Heisler locomotive

The Heisler locomotive is one of the three major types of geared steam locomotives and the last to be patented.

Charles L. Heisler received a patent for the design in 1892, following the construction of a prototype in 1891.^[1] Somewhat similar to a Climax locomotive, Heisler's design featured two cylinders canted inwards at a 45-degree angle to form a 'V-twin' arrangement. Power then went to a longitudinal drive shaft in the center of the frame that drove the outboard axle on each powered truck through bevel gears in an enclosed gearcase riding on the axle between the truck frames. The inboard axle on each truck was then driven from the outboard one by external side (connecting) rods.

In 1897, Heisler received a patent on a three-truck locomotive.^[2] As with Class C Shay locomotives, the tender rode on the third truck. Unlike the Shay, Heisler's design did not have a continuous string of line shafting running the length of the engine. Instead, the tender truck was driven by a line shaft above the shaft driving the main engine trucks, connected to it through spur gears. This patent also covered use of a 4-cylinder 'V4' cylinder configuration.

The Heisler was the fastest of the geared steam locomotive designs, and yet was still claimed by its manufacturer to have the same low-speed hauling ability^{[citation needed]}.