I started the project in September 2002 and it took me more than 7 years to carry it at the end.

I used the original Union Pacific drawings and I spent about one year to make the model's drawings.

The most part of them are made with a 3D CAD, while the others are hand made sketches.

The locomotive requires a minimum radius of curvature of 11 m (in my circuit is 11.5 m, but it should manage 11 m without problems).

UNION PACIFIC 4-8-8-4 "BIG BOY"

Scale 1:11,3
Gauge 5" (127 mm)

LOCOMOTIVE

Driving wheels Diameter 153 mm

Cylinders Stainless steel body with bronze piston and Lubro-Ring(r)
Bore 50 mm
Stroke 72 mm
Steam operated drain cocks

Piston Valves Stainless steel body with bronze piston and bronze piston rings

Boiler All stainless steel, TIG welded
Idraulic test: 24h @ 45 bar
Operating pressure: 6 bar
n. 4 stainless steel superheaters
Water capacity: approx. 27 liters
Fuel: Liquified Petroleum Gas (Propane)
Regulator: Rotary Throttle

Water supply n. 2 injectors, steam driven pump, electric pump (hidden in the tender)

Brakes n. 2 air cylinders acting on the 8 driving wheels

Air supply Steam driven pump and electric compressor hidden in the tender

Reverse gear Full operating by air and scaled from the original drawings. 
The front actuators are coupled by a cross-head located in the 
articulation point of the two main frames

Lubricators n. 4 mechanical lubricators for the steam cylinders and n. 2 
displacement lubricators for the steam pumps

Turbogenerator Steam turbine with electric generator

Whistle 4 tone steam whistle hidden in the left side dummy air tank

Size Length 2350 mm, weight 320 kg (estimated)


TENDER

Water capacity 50 liters

Brakes n. 5+2 air cylinders 

All the doors are hinged and operating

Into the tender there are a 12 V accumulator, a 12 Vdc no-oil air compressor and a 12 Vdc high pressure water pump

Size Lenght 1270 mm, weight 100 kg (estimated)