--- In STMFC@..., "David Ball" <davidball@x...> wrote:

Dennis (or anyone else),

Has it been determined the practical minimum radius the PROTO:HO couple can
be used for effective operation? I'm thinking literally how tight can the
radius be before it may cause problems for the coupler, not just that it
cope with typical tight radius like 18"

Cheers

David Ball

I was hoping that someone else would jump in here and save me the typing, maybe someone with first hand experience with our PROTO:HO couplers on tight curves, but it doesn't look like that is going to happen.

To be perfectly honest, we've never tried to determine what the practical minimum operating radius is. When you design a product to meet a certain criteria, say operation on 18" or smaller radius curves, you make whatever modifications are necessary to achieve that goal. If the coupler heads need to be overly large, the boxes overly wide, or the narrow boxes artificially flared wider at the opening, that's what you do, and accept those compromises as being necessitated by the original design criteria. The design criteria for the PROTO:HO was simply to put a scale size coupler head on a shank that would fit within the confines of a steam era center sill, and then make it compatible with the other magnetic couplers currently in use. How well it would work on train set radius was a secondary consideration, although the original layout drawings indicate that equal sized cars equipped with the PROTO:HO couplers should be able to negotiate a 15" radius curve. Notice I said equal sized cars. Problems arise when mixing equipment with different amounts of coupler overhand on these tight curves: freight and passenger cars, or freight cars and locomotives. Even a small 0-4-0 will have considerably more distance between the wheels and the coupler, and so this coupler will end up much farther from the track centerline on a sharp curve than the coupler on a freight car. Eighteen inch radius in HO scale is appx. 135' radius on the prototype, 15" radius is appx. 110'. When prototype curves are this tight they are no longer expressed in degrees, but in the actual radius in feet. Railroads build with radii in this range, such as rapid transit operations, typically use wide swinging radial couplers. The interurban railroads that had this sort of curvature used radial couplers on their locomotives so the coupler would follow the coupler on the cars. When these lines were dieselized, they typically needed to use small locomotives such as 44 tonners, which have short wheelbase trucks and minimum coupler overhang. I suspect the same applies to the PROTO:HO couplers.


Dennis Storzek