14. The Three Factors
Let us now consider the three factors identified above as they relate to the Boeing 747 & Concorde (reference: 3).
14.1 The Aerodynamic Efficiency (reference 3.1).
14.1.1 Boeing 747.
The Boeing Aircraft was produced from a stable which had by then a string of commercial successes covering a range of different world markets. Not unreasonably, therefore, we can conclude that their knowledge of aerodynamics was and is of an extremely high order and, that such knowledge was invested in the aerodynamic design of, the Boeing 747 hence, justifying the above award of an Excellence Rating of 1.
14.1.2 Concorde.
Consider, although at that time unable to match the commercial success of Boeing in the long range commercial Jet Powered Aircraft Market nonetheless, the combined experience of French & British engineers in Aircraft design amounted to a very formidable talent in both subsonic and supersonic flight. We may conclude therefore, that their combined aerodynamic expertise was and is even now of an extremely high order. It is true that Concorde was required to operate commercially at supersonic speeds, however, we can, with sound reason, conclude that the aerodynamic performance of Concorde at its supersonic cruise speed is at least on a par with that of the Boeing Aircraft at, it's cruise condition and, award it, also, an aerodynamic excellence rating of 1.
14.2 The Propulsion System (reference 3.2).
The essential difference between the installed Jet Engines of the Boeing 747 and Concorde Aircraft is that the Boeing 747 uses Fan engines and the Concorde, a Pure Jet type of engine.
14.2.1 Boeing 747.
In the Boeing case the engine employs a bypass ratio of something like 6:1 which means that six sevenths of the total air mass entering the Aircraft is caused to bypass the core engine. This means that of the total air mass entering the Aircraft only 14% is required to pass through the core engine's compressor. The core engine utilised in this way makes it possible to deliver a much larger Air Mass at a Resulting Velocity more closely matching that of its subsonic cruise speed, therefore accomplishing a much better Propulsive Efficiency.
14.2.2 Concorde.
On the other hand Concorde uses a Pure Jet type of engine in which the entire Air Mass Flow entering the Aircraft is required to pass through the engine's compressor, combustion, turbine, jet pipe and Aircraft propelling nozzle.
14.3 The Motion/Propulsive Efficiency (reference 3.3).
In each Aircraft the engines were specifically designed to meet the particular demand conditions required by the Aircraft.
The Boeing 747 is of a far greater mass than Concorde but required to operate at a subsonic cruise speed, whereas Concorde's cruise speed is supersonic. Consequently, the Boeing Aircraft requires a proportionately much greater thrust power on take off than that required to meet Concorde's requirements.
We can conclude that each of these different type of Jet Engine represented the ultimate in terms of thermal and mechanical efficiency conceivably attainable. Therefore, comparatively, the performance of their respective compressors, combustion, turbine and propelling systems were all very much of the same efficiency. Remember, that the efficiencies of all of these systems have been for over two decades of an extremely high order; indeed, their respective efficiencies have long passed that point where any further improvement can only be achieved at a cost out of all proportion to their actual worth. Similarly, the mechanical efficiency Fan/Compressor of the Boeing engine is no more than that of the general mechanical efficiencies attained throughout any modern type of Jet Engine.
It should be remembered, a unit of thrust, no matter from which type of engine it is delivered to the Aircraft, possesses exactly the same thrust value.
Not unreasonably, we therefore can conclude, that whatever the reason for the difference in the payload capability between the Boeing 747and Concorde it is not attributable to either the required thrust power, thermal or mechanical efficiencies of their respective engines at any demand condition nor to the aerodynamic efficiency of their respective airframes.
The aerodynamic efficiency of their respective airframes, thermal and mechanical efficiencies of there respective jet engines are all very much the same the only major differences between these two Aircraft being the difference in their respective cruise speeds and, also, the particular manner by which the thrust force of each Aircraft is both delivered and utilised.
The measure of the success of the marriage between the engine and Airframe, all other things being reasonably equal, is the Resulting Propulsive Efficiency of the Aircraft. In the case of the Jet Powered Aircraft a reasonable state of Propulsive Efficiency has only ever been achieved at Cruise conditions.
According to the Industry the single most important factor governing the Propulsive Efficiency of any modern Jet Powered Aircraft is determined by the difference between the Aircraft/engine's final jet velocity relative to that of the Aircraft's Velocity, at, its cruise condition. But, these engines were specifically designed to meet these conditions, in the Boeing Case, a jet engine was required which would deliver the required thrust at Cruise condition at a velocity/rate which, also, closely matched the Aircraft's speed/velocity at that condition. Therefore, the Boeing 747 required an engine capable of delivering very considerable thrust power at take off which could only be economically achieved by employing the much greater air mass flow capability of a fan jet type of engine. By comparison, Concorde's Pure Jet engines had to be capable of delivering the cruise thrust at a Velocity that more closely matched the Aircraft's supersonic Velocity.
