Infrared Signature of the F135 engine?

Unread postPosted: 15 Dec 2015, 07:28
by Corsair1963
We now know the F-35 in fact has a lower RCS than the F-22. My question is that also true of the Infrared Signature?

I started to wonder after looking at the design of the F135's exhaust nozzle. Which, appeared far more complex than the one on the F119 from the Raptor. Then after reading more on the design. (based on F-16 LOAN Program) I see it has a number of features not found on the aforementioned. Which, includes things like special coating, internal cooling system, longer travel of hot exhaust gases, etc. etc.

Re: Infrared Signature of F135???

Unread postPosted: 15 Dec 2015, 08:33
by hornetfinn
IMO, IR signature is practically impossible to guess. There are features in F-35 and F135 that could make it very possibly have lower IR signature.

1. Higher bypass ratio means there is more cool air available to cool the engine and exhaust
2. Longer length meaning that hot parts of engine are further away from exhaust giving somewhat more time and space to cool the exhaust gases and even out the heat
3. Being developed directly from F119, it's likely there are lessons learned from it and improved in F135. This includes also IR signature.

IMO, F-35 very likely has lower IR signature flying subsonic due to these factors and F-22 very likely has lower IR signature supersonic due to supercruise ability.

Re: Infrared Signature of F135???

Unread postPosted: 15 Dec 2015, 08:50
by popcorn
Also, 2 x F119 vs 1 x F135.

Re: Infrared Signature of F135???

Unread postPosted: 15 Dec 2015, 09:11
by Corsair1963
Seems very logical.....still trying to find sources to support at least some of those conclusion.

Re: Infrared Signature of F135???

Unread postPosted: 15 Dec 2015, 09:54
by charlielima223
interesting tid bit...

https://www.youtube.com/watch?v=FIKZjARXcos

this would lead me to believe that the different nozzle designs of BOTh F-22 and F-35 would have a slightly lower IR signature when compared to more conventional exhaust nozzles you see on other aircraft. Also at certain angles the engine nozzles of both Raptor and Lightning seem to be less visible.

Image

Image

Image

just me making a guess.

Re: Infrared Signature of F135???

Unread postPosted: 15 Dec 2015, 11:19
by Dragon029
For the purpose of comparing nozzle diameters:

e0go7D1.jpg

Re: Infrared Signature of F135???

Unread postPosted: 15 Dec 2015, 11:53
by hornetfinn
This is pretty good document about fighter aircraft infrared signatures:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA566304

Page 34 describes the main components of IR signature from different aspect angles:

Tail: Engine hot parts
2. Rear Quarter: Hot parts and exhaust plume
3. Beam to Forward Quarter: Airframe and exhaust plume
4. Nose: Airframe and intakes


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.

Here is also one interesting document about stealth features:
http://www.dror-aero.com/lectur/rcs3.pdf

I doubt you will find anything much more specific than those documents about signature reduction used in any specific aircraft.

Re: Infrared Signature of the F135 engine?

Unread postPosted: 15 Dec 2015, 15:21
by eloise
Another option is to dazzle or damage enemy's optical sensor by your LFR , the interesting part is imaging infrared sensor are easier to damage by laser compared to ancient conical reticle IR sensor
LRF.jpg

DIRCM effectiveness again EO sensor.jpg

power reqired to damage optic.jpg


https://books.google.co.uk/books?id=bBb ... &q&f=false
laser source.jpg

DIRCM (2).jpg

laser desinator Litening.jpg

Re: Infrared Signature of the F135 engine?

Unread postPosted: 16 Dec 2015, 11:03
by Corsair1963
Would TVC have any advantages in lowering the Infrared Signature???

Re: Infrared Signature of the F135 engine?

Unread postPosted: 16 Dec 2015, 16:24
by eloise
Corsair1963 wrote:Would TVC have any advantages in lowering the Infrared Signature???

No

Re: Infrared Signature of the F135 engine?

Unread postPosted: 16 Dec 2015, 20:20
by archeman
eloise wrote:
Corsair1963 wrote:Would TVC have any advantages in lowering the Infrared Signature???

No


Well...

It was an oversimple question and that probably prompted the oversimplified answer here.

There are widely different implementations of TVC, most have some effect on Infrared Signature. Some TVC solutions make the IR signature far greater than none at all.

