To follow up on this point and show what I mean, I did a *very* rough exercise with some *very* loose assumptions. I took a quick estimate of the average wing thickness of the F-22, getting about .25 meters, and multiplied it by the wing area of the F-22 minus the roughly rectangular area that is the fuselage in between the wings (because wing area usually includes the fuselage area between the two wings), 78-27=51, and got about 12.5~13 m^3. Now for the sake of this exercise, let's say the J-20's wings are half as thick. They seem thinner than the F-22's, though maybe not half as thick, but indulge me here. Assuming the J-20's wing area is about the same as the F-22's, that would mean on differences in wings alone the J-20 would be about 6 m^3 less voluminous, all else held equal. My point here is that thin but wide features are not volumetrically trivial, and by the nature of their thinness we sometimes miss that while an absolute difference in thinness between two features isn't significant their proportional differences can have sizable effects on dimension.I'm iffy on the cross sectional area, tbh. The F-22's verts are huge, it has larger and thicker tailplanes compared to the J-20's canards, and its wings seem to be thicker too. These differences will add up.
I estimated that the width of the F-22's fuselage is about 3.9 meters, and its height is about 1.6 meters. Obviously, the F-22's fuselage isn't a rectangle, but again, for the sake of simplicity and this exercise, let's treat it as such and let's also say that the cross section area of the fuselage is consistent across its length. Let's also assume the J-20's fuselage has identical cross sectional dimensions as the F-22, again for the sake of simplicity and this exercise. We know for a fact that the J-20 is longer than the F-22, let's say 20.5 meters to the F-22's 18.8. With these very loose assumptions, the F-22's fuselage volume would be 3.9*1.6*18.8. The J-20's would be 3.9*1.6*20.5. In other words, the difference in volume between the two fuselage's, if they were rectangular prisms, would be (20.5-18.8)*1.6*3.9, which is about 10.7 m^2. This is assuming that their cross sections are rectangles. Under the assumptions of this exercise, the J-20 would only be 4 m^2 larger than the F-22. However, as both cross sections are rather more close to trapezoidal or hexagonal, the base of difference between two fuselages with the same cross section but different lengths would be even smaller than if they were rectangular, and thus holding the assumptions over wing thickness the same you would get an even smaller difference.
Of course, this is where people will quibble with me and point out the F-22's fuselage is actually shorter than 18.8 m, and that its last stretch of length is all tail booms and tail control surfaces, *but* that is also true for the J-20, though perhaps to a lesser extent. Furthermore, I would argue at least some of that will be compensated by the fact that the J-20 has both smaller and thinner vertical tails, and by the fact that the J-20 has no horizontal tails. As I've emphasized in the previous paragraph, the volume contributions of wings and control surfaces should not be regarded as trivial, and in the F-22's 4 tails are not tiny by any margin. They are, in fact, *significantly* larger than their counterparts on the J-20, and not simply in area but also in thickness.
More to the point though, if the J-20's fuselage were even .1 meters smaller in both height and width (3.8x1.5), then its cross section in this exercise would be about a half meter smaller than the F-22's, and you would get a J-20 with a fuselage that is less voluminous than the F-22's despite being longer (3.8*1.5*20.5=116.85 vs 3.9*1.5*18.8=117.31). As I said earlier, these small differences can add up. A decimeter here or there can multiply into much great disparities. Measurement variance alone should compel a very long pause for anyone insisting that rough assumptions about comparative dimensions should tell us anything about extrapolated estimates (like the argument that the F-22 and J-22 look like they share "roughly" the same fuselage cross sections, so the J-20, by having a much longer fuselage, should definitely be greater in volume, which seems to be the most common justification for conclusions about the J-20's volume).
Are any of these figures accurate? H*LL no. I'll be the first to admit the entire exercise is built on a set of conceits, but the point of this exercise wasn't to present a . ccurate figures. It was to demonstrate visual size disparities in the fuselage of two planes may not reflect the presumption of great gulfs in volume that a judicious eyeballing might suggest. Even small changes in a number of parameters could defy the exaggerated expectations that may come from extrapolating a difference in length, so we ought to be very *careful* about presuming without *very* precise and *thorough* measurements. This is why I keep insisting, over and over again, that images can be misleading, and that planes are complex geometric shapes. It doesn't matter how incredulous someone thinks the idea that the J-20 may not be volumetrically bigger than the F-22 is. It may be, or it may not be, but we shouldn't be using visual impressions to pass confident judgements. We invented measuring tools for a reason. Eyes by their nature do deceive.
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