Jet Questions 66
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- เผยแพร่เมื่อ 13 ส.ค. 2015
- Order may not exactly match your list:
1) Modified turbofans for industry?
2) Jet dragsters... ... again...
3) Test cell bellmouth... ... again...
4) Power tools?
5) combustion air & cooling air - ยานยนต์และพาหนะ
I am a life long aviation enthusiast and I am starting to learn and study modern jet engines. I am fascinated by the quality and clarity of you Q and A videos. Just want to say thank you for the insight and understanding you provide.
A few weeks ago I was working on the 475th Fighter Group exhibit at the Planes of Fame Museum In Chino, Ca. There was a crew working on the P-38 Lightning getting it ready for an upcoming air show. If was fascinating seeing this aircraft with all it covers and inspection plates removed. Not a power tool in sight. Everything was done with hand tools. When you work with hand tools you can feel when something is not right. Then stop, correct the problem before continuing. If you strip the screw it’s not so bad. However when you strip the threads on the female side it going to take hours to fix.
Thanks! I wish I knew why these fascinate me so much - you do a great job explaining a technology that I never knew anything about. Keep 'em coming!
Agent JayZ, love your videos. You clearly love what you do. Every time I watch one I learn something. The most fun is when I realize I completely misunderstood some part of the machine and you teach me how it really works
One solution to cockpit air conditioning, although an old one and still in use by aircraft such as the CL-41 Tutor flown by the Snowbirds (Orenda variant of the J-85 engine.) use an expansion turbine driven by compressor bleed air (I think 8th. stage.) This hot compressor air is routed through the expansion turbine where it is decompressed and cooled to frigid temps. A second pipe with full hot bleed air runs alongside the expansion turbine and just downstream of the expansion turbine, a modulating valve receives both the hot and cold air and mixes the hot and cold air at a ratio selected by the pilot for personal comfort. Good system. You can make it snow (literally) in the cockpit or make it hot enough to roast your butt.
I once experimented with inlet cones and found the difference so significant that it was clearly measurable with household equipment. The air hates sharp edges, it rather takes a detour.
At 21:00 you talk about fastener costs. When i worked for Alcoa, I made aerospace fasteners and I was extremely surprised at the cost of some parts.We made this one tiny, tiny nut, possibly 2mm in diameter, that I could easily fit 60,000 USD worth in my pants pocket. If only there was a black market for the parts. lol
quick power tool story: AGM-28 missle, hyd access panel had LOTS of #3 phillips screws. used to use a speed wrench and a universal [to get lower screws inches above the cowl - J52 P-3]. pain in the butt,, LETS use air wrench!. remember the universal? have to hold it with a gloved hand; stripped the screw heads all the time; ruined the phillips bits; AND sent many universals and bit holders flying at some speed below the wing of the B-52. NO MORE POWER!
thanks for the question answer about powertools. I know I had a question some time ago about how to avoid equipment damage by doing things carefully, as I have surely stripped my fair share of screws, etc. great answer.
I watched a bunch of your videos and now sneak into the airport maintenance hangers and work on airliners.
Thanks for informing me regarding the jet cars! I never new that was why they 'bang' their way to the line! I thought it was for show. Take care.
DD
There are privately owned after burning jets in the US, Some guy has a F-100 ; Also there is a Mig 21. In the UK we have a Sea Vixen floating around, In South Africa there is a Lightening doing its stuff.
Great explanations as usual.!
good stuff. thanks from New Zealand
On that last question though, when looking at the LM1500 combustors, there appeared to be cooling air still bypassing that seal you pointed at to go through tiny holes between the nozzles. Film cooling for the first stage compressor nozzles perhaps? Unless I am missing an additional outer layer of cool air, it seems as though the air does flow past (but not slip past directly to the turbine). There appear to be micro holes drilled in for cooling, both on top and bottom of the nozzle blade. I noticed that the inner portion had an additional layer that would funnel air into those nozzles as well. The seal is there, but it looks like it is one lip further up. When you showed the next engine, it looked like the seals were almost identical. In any case, THANK YOU for that level of detail!
At first, I was somewhat confused by the legality of afterburner and variable nozzle engines, but was finally able to find an answer, at least, for me in the states.
Supersonic is not allowed over land (12/24 nautical miles off the coast and it is irrelevant). You can buy foreign engines with afterburners, but all sold in the states that are of US or ally origin are disabled/ removed. Mig 29? You can buy one with the afterburners.
This is, without a doubt, and incredible AQ video (as they all are). Loved it! The detail you show is second to none.
+Cody Smallwood Basically you've described it, except I think you meant to say first stage turbine nozzles. If you did, then that is correct.
Yes sir.
Im still blown away with your activity despite so many comments and questions!
Have a happy new year and keep on rocking!
Thanks for another great lesson. Some time in the future we should all be familiar with most of the systems of the turbojet engine from the inlet guide vanes to the afterburner and how these differ from gas generators and power turbines. When is the final exam?
Ha, Thanks for getting back to me! You did answer my question...It's all in the wording isn't it? Anyways, Keep the videos coming and keep stimulating my mind.
Ok.........I know that I was all about having a Ti fan blade to display in my living room, but I think I need that cutaway model in the living room now lol
Love the Arrow t-shirt.
Canadian Warplane Heritage Museum has them online... a newer, slightly different design.
thanks Jay.
