Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 19:58
by steve2267
I am creating this thread for discussion of the Low Observable nature of the F-135 engine to avoid the sidetracking of the DT-III aboard USS America thread.

quote="SpudmanWP"]Is this a 1st public view of the radar blockers up the tailpipe???

Image[/quote]

spazsinbad wrote:Chain Me Up & that Rear End View (BLOCKED by Censors) fillum attached


I saw this a week or two ago in a (possibly different) video, but didn't take the time to try to screenshot the frame and post.

This is the first view up the tailpipe I've seen of the F135 engine. IMO we are seeing the aft end of the low pressure turbine. I think the term "radar blockers" is misleading. I can't think of sticking some fixed thing in the back end of a turbojet or turbofan engine that would "block radar" without also wreaking havoc on the flow qualities of the engine exhaust and hence the thermodynamics and the efficiency of the engine.

The objects extending radially from the conical hub at the center of the engine appear consistent with vanes such as you see on an old fashioned wind mill on a farm. That is, they sure look like low pressure turbine vanes. I suppose you could put something in the back designed to "deflect radar" -- bounce the radar into the sides of the engine and shape the engine to try to trap the radar inside the engine similar to how the air intakes are shaped to also trap radar -- but let it spin around like a wind mill. Still, if you don't extract any energy from the "spinning", you are just creating blockage / drag inside the engine.

So IMO this is the rear of the low pressure turbine. And I expect shaping has been applied to the rear of the turbine, possibly to the consternation of the engine fluid dynamicists, to deflect radar into the engine sidewall, which itself has been shaped to "trap" radar reflections in the engine itself. I would also guess that some sort of ceramic coating(s), probably high in iron ferrites, have been applied to the rear of the low pressure turbine blades along with the interior of the back of the engine, to absorb the radar. The conical-shaped hub at the center of the engine is probably also shaped to reflect radar into the engine sidewall to prevent it from reflecting back out the end of the engine. Shaping the aft end of the engine to "trap" radar would be consistent with some statements from pilots and others that the F-35 possesses true all-aspect stealth.

I would not be surprised to learn that the Skunk Works guys "coached up" or otherwise assisted the P&W engineers in stealthifying their motors, as their relationship dates back to at least 1995 when LM entered into an exclusive arrangement with P&W whereby P&W would only work with LM on a shaft-driven lift fan engine.

Lastly, notably absent is a lack of afterburner flame holder structure in the aft end of the motor. I seem to recall videos of multi-stage afterburners lighting off. (I may be recalling a video sequence of an F-14 catapult launch in Topgun where you see multiple stages of the afterburner lighting. Now I cannot recall what I saw looking in the back of an F-16 at an airshow... Do F-100 / F-110 / modern 4th gen afterburning jet engines have some sort of flameholder structure in the back of the engine related to afterburner usage? If so, I would think that would be a radar reflector par excellence.

Several posts / papers have noted that the F135 implemented the afterburner in a new manner to avoid radar signature problems.

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 20:06
by SpudmanWP
steve2267 wrote:So IMO this is the rear of the low pressure turbine.


That's what I fist thought but .... where are the AB holders??

The only decent pic of a F135 cutaway is this one which shows the burners coming after the last LP turbine. Has anyone ever made them come before the turbines before? Looking at other engine cutaways I have yet to fine ones with such large blades as the last stage as in the F135 pic above.

Image

For a comparison, here is the F100

Image

One last question... In the above pic that I posted, is the F35 engine on since there are no hold-down chains and it's not under tow?

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 20:22
by steve2267
SpudmanWP wrote:
steve2267 wrote:So IMO this is the rear of the low pressure turbine.


That's what I fist thought but .... where are the AB holders??

The only decent pic of a F135 cutaway is this one which shows the burners coming after the last LP turbine. Has anyone ever made them come before the turbines before? Looking at other engine cutaways I have yet to fine ones with such large blades as the last stage as in the F135 pic above.

Image



I thought I had read they had somehow embedded the F-135 3-stage afterburner into the sidewall of the engine? I'll go see if I can find the quote. It may be in a PDF from a magazine or webzine article.

I have seen that F-135 cutaway image before, but never paid close attention. Based on your comment, it is very possible that what I am alleging is the low pressure turbine is not, in fact the low pressure turbine. I'm still having a tough time believing they (engine designers) would turn the engine flow through those vanes with the vanes being fixed. I would think that would be terribly inefficient, and very stressful from a materials (and weight) point of view. On the other hand, if they do spin, and they spin freely (aren't connected to anything), I would think they get up to a gawdawful high spin rate, which again introduces all sorts of stress issues, especially with such large span vanes.

The only other though that occurs to me is that if they are fixed, then perhaps the flow velocity in that part of the engine is not that high, and most flow acceleration, especially in reheat, occurs downstream of those blades / vanes?