The Aircraft Industry would have the Reader believe that the Propulsive Efficiency of Concorde flying at its supersonic cruise condition is on a par with that of the Boeing 747 at, its cruise condition. This endorses the claim, made earlier in this paper that the aerodynamic efficiencies of each of these Aircraft are on a par one with the other. If the final propelling nozzle Velocity of the Aircraft/engine matches that of the cruise Velocity of the Aircraft then, according to convention, the Aircraft's Propulsive Efficiency could be claimed to be 100%. Not unreasonably therefore, Concorde required an engine capable of delivering its required cruise thrust at supersonic velocity which is why the pure jet engine with its much higher final jet velocity (compared with that of the Fan jet type of engine delivering the same thrust) was chosen. Only in Concorde, employing a pure jet engine where the final jet velocity is supersonic, could any comparative value of Propulsive Efficiency be achieved. It was the notoriously poor Propulsive Efficiency of the pure jet engine when required to operate at subsonic speeds that resulted in the creation first of the bypass jet and later, the fan concept of jet engine. These later jet engines are capable of delivering a greater mass flow than the pure jet type of engine for the same thrust. Consequently, closer matching of the engine's final jet Velocity with the cruise Velocities of subsonic Aircraft could be achieved employing the bypass and fan concepts of jet engine. Hence the justification and reason for the adoption of these types of engine resulting in a much improved Propulsive Efficiency of all commercial Aircraft so equipped, thereby, superseding the roll and use of the pure jet type of engine in almost all commercial Aircraft flying today.
The trouble was and remains, regardless of all its undoubted technological brilliance this vast Industry is still having to virtually design and tailor the matching of every jet engine type with every different Aircraft type and, even then, is only capable of producing a Motion Vehicle that is capable of achieving a truly economic performance over an extremely narrow range of operational conditions, namely, at its cruise condition. Why?
Although the Concorde and Boeing engines in this illustration are totally different types, their respective Propulsive Efficiencies, according to the Industry's understanding and criteria in judging such matters, are on a par with each other. Similarly, the aerodynamic efficiency of their respective airframes are pretty much the same as each other, the thermal and mechanical efficiencies of their engines are all at peak efficiencies. By this we mean that whatever difference there may be, they are not sufficient to explain the comparatively poor payload performance of Concorde. The outstanding question still remains, namely, if the efficiencies of all the physical systems comprising each of these respective Aircraft are all on a par with each other, and the Motion Efficiency of each Aircraft is similar, to what do we attribute the very poor payload capability of Concorde compared to the Boeing 747? It is not the technology invested in either of these Aircraft, nor their respective aerodynamic efficiencies, nor the fact that one operates supersonically and the other subsonically. If none of the foregoing is the cause, what is? There can only be one answer. The answer is the degree of penalty incurred by the differences in the manner in which the thrust is delivered and utilised by each Aircraft. This, in turn, is determined by the simple fact that although Jet Powered Aircraft is primarily a Motion Vehicle that is caused to fly, it does not possess a closed fully integrated, Motion System Cycle. It comprises a Motion Vehicle propelled and caused to fly in REACTION to the ACTION upon it by two entirely differently acting Air Mass Motion Systems which are in effect forced to act as one, "Open Ended", Motion System. By "Open Ended" we mean that there is no motion gearing between the rate of Work done by the Aircraft (engine) in the ACTION half of it's Motion System, Air Mass Motion System No.1, upon the Atmosphere through which it is passing and, the rate of Work done in the REACTION half of the same Motion System by Air Mass Motion System No.2 (the atmosphere) upon the Aircraft. Consequently, it is the specific differences in the manner that the thrust is delivered to and, utilised by the respective Aircraft that is the fundamental cause of the difference in payload performance per unit of thrust power employed. If this is true then the evidence of the penalty must be there for all to see, the question of course is where will show? The answer is, in the comparative difference between the Specific Thrust of the Aircraft when each is operating at it's ideal Cruise condition i.e., the positive thrust at the disposal of the Aircraft per unit of Air Mass Flow through it's engines.
As things are, the improvements achieved in Propulsive Efficiency over the past four decades only improved the Propulsive Efficiency of the ACTION half of the Aircraft's Motion System. This was achieved by narrowing the gap between the final Jet Velocity delivered in the ACTION half of the Aircraft's Motion System comprising Air Mass Motion System No.1 and, the Resultant Aircraft Velocity at its Cruise condition. However, this involves only half of the Aircraft's Motion System.
