Real Life Minimum Curve Calc

@BillYo414 posted:

Surely people didn't spend all that money on the Allegheny and Big Boy without knowing if it would even fit on their rails, right?

They designed the Big Boy to run on straight track!

No wonder it doesn't have overhang in real life @gunrunnerjohn

Bill, there’s a great video I watched on You Tube of the NKP Berkshire on an Excursion trip. Can”t remember where it took place. But they had to grease the rails so that when it passed through it wouldn’t bind up on the rails. Unfortunately the work crew misunderstood and greased the top of the rail which resulted in slippage. If you can find it. It’s a good watch. After a number of tries it finally makes it through the gradecrossing. Seeing this was planned ahead of time. Someone must have known the minimum radius it could handle.
As far as the largest steam engines. Most are articulated. So if a Union Pacific 4-8-4 can handle a certain curve. I’m guessing a Big Boy could handle the same curve seeing it’s basically has 2 sets of 8 wheel drivers. I know a few roads that as locos got longer. They had to use blind drivers to negotiate some trackage.

@Dave_C posted:

So if a Union Pacific 4-8-4 can handle a certain curve. I’m guessing a Big Boy could handle the same curve seeing it’s basically has 2 sets of 8 wheel drivers. I know a few roads that as locos got longer. They had to use blind drivers to negotiate some trackage.

I seem to recall a conversation here where the #844 couldn't do curves some articulated locomotives would handle.

Not a problem, they just blind the drivers, add truck mounted couplers, and added over sized flanges......But seriously   Printed little booklets , and mapped there lines Listing everything from  crossings , what pond rail, ( you dont want to spread the rails and drop the engine on the ties) , the grades,  bridges and the speed  and weight restrictions, Curves were measured in thousands of feet .   The locomotives that had issues on curves ( that I remember ) were some of the S.F. , U. P.  , 10 and 12 coupled locomotives and that  huge ridged frame Pennsy T1?

If an 8 coupled locomotive will run through a given curve an articulated locomotives should not have an issue ( They dont blind their drivers)

@gunrunnerjohn posted:

I seem to recall a conversation here where the #844 couldn't do curves some articulated locomotives would handle.

True, but a lot is related to that UP Pedestal Type tender. UP 844 has a 22 foot ridged wheel base, account of this 80" drivers.

@Dave Koehler posted:

Curves were measured in thousands of feet .

I believe prototype curves are measured in degrees.

@Dave_C posted:

Bill, there’s a great video I watched on You Tube of ...

I'll have to see if I can find the video. I would love to watch it.

@Dave Koehler posted:

Not a problem, they just blind the drivers, add truck mounted couplers, and added over sized flanges......But seriously   Printed little booklets , and mapped there lines Listing everything from  crossings , what pond rail, ( you dont want to spread the rails and drop the engine on the ties) , the grades,  bridges and the speed  and weight restrictions, Curves were measured in thousands of feet .   The locomotives that had issues on curves ( that I remember ) were some of the S.F. , U. P.  , 10 and 12 coupled locomotives and that  huge ridged frame Pennsy T1?

If an 8 coupled locomotive will run through a given curve an articulated locomotives should not have an issue 9 They dont blind their drivers)

Are you saying they have like a field guide? Take a few measurements, compare values to the book, and get an answer?

@BillYo414 posted:

I'll have to see if I can find the video. I would love to watch it.

Are you saying they have like a field guide? Take a few measurements, compare values to the book, and get an answer?

Bill 

the simple answer  is yes.  Every foot of a railroad  is measured , straits curves, ( measured in Degrees and Yes Radius) , height ,  width , clearance and speed restriction's on a given route/line.  This was issued A booklet from the train crew and recorded up the chain of command to engineering department,  when a new class of loco. is wanted, it is given to deign engineers , who with the parameter's  supplied by the railroad build the locomotive .   Every thing documented.  You dont want the train crew  using a Bigboy to switch cars in the local brewery

With steam locomotives, The minimum radius (in degrees of curvature) was likely specified in the specifications sent to the builder when ordering.  On rebuilt steam locomotives, the minimum radius was calculated by Mechanical Engineers in the railroad's Mechanical Department.

With diesel locomotives, the builder does the calculations.  If you ever see an operating manual for a locomotive, look on the page with all the length, height, and width statistics;  there, you will find the minimum radius for the locomotive, not coupled.

You may be aware of the shared track over the Tehachapi Mountains in California (the line with the famous loop).  Southern Pacific owned the track and dispatched it, while Santa Fe was a tennant via trackage rights.  Santa Fe had two different sizes of 4-8-4s, and only used the smaller engines such as the 3751 between Barstow and Richmond, which included the Tehachapi segment, in passenger service.  The Santa Fe Operating Department wanted to use some of the larger engines such as the 3771 Class or the 2900 Class, in order to run longer passenger trains, so the railroad studied the situation.  They found that the larger 4-8-4's were -- on paper, at least -- just barely capable of negotiating curves in some of the Southern Pacific sidings, including the one at Cliff, which is actually on a narrow shelf between the mountain on one side and a deep gorge on the other side.  Santa Fe did measurements on-site and found that the SP sidings actually contained curvature sharper than what the track chart indicated.  Additionally, even if the track had matched the engineering chart, the tolerance would have been so close that it was risking derailment, and ANY Santa Fe derailment was always blamed on the Santa Fe by the Southern Pacific.

Santa Fe took the safe course and never ran any engine bigger than the 3751 on the Tehachapi segment.  SP ran articulated 4-8-8-2s with smaller drivers and their own 4-8-4s of a different design.

Handy info @Number 90! That's interesting, especially about SP and Santa Fe. It's just wild to me. I can whip up a model in CAD nowadays and just physically test minimum curve. Everything was done by hand back in the day and that impresses me.

I also might need to build a custom flat car for my layout and need to figure out how to calculate it