Though, to be honest, that's almost every topic when you take a deeper look at it. Too many people don't learn from the bruises they received after their novel "how hard could it be"-projects.
I am not a jet engine technician but was curious about jet engines and how they work so I clicked on your channel. I have to say that the information and technical details you provide have increased my understanding tremendously for a lay person. Thank you sir.
I mean this as sincerely and respectfully as possible; I have a profound respect and appreciate for your method of explaining the little things. "I'm not going to give you a one click link to buy, if you can't buy a book by it's name you wouldn't be able to read it anyway." Excellently put. It's why I miss the aviation maintenance field, it was full of extremely intelligent people with no nonsense attitudes. If you don't know something that you should reasonably know they're not going to spoon feed you but they'll go to great lengths to explain anything you want to know to better understand how something works. Once. (Which is perhaps the way it should be) your work and methodology is exceptional and I don't believe I've ever said it but I'm grateful for all the time you've taken out of your life to lay the stuff out barney style! Keep up the great work, eh!
JayZ, what an educational video. I shared this with the whole aviation community in America today which was shared several times over from my FaceBook site for new A&P mechanics in training. A big pat on the back for sharing your knowledge with all of us.
Thanks AgentJayZ. Excellent presentation. There is no such thing as an unimportant question, in the quest for knowledge. I appreciate your quest to explain things to people that ask questions they can't truly understand. Back in the 50's when I was being trained on Jet Engines, my instructor substituted the word impact for impulse, just to make it more understandable. It made more sense.
Now THAT is an answer!!! You wanna know? You really wanna know?? We'll sit tight and hang on because you're about have knowledge coming your way! Way to go AgentJZ. I love these long, detailed and yet simple and easy to understand explanations. BTW, I agree about the older manuals.
I know nothing about any of this stuff.. not my profession... But watching your passion made me want to continue to watch. I agree wanting to understand what you're going to be working on and how they work vs. "robotic" instructions. Adds more interest in your career and more likely to be happier with the work you do.
Gas turbines make me think of a perpetual motion machine, when combustion happens it doesn't blow out both ends of the combustor, it only goes out the back because the compressor pushes it out the back, but the compressor only spins because the combustion being forced out the back spins the turbine, you have the energy of the fuel and at start up the engine is spun getting the air moving, it all seems like a very fine balance.
Yup, but essentially that's the same with internal combustion engines. Ignition is usually before the piston reaches the very top so if the piston, crankshaft and everything were weightless it would reverse the engine. But since the mass of the flywheel, crankshaft and piston are moving in a certain direction it overcomes that first initial pushback and keeps rotating. New engines also change the ignition point to after TDC (top dead center) while at very low rpm, as while starting, in order to make it easier to get going. Older engines using fixed ignition systems can't do that, and that actually can cause injuries when kickstarting motorcycles. 😊
Kind of how the battery supplies energy to the starter which then engages the engine which has a belt connection to turn the alternator which charges the battery which supplies energy...etc., etc. Fine balance
Have often wondered what is going on inside these engines that makes them work as they do. Not an engineer. Not a mechanic. Flew puddle jumpers for a few years in the 90s. Thanks for the insight. Absolutely fascinating, with a great presentation. You are correct. I learned something today.
The 1950's G.E. stm. turbine manual is one of the best! and explains impulse and reaction forces very well and easy for a layman like me to understand!, they illustrate impulse forces with a tea cup!
i have always liked how you dig right in. from this side of the camera it seems a conversation,,must be strange on your side,,talking to a lens. thanks for all the time you invest!
Thank you Agent JayZ . for this in-depth explanation. I am going through A&P school now. I will be showing this to other classmates when we get back to Jet engine section again.
Very true about the older service manuals! I've got a old manual of my Boeing 502-6 that goes through the theory of operation. Great videos man!!! Cheers.
I am , by no means, a specialist on Turbine. I am just someone with a physics degree. I think the reason for the name "impulse" might have something to do with the physics's definition of the concept impulse. In short: impulse in physics is defined as the instantaneous change in momentum: Delta P(P stand s for momentum). The source of thrust to push on the turbine is produced by creating a difference in momentum. Let me explain: Newton third law says momentum must be conserved. Meanwhile, the speed of gas leaving the turbine is faster than its speed entering the turbine, therefore gaining momentum in one direction(momentum is a vector). However, momentum is conserved, that means the the turbine must 'lose' the same amount of momentum( it is equivalent to gaining momentum in the opposite direction )to ensure momentum conservation. therefore, the turbine accelerates in the opposite direction of the gas leaving the turbine. Again, I could be completely wrong here about why it is called "impulse turbine", and my explanation for newton's third law here is merely superficial. Edit: more detailed look at the equations: www.sciencedirect.com/topics/engineering/impulse-turbine
It's ironic that in the engineering world, the older manuals, produced without sophisticated text and graphics publishing software, put so much effort into explaining the details of the product, not just how to use it.
