Onward (locomotive)

The steam locomotive Onward had polygonal driving wheels. This rather ineffective locomotive with only one driving axle was built in 1887 by the Hinkley Locomotive Works in Boston for the Swinerton Locomotive Driving Wheel Company.

In 1887 the Swinerton Locomotive Driving Wheel Company in the U.S.A. received a unique locomotive boldly called Onward, which had been built by the Hinkley Locomotive Works of Boston. Its unique feature was that its wheels were not round. The company's founder, C. E. Swinerton, had specified that both driving wheels should actually polygons with 118 sides, each flat segment being about 2 inches (50mm) long. He wanted to prove that the line contact at the intersection of each segment would have better rail adhesion than a circular wheel, which was supposed to have only a point contact. However this was actually not the case as even steel deforms under enough pressure, so there is on fact a contact area even with a circular wheel.

The 4-2-2 locomotive had one single driving axle. This wheel arrangement had been abandoned elsewhere because of its poor adhesion. Probably it was chosen to emphasise the effectiveness of the invention. The Onward was tried on several north-eastern lines, but did not prove to be beneficial, and thus failed to convince practical railway men. It is likely that the non-constant radius would have caused tremendous amount of vibration.

It was sold to the Portland and Rochester Railroad, after the polygonal driving wheels had been replaced with conventional ones. After a few years the P & R sent it to the Manchester Locomotive Works for reconstruction as an ordinary eight-wheeler. "Onward" was cut up for scrap in 1905.

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