F-35B Lift Fan Drive Question

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I've been answering questions about jet engines since 2007, and this is one of the best ever. Let's squeeze our minds into goo over this one!
If you work on or with the F-135 engine, maybe you can share a bit of info.
If you are not in the know, but think you might have an idea... post at your own risk.
The basic question is "where does the power go?", when the lift fan is disengaged.
If you ignore that point, well...

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14 ноя 2023

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Комментарии : 144

@AgentJayZ 7 месяцев назад

Welcome to Jet City! If you are wondering where your comment is, read the description.

@hoilst265 7 месяцев назад

I was just glad you weren't tased and dragged off by men in dark grey suits and sunglasses at the end, with the last thing we see is them putting their hand over the camera lens before it cuts to static...

@Mentaculus42 7 месяцев назад

@@hoilst265 Why would that happen? The question has not been answered, and certainly no “secret sauce” has been “spilled”. If anything, it proves that the civilians are not supposed to know. AND if secret sauce might be spilled, maybe this is a cautionary example of the wrong question to throw out and get people to speculate on, even if we are not supposed to speculate.

@nadahere 3 месяца назад

The answer is simple. The engine is not oversized because the VTOL phase power requirement is obviously not greater than the power required for forward flight which has a drag component that is not present during the VTOL phase. When I researched the lift fan system some years back, a dog clutch was mentioned in the drivetrain engagement. I don't know if that was an authoritative source so can't vouch for the veracity. With language being imprecise, that could probably mean a one way clutch, sometimes called an overspeed clutch, where metal rollers are located between two concentric rolling elements [somewhat resembling a roller bearing] that wedge themselves between these elements to act as one for power transfer/transmission. I suspect that the clutch requires frequent replacement due to the large forces present. We have patented a torque dense [i.e. compact], infinitely variable [for gradual power transfer], high speed & torque, hydrodynamic transmission/coupler [torque converter] that would significantly reduce this frequent servicing. We have also patented a simple, infinitely variable, torque dense, positive engagement, transmission which does not utilize involute/spur gears. It is called 𝔽𝕣𝕚𝕔𝕥𝕚𝕠𝕟𝕃𝕖𝕤𝕤 𝔾𝕖𝕒𝕣 © transmission and is based on our reformulation of gearing theory. In e-VTOLs the use of either allows significantly smaller motors and batteries for same performance/application. Similar benefits are derived in turbo-engine apps with smaller, lower cost, more efficient engines along with other features & benefits. FYI, in the near future, we will bring out tech which enables antigravity with propulsion apps including interstellar travel, rendering all else but museum pieces/dinosaurs. If anyone can hook me up with SpaceX or any of Musk's companies, Pratt & Whitney, etc. to improve many of their offerings, we'd each benefit greatly. ヅ BTW, I'm a triple engineer, CE, ME, AE with penchant for nanotech, quantum biology, quantum physics, astrophysics and cosmology, among other things. ヅ PS. Excellent channel. TnX. Cheers ✈✈✈ 𝕄𝕀𝕃𝔸ℕ✈✈✈

@CrudeLuthier 7 месяцев назад

This was one of those ideas that hits all at once, essentially complete. I was headed to toddy time after a day of making guitars. Had my cup of box wine and a bag of chips. Somewhere between bending knees and hitting sofa cushion, I went "how the hell?" I'm just glad you didn't call me an idiot, but I can accept "best question ever", at least until you get a better one. Good show.

@TheSadDuck 7 месяцев назад

Seems trivial in a perfect world, but thank you for saying "you don't know." A sign of a master. Cheers!

@grahamj9101 7 месяцев назад

Greetings from your friendly neighbourhood gas turbine designer (retired)!. I did actually see a little bit of what was happening with the F-35B project at Rolls-Royce Bristol in the last few years before I dived out through the escape hatch - but I didn't see much as it was happening in a separate secure area. The lift fan, the so-called roll post system for attitude control, and the 3BSM swivelling jet pipe (I can't remember what the initials stand for), but not the variable nozzle, were all designed at Bristol. However, I believe that they have long since been transferred to Indianapolis. I vaguely recall seeing a general arrangement of the engine, and I have the impression of a variable NGV arrangement in the turbine - but it's only an impression and I could be wrong. You really do need someone from P&W to spill the beans on this one - if they can. I've recently seen a TV series here in the UK showing F-35Bs (both British and American) taking off and landing on HMS Queen Elizabeth. Engaging the fan and partially swivelling the nozzle, then opening up for a rolling take-off, using the ski jump, wouldn't be too difficult - unless someone leaves an intake blank in place and the aircraft takes a dive off the ski jump (yes, that was shown in the series). However, what happens for a vertical landing - as the F-35B can only land on a carrier vertically? There must be some clever controlled synchronisation of the movement of the nozzle and the thrust from the lift fan, otherwise the aircraft would fall out of the sky.

