Trackwork - Wye turnarounds

[Anonymous]

Hi you All,

I have a question about "wye" turnouts and tight radii.

My reference is John Armstrong's "Track Planning..." book.

I'm planning a little branch line for 1920's short equipment only running at slow speeds; I'm diligently laying out a wye turnaround using proper substitution radii etc. and am generally keeping to a minimum curvature of 18" radius...space is at a premium.

The RCR of a #2 wye is listed as 15", and John cautions against using turnouts w/ an RCR of any less than the minimum radius which intended equipment can handle. I note, e.g., that the minimum radius for a Bowser 442 Atlantic is 18", and even for a 040 Dockside, 18" min is recommended though the specs say 15" r. is doable.

Because space is very tight, I want to use the #2 wye turnouts for my wye turnaround, and since the RCR of the #2 wye is 15", it seems reasonable to just maintain that 15" radius between the turnouts.

My question is: In practice, can #2 wyes be used w/ equipment rated for 18" min. radius curves?..and, can I get away with continuing the 15" radius between them?

If not, how can #2 wye's ever be used?

Humbly,

Fred

[cuyama]

By the way, for those who don't have the Armstong book in front of them, "RCR" stands for "radius of the closure rail". This is the radius of the curving point rail when set for the diverging path (in the case of the wye, of course, both paths diverge).

As Fred notes, a #2 wye is roughly equivalent to a normal # 4 turnout. But turnouts vary from manufacturer to manufacturer and product line to product line, so the estimates given in Armstrong's book are averages, not absolutes. This is listed in Figure 5-4 (pg 48) in my early edition, it might be a different chapter and page in later editions.

QUOTE: Originally posted by Pioneer Zephyr

; I'm diligently laying out a wye turnaround using proper substitution radii etc. and am generally keeping to a minimum curvature of 18" radius...space is at a premium.

The RCR of a #2 wye is listed as 15", and John cautions against using turnouts w/ an RCR of any less than the minimum radius which intended equipment can handle. I note, e.g., that the minimum radius for a Bowser 442 Atlantic is 18", and even for a 040 Dockside, 18" min is recommended though the specs say 15" r. is doable.

Because space is very tight, I want to use the #2 wye turnouts for my wye turnaround, and since the RCR of the #2 wye is 15", it seems reasonable to just maintain that 15" radius between the turnouts.
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I think there are mutliple issues here. First, what is the true closure radius for the wye turnout you are considering? It might be more than 15"R, might be less, but you cannot tell specifically from Armstrong's chart. Second, it's worth noting that the actual length of the closure radius through the turnout is pretty short. It probably won't be acting on all the wheels of the loco at once, so the effect may be less abrupt than a ten-inch length of the same radius, for example.

For this reason, i personally would not use the logic of "well it has to get through that stretch of 15-inch-radius in the wye turnout, I'll just make it 15-inch-radius everywhere". Longer stretches of that radius will have a greater effect on the performance and reliability than the short stretch through the turnout (which, again, might acutally be more or less than 15"R).

QUOTE:

;
My question is: In practice, can #2 wyes be used w/ equipment rated for 18" min. radius curves?..and, can I get away with continuing the 15" radius between them?

If not, how can #2 wye's ever be used?

The answer is ... it depends. Since you already own (it sounds like) the potential problematic locos, it seems like the best bet would be to mock-up the scenario with a sample of the wye turnout and some flex track.

#2 wyes should be useful anywhere #4 regular turnouts may be used (assuming the smae manufacturer and product line).

My suggestion would be not to scrimp on the radius between turnouts, again because of the larger effect of longer stretches of tightly turning track. This is especially true if the track arrangement you are using involves any s-curves ... even 18" may be too tight without a length of straight track between.

Bottom line, the specific turnout you plan to use, the track configuration, and the rolling stock all will have effects that can't be ascertained from Armstrong's (excellent) analysis. You mentioned the key words "in practice". You'll be most certain if you mock it up and try it.

Regards,

Byron
http://www.modelrail.us

[Anonymous]

Byron,

Thank you so much for your thoughtful answer to my query.

The turnouts in question would be Walthers/Shinohara code 83's; W/S says simply that their turnouts meet the NMRA standards, and I haven't been able to get more precise info from them.

The Bowser locos I cite have not been purchased, though I like the 4-4-2 and expect to limit use in this particular area of the layout to small steam or maybe a doodlebug or the MDC box cab diesel (which I already have).

Your explanation of the short length of 15" radius in the RCR is helpful; and that being the case for the #2 wyes, your suggestion for a mock up sounds good.

Thanks,

Fred