Same here (Mech+Aero in my case, final year project was on turbomachinery). You wouldn’t have been an inmate of CUED for a few years would you? If so I might well have come across you at some point!
Now now boys. Don’t start that sissy name calling.
Once more:
No. You are in the Nevernever Land of physics. You are so far off that it is diffifult to conceive such a horrendous error of logical thinking. I have not seen such an illogical, completely out-of-touch statement in my life (I don’t think).
And again, an engine 10 times the size of another is not 10% less efficient (as you claimed). Way, way, way off my friend.
It is??? You mean if you increase the dimentions of a thing 10X it only increases in mass so little that it’s weight is “pretty much the same”???
Unless the wall were increased too??? Hmmm. A 10x increase in sixe excludes the thickness of the walls somehow?
A jet engine 10 times the size of another would have a casing “pretty much the same” thickness? It would weight “pretty much the same”???
Good Lord man! Go back to junior high school and take a freaking mathematics class!
Riiiighhht… If I’m so very wrong, please explain exactly how cutting a solit metal bar in half crosswise, then splicing the two ends together with a long piece of thin-walled hollow pipe (roughly doubling the overall length in the process) will double the overall weight, if the thin-walled pipe is of aluminium and the bar is of nickel-steel. The situation I’m describing for a statorless diffuser/air gap is exactly analogous in weight terms.
I’d love to hear the physical explanation you have for this…
Oh, and
Now kindly stop just contradicting everyone else and start f***ing arguing.
(you’ll lose anyway,but it’s getting really frustrating arguing with some guy who is such a numpty they think mere contradicition suffices as a rhetorical tool)
No, I was at a proper university - I was a member of OUED :twisted:
Bloody tabs! 
Dude, proved yourself completely void of any reasonable measure of intellect that may be required for debating anything when you said (describing a jet engine 10 times the size of another):
Please don’t debate with me anymore. I have no intention of debating with someone who has so little understanding of the world around them as to say something so inconceivably and inexcusably idiotic. Grade school children have more sence than to think something 10 times the size of something else has about the same mass, even if does not have to be 10 times as thick to withstand the greatly increased forces upon it.
Henceforth, I shall ignore every post you make, regardless of your comments. Debating with someone so utterly incapable of rationalizing something with any more reasonable sensiblility than you have proven yourself to posess is a waste of anyone’s time.
The stupidest thing of it all is that despite your unspeakable blunder, you defend it. :roll:
Bye bye now.
Right then, to war!
So, tell me, where did all the OUED lecturers go as undergraduates? :twisted:
Although I will admit the Oxford Uni Gliding Club are a good bunch - don’t ever tell anyone I said that though!
Bye bye now.[/quote]
Thank God for that. Now, if you’ll kindly do the same to all other forum members and go back under your bridge I’ll be a very happy man!
Maybe we should point out that in general the bigger an engine is the higher its thermodynamic efficiency??? Large marine diesels getting around 50%ish whereas small car engines are around 30%ish IIRC? Or would that confuse him? He clearly doesn’t have a scooby about what we’ve been talking about & wouldn’t know a swirl velocity if it knocked him off his feet :twisted:
We could then talk about carnot cycle efficiency & other boring stuff! 
QUOTE FROM:
http://en.wikipedia.org/wiki/Jet_engine
Has nothing to do with the book,but all is info about jet engine
turbojet (jet) engine is a type of air-breathing internal combustion engine often used on aircraft. The principle of all jet engines is essentially the same; they accelerate a mass (air and combustion products) in one direction and, from Newton’s third law of motion, the engine experiences thrust in the opposite direction.
The engine draws air in at the front and compresses it. The air is combined with fuel, typically ignited by flame in the eddy of a flame holder, and burned as an atomized mixture. The combustion greatly increases the energy of the gases which are then exhausted out of the rear of the engine. The process is similar to a four-stroke cycle, with induction, compression, ignition and exhaust taking place continuously. The engine generates thrust because of the acceleration of the air through it—the equal and opposite force this acceleration produces is thrust.