@Mentaculus42 7 месяцев назад

Many thanks for your contributions over the years. Taking the explanations provided by AgentsJayZ and the “enhanced” information provided by you has been a great educational experience. Does the F-135 engine have a “traditional bypass ratio” of a “turbofan” engine? Or maybe more accurately something like that found in the GE XA100 variable / adaptive-cycle engine? The possible use of as you noted; “I have the impression of a variable NGV arrangement in the turbine - but it's only an impression and I could be wrong.” Would not the use of variable area nozzle guide vane (VANGV) be consistent with the need for adaptive cycle engines to be able to vary the mass flow rate through the engine core (and still optimize for reasonable turbine efficiency with varying core flow velocities that would impinge upon the turbine blades if not “corrected”)? From a paper that talked about (VANGV) technology, it was noted that: “Variable area nozzle guide vanes were studied for different applications, such as turboshaft heavy duty gas turbines. Niche applications are tank main engines (AGT1500 and GTD-1250). Some applications exist where marine and industrial applications are benefitting from efficient operation at partial load.” Is this correct?

@bradbelcher338 7 месяцев назад

3BSM stands for 3 Bearing Swivel Module. I did some work on the liner system at a company I used to work at.

@DScottDuncan 7 месяцев назад

Good to hear from you and hope all is well. Thank you for the insight explanation of the fuzzy stuff... your knowledge is a treasure! DD

@Mentaculus42 7 месяцев назад

An unreliable reference stated that the bypass ratio on the F-135 was TWICE that of the engine it was derived from.

@frankely6378 7 месяцев назад

The Wikipedia entry on the PW F135 engine cites this article '"Genesis of the F-35 Joint Strike Fighter" Paul M. Bevilaqua, 2009 Wright Brothers Lecture, Journal of Aircraft, Vol. 46, No. 6, November-December 2009' when stating "The low pressure (LP) turbine drives the lift fan through a shaft extension on the front of the LP rotor and a clutch. The engine operates as a separate flow turbofan with a higher bypass ratio. The power to drive the fan-about 30,000 shp (22,000 kW)-is obtained from the LP turbine by increasing the hot nozzle area." So it sounds like they are using variable nozzles in the turbines to manage LP turbine output.

@ddegn 7 месяцев назад

Thanks for the info. Does anyone know what is meant by "increasing the hot nozzle area"? What is a "hot nozzle"?

@Mentaculus42 7 месяцев назад

@@ddegn Followed the rabbit down that hole also and asked myself that exact same question! What are they talking about exactly? I suspect that is in reference to increasing the mass flow through the core by varying the bypass ratio within the compressor stages in a variable cycle engine. The GE XA100, a probable replacement for the the existing non lift-fan version of the F-135 engine, has a three-stream adaptive cycle design can direct air to the bypass third stream for increased fuel efficiency and cooling or to the core and fan streams for additional thrust and performance. So if one goes through the history of the different engines that were considered for the F-35 and the engines that they were derived from, so what happened to the dual stream engines. Possibly the Pratt & Whitney F135 is a dual variable stream engine and when full power is needed a larger amount or air is diverted through the core which works in combination with increasing the hot nozzle area. Have more to say about this but no time at the moment. The F-135 engine has some serious compromises to be used as a power source for the lift-fan and the military are actively developing a more efficient engine for the A & C models of the F-35 to achieve a larger mission range which is badly needed for the Navy version! Will try to expand on this later.

@anythingsoccerpro1844 7 месяцев назад

Hot nozzle area is the nozzle that redirects right before the HPT after the combustion section.

@Mentaculus42 7 месяцев назад

@@anythingsoccerpro1844 But the terminology of “increasing or varying the area” of the hot nozzle is very interesting. As I can only assume that is due to something changing upstream, like more air flow OR more fuel burn but with constant air flow OR both to avoid overheating but generate more power. I go with the both which then requires the ability to push more air through the core, which is an acknowledged “mode” or capability of the follow on engine that is probably going into future F-35 A & Cs.

@grahamj9101 7 месяцев назад

@@anythingsoccerpro1844 The term 'hot nozzles' was used for the two rear nozzles of the Pegasus in the Harrier. However, I certainly wouldn't use the term for the (first stage) HP NGVs.

@axelknutt5065 7 месяцев назад

It’s comforting to know that it’s not just me, who have to close their eyes, draw with their hands, to visualise the mechanics of the inside of a jet turbine (about 5 mins in) - if Jay Zed has to do it, we all can with no shame!