Hey Jay,
hello from Germany and thanks for your great Videos.
In this Video, you showed us the cutaway of a J79 and the first stage turbine nozzles. Did i see right and the first stage of turbine nozzles is welded into this ring? If one nozzle is worn do you have to change the complete ring of nozzles? seems quite expensive.
Good stuff.
good luck mister
AMAZING !!!!!!!!!! KEEP GOING !!!
I have a sudden desire to get a combustion liner and turn it into a lampshade
Hi AgentJayz, i love watching your videos.
very informative they are.
I have a question:-
what is the difference between the shape and functioning of a fan blade(as in case of fan of a turbofan engine) and the compressor blade.
Are both the aerofoils or a the compressor blades are shaped so as to produce more pressure ratio per stage.??
Thank you.
Patty& JetEngines There is no real difference between the shape and function of a fan blade and a compressor blade: what we call a fan could equally well be described as a single-stage low pressure compressor. However, the design of the large fan blades you see behind the intake of a big turbofan is optimised to maximise mass flow, rather than pressure ratio. The design of core engine compressor blades is optimised to maximise the pressure ratio per stage, for minimum weight and reduced parts count. To demonstrate the advances made in this direction, the J79/LM1500 has a 17-stage compressor with a 13:1 pressure ratio: one of the latest big 2-spool turbofans has a 10-stage HP compressor with a pressure ratio of over 23:1.
Patty& JetEngines In a couple of videos, I address this very question. Have a look in the index of the playlist called Your Questions Answered.
Look for Compressor blade function, or Blades and stators.. that sort of thing. You will discover something you have not thought about before...
I can tell that by the way you've worded your question.
Thank you for your videos, +AgentJayZ!
In a stationary engine without a bell shape, the "sharp corner" that the air must follow also generates a lot of turbulence, right? Those vortices we see sometimes in fornt of stationary aircrafit illustrate this pretty well, don'they?
SnowRaptor Yes, and no. The lack of a bellmouth, or forward velocity of the engine, causes turbulence inside the inlet.
Vortices are outside the inlet, and are not caused by turbulence. They are cause by the vagaries and magic involved in airflow in regions of widely differing velocities and directions of flow. Like little tornadoes, they are mysterious and wonderful.
Many of my test videos show vortices entering the bellmouth, where there is no turbulence.
AgentJayZ Oh, good point, thanks!
SnowRaptor Please see my answer to Jeff Manning for another angle on what might happen to an engine without a bellmouth intake, as a result of the non-uniform and turbulent flow into the compressor. On the subject of vortices, I upset another subscriber a couple of weeks ago, which I regret, but I believe I knew what I was talking about. If an engine on test, or in a static installation, were allowed to run for any length of time with a so-called 'standing vortex' entering the intake, there would be a risk of it causing high vibration levels in the first-stage blades, resulting in fatigue cracking and possible blade failure. As I mentioned in a previous post, this happened in the original Marine Olympus installation, but I won't describe the problem and solution again here. If you want to see examples of visible standing vortices, then look for videos of C-17s elsewhere on TH-cam.
Hey jay I have a question Are there any gas generators or turbojets still in service that utilise a centrifugal compressor or are they all axial if so do you have any idea why
Hi Jay,
Thanks for all the awesome videos. You do a good job of explaining things.
What are the pros and cons of a free power turbine?
I'm having trouble finding much useful information on this. I have googled it and watched all the videos in your power turbine section. I'm sure you would have talked about this before, but I am having trouble finding anything about it even after watching literally hours of your videos. Hahahaha! Apologies if you have answered it before.
Would I be correct in saying that it allows everything to be at its optimum rpm at the expense of slightly reduced efficiency. As I assume a direct connection would be more efficient.
Keep up the good work.
cantunovic87 It is not less efficient. That assumption is made by everybody, and it is wrong. The two engines types have different handling characteristics. I have made a video discussing this . Check the Q index for PT6 vs TPE331 turboprops.
One is free power turbine, the other is single shaft. Both are very efficient, reliable, and popular.
AgentJayZ
Thank you. I will check it out. Much appreciated.
Hi Jay,
Have you ever heard of the J-93 engine?
I think it was a scaled up J-79
Hi! From multiple videos you uplaoded, I was able to build my understanding on jet engine principals upto diffuser. However, after diffuser when air enters combuster is where i dont understand further. What is the point of thrust in a turbojet engine?? I mean at what point/place exactly the thrust gets generated. Is it the final stage of turbine? Nozzle? If nozzle, then when nozzles are wide open, how is thrust getting generated?
Got a video for you... it has the word Books in the title. It's quite recent.
cool vid just subbed I wish I wasn't so lazy I would love to be an aerospace tech instead of a youtube addict
What do you with all the spare part since I bet you can't reuse them and how hard is it to sauce parts?
They have a lot of engines completely for scrap/ salvage
In reference to the LM 2500 as it relates to its turbofan counterpart, is there any horse power loss when the engine does not have the fan on it? As I watch these videos I think I understand that the fan is merely to produce an enormous amount of thrust and that's about it. When you don't need thrust you don't need a fan. But the fan helps take in air which might help with power but on the flip side it takes power to run the fan via a power turbine which might be about a wash when it comes to total power output. So is there any output horsepower change by adding or removing a fan?
Also thank you for responding to some of my questions. It makes learning about this stuff a lot of fun.
