Trapp Mountain 2-6-2 "Prairie" Locomotives of 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.

Specifications by Steve Llanso of Sweat House Media
Locobase ID14052
RailroadTrapp Mountain
Number in Class1
Road Numbers9
Number Built1
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase9'
Engine Wheelbase24.50'
Ratio of driving wheelbase to overall engine wheebase 0.37
Overall Wheelbase (engine & tender)48.29'
Axle Loading (Maximum Weight per Axle)
Weight on Drivers81500 lbs
Engine Weight102500 lbs
Tender Light Weight81000 lbs
Total Engine and Tender Weight183500 lbs
Tender Water Capacity4000 gals
Tender Fuel Capacity (oil/coal)5 tons
Minimum weight of rail (calculated)45 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter46"
Boiler Pressure180 psi
Cylinders (dia x stroke)16" x 24"
Tractive Effort20435 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.99
Heating Ability
Firebox Area83 sq. ft
Grate Area16.30 sq. ft
Evaporative Heating Surface1529 sq. ft
Superheating Surface
Combined Heating Surface1529 sq. ft
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 area14940
Power L14803
Power MT389.77

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