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 20:53
by spazsinbad
The first page of this thread has the quote about the possible/variable/3-stage AfterBurner (their guess) + PDF:

viewtopic.php?f=56&t=25691

Engine F135 & LiftFan STOVL F-35LightningII pp6ed.pdf
download/file.php?id=19133 (PDF 1.5Mb)
Powering the Lightning II
April 2012 Chris Kjelgaard

"...Another key feature of the F135 is its augmentor, or afterburner system. While available details of the augmentor are sketchy, the F135 is known to employ multi-zone (probably three-zone) fuel injection aft of the afterburner’s pilot light. These zones inject fuel independently, so that the afterburner does not act in an all-or-nothing way but instead provides a variable range of additional, smoothly transitioning wet thrust at the pilot’s command. 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 14Mb)

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 21:02
by SpudmanWP
So what we are seeing appears to the the AB Augmenters themselves.

Thanks for connecting the dots...

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 21:15
by steve2267
SpudmanWP wrote:So what we are seeing appears to the the AB Augmenters themselves.

Thanks for connecting the dots...


Yeah, I think you are correct. "Curved vanes" in Spaz' quote would seem to be the clincher.

I still am having difficulty wrapping my brain around the flow blockage / drag that the vanes would seem to cause.

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 21:18
by spazsinbad
We know from other material that there is a variable afterburner catapult shot to stop 'engine pop stalls' (new name for 'popcorn'?) [by ingesting catapult steam] similar to Super Hornet method devised - both all automatic during catapult.

I guess I can make a new video showing the variable launch with the added 'up the tailpipe view'? No? This is an OLD ONE.


Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 21:23
by SpudmanWP
Looking at that vid (thanks again Spaz), I can see tiny static "fingers of flame" (ie dark & light bands) coming from the augmenter so it seems that it does not rotate. That being said, the curvature can be gentle so as not to impose too much restriction to the flow.

Next question.. how much torque does this flow impose on the engine?

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 21:52
by spazsinbad

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 22:07
by optimist
one thing for certain is that it isn't an AB spray bar, the F-35 doesn't have one.

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 22:22
by madrat
If the stator is in line with the exhaust vortex it blocks line of sight with augmentation without impeding gas expansion. Maybe it's ceramic on one side with space shuttle tile material on the backside to resist infrared emissions

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 22:25
by sferrin
Has an integral spraybar/radar blocker, just like the F119 on the F-22.

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 22:40
by steve2267
optimist wrote:one thing for certain is that it isn't an AB spray bar, the F-35 doesn't have one.


Regarding no AB spray nozzle... I think we have come to the conclusion that the curved vanes, seen from behind the aircraft in the above video screencapture , is the engine augmenter. So it is the spraybar, if you will, it just looks like nothing we've come to expect as far as conventional afterburner plumbing.
spazsinbad wrote:
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 14Mb)
Engine F135 & LiftFan STOVL F-35LightningII pp6ed.pdf
download/file.php?id=19133 (PDF 1.5Mb)

Re: Low Observeability of the F-135 engine

Unread postPosted: 07 Dec 2016, 22:49
by steve2267
madrat wrote:If the stator is in line with the exhaust vortex it blocks line of sight with augmentation without impeding gas expansion. Maybe it's ceramic on one side with space shuttle tile material on the backside to resist infrared emissions


If I'm understanding you correctly, if there is significant swirl in the flow as it comes aft off the low pressure turbine (LPT), you could design a stator (i.e. a row of static vanes) to straighten out the flow, and at the same time, the stator blocks the view of the engine upstream of the stator. While they were at it, they figured out how to inject fuel into the flow using the stator vanes, thus killing a few birds with one stone.

Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 02:22
by sferrin
optimist wrote:one thing for certain is that it isn't an AB spray bar, the F-35 doesn't have one.


Yes and no. From AW&ST 3/17/11:

Pratt says screech is a phenomenon caused by pressure pulsations in the afterburner at low altitude and high speed. The problem was discovered during development testing around March 2009, having previously been encountered - and solved - in the F-22's F119 engine, from which the F135 is derived.

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.

Building on its experience with the F119, the fix for the F135 includes "minor hardware changes to the fuel system, reduced aerodynamic leakages and upgraded software," says Pratt, adding that the modified engine "now provides full max augmented thrust throughout the flight envelope."

Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 03:05
by spazsinbad
:devil: SCREECH - I thought it was an AFB somewhere? :doh:

viewtopic.php?f=56&t=15287&p=193006&hilit=Screech#p193006
Screech, the F135 and the JSF Engine War
17 Mar 2011 Graham Warwick

"For those of us who thought screech was the noise made by GE/Rolls and Pratt & Whitney in their war of words over the JSF second engine, here's the background to comments made this week about screech problems with the F-35's F135 engine.

Testifying before the House Armed Services Committee on Tuesday, JSF program executive officer Adm David Venlet said afterburner screech on the F135, which prevents the engine from sustaining full thrust, "caused us to avoid certain portions of the flight envelope." Instead, F-35s have flown to other points in the envelope to keep flight-test going. Kits are being installed to overcome the problem, he said.

So what is screech and what's the fix?

Pratt says screech is a phenomenon caused by pressure pulsations in the afterburner at low altitude and high speed. The problem was discovered during development testing around March 2009, having previously been encountered - and solved - in the F-22's F119 engine, from which the F135 is derived.

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.

Building on its experience with the F119, the fix for the F135 includes "minor hardware changes to the fuel system, reduced aerodynamic leakages and upgraded software," says Pratt, adding that the modified engine "now provides full max augmented thrust throughout the flight envelope."

