http://en.wikipedia.org/wiki/File:RRConway.JPG (open source)
Not quite as glamourous as the French connection (the movie), and nothing obviously to do with Wales is it?
Confused? Puzzled? Read on!
Yes, once again there is a picture of great big clunking jet engine on my blog. However, those of you interested and perhaps sad enough to read an earlier post of mine will have no doubt spotted my quibbles with one Professor Geel’s account of how the jet age transformation was ushered in. The issue here is not so much jet engines and the jet age. The bigger picture is how social science should understand major technological revolutions, and how perhaps we can bring them on. If we want to know whether Kindle will really kill the paperback or whether electric cars are going to be the next big thing, or if tablets will kill the desktop PC….then we need to understand how technological change happens. Geel’s offers us his Multi-level perspective (MLP), which I think is flawed.
The smaller picture is that Prof. Geel’s makes much in a key paper of his, of the historical significance of the American Military engine the J-57, which he claims made the Boeing 707 and Douglas DC-8 possible. Without such a great big turbojet engine these breakthrough designs, and the jet age, would have been much delayed. That is pretty much the standard argument ‘out there’.
I happen to think its inaccurate, which raises the question of understanding what technological niches turn out to be really important and what ones are less so.
As I explained before, this is ONE interpretation of the technical history of the time. There are other possible views.
Chief among them is to point out that very quickly those big Boeing 707s and DC-8s were being powered by turbofans by the end of the 1950s. Moreover, that pioneering work on turbofans was done by the British firm Rolls Royce. The photo above is their Conway turbofan engine, which was the world’s first low bypass turbofan engine to enter service. The name was taken from the Welsh river the Conwy, but Rolls Royce decided it had to be spelt simpler, otherwise the Americans might complain. They were hoping to sell quite a few of their Conways in the later 1950s.
The Conway itself was a commercial failure but a technical success-something British industry and governments have arguably excelled at since the 1950s. Only Lufthansa and BOAC used a few 707s with Conway engines in the early 1960s and it was the same for the DC-8-about thirty or so flew with the Rolls Royce engine. It was also used for the fifty plus Vickers VC10 jet ailiners, which was a marginal British jet airliner of the 1960s, only used by British airlines and a few ex-colonies. The Australian airline Quantas in the later 1950s, after it was clear they wanted the Boeing 707, were possible buyers, but in the end the deal fell through. The majority of American airliners waited for versions of the 707 and the DC-8 to be available with the Pratt and Whitney JT3D turbofan from 1961.
It is important to point out that the just like the American J-57, the Conway was designed in part for military applications, in particular it was planned to be used for a large jet powered British military transport aircraft (which was scrapped by the mid 1950s), and it did eventually power a small number of British Victor atomic bombers by the early 1960s. So in this sense Geels is correct: military technological demand did help subsidise the development of the key turbofan technology. By the way, this does not imply military research spending is vital for technological revolutions to occur but rather state or public spending and direction seems vital-it does not have to be directed in a military direction!
Therefore the Conway was technically influential at both niche and regime level. It proved by the mid 1950s that gas guzzling turbojets designed from scary atomic bombers did not have to be the only way to move people around in the sky. American engine manufacturers took notice and accordingly began making turbofans and tweaked conversions of turbojets. By the mid 1960s the turbofan was the most common ‘jet engine’ not the turbojet.
For those of you who are not familiar with the difference between a turbojet and a turbofan engine what you need to understand is that they are BOTH jet engines…or turbine engines….as engineers prefer to call them. However, the difference lies in their internal workings. The gas turbine is a rotary engine-which basically works by extracting energy from a flow of gas (or perhaps water)-at it simplest think of a shaft that can rotate and some kind of blades attached that can spin the shaft as water or super heated gases shoot by…the faster those fluids or liquids are, then the faster the shaft can turn and do work….by the 1920s a few clever types had figured out that one could have a turbine type engine to provide aircraft power…Maxime Guillaume appears to be the first to at least file a patent for this idea.
The most obvious way of doing this was by connecting the rotating shaft to a few gears and cogs and then a propellor…..and hey presto you have the turboprop engine….(although this was not what Guillaume had in mind, his patent was for a type of primitive turbojet). Probably the person most associated with developing the turboprop was the British aeronautical engineer AA Griffith, although he also was vital in developing the Conway turbofan engine having joined Rolls Royce as the second world war broke out.This reference to turboprops might confuse many people at this stage because they think that turboprop engines are propellor engines and are therefore totally different from jet engines…in fact turboprops are like jets insofar as they are a species of turbine engine, but the rotating shaft is connected to an external turboprop!
Confused? Read on!
