Question on Alco's double engined 855 in Nov. TRAINS, page 98....

[Overmod]

Span bolsters. Each truck has its own pivot pin (or attachment point for centerless trucks), around which it can turn. The two centers are joined by a common structure which itself is pivoted to the carbody proper. It's not uncommon to find the couplers on the span bolsters (which IIRC was the arrangement on the N&W 2300 steam turbine) rather than on the extended carbody.

My understanding is that this setup is as flexible as necessary. The history of the big double-engine GEs may be illustrative: the B-B+B-B trucked versions were much more successful than the C-C versions.

Where you get the weird truck arrangements is on the B-B-B locomotives with rigid carbodies, where some form of sophisticated lateral motion is generally used on the center truck, and the outer two are pivoted or otherwise allowed to turn in the 'standard' manner...

[Modelcar]

...Yes, we've seen several wheel arrangements similar as this but I'm trying to understand what set up they {the trucks}, were fastened to to allow turning and each follow the one in front of it if the engine had a rigid chassis......{That is if we're to assume they were pivited on pins....}.

[jchnhtfd]

I seem to recall a subframe for each pair of trucks. Not that unusual a set-up, really -- there were quite a number of Bo-Bo-Bo-Bo electrics with the same basic concept.

[Modelcar]

It is riding on four two-axle trucks. Question: If each truck is positioned on a pin enabling it to rotate...Are they then mounted on a subframe that is on a pivot....If not, how is the suspension of them positioned that enables them to follow the curvature of sharp turns....? I'm assuming the engine has a ridged frame along it's length.