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BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

Discussion in 'Steam Traction' started by Bulleid Pacific, Nov 23, 2009.

  1. LMS2968

    LMS2968 Part of the furniture

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    Has it, though? Hopefully, yes, but we won't know until the engine is out on the road, and only then if its work is comparable to that of the 1930s over, and this important, similar steep and tightly curved lines at similar speeds and weight haulage conditions. I hope it has been cured, but . . .

    Computer modelling can go so far, and it's quite a long way, but ultimately you have to try it for real. That's why the motor manufacturers carry out computer based crash simulations to check the performance of every new model, but then take several new and expensive examples of the finished car and subject it to actual crash conditions, writing off these vehicles in the process. The safety ratings are based on the results of these tests, not the computer model.
     
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  2. ianh1

    ianh1 Member

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    For those of you who have stuck with us through the years, here's one to feast your eyes on.

    DSC_0081.jpg
    This is a trial fit to prove everything goes into place before we rivet the buffer beam. The cab is sitting in the right place pending assembly of the frame extensions and hind beam. Looks good, doesn't it?!

    Ian
     
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  3. W.Williams

    W.Williams Well-Known Member

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    Are you suggesting the work conducted by the P2 team is non-conformant? If you are perhaps you should take that up with MottMacDonald. The idea that the P2 team would spend the money building and assembling the wheel assembly with a flawed design is absolutely for the birds.


    upload_2020-12-11_10-5-22.png

    Iv said this before but clearly it bears repeating. Modern materials have moved on considerably from the 1930's having in many instances drastically enhanced mechanical properties. That alone would go some way to solving previous failures.

    In the engineering I'm involved in, testing serves as the verification of the analysis conducted. Modern safety critical design is conducted on analysis, not testing.

    If the FEA had left any concerns then a physical specimen test would have been conducted. There are plenty of rigs out there with the force required to conduct such a test. Clearly the FEA has given an acceptable factor of safety and so they went straight to build. I would encourage you not to sew doubt where it is clearly unwarranted.

    Interrogating design through analysis is faster, cheaper, safer than reiterating physical specimens. Most modern design is conducted on analysis. Despite steam technology being a legacy, when building from new it would be remiss not to utilise the tools we have in the modern age to demonstrate conformance.

    Given the Engineering we are seeing conducted here with the Clan its similarly dubious (and I would argue similarly unwarranted) to suggest the Wheel-Axle interface issue seen in previous locomotives wont be resolved to the satisfaction of the VAB.

    Look at the quality in the above work. The machining of the horn guides alone is enough to convince any casual observer of the quality of the work being conducted.

    The idea that legacy issues cannot be solved by modern engineering practice and techniques is to me totally unwarranted. We all know these machines were often built with huge factors of safety. There is huge scope within the deign envelope of nearly all components to redesign to mitigate known issues. Note: Mitigation is not the total elimination of risk entirely which is only a pursuit of the very brave or daft. Good design doesn't seek to eliminate risk, but does seek to reduce it to manageable levels.
     
    Last edited: Dec 11, 2020
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  4. Bikermike

    Bikermike Well-Known Member

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    I think the idea that risk has been completely removed is fallacy. Anyone who has ever tuned anything for more power will tell you something will crop up somewhere.

    I would be very comfortable travelling on the Clan as I am sure they are doing all the checks, but anyone that thinks there is *no* risk is wrong.

    It's looking very good - credit to the team.

    I'm sure you've got better things to do, but the same pic with all the bits you've got in store in front would be very striking

    Edit - looking at the picture in detail. Are the sticky-out bits by the steps up the running plate the bottom of the smoke deflectors? I always thought they were one-piece plates. Are the bits now on structural? are they put on because you can, or because they are necessary?
     
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  5. 'Clan' Hengist

    'Clan' Hengist New Member

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    Hopefully, the next major picture will have a lot the 'Bits' currently stored attached to the frames! The major parts anyway. That's what the plan is currently. But will be a little while before we get that. The works will be closed from this week until the new year, so not much more will be attached for a week or so. As for the smaller parts, there are so many in storage that it would not be feasible to move everything down to the assembly shop for a photograph.

    If you want to see those when we next have an open day come along and have a look. Everyone will be welcome. As soon as we can, subject to COVID restrictions, an open day will be held. Information about that will be posted as soon as we have set a date.

