-Large diameter wheels will be fitted. Although smaller wheels would be better for acceleration, the use of large diameter drivers will reduce piston speed. This has several effects;

     -Stress on crosshead reduced.

     -Piston speed reduced, consequently less wear per driving wheel revolution.

     -Amount of steam required in cylinders per mile is reduced. This is important for long distance high speed cruising.

The locomotive has a very high tractive effort, due to the high boiler pressure, thus this will overcome any problems with acceleration.

-The use of caprotti valve gear is intended to ease overhaul. As the motion will be driven be a rotary shaft, the number of bearings will be reduced, and will be designed so as to be easily replacable. All components will use roller bearings in order to reduce heat and stress in the moving parts. The valvegear itself will probably take the form of a rotating drum, controlling steam admittance. Although this may require some additional design work, many of the flaws associated with conventional caprotti will be overcome. Also, by using a shaft to derive the motion, the valve gear will excert no hammerblow on the track. An advantage of this design is that the cylinder block could be converted to Piston valve derived motion if necesary. In that case, Walscherts valve gear would possibly be used. An alternative could be outside Stevenson link motion (Aka the experimental Ivatt 'Black 5'). The advantages of this later design is that whilst no eccentrics are required, it avoids placing excess stress on the crosshead. (Walsherts is derived from the motion of the crosshead).

-Spoked wheels are fitted in order to appease enthusiasts. With the exception of the Bullied-Firth-Brown type of disc wheel (Often incorrectly tittled 'Boxpok'), disc wheels tend to look plain and asthtically unremarkable. However, the back face of the spokes will be flared in order to improve rigidity.

-On this locomotive, a riveted boiler would be superior to a welded boiler. This sounds ridiculous as riveted boilers are less rigid than welded ones and are heavier. The Advanced Passenger Locomotive project proposes a welded boiler, the justification being that American locomotives used them. However, American locos also used cast steel frames which were totally rigid, therefore the boiler had very low stresses excerted upon it. Cast locomotive frames were unsuitable for British operating conditions, as they were too heavy. Today, the weight restriction situation has worsened, thus plate frames will have to be used to cut down on overall weight (They will also have holes cut out of them in stress free areas). Plate frames, as a matter of course flex and twist slightly during everyday running. A riveted boiler is able to bend slightly without cracking occuring. However, whilst every effort will be taken to ensure that a riveted boiler is fitted, current pressure vessel regulations may prevent the production of a new rivetted boiler. If so, the boiler MUST be correctly sprung to prevent any welds from splitting and causing destructive failure. It must be remembered that on most engines, the boiler is fixed solidly to the smokebox saddle and 'Floats' upon sliding blocks at the rear (This allows the boiler to expand).

-Coal firing is essential to the projects success. Whilst oil firing may have a few advantages, burning diesel would effectively make the whole activity pointless (Why not build a Diesel instead?). A mechanical stoker could be considered, however these devices usually created more pollution than hand firing. The tender will be fitted with a coal pusher in order to make the firemans job easier. Moreover, by improving the efficiency of the boiler, the rate of firing should be reduced to make the secondmans job tolerable. These efficiencies are;

       -Fitting of exhaust steam injector

       -All heated componants (Boiler, clinders etc) are to be well insulated

       -Large number of boiler tube used to increase heating area

       -High degree of superheat fitted

       -Roller bearings reduce friction

       -Optical alignment used to ensure tolerances are kept to a minimum.      

-The use of a trailing axle is not ideal for adhesive purposes. However, in order to gain as much energy as possible from the coal, a wide firebox is essential. As this will not fit between the frames, a trailing axle is essential. In order to ensure that tractive properties remain good, the design of the trailing bogie suspension must be carefully arranged.

-The use of devided drive is necesary for the four cylinder arrangement to be used. If all cylinders drove onto the same axle, the inside cylinders would need to be steeply inclined and would result in a highly pitched boiler. The devided drive arrangement, as used by the GWR provides almost no hammer blow (As opposed to the action of a two cylinder engine) and prevents the locomotive from 'Hunting' at high power output (When working hard at low speed, the front of an engine with large outside cylinders, such as a 'Hall', will oscilate considerably from side to side).

You mentioned that you have some reservations with the 5AT project. I must say that I am inclined to agree with you on the preference for four cylinders instead of two provided that ease of maintenance can be obtained for the inside cylinders. I wonder how long an unbalanced two cylinder locomotive will be allowed to operate on mainline tracks. Other than this, what other serious objection do you have to the 5AT and how would your design improve on it?

I am currently a student studying for A-Levels. As a result, I am currently rather busy. Whilst I have no formal Engineering Qualifications, I have researched the workings of the steam locomotive over a number of years, and have experience in the day to day running of a preserved railway. Since the project is in an early stage, asking for financial backing would be unwise since an investor would expect a return on a project which may not work. Therefore, until the design has been theoretically proven, the need for a backer will be resisted.

The likelihood of 2-cylinder power being restricted from the mainline is currently low since typical 4 cylinder engines, such as 'Kings' have higher axle loadings and are hence more restricted. However as maintenance declines on the network, hammerblow will become critical, and lighter 4-cylinder locos, such as 'Castles' will fare better. The intention of this design is to combine the benefits of these light but powerful engines with the increased ash pan capacity of a pacific.

My Serious objections to the 5at are as follows;

-The Aerodynamic casings. This will have no real effect on air resistance, since the area involved is so small. Generally, it is the side area acted upon by lateral air currents which cause problems, namely forcing the flanges against the rail, making the train harder to pull, and hence increasing fuel consumption. Indeed, their design may in fact increase air vortices beneath the smokebox and thus increase, not decrease any drag. The casing will cause maintenance problems, since it restricts access and could cause the cylinders to overheat (As was the case with the doomed Morniber Castle experiment). The nose cone idea has no value, but will make smokebox access more difficult, hence restricting inspection of crucial (And potentially lethal) items, such as the Superheater Banks. Additionally, why bother adding deadweight to an engine which is supposed to have a high route availability? The absence of such a pointless shroud on my design will allow more mass to be devoted to working components, such as fitting a comparatively larger boiler.

-Enclosed Cab. From my experiences (Albeit short ones) on locomotive footplates, a cab which is not entirely enclosed is preferable, since the small draughts created ensure that the air is kept fresh and cool. An enclosed cab would become extremely stale within a short time, due to the warmth given of by the backhead.

-The use of two cylinder drive is ludicrous. The 5AT engineers claim that the use of light motion components would eliminate the effects of hammerblow, yet it is imbalanced forces, not motion weights which are to blame. Whilst divided drive will not eliminate the effect entirely, it will vastly reduce it and also remove the tendency to ‘Waddle’ which two cylinders will cause.

-Oil firing. I know that on paper oil firing is superior to coal firing. However, my viewpoint is that if you have Oil, and you want an efficient engine, build a diesel. I believe that coal firing can compete on the same grounds, whilst maintaining that essential factor, a Fireman, not Knob twiddler. Nevertheless, the use of larger wheels on the pacific will reduce piston speeds and rpm. Technically therefore, less steam and hence less fuel will be required than the 5at when running at the expected cruising speed of 50mph. It is intended that the firemans duties will not be excessive, even at full power.   

I hope any other queries will be dealt with when the new design is uploaded