Talk:Planet (locomotive)

Key advance? & Influence of Hackworth's Globe ?

The Planet series of engines were so much more effective than the Rocket-like series, that according to an observer in 1834 the earlier engines were "useless... nearly abandoned". [1]. But exactly what was it, mechanically, about the new arrangement of the cylinders that made the new series so much more effective than their predecessors? Our article doesn't really explain.

Also, this website suggests that the re-arrangement was in fact a response to Hackworth's Globe, which had already begun construction at the Robert Stephenson works. Is there anything in this? Advocacy for overlooked heroes can get quite committed, so I was wondering if there was more than just one website pushing this? Jheald (talk) 20:20, 21 May 2012 (UTC)

Here's G.E. Sekon (2e, 1899) telling the Globe story [2] -- though according to him the design had already been pioneered in Bury's Liverpool. [3]. But Sekon seems generally hostile to the Stephensons, consistently trying to cut them down to size. And some of the material he uses to put them down seems to be pretty flaky, e.g. the story he tells of the Rocket's blast-pipe being stolen from Hackworth, while ignoring the account by Stephenson of its testing in Northumberland [4]. Jheald (talk) 17:40, 22 May 2012 (UTC)

I have read that there were two factors that made the new cylinder arrangement more effective. The more important one, which explains why the cylinders were moved to the front and the drivers to the rear, was weight distribution and its effects on traction. With the Rocket-type arrangement, the driving wheels were under the front of the locomotive. However, most of the weight, including the heavy firebox and cylinders, was at the rear, supported by the carrying wheels. This meant the driving wheels had relatively little weight bearing on them, which limited the maximum traction they could exert. Supposedly an aggravating effect was that when the engine was pulling, the force on the drawbar would tend to lift the engine's front end, further reducing the weight of the driving wheels on the rail and the traction available. Moving the driving wheels to the rear and the cylinders to the front would eliminate these effects by allowing the heavy firebox to be supported by the drivers.

The second factor, which explains the switch to inside cylinders driving a crank axle, was lateral stability. With short-wheelbase locomotives like the Rocket and Planet types, the piston thrusts, alternating between one side of the locomotive and the other, could generate a strong lateral oscillation, leading to a serpentine motion. Moving the cylinders inside the frames reduced this effect by shortening the distance between the pistons and the locomotive centerline, and thus the lever arm for the lateral torques generated by the pistons. Later the effect was reduced still further by lengthening the wheelbase in the 2-2-2 "Patentee" types.

Inside cylinders were never as popular in the U.S. as in Britain, perhaps because crank-axles are difficult to manufacture. In any case the gradual lengthening of locomotive wheelbases eventually eliminated the inside-cylinder advantage.

These factors are explained on pages 10 and 12 of The Illustrated Directory of Trains of the World by Brian Hollingsworth.

--Colin Douglas Howell (talk) 04:06, 20 August 2013 (UTC)

There was another advantage to the switch to inside cylinders which I had forgotten: an increase in thermal efficiency. Outside cylinders lost a significant amount of heat to radiation. By enclosing the cylinders within the hot smokebox, heat losses were greatly reduced. This is mentioned on this web page, which quotes from pages 113-114 of O. S. Nock's The Pocket Encylopaedia of British Steam Locomotives. --Colin Douglas Howell (talk) 22:12, 20 August 2013 (UTC)