@LiveLearnProjects 7 месяцев назад

The engagement and disengagement of the clutch isn't a random event, unlike a shaft breaking. It's a predictable input to the system. I think the not so clear answer lies in what the control system is doing to compensate fuel and other inputs to best stabilize RPM before, during, and after the event. I read it takes 2.5 seconds for the clutch to operate. I imagine a lot of those inputs are changing rapidly in this transient period to best predict and maintain RPM stability with the change in load.

@afterburner119 7 месяцев назад

I could talk hours and have horror stories about the RR LF Clutch system 😂. As they wear they cake that carbon everywhere. Learned the hard way you dont drop a washer while doing hysteresis probes on a RR LF. P&W had to buy me a new pair of jeans.

@AgentJayZ 7 месяцев назад

Hey! I didn't say it in the video, but I was hoping to hear from you.

@glensanford2665 7 месяцев назад

I would on the F35 in forward flight transitioning to vertical landing. In flight when top flap and lower duct are opened there would be a significant airflow into the lift fan. The top flap has significant forward tilt to help direct airflow down through the fan. This may result in significant windmilling of the lift fan thus reducing the RPM differential on the engagement clutch.

@afterburner119 7 месяцев назад

The best answer I can publicly give Jay is modes. Just research modes of operation ; f-35b. Will probably find some good CRS Reports about it. Its the entire powered lift system working as one, cause you must continue to provide enough cooling air at various profiles etc. All 3 airframes had to have a common GG as well, which goes back to the design/size question. Cheers @agentjayz

@Mentaculus42 7 месяцев назад

Good tip on CRS Reports & GAO also has something to say about F-35. Some here might find CRS REPORT “F-35 Joint Strike Fighter (JSF) Engine Options” interesting with wording of “to provide the necessary bleed air, the engine was required to run hotter, and early engineering assessments suggest that this increase in operating temperature could decrease engine life, driving earlier depot inductions and an increase in life cycle cost." AND “higher running temperatures, have caused accelerated coating distress on the blades." AND "some degradation in performance would be experienced to accommodate the lift fan that is part of the engine for the [the Marine Corps'] F-35B [variant]." AND “P&W states that the EEP [AN UPGRADED F-135 ENGINE] would mitigate current sustainment issues with the F135, meet the needs of the Block 4 version of the F-35, and provide $40 billion in lifecycle savings.” AND {FROM ANOTHER REPORT} “Current Aircraft Cooling System Demands Exceed Its Original Design requiring additional bleed air causing increased core temperature and significantly increased maintenance”!!

@theoriginalcitrussky062 5 месяцев назад

My head has been going squishy for the past few months trying to figure this out as well, and all the information I can ever find says exactly what your guy said, a forward shaft, a vertical lift fan and clutch like, duh. I started to think that there is no separate shaft or turbine for powering the fan so you’re explanation definitely makes me feel better. I’m no where near as intelligent or mechanically savvy as yourself and forget about experience actually touching a jet engine, I have none, but I’m glad I was close……and I’m happy that you could clear up a little bit of the mystery with this engine and it’s lift system

@two6520 7 месяцев назад

Wow a question that The Great Agent Jay-Z doesn't know. This is the first time I've seen him with no answer. He is human after all. Cheers mate

@Larpy1933 7 месяцев назад

Wonderful! Thank-you sir.

@andrewpbarry 7 месяцев назад

the gas generator is common between the A,B, and C models. It would mean really overbuilding the engines for 95% of the aircraft for the rare B model.

@acefighterpilot 7 месяцев назад

I don't know the answer, but I think a key hint is that the F135 generates less total thrust in horizontal flight than vertical flight. In horizontal flight, the F135 produces 28k lbf dry, whereas in the vertical, the F-35 hovers on 20k lbf from the lift fan, 18k lbf from the swivel nozzle, and 4k lbf from the roll posts. I think this tells us that in STOVL mode, the F135 functions as a high bypass turbofan of a given power, and produces the same power in the horizontal, but with less thrust due to lower bypass (and lower bypass generally means faster turning).

@compactc9 6 месяцев назад

Interesting! I had to find a picture of this thing, and it all looks like it has to work the way you described. It was definitely designed to have the extra power to run the fan in addition to normal thrust at the rear of the engine.

@zapfanzapfan 7 месяцев назад

Good question! There must be a compromise made somewhere in the design. Is it known if the engine has water injection? Harrier Jump Jet used water injection to allow a higher power setting for takeoffs and landings. It could carry enough water for 90 seconds.

@Mentaculus42 7 месяцев назад

P&W acknowledges “some degradation in performance would be experienced to accommodate the lift fan that is part of the engine for the [the Marine Corps'] F-35B [variant]." So the A & C aircraft have compromised engines to have commonality with B version! Thus the heavy push for a new engine!