    To answer Bikermike question, the vertical panels are indeed the lower part of the smoke deflectors. They are also part of the footstep section that leads up to the running plate. All of this plate work was fitted to check if it fitted correctly. It is not structural. We could not fit the upper smoke deflectors as the necessary bracketry has yet to be made and they are far too heavy to fit temporarily without the correct support in place. If one had slipped a potentially catastrophic accident might have taken place. Much better to leave them off until we can do the job correctly.
     
    Last edited: Dec 11, 2020
  6. LMS2968

    LMS2968 Part of the furniture

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    Try again. What I said was that the theory had not been proved in practice, and it's not unknown for the theory to be shown to be a little optimistic when translated into practice, which is why actual physical testing is still an important part in any development stage.

    Computer analysis, including F.E.A., can help massively and shorten the testing programme, but it doesn't eliminate it. In the end, the computer analysis is only as good as the software, and the quality, and completeness, of the data input - all done by (fallible) people.
     
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  7. std tank

    std tank Part of the furniture

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    This is interesting. The RCTS green book indicates that the damage to the driving crank axles on the P2s was caused by overheated big ends. Scoring of the crank axle was the usual result, making replacement necessary, but in a few cases the axle actually broke in traffic as a result of this weakening.
     
  8. W.Williams

    W.Williams Well-Known Member

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    Try again? I'm not the one casually attempting to undermine the work of professionals. Fallible professionals sure, but professionals whose work is typically checked and checked again.

    Again, if analysis leaves sufficient room for doubt, the next step is typically some specimen testing to cover what analysis couldn't/didn't. To my knowledge we didn't see specimen testing, ergo safe to conclude the report produced underwrites the design to the satisfaction of the Chief Engineers within the customer group and the VAB.

    Why sow doubt where it is not warranted? Whats your motive here?
     
  9. LMS2968

    LMS2968 Part of the furniture

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    No motive, just stating what happens in real life.
     
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  10. northernsteam

    northernsteam Member

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    From bitter experience I know that what you get out of computers is only as good as what is put in.
    Computer programs have to be thoroughly validated, input data checked carefully, and only people who know what they are doing allowed to do the work.
    So I would fully expect anything from MM to be top notch, likewise any other reputable consultants.
    But, incidents in the field can throw all that design up the chimney, and the failure be 'unattributable'.
    Having had some sight of the paperwork for all this I am assured that the matter is not concluded yet so don't panic!
     
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  11. ianh1

    ianh1 Member

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    A response from the technical team

    The decisions that have been made on the boiler came after the Boiler Team produced a report that; compared the advantages and disadvantages of steel and copper fireboxes, the benefits of increasing the boiler pressure for an operator, the likely differences in the boiler plate thickness, stay pitching and firebox water legs from adopting a steel firebox and the effects of an increase in boiler pressure on the mechanical components.

    Within the 74-page report, there were two Appendices; one of 5 pages listed the original BR drawings for the boiler, ashpan, fire grate, and superheater, their revision history, and identified those that are missing. Out of the 96 drawings, we are missing 14 of which the most significant is for the outer throatplate and the inner throat plate. The other Appendix of 38 pages was the Bill of Materials.

    One of the recommendations of the report was that ‘During the design of the boiler, confirm the differences between a 225 psi and 250 psi boiler and make a recommendation on working pressures at the end of the design phase’. That phase will start in the New Year and will also consider in more detail any effects on the mechanical components.

    Recent posts have raised concerns about the effect of the increased boiler pressure on the mechanical components. Before discussing the concerns, it is worthwhile listing the mechanical differences: -

    Frames - the same thickness (1 ¼”) as those on Britannia’s. The cut-out in the frames for the centre driving axle is smaller to suit the 9” diameter axle rather than the 10”

    Front Buffer Beam – ¾” thick rather 1” thick on the Britannia

    Cast Combined Frame Stretchers – development from those on the original Clans and Britannias and are the same as fitted to Duke of Gloucester.

    Hind Dragbox – same as a Britannia

    Smokebox Saddle – smaller diameter on the upper surface to accommodate the smaller diameter smokebox

    Exhaust Pipe in Smokebox Saddle – same as Britannia

    Slide Bar Bracket – same as a Britannia

    Motion Brackets – same as Britannia and Duke of Gloucester

    Cylinders – same form and fit as Britannia except liner internal diameter is 19.5” as opposed to 20”

    Pistons, Piston Rods, Crosshead, Walschaerts Valve Gear, Crankpins, Coupling Rods, and Connecting Rods - same as a Britannia

    Slide Bars – same as Britannia, Duke of Gloucester, Standard 5 and 9F

    Leading and Trailing Axles – 9” diameter - same as the modified Britannia axles i.e., solid rather than hollow with parallel wheel seat rather than with a 1:500 taper.