Jet engines take a relatively small mass of air and accelerate it by a large amount, whereas a propeller takes a large mass of air and accelerates it by a small amount. The high-speed exhaust of a jet engine makes it efficient at high speeds (especially supersonic speeds) and high altitudes. On slower aircraft and those required to fly short stages, a gas turbine-powered propeller engine, commonly known as a turboprop, is more common and much more efficient. Very small aircraft generally use conventional piston engines to drive a propeller but small turboprops are getting smaller as engineering technology improves.
The combustion efficiency of any given jet engine, like any internal combustion engine, is strongly influenced by the ratio of the compressed air’s volume to the exhaust volume. In a turbine engine the compression of the air and the shape of the ducts passing into the ignition chamber prevents backflow from it and thus makes possible the continuous burning and propulsion process.
Modern turbojet engines are modular in concept and design. The central power-producing core, common to all jet engines, is called the gas generator (described above). To it are attached peripheral modules such as propeller reduction gearsets (turboprop/turboshaft), bypass fans, and afterburners. The kind of peripheral fitted is dependent on the aircraft design application.
History
Since the dawn of powered flight, the reciprocating piston engine in its different forms (rotary and static radial, aircooled and liquid-cooled inline) had been the only type of powerplant available to aircraft designers. This was understandable so long as low aircraft performance parameters were considered acceptable, and indeed inevitable. However, by approximately the late 1930s, engineers were beginning to realize that conceptually the piston engine was self-limiting in terms of the maximum performance which could be obtained from it; the limit was essentially one of propeller efficiency, which seemed to peak as blade tips approached supersonic radial velocity. If engine, and thus aircraft, performance was ever to increase beyond such a barrier, a way would have to be found to radically improve the design of the piston engine, or a wholly new type of powerplant would have to be conceived. The latter would prove to be the case. The gas turbine (turbojet, or simply jet) engine, as subsequently developed, would become almost as revolutionary to aviation as the Wright brothers’ first flight.
The gas turbine was not an idea developed in the 1930s, the patent for a stationary turbine was granted to John Barber in England in 1791. The earliest attempts at jet engines were hybrid designs in which an external power source supplied the compression. In this system (called a thermojet by Secondo Campini) the air is first compressed by a fan driven by a conventional piston engine, then it is mixed with fuel and burned for jet thrust. Three known examples of this type of design were the Henri Coanda’s Coanda-1910 aircraft, the much later Campini Caproni CC.2, and the Japanese Tsu-11 engine intended to power Ohka kamikaze planes towards the end of World War II. None were entirely successful and the CC.2 ended up being slower than the same design with a traditional engine and propeller combination.
The key to the useful jet engine was the gas turbine, used to extract energy to drive the compressor from the engine itself. The first gas turbine to successfully run self-sustaining was built in 1903 by Norwegian engineer Aegidius Elling. The first patents for jet propulsion were issued in 1917. Limitations in design and practical engineering and metallurgy prevented such engines reaching manufacture. The main problems were safety, reliability, weight and, especially, sustained operation.
On January 16, 1930 in England Frank Whittle submitted patents for his own design for a full-scale aircraft engine (granted in 1932). In 1935 Hans von Ohain started work on a similar design in Germany, seemingly unaware of Whittle’s work.
Ohain approached Ernst Heinkel, one of the larger aircraft industrialists of the day, who immediately saw the promise of the design. Heinkel had recently purchased the Hirth engine company, and Ohain and his master machinist Max Hahn were set up there as a new division of the Hirth company. They had their first HeS 1 engine running by September 1937. Unlike Whittle’s design, Ohain used hydrogen as fuel, which he credits for the early success. Their subsequent designs culminated in the gasoline fuelled HeS 3 of 1,100 lbf (5 kN), which was fitted to Heinkel’s simple and compact He 178 airframe and flown by Erich Warsitz in the early morning of August 27, 1939 from Marienehe aerodrome, an impressively short time for development. The He 178 was the world’s first jetplane.
In England, Whittle had significant problems in finding funding for research, and the Air Ministry largely ignored it while they concentrated on more pressing issues. Using private funds he was able to get a test engine running in 1937, but this was very large and unsuitable for use in an aircraft. By 1939 work had progressed to the point where the engine was starting to look useful, and Whittle’s Power Jets Ltd. started receiving Air Ministry money. In 1941 a flyable version of the engine called the W.1, capable of 1000 lbf (4 kN) of thrust, was fitted to the Gloster E28/39 airframe, and flew in May 1941.