A kit has been developed for flight-test engines, and two have been modified. The production configuration will be validated this year in both the CTOL/CV and STOVL variants of the F135, Pratt says.

I have asked GE/Rolls whether their F136 has a screech-free stealthy augmentor. Watch this space for their answer."

Source: http://www.aviationweek.com/aw/blogs/de ... 0491972939

Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 04:15
by sferrin
spazsinbad wrote:


I did have to laugh. All those guys with the sound gear look like they're hold guitars and with the guitar music playing. :lmao:

BTW that bouncing you see there from 0:03 - 0:18 or so apparently is noticeable enough that it's a "must fix" issue. Don't recall where I read that specifically, but it was in some article today or yesterday. Probably in the one where they were implying a "cover up" on the F-35's progress. :roll:

Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 04:51
by spazsinbad
The chaps with 'air guitars' (sound recorders) are noted in the F-35B DT-III thread here: viewtopic.php?f=22&t=52450&p=356960&hilit=CERTIFIED#p356960 & viewtopic.php?f=22&t=52450&p=356578&hilit=grab#p356578 & viewtopic.php?f=22&t=52450&p=356506&hilit=guitars#p356506

Yes the bouncing catapult pilots have been commented upon ever since carrier catapulting videos were made available - first I have heard about it being a problem on the DOT&E 'maus92' memo thread. A thread about the wheels/nosegear says the NG is storing energy during the cat stroke to help lift the nose up OFF the catapult. I'll go find it. Look at this post & entries above also....

viewtopic.php?f=60&t=52449&p=356203&hilit=complication#p356203
&
viewtopic.php?f=60&t=52449&p=356205&hilit=Robust#p356205

Look at 'milestone F-35C' thread for slomo catapult pilot jerking action - one pilot even forgets to secure the visor which flies up under stress.


Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 05:03
by neptune
sferrin wrote:
spazsinbad wrote:


I did have to laugh. All those guys with the sound gear look like they're hold guitars and with the guitar music playing. :lmao:

BTW that bouncing you see there from 0:03 - 0:18 or so apparently is noticeable enough that it's a "must fix" issue. Don't recall where I read that specifically, but it was in some article today or yesterday. Probably in the one where they were implying a "cover up" on the F-35's progress. :roll:


...the bouncing appears to initiate at the release of the cat and stabilizes as the F-135 goes to max throttle...per Spaz's visor video..if the pressure on the nose strut is modulated then this indeed could be tuned out by software....
:)

Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 05:26
by spazsinbad
One would have to read the last to posts at the URLs in my last post above to gain detail about F-35C (& Shornet) nose gear. Without GILMORE saying more about what the problem is with the nose gear (I have not seen any other official negative comment about it) then we can only guess about cause/effect/cure or whatever is needed. Meanwhile I petition GILMORE to fix the bouncing boys in the Shornets as seen in this video:


Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 08:55
by neptune
spazsinbad wrote:One would have to read the last to posts at the URLs in my last post above to gain detail about F-35C (& Shornet) nose gear. Without GILMORE saying more about what the problem is with the nose gear (I have not seen any other official negative comment about it) then we can only guess about cause/effect/cure or whatever is needed. Meanwhile I petition GILMORE to fix the bouncing boys in the Shornets as seen in this video:




...alas, they have no software to fix, me thinks... :wink:

Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 14:19
by sferrin
spazsinbad wrote:A thread about the wheels/nosegear says the NG is storing energy during the cat stroke to help lift the nose up OFF the catapult. I'll go find it. Look at this post & entries above also....


Not sure I follow. There was a program years ago (I believe involving a T-38/F-5) where they used a modified nose gear that was energized and caused the aircraft to essentially, "pop a wheelie" to assist with rotation, enabling shorter takeoffs. Is this the kind of thing you're talking about?

Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 16:55
by barrelnut
From 0:43 onwards you can see what's inside the tailpipe.


Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 19:08
by spazsinbad
sferrin wrote:
spazsinbad wrote:A thread about the wheels/nosegear says the NG is storing energy during the cat stroke to help lift the nose up OFF the catapult. I'll go find it. Look at this post & entries above also....


Not sure I follow. There was a program years ago (I believe involving a T-38/F-5) where they used a modified nose gear that was energized and caused the aircraft to essentially, "pop a wheelie" to assist with rotation, enabling shorter takeoffs. Is this the kind of thing you're talking about?

Not sure what you have said IF you have read the references quoted. To be clear in the case of the F-35C on the catapult.

At this forum URL there is this: viewtopic.php?f=60&t=52449&p=356205&hilit=Robust#p356205
Complex & Robust
Flight International F-35 Special ? 2014? Magazine

"Mark Ayton explains the highly complex landing gear systems used on the F-35...

...The nose gear of the CV variant is a dual stage gas over oil cantilever strut with a staged air curve that provides a source of high energy, which helps the aircraft to achieve adequate angle of attack when released from the catapult during take-off from the aircraft carrier....

