Are we comparing apples with apples? Are we comparing airliners with a steam engine, or just the jet engine with a whole locomotive?

I recently visited Didcot and was struck by how basic steam locomotives are, – probably part of their appeal. Also I suspect much of the design work was by rule of thumb and trial and error. A single engineer (highly skilled) could have designed a steam loco, – could a single person design a modern jet? I doubt it.

I suggest it's a misunderstanding to think that jet engines are simple. Although the principle of driving a fan with exhaust gas might be easy enough, it's much harder to build a working engine. And another series of difficult development challenges to make it lightweight, efficient, maintainable and reliable. Hundreds of tough problems have to be solved, for example:

• For efficiency reasons combustion should take place at the highest possible temperature. Not far below the boiling point of steel. So the combustion chamber and blades at the hot end of the engine need to be made of something special, with special arrangements to keep them cool.
• The blades and ducting inside the engine are aerodynamic. The profile of the blades is critical in 3 dimensions and blade shapes and sizes are different at each stage of the engine.
• Most materials soften when heated. A turbine blade is not only very hot, but it spins at several thousand rpm. Centrifugal forces on the blade are high. The blade has to be constructed so that it doesn't stretch or break under demanding operational conditions. Not only that, but because blades have to be replaced, you have to find a way safe way of attaching them to the spindle that allows speedy maintenance.
• Again for efficiency it's important that the gap between blade tips and the ducting be kept as small as possible. That means turbine blades mustn't stretch or expand with temperature. If they do the engine will explode.
• The engine has to survive hitting a large bird at high speed
• One way of making turbine blades is to grow them as a single crystal from an ultra-pure Nickel Super-Alloy. Not easy!
• The maths is challenging too. For example, how much air do you have to compress at 3000m to maintain an output of 1MW? And how much power is needed to drive the compressor? How big does the combustion chamber need to be? How many stages, how many blades?
• Having solved the maths, how do you then design the compressor needed to deliver the right amount of air when the engine is taxiing on the ground, and accelerating down the runway, and climbing to operating height, and as it cruises? Whatever you come up will have to be a clever compromise.
• Clever compromises feature throughout the engine. It has to be strong and lightweight. It has to be solidly built and easy to maintain. It has to run as hot and fast as possible without breaking or catching fire. It has to safe and affordable.

Back in the day, steam engines presented equivalent difficulties. Early on much of the science was poorly understood, materials undeveloped, skills rare and technology primitive. Technology doesn't stand still and by 1920 the steam locomotive was pretty much as good as it could be. After 1920 only small improvements to steam reciprocating engines were left to do. Although steam was done, the technologies and benefits it had sparked continued.

I say that the steam engine is father to most modern technology. Although the Victorians couldn't build a jet engine, much of what we know and do is built on their foundations. If they hadn't done what they did, we wouldn't be making jet engines either.

Dave

You have got to be kidding. A 747 has six million parts, almost 200 miles of wire and five miles of tubing.

The cabin pressurising and air conditoning system alone is more hi-tech than any steam train ever made. Let alone all the stuff in the cockpit control panel and the systems it links to.

Groups of local enthusiastic amateurs regularly restore and run steam trains. I can't see them getting an old 747 off the ground and keeping it there in 50 years time. (Yes there are guys who restore WW2 planes, but most of them are ticketed aircraft engineers, and they are not working on 747s).

Hi Julian

Sixty years ago I was a steam loco driver.

I enjoyed every moment of it and I bitterly regret that I am now too old to drive as a volunteer.

I never objected to getting up at all odd hours and, if it was possible I would go back to firing and driving right now!

Why were there so many youngsters who would give anything to climb on board a "King" or "Castle" knowing that they had years of cleaning and firing before they grabbed hold of that beautiful handle and felt her get hold of the load.

Every job has some disadvantages and firing and driving steam locos no more than any other.

Were you a driver?

Richard.

This does raise the interesting question of how do you define technically advanced.

I would suggest it is not the same as complexity which would correllate strongly to the componant count.

Perhaps a helpful guide would be how the hardware 'manages' the particular physics involved in the device.

To take the example suggested of the Steam engine and the Jet engine the physics would be largely Thermochemistry (combustion) Thermodynamics (energy transfer) and Fluid dynamics (gas flow).

On this basis the steam engine having a less well developed theoretical model on all three counts than the Jet engine should be more technically advanced assuming that a closer understanding of what is actually going on with the physics allows a closer approach to an ideal design.

Simplicity does not per se equate to technical primitiveness. Jet nozzles can now be developed extremely precisely using finite element anlysis, something that was not possible when designing steam injectors for example. That said with modern computer modeling it should be possible to design a more technically advanced steam engine than anything that was around in the past. Maybe a new category for a Model Show Trophy?

So yes I would say the Jet engine is more technically advanced than the steam engine.

regards Martin

The difference between a B 747 and a B787 is almost as great as the difference between a DC-3 and the B 747, yet the B-52 bomber designed in the early 50s is expected to out last it's successors, the B-1, and B-2 and continue in service until at least 2050, a case of best for service.

Ian S C

The Fairey Rotadyne units were of course RamJets with no moving parts like fans and compressors. Also **** noisy.

The same applied to the internal combustion engine in the early 20th century. All the exotic stuff we take for granted today like super high compression ratios, high rpm engines, desmo valves, overhead cam, etc etc were all known about and used experimentally in the 1920s, but it was the state of the metallurgy that stopped them going mainstream until after WW2, when great advances in metallurgy were made.

Even steam turbines required exotic metallurgy back in steam engine days. There is a sugar mill near where I live (well about 800 miles away, close enough) at Bundaberg that is still powered by reciprocating horizontal steam engines — built and installed in 1948 because Australia didn't have the metallurgy to build steam turbines and post-war austerity measures forbade the import of turbines from overseas at that time. But they did have a local locomotive manufacturing works that could turn its hand to mill engines if need be. How cool is that?

well there is the Flying Scotsman ?

. . . . . . . and the Battle of Britain Class . . . and FireFly and . . . .

For their time, they certainly were very advanced: (don't know about the UK, but looking elsewhere)

– Some of the Canadian ones went through the "National Research Centre" wind tunnel for streamlining and flow analysis (the models still exist)

– Oils and superheating – oils had to be designed so as to not burn in the high temperatures associated with superheating;

– materials work; light/strong alloys for boiler courses, stay bolts, etc;

– Aluminium – some superstructure (at least "over here&quot were aluminium;

– the fully cast beds, cylinders, etc. are incredible to see, and pushed casting technology;

– welding – look at the German Kriegslok system for the movement from rivets to welded technologies; the west followed (or went in parallel – don't know)

– time keeping – time keeping, and just organization of complex interactions needed advancing as forced by the railways;

– non destructive testing methodology most likely had been advanced by the railways;

– computer controlled trains, computer controlled signalling, etc – even the knowledge advancement of the old signal frames in the UK might have been profound for the time.

————–

Yes, certainly, even a lowly olde-school Boeing 747 is a complex beast, and nothing like an A380 or 787 in complexity, but making an A380 at the height of development of the steam era would have been impossible.

For those doubters; is the era of advancement of air transport past its' prime? With the demise of the Concorde, what really has changed in aircraft design in the last 20 years? Fly by wire, sure, but it's old technology now. Carbon-fibre? sure, but its old technology now. Radar?? sure but…