+Seth Jensen The fan does pass a small amount of its airflow into the core engine, and GE even calls it a "core booster", so without the booster the LM2500 makes a little less HP. The bypass part of the fan is a way of converting the power of the core exhaust jet into a lower speed, higher mass flow of air which causes the huge thrust. By any conversion of energy flow (power) from one form to another always incurs some losses.
So I would say the boosting is counteracted by the losses of conversion, in a ballpark way of thinking.
+AgentJayZ so is that another way to say plus or minus a small margin, it is about the same either way?
Hey AgentJayz, could you kindly point me to one of your questions video where you talk about the compresor design vs the case. you explain why the compressor case is flat and the compressor core is cone shaped. I tried searching briefly but couldn't find it.
Thanks a lot
+darshanpatelh Try Your Questions 30.
Hey AgentJayZ,
i have a question about the gas generator, instead of having a duct that will use the gas to run generator in the back, why not connecting the generator to the main engine shaft? wouldn't be faster and more efficient power generation?
thanks
+Waleed ALmalik
Please watch my videos on power turbines.
If you then still have this question, you will need to look elsewhere.
Hey AgentJayZ, great videos!
I got a question, so when a plane is flying at 40,000 feet where the outside pressure is significantly lower, how does this affect the pressure inside the engine? Does the faster movement speed of the plane force enough air into the engine to keep the pressure constant with altitude, or does the pressure fall with height? If the pressure does fall, what effect does this have on the operation of the engine?
Also, recently I watched a plane crash documentary where they explained the jet engine's operation as "A series of fans moving air uniformly through the engine" or something along those lines. Immediately I thought about what your reaction would be if you saw that! (:
kuba kuba 1) - I think absolute CDP does decrease with altitude, so fuel flow needs to be reduced accordingly, even at full throttle.
How much? That's for the engineers and designers.
2) - that's a gross oversimplification of the process, so much so as to be not only useless, but misleading. Typical of a modern "documentary".
AgentJayZ 1) - Makes sense, thanks!
2) And now people who watched the documentary will come in here and ask you why the "fan" doesn't spin on a turbojet!
kuba kuba Backing up AgentJayZ's explanation, compressor delivery pressure decreases with altitude and I've explained this in previous posts. The compressors have a given design pressure ratio, so that, as atmospheric pressure decreases with altitude, the pressure they can deliver decreases similarly. This means that the mass flow of the engine decreases with altitude, as does the fuel flow and available engine thrust. However, the drag of the aircraft also decreases with altitude, because of the 'thinner' air, and less thrust is needed. An example I've used before is the RB211 in the Tristar. The engine's take-off thrust was 42,000lb, but at cruise altitude of around 35,000ft and at a speed of 520 knots, its thrust was about 9,000lb.
@ around 20 minuets you are standing next to a compressor. Why does the final stage appear to have less blades than the second to last stage?
Geo Each stage is designed to to its job best. The last stage has a different job, because it does not feed another stage. To know exactly why a certain number and shape of blades are chosen, we would have to ask the engineering team who designed the engine, but they are all gone now. That compressor rotor is from an Orenda type 14 , and that engine was designed in the late 1940s
Hey J, at what pressure and temperature does the combustion chamber run at. It seems a lot of attention is given to the temperature of the exhaust gas at startup , so can things go wrong?
+Jeremy Burch thx mate theirs a lot to go through.
I have looked through your videos and I have not stumbled upon this question, and, if you have answered this or cannot answer this question apologies... how does the variable nozzle expand and contract? Also what is it made of? Love the videos! I have been looking at jet engines since I was 5 with a huge question mark in my mind until your videos! I can't tell you enough how appreciative I am that you take the time to do this!
Ok never mind... found your jet nozzle video lol
For those viewers that want to "geek out" on the math involved in inlet air:
www.grc.nasa.gov/www/k-12/airplane/inleth.html
I have a question unrelated to this video, but wanted to make it a public question.
I was looking at the GE 9X and noticed a set of blades located behind the fan, in the bypass duct. I was wondering what they were for? They don't appear to be variable from the somewhat generic images I've seen. My only thought is that they are to straighten out the air flow to keep the turbulence behind the plane to a minimum? Perhaps aiding in shorter take-off intervals for other jets?
I'm not that familiar with this new engine, but what you are describing are stators for the fan. The fan functions to accelerate air rearward. Fan stators will help it do that in two ways:
They will remove a great deal of the spiral or rotating velocity from the discharge air, and ensure it travels directly backward.
Also, they can be configured to present a convergent pathway to the discharge air (exactly the opposite of compressor stators), and therefore convert any pressure increase caused by the fan into even greater velocity. That would increase thrust, and that's always good, right?
Graham will let us all know if I got that second point right...
Thank you. I thought about it a bit more after posting the question, and while watching yet another one of you're videos (I'm currently up to Q74 after ONLY a month of watching your channel, lol). Then it dawned on me that it may be some kind of stator/strut combo, since the bypass duct is unsupported on that end. But I'm hesitant about the strut part...
could a turbofan be used for industrial applications by "simply" replacing the fan with a coupling to the load? reusing the shaft and powerturbine normally used for the fan
Yes, that is one way to do it, and it has been done. Minimal design changes, so the lowest up front costs. The result is what is known as a cold end drive turboshaft engine.Some helicopter engines use the exact same layout, although they did not start life as turbofan designs.
