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THE effect of the propulsive efficiency is analysed for all speed regions and methods for obtaining optimum propulsive efficiency for any speed and environmental conditions are investigated for different type vehicles. Also, the importance of the propulsive efficiency is compared to other factors such as weight of power plant, specific fuel consumption, specific power ratio, specific thrust ratio, etc. Finally, on the basis of considering all power plant factors, it is shown how to achieve optimum propulsion for any vehicle at required operating conditions.

A review of some of the progress made in lift jet installations is presented in this paper. At the heart of it all is the low cost lightweight RB162 second generation lift jet which is simple and makes extensive use of glass reinforced plastics. Examples of plastic components are shown. The higher thrust/weight and thrust/volume ratio of a third generation lift jet are revealed. The weight of installed features is of comparable importance to the weight of the basic engine. Installed weight has been reduced over three lift jet generations, more than keeping pace with the improvements in basic engine thrust/weight ratio. Weight breakdowns are given for the V.T.O.L. equipment in a fighter‐type aircraft representative of all three generations. Progress on lift intake and exhaust jet deflectors is shown with reference to specific examples. Ground erosion is briefly discussed and shown to be greatly reduced by multiple nozzles and the rolling take‐off technique. Progress being made on some of the problems associated with installing eight lift jets in a V.T.O.L. strike aircraft is briefly discussed with reference to maintenance and instrumentation.

ADVANCES in engine technology are evaluated herein, and, for the purposes of improving future noise evaluation of commercial jet aircraft, adjustments to current evaluation techniques are suggested.

The experience gained since 1959 at MBB, Military Aircraft Division, in the development and flight testing of V/STOL combat aircraft having the capability to reach Mach 2 and to take off with after‐burning temperatures is described. The German project VJ 101 C and the US/FRG project AVS as well as the joint US/FRG V/STOL Technology Programme conducted during the years 1967 through 1970 serve as examples. The paper consists of two main sections:

IN reviewing the progress and promise of turbine‐engined transport aircraft, it is intended to cover pure jet, propeller turbine and compound turbine engines impartially. If the emphasis tends to fall on problems covering the installation and control of propeller turbines, this is because the author has been most closely connected with this type of engine in the past few years.

IT is well known that aircraft designers and operators are never satisfied for very long with the power available from the engines installed in their aeroplanes. They arc always demanding overload power or some form of boosting for special conditions such as take‐off on elevated or tropical airfields or for interceptor aircraft during climbs. In the case of turbo‐jet engines, one way of achieving this is by ‘reheating’ or, perhaps less ambiguously, ‘after‐burning’. There have been many references to this form of boosting which would lead one to assume that it is a very recent idea; in fact, a Meteor aircraft was flying with an experimental reheat power boosting system as long ago as 1944. While the system suffered from a number of troubles, it is of more than historical interest and some account of its performance may be useful in assessing the potential value of reheat.

The bulk of jet engine noise developed at high powers arises from the turbulent mixing of the jet efflux in the surrounding air, as judged from model experiments, and has a continuous spectrum with a single flat maximum. The high frequency sound arises from fairly close to the orifice, and reaches its maximum intensity at fairly large acute angles to the jet direction. Lower frequency noise arises from lower down stream and its maxima make smaller acute angles with the jet axis. The possible origins are briefly discussed in view of Lighthill's theory and refraction effects. The most intensesound has a wave‐length of the order of three or four exit diameters, and originates between five and ten diameters from the orifice. A semi‐empirical rule of noise energy depending on the jet velocity to the eighth power and the jet diameter squared gives a rough estimate of the noise level for both cold and heated jets. Further noise from heated or supersonic jets may occur through eddies travelling at supersonic speed and so producing small Shockwaves. Model experiments have shown that interaction between shock‐wave configurations in choked jets and passing eddy trains generates sound and this initiates further eddies at the orifice. The directional properties of this sound are quite distinctive, the maximum being in the upstream direction. Methods of reducing jet noise are briefly discussed.

SERVICING, at specified intervals, is essential to the safe and reliable running of all mechanical devices. This is, perhaps, even more important in the case of the jet engine than with other mechanisms. With this object in view, the following paragraphs outline the servicing requirements of the Derwent jet propulsion power unit.

SINCE man first aspired to fly the desire to take‐off and land vertically and to hover in flight has always presented a challenge to the engineer. To date only the rotary wing aircraft has achieved these aims in service but their shortcomings in terms of speed, range and economy have encouraged engineers to search for more elegant ways of achieving vertical flight.

The first gas turbine patent was granted in England to John Barber in 1791, and since then there have been numerous gas turbine inventions. These have been adequately described elsewhere, 1, 2 and I shall concern myself only with the developments which have led directly to recent British achievements.