J-20 5th Gen Fighter Thread VIII

Gloire_bb

Captain
Registered Member
The problem is the bold texts. You see, scientific research start by data gathering and sampling from the real thing. Less than that is just imagining, no matter how it seems to be close.
You see, I don't see immediately obvious mistakes for a reasonable(for public discussion) degree of approximation. Mass-produced aircraft aren't that complex in their shapes, and they go to great length specifically to eliminate excessive small details.
This makes net results certainly better than public statements with an unknown (unverifiable) degree of substance.

For instance, in 1940s US public sources quite widely used 16" armor belt figure for Iowa class - and it even made its way into tactical documents of other navies, despite shipbuilders telling that this number doesn't add up.

Also, given how production works (actual engineering, that is) - shapes are /probably/ close enough, for mass-production equipment. We are discussing a mass-produced plane here, not a stellarator.
A flawed methodology.
For now, I'll reinstate - the best available one which is both transparent and consistent for any comparison is this one.
You may add that 'due to a lack of competition', if internet fight is that important. But it's still the first and only one of its kind, and thus is the best just because.

The only alternative is to rely on public data points of absolutely unknown validity, meaning, and relative accuracy. They're unusable and descend discussion into religious debates of Lockheed, Chengdu, and Sukhoi churchesexpert estimates (i.e. unsubstantiated personal beliefs).

Yet we still need those consistent data points - the whole LO subject is just too important for LO aircraft to just skip, or even leave at LO yes/no level.
 

HighGround

Senior Member
Registered Member
You see, I don't see immediately obvious mistakes for a reasonable(for public discussion) degree of approximation. Mass-produced aircraft aren't that complex in their shapes, and they go to great length specifically to eliminate excessive small details.
This makes net results certainly better than public statements with an unknown (unverifiable) degree of substance.
Take a sphere and facet it into a dodecahedron. Would you expect both of these two shapes to reflect EM waves the same way. Take an RF beam with a wavelength of 3 cm. Do you expect that beam to interact the same with a dodecahedron with 7 cm edges as one with 2 cm edges. His model is constructed from polygons. Where there are edges and flat surfaces and corners in many parts of his model, a plane is smooth with much fewer flat surfaces and corners. Where in real life an RF beam might interact with a curved surface that has no corners, one edge, and no flat surfaces his model would have multiple edges, flat surfaces, and corners. He never dealt with these problem in his model. Can you get a rough idea of where the plane is reflecting RF energy at any specular angle? Sure you can but that’s not the same as the question how much, how tightly, etc. All those shape factors I just talk about introduce variance. If your variance overpowers the magnitude of scale by which your key performance parameter is defined (aka the significance) then you cannot answer the question you’re interested in answering. Even for comparative purposes, if the difference between two objects is at the millimeter level but your models can only be precise at the centimeter level, your error factors can drown out the difference, and you can’t say with any certainty which two objects is actually a better performer than the other. To answer more precise questions you need more precise models.


With VLO aircraft, we're talking -20db and beyond. These are tight numbers.
 

Gloire_bb

Captain
Registered Member
With VLO aircraft, we're talking -20db and beyond. These are tight numbers.
(1)Shape of the objects in question is simpler. They are built neither of spheres nor of dodecahedrons.
(2)Even then, at first level of approximation - even assuming that "all" objects are made of either spheres or all of them are made of dodecahedrons is already a result. It gets the general LO shape and its reflections. Because it's already a data point - just by that it's better than no usable data point at all.
(3)Your argument is quantitative - you aren't satisfied with the 'quality' of the model, not with the idea of modeling itself. The quality of the model is a thing that can be improved.
Our current problem is 'quantitive' - w/o @Silentflanker models, we don't have any comparative data points to work with at all.
It may even be really wrong now - but simply because of consistency, it's still the better data point - because the alternative to it is pure beliefs.

And, repeating the previous post, LO is too important for discussion to leave it out entirely, and simply count aircraft as "stealthy", "not stealthy" and "I believe its stealthy, f-16.net doesn't believe it's stealthy". We can't skip this discussion.
 

latenlazy

Brigadier
(1)Shape of the objects in question is simpler. They are built neither of spheres nor of dodecahedrons.
Complex shapes increases rather than decreases the need for precision.

(2)Even then, at first level of approximation - even assuming that "all" objects are made of either spheres or all of them are made of dodecahedrons is already a result. It gets the general LO shape and its reflections. Because it's already a data point better than no data point.

You can get general reflection patterns correct with a coarser model but it won’t spit out specific *measurement*. The measurement is the point.

(3)Your argument is quantitative - you aren't satisfied with the 'quality' of model, not with modeling itself. The quality of the model is a thing that can be improved.
Model quality is what dictates the accuracy of quantitative results. If you want to improve the model you need to talk about model quality.

Our current problem is 'quantitive' - w/o @Silentflanker models, we don't have any comparative data points to work with at all.
It may even be really wrong now - but simply because of consistency it's still the better data point - because the alternative to it is pure beliefs.
If your model is flawed you’re not solving the “pure belief” problem. You’ve supplanted one flawed basis of belief for another. Consistency is no mark of accuracy. You can be consistently wrong. There are many ways to be wrong and only a few ways to be right.

And, repeating the previous post, LO is too important for discussion to leave it out entirely, and simply count aircraft as "stealthy", "not stealthy" and "I believe its stealthy, f-16.net doesn't believe it's stealthy". We can't skip this discussion.
You can’t speculate your way into important knowledge and you won’t get closer by coddling flawed analysis.
 

by78

General
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