One problem with both of these early designs, which are called centrifugal-flow engines, was that the compressor works by “throwing” (accelerating) air outward from the central intake to the outer periphery of the engine where the air is then compressed by a divergent duct setup—converting velocity into pressure. The advantage was that such compressor designs were well understood in centrifugal superchargers but this leads to a very large cross section for the engine at rotational speeds that were usable at the time. A disadvantage was that the air flow had to be “bent” to flow rearwards through the combustion section and to the turbine and tailpipe. With improvements to bearings the shaft speed of the engine would increase and the diameter of the centrifugal compressor would reduce greatly. The shortness of this engine is an advantage. The strength of this type of compressor is an advantage over the later axial flow compressors that are still liable to foreign object damage (FOD in aviation parlance).
German Anselm Franz of Junkers’ engine division (Junkers Motoren or Jumo) addressed this problem with the introduction of the axial-flow compressor. Essentially, this is a turbine in reverse. Air coming in the front of the engine is blown to the rear of the engine by a fan stage (convergent ducts), where it is crushed against a set of non-rotating blades called stators (divergent ducts). The process is nowhere near as powerful as the centrifugal compressor, so a number of these pairs of fans and stators are placed in series to get the needed compression. Even with all the added complexity, the resulting engine is much smaller in diameter. Jumo was assigned the next engine number, 4, and the result was the Jumo 004 engine. After many teething troubles, mass production of this engine started in 1944 as a powerplant for the world’s first jet-fighter aircraft, the Messerschmitt Me 262. Because Hitler wanted a new bomber the Me 262 came too late to decisively impact Germany’s position in World War II but it will be remembered as the first use of jet engines in service. After the end of the war the German Me 262 aircraft were extensively studied by the victorious allies and contributed to work on early Soviet and US jet fighters.
British engines also were licensed widely in the US. Their most famous design, the Nene would also power the USSR’s jet aircraft after a technology exchange. American designs wouldn’t come fully into their own until the 1960s.
Types
There are a number of types of jet engines, all of which are based on the principle that air is compressed and used as an oxidizer for the fuel. Some examples are as follows:
Type Description Advantages Disadvantages
Turbojet generic term for simple turbine engine simplicity of design basic design, misses many improvements in efficiency and power
Turbofan power tapped off exhaust used to drive bypass fan quieter due to greater mass flow and lower total exhaust speed, more efficient for a useful range of subsonic airspeeds for same reason greater complexity (multiple shafts), large diameter engine, need to contain heavy blades. More subject to FOD and ice damage.
Ramjet Intake air is compressed entirely by speed of oncoming air and duct shape (divergent) very few moving parts, Mach 0.8 to Mach 5+, efficient at high speed (> Mach 2.0 or so), lightest of all jets (thrust:weight ratio up to 30 at optimum speed) must have a high initial speed to function, inefficient at slow speeds due to poor compression ratio, difficult to arrange shaft power for accessories
Turboprop (Turboshaft similar) jet turbine engine used as powerplant to drive (propeller) shaft high efficiency at lower subsonic airspeeds(300 knots plus), high shaft power to weight limited top speed (aeroplanes), somewhat noisy, complexity of propeller drive, very large yaw (aeroplane) if engine fails
Propfan turboprop engine drives one or more propellers. much like a turbofan but without ductwork higher fuel efficiency, some designs are less noisy than turbofans, could lead to higher-speed commercial aircraft, popular in the 1980s during fuel shortages, development of propfan engines has been very limited, typically more noisy than turbofans, complexity
Pulsejet Air enters a divergent-duct inlet, the front of the combustion area is shut, fuel injected into the air ignites, exhaust vents from other end of engine Very simple design, commonly used on model aircraft noisy, inefficient (low compression ratio), works best at small scale, valves need to be replaced very often
Pulse detonation engine Similar to a pulsejet, but combustion occurs as a detonation instead of a deflagration, may or may not need valves Maximum theoretical engine efficiency Extremely noisy, parts subject to extreme mechanical fatigue, hard to start detonation, not practical for current use
