Low Observeability of the F-135 engine

All about the Pratt & Whitney F135 and the (cancelled) General Electric/Rolls-Royce F136
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steve2267

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Unread post13 Jun 2018, 19:44

spazsinbad wrote:There are a couple of threads with pics/videos of the **** end with radar blocker butt this one is from the vid mentioned.

See beginning OP of this thread then same viddy here etc..... & variable A/B goes POP!



Spaz, is the "POP" you reference occuring at approximately 0:18, 0:49, and 1:10 of that video? What is that? Is that a programmed increase in A/B (fuel flow rate) after some distance or time has passed since hold bar release?
Take an F-16, stir in A-7, add dollop of F-117 & gob of F-22, sprinkle with AV-8B, stir well, then bake. Whaddya get? An F-35.
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vilters

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Unread post13 Jun 2018, 20:08

Man, man, man, man, man, man, where are the engine guys when you need them? ?

=> => => There is NO "radar blocker" in the tailpipe.

ALL afterburning engines.
"I say again :"
ALL afterburning engines need a flameholder to keep the AB flame under control, then the "burner space to create/convert fuel into energy, followed by the convergent into divergent nozzle.

=> What you see is the AB flame, formed and held in place by the flameholder and a gazilion small air holes all around that cool the exhaust and keep the flame centered.

All this to keep the EPR "Engine Pressure Ratio" as close to 1 as possible.
+> You don't want to create pressure. => You want to create speed.
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steve2267

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Unread post13 Jun 2018, 20:14

vilters wrote:Man, man, man, man, man, man, where are the engine guys when you need them? ?

=> => => There is NO "radar blocker" in the tailpipe.

ALL afterburning engines.
"I say again :"
ALL afterburning engines need a flameholder to keep the AB flame under control, then the "burner space to create/convert fuel into energy, followed by the convergent into divergent nozzle.

=> What you see is the AB flame, formed and held in place by the flameholder and a gazilion small air holes all around that cool the exhaust and keep the flame centered.

All this to keep the EPR "Engine Pressure Ratio" as close to 1 as possible.
+> You don't want to create pressure. => You want to create speed.


Uhh, Vilters... I believe in the midst of their aerospace sorcery, the wicked engineers at LM and P&W crafted an A/B flame holder shaped just so to mitigate / cancel / or otherwise trap radar energy in the most appropriate wavelenghts (S-band & X-band ?) such that the F-35 does not create a huge radar spike from astern. So the "radar blocker" is the A/B flame holder, just shaped 'specially so.
Take an F-16, stir in A-7, add dollop of F-117 & gob of F-22, sprinkle with AV-8B, stir well, then bake. Whaddya get? An F-35.
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SpudmanWP

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Unread post13 Jun 2018, 20:33

vilters wrote:=> => => There is NO "radar blocker" in the tailpipe.


Screech, the F135 and the JSF Engine War
17 Mar 2011 Graham Warwick

Pratt points out that the F119 and F135 are the only production engines with stealthy augmentors. Their design eliminates conventional spray bars and flame holders and integrates multi-zone reheat fuel injection into curved vanes that block the line-of-sight to the turbine.


Source (No longer online) http://www.aviationweek.com/aw/blogs/de ... 0491972939
"The early bird gets the worm but the second mouse gets the cheese."
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Unread post13 Jun 2018, 21:20

Good EnGynInfo HERE OR below: viewtopic.php?f=56&t=52566&p=357817&hilit=Kjelgaard#p357817

6 page PDF of article below: Engine F135 & LiftFan STOVL F-35LightningII pp6ed.pdf

download/file.php?id=19133 (PDF 1.5Mb)
Powering the Lightning II
April 2012 Chris Kjelgaard

"...Also, like the F119 augmentor, the F135 augmentor is stealthy: The design of the two engines’ augmentors places multi-zone fuel injection into curved vanes which eliminate conventional spray bars and flame holders and block the line of sight to the turbine when looking into the engine from behind...."

Source: http://militaryrussia.ru/forum/download ... p?id=28256 (PDF 12.5Mb)
RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
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spazsinbad

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Unread post13 Jun 2018, 21:25

steve2267 wrote:
spazsinbad wrote:There are a couple of threads with pics/videos of the **** end with radar blocker butt this one is from the vid mentioned.

See beginning OP of this thread then same viddy here etc..... & variable A/B goes POP!

Spaz, is the "POP" you reference occuring at approximately 0:18, 0:49, and 1:10 of that video? What is that? Is that a programmed increase in A/B (fuel flow rate) after some distance or time has passed since hold bar release?