Check out the X-31 'paddles' hanging out about 5' beyond the exhaust exit. An extreme example of exposing hot metal for all to view. (EDIT) Not metal really, "Made of carbon-carbon, the paddles could sustain temperatures of up to 1,500 degrees C for extended periods."

https://en.wikipedia.org/wiki/Rockwell- ... anding.JPG

Re: Infrared Signature of the F135 engine?

Unread postPosted: 17 Dec 2015, 01:36
by checksixx
Corsair1963 wrote:We now know the F-35 in fact has a lower RCS than the F-22.


Do we now?? LoL :roll:

Re: Infrared Signature of the F135 engine?

Unread postPosted: 17 Dec 2015, 06:26
by Corsair1963
checksixx wrote:
Corsair1963 wrote:We now know the F-35 in fact has a lower RCS than the F-22.


Do we now?? LoL :roll:



Are you saying you don't believe the F-35 has a lower RCS than an F-22???

Re: Infrared Signature of the F135 engine?

Unread postPosted: 17 Dec 2015, 13:41
by charlielima223
Corsair1963 wrote:
Are you saying you don't believe the F-35 has a lower RCS than an F-22???


I remember when the USAF made the statement that the F-22 is has an RCS of metal marble and the F-35 of a metal golf ball. It was pretty much wildly accepted and somewhat debated. Most saying that those RCS figures were at their most optimum of angles (or something like that). Than skip a few years later and you have a USAF General saying that the F-35 is stealthier than the F-22 when before we were all lead to believe the F-22 is the "cream of the crop".

http://breakingdefense.com/2014/06/gen- ... -starts/3/

The F-35’s cross section is much smaller than the F-22’s, but that does not mean, Hostage concedes, that the F-35 is necessarily superior to the F-22 when we go to war

The F-35 is geared to go out and take down the surface targets,” says Hostage, leaning forward. “The F-35 doesn’t have the altitude, doesn’t have the speed [of the F-22], but it can beat the F-22 in stealth.” But stealth — the ability to elude or greatly complicate an enemy’s ability to find and destroy an aircraft using a combination of design, tactics and technology — is not a magic pill, Hostage reminds us.


IMO this makes me think that the F-35 at multiple angles (not just at the most optimal) has the lower overall RCS. Of course the Gen. Hostage does mention design, tactics, and technology. This makes me think again that with the F-35's more comprehensive sensor fusion and wider array of sensors; the F-35 has a better time at staying undetected longer than the F-22 can. Essentially it can see and know more. My own opinion on how I understand and interpret what the General said of course.

Re: Infrared Signature of the F135 engine?

Unread postPosted: 17 Dec 2015, 14:02
by sferrin
checksixx wrote:
Corsair1963 wrote:We now know the F-35 in fact has a lower RCS than the F-22.


Do we now?? LoL :roll:


'cuz you know more than the General right? LoL :roll: This from the same guy who nearly burst a blood vessel in denial about radar blockers in the exhaust on the F-22. :lmao:

"The F-35’s cross section is much smaller than the F-22’s, but that does not mean, Hostage concedes, that the F-35 is necessarily superior to the F-22 when we go to war

The F-35 is geared to go out and take down the surface targets,” says Hostage, leaning forward. “The F-35 doesn’t have the altitude, doesn’t have the speed [of the F-22], but it can beat the F-22 in stealth.” But stealth — the ability to elude or greatly complicate an enemy’s ability to find and destroy an aircraft using a combination of design, tactics and technology — is not a magic pill, Hostage reminds us."

Re: Infrared Signature of the F135 engine?

Unread postPosted: 17 Dec 2015, 14:42
by Dragon029
According to Bogdan, Hostage was 'correct in terms of RCS in decibels'; it's also worth note that you can find sources on the marble vs golf ball quote from 2005, before the first F-35 was full assembled. What that leads me to believe is that the quote was simply based on preliminary virtual modelling for the F-35, or perhaps with physical RCS models that were overzealous with certain assumptions. It's also possible that minor changes to the design over the past decade have resulted in signature reductions; even if not much externally has changed (other than things like the IPP exhaust, etc), material changes and internal RAM / composite alterations could have resulted in reductions. For example, we know that in LRIP-4 they replaced about 100 components with carbon nanotube reinforced polymer versions.

