Trapp Mountain 2-6-2 "Prairie" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class 9 (Locobase 14052)

Data from Baldwin Negative 7478 as digitized by the DeGolyer Library of Southern Methodist University and archived at,337. See also DeGolyer Baldwin Specifications, Vol 62, pp. 284+. (Thanks to Chris Hohl for his 8 February 2015 email informing Locobase of the 9's tender capacity and weights.) Works number was 53164 in April 1920.

The Trapp Mountain was owned by the Arkansas Land & Lumber Company of Malvern and exploited the timber reserves on and near the Ouachita River. The AL&LC began operation in 1914 and was merged with the Wisconsin & Arkansas Land & Lumber Company in 1922. The new entity was then one of the largest suppliers of Arkansas soft pine lumber.

Baldwin's specifications pages for this logging Prairie contained the following "Hereafter" note by "K R" dated 7 May 1920:"Raise question of lagging and jacket on back head of boiler. Omitted from this loco. by mistake."

How embarrassing for the production team and for the quality-control group that should have caught that! Locobase wonders if the customer told Eddystone or Eddystone's field rep reported this on his return.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID14,052
RailroadTrapp Mountain
Number in Class1
Road Numbers9
Number Built1
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)9 / 2.74
Engine Wheelbase (ft / m)24.50 / 7.47
Ratio of driving wheelbase to overall engine wheebase 0.37
Overall Wheelbase (engine & tender) (ft / m)48.29 / 14.72
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)81,500 / 36,968
Engine Weight (lbs / kg)102,500 / 46,493
Tender Loaded Weight (lbs / kg)81,000 / 36,741
Total Engine and Tender Weight (lbs / kg)183,500 / 83,234
Tender Water Capacity (gals / ML)4000 / 15.15
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)5 / 4.50
Minimum weight of rail (calculated) (lb/yd / kg/m)45 / 22.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)46 / 1168
Boiler Pressure (psi / kPa)180 / 12.40
High Pressure Cylinders (dia x stroke) (in / mm)16" x 24" / 406x610
Tractive Effort (lbs / kg)20,435 / 9269.17
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.99
Heating Ability
Firebox Area (sq ft / m2)83 / 7.71
Grate Area (sq ft / m2)16.30 / 1.51
Evaporative Heating Surface (sq ft / m2)1529 / 142.05
Superheating Surface (sq ft / m2)
Combined Heating Surface (sq ft / m2)1529 / 142.05
Evaporative Heating Surface/Cylinder Volume273.77
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation2934
Same as above plus superheater percentage2934
Same as above but substitute firebox area for grate area14,940
Power L14803
Power MT389.77

All material Copyright ©
Wes Barris