Pennsylvania Railroad 'Q2' 'Duplex' 4-4-6-4

Designed by Chief Engineer Ralph P. Johnson
Built by Baldwin Locomotive Works 1944-1945.

CYLINDERS (4) Front 19 ¾ ins x 28 ins (502mmx711mm)
                        Rear 23 ¾ ins x 29 ins (603mmx737mm) COUPLED WHEEL DIAMETER 69 ins (1,752mm)
TOTAL HEATING SURFACE
(including superheater) 9,655 square feet (897m²)
GRATE AREA 121.7 square feet (11.3m²)
BOILER PRESSURE 300 PSI (2,068 kpa)
TRACTIVE EFFORT (INCLUDING BOOSTER) 115,800 lbs (52,526 kg)
TOTAL WEIGHT 466 tons (473.5 tonnes)
LENGTH OVERALL 124 feet 7 ins (37,973mm)

The emergence of the 'Q2' 'Freight Duplex' in 1944 was the final development of an ill-fated attempt to compete with the diesel onslaught. It followed the famous shark-nosed 'T1' 4-4-4-4 passenger giants of 1942 and the solitary 'S1' 6-4-4-6 in 1939.

The 'Duplex' arrangement basically incorporated four cylinders in a rigid frame eliminating the need for articulation. The Pennsy had already experimented with a 'freight duplex' in 1942, the 'Q1' 4-6-4-4. This ungainly looking locomotive boasted 77 inch coupled wheels and featured an unusual application of boiler streamlining. Its rear cylinders were placed almost underneath the firebox and drove forward in a most unconventional manner. The arrangement had already been tried by the Chesapeake and Ohio in 1937 with the first American 'duplex', the 'George Emerson'. Both locomotives had very short lives.

The 'Q2' was indeed a formidable machine. One of the class developing almost 8000 indicated horsepower under test, the Pennsy had all twenty six locomotives in service by 1946 and their ability to highball very heavy freight loadings became legendary. Advantages when compared with conventional locomotives included reduction of revolving and reciprocating parts, less mechanical friction, shorter stroke and improved cylinder performance at high speed. A significant difficulty encountered with the T1's was the tendency to go into almost uncontrollable wheel-slip, even at high speed, a problem overcome in the Q2's with the application of an electrically controlled automatic anti-slip device. Unfortunately the Q2's suffered in route availability because of their higher than usual axle loadings. This factor coupled with various maintenance problems and the ability of the other PRR large freight locomotive, the 'J1' 2-10-4, to operate over much more territory, together with the oncoming diesel stampede conspired to see them all retired by 1952.