Keep in mind too that RCS (obviously) varies with aspect; it's inevitable for example that the F-22 will have a smaller RCS than the F-35 in certain aspects or sectors; what I just wonder is whether those aspects or sectors are significant or even in the majority; ie, the F-35 might potentially just be stealthier from the forward aspect.

Ultimately though, both aircraft are going to be similar in RCS, so I personally just consider them more or less equivalent.

Re: Infrared Signature of the F135 engine?

Unread postPosted: 18 Dec 2015, 03:42
by That_Engine_Guy
Too many unknown variables, but here would be some leading indicators.

Bypass Ratio - the higher the better for IR

Turbine and Augmentor duct/nozzle cooling - advanced cooling of the Turbine and Augmentor not only reduces IR signatures, but prolongs the life of hot section parts. Read up on the PW F100 LOAN program. (They don't throw tech like that away after they invest in it, even if it's not used on the test engine series)

Core temperatures - hotter core, more power and efficiency, but higher IR (hence more advanced cooling as to not melt turbine hardware)

Of course this is all a moot point if the PLA is set higher than MIL.... :devil: Something about a 3000°F+ exhaust plume that isn't "IR conservative"

Keep em' Flyin' :thumb:
TEG

PS - Nozzle area or Aj as it's referred, is variable and would NOT be the size as measured externally on the engine. Remember, Aj is at its lowest at MIL causing a concentrated/higher velocity exhaust stream that would carry significantly further aft of the engine.

Re: Infrared Signature of the F135 engine?

Unread postPosted: 18 Dec 2015, 10:50
by meatshield
Love your work engine guy :cheers:

Re: Infrared Signature of the F135 engine?

Unread postPosted: 18 Dec 2015, 12:04
by hornetfinn
Dragon029 wrote:According to Bogdan, Hostage was 'correct in terms of RCS in decibels'; it's also worth note that you can find sources on the marble vs golf ball quote from 2005, before the first F-35 was full assembled. What that leads me to believe is that the quote was simply based on preliminary virtual modelling for the F-35, or perhaps with physical RCS models that were overzealous with certain assumptions. It's also possible that minor changes to the design over the past decade have resulted in signature reductions; even if not much externally has changed (other than things like the IPP exhaust, etc), material changes and internal RAM / composite alterations could have resulted in reductions. For example, we know that in LRIP-4 they replaced about 100 components with carbon nanotube reinforced polymer versions.

Keep in mind too that RCS (obviously) varies with aspect; it's inevitable for example that the F-22 will have a smaller RCS than the F-35 in certain aspects or sectors; what I just wonder is whether those aspects or sectors are significant or even in the majority; ie, the F-35 might potentially just be stealthier from the forward aspect.

Ultimately though, both aircraft are going to be similar in RCS, so I personally just consider them more or less equivalent.


It's also worth noting that the marble vs. golf ball quote was before any real world RCS modeling was done with real F-35s or even pole models. F-35 pole model was first rolled out of factory in 2009 and went soon to RCS testing. Real F-35s have been tested some years after that. There was no way anybody would have known exactly the RCS of F-35 in 2005. I think the golf ball sized RCS was just design threshold criteria. F-22 on the other hand was then operational and the RCS was known pretty well. However, I think if F-35 had better RCS than F-22, that doesn't usually matter that much as metal marble sized RCS is already insanely low and F-22 flies faster and higher. Of course having even lower signature is good to have, but we are getting to area where the improvements aren't that big deal currently. In the future it might actually be when radars get good enough to detect stealth aircraft at long ranges.

Re: Infrared Signature of the F135 engine?

Unread postPosted: 19 Aug 2016, 08:52
by brucealrighty
Not sure whether to put this here or in the bloated 'basement dweller' thread, but here it is.

http://www.defenseworld.net/news/16822/ ... 7a51stn7qD

Oh noes! Stealth is negated by IR signature! :doh:

http://www.defense-aerospace.com/articl ... shows-f_35’s-stealth-limitations.html

Re: Infrared Signature of the F135 engine?

