Chinese Engine Development

b787

Captain
Quite right superdog. Besides it doesn't make sense to compare a turbojet ( TJ200 ) with the much more complex turbofans that are the subject of this discussion.
why not ? probably you have a good math base? but i am sure you do not, because a larger engine or a lighter engine need to have the same efficiency in blade air compression on larger engines you add more blades, burn more fuel and you need larger fuel tanks on the aircraft.

TWR and SFC are therefore the parameters to measure that efficiency regardless is a big engine like NK-25, or a small one like TJ100
 

superdog

Junior Member
it is a false statement trying to justify the Chinese superiority in WS-10, all engines are divided in generations and you can prove it easily

TF-30 used on F-14 had a TWR of 6:1 TF-34 used on viking S-3 has a TWR of 5.6:1 these are 1960s engines
another 1960 engine is AI-25 used in JL-8 also from the 1960s

Modern engines can achieve rates of 9:1 or even 10:1, but in the 1950s Vk-3 only achieved 4:1

The engines you mention are of Yak-141, RD-41, which makes it contemporary of Al-31 a fourth generation and it was not intended for cruise but only as a lift engine, first tested on Yak-141 on 1987, so if you want to compare Yak-141 is only generation behind of F-35B, which uses 5th generation engine


I suggest you before trying to prove your forumlore go a check all the engines built since 1940s to the present
I provided plenty of examples and reasoning to support my points that:

You can't directly compare the "advanceness" or "generation" of engines in different thrust classes just by looking at their TWR numbers.

It is much harder for larger engines to develop the same TWR as significantly smaller engines

And your rebuttal is to resort to ad hominem circumstantial. You want to talk about my motives rather than evidence or logic. You also keep repeating the old rhetoric that newer engines tend to have better TWR than old engines, which everybody already knows and doesn't really disprove or address what other people has been telling you.

When can you come up with something better?
 

SamuraiBlue

Captain
I provided plenty of examples and reasoning to support my points that:

Actually most of it is either irrelevant or factually wrong.
Your assumption that "weight does not gain proportional to size since while you can create a larger cavity......" is wrong because if you use the same thickness of materials to make larger fan blades, axles or casing, your engine will quickly fall apart. This is especially true for fan blades because you're dealing with not just the material's own weight but also an extremely strong centrifugal force proportional to its radius.
Even for static parts, an increase in size means more material strength will be used to support the structure's own weight, therefore, if you use the same material, the total volume of solid parts will need to increase faster than the internal volume of the engine.

Basically most metal will not fall apart due to it's own weight.
It has enough tensile strength to maintain structural integrity for a relatively small size like engines.
What you are talking about is a large structure like a high scrapper with a large stress per square cm.

As for centrifugal force you do not want to add more weight especially at the tip since the force effects weight. Another point is with a smaller engine to gain power it needs to spin faster to gain the same amount of compression compared to a large engine.

This is the same reason why you can find insects or even birds with extremely long and slender legs, but rhinos and elephants can only walk with thick and stubby legs. If you enlarge slender leg animals to the size of an elephant they will immediately collapse. An ant can have an extremely high "TWR" (how much it can lift in proportion to its bodyweight) compared to an elephant, that doesn't mean the ant was "designed" more intelligently than the elephant. It was just the law of physics.

Comparing apples with oranges.
Since skin and bone's tensile strength is already near it's potential limit with it's own weight.
Various metal has 10~100 times more strength.
 

b787

Captain
When can you come up with something better?
you have not provided any thing, and i will prove it to you.

Make a list of all the modern aircraft you know powered by jet engines since the late 1930s to the present.

The early jet engines had TWR of around 1.4:1 these are in the mid 1940s in engines like 003, by 1948 this jumped to 2:1 in engines like RD-500 and by the time fighters like MiG-19 were developed that jumped to 3:1 or even 4:1, Al-7 is a good example , in the 1960s these went to 7:1 by the early 1970s you get engines in the range of 7.8:1 like F-100
Commercial jet engines have even lower TRW because they do not use afterburner as military ones, you can see this in the Trent family, a modern Turbofan for large aircraft like Trent 900 has TWR of almost 6:1 similar to engines for C-5 or An-124, but most engines are in the region of 4:1 or 5:1
 

superdog

Junior Member
Actually most of it is either irrelevant or factually wrong.

Basically most metal will not fall apart due to it's own weight.
It has enough tensile strength to maintain structural integrity for a relatively small size like engines.
What you are talking about is a large structure like a high scrapper with a large stress per square cm.

As for centrifugal force you do not want to add more weight especially at the tip since the force effects weight. Another point is with a smaller engine to gain power it needs to spin faster to gain the same amount of compression compared to a large engine.

Comparing apples with oranges.
Since skin and bone's tensile strength is already near it's potential limit with it's own weight.
Various metal has 10~100 times more strength.
A small solid piece of metal by itself is not going to fall apart, and that's not what I was saying. The problem is when you simply enlarge a small engine without using stronger parts and a proper structural redesign, and you put it under operational load, the engine will fall apart due to the thermal and physical strain.

The engine is not one solid piece of metal, and the majority of strain it receives does not come from its own static weight, so don't tell me this only apply to things the size of buildings, by focusing on the weight and size of an engine you're comparing the wrong attributes.

If you believe that we can just enlarge an engine without using stronger parts, then you have no idea on how physics work or how a turbine engine work. If you agree we do need stronger parts, than your assumption that

"a larger engine is a lot easier to develop certain amount of thrust since weight does not gain proportional to size since while you can create a larger cavity for combustion to increase thrust"

is wrong.

It all comes down to the square-cube law. Structural components gain weight proportional to its volume, but only provide increased structural strength proportional to its cross-sectional area. The bigger a machine is, the less "specific strength" (in quote marks because this unit is usually used to describe uniform materials) it will have, it means an enlarged machine tend to need a higher weight to volume ratio (density) in order to satisfy the same structural strength requirements. This is completely opposite of what you've suggested.

Another way to understand the issue is to consider that turbofan engines increase its power proportional to its cross sectional area, but increase weight proportional to its volume (not exactly accurate, but some do simplify it this way). This would be a more direct application of the square-cube law.

It is easier for smaller engines to develop higher TWR. You have to realize that this is not something I invented to trash talk about Japanese engines or whatever. Just go read a book about small turbofan engines, see it for yourself. For example:

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read p.18, p.387, etc.

It was proven by people in the business of making small turbine engines. You don't have to agree with my explanation, but it is futile to argue against facts.
 

superdog

Junior Member
you have not provided any thing, and i will prove it to you.

Make a list of all the modern aircraft you know powered by jet engines since the late 1930s to the present.

The early jet engines had TWR of around 1.4:1 these are in the mid 1940s in engines like 003, by 1948 this jumped to 2:1 in engines like RD-500 and by the time fighters like MiG-19 were developed that jumped to 3:1 or even 4:1, Al-7 is a good example , in the 1960s these went to 7:1 by the early 1970s you get engines in the range of 7.8:1 like F-100
Commercial jet engines have even lower TRW because they do not use afterburner as military ones, you can see this in the Trent family, a modern Turbofan for large aircraft like Trent 900 has TWR of almost 6:1 similar to engines for C-5 or An-124, but most engines are in the region of 4:1 or 5:1
And of course you continue to re-post the same stuff that does not refute my points in any logical way. Basically you're not listening to what others are saying, you just repeat your own words. At this point I don't expect to have any more meaningful conversation with you.
 
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