IFT PROPULSION IS HERE

Cue (NZERS), Issue 31, 15 September 1945, Page 5

IFT PROPULSION IS HERE

jyACK in the winter of Allied ■D pilots reported to their commanders the presence in the skies over France of German aircraft flying without propellers. The commanders were frankly sceptical, and even went so far as to give it as their considered opinion that the pilots had been seeing things.

But the experts pricked up their ears when, one by one, other pilots began to turn in similar reports. Fuller information was asked for and obtained, and the secret was out. Germany had introduced the jet-propulsion plane into aerial combat.

At the height of the flying bomb assault on Britain last year the world learned of the amazing success of a new jet fighter, the ’’Meteor”, in countering the menace. At that time still on the secret listdetails of its construction and performance have only recently been revealed —the ’’Meteor” was known to be intercepting and shooting down fly-bombs at a rate which, if it did not result in complete mastery over the new form of enemy attack, at least greatly reduced its effectiveness and helped to assure its ultimate defeat. The Germans had been the first to use jet planes in warfare, but the ’’Meteor”, which soon

came to be classed as the finest fighter in the world, and which represented the result of fifteen years of experimentation by the brilliant British aeronautical scientist, Air-Commodore Frank Whittle, proved itself .superior to the German type in every way.

The success 'of the jet-propulsion aircraft has served to* focus attention on the post-war possibilities of the new heat engine, known as. the gas combustion turbine, which gives it its motive power. The spectacle of propellerless planes, burning ordinary kerosene, streaking through the sky at sensational altitudes has given rise to visions of ships, locomotives, electricgenerating stations and perhaps even motor cars being powered on the same principle. The world has gone gas turbine-conscious practically overnight, just as it marvelled at and accepted in turn the steam-engine, the steam turbine and the internal combustion engine. ? h ■ ?

’ But the gas turbine, despite the wonders of its achievement, in the sphere of aerial combat, is still in its infancy, so much so that for the present at least its development has progressed only to the stage where its practical use is limited' to power units between a thousand and, say, ten

EXHAUST

thousand horsepower. It therefore becomes apparent that the employment of • jet-propulsion in the improvement of • the motor car, the power plant of which-is small, is still a distant goal, though admittedly within the bounds of possibility. Nor as yet, with the present peak of ten thousand horsepower, is the gas turbine suitable for adaptation to large electric stations, whose power plants call for a higher level of energy.

To the motor car owner familiar with all the ailments of the average automobile— spark plugs, worn piston rings and defective distributors, valves and radiators—the prospects of some day owning a car powered by a gas turbine are dazzling. The principle of jet-propulsion is simplicity

itself; with little more in the way of intricacies than in an ordinary windmill, it runs by air. The difference is that in the gas turbine the air goes through a process of compression, is heated in a combustion chamber and then expanded through a nozzle. As applied to an aeroplane, jet-propulsion works like a rocket except that, whereas the socket carries enough oxygen to burn its fuel, the jetpropelled plane uses oxygen drawn from the atmosphere. Provided it could be fitted with a big enough fuel and oxygen supply a rocket could travel to the moon; a jet-propelled aeroplane could never go higher than sixty-seven thousand feet, - where the air is too thin to permit of compression.

No one knows yet whether gas turbines could be made small enough to power motor cars effectively; certain it is that in the present stage of development they would be both delicate and costly. The main difficulty, of course, is metallurgical, and, as metallurgy and design improve, it may be found possible to produce a small, light gas turbine suitable for the motor vehicle, and burning almost any kind of fuel.

Like the steam engine, steam turbine and internal combustion engine, the gas turbine converts heat to power by expanding gases. Whereas the first three also depend upon the pressure of the gases to produce power the gas turbine relies mainly on expansion. Having been compressed, the air flows into the combustion chamber, where its oxygen mingles with the hydrocarbons of the fuel to- form a hot flame, and then heated to a temperature of a thousand degrees .Fahrenheit or more, the gas passes through the turbine nozzle, which speeds up its flow in exact y tn same way as the nozzle on a gar en hose increases the force of wa " ' The hotter the "gas the greater i expansion after it leaves the nozz

and the. more energy it delivers in spinning the turbine. It was found in early experimentation that turbines could net be run at high temperatures because the blades could not stand the intense heat, and today the big problem is to develop blades capable not only of resisting high temperatures, but also of resisting them for several years of constant service.

