Chengdu J-20 5th Generation Aircraft News & Discussions

[Deino]

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The engineer must first find out the optimum shape of the DSI Bump at various speeds, and then program the FCS computer to adjust the shape at that speed.

Indeed and I did not deny that possibility. However exactly that perfect or optimum shape is surely not that dent.

 

[Asoka]

Indeed and I did not deny that possibility. However exactly that perfect or optimum shape is surely not that dent.

"However exactly that perfect or optimum shape is surely not that dent."

I won't say "surely" regarding that "dent", unless I am an aeronautical engineer and did the computer simulation and modeling on DSI.

DSI is a new technology only demonstrated on US and Chinese planes, not even the Russian or European, or Japanese have demonstrated it yet. It requires a lot of Fluid Dynamic Modeling and Simulation on Supercomputer.

It is not something our eyes or mind could easily simulate through intuition.

 

[ptldM3]

I won't say "surely" regarding that "dent", unless I am an aeronautical engineer and did the computer simulation and modeling on DSI.

DSI is a new technology only demonstrated on US and Chinese planes, not even the Russian or European, or Japanese have demonstrated it yet. It requires a lot of Fluid Dynamic Modeling and Simulation on Supercomputer.

It is not something our eyes or mind could easily simulate through intuition.

You are really hyping things up, everything from the J-20 using its rudder to going vertical without afterburners is basic to all aircraft, for instance a Cesnna can turn without banking, it's called a rudder, an airliner can go ful verticall with no afterburners and horrible T/W ratio. There is no need to act like any of these things are some magnificent breakthroughs that are new to the J-20.

As for the DSI, the concept is old and highly overrated. All a DSI does is divert boundary layer airflow. The 1950s Mig-21 did the same thing except it used an adjustable nose cone. Intake ramps do the same thing. A DSI is much more simple than an adjustable nose cone or intake ramps because it is fixed and you don't need any fancy supercomputers for DSI, aircraft in the 1950s and 1960s did not use any fancy supercomputers despite having more complex air intake systems. The boundary layers and vortexes on an entire aircraft is much more complex that a single fixed DSI.

As for the J-20s DSI, I am curious as to the latest picture with what looks like a dent. If the Chinese actually pulled off something that regulates airflow without an intake ramp or external moving parts than its an innovative design approach to regulating aircraft more efficiently with less consequences (theoretically) to moving intake ramps.

 

[Asoka]

The Cone shape DSI Bump on the grey picture seems noticeably fuller than the yellow bird. Notice the yellow bird's landing gear bay door is open. It is at the lowest speed preparing for landing. We can't tell what speed the grey bird is at.

 

[Asoka]

We have been wondering how many J-20 will China able to produce each year. Producing J-20 is not just opening more production lines. The problem of producing enough critical components like airframe bulkheads and engine parts like high quality fan blades must be solved first.

China have invented the technique 3D Printing that combines with Intelligent Micro-Forging. Conventional 3D printing use Laser to melt layers and layers of deposited metal powders to shape a component. This have the inherent problem of having unmelted powder and tiny air bubbles in the component, creating potential softness and weakness that is unacceptable for high strength parts.

The Intelligent Micro-Forging technique solved most of those problems, and greatly increase the strength, stiffness, and fatigue resistance of the product.

It also greatly reduced the time from 90 days to 10 days to produce a large component. And reduced the amount of metal powder required by 90%, and instead of using the expensive laser, it enable the use of the inexpensive conventional electrical arc for melting, which is only 1/10 of the cost of the laser.

Those are big savings.

The largest component produced using this technique is 2.2 meters long and weight 260 kg. The company is developing facility to producing component of 5.5m x 4.2m × 1.5m in the future.

"该技术不仅适合于加工复杂的部件，且速度提高了许多，如制造一个2吨重的大型金属部件，工期从过去的90天，减为10天左右，同时，以金属丝材为原料，其成本为目前普遍使用的激光扑粉粉材的1/10左右，或者说，材料成本降9成，利用率则增加到8成以上。热源方面使用高效廉价的电弧为热源，成本为目前普遍使用的大多需要进口的激光器的1/10。

　　这一技术为张海鸥团队经过十多年潜心攻关才取得有成果，目前也刚刚突破，具体实用等尚继续需要进一步的研究，其实就是要造更大的设备，但是已应用的效果已相当喜人。报道时，打印出的高性能金属锻件，已达到2.2米长，重约260公斤，具备打印1800×1400×50毫米尺寸超大型零件的能力。现有设备已打印飞机用钛合金、海洋深潜器、核电用钢等八种金属材料。

报道中称，正在建设的微铸锻铣复合制造设备能制造5.5×4.2×1.5的金属锻件，这个单位自然为“米”，"

http://www.cjfh.org/news/zhongguojunshi/220690.html

 

[j20blackdragon]

 

[grey boy 2]

New picture (黄师傅，十三姨来了)

 

[grey boy 2]

Looks like the DSI bump of J-20 does changed in different situations

 

[Asoka]

Looks like the DSI bump of J-20 does changed in different situations

In addition to the dent, the Bump looks flatter. I wonder what speed is the plane flying at.

Looking closer, its clearly a large dent, not just a optical illusion.

This picture shows a smaller and less deep dent.

