Question on Mallet drivers: Did both swivel or only the front?

Only the front engine swiveled on Mallet and simple articulated locomotives.

Stuart

@Stuart posted:

Only the front engine swiveled on Mallet and simple articulated locomotives.

Stuart

Thanks for validating my ancient belief. And for being more precise on both simple and compound articulated locos.

Beyer-Garratt (England) manufactured articulated locomotives, both simple and compound (Mallet),  that did have two swiveling engines, one under each end of the central boiler and coal compartment. They were shipped all over the world, except North America,  by this English company. Double-Fairlies are similar in construction.

Articulated Locomotives by Lionel Wiener and Articulated Locomotives of North America by Robert A. Le Massena are both excellent resources for information on articulated steam locomotives.

@hokie71 posted:

I have long thought that the rear drivers on Mallet locomotives were fixed and the front drivers swiveled. Wikipedia appears to agree with this. I was reading Dixon's book "N&W steam: the last 30 years" and he states both drivers swiveled. The diagrams in the book for the Y6 and A are inconclusive and  I have no more books to check this out so... I thought I would see what our experts say and whether this varied.

I have that book and I don't remember Mr. Dixon ever making any such statement. Tom Dixon knows better than that. Can you clue me in as to what page you found this statement on?

@Big Jim posted:

I have that book and I don't remember Mr. Dixon ever making any such statement. Tom Dixon knows better than that. Can you clue me in as to what page you found this statement on?

Dixon is amazing, in fact he signed my book. no intent to cast shade on his remarkable body of work.  Check page 8, left column.

I've never heard of any of the prototype common articulated locomotives having the rear drivers swiveling.  Yes, many models do that, but that's just to fit them into our tiny RR empires.  None of my scale articulated locomotives have the rear drivers that swivel.

Strictly speaking, a "Mallet" articulated is a compound locomotive. They were named for Anatole Mallet, a Swiss mechanical engineer, who developed the concept. A "simple"articulated locomotive, in which the cylinders and steam pressures are the same size on both engines, is not a "Mallet" articulated. Compounding was also used on some non-articulated locomotives, like Baldwin's "cross-compound" locos, in a system devised by Baldwin's Board President and engineer Samuel Vauclain ("Vauclain compounds").

The rear engine on all American articulated locomotives was firmly attached to the frame. It did not swivel. Only the front engine moved independently from the frame.

I think it would be a little more accurate to say that on an articulated locomotive, the frame consists of two "articulated" (flexibly joined) sections:  the rear section is rigidly fixed to the boiler, while the front section is free to move back and forth laterally under the boiler. The articulation joint allows lateral movement, but very limited (if any) vertical movement.

Mr. B. Smith, you said it better than I did. Thanks.

Thank you, Mr. Melvin.  

@hokie71 posted:

Dixon is amazing, in fact he signed my book. no intent to cast shade on his remarkable body of work.  Check page 8, left column.

Ok, I see what you are speaking of and I think that a bad choice of words can be read in a confusing way.

To quote Mr. Dixon's book: "The two sets of cylinders and drivers (called engines) were swiveled under the boiler, so that the actual driving wheel base was short enough to negotiate existing lines."

The word "articulated" would have been a much better word to use instead of the word "swiveled". Note that the sentence does not specifically say that both engines actually swivel independently.

I can see where someone not familiar with articulated locomotives could misunderstand what was meant to be said.

Rest assured that on the type of articulated locomotives we are speaking of here, the rear engine is firmly attached to the boiler and that the front engine is connected to the rear engine by an articulating pin which allows the front engine to swivel at that point.

Actually, neither engine actually swiveled on its axis.    The swivel point was between the two engines.    The front engine turned, I guess you could say swiveled under the boiler.

A real swiveling loco was a Mason Bogie.    The driver frame and cyiinders swiveled on about its midpoint under the boiler like a freight car truck, but not as sharply.

To add to the confusion, some model railroad manufacturers make models of articulated engines where both sets of drivers pivot/swivel, so the boiler overhang in front isn't as great on our very sharp (compared to the prototype) model railroad curves.

Maybe it would be clearer to say that the front engine of an articulated loco can "swing" (rather than "swivel") from side to side on the articulation pin.