Unread postPosted: 07 Jul 2017, 21:49
by spazsinbad
A Closer Look at Stealth, Part 5: Nozzles and Exhausts
07 Jul 2017 Dan Katz

"F135 Engine
In designing the nozzle of the F135 engine that powers the F-35 Joint Strike Fighter, Pratt & Whitney aimed to rival the low signature of the nozzles on its previous F119, while beating it on maintenance costs. The F135 nozzle comprises two overlapping sets of 15 flaps, offset so outer flaps are centered on the gaps between the inner flaps. The inner flaps are thin, have metallic exteriors and straight sides and terminate in inverted “V”s. The sides create rectangular gaps between them with the nozzle fully diverged. The outer flaps, which Pratt calls “tail feathers,” are thicker and covered in tiles with blended facets. They terminate in chevrons that overlap the ends of the inner flaps to create a sawtooth edge. Toward the fuselage, the tiles end in four chevrons and are covered by additional tiles (not attached to the engines in this photo) that terminate fore and aft in chevrons and interlock with adjacent tiles in sawtooth-fashion.

The F135 nozzle likely suppresses IR signature using multiple methods. The trailing-edge chevrons create shed vortices, shortening the plume, while their steeper axial angle likely directs cooler ambient air into the exhaust flowpath. The inner surfaces of both sets of flaps are white and covered in minute holes similar to those on the F119, which might supply cooling air. The space between the tail feathers and the trailing chevrons may also contain ejectors to provide even more cooling air. The tiles and inner flap surfaces are likely composed of low-emissivity, RAM composites."



Source: http://aviationweek.com/defense/closer- ... es-1655211

Re: Infrared Signature of the F135 engine?

Unread postPosted: 07 Jul 2017, 22:27
by white_lightning35
But, but, muh hotter than the sun engine which makes the f-35's stealth obsolete!

Re: Infrared Signature of the F135 engine?

Unread postPosted: 07 Jul 2017, 23:02
by tacf-x
The general logic employed amongst basement dwellers is, "Oh it's a big engine, so it must be HOT."

Although the F135 may operate at fairly high TITs, what's relevant is the temperature profile at the nozzle exit. All of the features described above should be quite useful in minimizing heat signature. The technologies developed for AETP would lead to even lower IR signatures.

Re: Infrared Signature of the F135 engine?

Unread postPosted: 07 Jul 2017, 23:15
by eloise
tacf-x wrote:The general logic employed amongst basement dwellers is, "Oh it's a big engine, so it must be HOT."

Although the F135 may operate at fairly high TITs, what's relevant is the temperature profile at the nozzle exit. All of the features described above should be quite useful in minimizing heat signature. The technologies developed for AETP would lead to even lower IR signatures.

That true, high bypass engine and spike nozzles reduce IR signature alot.
Image
Image

Re: Infrared Signature of the F135 engine?

Unread postPosted: 08 Jul 2017, 16:09
by mixelflick
Pretty straightforward and not hard to believe: The F-35 is stealthier than the F-22.

If it wasn't, we'd be going BACKWARDS in our knowledge of stealth aircraft. Look at it that way!?

Re: Infrared Signature of the F135 engine?

Unread postPosted: 08 Jul 2017, 16:18
by lbk000
mixelflick wrote:Pretty straightforward and not hard to believe: The F-35 is stealthier than the F-22.

If it wasn't, we'd be going BACKWARDS in our knowledge of stealth aircraft. Look at it that way!?

I think there's the assumption that we would reserve all our best technologies only for ourselves. Also some people are fearful that the implication would compromise the inviolable status of the F-22 as the superlative A2A god-plane.

Re: Infrared Signature of the F135 engine?

Unread postPosted: 09 Jul 2017, 21:47
by ricnunes
lbk000 wrote:If it wasn't, we'd be going BACKWARDS in our knowledge of stealth aircraft. Look at it that way!?

I think there's the assumption that we would reserve all our best technologies only for ourselves. Also some people are fearful that the implication would compromise the inviolable status of the F-22 as the superlative A2A god-plane.[/quote]

Yes indeed!
Moreover the people that make those assumptions forget that the F-35 will only be sold to trusting and close allies to the USA (at least until something better than the F-35 doesn't come out - which should take "a while").
For example, was the F-35 offered to Brazil or India? Offered to Kuwait, Qatar or Saudi Arabia? of course not and why not? Because those countries are not "trusted US Allies", simple as that I believe...

So potential hostile countries could get advanced Stealth (and other) technologies due to them being exported is a bit of a moot point when it comes to the F-35 exports.