With a satellite photo the pixels give us a fixed error range for the measurement. In that picture, you had an object with a known length that could be used as a ruler. In Deino’s picture that was the J-15. First we can establish that the J-20 is shorter than the J-15 in the picture. Therefore the J-15’s length would be an upper bound. Then we could find out the dimension of each pixel using the J-15’s length, and then find the length of the J-20, or alternatively find the dimensions of each pixel using the J-15’s length, then find how many pixels shorter, roughly speaking, the J-20 is. Either method confirm that the J-20 must be shorter than 21 meters, but the key here is recognizing that 21.19 meters is an upper bound. The J-20 is very clearly shorter than that.
Given Geino’s photo, I have no idea which pixel was picked as so-called upper bound. That reference line even occupied one or two pixel whereas each pixel indicates approximate half meter or more.
However, with uncountable pixel, that AIM-9’s length is almost certain, and one or two alternative pixel won’t influence the measurement.
In the satellite picture we have an instance where each pixel has the same dimensional relationship to the known object length and unknown object length. That is much better estimate than picking something with no verification of its dimensional relationship to the object you’re trying to measure.
I checked that satellite photo quoted by Deino again, and I got EXACTLY same length for both J-15 and J-20. In the photo below, we can see clearly that only wingspan remained outside.
This is your fixed error range.
EDIT: Hold on, are you trying to find a “lower bound” length based on the assumption that the J-20’s weapons bay can be no smaller than the F-22’s? Because if that’s what you’re trying to do, you are making a pretty big assumption that’s going to be prone to error. There’s no guarantee the J-20 would have the same length weapons bay as the F-22. It could easily be a bit shorter or a bit longer, but a difference of even .1 meters (that’s 10 cms) could scale to an error of over .5 meters, or more.
Furthermore you’re inviting two potential sources of error here. Unless you have the actual length of the F-22’s side weapons bay, you’d have to find the relationship of the F-22’s weapons bay length to the length of the overall plane by measuring out pixels. That’s an added source of error after assuming they must have the same weapons bay length. Then there’s a third potential source of error, which is finding the relationship of the weapons bay length of the J-20 to its overall length. The worst thing about these sorts of errors is that there’s no fixed range by which values must fall under (which is not the case with the satellite photos). I could blindly decide that the J-20’s side weapons bays could be bigger or smaller than the F-22’s on some arbitrary whim by any small amount, and that could change the results significantly. Or I could miss either plane’s weapons bay length to overall length ratio by a small factor and have that compound into a greater error.
Nonetheless, I tried that method, assuming that’s what you were trying to do, using a three view of the F-22 as a reference. If I included the tip of the sawtooth I got a weapons bay length of around 3.4 meters. If I excluded the sawtooth tip and went with the vertex, I got about 3.25 meters. Assuming the J-20 had a weapons bay of the same length, both would keep the J-20 well below 21 meters long.
The reference substance we set here was not length for weapon bay but that AIM-9X missile. Also according to the missile, the 18.9 meter known for F-22 was confirmed. Then the only gap here is what a length for the combat missile which should be used for J-20. This length we assumed is just 3 meters. For safety, we also assumed that pylon won’t be stretchable so that J-20’s weapon bay could possibly be shorter than F-22’s. Hence, we still got a length longer than 21 meter significantly.
Here is method for science not literature one taught. For only play, we can make a bet here, the debate will be paused. let’s wait to see the final data will be published officially, will you dare to put bet here? If I loose, I quit this forum and asking for my ID banned forever, if you loose, by that time you have to give up your ID and you announce you will never return this forum.
I know this will be a heavy oath. After last bet I won, I ever promised myself never bet on aviation with others.
However since many people say that 23 meter was from me and actually that was I quoted from others (see the searching result) whereas the data I reckoned was 21 meter, I have to sacrifice sth important.
Before you accept this challenge, pay attention to my words, you are betting with a man with a long tough working experience. I am not copying a swearing from TAKEN
Yano, rather than putting everyone in the box of Chinese conspiracists (and yes, there are a lot of them on the interwebs), you could just come out and admit that you used a flawed methodology. I don’t need to be a Chinese ultranat with a fantasy interest in the J-20’s performance (quote me at any point where I even remotely indicated that I think the J-20 must be unbeatable *rollseyes*) to insist on an accurate measure of length (Nor does Deino, who’s German btw). An accurate measure of length is an accurate measure of length.
Your accurate measure based on an commercial photo by google earth, and even the pixel which indicates the length was occupied by reference line. That’s greatly accurate.
For all I know the J-20 will be stuck with AL-31 class engines and never come to anything. If you want to argue the ambiguity of performance on other grounds, that’s fine. If you want to argue it will be heavier, I will simply say weight is hard to tell from a picture (After all, how do you know it’s overweight? Where did you see the official weight figures?). If you want to say its engines will suck, I will simply say that depends on whether the WS-15 will have the same problems the WS-10 did, and whether they will end up needing to export Russian. If you really want to believe the J-20 will have crap performance there are plenty of points to nitpick on. But. An accurate measure of length is still an accurate measure of length, and you seem incapable of accepting better methods that don’t conclude what you want them to conclude.
Don’t make it personal, your pleading shows There Is No Silver under Ground. One like Swerve don’t know we have such idiom for you. And if I do not use google translator, I will know better how to translate Chinese idiom to describe your behavior.
