Cut off smokebox fronts

[De Luxe]

I always wondered why some steam locomotives had cut off smokebox fronts while most had not. Especially many articulated engines. From the big articulateds, I can only recall UP´s Big Boy & Challenger having round smokebox  fronts, while almost all other big articulateds had cut off ones. I really would like to know why. Also wheen looking at rigid frame locomotives it´s interesting to see, that UP and SP 3 cyl. steamers had cut off smokebox frontss, while the RG managed to keep a round smokebox front on their 3 cyl. Mountains. So what where the reasons for so many roads chosing cut off ones especially for their articulateds?

[Penny Trains]

I don't have any facts to back it up from accredited sources or anything like that, but I always assumed it had to do with the requirements of the front engine unit.  Or more specifically the amount of swing required for the steam pipe connecting the boiler to the pistons of the front engine unit.

[RME]

Or a cutaway for the center cylinder and VG and maintenance access to that area, on rigid-frame three-cylinder power.

I think this means cutoff smokebox front, not the "door" itself.  Remember that the smokebox needs to accommodate no steam pressure, so the only thing governing its shape is gas flow, typically in a Master Mechanic setup with 'self-cleaning' screens.  I think esthetics may have played some part in three-cylinder smokebox design; if I recall correctly the New Haven and Lehigh Valley three-cylinder engines had a round smokebox front with centered door.

[M636C]

While I can't think of an example in the USA, another reason for cut off smokebox doors, and matching smokeboxes was streamlining of locomotives, where the smokebox was cut down to improve aerodynamics.

The first example of this was Nigel Gresley's W-1 4-6-4 No 10000, where to avoid a cut off door, a very small diameter door was fitted. However, I think there was a photo of the locomotive under construction showing a conventional smokebox with full size door projecting above the frames of the casing, where a cut down door might have been applied in the style of the A4, but was not.

Gresley's A4 Pacific had a very abbreviated door to allow the "Bugatti nose", although this was concealed by the streamlined casing and a cosmetic flat outer door. Willian Stanier's "Coronation" didn't need as much of a reduction in the smokebox, so it had a circular door but a sloping top to the smokebox.

A similar situation existed in Germany, where Richard Wagner's Class 05 had a cut down smokebox, and the feed water heater moved behind the stack. The later and more numerous 01-10 and 03-10 streamlined Pacifics had the feed water heater moved forward and slightly down to clear the casing, which became very obvious post WW II when the streamlining was removed. All of these that survived were eventually rebuilt with a conventional shaped smokebox door, in some cases concealing the feed water heater in the same location, or with different mixing-type feedwater heaters of different designs in East and West Germany.

But these were definitely examples where the door, as well as the smokebox was cut down.

You can't really mention this subject without including Oliver Bullied. His Q-1 heavy freight 0-6-0 had what is best described as "horseshoe shaped" smokebox and boiler cladding to allow use of insulation material that could not be contained under normal cladding (said to be a wartime exigency) but a circular smokebox door.

Bullied's Pacifics, both the Heavy "Merchant Navy" and the Light "West Country" had strangely box-shaped smokeboxes concealed by the angular streamlining and what is best described as a "parabolic" smokebox door.

To return to the USA, The Norfolk and Western Y6a and Y6b both had a severely cut back lower smokebox but a small circular door.

Peter

[De Luxe]

I edited the post now from door to front! Door was indeed a bad choice as the door can actually have any shape and doesn´t need to have the same shape like the whole front. What I´m trying to find out is: How did the RG manage to obtain an aesthetically more pleasing round smokebox front on their 3 cyl. Mountains while UP and SP didn´t manage to do so on their 3 cyl. steamers? How did the UP and D&H manage to build their Challengers (and Big Boys in case of the UP) with round smokebox fronts while most other articulateds had cut off ones? I do believe that a round smokebox front always looks much better than an a cut off one, so I wonder why so many roads went for the ugly cut off ones although there was proof that it also works fine with round smokebox fronts. For example I never heard of the RG Mountains having trouble to access the 3rd cyl. because of the round smokebox front or the D&H and UP Challengers (and Big Boys) having clearance problems or whatever because of the round smokebox front.

@Peter: yes, the German 05, 01.10 and 03.10 classes looked very ugly and weird below their streamlining casings because of their cut off smokebox fronts. At least that was changed soon to round smokebox fronts once the engines were destreamlined during and after the war.

[BaltACD]

For those of us who are having trouble visualizing the nuances of what is being discussed - some pictures would help your explanations.

[Penny Trains]

Here's a N&W Y6b.  Note how the lower part of the smokebox isn't rounded to match the rest of the boiler, but rather is cut away to accomodate the large steam pipes.  The Y6b's were traditional compound mallets so the pipe led foreward from the rear engine unit wherre the steam was used first.  Also, the Y's had angled stacks and the 2187 had an oblong door.

[ACY Tom]

If space is needed for any kind of mechanical apparatus below the smokebox, there's no reason the smokebox shape couldn't be adjusted to suit. The smokebox space was routinely intruded upon to clear Superheater headers, front end throttles, various components of feedwater heaters, etc., so there doesn't seem to have been any special magical importance to a purely cylindrical shape. 

Tom

[pajrr]

Asthetics didn't matter most of the time. Building something that got the job done ALL of the time is what was important. Remember the marketing slogan for Volvo from the movie "Crazy People"? "Volvo--Boxy but safe"

[BigJim]

Penny Trains

Here's a N&W Y6b.  Note how the lower part of the smokebox isn't rounded to match the rest of the boiler, but rather is cut away to accomodate the large steam pipes.  The Y6b's were traditional compound mallets so the pipe led foreward from the rear engine unit wherre the steam was used first.  Also, the Y's had angled stacks and the 2187 had an oblong door.

The Y6b's that have the oblong smokebox door were originally built with the hot water pump mounted crossways under the front of the boiler. This pump was later relocated lengthwise to the fireman's side of the boiler and a change to the round smokebox door. 

[Penny Trains]

BigJim

The Y6b's that have the oblong smokebox door were originally built with the hot water pump mounted crossways under the front of the boiler. This pump was later relocated lengthwise to the fireman's side of the boiler and a change to the round smokebox door.

I was curious about that, thanks for the info!

[tomstamey]

Part of the reason was how elesco feedwater heaters were mounted. Pictured T&P elesco mounting would have blocked opening the smokebox front if not cut.  Others with it indented into the top of the smokebox would allow the whole front to clear.

[tomstamey]

Part of the reason was how elesco feedwater heaters were mounted. Pictured T&P elesco mounting would have blocked opening the smokebox front if not cut.  Others with it indented into the top of the smokebox would allow the whole front to clear.  Other appliances on the pilot decks could require clearence on the bottom, etc.