@davidshutt2273 7 месяцев назад

I guess we won't be seeing an exploded pictorial for that anytime soon. Thanx JZed

@deSloleye 7 месяцев назад

Pity you don't want guesses. This is a really, really great question with a few possible mechanisms. Most of them are interesting.

@keithsharratt3402 7 месяцев назад

The operative word that comes to my mind , "blend"

@Guysm1l3y 7 месяцев назад

"I don't know" is a perfectly good answer for a question like this. Rather than speculating or guessing while pretending to know, walk people through the crux of the question. Great video! And knowing Rolls Royce, I bet it's a clever solution, whatever it is. As far as how to engage the fan clutches when flying, I'm 75% sure I heard a test pilot in one of the JSF documentaries talk about how the fan door (that goofy scoop shaped thing) actually directs air down through the fan to get it spun up before the clutches engage. Another point: keep in mind that most of the engine's bypass air is directed out to the "roll post" nozzles in each wing during hover mode to generate a non-trivial amount of thrust. That could play into how the balance is maintained with the gas generator section.

@Mentaculus42 7 месяцев назад

Without some proper speculation based on some extrapolation of the few clues available that allow one to iterate over reasonable technical solutions, it will be difficult to have some fun. It is educational to go through the process with the input from knowledgeable sources.

@gordonlawrence1448 7 месяцев назад

Engine management systems have changed silly amounts in the last 20 years. I can't go into too much detail other than to give some example specifications of the microcontrollers that could be used for such systems. Microcontrollers used to run at about 10MHz back then. DSP's (sometimes used in high performance control systems) a bit faster. When the ECU was being designed there were microcontrollers running at 100MHz+ so the same code would run in 10% of the time. DSP (digital signal processors) have also got way faster. The architecture of motor controllers is they do everything in a loop and a "watchdog timer" makes sure they do not go nuts and lock up by starting the software from scratch if it is not reset. Reseting the watchdog is the last thing to happen before the software starts again. There were already FPGA's out there which could also be configured as a microcontroller. More expensive but with the advantage of being capable of effectively changing the CPU through firmware updates. The systems I worked on were for high performance rally cars. These had a watchdog as fast as 10ms. Theoretically that would mean 1ms loops were possible then and about 0.5ms loops possible now. If the fan speed is being monitored then as soon as it is accellerating due to disengaging the lift fan then fuel could be reduced to reduce the RPM of the engine. Even if the software is 10 times longer for a turbofan engine compared to an ICE (I doubt is as there are some things that do not need to happen in a Turbojet EG spark timing) and possible a few more things happening. I would guess (wild stab in the dark) that the software is about twice as long. So say worst case 5ms loop. That would mean that in an engine spinning at 12,000 RPM (to keep the maths easy) you would have 200 revolutions per second. So the fuel would be reduced in just 1 revolution

@MacPoop 7 месяцев назад

I have to agree with this; Definitely some uber-modern uber-sophisticated electronic engine control tomfoolery going on in conjunction with mechanical advancement on the mechanical side of things.

@Mentaculus42 7 месяцев назад

I understand what you are saying with regards to the “engine controller electronics & software” (have graduate degree in ME / EE control systems) but the issue here is significantly more complex with regard to “balancing the interchange of power” (along with transitioning) between different parts of the system. AND to do it without overheating parts of the hot section of the core. ALSO, the amount and changes of amount of bleed air on the F-135 engine are impressive. Everything is interacting and “coupled to each other” which makes the “control system” rather nontrivial! The more I dig into the F-135 & F-35 B, the more impressed I am with its COMPLEXITY!! It is rather amazing what it took to improve upon the Harrier Jump Jet!

@stormeagle28 7 месяцев назад

As far as I know about that, the clutch for the lift fan has to be engaged at low engine power and full (needed) engine power (or lift fan load) has to be applied after a mechanical lock on the clutch has been closed, so that there is no load on the carbon-carbon clutch disks anymore. The engine system is very likely working as single-shaft turbine helicopter engines work. They can run idle at full rotor speed and they can deliver output power to the drive shaft at the same rotor speed.

@acefighterpilot 7 месяцев назад

That's because engine torque varies as a function of blade pitch in a helicopter. I don't think there is blade pitch on the lift fan, it's a blisk design.

@stormeagle28 7 месяцев назад

@@acefighterpilot It explains why the turbine engine can work with and without delivering power to the lift fan. The same is true for airliner APU systems, which deliver a lot of horsepower contained in compressed air out of their compressor stages (bleed air) to the air turbine starters on the main engines during engine start. Taking this air out of the APU turbine engine doesn't prevent it from running stable, it keeps running under both conditions.