'TEG' where are you? So my guess would be the consistent POP is when the variable A/B - NOT AT FULL for catapulting - goes to FULL at a short distance down the cat track which can be seen more or less at same time as 'POP goes the A/B'.

Goback to page 1 & scroll down & elsewhere for VARIABLE AFTERBURNER specifically designed in samesame Super Hornet.

Stevie may WONDER 'bout sound synchro: viewtopic.php?f=56&t=52566&p=358044&hilit=variable+catapult#p358044

Could be a slight POP STALL since corrected?: viewtopic.php?f=56&t=52566&p=357806&hilit=variable+catapult#p357806

LOTsa YadaYADAyaDA: viewtopic.php?f=57&t=28046&p=314601&hilit=variable+catapult#p314601

MOar on testing: viewtopic.php?f=22&t=16196&p=205241&hilit=variable+catapult#p205241

Last one - mebbe?: viewtopic.php?f=22&t=15953&p=201921&hilit=variable+catapult#p201921
RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
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steve2267

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Unread post13 Jun 2018, 23:02

The "POP" seemed to correlate with a sudden increase in flame intensity / AB brightness. Would that happen during a "pop stall"?
Take an F-16, stir in A-7, add dollop of F-117 & gob of F-22, sprinkle with AV-8B, stir well, then bake. Whaddya get? An F-35.
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spazsinbad

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Unread post13 Jun 2018, 23:19

Why not correlate that all into "this is the sound made when the variable A/B goes to FULL going down the catapult track"?

I did not make the original video although I may have edited it - I forget - maybe the POP is completely erroneous. Do we hear pops on other catapult videos? Am I going to look for them? Hell no. Do we hear complaints about catapulting? Hell yeah - about the HMDS visor / nose gear / green glow / pilot restraint the list is endless BUT NO POP STALLS BABY! YAY!
RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
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Dragon029

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Unread post13 Jun 2018, 23:22

It'd be what Spaz mentions; those jet blast deflectors can only withstand so much for so long, so for heavy launches requiring an afterburner they'd likely avoid full afterburner until the last moment prior to catapulting. Whether this is triggered by the pilot (with the catapult operator pressing their button when they see the jet plume hit max AB) or is automated / triggered by acceleration I don't know (though I'd lean towards the former; pilots are meant to have their hands off the controls at launch).
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That_Engine_Guy

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Unread post20 Jun 2018, 15:46

vilters wrote:Man, man, man, man, man, man, where are the engine guys when you need them? ?


Agree - "Flameholder"

I'm sure it would be 'possible' to design the flameholder with different properties to help deflect radar, but they do take quite a beating to be coated with anything that isn't VERY durable.

TEG
[Airplanes are] near perfect, all they lack is the ability to forgive.
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spazsinbad

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Unread post20 Jun 2018, 16:09

Dragon029 wrote:It'd be what Spaz mentions; those jet blast deflectors can only withstand so much for so long, so for heavy launches requiring an afterburner they'd likely avoid full afterburner until the last moment prior to catapulting. Whether this is triggered by the pilot (with the catapult operator pressing their button when they see the jet plume hit max AB) or is automated / triggered by acceleration I don't know (though I'd lean towards the former; pilots are meant to have their hands off the controls at launch).

Somehow I missed your post earlier. Apologies. If you have followed my links then it is clear why there is a variable afterburner for the F-35C similar to the reason why there is one in the Super Hornet - POP STALL and mitigation of same. As you mention there is a side benefit but not the main reason why a variable afterburner for catapulting is AUTOMATIC in both cases. The aircraft software only allows so much then going down the cat track the full A/B is allowed. VOILA! We have seen this demonstrated now in a few videos already cited. JBDs are tough and have been modified or will be modified to deal with the F-35C in afterburner. The transition from less A/B at start to more some way down the track is NOT controlled by the pilot but is in the aircraft software. We have seen photos and videos of F-35C pilots with BOTH Hands on the grips forward. The throttle is NOT mechanical but software controlled - there are explanations about the throttle on this forum. Are any more internal links required?

On page three this thread there is a PDF link about these 'catapulting matters' (page 7 has the second page explanation from the amiable butler about variable A/B when catapulting (quote below): viewtopic.php?f=56&t=52566&p=357924&hilit=read#p357924
F-35c & Hornet Catapulting Info 08dec2016 pp105.pdf
download/file.php?id=23937 (PDF 10.85Mb)
"...Super Hornet engineers gained valuable experience during JBD trials that led to a change in how the aircraft is launched. During testing, hot air was inadvertently recirculated into the air intake of the Super Hornet, prompting a “pop stall,” or hiccup in the airflow for the propulsion system. The result was a dangerous fireball coughing from the back of the Super Hornet, says Briggs.