The main difficulty here is that optimal fan speed is often different from desired shaft speed for the industrial application, so a gearbox may be needed.
@@AgentJayZ Thanks, It did seem like an obvious possiblity to reuse some of the engineering that went into that. My doubt was if it couldn't work because the turbine for the fan wasn't designed to extract "all" the energy from the hot gas
Yes, some efficiency is lost. This is part of the end cost. In some applications, fuel consumption is not an important concern.
With your description of airline engines and not having a bell inlet, I understand the physics, and would like to ask that when an airliner is taking off, you sometimes see a 'cloud' following that sharp path you drew, I'm presuming this Is because takeoff is slower than the ram recovery speed ?
Aidan Brown I think you've answered yourself.
Thanks, I was just double checking
many videos ago you promised explaining a compressor stall perhaps I missed it if so sorry if not are you still doing one? just about anything I know about turbine engines I have learned here so Thanks
+David Moes Over the years I've spent explaining my videos on TH-cam, I've learned there are a vast number of people with a seemingly inexhaustible capacity to misunderstand, reinterpret, and argue with almost anything I present.
I am being careful, and hope to make a meaningful contribution soon.
+AgentJayZ Yea I understand I promise I will not argue with you, at least when it comes to turbine engines. on what the best beer or scotch on the other hand..........
Hey man I overhaul cfm 56 fuel systems and some jt8 fuel systems in the U.S. I have some cool photos that I would like to share.
I love professors ☺😊
Can you please explain to me what is compressor surge? & how it happened and if you have photos for compressor that subjected to surge send them to me. Thanks
+Adham Saboun May I suggest that you look elsewhere in this post for a discussion on this topic?
Do industrial turbines ever use a king shaft for power output the same way they are used to drive accessories?
Need to clarify what you mean by:
Turbine... do you mean turbine engine or turbine. They are not the same thing.
King shaft... Never heard that term.
@@AgentJayZ turbine engine such as rolls Royce ae3000 which has a shaft geared to and perpendicular to the N1 shaft. The other end drives an accessory gear box with fuel pump, oil pump, hyd pump, generator, etc.
I've checked, and there is no engine listed as a RR AE3000, but there is a lot of info out there on the AE3007, which is an aviation engine.
The AE3007 is a two shaft engine, so any shafts geared to a main rotor would be driven by the HP shaft, also known as the N2.
Typically the N1 shaft is not used to drive any accessories except speed pickups.
Every modern gas turbine has a radial drive shaft, driven by the HP system, but it is never used as a drive shaft through which the bulk of the power is transmitted. It transmits a small portion of the total power to the accessory gearbox, to drive oil pumps, fuel pumps, tachometers, etc.
To my knowledge:
-There isn't an single industrial gas turbine engine that has a bevel drive integral to the rotor shaft in order to have the main drive shaft be at a 90 degree angle.
-There isn't an industrial engine with an integral power turbine that is placed at 90 degrees to the main rotor.
-There isn't an industrial gas turbine engine that has an integral power turbine which also has an integral 90 degree gearbox.
Aside from that, the output shaft from a single shaft industrial gas turbine engine is the main rotor, and can used to drive any separate gearbox you want, that can have an output at any angle.
Also aside from the above examples, any industrial gas turbine engine functioning as a gas generator can drive it's separate power turbine through any arrangement of turns of the ducting the designer of the installation chooses.
Jay, what happened to your remote mic? It sure sounds better with your voice HERE vs. waaay over there. :-)
19:39 I don't care, I wan't it fast!!! (or was that about how accurate you can assemble it?)
Correct me if I'm wrong as I've learned most of what I know in jets from your videos:
the orenda burners you just showed ate cans burners while the j79 is annular can burners. If I got this wrong could you compliment the video where you draw them with real footage of each type of burner ?
louigi600 They are combustors, not burners, but otherwise your description is right. Burners is a term the UK people use for what Americans call fuel nozzles. In the same way the Brits use the name flame tube for what Americans call combustion liners. As we see here in comments every day, you can call the different parts anything you want, but it helps avoid confusion if you stick to the standard, generally accepted definitions.
+AgentJayZ I say intake casing, you say front frame: I say intermediate casing, you say mid frame: I say snubber (but R-R Derby says clapper), you say mid-span shroud - but let's not call the whole thing off. I'm fairly familiar with Stateside gas turbine terminology and I do try to translate, when I think about it. I could use the term flame tube, or combustion liner, or even 'can' interchangeably for an engine that has several individual combustion chambers, and I might describe it as having a cannular combustor arrangement, if all the cans are contained within a single outer casing. Combustor is a term I also use, although I believe it to have originated on your side of the Pond. For me, the term combustion chamber implies an annular combustor, which is contained within a combustion chamber outer casing (CCOC) and a CCIC. I could go on ..... but won't.
Hey Jay, on the first engine shown you mentioned that it had no jet pipe on it but that long pipe from the turbine back is what? I thought that provided some restriction before the variable nozzle, and you guys use it to put a load on the lm1500 to test after a rebuild. Thanks and great vid as usual.
Greg ory The long tapered thing on the end of the gas generator is a testing device used in place of a dynamometer to measure the engine performance. Since the LM1500 makes 10,000 shaft horsepower when mated to a proper power turbine, and since a mechanical dyno that can measure 10,000 horsepower is not an easy thing to build, They use a jet pipe (A gas accelerating nozzle) to measure the thrust generated by the engine, and thus calculate the horsepower that it would produce, if it were connected to a power turbine.