...There are two reasons for having a staged shock strut for the nose gear on the F-35C CV variant.... The second is to store energy gained from the compression of the strut under the high pressure effect of the catapult. When the catapult lets go of the launch bar, the energy is released, providing a rotation that helps achieve the angle of attack necessary to get off the deck.

Similarly when the aircraft hits the deck on landing the strut is compressed and energy is stored to help rotate the aeroplane and get it back off the deck if the arrestor cables are missed and a ‘go-around’ or ‘bolter’ is required. Bolter is the term used when the aircraft’s tail hook misses the arrestor cables on the carrier deck forcing the pilot to go around for another landing...."

Source: Not now at original URL - download article here: download/file.php?id=23692 (PDF 1.44Mb)

Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Dec 2016, 19:57
by spazsinbad
'barrelnut' Thanks for headsup about A/B & nosegear compression on catapult - here is a slow motion clip from that video:


Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 00:54
by sferrin
barrelnut wrote:From 0:43 onwards you can see what's inside the tailpipe.



Looks like sparks in the exhaust there at 4:52. :shock: And like a friggin' meteor at 4:58. Like the whole a$$ end of the plane lit up. It's actually lighting up the wingtip vortices at 5:09 :drool:

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 01:37
by sferrin
spazsinbad wrote:Not sure what you have said IF you have read the references quoted. To be clear in the case of the F-35C on the catapult.


Sounds like we might be talking about the same kind of thing. I didn't know it ever went anywhere.

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 02:05
by steve2267
At 6:36 in the video, there is a good view of the nosegear extending during a cat shot. Is this extension the "push" mentioned above to help the aircraft achieve the proper AOA for takeoff?

F-35 Lightning II-CVN-69 Aircraft carrier @ 6:36 on Youtube

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 05:20
by spazsinbad
'sferrin' speak in riddles if you must but I have no clue to what you are referring by using 'it'. I could guess but won't.
"...I didn't know it ever went anywhere."


To answer 'steve2267': You will have to imagine the forces unleashed at the end of the catapult stroke when the shuttle is stopped by the water brake while the aircraft - having been dragged without remorse nose down - is suddenly released. Then while the nose gear is still on the deck the energy stored in that gear pushes the nose up as the aircraft flies off the deck. Yes the nose gear drops down but no energy released in that - the NG is off the deck then and just gravity drops.

I'm making a catapult PDF to fit the file size limit here and found this pic which MAY show the nose wheel just as it is lifting off the deck - I cannot say with certainty however.

http://3.bp.blogspot.com/--8f_CuL0iX8/V ... 8d53_b.jpg

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 06:43
by steve2267
Stoopid questions:

Just to be clear, after the catapult shuttlecock (or whatever you call the doodad dragging the aircraft by its nosegear) releases the nosegear, the nosegear is compressed. As the aircraft rotates, the energy stored in the compressed nosegear strut is magically released and the nosegear exerts an upward thrusting force on the aircraft resulting in an additional nose-up pitching moment, thus helping the aircraft reach the correct AOA / takeoff pitch attitude -- correct?

After watching another video of the nosegear engaging the cat shuttlecock, I see that the bar from the nosegear to the shuttlecock is at a downward angle, so that as the shuttle moves forward, dragging the aircraft behind it, it is also pulling down on the nosegear, compressing it.

I saw the bouncing (i.e. vertical oscillations) of the aircraft at the beginning of the cat shot, but just thought that the F-35C bounces a little more than other aircraft. I recalled other aircraft oscillating too, but maybe not as much. Is it truly "a problem"?

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 06:53
by spazsinbad
I'm working on a laptop which sometimes can be exceedingly slow along with this forum and yet 'soon' the 'catapult PDF' will be uploaded which may answer some future questions. Yes the doodad at the front that is connected to the aircraft that subsequently pulls the aircraft down the catapult track is called the shuttle. There is a more explicit video some where (would you believe in a catapult thread?) why we are talking about this in an LO Engyn thread I have yet to divine but - whatever. Meanwhile a Shornet Video Catapulting in SloMo: watch the 'bouncing baby boyo'

And I have not seen any other info about a 'problem' with F-35C catapult bounce - sure they bounce ANDbut so do other aircraft. Ashore the F-35C has been tested on all the catapults including EMALS why have we not heard about this before?

Here we go - first a slomo first catapult afloat... OK maybe one of the first.... AND lastly but not LEASTLY - HOWL!!!!!!!








Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 07:28
by spazsinbad
You didn't ask for it & no one wants it so here it is.... All you can read about F-35C & some Hornet Catapult Info in 105pp.

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 12:57
by sferrin
spazsinbad wrote:'sferrin' speak in riddles if you must but I have no clue to what you are referring by using 'it'. I could guess but won't.


"It" being the notion of using an energized nose-gear strut to assist with rotation to shorten takeoff. That's what they tested late 80s/early90s on an F-5 or T-38. The tests were successful but then I never heard another word about it.

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 13:07
by sferrin
spazsinbad wrote:And I have not seen any other info about a 'problem' with F-35C catapult bounce - sure they bounce ANDbut so do other aircraft. Ashore the F-35C has been tested on all the catapults including EMALS why have we not heard about this before?