By the 1930s a pair of clever fellows working quite separately (Frank Whittle and Hans van Ohain to be exact) were among an elite of innovators who realised if one dispensed with the propellor alltogether…..one could in theory just propel the aircraft on the exhaust gases alone…..the trick was to stick a compressor in front of the gas turbine engine (this forced air towards the gas turbine at a much faster rate). That fast flowing air was then mixed with fuel (typically highly flammable Paraffin or called Kerosene in American) in a tiny combustion chamber. Now the velocity and potential energy of the gas produced was enormous. And the hot jet of exhaust that flew out of that provided a motive force in itself, espeically if it was chanelled by a narrow apperature-the nozzle or propelling nozzle which acts a bit like a funnel.
The problem with the turbojet engine is that it has to use quite a bit of fuel and combustion and quite a bit of devillish tricky messing around with compressors and nozzles to get a fast enough exhaust jet coming out……and that means higher fuel consumption. In the 1950s they were not worried so much about the cost of that….but they were worried about fuel consumption…..early turbojets had often quite poor fuel consumption…..on the plus side the actual number of moving mechanical parts in a well designed turbojet is smaller than other engine options so that mechanical reliability was often better…they were simpler engines in many ways.
Turbofans were a design half-way house between the purity of the turbojet, and the mechanical messing around of the turboprop……instead of propelling the aircraft solely by the exhuast of the turbojet…the idea of the turbofan was to have the thrust coming from an internal fan positioned well before the jet nozzle. In fact this ‘fan’ was in reality for all intents and purposes an internal mini-propellor!
So the turbofan splits the incoming air: part goes as normal through a series of compressors which squeezes air fast into a combustion chamber which then shoots that through a standard nozzle arrangement giving an exhaust jet which moves the aircraft forward. However, another part of the air stream is bypassed around some of the compressors and the combustion chamber, and basically propels the aircraft forward much like a propellor does…although this bypassed air is usually funneled through a combined nozzle….so that the two propulsive streams combine efficiently after quite a bit of jiggerry pokery…..and the result is greater efficiency in that less fuel needs to be burned and there is less noise…..the downside is that you get a slower engine, but in fact civilian aircraft do not need or want very high speed…just enough to climb fast, and then be able to climb over bad weather if they need to.
High bypass turbofans have a lot, or most, of their air bypassing the engine core, whereas low bypass engines have much more of their air being funnelled into the engine core like a turbojet. That means that a high bypass engine is a bit more like a turboprop in performance and that means it is slower but uses less fuel. A low bypass turbofan is faster and uses more fuel.
Generally, the interest today is in very high bypass ratio engines-which usually reduce noise and fuel consumption. However, back in the 1950s the goal was to get something that could provide thurst comparable with a turbojet like the J-57, but use less fuel.
This is why the Rolls Royce Conway low bypass Turbofan attracted attention. The Conway had a bypass ratio of 0.3. This means for every 1 kg of air that the engine pushed through the core/nozzle system, another 0.3 was funneled off by the ducted fan at the very front and then redirected back towards the nozzle exhaust section. Modern jet engines have much higher bypass ratios.
The Rolls Royce Trent 900 which powers the giant Airbus A380 ‘superjumbo’…has a bypass ratio of 8.7 to 1…..meaning eight times as much air is pushed around the engine core as is pushed through it…..[this engine is currently being examined after a fire incident and a number of other safety checks]
In the end, the story of the Conway is not all that forlorn. It was a technical success and showed the way forward for civil jets-whereas the J57 did not beyond an initial window period of the late 1950s when admittedly it did help to get the big jets airborne and sold. In this regard, the technical niche of turbojets became in evolutionary terms quickly obsolescent. The lesson from that is to emphasise the non-linearity of technological innovation-something which Geels does mention. By this is meant that idea that one technological niche can reinforce a major change for a short period but then be reversed or supplemented by another technical niche. Technological innovation does not proceed in a smooth linear fashion like dominos falling……
The constant between the two technological niches (the American J-57 niche versus the British Conway turbofan niche) was in BOTH cases state led planning, direction and finance, in part for military ends. Without this state ‘push’ neither the Conway nor the J57 would have seen perhaps as much by way of success…or perhaps the airlines would have gone direct to turbofans after a longer time period….or experimented more with turboprops for longer than they did. The fascinating thing is that the better technology, in the sense of more efficient turbofans, were not vital in making a technical success of large jets…..evolutionary success is not about the most efficient but merely what works at a given time. This deepens our understanding of technological revolutions somewhat from Geel’s rather Spartan picture. Moreover it directs our attention to a key actor: the state.
And as a postscript I might add that by the mid 1950s Rolls Royce decided to make a smaller cut down version of the Conway turbofan, called the Spey (and later another variant called the Tay) which were both greater commercial successes powering smaller jet aircraft.
Which only leaves the pressing question why do Rolls Royce name all their aero engines after British rivers?