Wikipedia:Reference desk/Archives/Science/2025 April 30

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April 30

Baa baa choo choo

What was the maximum speed of one of these "little sheep" while pulling a train of 400 tons? I was only able to find the maximum speed when travelling light (50-55 km/h) -- by how much would a 400-ton train (such as a typical armored train from that era) slow it down? 2601:646:8082:BA0:D86C:E2FE:4764:1AB0 (talk) 03:19, 30 April 2025 (UTC)[reply]

The Russian Wikipedia gives the traction as 8700—9500 kgf. At which speed does rolling resistance + drag of a typical 400-ton train equal about 9000 kgf? (Are these metric tons?) I bet this is an order of magnitude higher than 50–55 km/h, so my best guess is that it takes 15 to 30 minutes for the train to come up to maximum speed, but that speed would still be in the 50–55 km/h range.  ​‑‑Lambiam 08:47, 30 April 2025 (UTC)[reply]

At 1.85 square metres of grate area and a somewhat realistic efficiency, I guesstimate that its sustained power is no more than about 100 to 150 kilowatts. With the rolling resistance of a 400 tonne train, that's maybe 40 km/h. But with the cut-off wide open for more traction, efficiency drops. Could be interesting to look into, but I've no time right now. PiusImpavidus (talk) 16:19, 30 April 2025 (UTC)[reply]

The Russian Wikipedia gives the power as 550—720 hp, which amounts to about 400—530 kW.  ​‑‑Lambiam 22:27, 30 April 2025 (UTC)[reply]

It was a very rough guesstimate. In any case, it serves to demonstrate that it's most likely limited by sustained power, not by traction. At 85 kN traction, 400 kW power is reached at only 17 km/h.

All versions appear to have had the same firebox, so differences in sustained power can only be caused by differences in efficiency. And the slower you go, the more traction you need to reach maximum power, so a later cut-off, leading to less efficiency and less power. The 400 to 530 kW figure may have been measured using a train of less than 400 tonnes, giving more power. Although not too light a train, as power would normally mean drawbar power, which gets less if the train is too light and a larger fraction of the power is wasted on moving the loco itself.

To get an accurate answer, we need detailed performance data on these locomotives, and considering that steam locomotive design was often more art than engineering, such data may never have been collected. Absent that, any number between 30 and 45 km/h sounds totally believable to me. PiusImpavidus (talk) 11:00, 1 May 2025 (UTC)[reply]