6202 Turbomotive/46202 Princess Anne

The Northumbrian was the first to have a firebox that was part of the boiler and not separate and to have a smokebox. Unlike Rocket, it also had frames and cylinders attached to the frames, albeit at the firebox end.
About the only thing on Rocket that existed on Evening Star was a firetube boiler barrel and a blastpipe, of sorts.

 

Rocket is seen, and rightly so, as the origin of the modern loco, although she herself was in many was a development of Lancashire Witch. Northumbrian was a modified Rocket class loco. Rocket's claim is that she was the locomotive which proved the viability of locomotives to haul trains at speed over a long distance; prior to this the majority of L&MR Directors were in favour of stationary engines with cable haulage.

Almost all subsequent locos were developments of the Rocket principle, including the four new Rockets ordered by the L&MR. they were not identical to Rocket herself, so the development process started in 1829.

You can argue about the origin of the species and claim it started at such a loco because it had this or other bit attached, but ultimately, all roads lead back to Rocket.

 

So the major inovation between the boilers of Rocket and Northumbrian would be the throatplate, so to muddy the waters further was Northumbrian the first with a throatplate, or was there a boiler with a throatplate in use on another 'style' of loco, or indeed stationary/marine use inbetween?

 

Rocket's boiler had a tube plate at each end, similar to a modern smokebox tubeplate. The firebox was a simple saddle mounted separately behind the boiler.

 

Wheels?

 

Fire? Tender?

 

Never realised Evening Star had wooden wheels.

 

So that's the reason it's banned from Network Rail...

 

Rocket combined two major advances, the one which is always remembered was what was the mutitubular boiler - an absolute first.

The other was the simple motion with the the pistons coupled directly to the wheels with just a coupling rod between the end
of the piston rod and the crank pin. This had been developing since the original Stephenson locomotives of 1825 on the Stockton and Darlington,
abandoning vertical cylinders necessarily needing spindly and intricate connections to the wheels. Robert Stepenson had away in
South America and after three years returned in November 1827 and saw the arrangement that Rocket was to have under the steam road
carriages that were tried at that time. Just within two years came the Rocket.

It combined the blast pipe, the simple motion, and the multitubular locomotive boiler. It was putting them all together that made it such a breakthrough
and such an absolutely convincing demonstration. All sorts of other things were tried - and quite a number seemed to show some success - but to the end,
when steam locomotives were last designed in quantity in the 1950s, they were basically quite the same boiler with a blast pipe and the same drive.

As Cartman in contribution 54 puts it: take someone who had been on the footplate in the 1830s, put them on any of the last steam locomotive
and having got over the size and all the extra controls they'd be at home.

NB In the 1820s slide bars were not easy to make, there were not yet planing machines, certainly not precision grinding, and truing them up was by hand
- filing, checking they were flat and parallel with blue, scraping. Decidedly light but Rocket did have the precursor of a bar frame.
Robert also promptly realised what could be improved and had, within the next twelve months: understood the Rockets tubes were too large to be ideal
and gone immediately to practically the still standard size , to obviate a major shouldering effect he first reduced the angle of the cylinders - Rocket was altered later -
and then made them horizontal on Planet, having introduced smoke box and firebox the same size as the boiler barrel on the Northumbrian.
It was a crescendo of practical innovation. He had also grasped the basics of efficient thermodynamics already: expansive working and the
great importance of avoiding cylinder condensation.

 

Just on that last point: I understand that cylinder condensation is avoided on later non-superheated locomotives by driving with the regulator not fully open. Was that done on those early locos, even when variable cut-off had only just been invented?

 

Rocket had a fixed cut-off, calculated at 98%, so the regulator was the only means of control.

What is often forgotten about Rocket is that she wasn't designed as a traffic engine, but to meet the conditions of the Rainhill Trials. These took place over a 1 1/2 mile course with an extra 220 yards at each end for acceleration and deceleration. There would not be a continuous effort being made, but rapid acceleration was needed, hence the fixed gear. Her predecessor, Lancashire Witch, did have a degree of cut-off control, but this was left out of Rocket for simplicity. Despite, this, she did successfully work trains on the L&MR. These were mostly ballast duties rather than passenger workings, in the intervening eleven months between the Trials and the Railway's opening progress was such that she was by then obsolete.