Integral rocket Ramjet Essentially a ramjet where intake air is compressed and burnt with the exhaust from a rocket Mach 0 to Mach 5+ no particular atmospheric limit (can run exoatmospheric), good efficiency at Mach 2 to 5 similar efficiency to rockets at low speed or exoatmospheric, inlet difficulties, a relatively undeveloped and unexplored type, cooling difficulties
Scramjet Intake air is compressed but not slowed to below supersonic, intake, combustion and exhaust occur in a single constricted tube can operate at very high Mach numbers (Mach 8 to 15)[1] (http://www.dod.mil/ddre/downloads/ddre_briefings/Merging_Air_and_Space071603.pdf)
still in development stages, must have a very high initial speed to function (Mach >6!), cooling difficulties, inlet difficulties, very poor thrust/weight ratio (~2!), airframe difficulties, testing difficulties
Turborocket An additional oxidizer such as oxygen is added to the airstream to increase max altitude Very close to existing designs, operates in very high altitude, wide range of altitude and airspeed Airspeed limited to same range as turbojet engine, carrying oxidizer like LOX can be dangerous
Components
The components of a jet engine are standard across the different types of engines (noted above). The parts include:
Air Induction
For subsonic aircraft, the air intake to a jet engine presents no special difficulties, and consists essentially of an opening which is designed to minimise drag, as with any other aircraft component. However, the air reaching the compressor of a normal (not scramjet) jet engine must be travelling below the speed of sound, even for supersonic craft.
Compressor Fan
The compressor is the series of fans that are spaced very closely together. Each fan compresses the air a little more. Energy is derived from the exhaust fan (see below), passed along the shaft.
Shaft
This carries power from the exhaust fan to the compressor, and runs most of the length of the engine. There may be as many as three concentric shafts, rotating at independent speeds, with as many sets of exhaust fans and compressors. Other services, like a bleed of cool air, may also run down the shaft.
Flame Cans or Flameholders or combustion chambers
These are combustion chambers where fuel is continuously burned in the compressed air.
Turbine fans or Exhaust fans
These gather energy from the hot expanding air rushing out of the engine. This energy is used to drive the compressor through the shaft, or bypass fans, or props, or even (for a gas turbine-powered helicopter) converted entirely to rotational energy for use elsewhere.
Afterburner (optional)
(mainly military) Produces extra thrust by burning extra fuel, usually inefficiently, at the exhaust.
Exhaust
Air, once cooled and expanded, is vented out the back of the engine. Exhausts are designed to maximize thrust, since venting hot air does not provide nearly as much thrust as venting fast-moving cool air.
Supersonic Nozzle
The standard aerodynamic reference frame is attached to the aeroplane. Air must travel through the engine at subsonic speeds, to sustain operation of flow mechanics at the blades of the compressors and turbines. The supersonic nozzle is needed to convert the pressure and heat to velocity, and consequently momentum of the expelled air. A de Laval nozzle tapers down to a neck, accelerating the gas up to sonic speed, and then the nozzle opens out again. The hot gas thus expands and cools whilst pressing on the inside of the nozzle at a rearward facing angle. This accelerates the air even further; forming a powerful supersonic exhaust jet. The reaction on the inside of the nozzle multiplies the thrust up and accelerates the vehicle.
Design considerations
The various components named above have constraints on how they are put together to generate the most efficiency or performance. Important here is air intake design, overall size, number of compressor stages (sets of blades), fuel type, number of exhaust stages, metallurgy of components, amount of bypass air used, where the bypass air is introduced, and many other factors. For instance, let’s consider design of the air intake.
[edit]
Air intake design
For aircraft travelling at supersonic speeds, a design complexity arises, since the air ingested by the engine must be below supersonic speed, otherwise the engine will “choke” and cease working. This subsonic air speed is achieved by passing the approaching air through a deliberately-generated shock wave (since one characteristic of a shock wave is that the air flowing through it is slowed). Therefore some means is needed to create a shockwave ahead of the intake.