@louisz7043 7 месяцев назад

Very interesting question! (and congrats on the channel btw). So I came here to post my thoughts but I've essentially been beaten to it by @incandescentwithrage and the patent he linked to. Basically, any form of flow restriction downstream of the LP turbine controls the pressure there and is a very powerful knob to control the speed of the LP spool without affecting the HP section (much). With a fixed nozzle, the geometry of this section is the main way the N1/N2 ratio is set by "finely tuning the flows" as your questioner put it. With a variable nozzle, required anyway for afterburning or thrust vectoring, much more control is possible. In fact the Olympus engines on Concorde scheduled the nozzles to optimise N1/N2 for efficiency during supersonic cruise even though the afterburners were not used in this phase of flight. Since the power extracted by the LP turbine depends on the pressure drop across it, reducing the downstream pressure diverts more power to it at the expense of fan air thrust (because the lower pressure means less expansion to ambient in the nozzle). Its all about shuttling the power round by modifying the airflow, rather than generating more power in the hover. The propulsive efficiency of the lift fan would be greater than that of a jet efflux at low speeds, so you can get a net gain in overall thrust (as pointed out by @acefighterpilot) for the same power expenditure.

@CrudeLuthier 7 месяцев назад

Very cool! This will keep me awake at night. If I understand what you're saying, the lift fan power shaft is a direct extension of the LP section, and it's possible to maintain overall balance in both modes just by clever puckering of the variable nozzle?

@louisz7043 7 месяцев назад

That's my guess anyway. As that patent states, there may be other vents or ramps if the nozzle alone doesn't provide enough variation.

@Mentaculus42 7 месяцев назад

Thought that patent was a good start. ⁠ The patent was quite informative and mentioned that the low pressure turbine can be “unloaded” by decreasing the back pressure from the aft nozzle by increasing its diameter ( thereby increasing the pressure differential across the low pressure turbine allowing for higher power generation). So of course I have spent hours reviewing F-35 Bs transitioning from horizontal to / from vertical configuration and paying attention to what the aft nozzle is doing. The conclusion is the the aft nozzle is somewhat MORE CONSTRICTED in vertical configuration, but also kinda dances around in diameter. So I am not sure what is going on. I am placing my bet somewhere else, but the aft nozzle can get interestingly active at times so it must be part of the answer. The only time a video showed the aft nozzle increased slightly more than a little bit in diameter was when the F-35 B was in vertical configuration and at takeoff power (and stabilized) and transitioned within about 2 seconds to a SHORT TAKEOFF CONFIGURATION and released brakes. During vertical takeoffs and landings the aft nozzle stayed constricted but the diameter could oscillate a bit at the moment of landing. The aft nozzle diameter definitely has a role to play but unless the LP turbines’ power output are extremely sensitive to this, something more is going on.

@MacPoop 7 месяцев назад

Wow. So this question definitely made my own brain itch and wiggle a bit. As we were asked not to geuss in the comments, I'll keep my own theories and conjecture as to how the F-35B lift fan works to myself. Poring through comments as we speak, hoping one of the RR guys filled us in 😉

@dalebraun5497 7 месяцев назад

This is from a 2019 Lockheed-Martin flyer on the F35B: SHAFT-DRIVEN LIFTFAN® STOVL operation is made possible through the patented shaft-driven LiftFan® propulsion system. This propulsion approach overcomes many of the temperature, velocity and power challenges of direct-lift systems. I would imagine the word "patent" will preclude getting much more information.

@Mentaculus42 7 месяцев назад

Doesn’t patent mean the opposite ‽

@ronblack7870 7 месяцев назад

unless there are classified patents all patents are public so that someone knows what someone else deems their property.

@Mentaculus42 7 месяцев назад

GREAT QUESTION ‼️ I have to know the answer! You just can’t throw out a great “mind teaser” like that and say NO SPECULATION!! There is educated speculation, morosophism and dumb guessing. Maybe everyone can learn, or maybe not ‽ Personally, this is the question that keeps on giving.

@TheSadDuck 7 месяцев назад

I feel the same way! Brilliant engineering puzzle.

@waynemacleod3416 7 месяцев назад

you mentioned that the lift fan is only enguaged at low power. that might be a clue its self. with computer control, they can pre-empt throttle control in anticipation of the clutch enguaguing/disenguaging. with the lift fan on the engine might actually have to be running at high/full power, and hence why the "low power requirement during activation.

@grahamj9101 7 месяцев назад

But the lift fan must be engaged at high power, otherwise how does an F-35B transition from wing-borne flight, to make a vertical landing on a carrier?

