Well, if we assumed that was the case, that would mean its intended engines are going to have different dimensions.
J-20... The New Generation Fighter III
- Thread starter siegecrossbow
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Re: J-20 Mighty Dragon from a rare angle
Hmmm ... but there's something strange on that photo !?
It seems to be different on both sides if You change the brightness & contrast and additionally either someone "doctored" a bit on it to hide something (maybe between the engines under the belly ?) or he (or she) simply errased the landing gear.
Any idea ??
Deino
The J-20 DSI intake is prominent from a rear port-side view of the stealth fighter.
I just noticed the J-20 ventral fins shield the jet engines' radar and infrared signature from a lateral scan.
[Note: Thank you to HouShanghai and "HK299792458" for the picture.]
Hmmm ... but there's something strange on that photo !?
It seems to be different on both sides if You change the brightness & contrast and additionally either someone "doctored" a bit on it to hide something (maybe between the engines under the belly ?) or he (or she
) simply errased the landing gear.Any idea ??
Deino
Attachments
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J-20 - 11.8.11 - gear edited.jpg
Re: J-20 Mighty Dragon from a rare angle
The landing gear has been erased.
Hmmm ... but there's something strange on that photo !?
It seems to be different on both sides if You change the brightness & contrast and additionally either someone "doctored" a bit on it to hide something (maybe between the engines under the belly ?) or he (or she
Any idea ??
Deino
The landing gear has been erased.
Re: J-20 Mighty Dragon from a rare angle
That seems about right. I could sorta see shadows cast by the landing gears.
That seems about right. I could sorta see shadows cast by the landing gears.
Martian
Senior Member
Deisgn+performance characteristics of fighter and commercial jets are not comparable
Two points:
1. Your picture of a commercial airliner is not a good analogy. I provided a picture of a jet fighter from BAE Systems. Commercial jets have gigantic engines and are not comparable to small fighter high-performance jets.
For example, a fighter jet carries one (or two) occupant. A commercial jet carries hundreds of passengers. You should not use a commercial jet engine to make a point about a fighter jet. Look at the BAE Systems picture of a fighter jet. If you can shield the hot engines themselves, the infrared detectability of the fighter plane drops dramatically. If this thread were about civilian passenger jets, I would agree with you. With regard to the J-20 stealth fighter, I am pretty sure that you're incorrect.
I have never heard of a commercial jet liner being designed to minimize its jet engine infrared signature. However, it is well-known among fighter-jet designers that IR-seeking missiles pose a serious threat and fighter-jet engines are designed to minimize their IR signatures.
Also, it is inappropriate to use a picture taken at sea level. Fighter jets fly at 60,000 feet and the air is considerably colder. Furthermore, as the jet flies at hundreds of miles per hour, the exhaust is quickly left behind and disperses. Your picture of the commercial jet liner is not analogous for three reasons: gigantic engine to carry hundreds of passengers, not at altitude for the exhaust to blend with really cold air, and not moving to disperse the exhaust.
Infrared signature of aircraft showing jet exhaust fumes
(Credit: BAE Systems. Link: )
2. The general rule is "more surfaces tend to reflect more radar waves." However, there is an exception to the general rule. If a fighter jet is designed to follow planform alignment, the increased RCS is minimal. Hence, the extensive use of planform alignment design on the J-20 and F-22.
Side-topic: Regarding the PSing of erasing the left tire on the J-20, it is possible. If someone took a real photograph and removed a wheel, they could fool me. I can only make an educated guess on whether the bulk of a photo is real. A subtly altered and blended picture is beyond my skill level. You would have to ask a professional and that's still iffy.
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jet engine plume profile (Source: )
I'm going to guess this is a commercial jet plane sitting on a tarmac. Anyway, the infrared photo shows that the hottest part is the jet engine itself at approximately 150 degrees F or more. If ventral fins were in place, it would shield the hottest part of the airplane from lateral infrared detection.
Remember, I am only claiming the J-20 ventral fins contribute to its lateral infrared stealth. Everything that I have said is common sense. Basically, the oven/jet engine is the hottest part of the plane. If ventral fins block your view of the oven then the oven's infrared signature has been reduced. While the air surrounding the oven is warmer than ambient air, it is much lower in temperature compared to the oven. Voila, we have reduced IR. It is only straightforward physics.
Two points:
1. Your picture of a commercial airliner is not a good analogy. I provided a picture of a jet fighter from BAE Systems. Commercial jets have gigantic engines and are not comparable to small fighter high-performance jets.