The earliest types of supersonic aircraft featured a central shock cone, called an inlet cone, which was used to form the shock wave. This type of shock cone is clearly seen on the English Electric Lightning and MiG-21 aircraft, for example. The same approach can be used for air intakes mounted at the side of the fuselage, where a half cone serves the same purpose with a semicircular air intake, as seen on the F-104 Starfighter and BAC TSR-2. A more sophisticated approach is to angle the intake so that one of its edges forms a leading blade. A shockwave will form at this blade, and the air ingested by the engine will be behind the shockwave and hence subsonic. The Century series of US jets featured a number of variations on this approach, usually with the leading blade at the outer vertical edge of the intake which was then angled back inwards towards the fuselage. Typical examples include the Republic F-105 Thunderchief and F-4 Phantom. Later this evolved so that the leading edge was at the top horizontal edge rather than the outer vertical edge, with a pronounced angle downwards and rearwards. This approach simplified the construction of the intakes and permitted the use of variable ramps to control the airflow into the engine. Most designs since the early 1960s now feature this style of intake, for example the F-14 Tomcat, Panavia Tornado and Concorde.
In one unusual instance (the SR-71), a variable air intake design was used to convert the engine from a turbojet to a ramjet, in flight. To get good efficiency over a wide range of speeds the Pratt & Whitney J58 could move a conical spike fore and aft within the engine nacelle, to keep the supersonic shock wave just in front of the inlet. In this manner, the airflow behind the shock wave, and more importantly, through the engine, was kept subsonic at all times. Additionally, and unusually for this engine, at high mach, the compressor for the J58 was unable to carry the high air flow entering the inlet without stalling its blades, and so the engine directed the excess air through 6 bypass pipes straight to the afterburner. At high speeds the engine actually obtained 80% of its thrust, versus 20% through the turbines itself, in this way. Essentially this allowed the engine to operate as a ramjet, and actually improving specific impulse (fuel efficiency) by 10-15%.
Finally, there is strong theoretical and experimental support for the idea that using a heat-exchanger to cool the air at the intake can increase the density of the air and thus reduce the necessary compression. This would create lower temperatures that permits lighter construction alloys to be used, reducing the engine’s weight by several times. This leads to plausible designs like SABRE that might permit jet engined vehicles to be used to launch straight into space.
THIS WILL BE PART OF MY FUTURE BOOK TITLED: “THE ART OF CUT AND PASTE”
Size is a bit of an over-simplification as it mostly goes on pressure ratio, but size does have an influence too. However, since he can’t get into his head that nickel alloy is denser than air (although both apparently less dense than the contents of his skull!) I wouldn’t even try to get on to talking about Joule/Diesel/Otto cycles and the reasons Diesel engines are more efficient than petrol ones.
But yes, it does appear he wouldn’t recognise a scooby if one bit him on the arrse.
Do you remember the TV show “How” and the two milk bottles? One form the 40s twice the size of the modern one. I think it went “how can I get the milk in this large bottle into this small one”. And then they empted one into the other and it all goes in. The volume was the save, the thickness of the glass was not.
Reminds me of a drinking session on HMS Niad in the PO’s mess. They had a big glass dick and this wise guy said “they modelled it on me” and my quick response was “must be thick glass them”. That got lots of laughter from his mats and me several drinks.
Deisel? Geez. No wonder they ate the metal up at the rear of those early engines. It takes high temps to get diesel to burn. Do you suppose that was part of the problem?[/quote]
you obviously have neither a clue about combustor design (primary air, secondary air, control of the TIT) nor do you seem to understand basic thermodynamics, else you weould know that the aim is to have
a) the combutor pressure as high as possible and
b) the temperature of the gases reaching the first tubine stage as high as possible
to improve thermodynamical efficiency of the engine.
Obviously there are limits set by the properties of the materials used in manufacturing the combustor casing, the turbine nozzle guide vanes and especially the first stage HP turbine (melting point, creep).
Also obviously the fuel needs to be mixed with air in the proper chemical ratio to provide proper combustion, but this flame is very hot (+2000°C), another problem is that the velocity of this primary air has to be so slow that the flame will not be blown away from the injector.