Because we typically don't hear about something until we hear about something. (Which may not be the moment it's noticed. Also, maybe they thought it was something they could live with -all aircraft "bounce" to one degree or another- but subsequently decided they couldn't.) I'll see if I can track it down later. I'm certain it's from the recent report that's been making the rounds though.

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 13:32
by vanshilar
sferrin wrote:Because we typically don't hear about something until we hear about something. (Which may not be the moment it's noticed. Also, maybe they thought it was something they could live with -all aircraft "bounce" to one degree or another- but subsequently decided they couldn't.) I'll see if I can track it down later. I'm certain it's from the recent report that's been making the rounds though.


Or because Gilmore is trying to find new things to complain about to try to show the F-35 program is falling behind as it continues to resolve previously-mentioned problems.

Two years from now he'll be complaining about the shade of gray being used.

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 13:36
by spazsinbad
sferrin wrote:
spazsinbad wrote:'sferrin' speak in riddles if you must but I have no clue to what you are referring by using 'it'. I could guess but won't.


"It" being the notion of using an energized nose-gear strut to assist with rotation to shorten takeoff. That's what they tested late 80s/early90s on an F-5 or T-38. The tests were successful but then I never heard another word about it.

This is what 'johnwill' wrote on another thread recently & pointed to - albeit indirectly - with this reference on page 2:

viewtopic.php?f=60&t=52449&p=356203&hilit=complication#p356203
"Exactly the same functionality for both airplanes [F-35C & Shornet]. As far as I know, all Navy catapult launched airplanes that use nose gear launching use the same process. Bridle launched do not, because they do not compress the nose gear. Even the F-111B I helped test 48 years ago had the same compressed strut design.

Notice the launch bar is connected to the shuttle at a 45 deg angle, so when the the bar pulls on the gear it is pulling forward and down. Look at the F-35C videos and you will notice the airplane nose drops abruptly and oscillates a couple of times as the airplane starts to move. The strut has compressed the air/oil in the cylinder until it hits bottom, then the tire is compressed and causes the oscillation. When the shuttle releases the launch bar, the tire expands and the shock strut is extended, both of which force the nose of the airplane upward to get the desired AoA."

viewtopic.php?f=60&t=52449&p=356206&hilit=compressed#p356206

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Dec 2016, 16:03
by johnwill
I was wrong about the tire being the source of the oscillation. Clearly the strut is also oscillating.
It's easy to modify the oscillation. Just change the diameter of the orifices used to provide damping to the strut. Nitrogen pressure that provides spring force can also be adjusted. What makes it difficult is conflicting requirements for the damping at the start of the cat sequence, rotation, and landing. Like everything else in airplane design, comprises are necessary.

Re: Low Observeability of the F-135 engine

Unread postPosted: 11 Dec 2016, 21:24
by sferrin
Going back to the engine, what exactly is happening here at 4:58? The engine goes from what appears to be maximum afterburner to I don't know what. Almost as if the engine explodes and the whole back end of the fuselage is blocked out by a massive fireball. I'm not saying the engine malfunctioned or anything but something definitely changes there at 4:58, and it stays this way for the rest of the launch and climb out. You can even hear a noticeable *pop*.

Fireball.png



Re: Low Observeability of the F-135 engine

Unread postPosted: 11 Dec 2016, 22:17
by spazsinbad
In several places now there is mention of the F-35C variable afterburner especially codified for catapulting to alleviate 'pop stalls', if steam is ingested during the catapult stroke, especially at beginning as the aircraft starts down the track, one would guess. This variable afterburner was built in from the start from the experience with the Super Hornet which had variable afterburner added AFTER it was first built to again alleviate pop stalls experienced without this function. In the case of the Shornet the A/B is at 125% power before launch going to full A/B at 150% by the end of the stroke. AFAIK we can only guess that a similar situation applies to the F-35C during catapulting. There are now several videos which reference this change from part A/B to full A/B on this forum, usually accompanied by the air guitars I guess to add or listen to the pop stall - if it is there - but of course the noise is what they measure.

In the video I hear a few things particularly the shuttle hitting the end of the catapult track as it is stopped by the water brake. One may wonder how well the sound is accurately synchronised to the video action also. Remember the noise probably overwhelms the video sound recording at that particular time with some sound clipping due to loudness levels etc. The 'clacking' constant rhythmic sound - to me - sounds like igniters sparking off as in engine start but of course that engine has started - this 'clacking' could be audio clipping noise but only my guess. Video CLIP will be on Utube.... now.

Another guess (I have never been near an afterburning engine) perhaps the metal is expanding noisily? These guys know:

:devil: See no evil, Hear no evil, Speak no evil but FEEL THE EVIL :devil:

http://www.dtic.mil/ndia/2007test/Fischer_SessionH4.pdf (6.4Mb)


Re: Low Observeability of the F-135 engine

Unread postPosted: 12 Dec 2016, 03:52
by eloise
spazsinbad wrote:In the case of the Shornet the A/B is at 125% power before launch going to full A/B at 150% by the end of the stroke

125% afterburner ? like higher than the maximum ?

