Sir William A. Stanier, FRS

Why would this be an issue on a loco with a turbine and CVT, as opposed to a turbine with fixed transmission?

Dave

 

With such a transmission, the idea is to run the turbine at its optimum speed and steam flow (i.e. constant power). If it is to be a constant power transmission it needs to match a constant power output of the boiler so you cannot mortgage the boiler to get high output spikes when required, one of steam's great assets.

 

If I remember rightly the turbine on the original 6202 had six (?) steam nozzles which the driver turned on or off according to the load requirements, so as Saggin' Dragon points out above, running the turbine at constant speed does not equate to constant power. For that matter how could it? Sometimes the train will be climbing, sometimes descending and sometimes running on level track, just the same as a conventional reciprocating loco or a turbine with fixed gearing. Constant speed, however, should equate to optimal efficiency.

Dave

 

Yes, constant speed does not equate to constant power, but that is what you are trying to achive with an infinitely variable transmission. i.e. you have a constant input speed and constant torque and you match your output speed and torque to this, generally adjusting the speed as the torque varies.

 

I don't think that is correct. The input input speed should be constant, and dictated by the point of optimum efficiency of the primary power source, but the input torque will not be constant.

The output speed is determined by the speed of the vehicle at that point in time, because the output will be connected to the wheels. The required output torque would be be determined by the conditions at the time. In the case of a train, for example, determining factors would include gradient, weight being pulled, headwind and whether accelerating or decelerating, rolling resistance etc.

The driver would need to ensure that the output torque matched the requirements prevailing at that time, and would do this by VARYING THE INPUT TORQUE, by whatever means is provided on the primary power source.

That's how I see it anyway.

Dave

 

Deleted

 

I'm not aware of any at Crewe works, although there are some at Harrow showing the boiler being removed, a replacement bogie bieing fitted and the frames standing bereft of the boiler. See Peter Tatlow's 'Harrow & WEaldstone 50 Years On' (2002 / 08) The Oakwood Press, Usk ISBN 978 0 85361 680 1

 

Back to the CVT, surely the major point is that the engine may be running at optimum rpm to deliver maximum power output to the transmission at all vehicle speeds. How long enough steam might be available to deliver that maximum power output is a subtly different issue.

 

It isn't that subtle. With a steam engine, power output is largely a function of the boiler. The boiler's ability to produce sufficient steam would have a far greater effect on a turbine optimised for a particular speed than on a reciprocating engine, or even a turbine designed to perform over a given rpm range.

 

That is true, but just to reiterate one final time, with CVT maximum power would be available at all vehicle speeds IF REQUIRED. There is no suggestion that such a locomotive would spend it's time flying around the network developing full power at all times.

Maximum power would be needed in short bursts, say when accelerating or climbing, just the same as any reciprocating engine or fixed speed turbine (6202). The point is that that maximum power is available when required, plus at other times the turbine will at least be running at optimum efficiency.

Anyway, the discussion has been fun but completely hypothetical, as the concept will never be built.

Didn't 6202 complete something like 400,000 miles, so must have been reasonably successful. Possibly the future for steam traction, if the end of steam hadn't been looming?

Sorry for the massive swerve off topic

Dave

 

There's also the Nord Compound, which passed from the National Collection to a private owner before being sold again to a French railway museum. A pity really, as it was the nearest available thing to a De Glehn Atlantic and thus arguably a vital part of the story of British steam locomotive development.

 

The Austerity Respite was briefly an NRM loco, though never restored. Sold to a private individual an replaced by another if the class which is being restored.
Another omission retrospectively corrected. Not so for either of the WD tender loco types or an 8F for that matter.

 

But given that we have WD tender locos and 8fs in private ownership, there is no pressing need for the NRM to add either type to their collection.

 

Not now, I was merely commenting on them having been overlooked in the first place.

 

I see.

 

Deleted

 

That's an interesting post.

Presumably the 833 day overhaul was the rebuild into conventional format?
The first (363 day) overhaul may have taken that long because of wartime priorities?

Could there have been accountancy reasons for rebuilding 46202 as 46242 after Harrow?

Perhaps this should have been a dedicated thread as the loco does seem to have had an interesting history.

By the way, since my previous post (which was meant to be my last on this) I have started to read the links from the Wikipedia page to a series of articles in the Engineer describing a ride on 46202 from Euston to Liverpool. Not finished yet as it is getting late, but it is an interesting read.

Dave

 

We aren't comparing like with like here: i) 6202 would often be stopped for defects where a conventional pacific would be allowed to continue as much of it was an unknown quantity to the average fitter / foreman; and ii) any problem within the turbine / control unit / transmission could not be repaired using spare parts in stock; they would need to be procured from Metropolitan Vickers, and since they wouldn't hold them in stock, time was lost while they were being made from scratch.

6202's and 6242's frames were not the same: the trailing end frames (rivetted on, I'll grant) were different, but beyond that 6202, in both forms had roller bearings while 6242 had plain bearings to the end. The horn gaps needed for roller bearings were very much wider than those for plain, so a complete swop wouldn't work. I also suspect (but have never proved) that 6202's frames were 1.25" thick, as with 6200/01, while 6242's were the standard 1.125" so cutting and shutting doesn't work.

During the rebuild, 6202's frames were cut at the intermediate horn guides and new front frames from that point forward were fitted, thereby shortening the wheelbase by nine inches as per the Coronation wheelbase. After Harrow, her front frames were damaged and would have needed some repair anyway. Much of the damage to 6242's frames was concentrated on the right hand front section forward of the outer cylinder, and replacing this section alone would not be difficult job. Allan C Baker, who worked in Crewe Works (later) relates that when returned to traffic, complaints were received of smoke entering her cab. It was found that the cab roof was slightly low due to damaged cab mounts on the frames as a result of Harrow, and packing had to be added to restore the cab to its correct height.

As above, the loco did not receive new frames, or those from 6202, but the existing frames were repaired. 6242's repair was more protracted than you state - the accident was on 8th October 1952 and she returned to traffic (according to her Engine History Card) on 26th October 1953, over a year after the collision, spending 291 (working) days in the Works.

The different front running plate arrangement is often quoted as evidence that 6202's front frames were used. These are simple pieces of plate and angle brackets and are of no significance. In any case, those on 6202 were destroyed in the accident. The real link is that 6202 was rebuilt with this arrangement (which isnt the same as that on a Princess) and so 6242 was repaired in the same manner. I suspect someone in Crewe Drawing Office didn't like the 'utility front' (I agree with him!) and used the original arrangement on the rebuild and repair.

No gun play, mate! The rebuild of 6202 and repair of 6242 have been of great interest to me and I have tried to find out as much as I can. The repair, and particularly what happened to the remains of 6202 from 9th October 1952 and withdrawal as late as 22nd May 1954 are shrouded in mystery.