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The engines are Rolls-Royce/SNECMA Olympus 593 Mark 610 turbojets. Turbojets -- not high-bypass fans. High-bypass fans offer good fuel flows in the lower atmosphere but they tucker out at high altitude/high speed. Worse yet, they are heavier than turbojets. Turbojets may seem to be relics of the past but at 2.0 Mach, the turbojet is the right engine. With afterburner, or reheat to use the British term, each of four engines produces 38,050 pounds of thrust on takeoff. In 2.0 Mach cruise, it is another story -- but more about that later.

Powerplant Specifications
Engine Model Olympus 593 Mrk610 turbojet
Engine Manufacturer Rolls-Royce/SNECMA
Number fitted Four
Maximum thrust produced at take off, per engine 38,050 lbs (170 KN) (with afterburner reheat in operation)
Maximum thrust produced during supersonic cruse, per engine 10,000 lbs
Reheat contribution to performance 20% at full thurust during take-off

 

THE ENGINES

From jp le moelt books
Lien vers fuselage
Paie ailes
Tu144
Consommation
Mach
Poids souhaité
Mur du son

A long profiled nose, an elegant fuselage, a pair of artistic wings, a sophisticated interior and a brain of performing neurons would not suffice to make me a veritable supersonic bird. I was still missing an essential element : my engines.

The conception of a jet engine for a supersonic transport was a veritable challenge. It was the primary cause of the failure of the Tupolev 144 project. It is also the principal reason for the freezing of my further development, because of excessive noise and fuel consumption.

The conception of a jet engine is a perpetual compromise between thrust and drag. The lowest possible specific consumption, that is the best possible utilization of the energy contained in the fuel, is obviously obtained by jet engines with a high level of dilution, still called the 'turbofan' (1).



But alas, they are not fit for supersonic flight because of a too great master cross-section (2) . It was therefore imperative to work on a pure jet engine.






The chosen engine makers were Bristol Siddeley and SNECMA. The heart of the jet engine retained was the Olympus, a pretty name which invoked the home of the Greek god Zeus - I saw this as a good omen! Having escaped a 1957 governmental decree which designated Rolls Royce as sole engine maker in Great Britain, the baby of Bristol Siddeley was mounted on the Vulcan bomber. We were surrounded by mythology. Developing the engine to serve both subsonic and supersonic flight was not any easy task !

The blades of the compressor of a jet engine serve, as the name indicates, to compress the air before mixing it with the kerosene in the combustion chamber. They are similar to mini-propellers.

The propellers, until now, have atavistic aversion to supersonic flow. So, to satisfy this limit it was imperative that the air flow speed be reduced to Mach 0.5. What a waste, one might think! Wrong: this reduction in speed results in an appreciable increase in pressure, thus less work for the gay blades. Time for a technical explanation. The relationship between the speed and the pressure of a gas in motion is simple: they vary inversely. So far, no problem, except that… at supersonic speed a decrease in speed (thus an increase in pressure) is obtained by a convergence (narrowing of the passage), while at subsonic speed the same phenomenon is obtained by a divergence (widening of the passage).

You can immediately imagine the problem caused with the air entry of a polyvalent jet engine which must adapt to both subsonic and supersonic speeds. So, my poor Olympus (who had never passed the sound barrier) had to be specially outfitted: variable geometry air intake and exhaust pipes on demand, a divergent and convergent style. The manufacturers of supersonic jet fighters already knew this problem. They had solved it in a rather rustic manner. Their war birds seldom flew more than a few minutes at supersonic speeds and they did not worry about fuel consumption. There were further complications. Because of the position of my engines and the form of my wings, the air intakes are not interchangeable. To each his own problem.


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(1) A great part of the thrust is given by this new kind of propeller with multiple blades.
(2) Width of the largest section, a source of drag.


