Olaf Rasmussen Wrote:
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> At least to me, it was a bit mysterious just how
> the Hagans system of articulation worked. The
> Hagans system was designed in an effort to develop
> locomotives that had all the advantages of
> articulation in travelling on tightly curved track
> without requiring flexible steam joints, gear
> drives or more than the two cylinders of rigid
> framed locomotives. A number of different systems
> using rod connections were developed, the most
> successful being the Klose system and the Hagans
> system. Apparently these systems were only used on
> narrow gauge railroads. The Hagans system as used
> on the North East Dundas Tramway is actually
> fairly easy to figure out when you visualize the
> motion of the rods as the engine moves and the
> rear 0-4-0 assembly swivels.
That style of locomotive kind of breaks the Whyte system of classifying wheel arrangements. These types of oddball arrangements weren't included in the original system as they were either rare or not yet invented when the system was developed circa 1900. Whyte certainly isn't set up to deal with hybrid rod/lever drives. It's tempting to call the one pictured above a 2-6-4-0 (and probably most people do) but it could also be called a very peculiar 2-10-0, and doing so is arguably more fitting with the purpose of the Whyte system. The Whyte system is more focused on power sets than articulation* and all powered axles on the Hagans locomotive are driven from the same engine and must all rotate together. I've seen some writers denote Hagans engines using a plus sign similar to how garratts are usually handled, presumably less out of necessity (there are no unpowered axles to cause confusion like on a garratt) than for convenience and informative purpose. It might be a fair way of handling an oddball such as this.
*The primary focus on power sets is why German types like the class 44 and class 50 are called 2-10-0; the 10 driving wheels are all one power set, even though the lead drivers are articulated with the lead wheels using the Krauss-Helmholtz arrangement. Such engines track like 4-8-0's. Likewise that's why a PRR T1 is a 4-4-4-4 even with a rigid frame; the driving sets are independently driven from separate engines.