What an eloquent and informative explanation of Newton’s laws, Aerodynamics and Jet Turbine Design to say In layman’s; “fast air pushes the windmill on the back of the jet engine and keeps the other windmills spinning” gotta love it though, lots of brilliant insight into the thought that goes into every detail of it all. Thanks mate.
The easiest example to explain the reaction turbine is the plane's wings. The same working principle of the lift caused by a plane's wing due to velocity and pressure variation.
Great session. Almost easier to visualize when you think of water hose spinning a disc. The proper angle gives higher rotation. Or toy pinwheel you find the right angle to blow on it to spin it faster
One of my first flight instructors asked me how airplanes actually fly, I scrambled to find an answer because I wasn't really sure and I was just starting with the theoretical knowledge. After multiple tries, I gave up and he pulled out some money from his wallet and set it on the table. Nuff' said haha. AgentJayZ reminded me of that legendary moment at the beginning of the video. Thank you Agent Jay!
Hey JayZ, been watching you for years. I became an aircraft tech and you made going through the books muuuch easier. Really surprised to see that this topic was never covered before! Anyway, I just wanted to add (and confirm whether my memory serves well...) IIRC the proportion of reaction/impulse of a turbine depends on the application, i.e. a turboshaft turbine would be more impulsive (or less reactive) than a jet turbine, since you want to maximize torque and can allow for less gas velocity exiting the turbine. And vice versa. To be honest I wasn't sure anymore and would have to go through my neato notes with the vectors and all, but since you showed the air starter turbine being purely impulsive I'm a little more confident with my memory. But this is JETcity, so sorry if it's irrelevant! Thanks, again great stuff!
An instructor of mine flew the VC10 for EAA. They went bust, and he retrained on the 707. When he returned he told me the 707 flew, due to the engines being not balanced, this caused the wings to flap, and THAT is what created the thrust..
love your passion, i retire next month....gosh where were you as a teacher back in 1977/1982....power plant operator i am , steam plant and now a ge lm6000 operator ,8 units.....but time to retire.....
How could anybody retire from running half a million horsepower? Man, oh, man... you got the bragging rights! I know its all not connected to one control, but jeez. A gearhead's dream.
Really well presented. Based on your accent, I suspected you were 🇨🇦Canadian🇨🇦. Then you mentioned curling and removed all doubt. Thanks for making this video.
Hi @AgentJayZ - I have discovered your videos just recently and they're awesome! I have learned a lot from them - and that's from an Aeronautical Engineer and a 20+ years turbine engine user (pilot). One thing that I couldn't get my head around since my Uni days - how do centripetal turbines work? How do they differ from the axial ones?
3:05 Finally got an answer to that, which I actually also asked about some time ago but didn't got an satisfactory answer to. So up to 90% of the energy can be extracted, actually in the neighborhood to what I thought it had to be, good stuff.
It's all the same but it is all different. :) This is so true in a wide variaty of fields. The fundamental principles stay always the same and only the details are changing. I also like the older books more. First you need a solid fondation, then you can start to build on it and become a specialist. Great video as always!
Dear AgentJayZ, You told me to send my question here rather than Facebook. I am a self taught but very capable automobile and pickup truck mechanic. I know all the basic and some intermediate garage skills. Where would I need to start to build up my knowledge foundation if I wanted to build my own jet boat? What are the most critical things I would need to know to not die from a critical failure? If I may add this, where would someone in the USA get a hold of a New Zealand style race boat? I cannot thank you enough for your time and for posting these videos!
There is a channel by Reagan Williamson in NZ. He owns and has built NZ 777. It is a former world champion. He knows boats, and jet boats. He also owns a mechanical shop that can make anything happen. I would ask him a few questions... Finding a suitable powerplant will be an adventure in itself. You can decide for yourself if you want a professional to look it over. Jet City Turbines would be my suggestion for that... of course!
Why have I just gone onto Amazon and bought a book on Aircraft Powerplants? Ah well, no knowledge is ever wasted. 😊 Thank you for interesting me in a new subject due to all the videos of yours which I have found by chance.
So, in the theoretical limit a pure reaction turbine would rely on aerodynamic lift only while a pure impulse turbine would rely on the deflection of mass?
The reaction that happens in the reaction turbine is the reaction force in the opposite direction of the acceleration of the gases between the blades pairs.
Like watching your video. I worked the assembly floor in Middletown Ct on JT8s and J59s back in the late 70s. Before that I was an avionics Tech on P3s. I went with communications. Someone once told me that being an auto mechanic was more lucrative that an A&P with all the FAA crap.