Re: Low Observeability of the F-135 engine

Unread postPosted: 12 Dec 2016, 04:10
by spazsinbad
Agree - deliberately confusing - because I'm tired of repeating this post so here goes.... 2 page article PDF attached.
JBD Testing A Key Step For Joint Strike Fighter
18 Jul 2011 Amy Butler; Aviation Week & Space Technology

"...Even without the more extensive data provided by today’s sensor array, 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.

Having completed the first phase of JBD trials with a single F-35C, engineers are eager to test a more realistic scenario with one aircraft in front of the deflector and one behind.

Because of this lesson, the limited afterburner setting was designed into the F-35 in its infancy...."

Source: http://www.navair.navy.mil/lakehurst/nl ... esting.pdf

Re: Low Observeability of the F-135 engine

Unread postPosted: 12 Dec 2016, 04:30
by sferrin
Yes, but that flame at 4:57 is anything but "minimum after burner". Looks more like maximum here:





What's going on at 4:58 looks like something else.

Re: Low Observeability of the F-135 engine

Unread postPosted: 12 Dec 2016, 04:39
by spazsinbad
Bewdy is in the aye of the beholden - in my video clip at second 18 or thereabouts I see the burner 'popping' to full some short distance down the track. It is similar to the day time video where the same phenomena seen. However if you see the same video differently then so be it.


Re: Low Observeability of the F-135 engine

Unread postPosted: 12 Dec 2016, 04:43
by sferrin
It's not a matter of what I see, the picture speaks for itself. 4:58 is very different than 4:57. 4:57 looks more like what you'd see as "maximum" on the test videos I posted. 4:58 looks like. . .more. :shrug:

Re: Low Observeability of the F-135 engine

Unread postPosted: 12 Dec 2016, 13:22
by optimist
to me it looks like the auto light meter on the camera is being overexposed. As the plane moves, it gets a better look up the pipe, goes overexposed, it then re-adjusts

Re: Low Observeability of the F-135 engine

Unread postPosted: 12 Dec 2016, 14:23
by sferrin
optimist wrote:to me it looks like the auto light meter on the camera is being overexposed. As the plane moves, it gets a better look up the pipe, goes overexposed, it then re-adjusts


Did you watch the video with the sound on? It's definitely NOT a light meter.

Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Dec 2016, 05:34
by spazsinbad
Super Hornet does the auto A/B night catapult dance at beginning of this video (the rest of video not that interesting). Note at the end of the cat stroke the left anti-collision light flash affects the film then the right one flashes as the aircraft lifts off. I'll post an edited version with slo mo of cat soonish. There are cat SusPEnD/BolTer/arrest bits also.


Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Dec 2016, 06:42
by spazsinbad

Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Dec 2016, 15:21
by sferrin
Okay, I'm convinced. :thumb:

Re: Low Observeability of the F-135 engine

Unread postPosted: 10 Jul 2017, 23:28
by spazsinbad
On page one of this thread a '3 stage afterburner' is mentioned whereas in the recent 'test pilot' lecture video the pilot says 'four stages' (when tanking at heavy weight high altitude behind the iron maiden). https://www.youtube.com/watch?v=faxuDFHJ3NY

Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Sep 2017, 01:00
by white_lightning35
https://www.google.com/url?sa=t&rct=j&q ... B18XOIuiMw

FALSE, they will already be dead.

On a more serious note, is there much literature discussing the feasibility of using advanced microphones to perhaps detect stealth jets? I wonder how far these could range, and if they are at all practical.

Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Sep 2017, 05:22
by archeman
white_lightning35 wrote:https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0ahUKEwir7I77sqjWAhWGYyYKHarTBsIQFgg-MAY&url=https%3A%2F%2Ftwitter.com%2Flockheedmartin&usg=AFQjCNGCqNku4ApEigpeRZnSB18XOIuiMw

FALSE, they will already be dead.

On a more serious note, is there much literature discussing the feasibility of using advanced microphones to perhaps detect stealth jets? I wonder how far these could range, and if they are at all practical.


Well how do you know what your listening to?
Just check out for a moment, this graphic of traffic just over Persian Gulf FOR JUST A SINGLE AIRLINE then mentally add in the other Airlines and then add non-stealth military traffic at various altitudes and then try to imagine your advanced microphones trying to sort out all the various sounds echoing around.

I get that you're trying to locate a stealth aircraft that may or may not be out there somewhere but it isn't clear how you could do that without the assistance of a completely empty location for hundreds of miles.

Image

Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Sep 2017, 14:28
by steve2267
archeman wrote:
Well how do you know what your listening to?
Just check out for a moment, this graphic of traffic just over Persian Gulf FOR JUST A SINGLE AIRLINE then mentally add in the other Airlines and then add non-stealth military traffic at various altitudes and then try to imagine your advanced microphones trying to sort out all the various sounds echoing around.

Image


System of systems?

I'm not saying this will work, but...

If you can build a database of acoustics -- a library of acoustic signatures of all known aircraft, if you will -- then build a real-time "map" of all acoustic signatures... simply subtract all the locations of "known" aircraft from sources such as this, then subtract all "radar" contacts of "known" aircraft (e.g. radar contacts of known military jets)... and you are left with a sets of "unknowns" which may, or may not, be stealthy bogeys.

Not saying this would be easy, or in the end be successful, but isn't that how you would have to approach it?

