NOTES ON THE WAR

Evening Post, Volume CXXXVII, Issue 17, 21 January 1944, Page 4

NOTES ON THE WAR

POWER FOR PLANES

GAS TURBINE PLANT

The jet-propelled aeroplane of Group Captain Frank Whittle has not yet appeared in action, but the publicity given to the invention from time to time has aroused the greatest interest even outside the engineering world. There is not much which has appeared in print to give any real indication of the nature of Whittle's solution of a problem which has engrossed engineers for fifty years, indeed, ever since Parsons introduced his first successful steam turbine. The Whittle machine, whatever its secret, has been hailed generally as a great revolutionary development, comparable indeed to the steam turbine, the gas engine, and the various other forms of internal combustion engine. The wellknown expert G. Geoffrey Smith, whose articles in "Flight" in 1941-42 attracted much attention and who has been recognised as a leading authority on the gas turbine and jet propulsion, has declared that "we are on the threshold of a new era of power generation by means of rotary units." The following details are from the latest information to hand on this fascinating topic of the day. Jet Propulsion. "Jet propulsion is defined as a thrust created by a stream of air projected to the rear of the plane at a speed approaching the speed of sound. That force is given off by a rotary compressor and a gas turbine. Details of aircraft now under production are naturally not released, but some indication is given by the patent taken out by the British Fairey Aviation Company recently for the jet-propul-sion system. The description of the patent stages: 'In its simplest form, the Fairey device consists of a chamber divided into two main compartments. One of these is in the form of an air intake, the other is an explosion chamber. The device is installed in the aircraft with the air intake facing for-1 ward, and the orifice of the explosion chamber pointing to the rear. When the aircraft is in flight, air pressure is built up in the intake chamber, while a valve located between the latter and the explosion chamber remains closed. When this valve is opened to allow the compressed air to enter the explosion chamber, fuel is injected through the nozzle, the valve is closed, and the explosive mixture fired. The discharge which follows produces a propulsive effect.' , Underlying Principle. "There are various systems, but the underlying principle is the same in all. Expressed very simply, air is taken in and compressed, then heated by being driven into a combustion chamber where paraffin or heavy oil, or even powdered coal, is burning. Thus there are two elements of foree —the one compressed air trying to regain its natural" pressure; the other the expansion caused by burning. Together their power is enormous. The compressed gas mixture moving fast towards the only exit or exits is ready to pirst out with almost force. That is the power -jvhich i presses on the air behind the,,-aero-plane and pushes it forward (like all great technical advances jet-propulsion represents a fundamental simplification of technique enabling greater energy to be applied more economically and hence with greater effect). So instead of an engine driving airscrews which create a slipstream which in turn propels the aeroplane, the engine discharge directly produces the propulsive effect. It may be compared with driving a car on top or direct gear as against bottom indirect gear. The present type of aeroplane is believed by many experts to be nearing the limit of speed potentialities since control tends to be lost as the speed of sound is approached. The jet-propelled aircraft is not subject to these limitations. Higher Efficiency. "The Swiss expert, Stemmer, points out that the jet-propulsion engine is far more efficient than the normal internal combustion engine. The loss of heat due to the walls of the combustion chamber, to frictional losses, to exhaust losses through incomplete combustion, and other smaller percentage ] losses of power total between 65 per cent, and 70 per cent., so that the normal efficiency factor of the internal combustion engine is only 30 per cent, to 35 per cent. The jet-propulsion engine, however, is subject to far lower losses of energy, and the efficiency factor is estimated at about 80 per cent. —2£ times higher than that of the internal combustion, engine. Stemmer also calculates that the ceiling of jetpropelled aircraft will be incomparably higher than that of present types. It will also be far more economical in fuel since the engine can be shut off for a great part of the flight. Moreover G. Geoffrey Smith states that jetpropulsion engines require less vola-. tile fuel—paraffin, Diesel oils, and tar oils can be used instead of the expensive high-octane spirit now-used in aeroplanes. By the suitable'proportioning of the components, the main com : pressor system could also supply air to warm and change the pressure in the cabin and prevent icing. The absence of airscrew enables the aircraft to be of low build. It may be possible to dispense with heavy and complicated undercarriages and retracting gears. The cost of man-hours in production and the weight are materially reduced. There is better locomotion, for the pilot can range with an unrestricted field of vision." To critically-minded people with some knowledge oft the subject it will be apparent that the foregoing information from overseas gives away no secrets and does not explain at all precisely how and where Group Captain Whittle has succeeded where so many predecessors and contemporaries have failed, especially in the initial efficient compression of intaken air—the crux of the whole problem. That achieved, it is not difficult to imagine how the rest may follow and success in this respect should lead to far-reach-ing developments. For the moment, however, and until more details are released there will linger, in many minds, a certain degree of scepticism.