Shenyang FC-31 / J-31 Fighter Demonstrator

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Blitzo

Blitzo

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delft

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siegecrossbow said:
Here is a closeup image of the 3D printed support struss similar to the one used on J-31. I don't think that this particular image has been posted.

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Ua0Wqti.jpg
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I expect that weight can be save by choosing non-square intersections of ribs.
 
thunderchief

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shen said:
You are right of course that wavelength is ultimately determined by temperature. Early IR missile such as the AIM-9B with PbS based detector sensitive to around 1 micron band can only track very hot objects such as the tailpipe of a jet. Later, "all-asepct" AIM-9L tuned for around 4 micron band can detect the plume of the exhaust. The latest IR sensors are sensitive into the true long wave IR band of 8-12 micron. That means even very small temperature difference can be detected. For example, all object moving through air compresses the air in front of it, compression cause the air to heat up, greater speed increase compression and thus heat. A F-22 supercruising at high altitude is the ideal target for long wave IRST. Eurofighter's PIRATE IRST claims capable of detect subsonic fighters from 90 km from front and 145 km from rear, and 10% great against supercruising fighter.
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Photons emitted at higher temperatures have higher frequency and therefore higher energy . This is important because electrons in sensors need to be excited (pass to higher energy level) so sensor could work , and for that they need certain quantity of energy which would be supplied by photon . You are right that older sensors require higher temperatures in order to work , because their electrons require more energy .

Modern sensors could detect photons emitted at lower temperatures, even up to 10 degrees Celsius (for example this
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) . But even for them, absorption coefficient rises with higher frequency
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. Or in simpler terms, again you would detect object with higher temperature easier (at larger distance)

Final consideration is purely practical . Modern sensors made of HgCdTe (and to extent InSb) require cooling to be effective at lower temperatures (usually with liquid nitrogen) . That means they are not that effective in military searches where you need to keep sensors running for hours in order to pickup something. They are better in situations when you already have contact and you need to lock your IR sensor on it .
 
siegecrossbow

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Assuming the IRST can pick up, track, and engage a target at the range claimed in the spec:
how can a radar guided missile like the AIM-120 actually acquire and track the target if the radar couldn't find it? Does it track the stealth enemy aircraft via datalinking with the IRST?
 
vincent

vincent

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siegecrossbow said:
Assuming the IRST can pick up, track, and engage a target at the range claimed in the spec:
how can a radar guided missile like the AIM-120 actually acquire and track the target if the radar couldn't find it? Does it track the stealth enemy aircraft via datalinking with the IRST?
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Stealth planes can be picked up by radar, the detection range is very low, that's all.
Maybe the plane can guide the missile to the general area of the target using datalink, then let the missile guide itself with its radar
 
shen

shen

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thunderchief said:
Photons emitted at higher temperatures have higher frequency and therefore higher energy . This is important because electrons in sensors need to be excited (pass to higher energy level) so sensor could work , and for that they need certain quantity of energy which would be supplied by photon . You are right that older sensors require higher temperatures in order to work , because their electrons require more energy .

Modern sensors could detect photons emitted at lower temperatures, even up to 10 degrees Celsius (for example this
Please, Log in or Register to view URLs content!
) . But even for them, absorption coefficient rises with higher frequency
Please, Log in or Register to view URLs content!
. Or in simpler terms, again you would detect object with higher temperature easier (at larger distance)

Final consideration is purely practical . Modern sensors made of HgCdTe (and to extent InSb) require cooling to be effective at lower temperatures (usually with liquid nitrogen) . That means they are not that effective in military searches where you need to keep sensors running for hours in order to pickup something. They are better in situations when you already have contact and you need to lock your IR sensor on it .
Click to expand...

At low altitude, especially with humid air, absorption of long wave IR is indeed range limiting. But that's not a problem at high altitude above the clouds where the air temperature and humidity are low, and that's where F-22 is designed to supercruise.

My understand is that fixed IR sensor installations use Stirling engine based cryocooler, not gas cooling. Like this,
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D

delft

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shen said:
At low altitude, especially with humid air, absorption of long wave IR is indeed range limiting. But that's not a problem at high altitude above the clouds where the air temperature and humidity are low, and that's where F-22 is designed to supercruise.

My understand is that fixed IR sensor installations use Stirling engine based cryocooler, not gas cooling. Like this,
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Click to expand...
Sounds interesting, but how large would a liquid nitrogen bottle be to provide the same cooling over a sufficiently long time? Agreed, if you are going to refuel the fighter in the air you cannot top up the liquid nitrogen bottle.
 
b787

b787

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vincent said:
Stealth planes can be picked up by radar, the detection range is very low, that's all.
Maybe the plane can guide the missile to the general area of the target using datalink, then let the missile guide itself with its radar
Click to expand...
stealth planes are only stealthy in name, radars can pick them up, specially in the long wavelength, however for old aircraft a stealthy aircraft might be difficult, but for modern radars, stealth is just a commercial ploy, stealth aircraft are in many ways obsolete,speed will be always the most important thing, S-500s will deny the sky to any stealth machine.

Anyway that is my opinion since i see the 6th generation is supposedly hypersonic
 
kwaigonegin

kwaigonegin

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b787 said:
stealth planes are only stealthy in name, radars can pick them up, specially in the long wavelength, however for old aircraft a stealthy aircraft might be difficult, but for modern radars, stealth is just a commercial ploy, stealth aircraft are in many ways obsolete,speed will be always the most important thing, S-500s will deny the sky to any stealth machine.

Anyway that is my opinion since i see the 6th generation is supposedly hypersonic
Click to expand...

Anything made by man can be countered by another man. That has and always will be a true statement.
Stealth is not about total invinsibility.. like you said it's all about detection ranges which translates to time which translate to options. That's all stealth is and in many cases that's enough.
In combat a split second advantage over your foe may be all that is needed. Principally the same goes with speed. The faster you go the less time your foe has to react or counter. Same thing different variable.
 
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