It is interesting to consider how these levels of claimed Propulsive Efficiency were achieved in each instance. In the Boeing case, this was achieved by ensuring that the Final Jet Velocity of the Aircraft/engine more closely matched the subsonic Cruise speed at which it was designed to operate than would have been possible using a pure jet delivering the same thrust. In the Concorde case, the opposite was true; the Aircraft was designed to fly at supersonic speed, its Cruise Velocity more closely matching the supersonic Final Jet Velocity delivered by its pure jet engines than would have been possible to achieve using a bypass or fan type of engine delivering the same thrust. Here then, we have two entirely different approaches to achieving compatible Propulsive Efficiencies.
It should be remembered that the quantity of Air Mass delivered to Aircraft's intake and the Jet Engine's compressor occurs in the REACTION half of it's Motion System, Air Mass Motion System No.2. In the case of the Boeing this is appreciably more than that of Concorde. Logically, in physical determination, any gain in the Thrust Effectiveness of the ACTION half of the Aircraft's Motion System No.1 as the Aircraft acts upon the Air Mass (atmosphere) Air Mass Motion System No.2 through which it is passing will always be greater than the propulsive loss incurred in the REACTION half of the Aircraft's Motion System No.2 where in its reward flowing REACTION to the Aircraft's forward motion does work upon the Aircraft and, so it is, in this instance. It is here, in the REACTION half of the Aircraft's Motion System formed by Air Mass Motion System No.2 (the atmosphere) where the difference in their respective payload capabilities per unit of fuel per unit of thrust in time was and is determined by the difference in their Specific Thrust performance hence, the difference in their respective payload capabilities per unit of fuel consumed per unit of time.
The total inlet area to the Boeing Aircraft/engine is more than twice that of the Concorde engine. When both Aircraft are at the cruise condition, the inlet Velocity of the subsonic Boeing's engine is less than half the inlet Velocity of the supersonic Concorde's engine. All other things being relatively equal, as argued in the foregoing, the deciding factor determining the respective payload capabilities per unit of thrust delivered, is the ratio of Thrust Penalty incurred at the Inlet to the Aircraft/engine in the REACTION half (Air Mass Motion System No.2) of the Aircraft's Motion System per unit pound of the GROSS THRUST delivered to the Aircraft in the ACTION half of the same Motion System (Air Mass Motion System No.1).
A simple calculation reveals that at the cruise condition the SPECIFIC THRUSTpenalty in the case is Concorde is considerably higher than that of the Boeing Aircraft. This is because of the must greater negative thrust impact/penalty that the squared supersonic Velocity of the Air Mass entering Concorde has upon the inlet to jet engine per unit of frontal area compared with that upon the inlet to the Boeing Aircraft engines at it's Cruise condition per unit area (Reference the Introduction for the reason). As a direct consequence, the positive thrust at the disposal of Concorde per unit of Air Mass through the Aircraft via it's engines is so very much poorer than that in the Boeing case even although the frontal area of the inlets to the Aircraft is more than double that of Concorde itself. This is because the Velocity component in the basic the Thrust Equation of Mass X Velocity becomes the more important factor in the resultant Thrust of a system because the Kinetic Energy possessed by the system as shown in their the relationship between Mass and Velocity as defined in it's equation, KE = Half the Mass Times the Velocity Squared.
It is here that the economic and therefore the commercial viability of Concorde was rendered a non starter before it left the drawing board, quite regardless of it's otherwise undoubted technological brilliance. It was here that the inevitably poor payload capability of Concorde per unit of thrust power delivered was decided and, the economic/commercial battle lost.
The practice of using the relationship between the final Aircraft/engine Velocity delivered by the ACTION half of the Aircraft's Motion System (Air Mass Motion System No.1) on the other hand, and the Resultant Aircraft Velocity at the same demand condition on the other, as being truly representative of the Propulsion Efficiency of the Aircraft reveals the fundamental misconception as to what the true Propulsive Efficiency of the Aircraft actually is.
A Jet Powered Aircraft is a Motion Vehicle. Therefore, its Propulsive Efficiency must be a direct measure of the Velocity of Air Mass passing throughout the ACTION half of its Motion System(Air Mass Motion System No.1) compared to the velocity of the Air Mass comprising the atmosphere (Air Mass Motion System No.2) forming the REACTION half of the Aircraft's Motion System then and only then, can it's, Propulsive Efficiency be claimed to be 100%.
A more realistic, representative Propulsion Efficiency equation should comprise an integrated Velocity equation taking into account the different Velocities encountered throughout the Aircraft's entire Motion System; this, the existing equation fails to do.
The resulting reduction of the effect of the GROSS THRUST delivered to a NET THRUST value is largely due to the fact that a Jet Powered Aircraft in motion/flight does not possess a complete, fully Motion integrated Air Mass Motion System Cycle. This diminution in effectiveness of the GROSS THRUST has nothing whatsoever to do with any law of physics or a price to be paid simply because the Aircraft is in motion. This is entirely due to the particular manner in which Newton's 3rd Law of Motion itself is actually utilised by all Jet Powered Aircraft.
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