FY2020 DoD Budget

The F-135 is a much hotter engine with a lower bypass ratio no matter how somebody tries to spin it. A lot of other cr*p doesn't change that fact.

You can't summarily reject other techniques just because you aren't conversant with them.

F-15 today hasn't benefited at all? Same engines today as 1970? lol.

Even the F-15SE wasn't claiming any meaningful infrared signature reduction.

The fact is that the USAF and USN still has 2000 of these legacy big hot targets in service. All doomed based on IR according to junior LM marketeer wannabe.

Hence the investment in standoff weapons for those platforms. As events over Yemen have shown,
there's plenty of ersatz IR SAMs and FLIR out there that are real threats to aircraft that don't posses
meaningful IR signature reduction.

You can't summarily reject other techniques just because you aren't conversant with them.

Not really. I'm just doing what you are doing. Ignoring the rest except in your case, you're ignoring the most plain & obvious thing.

Even the F-15SE wasn't claiming any meaningful infrared signature reduction.

Not sure why would the F-15 want to do so when its engines are already significantly less hot. Its like saying the A-10 should claim no 1 for IR signature because of its turbofan engines. Everyone already knows that as a fact except maybe the magic plane rah rah band. On the rest of the plane, why can't legacies use low-E paint?

Of course the F-35 needs brilliant thermal IR signature management. Its running the hottest engine out there. If they didn't do anything, the plane would be more of a lighthouse than it already is.

What should be 101 since 1985.
https://apps.dtic.mil/dtic/tr/fulltext/u2/a620840.pdf

Except for molecular emissions of the exhaust plume and emissions from hot metal parts related to the engine, radiation emitted and scattered by the airframe is the dominant part of the aircraft IR signature. The magnitudes of the airframe components are largely governed by the emissive-reflective properties of the surface coatings, i.e., paints.

Example.
https://www.dst.defence.gov.au/sites/de ... _Hires.pdf

Of course an F-15 has a higher niratam rating than a magic plane. But not clear why the niratam rating for an F-15 would be higher than an F-35....

P.s. waiting for someone to say because it has 2 plumes.

I'm jumping in late not having read all the previous 'hot engine' IR posts (because this is the F2020 DoD Budget thread) to point to this thread with probably good info especially from you guessed it 'hornetfinn', 'TEG' & other good contributors:

Infrared Signature of the F135 engine? http://www.f-16.net/forum/viewtopic.php?f=56&t=28509

Not really. I'm just doing what you are doing. Ignoring the rest except in your case, you're ignoring the most plain & obvious thing.

Because it's been the focus of signature reduction efforts datings back to at least the SR-71 since
that's the only infrared signature that the detectors of the period leading up to the late-70's could see.

All-aspect has been the focus for the last 30 years. Because that's where the threats are.

Not sure why would the F-15 want to do so when its engines are already significantly less hot.

Which is why both GE and P&W offered LOAN as a backfit to the F110s.

The reason you haven't seen a concerted effort to reduce the exhaust signature is that
the rest of the aircraft would still be awful. It's a function of projected area and a
lack of a plausible cooling scheme for surfaces.

Its like saying the A-10 should claim no 1 for IR signature because of its turbofan engines.

That was in fact the claim that high-bypass turbofans would reduce IR signature for the A-10.

On the rest of the plane, why can't legacies use low-E paint?

Why can't legacies use active cooling of surfaces?

Of course the F-35 needs brilliant thermal IR signature management

Because it's trying to survive in a high-end threat environment

What should be 101 since 1985.
https://apps.dtic.mil/dtic/tr/fulltext/u2/a620840.pdf

Except for molecular emissions of the exhaust plume and emissions from hot metal parts related to the engine, radiation emitted and scattered by the airframe is the dominant part of the aircraft IR signature. The magnitudes of the airframe components are largely governed by the emissive-reflective properties of the surface coatings, i.e., paints.

Example.
https://www.dst.defence.gov.au/sites/de ... _Hires.pdf

Of course an F-15 has a higher niratam rating than a magic plane. But not clear why the niratam rating for an F-15 would be higher than an F-35....

P.s. waiting for someone to say because it has 2 plumes.

"F-35 and F-22 engines have both pretty well buried hot parts. For example F135 has unusually long exhaust pipe which narrows down the viewing angles where hot parts are visible. AFAIK, both have active cooling measures for airframe and exhaust nozzle and also exhaust gases. As seen in those pictures, both also have exhaust nozzle and also hottest part of exhaust gases well hidden behind tail components from most viewing angles. Of course all jet fighters can be easily seen by IR sensors from behind due to massive amount of heat generated by the engine. However the most important part is frontal and beam aspect angles. One important thing is solar reflections from canopy and airframe which are large contributors in IR signature of regular aircraft. Both F-22 and F-35 likely have very well suppressed solar reflections due to coatings used."

For the rest of us that live in the real world, the biggest IR signature comes from the engine. How many of those "numerous" F-15 losses have not come in the direction of the tailpipe?