@outriding 7 месяцев назад

Low lift fan power while inlet vanes are closed. The difference between power and rpm.

@danielcgomez 7 месяцев назад

great question indeed! ...but I haven't gotten to that one yet, I'm still trying to figure out how the system achieves 'Pitch' & 'Roll' control!

@AgentJayZ 7 месяцев назад

Your answer is on the Wiki page. RR calls them roll posts.

@aceofspadesInd 7 месяцев назад

Nice flags

@sjwatt 6 месяцев назад

Is it possible that the LP-turbine has variable stator vanes/nozzles to alter it’s energy conversion under liftFan load?

@AgentJayZ 6 месяцев назад

That would be a good idea, but I can't confirm such a feature exists.

@SuperAnatolli 7 месяцев назад

Question straight from the sofa: Is it possible to use some hatches that opens some airflow through the lift fan during fligth, to spool it up before engaging the clutch? I don't have a clue, just asking.

@AgentJayZ 7 месяцев назад

A good strategy when seeking a clue is to first do a search. The Wiki page is good, and there will be more sources listed. After a few minutes, you'll know a lot more. Best of all, you did it yourself.

@SuperAnatolli 6 месяцев назад

@@AgentJayZ Lots of dead links in reference list at the wikipage, but I found useful info on other places. I now know how the clutch works and it should not be any major problem (just learning to control the jet engine in combination with clutch) to engage the fan in mid air.

@High_Alpha 7 месяцев назад

I think you are correct... I mean I have no basis to confirm this other than critical thinking. But I agree that it's an overpowered accessory drive situation rather than a power turbine situation. Otherwise yes, there would be no way (other than diverting turbine gas flow magic) to prevent overspeeding the turbine (and all the bad stuff that comes with that). Also, yes to achieve this the core would need a LOT of EGT headroom to provide for the torque to drive the fan when required. This would also tally with the clutch and also makes sense given the Harriers biggest limitation was temps in the hover. So it would make sense to try to engineer this issue out in the next VTOL aircraft design.

@54alko 7 месяцев назад

Here is a couple of images of the engine and lift fan, en.wikipedia.org/wiki/File:Engine_of_F-35.jpg As these images are under a GNU licence it is legal to copy them

@incandescentwithrage 7 месяцев назад

Your description seems very similar, but not identical to US5209428A (Google patents). In that design they vary the size of the core exhaust, to give more power to the low pressure turbine during lift fan clutch engagement. Mixed flow, as others have said.

@Mentaculus42 7 месяцев назад

Interesting Patent from 1993! Also include in patent is the bypass air around the core that gets diverted to the control nozzle assemblies 40A and 40B used for the wing thrusters. This division probably also diverts additional airflow to the core. The normal mode is unrestricted while vertical mode is probable significantly restricted for the bypass/bleed air for the wing thrusters. From the diagrams of the F-135 that I have seen this aspect is rather vague.

@incandescentwithrage 7 месяцев назад

@@Mentaculus42 Yep, it seems to describe a way of achieving what is functionally a variable bypass ratio on demand by changing the core to nozzle cross sectional area ratio, nicely timed with the clutch. It'd definitely explain where the extra power goes, if that design works. Just to clarify.. I'm not "in the know" but stumbled upon it by searching first for the LM and then RR trademarked names for the liftfan, with just additional terms patent. Maybe the patent was very ahead of it's time and left to die as it's history suggests. Maybe the company was acquired and instructed to let it die. Maybe Google accidentally linked the correct patent to the search terms by inference based on previous browsing patterns. Impossible to tell either way from the outside of both LM, RR and Google, but interesting.

@Mentaculus42 7 месяцев назад

@@incandescentwithrage The patent was quite informative and mentioned that the low pressure turbine can be “unloaded” by decreasing the back pressure from the aft nozzle by increasing its diameter (thereby increasing the pressure differential across the low pressure turbine allowing for higher power generation). So of course I have spent hours reviewing F-35 Bs transitioning from horizontal to / from vertical configuration and paying attention to what the aft nozzle is doing. The conclusion is the the aft nozzle is somewhat MORE CONSTRICTED in vertical configuration, but also kinda dances around in diameter. So I am not sure what is going on.

@incandescentwithrage 7 месяцев назад

@@Mentaculus42 Congrats on the dedication of time to review footage. Yeah, the only way (I can think of) that would conceivably allow a system based on both the patent, and your observations, to co-exist would be wing thrusters fed with air sourced just aft of the LP turbine, in effect killing some of the back pressure and unloading it. Nozzle movements would then be fine balance lift fan/nozzle thrust. All diagrams I have seen suggest this is not the case, wing thrust being seemingly sourced further forward.