Air flow into the intake changes according to various speed, Altitude, Angle of Attack, and tightness of the turn. Changing the shape of the Bump could deliver smooth air flow into the engine at wide ranging, various conditions, without the use of cumbersome machinery and diverters.

 

[cirr]

New picture (黄师傅，十三姨来了)

The13th LRIP?

 

[grey boy 2]

An old new picture

 

[psr540]

The Cone shape DSI Bump on the grey picture seems noticeably fuller than the yellow bird. Notice the yellow bird's landing gear bay door is open. It is at the lowest speed preparing for landing. We can't tell what speed the grey bird is at.

View attachment 368109

None sense too much. It's an illusion, the DSI bump is bottom aligned with that hexagon patch, further down from there is just painting.

 

[gambit]

It is not a proof. But to make a flexible surface that is adjustable is not beyond anybody's ability. The value of adjustable DSI is to allow optimum airflow to the engine at various speed from low subsonic speed, to transonic speed and supersonic speed.

The engineer must first find out the optimum shape of the DSI Bump at various speeds, and then program the FCS computer to adjust the shape at that speed.

This kind of innovation that is not hard to copy once someone has demonstragted it and proved that it works. I expect more plane will use it in the future. This kind of adjustable DSI saves several hundred kilograms of weight and save the internal space for the machinery to adjust airflow and get rid of the troublesome boundary layer.

DSI is a major innovation invented and patented by Lockeed Martin. It is an example of Think-Outside-of-the-Box invention.

Yeah...What you are talking about as something 'new' from China is actually decades old from the US. It is called the 'spike' on the F-111.

http://f-111.net/models/inlets/index.htm

The main purpose of any inlet airflow control mechanism, no matter how complex or simple, is to slow down supersonic air to subsonic PRIOR to contact with the engine. This is solved.

But the next problem is on how to control this process at as much flight environments as possible.

In order to understand the complexities of inlet air control, especially for the interested laymen, Lockheed produced this document...

http://www.enginehistory.org/Convention/2013/HowInletsWork8-19-13.pdf

The SR-71 is an extreme but that is precisely why we should understand the SR-71's engines.

While the SR-71 is an 'extreme' aircraft, it operates at altitudes borderline suborbital and cruises at speed too high for most materials, it cannot reach those extremes in an instant. In other words, before it cruises at Mach 3+ at 85,000 ft, it must starts from 0 kts/hr at 0 ft altitude and travels gradually thru several atmospheric layers of diverse air density that affects airflow, going from most dense at sea level to least dense at 85,000 ft. Every engineer, even the software kind, knows that the wider the range of the operating environment, the more robust and complex the mechanism must be to compensate for the greater amount of variables. This make the SR-71's engines ideal for understanding how other inlets works.

The relevant section in the above source is section 3.7 on subsonic inlets. Basically, it means you cannot simply slow down supersonic air abruptly. It must be done gradually.

Therefore the inlet must be designed to treat the air very carefully, which means very gentle turns and slow diffusion, to prevent the airflow from separating from the inlet walls and forming eddies and vortices. If this is done properly, the available total pressure will be converted efficiently to static pressure.

To put it another way...EVERYTHING must be done at subsonic velocities. Therefore, before going to supersonic environment, we must understand how to best create controlling mechanisms for the subsonic regime.

The reason why the F-111, F-14, F-15 and other aircrafts that have complex inlet supersonic air control mechanisms is because we want to have greater control of airflow in the subsonic regime. Less complex mechanism, like the DSI 'bump', means lesser control. Or less fine grained control.

Most people perceive 'sea level' to mean literally sea surface altitude -- 0. But in practice, like how aviation views it, sea level do have a range where air density is relatively uniform enough where aerodynamics and engine performance do not have enough variations to affect flight. That range is from 0 to approximately 1000 ft, or roughly 300 meters.

On the F-111 where the jet's mission is to fly at Mach in that 'sea level' altitude range, where air density is greatest, if supersonic airflow is not slowed down to subsonic speed in a controlled manner, the TF30 engine can literally explode from violent unstarts. Just because you have sea level dense air for aerodynamics and jet engine operations, that does not mean you are safer than in lower density air. This is why some aircraft designs are best at a certain altitude range, while some designs are best at other altitude range.

For the DSI, the moment you want that 'bump' to be variable in any dimension, you deviate from the original philosophy of the DSI, which is about physical simplicity and weight saving.

Understanding basic inlet philosophy and experience is why your claim that the J-20 have a variable DSI system is at best suspect. That does not mean it cannot be done. It was done on the F-111.

 

[cirr]

Looks like 2 regiments of J-20s end of 2017 are on

Let's have 200 J-20A1-Ns for starters and at least 600 J-20B/C/Ds... to follow

 

[Asoka]

Looks like 2 regiments of J-20s end of 2017 are on

Let's have 200 J-20A1-Ns for starters and at least 600 J-20B/C/Ds... to follow

Let's have a minimum of 1000 J-20 by 2030. That's adding ~100 planes per year. If ShenYang don't have enough J-11, J-15, J-16 orders, they can have one or two J-20 production lines. Spread the production capacity around the country. So we can have another 1000-2000 J-20 easily, if we want to, or need to.

No one can compete with the Giant Panda, when it comes to producing things.

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