Even my missile used contains much more pixels than your Deino’s entire aircraft.
Do you know that accuracy of result determined by accuracy of instrument?
Rather than me being on some inane crusade to prove the J-20 is of a certain length, you seem to be on an inane counter-crusade against anything that indicates it’s shorter than you think.
Same criticise also proper to yourself.
I somehow doubt I’m the wishful thinker here, but if you must know, I have an interest in an accurately assessing China’s growing military capabilities.
Here we saw your confession!
I’m sorely aware of the less than serious ways people can underestimate that. Neither underestimation nor overestimation are desirable. Accurate estimation is, and that requires sound method and good logic. I see lazy logic being thrown around, such as the J-20 must be a long range interceptor meant to take out tankers. That doesn’t fit the PLA’s air doctrine, the fighter’s aerodynamic features, videos and pics of its maneuverability tests, or our best measurements of its size. I find the long range assumption particularly laughable, because not only does it assume a greater size than our best measurements, but it assumes that the J-20’s engines will be fuel efficient enough to take advantage of increased volume for longer range.
If you must crack the mystery of my heritage, I was born in China but grew up abroad (more than 4/5ths of my life was spent in either Canada or the US). Some of my hobbies are American politics and watching the NBA. I used Chinese in my PM (which is practically my second, not first, language) in an attempt to better communicate, since I can barely understand your English, especially when you’re making technical points that I’m genuinely interested in. Call it an unrequited gesture of good will. So much for your “he’s another Chinese nationalist!” suspicions.
You should care about how well you’re communicating. There is virtually no point having a discussion if you don’t care about being understood. I wasn’t laughing at your English. I was pointing out how you needed to communicate better for us to have a discussion/debate. I don’t usually feel the need to point out the less than perfect English some members of this forum have, but the problem is that your English is particularly hard to understand. I can’t speak for the other members, but I often have to take significant liberties guessing at what you mean to say. If you want an example…well
…That comes to mind. Sorry, I can’t do the English-Chinese word substitution trick for everything. I can tell when that’s happening, but at some point it’s just pig latin to me. Sue me for my imperfect language switching abilities. That’s just the peril of assuming that I must be some Chinese person pretending to not be Chinese being able to perfectly understand your substitute of Chinese words with English with no change in grammar.
And as I recall, you dug yourself into this one when you foolishly decided to try to nitpick on my English on a point that ended up highlighting your difficulty with the language. Which, btw, is another instance of how difficult it can be to understand you. It took me a while before I realized that you had thought that I was using “clearly” to refer to the satellite picture, when in fact I was just using clearly as another synonym for obviously…at least that’s what I think you were trying to do. See what I mean? (And no, it is not semantically wrong for me to use clearly instead of obviously).
There you go again, nitpicking on irrelevant things.
Your correction are also warmly welcome after the google translator which I deal with Falsa Fremda Diablo was abandoned by me for understanding from others. Flaunting your English via so many words won’t prove your knowledge of measuremnet.
Unlike Swerve who are qualified for teaching English, I am qualified for teaching how to use equipment to measure objects, and for decades I have been doing such kind of job.
The slightly smaller ruler would hardly make up for the bad discrepancies in length assuming different missiles. I got 17.9 meters using a 3 meter weapons bay length assumption with that ruler. Even if I went with a smaller one assuming a length of 3 meters would still yield comically bad results.
Also, I do believe I addressed the problem of not knowing how much extra space is needed for the missile to clear the weapons bay. I also didn’t need to be that precise to make my point after all, since my point was that the weapons bay is a very bad and ambiguous ruler to measure length.
The PL-8 is phased out, but that’s irrelevant. If you read carefully, I used the PL-9, which has about the same length and will be in service for a while.
According to the unsupported data from wiki, the length of PL-9 even slightly longer than PL-8. When I used PL-8, I dig a whole for you, clearly you didn’t realize that. Now its my turn to use the word “clearly”, and I’ll keep the right to use it again.
I used different coloured ribbons because it’s easier to see. No party hat tricks here.
Am I proficient in my understanding of aerodynamics? Most certainly not. I ask enough questions in this forum to try to get a better handle of the topic. However, understanding how to measure something properly does not require a degree worthy knowledge of aerodynamics. It is high school level science.
Anyways, it would be nice if you could come up with substance to refute my point on the ambiguity of your beloved weapons bay measurement method rather than resort to personal attacks and baseless accusations. If you really think my methods are so flawed, do one better. Demonstrate your weapons bay measurement your way and explain why it must be a better method, instead of crying to an imaginary ref.
In the photo presented above, the reference line limited length of weapon bay from either F-22 and J-20. The limitation based on a length of J-20’s weapon bay apart from those extension formed by triangle tooth and obligue BHK, we can see clearly that space that was cut from F-22’s weapon bay was significantly longer than J-20, ergo, we presumed that length of J-20’s weapon bay is shorter than F-22, no matter on what aspect. Even then, the length of J-20 is longer than 21 meter. Certainly, the 18.9 meter as known data for F-22’s length was verified for ensuring the scale between either AIM-9X as missile or missile bay and F-22 in image.
What I blamed not is one’s knowledge but logic for thought, and I doubt your logical capability will grow fast as my English capability.:diablo:
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