I was most interested to read about Mr Wardale's proposed 4-6-0 (SR272/273) and fine-looking it is too, with perhaps the exception of the Manorbier Castle smokebox front! I completely endorse his analysis that steam as we know it may indeed become unviable with regard to main line operation. So it is encouraging that someone has come up with a new proposal as opposed to building a replica.

However, I cannot help thinking that it is not revolutionary enough. It is probably fair to say that everything necessary for the steam locomotive to compete more effectively against its more 'fashionable' contemporaries has already been invented. However, so far this technology has neither been developed far enough, nor has it all been put together on one machine. The steam locomotive deserves an opportunity to demonstrate its full potential. Any new design of engine has to be the best possible, without fear of introducing new features, and pushed ahead with a determination to sort out the problems. Looking at the specification of the proposed '5AT', I cannot help but worry that Mr Wardale has been afflicted a little by the steam locomotive designer's traditional conservatism.

Historically, this has meant that there was comparatively little in the way of pure research and the diesel manufacturers wound up laughing all the way to the bank.

Mr Wardale is rightly concerned about hammer-blow on a two-cylinder machine. Astonishing therefore that the engine has been drawn with ordinary Walschaerts valve gear, which will contribute considerably to the reciprocating masses. Surely a more sensible alternative would be to use British Caprotti valve gear, which has no reciprocating mass at all, and gave good results?

Probably the strongest argument for rotary cam valve gear on such an experimental machine is that in order to change completely the characteristics of the valve events, all you have to do is insert a different set of cams.

Certainly with regard to valve gear, Chapelon himself was very clear. "Poppet valves are necessary.... on locomotives with very high superheat to avoid the necessity for lubrication of admission ports of piston valves and thereby protect the oil from cracking effects and retain its value as a lubricant.”

Chapelon also outlined the problems with inertia and the amount of space taken up by modern piston valves. He pointed out that in order to achieve the same valve opening as a piston valve with a travel of 200mm (8in), a poppet valve only had to be lifted off its seat by a mere 30mm (1” approx), with a corresponding reduction in inertia forces.

The other surprising feature is the omission of compound expansion. Because of its more even torque, the compound engine is less susceptible to slipping than a simple, an important feature for operating on today's railway. It is also reputedly a better-balanced machine and therefore kinder to the permanent way.

The compound engine is also more efficient. Mr Wardale makes the case for simple expansion being just as effective but, historically, it is the compound that has always led the way to greater thermal efficiency, leaving the simple expansion machine to catch up.

I hope Mr Wardale has not been discouraged and disheartened by his experiences in China and with the ACE project which he wrote about in his book The Red Devil.

A more radical solution is surely the only solution, and Mr Wardale should be encouraged wholeheartedly to think in this way. If steam traction could be brought to the same level of effectiveness and economy as its more fashionable counterparts, could some TOC not be tempted to use it to enhance its prestige on some services?

When the railways dispensed with steam, they threw away what had made them special. What replaced it has made valiant efforts to be anything more than mundane and prosaic but has not really succeeded in capturing the public imagination. Who is to say that if steam could be made competitive, the railways would riot like it back, at least just a little!

Angus Eickhoff, by e-mail