@Mentaculus42 7 месяцев назад

@@incandescentwithrage I agree, and the available diagrams conspicuously neglect to show any detail on where that bleed air is taken from. I know some people would think going down this rabbit hole is crazy but things like this bug me and I get exposed to a lot of new ideas, so write it off to being a hobby.

@Jonathanbaker 7 месяцев назад

Piston Compound-Turbo. Is there are a place in the future for them? Not a turbine question sorry.

@deSloleye 7 месяцев назад

Did you get this thought from Greg's Airplanes and Automobiles channel? If not, check out his latest video on the topic, it's pretty fascinating

@Jonathanbaker 7 месяцев назад

@@deSloleye yes the video is ok. There is much moor on the subject hence me asking some one that knows. Technical details etc.

@deSloleye 7 месяцев назад

@@Jonathanbaker it was one of his shorter, lighter ones. I'd like an explanation of the blow down turbine, for instance.

@Mentaculus42 7 месяцев назад

@@Jonathanbaker Greg just barely touched on all the different variations of turbo-compounding.

@41istair 7 месяцев назад

Worth a read from UK Gov this year: *Service Inquiry into the loss of F-35B Lightning ZM152 (BK-18)* PDF, 15.4 MB, 148 pages Loss of F-35B Lightning ZM152 (BK-18) of 617 Squadron RAF, embarked on HMS QUEEN ELIZABETH 17 November 2021 OFFICIAL - SENSITIVE

@lacombar 7 месяцев назад

Just skimming through, did they really forgot to remove the blank from the left intake ? Oh my...

@grahamj9101 7 месяцев назад

@@lacombar Yes. My son, who's in the military, sent me some sick joke type stuff that was circulating around the military, immediately after the incident. Fortunately, the pilot survived after ejecting, rather than going under the ship, as his 'chute snagged on the corner of the ski jump. It was shown in a recent UK TV series about HMS Queen Elizabeth. Having been pulled back onto the deck, the pilot walked away, but had some burns to his face, caused by the canopy detonation cord.

@michaelwilkes0 5 месяцев назад

can it adjust the main variable nozzle fast enough to absorb that power? doesnt seem like you would want an uncontrolled burst forward, but maybe you do.

@shamalv12 6 месяцев назад

Augmentor and nozzle probably limits spikes with varied back pressure

@TimSmith-vl4qk 7 месяцев назад

question what happens if you replace the blade with Tungstensteel blade

@BrandonKent136 6 месяцев назад

The F135, unlike the f119, has a 2 stage low pressure turbine. This is probably the reason.

@GeofreySanders 6 месяцев назад

What's the approximate life expectancy of a catastrophically unloaded power turbine? Does a human operator stand a chance of throttling down in time? Can electronic automation act quickly enough to save the rest of the engine?

@AgentJayZ 6 месяцев назад

A second or two. Not a chance. Electronic and hydromechanical systems have been developed that can save the PT if its drive shaft breaks.

@louisz7043 7 месяцев назад

Sorry, should be "to control N1".

@AgentJayZ 7 месяцев назад

See those three dots to the right of the heart... click 'em, and you are given the option to edit your comment.

@louisz7043 7 месяцев назад

@@AgentJayZ Thanks Jay.

@sandipdas5684 7 месяцев назад

Explanation of aeroplane engines from you is looks it is very easy but country like US UK France Russia and China are able to make a engine and others are not...my question is what is the crucial technology?

@stopthephilosophicalzombie9017 7 месяцев назад

There are many high tech parts to a jet turbine.

@zapfanzapfan 7 месяцев назад

The political will to spend the money is the crucial limitation.

@paulhawkins6415 7 месяцев назад

Making the turbine blades survive at a higher temperature as possible.

@Acroposthion 7 месяцев назад

@@zapfanzapfanYep. Money and resources.

@stopthephilosophicalzombie9017 7 месяцев назад

@@zapfanzapfanThere's an entire tech and intellectual infrastructure needed for jets and the high tech metallurgy and design computation required to build them. That's why Zimbabwe will never build jets.

@systemshock869 3 месяца назад

I asked someone I know who is incredibly high up in wall street about the GME debacle and he gave me an answer that was so basic and unrepresentative of the whole situation that it kind of confirmed my suspicions..

@jaronvaughn4520 5 месяцев назад

Real engineering channel has a video on the f35b lift fan. Its a very powerful engine with a very light weight single stage lift fan.

@spiroskatsikas 2 месяца назад

There are doors at the rear behind the lift fan these doors open and vent the 20,000 pound of thust behind this fan and also rear of the plane back to rear turbines i believe, may be wrongs 😅

@AgentJayZ 2 месяца назад

That's got nothing to do with the discussion, but thanks for the enthusiasm!