    Leading and Trailing Wheels – same as Britannia

    Driving Axle – 9” diameter compared to 10” diameter on Britannia and with the same modifications i.e., solid rather than hollow with parallel wheel seat rather than with a 1:500 taper

    Driving Wheel – same as Britannia other than 9” bore for the smaller axle

    In summary, the principal mechanical difference is the diameter of the driving axle. Mechanically 72010 shares many parts with the Britannia which was designed for 250 psi.

    Concerns were raised about wheels becoming loose on the axle, increased stresses on the frame, wheel fit and bearing life.

    Looking at each of these: -

    Loose wheels – this happened to several Britannias locomotives when originally introduced. The axles were modified and 72010 will use the modified axle, however, Bill Harvey (Norwich shedmaster who maintained the Britannias there) wrote that between 1957 and 1961 (after ½ million miles of running) there were 16 recorded cases on the Britannias, where the axles shifted. He writes that these were a direct result of high-speed wheel slip incidents, the first of which happened to 70013 “Oliver Cromwell”. What is not absolutely clear is whether these engines had the modified axles.

    During these events, the inertia forces of the reciprocating parts and the centrifugal forces of the rotating parts rapidly exceed the nominal piston thrust, as they increase as a square of rotational speed and it is these forces that are the most damaging in a high-speed slip.

    The risk of wheels becoming loose because of a high-speed slip are the same for a Britannia and a Clan and is independent of boiler pressure.

    Impact on Mechanical Structure - the calculated maximum piston thrust (at Forward Dead Centre and Back Dead Centre) assuming a 10-psi pressure drop through the superheater is 285 kN (28.66 tons) for a Clan, 335kN (33.66 tons) for Britannia and 319 kN (32 tons) for 72010, so from thrust alone the loads are no worse than those for a Britannia’s.

    72010’s frame is the same thickness and profile as a Britannia and also uses Duke of Gloucester’s frame stretchers, so the performance is expected to be no worse. During the build, to minimise fatigue cracks, we are paying particular to eliminating stress raisers by making sure corners are radiused, drilled holes chamfered, burrs dressed and edges of gas cut plates dressed.

    Roller Bearing Life – this is principally dependant on loading. This has been assessed using Timken’s bearing life methodology. With a 225-psi boiler, the bearing life is 2 million miles, with a 250-psi boiler the bearing life is assessed at 1.4 million miles. Both these figures assume that the bearing is assembled and maintained correctly.

    Press Fit – the maximum interference on the Clan is equivalent to the minimum permissible interference on the Britannia. It should be feasible to obtain an interference fit between wheel and axle as good, or better than the BR7. We will be considering the effect of a higher interference on the wheel centre (i.e., hoop stresses), throughout this we will be consulting with accredited wheelset suppliers.

    Once the wheel is seated, the force required to press the wheel off is substantially greater due to stiction (the force required to initiate movement between a sliding pair of components). Bill Harvey reports that the initial force required to press off 70013’s wheels was 220 and 270 tons for the left and right wheels respectively – i.e., over twice the press on force of 100 to 130 tons.

    Boiler – there were concerns about an increase in plate thickness affecting weight, stays, VAB reaction.

    Plate thickness - During the design phase, all plates will be assessed on an individual basis against ‘BS 2790:1992, Design and manufacture of shell boilers of welded construction’. Any increase in thickness due to rounding up on size, because of metric size plate will cause a weight increase; however, this is expected to be within the weight saving by the elimination of lap joints and rivets.

    Changes are not expected to significantly change the weight of the boiler. The Britannia boiler was rated at 250 psi and Clan at 225 psi. Despite the difference in pressure, only 4 of the boiler plates are different in thickness: -

    a) Inner and Outer Firebox – off the 10 firebox plates, only two (the outer throat plate and the outer backplate) are thicker on the Britannia by 1/16” of an inch. The inner firebox plates are the same thickness for both classes.

    b) Boiler Barrels – the first and second rings are thicker on the Britannia by 3/32”

    Using commercially available metric plates introduces another dimension. Taking the front barrel of the boiler as an example and calculating the plate thickness using BS2790 gives a minimum thickness of 10.06 mm for a 225-psi boiler; for the 250-psi boiler the minimum thickness is 11.1 mm. 11 mm boiler plate is not commercially available, 12 mm is. So even though you might want a 225-psi boiler, you would get a 250-psi capable boiler unless you went to the extra expense of having 10.06mm plate specially rolled.