Temperature control is achived by adding secondary air to the combution gases still within the combustor, using a perforated combustor liner, so that the hot gases reaching the turbine have a temperature (TIT) of about 1000°C max (with modern materials and turbine cooling), older engines had TITs around 700-800°C. Additionally the HP turbine blades and the nozzle guide vanes are today cooled with air bled from the HP compressor, using little channels and holes to provide a “cool” (400°C) air film around the critical parts.
So if the combustion section is properly designed and the engine operated within it´s design limits, the flame will never touch either the combustor walls or the turbine. Gas turbine operate with a huge amount of excess air, which is not used to support the combustion, but used for internal temperature control. This is also the reason why you actually can breathe gas turbine exhaust gases (done it often enough, standing in the hot APU exhaust air of a MD-11 while waiting on the ramp during winter).
The problem with the early engines was not the fuel, but still inefficient combustor design, coupled with inferior materials.
I also noticed that you mix up terminology and don´t seem to understand the principles an axial compressor is working under.
Jan
He also doesn’t seem to understand what a stator is/does, and why omitting one would mean that you could increase the length of an engine by 10x and have it weight about the same. But apparently we’re the thick ones for understanding this… :roll:
Oh! I thought this thread was deleted. Ok, so let’s look at the facts from the REAL experts to see if his claim that a jet engine 10 times the size of another “weighs about the same”, or such.
Here are the specifications for several currently used General Electric commercial turbojet engines. If you look at these specifications, you will notice:
Turbofan Engines
CF34-3A
Diameter: 49 inches
Weight: 1,625 lbs.
CF34-8C1
Diameter: 52 inches
Weight: 2,350 lbs.
That is an increase of only 3 inches diameter, and an increase in weight of 2,185 lbs, which is more than the smaller jet engine weighs!
Let’s look at a few more.
CF34-10D
Diameter: 57 inches
Weight: 3,800 lbs.
CF6-50C1/C2
Diameter: 105 inches
Weight: 8,966 lbs.!!!
CF6-50E2
Diameter: 105 inches
Weight: 9,047 lbs.!!!
From this we can clearly see, that one jet engine of 57 inches (2,350 lbs.) which is less than twice the diameter weighs far less than half as much as another at 105 (8,966 lbs.). That’s a difference of more 6,616 lbs, 3.82 times the weight, or a 382% increase in weight. The other 105 in. engine weighs 81 lbs. more than the first!
Naturally, these weights would vary by a small percentage from one manufacturer to another by diameter, but you can see how a jet engine of one size weights far, far more than “about the same as” another twice it’s size.The difference is tremendous, more like 3 times the weight by size.
Turboshaft Engines
CT7-2A
Diameter: 27 in.
Weight: 429 lbs.
CT7-8
Diameter: 26
Weight: 537 lbs.
That’s a difference of 1 inch and 108 lbs! Imagine if one were twice the diameter of the other! Whew!
Here’s a list of them:
http://www.geae.com/engines/commercial/comparison_turbofan.html
So, there you have it. A jet engine twice the size of another weighs far, far, far more than “about the same as”, regardless of what type of jet engine it is. Now one that is 10 times the size of another, like the original claim… well, you can see how ridiculous it is to think they could weigh about the same, eh? Everyone makes mistakes. It would serve you better to owe up to the error and let it pass at that, instead of fervently trying to substanciate the unsubstanciable. Why not give that a try?
Wow! I’ve found the internet equivalent of marching in front of a brass band, bellowing ‘I am stupid’.
The example under discussion:
Take a reference jet engine.
Now, remove the stators and extend the engine so that the airflow at entry to each rotor stage is roughly as it would have been, had the stators not been removed.
The modified engine will be far longer than the reference, due to the larger gaps needed between rotor stages. But the stators have been removed, saving weight, and the engine is longer, making the casing heavier. It is a reasonable first approximation to say that the weight of the engine will be unchanged, although there will be an efficiency penalty.
That has been explained repeatedly, and if you still don’t get it, I submit that you have blown your mind with drugs walting as a hippy.
Ironman I understand what you are saying but to make the claim that diameter is proportional to engine weight is silly. Im sure there is a 3rd world country out there that might develop a jet engine which is the same size as an American or British engine. And that those our engines could way much less. Same type of thing with todays armored cars. Factory model same size as armored model but the weight is not even close.
