Fred Starr recollects… - Knocking on the door of opportunity

Materials World magazine
,
2 Apr 2014

As someone who has always worked alongside mechanical and chemical engineers, I was envious of their ability to design pressure vessels and chemical process equipment.

In contrast, my specialism – metallurgy – was basically an experimental, not a predictive, discipline. Progress was maintained using brainpower and experience. New alloys came about through the casting and forging of trial batches of materials. These would then be subject to mechanical testing, before the best materials began to be made on a tonnage scale. A man from British Steel once told me that it took 10 years to get a new steel into production. Clearly, what was needed was some kind of shortcut that would obviate this long, costly procedure.

I came to realise that other branches of engineering also had to lean on experimentation when taking on anything novel. And even when the design work is straightforward, factors of safety disguise factors of ignorance. Nevertheless, what these other disciplines possessed were techniques that enabled anyone who could understand a mathematical equation to do some simple design. So in my time, I have been able to do the preliminary design for high-temperature autoclaves and heat exchangers.

More recently, in retirement, I have been attempting to show that if Sir Frank Whittle, inventor of the jet engine, had been supported by the Government, Britain could have had a jet aeroplane flying 10 years earlier than it did. We might then have had such superiority in the air that WWII would have been averted. Sadly, among the people at the Air Ministry who opposed Whittle was Arnold Griffith, of critical crack fame, who was pushing his own gas turbine turboprop, in addition to even more outlandish proposals. So Sir Frank did not get any direct financial support until 1938, and the engine was never built.

The easy part of my assessment has been the mechanical engineering of Whittle’s jet engine demonstrator, as he called it. What has proved a much more intractable problem is deciding whether even the best high-temperature alloys that were around in 1930 would have been good enough.

Of all the advances that metallurgists most like to boast about, our contribution to the development of the gas turbine is the most popular. How many times have I read that, without the superalloys, the jet engine would have been a non-starter? It is just not true. The early British and German jet aircrafts relied on much cruder materials.

Furthermore, by the early 1930s, piston engine exhaust valves were being made from heat-resistant austenitic stainless steel. In principle they should have been adequate for Sir Frank’s demonstrator, where, at the price of weight and complexity, temperatures and stresses were quite modest. It is possible to show, with some confidence, that providing the valve alloys were good enough, the demonstrator would have worked. My hunch as to whether these alloys would have had the necessary creep resistance is much less certain. We do not have reliable creep data from that period, and the materials themselves are obsolete. But if metallurgy were as advanced as it might be, I would have no trouble, from a knowledge of their compositions and microstructures, in calculating stress rupture properties.

There have been advances during my career. Programmes such as Thermocalc and MTDATA can predict which precipitates and other phases will form in an alloy. But such programmes assume, in effect, an infinite amount of time for reactions to come to completion. If I can give a homely example – when making toffee, butter and sugar are melted and stirred together, but the type of toffee produced depends on how good the stirring was and for how long the mixture was heated.

So, in guessing how well these now obsolete stainless steels would have performed, the best I can do is to draw analogies with modern materials. But is another opportunity is being lost by the metallurgists of today in not persistently knocking at a door marked APP – alloy prediction and performance? My tired old brain hopes not.

Fred will be discussing the issues raised here in more detail in a talk entitled Lost Opportunities – Whittle’s Turbojet Demonstrator of 1929 at the western branch of the Newcomen Society in Bristol, UK, on 17 April.  For more information, visit www.newcomen.com