The design fix was the creation of a limited afterburner setting for launch. Engineers crafted software such that the engine is at 122% of military power when a pilot sets it to afterburner. By the time the jet reaches the edge of the deck, the system automatically opens the throttle to full afterburner at 150% of power without intervention by the pilot, says Briggs.... ...Because of this lesson, the limited afterburner setting was designed into the F-35 in its infancy...."
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Unread post22 Jun 2018, 23:14

I don't think any of you have actually been near a compressor surge/stagnation/stall event or AB blowout. The noise in that video above (sorry I only watched the one) is not a stall. It sounds like a mechanical thud.

Compressor stalls are much MUCH louder, and would have been accompanied by a significant fireball and or complete loss of AB.

Stall or AB blowouts events with the PW-220/229 series will cause the DEEC to command immediate AB cancellation and AB inhibit until the throttle is recycled to MIL and back into AB range.

Here are some examples;
https://www.youtube.com/watch?v=jFiaT1yIKOM
https://www.youtube.com/watch?v=KrErfnFEjx0
https://www.youtube.com/watch?v=mQNUrYoFM2E
https://www.youtube.com/watch?v=x51UYlumFS8 @4:20 mark

Keep 'em flyin' :thumb:
TEG
[Airplanes are] near perfect, all they lack is the ability to forgive.
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Unread post23 Jun 2018, 01:23

Thanks 'TEG' I'll check out the videos. Probably the original sound was not synchronized (as surmised in another thread), with perhaps the 'thud' being something catapult related (shuttle hitting the end/water brake?) or just 'a noise' introduced by the very loud partial A/B messing with the sound recording device (feedback/over loud freqOut). Then repeats <sigh>
RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
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Unread post24 Jun 2018, 10:16

I had one in the late 80's on a P&W engine.

Transfer from EEC to BUC and BANG! ! ! => Flame on the back, flame out in front, dirty pants, but the engine recovered.
Every flag on the EHR was tripped.

A couple of years later, i was on the ground looking at our F-16 demo training.
Slow speed High AOA pass, pilot going to burner and BANG !!! + Flames from the nozzle, flame out in front.
Guy did the right thing, back to mil, stabilise and land.

The BANG! is a real BANG, you can not miss it..
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Unread post24 Jun 2018, 10:42

Funni Wot Youse Found Wen Not Lookin' - lots of variable catapult F-35C engyn info here. I should put this on the top of me list eh: viewtopic.php?f=57&t=28046&p=314601&hilit=Hornet+Catapult+stall#p314601
F-35 Joint Strike Fighter (JSF) 2015
Jan 2016 DOT&E

"...F-35C [PROBABLY BEST TO GO TO THE REFERENCE URL ABOVE FOR ALL OF IT (over and over/out)
... In addition to the principal goal, the test points addressed: [page number 77] NOW ATTACHED!

▪ Minimum end airspeed for limited afterburner and military power catapult launches. For catapult launches that use afterburner, engine power is initially limited to less than full afterburner power while the aircraft is static in the catapult, but then automatically goes to full afterburner power once released. This power limitation was in place to reduce thermal loads on the Jet Blast Deflectors (JBDs) behind the aircraft. [Variable A/B is by DESIGN similar to that of the Super Hornet and experience of same so we can add the amiable Butler reference not noted by DOTE]…

...- Flight deck JBDs may require additional side panel cooling in order to withstand regular, cyclic limited afterburner launches from an F-35C. JBDs are retractable panels that re-direct hot engine exhaust up and away from the rest of the flight deck when an aircraft is at high thrust for take-off. Even with this additional cooling, however, JBDs may be restricted in how many consecutive F-35C limited afterburner launches they can withstand before they will require a cool down period, which could affect the launch of large “alpha strikes” that involve every aircraft in the air wing, a combat tactic the Navy has used frequently in past conflicts. F-35C limited-afterburner launches are required when the F-35C is loaded with external weaponry and in a heavy, high-drag configuration. The Navy estimates that an F-35C will have 3,000 catapult launches over a 35 year expected lifespan, but that no more than 10 percent of these launches will be limited-afterburner. [General idea of V A/B: viewtopic.php?f=22&t=27772&p=299447&hilit=variable+afterburner#p299447 ] [More on the V A/B for both aircraft: viewtopic.php?f=57&t=26634&p=281244&hilit=variable+afterburner#p281244 ] & [ a goodly explanation here: viewtopic.php?f=22&t=15953&p=201921&hilit=variable+afterburner#p201921 ]

Source: http://www.dote.osd.mil/pub/reports/FY2 ... f35jsf.pdf (1.1Mb)
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2015frontcover.png
RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
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