For those of you that followed the original J-20 thread and continued onto this thread, you remember that Gambit has made a big deal about "edge diffraction."
Also, Gambit makes a big deal about "edge diffraction" again with regard to Australia Air Power's point #1. To wit:
I have already mentioned that "the resulting error will be mitigated...by edge treatments."
However, I want to ask all of you an important question. Why isn't the supposed "military professional" informing you that NASA considers edge diffraction effects to be trivial?
Planet Quest: Technology - A Close Look at Diffraction
"A Closer Look at Diffraction
When an electromagnetic wave passes by an obstacle in space, the wave is bent around the object. This phenomenon is known as diffraction.
The effects of diffraction are usually very small, so we seldom notice it."
After all the articles that Gambit has read on edge diffraction, why hasn't he ever told you that Jet Propulsion Laboratory/NASA states the effects of diffraction are trivial?
I did tell you guys that Gambit will mislead you to pursue his anti-China agenda. He hides behind technical terms to make false claims. In contrast, I explain "backscatter from edge diffraction" in understandable terms and provide a citation from a mainstream source.
Do you trust NASA's claim that "edge diffraction" is trivial or would you rather trust Gambit's anti-China agenda that "edge diffraction" is a really big problem (and only for the J-20, but not for the F-22 or F-35)?
[Note: The web address for my citation shows its from "jpl.nasa.gov".]
Here is the difference between you and I: critical thinking skills.
The NASA source is an explanation of
WHAT is edge diffraction and how does it pertain to certain applications...
All telescopes must take diffraction into account. In the case of telescopes intended to resolve objects (planets) that, at best, will appear as a single pixel in the image, diffraction must be managed to allow that pixel to shine through.
In other words, different needs will deal with certain properties and/or behaviors differently. This is not just about edge diffraction effects but for all things in life. For NASA, the astronomers are not trying to hide anything. They need to understand edge diffraction effects so they can deal with it to
REVEAL very faint objects.
For military purposes such as 'stealth', it is a different need so even though the basic understanding of edge diffraction effects is still the same, we must deal with it differently because we are trying to
CONCEAL some things. That is why snipers pay close attention to details that could reveal their positions. That is why there are so many arguments about the PAK-FA's data measurements probes typical of developmental flights.
Another example of this is the wheel. Most people could not conceive of the tank tread as a wheel but that is exactly what it is: a mechanical wheel. We understand the basic principles of sidewalls, tread dimensions, flexibility, and so on...But for different needs, we created the 'tank tread', the typical rubber 'tire', the old wooden and steel wagon 'wheel', and so on...For different applications.
You want to dismiss these effects because you have a substantial emotional investment in the J-20 out of nationalistic pride. If these effects are so trivial, then why are they such a big deal for any one who is trying to develop a 'stealth' aircraft. The reason is because they, like me, exercised their critical thinking skills and determine that different needs require different methods of negotiations of these effects. That is why the Iranians published their report that different tools such as GTD must be employed at different locations on a complex body. That is why we have something called Iterative Physical Optics (IPO) to deal with cavity RCS measurement...
PIER Online - Computation of EM Field Scattered by an Open-Ended Cavity and by a Cavity Under Radome Using the Iterative Physical Optics
Abstract:
It is always a challenge to predict Radar Cross Section (RCS) of a full scale military platform with a good accuracy. Most of the time antennas and cavities are the main contributors of aircrafts RCS. Several methods have been developed to compute the RCS of cavities such as analytical methods (modal methods) and asymptotic methods (geometrical optics (GO) methods and physical optics (PO) methods). This article presents the Iterative Physical Optics (IPO) method which consists in an iterative resolution of the Magnetic Field Integral Equation (MFIE) to compute the currents on the inner walls of the cavity. This method allows computing arbitrarily shaped cavity with a good accuracy even for cavity with a depth inferior to the wavelength. Comparisons of IPO results with Rays and Finite element methods show a better accuracy of IPO than Rays especially for cross polarization. But computation time represents one of the main limitations of the IPO method. We present here a new formulation of the Segmented IPO method which coupled with the generalized reciprocity theorem decreases significantly the complexity of the method and consequently the computation time. The S-IPO method has been validated by comparisons with Modal method and measurements. We have observed that the repartition of the electric currents density on the inner walls of the cavity is quite the same with IPO and S-IPO computations. Lastly we propose an evolution of the IPO method we have developed to compute the RCSof cavities under radome. This method has been validated by comparison with finite element results.
Does APA know about IPO? If not then why not?
This is why no one who has relevant experience in this matter do not take seriously your video, the one that boosted your ego with your repeated boast of view count. Talk about vanity...
What APA did was wrong on several levels, but the most egregious are two: questionable physical dimensions and the use of physical optics (PO) as the
ONLY tool.
Did China give APA the precise physical dimensions? If not, then why is it wrong for us to be suspicious that what dimensions APA used are undersized and therefore their data are naturally skewed towards a smaller RCS, the one that you have so much emotional investment in? The computing adage 'Garbage in. Garbage out.' is very true when the basic information required is in doubt.
You once argued since the US never allowed anyone to have his own independent analysis of the F-22 but everyone pretty much acknowledged that the F-22 is the premier 'stealth' aircraft, why not give the J-20 the same latitude? That is a reasonable argument but only on its surface.
If I apply for a loan, the lender will look at two main factors: income and credit history. Income is a variable. I may receive a pay raise or not or even a reduction. I may continue to have employment or be terminated. The lender does not know but only have some faith based upon income history. Credit history is a different issue. It is established and quite unalterable. The lender can look at my credit history and assess my ability to repay debts of various sizes. Income and credit history are like the parallel rails for a train.
Does China have a history that involve an F-117 equivalent? The reality is that the US does not care what people believe about the F-117, let alone the B-2 or the F-22. But the reason why people are willing to give US a healthy measure of their faith is because of established combat record of our 'stealth' aircraft, as in credit history, and our lead in aviation, as in potential income. Chinese aviation is still far behind US but here you are asking intellectual 'lenders' to exercise faith in its military variant when contrasted against US military aviation history and combat record?
One of the pair above is the size of a bird for radar detection. When China can demonstrate the same then intellectual 'lenders' will be willing to give China the same faith as they have given US.
