Does anyone know what is the smallest turning radius on DLR? I found this topic (viewtopic.php?f=2&t=2664&start=10) that says it's 278' at the diorama, but the tightest turn is actually at the roundhouse.

Anyone know what that might be?

I have no idea, Preston, but it's a great question!

I seem to recall that on 1:1 railroads they refer degrees of curvature and not radius, but you can get the radius from the degrees of curvature, and I know that all models are much tighter turns than the prototype.

Either number, radius or degree of curvature, will work for me. What I really want to know is if the rear pilot wheel on the Holliday will hit the inner crosshead guides when going around a curve, so I need to know what that turn is.

Hi Preston,

Sorry to darken your day with my idiocy. You should be able to get a pretty good approximation of those engine shed turn radii from Ade in England's scaled map. One question: do they ever park #1 or 2 on the easternmost storage tracks?

Also, (from your side view of #1): does the cylinder cock linkage run inside the crosshead guides?

Yep. Steve (D) got a good picture of her coming out the east track (#4?) one morning: http://miceage.micechat.com/stevedegaetano/sd050107b.htm

The cylinder cocks are in line with the cylinder's center line, which is between the crosshead guides. The linkage actuator is inside the crosshead guides. Here's a view of the cylinder's rear: http://whiskeybeforebreakfast.files.wordpress.com/2012/04/4-11-2012-9-44-30-am.png

I can take the approximate scaled measurements myself from google earth to get the curve radius, but in the unlikely event that there is an officially sourced answer, I'd like to have that first

I wouldn't be at all surprised if the overhead layout drawings have been, or are now, on e-beigh. I tried Google satellite (not, I think, in hi-res), but couldn't see nuthin.

Blowing up Steve's #1 blowdown photo, I still can't tell how close the truck wheels come to the linkage. Is that the pertinent curve? Compared to O27, it's dead straight!

I have seen the Holliday with the Holiday 2 and EP Ripley with Holiday 5 leave the roundhouse. I couldn't tell the swing of the pilot truck because I saw it once from the monorail and the other from the tender of the Ripley at Toontown depot. With the number of stalls being 4, supposing they had all 5 engines, where would the 5th one be?

Indeed! Maybe double-stacked with another engine?

Anyway, for the turning radius I made a pretty simple assumption.

Since there are 4 wheels on each rail, when going around a curve, each wheel can be approximated as a point on a curve. Connecting these points describes an arc, which we can then get its radius.



There is “play” with these points also because the wheels have thickness to them. (Technically, the driver wheels cannot deflect because they are rigid in the frames). In the above picture, I deflected the pilot truck until the rear wheel is near but not in contact with the inner crosshead guide. Then I draw an arc connecting the 4 wheels together.

This process gives an arc of about 1350″, or 112′, which is less than my assumed smallest curve of 139′, and certainly much less than 278′ on the mainline.

So indeed, there’s plenty of room for the pilot truck to turn. Generally, rail curves are made to be as large as possible, so in reality the pilot truck does not swing that much.