I haven’t been assuming anything. This entire discussion started with me pointing out a source saying the J-20’s subsonic sustained turn rate was comparable to the F-16 with the implication that it’s STR was very good, you trying to argue the F-16’s STR was bad, and me questioning whether you were making an informed comparison while pointing to evidence that suggests otherwise. I’m not the one trying to contort the piecemeal interpretation of evidence and a shoddy foundation of science and engineering topics to fit my pet theories. I’m not the one trying to write fanfiction here.
Aerodynamics thread
- Thread starter siegecrossbow
- Start date
Yes you do.
This is analogous to, how much the shape of each division would affect the result of a numerical integration. The answer is, the shape is negligible as long as each division is narrower than the characteristic variations of the function to be integrated.
The paper from Virginia Tech used 960 panels to perform their calculations. In order to debunk their model with concerns of geometric differences, even without detailed calculations, at the very least, you would have to show that, turbulence and waves at supersonic speeds, have dimensional variations less than the geometric differences of the objects involved. Otherwise, the effects of those geometric differences on the calculation of drag, would just average out to minor fluctuations.
You failed to mention or show any of the above and hence, you don't have a legitimate claim, but just presented some other speculations.
Academic papers canbe right or canbe wrong. But taking unsupported pot shots like yours, is only being unfair to the authors.
But aren't you making amateurish guessworks yourself, while trying to make your claim sound anymore legitimate. And over and over again too.
Nope. Anyone with a rudimentary comprehension of how drag and air resistance works could tell you that the flat plate would have less air resistance than a full bodied 3D object. The former, especially while laying flat, has far less surface area facing the direction of the free stream, and resistance is a function of surface area. Furthermore, air resistance is not just a function of surface area. Geometry matters significantly due to second order forces like turbulent flow. It's why a square and a sphere with the same surface area don't have the same drag profile, and why drag is still calculated experimentally either in a wind tunnel or a *3D* simulation.
If you do an incomplete integration, you will get an incomplete function.
960 panels means nothing if you neglect a full geometric dimension. Last a checked the J-20 isn't a flat plate, and aerodynamics doesn't function off surface area alone. Last I checked a sphere and a square can have the same surface area and have very different aerodynamic profiles. You can't collapse geometry for a function that is dependent on geometry and then call your output accurate.
Ah. Right. I'm speculating about the model that was in the study. I just imagined that it wasn't a physically accurate model built by measuring a physically imprecise 3 view.
Is it amateurish to argue that you can't simulate the drag profiles of a 3 dimensional shape using a 2 dimensional input? Is that what the professionals do in their wind tunnels?
Last edited:
I like to read SD, because it is more informational than most other military forums. But it is this kind of argument for argument sake, that is killing this place. Somebody who has no idea of how to do numerical calculations, trying to take a pot shot on an academic paper........
And
for context.
And this, by Andraxxus again, for some more about what happens to sustained turn rates at different flight regimes.. Not a fan of the analysis by video, but his commentary about the actual flight dynamics involved is useful.
No one's arguing for arguing's sake. You may like what the study's conclusions are and are unwilling to let it go, but it's just a bad study using poor methods. If you could get accurate figures with methods like that they wouldn't be using 3D models for wind tunnels and simulations at actual design bureaus.
Speak for yourself. I used to build numerical models in my last job.
Last edited:
First, you talked about the geometric differences of a square and a trapezoid. For which, I gave you a reply based on dimensional variations of turbulence and waves at supersonic speeds, message #2945. You just changed the subject to the differences of 2D and 3D models, message #2947.
But you didn't even realize that, the front drag of a 2D model is just zero. There is nothing to be calculated at all with such an input. You are only making strawman arguments against the paper from Virgina Tech, i.e. their unreleased model simply can't be 2D, as their calculated front drag isn't zero.
And you still want to tell me you built numerical models........
Jura The idiot
General
I briefly went from:
to here
and the question is by how much "Drag Estimation" shown in that presentation would change if data from a wind tunnel were available
My point about the difference between a square and a trapezoid is called an analogy. It’s the exact same point as pointing out the difference between a 2D object and a 3D object. The point is you can’t accurately use one shape that’s different to represent the characteristics of another.
It’s irrelevant if the model is parameterized as a 2D surface or a flat 3D object (And in fact you *can* get a nonzero output for drag calculated against a 2D object, if you simplify drag down to interaction with just the surface of the object, since surfaces are two dimensional. After all drag is a dimensionless coefficient, so yes, I do know what I’m talking about here and you clearly don’t). The point is the same. They’re using a highly imprecise model to represent the thing they’re actually interested in, which is the J-20. If the model they’re using is imprecise then so will be their output. That is the point. That’s not a straw man argument. I’m not attacking something the study doesn’t say. I’m directly critiquing an element of the study that is essential to how it works. So far you haven’t been able to refute the substance of my point at all. Your only retort this entire time has been to try presume that I am not in a position of authority to critique the model, but if we’re going to resort to appeals to authority here, let’s ask whether you have the authority to claim good judgement for what studies are bs and what studies aren’t?
Last edited: