FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1941
1941 - 2218.PDF
I9O FLIGHT SEPTEMBER 25TH, 1 JET PROPULSION of AIRCRAFT PART III.—The Thermal Jet Principle : Influence Upon Design of Aircraft Generally Further British and Foreign Schemes Reviewed By G. GEOFFREY SMITH TUilS week, in the review ot types of jet propulsionplants of various countries which /'light has collectedover a period of years, the designs of pioneer French and British experimenters, a very recent Swiss design, the Eichelberg, and a further. Whittle scheme are illustrated and described. The two preceding articles have aroused considerable discussion and controversy. Several correspondents, whilst expressing their interest, have intimated that the notion of jet propulsion without an airscrew seems to them very futurist. Others, although intrigued, regard it as one £ of those "new - iangled " ideas in an entirely new field of development with little hope of success. The technical interest of the pro- posed schemes is undoubted, though many confess in- ability to follow clearly the working of the plants, since so many new principles are introduced. With this view some sympathy may be ex- pressed, as the particulars available are, necessarily at present, incompletely detailed. Previous notes have largely dwelt upon the functioning of plants when in motion, and some correspondents appear to have found it difficult to visualise a start. This is rather surprising, particularly in the case of reciprocating plants where the starting-up of one engine by any of the usual methods—electric, compressed air or cartridge—will suc- cessively bring the whole plant into operation. With the turbine plants, starting is admittedly not so obvious. Generally either an electric motor or a small auxiliary air compressor, driven by any means available, will be neces- sary to start the turbine rotor and to raise an initial pressure to support the combustion of fuel. How It Works In an endeavour to make the principle readily under-, standable, let us reduce the "thermal jet" to its essential terms. Again it should be stressed that it must not be regarded as a "rocket" system for one very important reason: in a rocket the necessary oxygen for supporting combustion is contained in the explosive material employed IN this, the third 0/ four articles discussing the possibilities of the propulsion of aircraft by jet impulse reaction, that is without ths aid of the conventional airscrew /engine combination, we review more British and foreign power plants. The important effect upon the design of aircraft generally were jet pro- pulsion to be proved to be efficient is also indicated. Previous articles of this series appeared in "Flight" of August 28th and September 11 th. Thermal jet systems carry fuel only and obtain the neces- sary oxygen from the surrounding atmosphere. All schemes have three common features : means for com pressing air ; means for adding heat to the air by the combustion of a fuel such as paraffin ; means for the expan- sion of the resulting gas-air mixture. Perhaps the simplest illustration is given by the 1908 scheme of the French engineer, Lorin. In this a conven- tional engine exhausts directly through a discharge funnel to produce a propulsive reaction. Here the three features mentioned above are evi- dent. Air is compressed in the cylinder, there is com- bustion of fuel and the effluent expands in the dis- charge funnel. Apart from the energy used in drivir.i; the usual auxiliaries, the engine functions solely to produce the reactive jet. No power is taken off the engine crankshaft. Lorin visualised multi-cylinder units of this type, as shown in perspective, installed in the wings of aircraft. By modern standards this design is only of historical interest. Nevertheless it deserves an honourable mention, as it was the original suggestion to employ a reciprocating engine and use part of the combustion energy to compress the air It will not have escaped notice that by employing jet propulsion, whether the power plant or plants are located in the fuselage or in the wings, a number of important modifications in aircraft design become possible. The absence of an airscrew confers manifold advantages. For instance, the fuselage may be quite low, a welcome im provement as regards servicing and stowage. As the usual airscrew clearances are unnecessary, the undercarriage may be relatively low and of lighter construction. Indeed, it may be questioned if the weight and complication and cost of mechanism to enable the undercarriage to be retracted is justified under such conditions. Should the undercarriage proper be eliminated, whatever speed may be lost due to The 1908 Lorin scheme. A conventional engine is emgloyedsolely to produce a reaction jet. The lower sketch shows a proposed multi-cylinder layout for wing installation. In the Morize "ejector " scheme, fuel and air are supplied toa combustion chamber which discharges into a convergent- divergenb.tube. Air enters the forward end of the tube bysuction, joins the gas stream, and discharges at the rear.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
