This tiny engine was built by Peter Cooper to show that automotive power was possible for the new B&O. Inside a five-foot tall vertical boiler were a firebox burning anthracite coal and boiler flues cobbled together from musket barrels. A fan created an artificial draft over the grate.
In size a powered handcar, Tom Thumb was gear-driven, the cylinder rod turning a flywheel through a crank as the flywheel teeth engaged the front wheels. Cooper estimated the engine generated 1.43 horsepower, three times that of the Rainhill Trials' Rocket. Originally designed to cope with the sharp curves in the B&O's first few miles, the Tom Thumb demonstrated its tight turning radius in a test at Mount Clare. H B Latrobe, of the B&O and brother of the railroad's Chief Engineer John Latrobe, wrote a description of the outcome in a letter to Howard in 1877.
Cooper, "with his own hand, opened the throttle, admitted steam into the cylinder, when the crank substitute operated successfully with a clacking nois, and the machine moved slowly forward, with some of the bystanders, who had stepped upon it."
Kinert perhaps overstates Cooper's ingenuity when he claims that Cooper preceded Stephenson in the use of a multi-tube boiler and forced draft. (Stephenson's layout would be widely used; Cooper's not at all.) On the other hand, Latrobe's summary of the fateful first movement doesn't understate the import of the moment: "And this was the first locomotive ever built in America, and this was the first transportation of persons by steam that had ever taken place on this side of the Atlantic on an American locomotive."
Latrobe's description of the famous first trip to Ellicott City on 28 August 1830 is worth seeking out (see Howard's book online at Google Books). After demonstrating its ability over 13 miles outbound and several miles return, the Tom Thumb was met by a horse and car set at the Relay House by stage proprietors Stockton & Stockton. In the race that followed, the Tom Thumb had established a good lead until its fan-blower drive belt slipped off and the engine lost steam. The horse won the race, but steam power had been proved practical.
The 1926 replica built by the B&O, whose data is given in Staufer's diagram, differed considerably from the original. To allow it to draw any reasonable carriage, its single cylinder measured 5" (127 mm) x 27" (685 mm). 38 two-inch (50.2 mm) tubes, each 27" long, yielded 28.42 sq ft (2.64 sq m) of heating surface area. Together with the firebox's 11.5 sq ft (1.07 sq m), the total came to 39.92 sq ft (3.71 sq m). Boiler pressure was set at 90 psi, which generated a calculated tractive effort of 820 lb (371.95 kg or 3.65 kN). Adhesion weight on the geared driver was 5,800 lb (2,631 kg) and engine weight was 10,800 lb.(4,899 kg).
Photos and films show this version to bave placed the geared wheels at the rear and thus it operated as a 2-2-0.
|Principal Dimensions by Steve Llanso of Sweat House Media|
|Railroad||Baltimore & Ohio (B&O)|
|Number in Class||1|
|Locomotive Length and Weight|
|Driver Wheelbase (ft / m)|
|Engine Wheelbase (ft / m)|
|Ratio of driving wheelbase to overall engine wheebase|
|Overall Wheelbase (engine & tender) (ft / m)|
|Axle Loading (Maximum Weight per Axle) (lbs / kg)|
|Weight on Drivers (lbs / kg)|
|Engine Weight (lbs / kg)|
|Tender Loaded Weight (lbs / kg)|
|Total Engine and Tender Weight (lbs / kg)|
|Tender Water Capacity (gals / ML)||52 / 0.20|
|Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)||0.40 / 0.40|
|Minimum weight of rail (calculated) (lb/yd / kg/m)|
|Geometry Relating to Tractive Effort|
|Driver Diameter (in / mm)||30 / 762|
|Boiler Pressure (psi / kPa)||50 / 3.40|
|High Pressure Cylinders (dia x stroke) (in / mm)||3.5" x 14.25" / 89x362 (1)|
|Tractive Effort (lbs / kg)||124 / 56.25|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)|
|Firebox Area (sq ft / m2)|
|Grate Area (sq ft / m2)|
|Evaporative Heating Surface (sq ft / m2)|
|Superheating Surface (sq ft / m2)|
|Combined Heating Surface (sq ft / m2)|
|Evaporative Heating Surface/Cylinder Volume|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation|
|Same as above plus superheater percentage|
|Same as above but substitute firebox area for grate area|