A higher bypass ratio might help to cool down the engine. Engine deflectors like those on the f-22 helps significantly. However the F-35 has an engine that is way hotter (for a simple fact to generate more thrust) and has a lower bypass ratio than the F-110 which means the F-110 can cool better. Its very easy to ignore fact when trying to demonise anything but demonising a plane that is served with pride as a primary interceptor sounds ridiculous

I agree F-110 plume is cooler than F-135 since the higher bypass ratio and lower thrust
However, while the jet plume is the hottest part, depend on the aspect of the aircraft with IR sensor it is irrelevant to IR detection distance, in simple words, in many aspects, the engine nozzle and the jet plumes are blocked from the sensor view and therefore they do not contribute a great part to total IR signature in these cases
For example:

that simple diagram not necessarily applied to F-35 vs F-15 case, but i am sure youcan get the idea
IMHO, F-35 is extremely good at hiding its engine nozzle from most directions

So unless they are in afterburner the factor that determines IR sensor detection range will be the airframe size, F-15 is obviously bigger, that is not an advantage against an optical sensor

Furthermore, F-35 has 2 big vents for nacelle bay ventilation by ambient air, that is a good way to reduce skin heating from engine

It is a great mistake to talk about F-35 IR reduction measure and not mention the design of F-135 nozzle.
The naccel bay ventilation air is used to cool down the nozzle flaps

The engine blocked is also cooled

Finally, testing has shown, a serrated nozzle will reduce exhaust plumes length

Garrya, thanks for all that impressive detail which shows conclusively that IR emission reduction was an important part of the F-35 design too as I previously worried about that issue. They really did think of everything !

Plume size also is dependent on engine thrust. Higher thrust = bigger plume. If one sees how big a plume can get, one would understand the extent of usefulness are the IR blockers.

Air-frame size again generates aerodynamic heat, the faster the plane goes. A low subsonic low altitude speed is not going to have a significant difference. More importantly, is the surface area from the front really dramatically different between the planes.

I'm not questioning the F-35's IR signature. It need to reduce what is clearly a much higher TIT. Granted, the F-15 has a massive RCS. That part of the science is clear, no arguments there. However if someone makes a claim that the F-15 has a massive IR signature, the onus is on those people to prove it.

P.s. Wasn't LOAN tested on the F110-GE-129?

Plume size also is dependent on engine thrust. Higher thrust = bigger plume. If one sees how big a plume can get, one would understand the extent of usefulness are the IR blockers.

Air-frame size again generates aerodynamic heat, the faster the plane goes. A low subsonic low altitude speed is not going to have a significant difference. More importantly, is the surface area from the front really dramatically different between the planes.

I'm not questioning the F-35's IR signature. It need to reduce what is clearly a much higher TIT. Granted, the F-15 has a massive RCS. That part of the science is clear, no arguments there. However if someone makes a claim that the F-15 has a massive IR signature, the onus is on those people to prove it.

P.s. Wasn't LOAN tested on the F110-GE-129?

F100-PW-200

http://www.f-16.net/f-16_versions_article20.html

Free LM PDF: F-35 Air Vehicle Technology Overview https://www.lockheedmartin.com/content/ ... erview.pdf (3.1Mb) 4 Page extract below LOAN & Heat management full PDF is the go.

Plume size also is dependent on engine thrust. Higher thrust = bigger plume. If one sees how big a plume can get, one would understand the extent of usefulness are the IR blockers.

F135 hot part is better buried than F-110 and F-100, i guess partly because F-135 has fewer compressor stages ( 3-stage fan, 6-stage high-pressure compressor) compared to F-110 (3 fan and 9 high pressure compressor stages) and F-100 (3 fan and 10 compressor stages). Thus, the exhaust plumes have to move a longer distance before it is shown outside the nozzle.

Hence, while F-135 has higher thrust, its plumes is not necessary longer outside the nozzle and imho, 1 plume is smaller than 2 plumes
Without any doubt, at full thrust, plumes can get very big and extend far further than the engine nozzle, but then once you are at max AB then you are as bright as a forest fire

Air-frame size again generates aerodynamic heat, the faster the plane goes. A low subsonic low altitude speed is not going to have a significant difference

I don't think both planes will fly at low subsonic all the time, especially for F-15 due to the massive RCS, it will be engaged by SAM and interceptor from further and more often, thus it must attack enemy from longer range, to do that you probably need to climb and accelerate, in short, flying slow is easier to follow in an F-35

More importantly, is the surface area from the front really dramatically different between the planes.

Not very dramatic but F-35 has others IR signature reduction measures such as cooled engine blocker, cooled nozzle, serrated nozzle, big scopes for nacelle bay ventilation, somewhat better nozzle shielding

Garrya, thanks for all that impressive detail which shows conclusively that IR emission reduction was an important part of the F-35 design too as I previously worried about that issue. They really did think of everything !

You are welcome

The mistake being made here is the use of the "all else being equal," mindset. When comparing the F-15/F-100/F-110 vs an F-35/F-135, all else is not even remotely equal. There's no metric or spectrum, where an F-15 is less visible (or has superior IR characteristics) than an F-35. As has been stated repeatedly, the engine/nozzle/airframe design, location, and techniques used on the F-35, result in a much smaller signature, from any viewing angle.