Longer, yes. But 10 times the size and weigh about the same? Ofcourse not! Even if the engine used a centrifugal compressor instead of an axial compressor (smaller in diameter & lighter) you are increasing the length of the engine which to some degree counters the decreased diameter. You are also not changing any of the other major components of the engine to any degree that approached 10 times in size comparrison!!!
The following explains how the difference between an centrigugal compressor (typical in older jet engines) has an efficiency greatly exceeding 10% less than an axial compressors (typical of modern jet engines):
“Since compression ratio is strongly related to fuel economy, this eightfold increase in compression ratio (read: over earlier, centrifugal compressor engines) really does result in an eightfold increase in fuel economy for any given amount of power, which is the reason there is strong pressure in the airline industry to use only the latest designs. Mitigating this savings is the fact that drag increases exponentially at high speeds, so while the engine is able to operate far more efficiently, this typically translates into a smaller real-world effect. For instance, the latest Boeing 737’s with high-bypass CFM56 engines operates at an overall efficiency about 30% better than the earlier models.”
http://en.wikipedia.org/wiki/Jet_engine
Therefore, your contention that a jet engine (presumably axial comressor engine?) would weigh about the same as another (presumably centrifugal compressor engine? - stators) if you removed the stators (axial compressor - no stators) is absurd. As an extreme example, an axial compressor in a jet engine does not weight 1/10 of that of a centrifugal compressor. Hence, with current technology, it is not possible to make a jet engine with ANY type of compressor that could be 10 times the size of another and only 10% less efficient, regardless of the materials used to build it!!!
And you say diameter is not proportional to engine weight? Dude, I just showed you real examples (not fantasy examples) that show that in the real world (not the imaginary one), it is indeed directly related.
The original post, now deleted out of embaressment, was a simple discussion and a simply absurd claim was made. The statement was that an engine using a fan similar to a household fan (presumably) instead of a jet engine type of fan, 10 times the size of typical jet engine would be roughly 10% less efficient and “weigh about the same”.
This is absurd, as I have shown with technical data from current jet engines. Notice that in turboshaft engines, a slight increase in diameter (size) relates to a large change in weight. These engines do not employ a large fan in the front (like a turbofan engine), leaving the only fan-like component to be the compressor. Comparing such engines, you can clearly see that a slight increase in size relates to a large increase or decrease in weight.
Hence, with turboshaft engines (not turbofans), the statement that one 10x the size of another would weigh about the same is completely ridiculous.
When comparing turbofan engines, the statement becomes even more absurd, since you now have a large composite-blade frontal induction fan (light for it’s size because of composite materials) to add to the weight of the engine. Thus the statement is even more absurd when considering turbofan engines!
To make it all the more ridiculous, the statement,
…is also absurd, because an induction fan in a turbofan engine requires highly aerodynamic fan blades which are intricately formed. A “household” type of fan would not have it’s blades conforming to the shape of the fan housing. Clearly, a 10% decrease in efficiency is so far from reality as to be absolutely ridiculous as well.
pdf27, I suggest that if you are going to chatter about how jet engines work (or anything at all for that matter), you should watch the videos on the following site before you put your “Whittle Lab” knowledge into words. Appearently, you did not learn a damned thing there:
http://www.geae.com/education/genx/theatre/genx_theatre_go.html
…or perhaps one of NASA’s excellent jet engine web pages.
So we see now that a highly modified jet engine in the real world cannot be 10 times the size of another and weigh about the same, or be only 10% less efficient, particularly since it would not survive the increased temperatures caused by the axial compressor desing, regardless of what materials it was made of. Your fantasy engine is about a century away my boy. It will be a very long time before we have materials like that! :lol:
Now stop spewing bullshit for the impressionable to suck up. Ok? If you had simply said, “Oh, yea, that was wrong. I guess I meant…” you could have avoided your silly ranting, bitching, name calling, and ultimately, embaressment. Learn from it, finally, will you? That is a better behavior model than the one which you typically practice.
Quoting my post and reading what it said are two different things. Read my post, then reply based on what I said, not what you though I said.
I understand that you are squirming now because it’s all in the light. It will pass. Be patient.