J-20 5th Gen Fighter Thread VIII

[Stealthflanker]

It is the same principle of discrete representation of analog signal (DC conversion). The minimum digitalization sampling rate is twise the maximum component frequency of the analog signal. Since analog signals bandwidth is infinite in theory, the digitalization sampling rate should be infinite too, but in practical terms we take the highest frequency whose power is detectable as the max, therefor we have a minimum sampling rate. If HW allows, the higher the rate the better, which push the high end boundry further. Here a signal is a function of time.

This principle is universal beyond signal processing. To faithfully represent a spetial object, just replace time with distance, everything else is the same.

The principle is that a discrete representation of a continious curve can be achieved faithfully (without loss of information) by series of discrete sampling points if the sampling frequency (in time or space) is two times of or higher than the component "frequency" of the continious curve (over period of time or distance).

This sounds more like i have to increase the "sampling rate" by reducing the angle. Currently i take sample in my simulation every 3 degrees. Maybe i can try 0.02 deg but. Statistics will reduce the data.

 

[latenlazy]

This sounds more like i have to increase the "sampling rate" by reducing the angle. Currently i take sample in my simulation every 3 degrees. Maybe i can try 0.02 deg but. Statistics will reduce the data.

I don't think you're getting it. You cannot measure a 1 mm difference with a ruler that only counts in centimeters (or in this case, meters).

 

[taxiya]

This sounds more like i have to increase the "sampling rate" by reducing the angle. Currently i take sample in my simulation every 3 degrees. Maybe i can try 0.02 deg but. Statistics will reduce the data.

Honestly, I don't think any home computer is capable of doing meaningful job. The computing power required for a reliable job is probably more expensive than measuring a physical airframe in a radio dark room. Computer simulation is only to assist making the airframe, and it is done by super computers.

 

[Stealthflanker]

You can get *a* result but it's not the *same* result as the real world object you're analogizing. Those equations need to interact with physical geometric parameters to spit out meaningful results for a 3D object, since the object of interest is not a point or a line or a flat plate. If your model object is coarser than the real object you're analogizing so to will be your model output. If the level of difference for significance is tiny (in this case the difference between 0.01 and 0.001 is massive in significance but tiny in absolute quantities) your coarser resolution overwhelms your level of significance.

and the problem is how coarse is coarse or how fine is fine and how to achieve that. Like there honestly no real numbers on "width and length" of Polys and if they were curved how do you even measure the "resolution" of it ?

and most importantly what do i get in return.

If everything could be achieved with hobby enthusiasm we wouldn't need expensive equipment and corporate financing to build all those cool engineering projects.

Yeah then what ? Do you want me to stop ? or something else ?

 

[latenlazy]

Honestly, I don't think any home computer is capable of doing meaningful job. The computing power required for a reliable job is probably more expensive than a physical airframe in a radio dark room.

I wouldn't go that far. You can get some pretty expansive vector computational power daisychaining GPUs these days. But you would need a lot of GPUs.

 

[latenlazy]

Does it ? Like the relationship is Lambda/D tho Let's say you have that 7 cm long poly and 3.5 cm wavelength.

The mainlobe width would be 0.035/0.07 The resultant would be 0.5 Radians. and 3.5 cm wavelength vs 2 cm long facet would have
0.035/0.02 = 1.75 Radians Well smaller length give larger lobe.

Are we really talking the same physics ? Mine is a well known equations to predict antenna mainlobe from its dimension. Since RCS is basically antenna gain and the radiation patterns defined the same way in Far field, the relationship would be the same.

You can get *a* result but it's not the *same* result as the real world object you're analogizing. Those equations need to interact with physical geometric parameters to spit out meaningful results for a 3D object, since the object of interest is not a point or a line or a flat plate. If your model object is coarser than the real object you're analogizing so to will be your model output. If the level of difference for significance is tiny (in this case the difference between 0.01 and 0.001 is massive in significance but tiny in absolute quantities) your coarser resolution overwhelms your level of significance.

Then what ?

If everything could be achieved with hobby enthusiasm we wouldn't need expensive equipment and corporate financing to build all those cool engineering projects.

 

[Stealthflanker]

I don't think you're getting it. You cannot measure a 1 mm difference with a ruler that only counts in centimeters (or in this case, meters).

I'm getting it.

Taxiya is describing something similar as how you emulate a Sine wave with square wave. Or when you are using Simpson's rules to measure uneven objects. While you dont seem to get how RCS is similar to antenna.

 

[latenlazy]

and the problem is how coarse is coarse or how fine is fine and how to achieve that. Like there honestly no real numbers on "width and length" of Polys and if they were curved how do you even measure the "resolution" of it ?

and most importantly what do i get in return.

I already told you how coarse is coarse and how fine is fine. If your significance is determined by centimeter levels of difference you need at least centimeter if not millimeter level resolution (ability to measure 0.01-0.1 m^2). If your significance is determined by millimeter levels of difference you need millimeter level resolution (ability to measure 0.001-0.01 m^2). Otherwise, stochastic errors overpower significance.

Yeah then what ? Do you want me to stop ? or something else ?

Do whatever you want. But I think insofar as contribution to public discourse is concerned it would be misleading not to discuss limitations and problems with analytical methodology and its output. What an analytical exercise *can't* tell us is as important a conversation as what it "can* tell us if the goal is to promote better knowledge and get a more accurate picture of a subject matter. If a piece of analysis just isn't good enough to draw meaningful conclusions then that discussion should be had. Sometimes efforts are noble but don't lead to a productive outcome and that's fine. If you want to keep trying to do this mode of analysis that's your prerogative. I/we are just telling you what would need to be improved for the results to be actually meaningful.

 

[latenlazy]

I'm getting it.

Taxiya is describing something similar as how you emulate a Sine wave with square wave. Or when you are using Simpson's rules to measure uneven objects. While you dont seem to get how RCS is similar to antenna.

No...it's not that I don't get that RCS is like an antenna. It's that you don't seem to want to accept that a complex 3 dimensional shape does not emit like a dimensionally reduced point.

 

[Stealthflanker]

I already told you how coarse is coarse and how fine is fine. If your significance is determined by centimeter levels of difference you need at least centimeter if not millimeter level resolution (ability to measure 0.01-0.1 m^2). If your significance is determined by millimeter levels of difference you need millimeter level resolution (ability to measure 0.001-0.01 m^2). Otherwise, stochastic errors overpower significance.

Well it's not much TBH and i would love to see at least one academic source doing this. Like if it curved surface.. do i need to break it down to something like 1 mm box ?

But then you can no longer claim it will provide smaller lobe when pitted against larger wavelength.

Do whatever you want. But I think insofar as contribution to public discourse is concerned it would be misleading not to discuss limitations and problems with analytical methodology and its output. What an analytical exercise *can't* tell us is as important a conversation as what it "can* tell us if the goal is to promote better knowledge and get a more accurate picture of a subject matter. If a piece of analysis just isn't good enough to draw meaningful conclusions then that discussion should be had. Sometimes efforts are noble but don't lead to a productive outcome and that's fine. If you want to keep trying to do this mode of analysis that's your prerogative. I/we are just telling you what would need to be improved for the results to be actually meaningful.

I always discuss them tho. like the importance of statistics and i havent done them yet. also the lack of at least agreed standards.