Minimum radius education

@lionel1946 posted:

Hello all. Need some help. Was looking up some info on transition era diesels, and wiki provided the following (which I will assume is correct).

Alco RS-1

Length: 55 feet 5.75 inches

Wheelbase: 40 feet 5 inches

Minimum curve: 116 foot radius

 

EMD F-3

Length: 50 feet 8 inches

Wheelbase: 39 feet

Minimum curve: 251 foot radius 

 

Wow...this is when you suddenly realize that not all threads on this forum refer to toy trains!!!

Just for kicks I converted the minimum radii to 1:48...   In O3R parlance that would be O-58 and O-125 curves, respectively.  An O2R spec would be 29" and 62.5" radii, respectively.  Interesting.

But, I doubt that's relevant to hauling a train at some speed!

Can't answer your question, but I'll be interested in hearing from them that knows!

KD

I thought prototype curves were measured in degrees, not radii?

Ithink some factors that [ironically] apply to models applies in prototypes -- truck wheelbase, axles per truck (and the arrangement)truck swing, and distance between the bolster and the end sill.

Probably the same reason that it varies in models, limitations in the amount a truck can swing, distance between wheels, prob also the distance between the trucks on the engine, the wheelbase center to center on the trucks I would guess. 

The OP's wheelbase of 39 feet for the EMD F3 is measured from front axle to rear axle.

My source shows the ALCO RS-1 with an inch shorter wheel base than the OP's source. It too is measured front axle to rear axle.

Source:

Model Railroader

Cyclopedia - Volume 2

Diesel Locomotives

Compiled by Bob Hayden

@AGHRMatt posted:

Ithink some factors that [ironically] apply to models applies in prototypes -- truck wheelbase, axles per truck (and the arrangement)truck swing, and distance between the bolster and the end sill.

I think they are both 4-axel locos Matt (2-axel trucks), but I had considered a difference in truck wheelbase. Didn't want to expose MORE of my lack of knowledge.

@lionel1946 posted:

Hello all. Need some help. Was looking up some info on transition era diesels, and wiki provided the following (which I will assume is correct).

 

You raised a good question, Jay.  However, you are always on thin ice when you assume that something on Wikipedia is accurate.  Always check the sources of information at the end of the article.

But, back to your question, if you study prototype photos of RS1's and F3's as built, there is a difference in the size of the fuel tank and other appliances and compartments hung underneath the frame.  The F3 has batteries and main reservoirs behind the No.1 truck, whereas the RS1 has batteries mounted differently, with higher ground clearance.  Most RS1's only had the battery box down below, but some also had fuel or water tanks there with very high ground clearance.

The official operating manuals published by the builders for those two respective locomotives will have official data for measurements and minimum curve radius.  There are certain clearance standards that are adhered to in the design of mass produced locomotives, and ground clearance on the inside of the curve is one of them.  If an RS1 was ordered with a large fuel tank, then the minimum radius for that RS1 would be increased.

Since the F3 was designed to be a road locomotive, there was no reason to make it capable of going down snaky industrial tracks with very sharp curves.  The RS1, however, was sold as a universal locomotive that could be used in passenger, freight, and yard service.  The sharpest curve an F3 would have been designed for would be a wye switch for turning the locomotive.  In 1946, when the F3 was introduced, wyes had been able to accommodate steam locomotives, which are more rigid than an F3.  Some RS1's, on the other hand were replacements for little electric locomotives on interurban railroads which typically were able to have sharper curves on auxiliary tracks.