turnout is not level longitudinally - as on a grade - there is automatically some tilt - however small - created in at least one of the diverging paths. In the prototype, with small grades, high turnout frog #s and very small divergence, this tilt will be very, very slight and of no real consequence because it's within normal track tolerances.
However, on the model with sharp curves, small frog #s, much steeper grades, and much quicker divergence, that automatic tilt is easily visible. The automatic tilt was definitely visible on my HO 18" radius turnouts with an 18" radius continuing divergence on 4% grades. I called the tilt superelevation in my previous post, which probably confused the issue, although they are basically the same thing. The diverging curve across the grade gets an automatic tilt; the tilt from superelevation is usually intentional.
In the case where the turnout diverges down grade, the automatic tilt will be negative, ie., the outer rail of the curve will be lower than the inner rail. A transition after the turnout is needed just to bring the 2 rails level again.
We are all agreed that the turnout itself must be flat across both dimensions. I am just pointing out the natural consequence of that position. Not putting sharp turnouts on steep grades will help mitigate this consequence.
Fred W
Phoebe Vet The problem turnout that caused me to post what I did was an Atlas snap switch transitioning to a 3% grade right out of the diverging leg. I also have an Atlas #6 that is a little finicky but only occasionally that is on a 4% grade and both legs gradually transition to flat beginning about 2 inches out of the switch. I know, I know. I will never again have any grades that steep. Live & learn.
The problem turnout that caused me to post what I did was an Atlas snap switch transitioning to a 3% grade right out of the diverging leg. I also have an Atlas #6 that is a little finicky but only occasionally that is on a 4% grade and both legs gradually transition to flat beginning about 2 inches out of the switch.
I know, I know. I will never again have any grades that steep. Live & learn.
Did the diverging route transition to that 3% grade with a nice parabolic vertical easement about 3 feet long? Or did the grade on the snap track simply launch into the grade?
I have a nice curved turnout on a superelevated curve and a 2% grade. There are no abrupt changes in rail/roadbed geometry anywhere near the turnout. The only concession I have made is to include a guard rail on the inside rail to guide approaching wheels away from the outside rail point. The tighter radius transitions to a lesser grade, but it's a proper vertical easement and doesn't happen until well clear of the frog. Nothing I own has any problems with it - but I am running small 2-8-2s, not high drivered 4-14-4s.
As for hairy grades, my immediate prototype had 2.5% grades (which I will model with visible trackage) and one route farther west had a 6.8% grade. Heavily-ballasted Co-Co motors replaced the original rack motors when it was converted from rack to adhesion. Two of them led a four-car EMU train down the decline. Without them, the light-footed passenger cars would have become steel bobsleds.
Chuck (Modeling Central Japan in September, 1964)
fwright Trains going through a switch don't care about level, but they do care about flat. There is one other caution that nobody has mentioned. Assuming the slope is parallel to the straight path of the turnout, there will have to be some superelevation of the curved path as it turns from the slope. The sharper the turnout and accompanying curve, the greater this superelevation will be. The worst case is when the turnout diverges down slope. Then the superelevation will be negative - the outer rail is lower than the inner by virtue of being further down the slope. In most cases - particularly on a 2% grade with a reasonable radius and frog number - this slight superelevation, positive or negative, will not affect anything. But on 4% grades and 18" radius curves, the superelevation, especially when negative, does become noticeable. Don't ask me how I know this.If the superelevation bothers you, you need to transition to "flat" on the curved path rather gently, but you can start almost as the paths diverge. Or, if it looks good (and positive), perform the transition at the end of the curve.my thoughts, your choicesFred W
Trains going through a switch don't care about level, but they do care about flat.
There is one other caution that nobody has mentioned. Assuming the slope is parallel to the straight path of the turnout, there will have to be some superelevation of the curved path as it turns from the slope. The sharper the turnout and accompanying curve, the greater this superelevation will be. The worst case is when the turnout diverges down slope. Then the superelevation will be negative - the outer rail is lower than the inner by virtue of being further down the slope.
In most cases - particularly on a 2% grade with a reasonable radius and frog number - this slight superelevation, positive or negative, will not affect anything. But on 4% grades and 18" radius curves, the superelevation, especially when negative, does become noticeable. Don't ask me how I know this.
If the superelevation bothers you, you need to transition to "flat" on the curved path rather gently, but you can start almost as the paths diverge. Or, if it looks good (and positive), perform the transition at the end of the curve.
my thoughts, your choices
Superelevation is introduced in the prototype when it is desired to have a higher maximum speed on a curve than is permitted for that degree of curve with the allowable maximum unbalance, or to reduce wear on the high-side rail, or both. But otherwise it's not essential to have superelevation in a curve.
As others have alluded to above, vertical curves within turnouts are verboten. The distance between the turnout and the nearest approach of a vertical curve vary among railways as each Chief Engineer has his own idea what's acceptable and what isn't. It usually varies with maximum authorized track speed, too, e.g., it might be permissable to introduce a substantial vertical curve immediately beyond the last long tie of a turnout to an industrial spur, but not in a main track permitted 70 mph freight.
I would recommend getting a higher-number turnout if you put it on an incline. I have a #10 on the top end of a 2% grade in my layout witht he diverging track going to the second track of a doubletrack main.
I also have the turnout mounted on a piece of basswood (I'm using WS foam risers for the incline) so I have the basswood board to facilitate mounting a Tortoise machine below it.
Dave
Lackawanna Route of the Phoebe Snow
I am going to disagree with the last statement...sorry, PV.
It is okay to have a change of grade immediately outside the confines of a turnout as long as it is a gradual one. So, over, say, the length of your typical wheelbase/item, you would not want a change of grade on any of the three exit's/entrances to be more than about 1/4%. I feel strongly that properly adjusted couplers mated to like couplers will be okay. I would wonder about a long driver base on a steamer, though, and a person is always advised to check it out for himself before committing himself and gluing things in place with ballast.
I think, on the other hand, that you would be ill-advised to have a change in super-elevation or a curve, or both, too soon through a turnout. Such characteristics do threaten to cause derailments or stresses on couplers. I have found out the hard way. But I do have several turnouts on grades where the grade changes within inches, and I have no troubles whatsoever. I just made darned sure the grade changes were gentle until the turnout would have been cleared, and then gone onto the portion of more rapid change in the parabola. Before that point, there is no superelevation, and no curve beyond the frog for some distance, say about 6". This is out on my main where typical speeds are near 40-70 scale mph, and where if things can go wrong.....
-Crandell
Like Tom said. Trains going through a switch don't care about level, but they do care about flat. Be sure there is no change in grade for the length of your longest car in all three directions from the switch.
The biggest place like this where you'll run into problems with a turnout is on a vertical curve (transition from the flat to a grade). This will be especially bad if the vertical curve distorts the turnout and binds the points. It can also cause problems with long wheelbase locos and cars. The turnout should be fine as long as it's mounted flat (noting the difference between "flat" and "level").
I don't see any problems as long as the switches are on the same incline and level with respect to each other.
RF&PRR