Hi,
My name is Ak and I have a "spleen": For aesthetic reasons, I aspire to have easements at the beginning of curves or adjacent to switches. Why? Because close-coupled passenger cars look odd and not very realistic when re-entering straight track after a "normal" curve without easement. At least three forum members encouraged me recently to have my coming-out. Now:
Definition & motivation
A track transition curve, or spiral easement, is a mathematically calculated curve on a section of railroad track, where a straight section changes into a curve; the outside of the curve is gradually raised until the correct degree of bank is reached. While used for the prototype to prevent sudden changes in lateral acceleration, it is of interest for the model railroader for cosmetic reasons: The changeover between a rather tight curve and straight track results in a unattractive misalignment between the locomotive and a coach on two trucks.
More theory
In his terrific book, "Track Planning for Realistic Operation", the late John Armstrong discussed radii limits on pages 73-77. Pushing these operational limits, he demonstrated that the main issue with tight radii occurs when transitioning from tangent (straight) track to curved track. That is the point where the curve places the most strain on couplers and axles and is most likely to cause derailments or decoupling, dubbed by him “coefficient of lurch”. A spiral easement – a section of track that transitions from curve to tangent – reduces the coefficient of lurch and allows a tighter radius than otherwise possible. On page 75 he showed an example where an 18” radius HO curve with spiral easement creates less stress on the train than a 24” radius curve without the easement.
C-track and you
One of the niceties of C track geometry is the presence of many different curve radii. If one had sufficient space and planned to employ C track, I would advise to use easements - i.e., a single piece of larger radius curve - where the beginnings of curves are visible. E.g., incorporate one piece of R3 curve between a straight stretch and a curve "ruled" by R2 radius. The larger the better. Inserting only a short straight track (either 24064 of 24077) or by "counterbalancing" a R1 with a very wide radius track, as R4 or R5, instead, nicely defuses (even R1-based) S-curves. On my layout(s) this works fine for all kind of motive power and rolling stocks, European and US, coaches and freight cars, both pulling and pushing.
Photographic evidence
Below - see attached photo - is an illustration of the positive effect of easements - in this case a piece of curved R9 track, respectively - at the beginning at all types of M* C-track radii (R1/R2/R3/R4/R5): All 27 cm coaches glide smoothly into the curves, whether the R9 is followed by R1 in the front or R5 in the back.
Previous forum discussions
First serious mentioning of this topic:
https://www.marklin-user...3----why.aspx#post205146Most recent discussion on this topic:
https://www.marklin-user...f-layout.aspx#post474629Tip of the day
Forum member Kimballthurlow pointed out that the R9 piece of track - being a 12.1° curve - is difficult to combine with the M* 30° standard curve segment. Indeed, "taming" the 24912 is a challenge (as long as one does not resort to a saw). Hint: Combining 24912 (12.1°) + 24206 (5.7°) + 24912 (12.1°) leads to 29.9° which is close enough to obtain a 30° curve; e.g. one of the visible 180° "turns" on my former layout "Slumburg" consisted of 1 x 24912 (12.1°) + 5 x 24230 (150°) + 1 x 24206 (5.7°) + 1 x 24912 (12.1°).
To be continued?
Alsterstreek attached the following image(s):