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The crossing of the transonic barrier requires an increase of thrust. Four Olympus engines, at full throttle and champing at the bit, would puff in vain before the barrier. They would not have enabled me to take off at the weight planned for me. To reduce my weight when my cargo and passenger load amounted to only 6% of my total weight would have been suicidal. Therefore, we had to fire up Olympus: commonly called afterburning or reheat (1), a device used by supersonic fighters for their foray above Mach 1. Afterburning pushes strongly but delivers as a bonus a bucket full of decibels.

Moreover, its efficiency is horrible, lower than the first gasoline engines. Of course, at 25,000 feet the noise caused by the passage above Mach 1 would have bothered only the rare birds flying at that altitude. But used at take off, the noise level would outpass the norms already being imposed. Alas, there was no alternative to this inelegant manner to increase the thrust. The optimists estimated that the human ears would eventually grow accustomed to the noise.

This was the case at least in part. On the other hand, retaining even a small percentage of the heating during the flight - the principal reason for the failure of the Tupolev 144 - was out of the question for us. On the London or Paris to New York flight we would have only a few pounds available for passengers; the rest being confiscated by the fuel. To solve this problem we could not count on the experience of the manufacturers of military aircraft. We had to solve it ourselves.

The design of the air intake for the Olympus and the modular design of the exhaust nozzles solved the problem. Above Mach 1.7, Olympus managed without afterburning. The next generation of supersonics will have to do without: noise level norms make it inevitable.







Poor Olympus! they really gave him a hard time. Every day, a new problem to resolve: a special request of a customer, a new regulation, the desire of my designers to make me perfect, absolute security; all these added to my weight, pound by pound, kilogram by kilogram. And Olympus had the task of pushing them.

This meant: additional thrust, thus additional fuel, thus added weight, which…? An infernal sequence! My original 140 tons were now 170. The moment arrived when Olympus balked. He had done his best. He had been fitted with blades made of titanium - and at what cost! All sorts of appendages were attached in front and to the rear. It was impossible to ask him to furnish another pound of thrust. It was time for me to lose some weight ...

Thanks again Mr Le Moel


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(1) As says the word, the afterburning or reheat consists in injecting kerosene at the jet engine's exhaust , thus making it act like a rocket.
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THRUST AND POST-COMBUSTION


The thrust

This is one of the rare moments when you really feel the acceleration and become conscious of maximum energy output. The thrust of each engine is 17,260 Kg (38,000 lbs).
The strong, steady acceleration brings the aircraft to a takeoff speed of 360 km/h (225 mph) in 30 seconds over an average distance of 1,500 m (4 920 ft). By comparaison, this is the equivalent of sports car accelerating from 0 to 100 km/h (0 to 62 mph) in eight seconds.
Approximately ten secondes after takeoff you will hear the landing gear being secured.



Post-Combustion

The thrust in relation to aircraft weight is 1.66 times greater than that of a B.747. This explains Concorde's relatively short takeoff time.
This powerful thrust comes from a normal jet engine with the addition of a post-combustion system. The aim of post-combustion is to reheat the exhaust gases from the engine to increases thrust by 27%.
Post-combustion is used for takeoff and is cut by the pilot after 30 seconds to lessen noise. At this time you can feel a slight braking sensation.

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The postcombustion.
In order to increase the push of a turbojet could be burned additional fuel in the take off and also in order to cross the transonic zone of Mach 1, point in which the aerodynamic resistance increases in considerable form. Upon appearing the airplanes to reaction, the pilots called to this problem "the barrier of the sound." The Concorde uses the Postcombustión between Mach 0.9 and Mach 1.7. The Postcombustión increases the temperature and the energy of the gas in the nozzle equally and allows to obtain 10 120 percent between a more than push. This supposes practically have the equivalent push to a second motor, but it demands to have a complex nozzle, variable in profile and area. When the Postcombustión is selected the nozzle it opens up more adopting a profile internal first convergent and after divergent order to provide supersonic push. This process is extremely noisy and is only used in supersonic airplanes..