The jet pipe is a piece of test apparatus and does not leave with the gas generator when it goes back to its owners. Jay was referring to the gas generator itself and didn't specify that little detail.
The LM1500 gas generator does not ever have a variable nozzle, you have to remember to keep the J79 and LM1500 separate in your mind.
In a jet engine, restrictions in the gas path are a bad thing. There is nothing in front of the variable nozzle of a J79 engine except for a long tube and some fuel spray bars and flame holders.
Ok the afterburner pipe on the j79 is non restrictive its just the variable nozzle providing restriction. The pipe in this vid is something specific for testing the lm1500 not a part of the j79. Thanks for the detialed response!
Greg ory Glad I could shed some light on the matter for you. :)
+Greg ory I would describe what you see on the back end of that LM1500 as a 'slave' jet pipe and fixed final nozzle assembly, possibly adding 'for ground use only', to be pedantic - but then some industry test cells did use 'slave' GUO jet pipes for the testing of some jet engines. OK, the jet pipe you see isn't the afterburning jet pipe and con-di nozzle assembly of the J79, but they are both performing exactly the same basic function. AgentJayZ tells me that the 'slave' assembly gives less thrust than the J79 jet pipe and nozzle, but then it wouldn't necessarily, unless the LM1500 was being run at a comparable and corrected rating equivalent to a given rating of the J79.
+Ryan Willis To add a little levity to the proceedings, I remember (yes, the old *** is at it again!) walking past a storage area with a colleague and seeing a long transportation case, almost certainly for a Viper engine jet pipe. On one end was stencilled in large letters the words, "Bellows this end". We both had the same thought, "What does it do at the other end?"
Hey Jay, great vid as usual! One question...If afterburning technology is banned from all but military use, how do display teams like "The Starfighters" (F-104's) attain these aircraft for civilian use? Thanks so much!
Merlyn Sk I don't know. We have worked on several engines for the Starfighters. Next time they come up for a test run, I'll ask them your question. Maybe they'll answer.
Thanks Jay...much appreciated. I also added a couple of thoughts to your second last vid on starters. I hope it was applicable to the question.
Merlyn Sk Wouldn't it be different if you get a complete device and use it as intended as compared to modifying it for something like drag racing? I suppose the logic is that as long as it's used as intended, it's ok, but when you start using it differently, it becomes inherently unsafe.
Merlyn Sk It is perfectly legal to privately own supersonic jet aircraft in US (but it is not legal to fly supersonic over lend) and it is legal to privately own jet engine with afterburners.
If you have money and want you can now buy and privately own FAA certified in the experimental exhibition category MiG-29 complete with 2 Klimov RD-33 afterburning turbofan engines in US
It is one of two privately owned and flying in the world.
Here is link if you are interested to own it www.trade-a-plane.com/detail/1740438.html
How are the land speed record cars which use afterburners from fighter jets allowed to use them or do they get special permission I know with the bloodhound supersonic car uses a RR e200 from the eurofighter was donated by the RAF is this an exeption
But why don't they use turbo fans for power generators? In planes, as you've stated, most of the thrust comes from the fan so why not harness the power of a fan as well? Or does the power used to spin the fan negate any advantage?
cdangers I don't think you are clear on how these engines work. Please watch my videos on power turbines,. You may enjoy them.
cdangers In a turbo fan the fan is the thing powered by the engine core, it does not generate power itself. It consumes it and turns it in to thrust. The power that it would use is what the industrial engines use to perform their work. So if you had the fan you'd get no useful work out of the engine.
cdangers
What would be the point of that? Would you like your power generator to take off? The fan does not magically produce power.
Are there any hybrid gas-turbine electric engines used in any vehicles (ground or water)? Would that make any economical sense? I'm thinking of a diesel-electric locomotive but using a gas turbine instead of a piston engine.
Also, how small can you make a gas generator? Would the fuel consumption scale down with the size of the thing, or is there a minimum size under which you wouldn't really go to get any benefit over a piston engine?
johndoe1667Some ships use this, gas turbines are utilised to provide electricity. Electric motors then turn the props.
The UK's type 45 destroyers are one example
johndoe1667
As Jay already said quite often, a gas generator not running at 100% is very wasteful. So it's useless on a car, except if you would haul around large battery packs that would charge while the the power is not needed for driving. A gas turbine and a piston engine are equally efficient in fuel usage.
superdau I know. That's why I asked about scaling it down. Maybe being able to turn it on and off when needed. Question is how scalable is the solution? What is the smallest vehicle it's usable in? We know it's used in ships, but why not trains or huge trucks?
johndoe1667
Sure you can scale the turbine engines down (with the disadvantage that scaling down almost any engine technology makes it less efficient). There are RC model sized gas turbines. But the main problem is still the usage pattern. The all-or-nothing output of gas turbines just does not suit the usage patterns even of bigger vehicles like trucks and trains. If I remember correctly (I think Jay said it in a video) turbines don't like fast on-and-off cycling either. You would need huge intermediate energy storeages for the 50% load application, because the gas turbine can't give you that. One of the main benefits of a gas turbine is the amount of power you can get for a certain amount of engine size/weight. Neither of which are really an issue in trucks and trains.