    Weight and Route Availability - The reduced weight of the Clan was principally achieved by fitting it with a smaller diameter boiler and smaller firebox. This saved 4 tons 5 cwt in empty weight. In working order, the Clan was 5 tons 10 cwt lighter than the Britannia.

    Since the closure of many secondary routes (The Somerset and Dorset, the Port Road from Carlisle to Stranraer, etc) the need for a lower axle weight has diminished and on today’s railway with most routes capable of taking a 25-ton axle load, gauging issues govern route availability rather weight.

    The coupled wheelbase is the same as a Britannia, so 72010 will have the same route availability as Britannia’s running on today’s network.

    Firebox - a key area that will get a lot of focus is firebox staying. With a steel firebox, there is a need to increase stay flexibility to reduce bending stresses in them. This can be done in several ways – increasing firebox water legs, Monel metal stays, use of flexible stays, or fillet welded stays. This is going to be the area that will require the most study to achieve the best solution and, in the end, maybe a combination of all 4. Achieving a good design here is key to the success of a steel firebox and is by far the most demanding task.

    VAB Reaction – to the VAB the boiler is a ‘black box’ and the VAB will accept the work of the Notified Body that approves the design and manufacture of the boiler.

    Performance – the Clan’s grate area is 36 sq ft and the Britannia’s is 42 sq ft. Grate area and the ability to burn coal is one of the key factors in determining locomotive power, so 72010 will never match a top-notch Britannia, however, it has the potential to be a reliable top-end Class 6/bottom end Class 7, satisfy the original intent of its designer and be a flexible machine that will appeal to tour operators.
     
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  12. jnc

    jnc Well-Known Member

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    Wow, what a detailed post! The issues have pretty clearly been looked at fairly thoroughly. :cool:

    Noel
     
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  13. Bikermike

    Bikermike Well-Known Member

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    Very informative response.
    To me it sounds like much of this was the natural progression on the 2nd lot of Clans (boiler pressure aside), with the development from DoG in particular giving a robust engine for it.

    I don't think the standard design brief really looked towards future optimisation, but an HP Clan with all the improvements would be nudging up to a 6-and-a-half p by the sounds of it - with a fractionally lower axle load than a 5MT (19 v 19.5 according to Wiki)
     
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  14. Steve

    Steve Resident of Nat Pres Friend

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    Thanks for a very informative and detailed post. It made very interesting reading.
     
  15. class8mikado

    class8mikado Part of the furniture

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    If i Recall from the Gospel according to Cox that part of the brief for the standard designs that they should be over-boilered and not over draughted as it was considered that thus would give the best economy and lowest running costs, with the potential for higher power outputs ( at the expense of etc) if so required...
     
  16. W.Williams

    W.Williams Well-Known Member

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    What a great post, fantastic detail. Particularly like the level headed pragmatic approach in plate thickness.

    If I were part of the Clan project I would be ferreting around various universities asking them to take on the Firebox Stay conundrum as a These project with a fully defined FEA study thrown in.

    Its a hugely complex issue but the use of analytical tools could yield some very pertinent insights for an optimal stay pattern and geometric layout.
     
  17. class8mikado

    class8mikado Part of the furniture

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    One hopes that this has already been done by the relevant 'experts'. Nothing like asking the right questions when wanting the right answers
     
  18. MellishR

    MellishR Resident of Nat Pres Friend

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    I think they may be following the Duke of Gloucester team in fixing the front ends of the slide bars to the cylinder covers. They certainly should do so or have a jolly good reason why not.
     
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  19. ianh1

    ianh1 Member

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  20. marshall5

    marshall5 Well-Known Member

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    I have a question re Clan cylinders. It appears that the castings are the same as the Britannia's but linered down to 19 1/2" compared with the Brit's 20" dia. Now, both the Brits and the 9F's are quoted as 20"dia x 28" stroke so what is the difference between the 70/72xxx and 92xxx cylinder castings? Anybody know?
    Cheers,
    Ray.
     
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