Prior to The War engineers on both sides of the English Channel were at work on a new type of engine. Using a turbine to draw air in and a jet of hot exhast gas to turn the tubine and push on the way out the turbojet (see the image below) rendered previous propeller aircraft obsolete by the end of The War.
Photo from Propulsion - Intermediate.
Within ten years of VE and VJ day turbojet aircraft like the Lockheed F-104 Starfighter (below) could fly almost twice the speed of sound.
(Photo from Wikipedia.)
Despite the tremendous improvements from the turbine driven Turbojet there were limitations. For one thing, turbojets are gas guzzlers. Newer technologies, like the Turbofan engine provide comparable, if not better thrust, while consuming fuel at a far more relaxed pace. (In fact very likely your holiday jet is driven by a Turbofan.) But fundamentally a Turbofan is in many respects little different from a traditional turbojet, both engines have a turbine and that turbine spins at a speed related to the forward speed of the aircraft. Now imagine, you are a turbine blade, I know its not the sort of position one imagines themselves in all that often. You are spinning round a shaft (turbine) thousands of times a minute, super highly compressed air is blasting past under such pressure that kerosene is igniting spontaneously. Now lets go faster. At some point the turbine blade will break, we just cannot make them strong enough and durable enough. That turbine breaking point corresponds very roughly to an aircraft forward speed of three and one half times the speed of sound.
Well jets are fast, until you spend 12 or 14 hours over the Pacific ocean in economy class, if you are more than about 4 feet tall, those 12 or 14 hours feel like eternity. There has to be a way to make airplanes go faster.
As it turns out long before Frank Whittle and Hans Von Ohain had dreamed up the jet engine Rene Lorin of France had already patented a faster technology.
The limit to the speed of a jet engine propelled aircraft is the turbine, so the obvious solution? Remove the turbine. Imgine an aircraft racing forward at something near, or faster than, the speed of sound. Now as the aircraft moves forward it displaces huge amounts of air, but some of that displaced air is directed down a tube. As the air rushes down the tube some kerosene or hydgrogen is injected into the tube, then suddenly the tube constricts. The temperature will shoot up causing the kerosene or hydrogen to ignite, pushing the temperature way up. The air cannot expand, there is no room, so the pressure builds, then suddenly the tube ends and the super dense, super hot air expands rapidly, creating thrust. Such an engine, or Ram Jet can accelerate an airplane to something between three and five times the speed of sound. Which sounds great until you realise you are still going to spend something like six or seven hours flying to New Zealand to tell Peter Jackson that Lord of the Rings needs a Tom Bombadil.
(Photo from Wikipedia.)
The problem with Ram Jets is that as the aircraft goes faster, the air compresses to higher pressures and temperatures which ultimately make the heat from the burning fuel a negligable factor. Put simply, as the heat from compression builds, the heat kills the engine's effiency to the point where speed will effectively shut the engine down.
What is required is an engine that will not compress air after the addition of fuel.
(Image from: Wikipedia.)
Such an engine was first conceived in the 1950s but only in recent years have the first Supersonic Combustion RAM or SCRAM Jet seen light of day.
The SCRAM Jet is significant becuase it makes possible a dream. A dream of affordable Earth Orbit. In my next posting I hope to describe what I believe space flight will look like in about 30 years, which when you think about, is almost the age of the Space Shuttle.
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