The idea isn't new. Gas turbines have been used in vehicles as long as there are gas turbine engines, starting with the 40ies of last century. There have been and are trains, busses, trucks using gas turbines, but most of them were/are concepts, showing again and again that they are not really suitable.
If you don't care for efficiency they are actually installed in vehicles like tanks for example. But because even there you can't throw efficiency out of the window completely, tanks can have huge battery packs or even secondary generators for idling.
They might come up as a "power-charger" for electric vehicles to increase the range significantly. There you could run the engine at a very well known load and small size may be an advantage.
johndoe1667 Locomotive has already been done, Union Pacific GTEL. There is great vid here on YT of these locos.
What would happen if you were to spray a mist of oil into the gas generator of any given turbine engine? What would it take to disable the engine?
+Lou Herman That is the kind of question that would be asked by a terrorist... or at the very least, a determined vandal.
You now, Lou Herman... go suck on it.
+AgentJayZ my sincere apologies. I was wondering if there would be any way to disable an aircraft without damaging the airframe. my question was merely supposed to be a thought experiment. You do raise an excellent point that I hadn't thought of. Once again I do apologize, I'm not a terrorist I swear.
P.S. thanks for the swift answer, as hostile as it was.
I get a lot of questions about what's the worst thing... what Would happen if...
Sometimes from gouls who just want to see people die, sometimes from who knows what.
You seem like a nice guy, and it appears I was mistaken.
It's very easy to disable an engine, but, just like talking about what's the best way to wreck anything.. I think I'll just take a pass on that one, OK?
+AgentJayZ Absolutely fine, Thank you anyways.
+Lou Herman I think you asked an intelligent question in a very unintelligent way. There are obvious things that can disable a jet engine, which are widely known. A flight of Canada Geese going into the engines of an A320 can result in it landing in New York's Hudson River. A thick cloud of volcanic ash over Indonesia can clog up the engines of a B.747 and turn it into the biggest glider in the world. Engines do not like ingesting so-called 'foreign objects', which can cause 'foreign object damage' (FOD). Further than this, I will not go. However, going off subject slightly, I do recall having to design a manifold for the intake of an industrial gas generator, specifically for the injection of inhibiting fluid. This would be done during a 'dry motor' cycle (running the engine on the starter with no fuel and no ignition), to provide some protection to those gas path components that might be subject to corrosion during an extended shutdown. The fluid might even have been something as well known as WD-40 .....
I might have missed it but I think you never mentioned *when* a compressor stall can occur.
I know it is a rare thing, I know it can happen if you override the control unit and control the pitch manually (->"VSXE-2: The Second Day").
But what other circumstances can cause it?
Great videos as always!
Kalimerakis I have a couple of quick examples of causes of compressor stalls. First, maneuvering the aircraft in such a way as to disrupt inlet airflow (F-5's with twin J-85's were famous for this for a time until, I believe, changes were made to the IGV's. Also flying into the turbulent jet wash of a aircraft you were following too closely could induce a compressor stall. A second common cause was often related to a malfunctioning compressor bleed valve.
Thank you, Merlyn!
Kalimerakis That reminds me, I don't think +AgentJayZ has done a video on compressor stalls.
Anyways, I think the first set of engines for the first 747 had issues with compressor stalls, but I don't know what exactly was causing it. I do know that the test pilot could induce one when asked to, and apparently had to show an exec at P&W what caused it before they fixed it.
It was part of a documentary, so I'm not sure if it's accurate or just drama added for TV.
44R0Ndin Let's get the terminology of 'stall' and 'surge' sorted, as the words can and have been used casually and interchangeably in the industry, which I believe to be incorrect (but I've been told I'm pedantic). When I first started as an apprentice, if an engine 'coughed' on test, which it might occasionally when the fuel system hadn't been set up properly or the throttle man mishandled it, the event was usually described by the test crew as a 'stall'. However, the more commonly and accurately used term for such an event is 'surge'. This is when the flow through the compressor(s) transiently reverses, there's a loud bang and flames come belching out of the engine intake. Engines can run 'off-design' with one or more stages of their compressors partiallly 'stalled', but not actually go into a full-blown surge. All compressors can have a graph known as a 'compressor characteristic' drawn for them, the most important line on which is the 'surge line'. Below this can be drawn a 'working line', which represents the pressure/mass flow/speed relationship along which the engine can safely be operated. The difference between the two lines is the 'surge margin'. The surge margin can be degraded by accelerating the engine too fast, accidentally or otherwise, and the engine may then surge. The surge margin can also be degraded by loss of compressor efficiency, if, for instance, blade tip clearances become excessive, as a result of wear. It can also occur transiently when the compressor casings heat up more rapidly than the compressor rotor during acceleration of the engine. I recall seeing a DC10 taking off at JFK years ago: one of its engines surged three times in rapid succession during the take-off roll. More recently, I was a passenger on a B.737 landing at dusk at LHR. The right-hand engine surged on selection of reverse thrust and there was a bright flash of flame, which illuminated the whole engine nacelle.
grahamj9101
First off, hello fellow pedant!
Just so I'm clear on this, surge vs stall is a matter of severity, right?
Would this set of definitions work?
Surge = Mild upset of airflow in one or a few stages of the compressor. Usually makes a thump or bang, rarely shooting flames out of the engine. Mostly harmless.
