speeds of the order of 1,500 to 2,000 m. p.h. before Its specific consumption becomes competitive with that of the turbojet.

The major limitation of the engine in question is that when it is at rest, there is no ram effect * and hence no thrust. To obtain the necessary pressure ratiothe ramjet needs external assistance to reach the designed operating speed and become self-sustaining **. The ramjet produces thrust only when some other propulsion system has brought it up to the necessary speed.

For these reasons it was used mainly in guided missiles and the necessary acceleration thrust was provided by solid booster" rockets which could be jettisoned" in flight without undue difficulty. Because of its inherent" simplicity the ramjet found application as a rotor tip "-drive unit*** for small helicopters, in spite of its high fuel consumption at subsonic air speeds.

The ramjet is supposed to reach its greatest overall" efficiency somewhere in the range of Mach 4 to Mach 10 (hyper-velocity). Unfortunately", there are two factors which tend" to set an upper" limit to the speed at which the ramjet will be at its best. Both limitations are due to high temperature.

The first factor is that entry" air is heated by compression. At a flight speed of 3/4 mile/sec. the rani temperature **♦* is 580° С and the internal surfaces of the engine become heated to a temperature only a little lower than this. At 1 mile/sec. the ram temperature is 1,020° C, and it is evident that further increases in speed will result in increases in ram temperature. But the temperature of the gases leaving the combustion chamber must be appreciably" higher than the ram temperature to produce thrust, while the fuel flows avail able** are too small to be used for effective cooling. Since material strength properties are seriously reduced at high temperature. It follows* that an increase in temperature demands improved materials for the combustion chamber and other parts or direct cooling of these Items " for the engine reliability not to suffer

The second factor is that high ram temperatures of hypersonic flight limit the combustion temperature r i s e and therefore limit available ramjet thrust. Due to dissociation of combustion products a significant* increase in gas temperature can no longer be achieved, at least with chemical fuels currently" in use.

The advances in rocket technology led*" many people to belittle the future of supersonic air-breathing engi-

• ram eftect - скоростной напор ♦* self-sustaining - автономный в полете

»*» rotor tip-drive unit - реактивный двигатель на конце лопасти несущего винта (вертолета)

•**« ram temperature - температура торможения

nes. However, with several "Earth-satellites having been put into orbit, there has been a revival of interest in the potential of ramjet engines.

If hypervelocity flight within the atmosphere is desired, the rocket engine may find serious competition from the air-breathing hypervelocity ramjet. It appears that for flight within the Earths atmosphere a ramjet-powered vehicle will have a tremendous advantage in weight, range or payload over a rocket-powered vehicle. For instance, the ramjet as compared with a rocket engine will need a smaller supply of vehicle transported propellants* to produce a given thrust for a given period of time. This savings of propellant is of great importance.

So* there appears a promising" future for hypervelocity ramjets. Some scientists suppose that ramjets are likely to have a considerable impact s* on air transport in coming years. Though much research and development work is still needed, particularly in such areas as hypersonic inlets, materials and cooling techniques, and real-gas kinetics, Mach 7 to 10 engines are expected" to appear in the near future.

Aerodynamic testing facilities now in use or under development will be adequate for most of the hypersonic inlet work. However, high temperature subsonic and supersonic facilities will be needed to investigate subsonic and supersonic mixing" and combustion under realistic conditions and high temperature hypersonic propulsion test facilities will be needed for full-scale*" testing of engines.

УПРАЖНЕНИЯ

Грамматические упражнения

1. Переведите группы слов, содержащие прилагательные, употребленные в качестве правого определения (§ 89).

Обратите внимание иа то, что прилагательные, не имеющие пояснительных слов, при переводе можно поставить перед существительным.

Образец:

The energy available from fission...

Энергия, получаемая в результате расщепления...

Энергия, которая получается в результате расщепления...

The energy available was used...

Полученная энергия была использована...

Энергия, которая была получена, использовалась...

1. The model available is...

The model available for the test is...

2. The amount of radiation present influences...

The amount of radiation present in the atmosphere presents...

4» 09

3. Any changes necessary must be made...

4. The highest speed possible is obtained...

5. The simplest form of engine imaginable is a rocket...

6. The molecules free to vibrate are...

7. Layers close to the earth are influenced by...

8. Components common to most turbines are made...

2.. Переведите группы слов, содержащие в качестве правого определения словосочетания существительного с предлогом (§ 90).

Обратите внимание иа то, что значение этих сочетаний не всегда легко вывести из значения существительного и предлога, поэтому их необходимо запомнить. Примените способы перевода, приведенные в образце.

Образец:

The model under construction.

Модель, которая разрабатывается. Разрабатываемая модель.

1. The method in use preceeded...

2. The type of missile under consideration gained...

3. The program under development was suggested...

4. The aircraft now In service were constructed...

5. The types of power plant in existence satisfy...

6. Any speed indicator now in operation possesses...

3. Переведите предложения, обращая внимание иа перевод слов, выполняющих функцию правого определения (§ 89, 90).

1. The scales in common use to-day are the Fahrenheit, Kelvin and Centigrade.

2. Very little has been published about guided weapons in production or under development.

3. The voltage of a generator in operation tends to change when the load changes.

4. The object of mathematics is to discover the equations which express the mathematical laws of the phenomena under consideration.

5. The model in question is a checked mathematical description of a complex system.

6. Beta radiation was originally assumed to be the emissions of "beta" rays, but later investigation showed that the particles in question were electrons.

7. We are aware that the same general mathematical treatment is applicable, whether the material in question consists of a single pure radioisotope or of a complex mixture of such isotopes.

8. The material for the report has been derived from recent sources available.

9. Most laboratories have small machines of various kinds available for demonstration purposes.

10. The atomic number tells the number of protons present.