@jacksonboone8396 7 месяцев назад

Stop the 35 & put the money into the 22. 35 is junk. Just ask anyone at Eglin.

@Mentaculus42 7 месяцев назад

Money is going into sixth-gen with possible new engine from this program being retrofitted in F-35 As & Cs to overcome F-135 engine compromises for B version. The sixth-gen platforms are addressing the “short comings” of F-35, especially the C version for the navy. The navy is pushing hard to get the Boeing MQ-25 Stingray stealthy refueling aircraft out as a bandaid for the F-35C.

@Guysm1l3y 7 месяцев назад

LOL nope.

@Mentaculus42 7 месяцев назад

@@Guysm1l3y Who r u referring 2? Besides it is the best Harrier replacement that money could buy! It is the future of integrated weapons platforms. It is a perfectly cromulent aircraft!

@ianmangham4570 7 месяцев назад

@@Mentaculus42😮Obviously! he's talking to the comment at the TOP of this thread.DOH! 😅

@Mentaculus42 7 месяцев назад

@@ianmangham4570 It is actually “obviously” not clear as there are plenty of people who are fanboys of the F-35 and some of them would take umbrage at what I said as it is a partial criticism of the F-135 engine. Also some people don’t directly reference and just use position.

@larryphillips4164 7 месяцев назад

The F-35B's vertical take-off and landing (VTOL) system, featuring the innovative LiftFan, is a complex piece of engineering. The F-35B is powered by the Pratt & Whitney F135 engine, a variant specifically designed for the STOVL (Short Takeoff and Vertical Landing) capabilities of the aircraft. To enable its VTOL capabilities, the F135 engine is connected to the LiftFan, located at the front of the aircraft, via a drive shaft. This drive shaft is linked to a clutch mechanism. When the aircraft is in conventional flight mode, the clutch disengages the LiftFan, allowing the engine to function normally. For vertical takeoff or landing, the pilot activates the VTOL system. This engages the clutch, connecting the drive shaft to the LiftFan. The engine's thrust is then partially diverted to the LiftFan. The LiftFan itself consists of a vertically mounted, two-stage, counter-rotating blower, which is driven by the engine via this shaft. When engaged, the LiftFan provides additional lift to the aircraft, enabling it to hover, take off, and land vertically. Simultaneously, the engine's rear nozzle swivels downward to provide additional lift. This nozzle, known as the 3-Bearing Swivel Module, directs the engine's exhaust downward during VTOL operations. Additional control during VTOL operations is provided by smaller ducted fans located in the wings and control surfaces, which ensure stability and control when hovering. This intricate system of mechanical and aerodynamic components allows the F-35B to seamlessly transition between conventional and vertical flight, a key feature that sets it apart from other fighter aircraft. The clutch system plays a critical role in this process, allowing for the efficient transfer of power between the engine and the LiftFan. The carbon nanotube clutch disk designed for the F-35B is a fusion of cutting-edge materials, combining carbon nanotubes with a selection of superalloys, high-performance steel, and ceramic coatings. Carbon nanotubes form the core of the disk, offering unparalleled strength and thermal conductivity, embedded in a high-temperature resistant Kevlar matrix. Superalloys, particularly those based on nickel, titanium, or cobalt, are employed in the most stress-prone areas for their stability under extreme conditions. High-performance steel adds toughness and wear resistance to the spline areas, while ceramic coatings on the surface enhance heat resistance and reduce friction. This sophisticated material blend ensures the clutch disk is not only robust and durable but also capable of enduring the intense operational demands of the F-35B's propulsion system. This certain type of clutch is only found in the Domestically owned American F35B while outsourced F35’s utilize a carbon fiber based clutch system.

@AgentJayZ 7 месяцев назад

"Allowing the engine to function normally" Blah... this explains nothing. That is the issue we are talking about in this vid. Nothing else.

@pbasista 7 месяцев назад

This is a generic comment which mostly repeats what was said in the video. It almost seems like it was generated by an AI that has been learning from a few Wikipedia articles and a bunch of marketing materials. I see nothing of a particular value can be extracted out of it.

@3SPR1T 7 месяцев назад

I've found a declassified cutaway, it shows that the clutch is close to the lift fan but I can't really make out to which stage it's connected to. freighter.flyteam.jp/newsphoto/2741/src.jpg

@Mentaculus42 7 месяцев назад

That image is rather unhelpful when it comes to the engine but at least it is a “caricature” of the correct engine. It is as if they purposefully try to misdirect. As if the Chinese & Russians don’t have detailed info on engine considering their persistent espionage. It seems like the taxpayers are treated like mushrooms.