Stall = Severe upset of airflow in ALL stages of the compressor. Always makes a loud bang noise, occasionally flames shooting out of the engine. Moderate chance of damaging the engine.
If it's not that, my next guess is that a stage of the compressor experiences a "surge" if the blades and/or stators of the compressor are aerodynamically "stalled", and therefore there is no such thing as a "compressor stall" only compressor surge.
If it's not either of those two, please explain to me, as I want to get it straight in my head.
Any plans to build a Frankenstein engine out of all them spare parts? Just to throw frozen chickens in and generally piss around with? TH-cam it right up!
We have a few scrap engines that are large, not running, but otherwise complete. They are too big for a "spare time" project. Thousands of hours of disassembly, cleaning, inspection, rework, and reassembly. Using special tools and shop equipment.
Then it's a team effort to get it into the test cell; the fuel bill would be in the thousands, and there is a substantial test cell rental fee. After all that... it would appear to be the same as any other engine test that we do, except it would be of an engine nobody needs or wants.
It's a lot of work, and nobody wants to do all that just so I could throw viewers suggestions into it, Come to think of it, I don't think I do either.
AgentJayZ you stated, in Q65, that a 1400 SHP turboshaft will get beat by a 1500 HP piston engine. Has the racing team thought about switching to a GE T700? It's "only" 1536-2638 SHP. LOL
Alfredo Pacheco Jr It's also only another half million dollars, plus a complete redesign of the boat... which means a new boat.. plus figuring out how best to adapt and use it in a race boat as opposed to a helicopter.
It's coming, but not next week...
AgentJayZ Oh, come on. If these guys can put a jet engine on a truck and create a makeshift A/B, I'm sure you guys can come up with something. ;-)
Would the racing league be upset if you showed up with a boat capable of holding an F414 engine (granted you'd only have enough fueled onboard for a few min before you burned it all up)?
Hey, JayZ, I've got a question, but I'm not sure if you deal directly with these things, so here it goes:
What kind of specifications are taken into account when deciding whether to use 1, 2 or more power turbine stages? Do more stages provide more torque or something like that? Besides the cost, weight and maybe lower moment of inertia, what advantages would we get form less PT stages?
Thanks!
SnowRaptor Just to be clear, I was referring to industrial engines. But aircraft related replies will also be welcome =)
SnowRaptor That's a design issue, for the engineers. We are not involved with that at all.
AgentJayZ Thanks!
SnowRaptor Sticking to the subject of industrial and marine power turbines, cost, efficiency, output speed and even weight can come into the equation. To give you a specific example, the Marine Olympus ('B'-rated) had a single-stage power turbine, running at 5,660rpm delivering 27,250SHP (why do I still remember these numbers?). The equivalent Industrial Olympus had a larger diameter 2-stage power turbine running at 3,000rpm (50Hz UK mains frequency) giving 20MW. Blade speed is important in terms of the ability of the turbine to extract power from the gas flow. A smaller diameter turbine running at 3,000rpm would have needed more stages, been less efficient, possibly heavier and certainly more expensive. However, the R-R designed power turbine for the uprated mark of Industrial Olympus ('C'-rated) that AgentJayZ has shown us had a 3-stage power turbine running at 3,000rpm, giving 30MW, the extra stage being necessary because of the increased power.
grahamj9101 Thanks, I see that the number of stages seem to be limited to the *force* on each stage (blade), since power transfered from the gas to the blade is equal to the force on the blade times its tangential speed. So each higher RPM and larger rotor can take more power than lower RPM and smaller rotor. I'm simplifying out the blades per rotor variable, but the seame reasoning would apply to the torque from the rotor on the shaft.
Regarding the uprated Olympus, that sort of changes to the design are there to provide this 50% increase in useable power? Larger compressor/combustors?
Great, thanks again for taking the time to explain things.
The shape of the intake lip is a big issue because of the conflicting conditions and requirements. Airliner intakes are a compromise to get reasonable static thrust while retaining low drag at cruise speed.
Early designs such as on early-model 707s had a cruise-optimised nacelle and pressure-differential-actuated auxiliary intake doors around the lip that opened at high power/low airspeed conditions: th-cam.com/video/qsUL9Xc3a2g/w-d-xo.html
A similar system is used on the Harrier air intakes: th-cam.com/video/lu54pdBsA-o/w-d-xo.html
Most supersonic designs in fighters have sharp-edged intakes and also use auxiliary doors in static conditions.
hey Jay, have you ever had the privilege of working with a Jumo004?
also, how do someone like me get into your line of work. cause this is amazing!
***** Priveledge? Those are historically significant, but they are crap.
AgentJayZ
Yes, and they are also rare, hence the privilege!
Not only that, but it was revolutionary! the only other engine that was produced in any significant number was a centrifugal engines
***** I would love to see one in a museum, but I doubt if I'll ever get to touch one.
If an engine were to be run without the bell shaped inlet, I'm guessing there'd be excessive injestion noise, increased fuel consumption, inaccurate gauge readings, and compressor stall?
Jeff Manning It would run OK, but would have more inlet noise. It would make less power for a given RPM and EGT. It wouldn't stall and the gauges would still work well.