I suppose the first question one would have to ask is if the acoustic sensors are able to distinguish multiple sources from different ranges / bearings. If not, then the problem just got a lot harder.

Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Sep 2017, 18:58
by XanderCrews
sferrin wrote:Has an integral spraybar/radar blocker, just like the F119 on the F-22.


Yup

Re: Low Observeability of the F-135 engine

Unread postPosted: 15 Feb 2018, 23:10
by flateric
some soft porn of F135-PW-600

Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Feb 2018, 16:52
by mixelflick
I thought in years past the Soviet Union deployed a system called, "big ears" to detect incoming American bombers.

Or is that in the same league as "plasma stealth" ?

Re: Low Observeability of the F-135 engine

Unread postPosted: 17 Feb 2018, 12:24
by flateric
Dunno about ears, but plasma stealth tech exists and was used on Meteorit cruise missile, masking inlet.

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 03:15
by elvis1
From the Program Updates Thread at: viewtopic.php?f=58&t=13143&start=435
spazsinbad wrote:
Pentagon And Lockheed Martin Deliver 300th F-35 Aircraft
11 Jun 2018 LM PR

"...The first 300 F-35s include 197 F-35A conventional takeoff and landing (CTOL) variants, 75 F-35B short takeoff/vertical landing (STOVL) variants, and 28F-35C carrier variants (CV) and have been delivered to U.S. and international customers. More than 620 pilots and 5,600 maintainers have been trained, and the F-35 fleet has surpassed more than 140,000 cumulative flight hours...."

Source: https://www.f35.com/news/detail/pentago ... 5-aircraft



I thought that the video at 1:37 really showed the "radar blocker" / AB assembly well. Didn't want to comment in the Program Updates thread for this though.

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 12:18
by spazsinbad
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!



Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 16:57
by ricnunes
mixelflick wrote:I thought in years past the Soviet Union deployed a system called, "big ears" to detect incoming American bombers.


You mean, a system invented by the British during WWI to detect incoming enemy (German) Zeppelins and aircraft?

https://www.thevintagenews.com/2017/02/ ... -aircraft/

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 19:44
by steve2267
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?

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 20:08
by vilters
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.

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 20:14
by steve2267
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.

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 20:33
by SpudmanWP
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

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 21:20
by spazsinbad
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)

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 21:25
by spazsinbad
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

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 23:02
by steve2267
The "POP" seemed to correlate with a sudden increase in flame intensity / AB brightness. Would that happen during a "pop stall"?

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 23:19
by spazsinbad
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!

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jun 2018, 23:22
by Dragon029
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).

Re: Low Observeability of the F-135 engine

Unread postPosted: 20 Jun 2018, 15:46
by That_Engine_Guy
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

Re: Low Observeability of the F-135 engine

Unread postPosted: 20 Jun 2018, 16:09
by spazsinbad
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...."

Re: Low Observeability of the F-135 engine

Unread postPosted: 22 Jun 2018, 23:14
by That_Engine_Guy
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

Re: Low Observeability of the F-135 engine

Unread postPosted: 23 Jun 2018, 01:23
by spazsinbad
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>

Re: Low Observeability of the F-135 engine

Unread postPosted: 24 Jun 2018, 10:16
by vilters
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..

Re: Low Observeability of the F-135 engine

Unread postPosted: 24 Jun 2018, 10:42
by spazsinbad
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)

Re: Low Observeability of the F-135 engine

Unread postPosted: 13 Jul 2018, 23:34
by spazsinbad
POP STALL not mentioned in this F-35C Catapult Overview by USN F-35C Test Pilot (first arrest ever on a CVN way back).
F-35 Carrier Suitability Testing
17 May 2018 Tony Wilson

"...F-35C Control Laws
The F-35 uses non-linear dynamic inversion control architecture that is operated in three redundant Vehicle Management Computers (VMCs) to provide fly-by-wire control. The Control Laws (CLAW) that augment aircraft dynamics and provide stability are common amongst the three variants; however, each variant’s CLAW has been optimized and contain advanced features to reduce pilot workload and provide carefree handling for specific task (i.e. hovering in an F-35B). For the F-35C, these optimizations include, but are not limited to, shipboard launches and recoveries.

A shipboard catapult launch can be divided into three distinct phases: acceleration, rotation, and flyaway. The launch starts with an acceleration. The aircraft is attached to a shuttle on the deck by a launch bar on the nose strut. The shuttle, attached to a steam powered piston under the deck, provides the motive force to accelerate the aircraft to a safe flyaway speed. During this phase, the CLAW prepositions the control surfaces to provide aircraft rotation upon shuttle release. The horizontal tail is scheduled to achieve roughly 12.5 degrees per second of pitch rate at operationally representative aircraft weights, Wind Over the Deck (WOD), and energy imparted on the aircraft by the catapult. Next, the launch bar is released from the shuttle at the end of the catapult stroke; stored energy in the nose strut and aerodynamic moments generated by pro-rotation control surfaces (symmetric horizontal tail trim, symmetric ailerons and toe-in (trailing edge inboard) rudders) combine to provide a smooth and quick aircraft rotation. Finally, during the flyaway phase, the CLAW transitions from pro-rotation to pro-lift to optimize lift and minimize sink once airborne. The pro-lift control surfaces are symmetric trailing edge flaps (TEFs) and symmetric ailerons.

