Infrared Signature of the F135 engine?

All about the Pratt & Whitney F135 and the (cancelled) General Electric/Rolls-Royce F136
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Dragon029

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Unread post17 Dec 2015, 14:42

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.
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That_Engine_Guy

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Unread post18 Dec 2015, 03:42

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.
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meatshield

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Unread post18 Dec 2015, 10:50

Love your work engine guy :cheers:
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hornetfinn

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Unread post18 Dec 2015, 12:04

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.
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brucealrighty

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Unread post19 Aug 2016, 08:52

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
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spazsinbad

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Unread post07 Jul 2017, 21:49

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
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4_SOS5Gallery_F135_Pratt-Whitney.jpg
RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
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white_lightning35

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Unread post07 Jul 2017, 22:27

But, but, muh hotter than the sun engine which makes the f-35's stealth obsolete!
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tacf-x

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Unread post07 Jul 2017, 23:02

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.
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eloise

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Unread post07 Jul 2017, 23:15

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.
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mixelflick

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Unread post08 Jul 2017, 16:09

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!?
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lbk000

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Unread post08 Jul 2017, 16:18

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.
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ricnunes

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Unread post09 Jul 2017, 21:47

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.
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