For example, a fighter jet carries one (or two) occupant. A commercial jet carries hundreds of passengers. You should not use a commercial jet engine to make a point about a fighter jet. Look at the BAE Systems picture of a fighter jet. If you can shield the hot engines themselves, the infrared detectability of the fighter plane drops dramatically. If this thread were about civilian passenger jets, I would agree with you. With regard to the J-20 stealth fighter, I am pretty sure that you're incorrect.
I have never heard of a commercial jet liner being designed to minimize its jet engine infrared signature. However, it is well-known among fighter-jet designers that IR-seeking missiles pose a serious threat and fighter-jet engines are designed to minimize their IR signatures.
Also, it is inappropriate to use a picture taken at sea level. Fighter jets fly at 60,000 feet and the air is considerably colder. Furthermore, as the jet flies at hundreds of miles per hour, the exhaust is quickly left behind and disperses. Your picture of the commercial jet liner is not analogous for three reasons: gigantic engine to carry hundreds of passengers, not at altitude for the exhaust to blend with really cold air, and not moving to disperse the exhaust.
Infrared signature of aircraft showing jet exhaust fumes
(Credit: BAE Systems. Link: )
2. The general rule is "more surfaces tend to reflect more radar waves." However, there is an exception to the general rule. If a fighter jet is designed to follow planform alignment, the increased RCS is minimal. Hence, the extensive use of planform alignment design on the J-20 and F-22.
Side-topic: Regarding the PSing of erasing the left tire on the J-20, it is possible. If someone took a real photograph and removed a wheel, they could fool me. I can only make an educated guess on whether the bulk of a photo is real. A subtly altered and blended picture is beyond my skill level. You would have to ask a professional and that's still iffy.
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jet engine plume profile (Source: )
I'm going to guess this is a commercial jet plane sitting on a tarmac. Anyway, the infrared photo shows that the hottest part is the jet engine itself at approximately 150 degrees F or more. If ventral fins were in place, it would shield the hottest part of the airplane from lateral infrared detection.
Remember, I am only claiming the J-20 ventral fins contribute to its lateral infrared stealth. Everything that I have said is common sense. Basically, the oven/jet engine is the hottest part of the plane. If ventral fins block your view of the oven then the oven's infrared signature has been reduced. While the air surrounding the oven is warmer than ambient air, it is much lower in temperature compared to the oven. Voila, we have reduced IR. It is only straightforward physics.
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The only real point of disagreement is the idea surfaces+stealth part. Yes planform alignment (among other rcs techniques), when applied to a surface, will reduce it's rcs. But if the aircraft didn't have that extra surface in the first place it would have a smaller all round rcs (you can align all you want, that extra surface will still return some of the radar waves)
Basically, the j-20 as it is right now will have a larger rcs from most if not all aspects compared to a j-20 without those ventral fins.
My point is that the ventral fins are there for aerodynamics and any benefits to IR stealth is incidental. I'm not a designer of sraam's so I can't really say how much IR the ventral fins can hide (I imagine higher altitudes won't be much of a problem -- I believe all aspect ir missiles were able to home in on the heat from the very fuselage of the aircraft?), but personally I'd rather they just design an f-22 style nozzle and get rid of the ventral fins if possible. Not good for radar vlo.
And I never used the airliner as an analogy, I only mentioned that the video showed airliners along with a couple of fighters.
Basically, the j-20 as it is right now will have a larger rcs from most if not all aspects compared to a j-20 without those ventral fins.
My point is that the ventral fins are there for aerodynamics and any benefits to IR stealth is incidental. I'm not a designer of sraam's so I can't really say how much IR the ventral fins can hide (I imagine higher altitudes won't be much of a problem -- I believe all aspect ir missiles were able to home in on the heat from the very fuselage of the aircraft?), but personally I'd rather they just design an f-22 style nozzle and get rid of the ventral fins if possible. Not good for radar vlo.
And I never used the airliner as an analogy, I only mentioned that the video showed airliners along with a couple of fighters.
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Engineer
Major
Not true. If the ventral fins hides an even bigger RCS contributor from view, then it is an overall reduction in RCS.
Are you referring to the fact that the ventral fins may conceal the engine nozzles from the sides?
Engineer
Major
Yes. It has been my belief that the ventral fins are there to stay. If they are so bad for RCS, I'm sure Chengdu would have found some ways to extend the dorsal fins to compensate.
That thought occurred to me too. In this case this would likely be the engine nozzles and tapered rear fuselage to a degree. But it will only lower the rcs from the sides. Frontal and rear will likely increase marginally.
But in most cases, less exposed surfaces=smaller
Personally I'm still hoping for stealthier nozzles
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