{{Short description|American steam locomotive, 1944–1945}}{{No citations|date=February 2025}}{{Infobox locomotive | name = Pennsylvania Railroad class Q2 | powertype = Steam | image = PRRQ2p6.jpg | caption = PRR Q2 prototype #6131 | designer = | builder = Altoona Works | ordernumber = | serialnumber = | buildmodel = | builddate = 1944–45<ref name="harley" /> | totalproduction = 26<ref name="harley" /> | whytetype = 4-4-6-4<ref name="harley" /> | uicclass = 2'BC2' | gauge = {{track gauge|ussg|allk=on}}<ref name="harley" /> | leadingdiameter = {{convert|36|in|m|3|abbr=on}}<ref name="harley" /> | driverdiameter = {{convert|69|in|m|3|abbr=on}}<ref name="harley" /> | wheelbase = {{convert|26|ft|4.5|in|m|abbr=on}} (driving)<br />{{convert|20|ft|4|in|m|abbr=on}} (rigid)<br />{{convert|53|ft|5.5|in|m|abbr=on}} | valvegear = Walschaerts | length = {{convert|124|ft|7.125|in|m|3|abbr=on}} (locomotive and tender)<ref name="harley" /> | width = {{convert|11|ft|4|in|m|abbr=on}} (storm windows open)<ref name="harley" /> | height = {{convert|16|ft|5.5|in|m|abbr=on}}<ref name="harley" /> | weightondrivers = {{convert|393000|lb|kg t|abbr=on}}<ref name="harley" /> | locoweight = {{convert|619100|lb|kg t|abbr=on}}<ref name="harley" /> | tenderweight = {{convert|430000|lb|kg t|sigfig=3|abbr=on}}<ref name="harley" /> | locotenderweight = {{convert|1049100|lb|kg t|abbr=on}}<ref name="harley" /> | tendertype = PRR class 180F84, 8 axles, with conductor "doghouse" | fueltype = Soft coal | fuelcap = {{convert|39.86|ST|t LT|abbr=on}}<ref name="harley" /> | watercap = {{convert|19020|usgal|abbr=on}}<ref name="harley" /> | consumption = {{convert|12.5|t|abbr=on}} of coal per hour<br/>{{convert|16600|usgal|abbr=on}} of water per hour | poweroutput = {{convert|7987|hp|abbr=on|lk=on}} (indicated)/ {{convert|6645|hp|abbr=on|lk=on}} (drawbar)<ref name="withuhn"/> | tractiveeffort = {{cvt|100816|lbf|kN}} / {{cvt|115816|lbf|kN}} (with booster) | factorofadhesion = 3.9 | operator = Pennsylvania Railroad<ref name="harley" /> | fleetnumbers = 6131, 6175–6199<ref name="harley" /> | lastrundate = 1951 | frontcylindersize = {{convert|19+3/4|x|28|in|0|abbr=on}} | rearcylindersize = {{convert|23+3/4|x|29|in|0|abbr=on}} | boiler = {{convert|106|in|m|3|abbr=on}} | boilerpressure = {{convert|300|psi|MPa|abbr=on}} | disposition = All scrapped }}
The Pennsylvania Railroad's class '''Q2''' comprised one prototype and twenty-five production duplex steam locomotives of 4-4-6-4 wheel arrangement built between 1944 and 1945.<ref name="harley">{{cite book |title = Classic Power 5: Pennsy Q Class |author = Harley, E.T. |year = 1982 |publisher = N.J. International |location = Hicksville, New York |isbn = 0-934088-09-8 }}</ref><ref name="staufer">{{cite book |title = Pennsy Power |author = Staufer, Alvin |year = 1962 |publisher = Staufer |id = LOC 62-20872 |pages = 216–225 }}</ref><ref name="reed">{{cite book |title = Loco Profile 24: Pennsylvania Duplexii |author = Brian Reed |date=June 1972 |publisher = Profile Publications |location = Windsor, Berkshire, UK }}</ref><ref name="withuhn">{{cite book |title = American Steam Locomotives: Design and Development, 1880-1960 |author = William L. Withuhn |year = 2019 |publisher = Indiana University Press |location = Bloomington, IA |isbn = 978-0-253-03933-0 }}</ref>
They were the largest non-articulated locomotives ever built and the most powerful locomotives ever static tested, producing 7,987 cylinder horsepower (5,873 kW) on the PRR's static test plant{{Clarify|date=October 2023|reason=Cylinder horsepower is a calculated number, not a measured number. This should probably be indicated horsepower.}}. They were by far the most successful duplex type. The duplex propensity to slip was combated by an automatic slip control mechanism that reduced power to the slipping unit.
The Q2 locomotive was 78% more powerful than the locomotives that PRR had in service at the time, and the company claimed the Q2 could pull 125 freight cars at a speed of {{convert|50|mph|abbr=on}}.<ref>[https://books.google.com/books?id=gN8DAAAAMBAJ&dq=Popular+Mechanics+Science+installing+linoleum&pg=PA13 "4-Cylinder Engine Has 78% More Power."] ''Popular Mechanics'', December 1944, p. 13.</ref> These were an improved version of the previous Q1 class, which was a 4-6-4-4 dual-purpose engine instead of a 4-4-6-4 freight engine.
Despite the overall success, the Q2s were all out of service by 1951. With dieselization, they were among first for withdrawal since they were slightly more capable than the J1 class 2-10-4s under the PRR's 50 mile-an-hour freight train speed limit, but with far-higher operating and maintenance costs. The final Q2, 6199, had a power output of {{cvt|7987|hp|kW}}.
== References == <references />
{{PRR locomotives}}
Category:4-4-6-4 locomotives Category:Duplex locomotives Category:Experimental locomotives Q2 Category:Steam locomotives of the United States Category:Scrapped locomotives Category:Freight locomotives Category:Standard-gauge locomotives of the United States Category:Streamlined steam locomotives Category:Railway locomotives introduced in 1944