The United 'States is putting ships run by gas turbine units of five thousand horsepower or less into service this year. The advantage of the gas turbine as a marine power unit are easy to see: valuable space is saved by the absence of a boiler, no heavy condenser is needed for distilling feed water, and the weight per horsepower produced is only a fraction of the weight range of existing engines. But there is one main disadvantage. Ships have to be reversed quickly, and there is a difficulty in connecting the gas turbine to the propeller. The use of electric drive to make a gas turbine

ship reversible being too expensive, experimentation has been carried put with hydraulic drive and also with propellers with a reversible pitch.

Already there is a gas turbine locomotive in existence, a 2,200-horse-power engine, with electric drive, having been built in 1939 for use on the Swiss Federal Railways. Other than in aircraft, it is in the field of locomotives that the gas turbine appears to have the greatest immediate prospect of successful and economical employment, combining as it does both the desirable operating characteristics of Diesel electric and the economy of steam. It provides fast acceleration and has no water stops or track pound, and in addition it will be much more compact and cheaper to build than either the steam er Diesel engines.

If the gas turbine has not yet progressed far enough to (fit it for use in big electric power stations, it can certainly fill the bill where small electric plants are required or even for

subsidiary plants to help out laigei units during peak periods. It will probably be a long time before gas turbines can be expected to replace existing steam turbine plants, but'it has to be borne in mind that its waterless operation fits it for power generation in dry country—a factor which is likely to hasten, if anything, its development in this direction.

In the meantime it is in the sphere of aeronautics that the possibilities of the gas turbine are attracting most attention, and those' gain in importance at a time when aircraft designers are thinking in terms of planes that can travel at five hundred miles or more an hour and at altitudes ranging up to forty thousand and even fifty thousand feet. Admittedly, the more rifled air at high altitudes serves to reduce the engine . output of the jet-propelled plane, but this loss. is largely offset by the reduced drag on the wings and fuselage and the consequent burning of less fuel. At 150 miles an hour and forty thousand feet a propeller-driven plane performs twice as well as a jet plane;. at three hundred miles an hour they are about equal; and at 550 miles an hour the jet plane performs twice as well.

American experimenters, working with Whittle’s design as a basis, have produced a jet-propelled plane which has undergone successful trials. Appearing at a distance like a conventional lighter, it moves without vibration, and the cockpit is so motionless that a vibrator had to be installed so that the pilot could shake the instrument panel slightly, and so make Sure that none of his instruments had jammed Because the jet is behind him and issues at nearly the speed of sound the pilot cannot' hear the plane, while the machine is simian j noiseless to .an ;observer on the

ground until it has passed him. The plane needs virtually no warming up, and is started in a few seconds by a mechanism similar to the starter of a motor car.

The P-59, as the American plane is known, was built by the Bell Aircraft Corporation and powered by a modified Whittle engine made by the General Electric Co. of America after the Royal Air Force had made details of

the engine available to the United States Army Air Force. Since its successful trials were- carried out the United States, like Britain, has had both jet—planes and the gas turbines to drive them in full production.

It is now known that the German* had two jet-planes in combat during the final stages of the air war over Europe. One was a twin-engine, & s turbine, jet-propelled pursuit pan , and the other was an egg-s* c d tailless interceptor—the first sue ful rocket plane. These two * < represent the natural' off-s 10,0

German experimentation with rocket and flying bombs, though, of course, the sixty ter . seventy—mile climb claimed for the V-2 rocket is miles higher than air-inhaling jet-engines will be able to attain.

Whether or not Britain’s ’’Meteor’’ would have been used in action in great numbers in the Tar East will not now

be known, but it is in the post-war possibilities of jet-propulsion that interest ’is mainly centred. It is believed that the gas turbine driving a propeller will prove to. be more efficient than existing engines for powering aircraft at lower speeds and altitudes, but for high speeds and high altitudes the jet-propelled machine seems certain to be the plane of tomorrow.