The catapult launch control law logic is evoked when the launch bar is commanded down while the aircraft is on deck; positioning the control surfaces for pro-rotation based on gross weight and the aircraft’s CG. The pro-rotation configuration is designed to achieve a positive flight path as quickly as possible following catapult launch in order to minimize sink. Additionally, catapult launch logic causes a 30-pound throttle detent to engage at the 100 Engine Thrust Request (ETR) MIL gate, Nose Wheel Steering (NWS) is disengaged, and engine AB Limit (ABLIM) is activated. The ABLIM feature is designed to reduce thermal heating of the tail boom, empennage structure, JBD panels, and flight deck. If throttle position is set for ETR > 122% during the catapult launch sequence, ABLIM control logic will automatically limit ETR to 122% power prior to launch. When a catapult launch is declared or longitudinal acceleration (Nx) > 0.5 g, the ABLIM feature will clear, allowing thrust to increase up to the commanded power setting during aircraft acceleration down the catapult track. The Flight Control System (FLCS) uses multiple sensor to provide feedback to the CLAW to declare a catapult launch:

1) ETR ≥ 95% and longitudinal acceleration (Nx) > 2 g or Calibrated Airspeed (VCAS) > 100 kts
or
2) ETR < 95%, wheel speed > 20 kts, and Nx > 2 g or VCAS > 100 kts

As the launch bar leaves the shuttle, the pro-rotation control surfaces begin to be removed as Angle of Attack (AOA) or pitch rate increase to protect from over-rotation. The control system commands 20 degrees AOA initially but backs off to 15 degrees as AOA passes through 14 degrees AOA. This command is then blended back to zero once a one-degree flight path (gamma) is achieved. If AOA and pitch rate do not increase prior to the aircraft rolling off the deck edge, the pro-rotation aids are removed quickly once weight-off-wheels is sensed and replaced with pro-lift aids. Once airborne, catapult launch mode is disabled. The control law reschedules surfaces from pro-rotation to prolift positions in order to minimize sink and to enhance fly-away characteristics.

The CLAW also augments the roll axis during catapult launches. Roll rates and bank angles induced by asymmetries and crosswinds at the deck edge are removed via a launch roll trim mode that commands differential flaps and ailerons during a catapult launch. Launch roll trim activates when VCAS exceeds 100 knots and is reset as the aircraft leaves the deck. Additionally, a bank assist was added to hold wings level on flyaway. Bank assist activates at Weight off Wheels (WoffW) and attempts to maintain a wings level attitude (zero degrees bank angle) during flyaway for 10 seconds. The pilot may override bank assist at any time with a lateral stick input...."

Source: download/file.php?id=27756 (PDF 3Mb)

Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Jan 2019, 14:20
by doge
I found a B type photo, so I will post it.
https://www.instagram.com/p/BssIGDHgrvP/
(It's a photo by an aviation photographer, so It's thought that It's not a Collage or CG.)

Re: Low Observeability of the F-135 engine

Unread postPosted: 16 Jan 2019, 14:38
by spazsinbad
Pic Zoomed

Re: Low Observeability of the F-135 engine

Unread postPosted: 23 May 2019, 10:08
by doge
This is an A model.
It only looks a little bit. (almost! :doh: )

Re: Low Observeability of the F-135 engine

Unread postPosted: 19 Jun 2019, 07:47
by doge
It's A model of Paris AirShow 2019.
It looks faintly... 8) (The whole is...Just a little more...!! :crazypilot: )
Image
Image

Re: Low Observeability of the F-135 engine

Unread postPosted: 04 Jul 2019, 10:17
by doge
This is an A model.
I finally found the overall picture of the A model. 8) (Almost the whole is visible.)
This completed the collection of the A, B, C, 3 type engines. :applause: (but, nevertheless, Perhaps I will continue to collect and search... 8) )

Re: Low Observeability of the F-135 engine

Unread postPosted: 08 Sep 2019, 16:11
by doge
It's looking into this side from the shadow... ┃ 8)

Re: Low Observeability of the F-135 engine

Unread postPosted: 09 Sep 2019, 01:23
by element1loop
One thing that's perhaps being missed here is that it not only blocks the hot section exhaust from direct exposure (and as discussed an RCS reduction, plus augmenter) it will also induce a strong twist in the nozzle's air-flow, which then mixes the outer cold concentric bleed-air in with the central hot expanding core-air, thus rapidly reducing the NET temperature in a dry-thrust exhaust gas before it exits the end of the nozzle. Thereby reducing dry-thrust IR signature via both a direct shielding, and an indirect air-mixing means.

Re: Low Observeability of the F-135 engine

Unread postPosted: 01 Oct 2019, 10:37
by doge
Bokeh. 8)
F-35 AF-87 Switzerland June 7, 2019.jpg
F-35A engine.jpg


B of MCAS Miramar Air Show 2019.
F-35B MCAS Miramar Air Show.jpg
F-35B engine.jpg

Hello~. 8) (Look in)