Jeff Manning If a J79/LM1500 (or an Avon, or an Olympus - or any other similar engine) were to be run on test for any length of time without a bellmouth intake, I would also be concerned about flow separation from the sharp edge of the intake casing. There would be a risk of this causing a non-uniform flow into the front face of the compressor and giving the first-stage blades a 'hard ride', resulting in excessive vibration and fatigue cracking at low lives.
Jay, what would it take to fit two T-58s into the jetboats? Since they're in an unlimited class, would there not be any race regulation issues?
ladams00 Same reason a twin engine car is not a good idea. Weight and size make it unwieldy in the tight stuff.
Ladams I also agree, being able to half the gear ratio, same acceleration but double force top speed, so top speed ~200+ mph
Since it rides on the water not it in
+AgentJayZ Bugatti veyron? Twin v8
Aidan Brown No more a Twin V8 than a V8 is a twin inline 4. Its not two engines. They describe it like that to illustrate that the pistons in each bank are staggered and not inline, allowing the engine to be shorter and lighter, its very misleading. All 16 pistons are part of the same engine block and attached to the same crank shaft. From the outside it looks no different than any other overhead cam V type engine.
Hi can you explain hot section technologies? what is hot section?
thankx
Bibhu Prasad Nayak It's just a shorthand reference to the part of the engine aft of the fuel nozzles. It's the hot part.
+AgentJayZ hello please have the videos in Spanish?
AgentJayZ... please retire the bellmouth question. You need a Cue-card listing all the Q-videos that you talk about bellmouths. Just hold it up for every follow on bellmouth question you get.
On a side note, did you get that T700 engine information I sent your way?
Sjoerd van Keulen I keep asking folks to use the index to that playlist...
Yes, thanks! Still looking through it.
I hate to argue with you but there isn't a hard and fast law about owning after burning engines running variable nozzles, at least not in the US or UK. The last two land speed record holders, Thrust 2 and Thrust SSC used afterburning jet engines. Reheat as they would say. Thrust 2 has a Rolls Royce Avon 301R (16,000 pounds thrust with reheat) from an English Electric Lightning and ThrustSSC used two Rolls Royce Spey 205s (25,000 pounds thrust if they really were 205s, 20,500 if 203s) from the British F4-K Phantom. You can see the nozzles working and hear Andy Green commenting on their position in the onboard videos.
Their next attempt with Bloodhound will use a Eurojet EJ200 (20,000 pounds thrust with reheat).
The American Eagle land speed record car has a J-79 as did Craig Breedlove's Spirit of America. Spirit of America Formula Shell LSRV was getting 22,650 pounds of thrust on pump gas, sponsored by Shell (Royal Dutch Shell amusingly). It crashed at 675mph and he walked away.
So, five afterburning cars, four run in the US, two with US sourced J-79s.
cageordie I don't think I can post the youtube link, the video ID is zL77yBUOZhQ if you are interested. In the cockpit view you can see he has full lock on the steering at near supersonic speed. They idled the engines until the residual thrust got them to 100mph then went to full military, running up the engines at slow speed could suck in the desert instead of air. By the last run the burners were melting the rear body panels.
cageordie These guys were superstars with records of impressive achievements in land speed racing before they approached their respective air forces, and they got some pretty special help.
As with all general rules.. there are exceptions.
cageordie In most countries in world is not illegal to own after burning engines running variable nozzles (maybe is illegal in North Korea), There is many privately owned IAR-93B (Romanian airplane with Rolls-Royce Viper Mk 633-47 afterburning turbojets) across world MiG-21, even Paul Allen bought Ukrainian MiG-29UB (2 × Klimov RD-33 afterburning turbofans) here is FAA registration for that plane registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=29UB. According to FAA there is 5 privately owned MiG-29 in US all equipped with after burning engines running variable nozzles (Klimov RD-33 afterburning turbofans) (registry.faa.gov/aircraftinquiry/AcftRef_Results.aspx?Mfrtxt=&Modeltxt=MIG-29&PageNo=1)!!!
Hi AgentJayZ, I realise that I'm stating what you already know all too well, for which I apologise, and I know it has come up before. However, could I suggest that you make it clear (again) to your subscribers that, when you test a gas generator, you are effectively turning it back into a turbojet by bolting a 'slave' jet pipe and fixed propelling nozzle onto the back end? This is done so as to reproduce the 'back pressure' of the power turbine it would otherwise be feeding, in order to measure the various performance parameters accurately. The gas generator is then producing thrust, exactly as it would as a turbojet, and the thrust could actually be measured, if the test stand incorporated a load cell arrangement.
grahamj9101 Yeah, I'll agree to everything you are saying, except our restrictive tail cone produces less thrust than the actual turbojet nozzle.
+AgentJayZ OK, yeah, but your "restrictive" nozzle should be sized for the LM1500's industrial rating and application, which is presumably at a lower TET/EGT than the J79. However, if you put a J79 converted to LM1500 on the test stand with that jet pipe, but with a fixed nozzle that was sized to be equivalent (good weasel word!) to the closed con-di nozzle, fuelled the engine with Jet A/Jet A-1 (or whatever) and ran it up to max dry/military power, then it should give military power thrust. It might even give that thrust at a slightly lower TET/EGT, because the jet pipe and nozzle should be marginally more aerodynamically efficient than the J79 afterburner jet pipe and closed con-di nozzle. If this were not the case, then I would ask, what else have you changed and WTHIH?
amigo por favor en español gracias
Thanks JayZ!