"The pressure and speed of the gases passing through the impulse turbine remains essentialy the same, the only change begin in the direction of flow. The turbine absorbs the energy required to change the direction of the high-speed gases". In my opinion, while the pressure does not change significantly, the speed decreases.
I agree. I'm thinking that's the reason almost all gas turbines are designed as a mixture of impulse and reaction. To keep the velocity up for the next stage...
just like my old mentor said to me when i still work as a automotive helper mechanic. all engine are the same and have the same priciples on how it works. its just the technology and application that is diffrent. from an automotives perspective
“If you can’t look up a book and find it by it’s name, you probably won’t be able to read it.” Never heard any truer words. Great video and content like always.
Impulse turbines extract the most power per turbine stage, theoretically up to twice the power of the very common 50% reaction turbine. Therefore ideally they could be used in jets, and could cut the turbine's length and weight by a big factor. The reason that they are not used in jets is that there are severe issues with leading edge heating in these turbines. In effect they can't be cooled around the leading edge, which is also where heating is maximal. They are very commonly used in water and steam turbines where heat is not a problem. It is also common in cold air starter turbines (cold being the operative word), like the one shown here, where this design can result in the lightest possible starter turbine. On the other hand, a reaction-impulse turbine can be cooled, due to the comparatively "fat" leading edge, so it is suitable for gas turbines. A 50% reaction turbine also offers the least frictional loses.
Schmerrr.... if they were better, they would be used. Military fighter jet engines make no compromises, and leave nothing on the table. Performance above all.
@@AgentJayZ As an aerospace engineer I have to disagree with you on that. Military fighter jets are nothing but a series of compromises that as a whole are what the engineers think is best for a specific applications's constraints, limitations and requirements. Impulse turbines can't be used in a gas turbine application because the sharp leading edge can't be cooled effectively. That is straight from the mouth of a professor (who's an expert in gas turbine combustion) who was my teacher in a jet propulsion class, a class that later on as a graduate student I was the TA in. A simple analysis shows that an impulse turbine can extract twice the power of a 50% reaction turbine. That was also taught in class, and as a TA I taught it to students. You can also see it for example in "Mechanics and thermodynamics of propulsion" by Hill and Peterson, chapters 8, 12. From this it is obvious why for a required power output an impulse turbine can be made shorter and lighter than a reaction-impulse turbine, and that can obviously be desirable in a fighter jet. Problem is, such a turbine is guaranteed to overheat, so a different compromise must be made.
Hi! Enjoying you're an expert in the field, one question: I've studied that an impulse blade is that where degree of reaction is zero -hence the blade geometry, from the symmetrical velocity triangles- and that other blade where R > 0 is working as a reaction one. What is then a reaction-impulse turbine? Regards
Many thanks for not going into high & low pressure like they do with lift of a wing. Once someone explained to me that the reason a wing creates lift is simply because more atoms are hitting the bottom of the wing than the top, it made it more real than talking in terms of pressure.
I had a career lifetime in the design of gas turbine engines and I'm sorry, but I have to tell you that the "more atoms hitting the bottom of the wing" is not the way a wing (or a turbine blade) works. Pressure difference between the 'pressure surface' (the concave side) and the 'suction surface' (the convex side) is a fact.
I agree. I think the pressure on the "pressure surface" is raised, much more than it is lowered on the "suction surface". I guess the debate is about how the difference is created... In my tiny brain, anyway!
@@AgentJayZ The opposite is actually true - pressure drop on the suction side is much greater than pressure rise on the pressure side. As a reference, see for examples measurements in this NASA paper: ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19870016600.pdf. In page 26 there is a graph of the pressure distribution over an airfoil. Pressure is displayed as a coefficient, which is the change in pressure from ambient relative to dynamic pressure. So in this graph, the peak pressure drop on top is 3.7 times the dynamic pressure (Cp = -3.7). On the bottom however, pressure rise at its highest is exactly equal to the dynamic pressure (Cp = 1). It can also never be more than 1 because at that point all of the airflow speed was traded for pressure. In this example the top ("suction") surface is responsible for 80% of the total lift, 4 times more than the bottom ("pressure") surface. Note too how well theoretical calculations (using circulation theory) match with measurements.
It's not supposed to be fun? See, this is why I prefer a person that does something passionately vs as a job. For instance the countless parts changers in any mechanical industry, that only change parts, but cannot troubleshoot or design a simple tool to get the job done. There is a huge diffrence when you can visualize in your minds eye how and why something is done, instead of just doing it for the sake of getting it done. As soon as you start doing something without a pssion for it, that certain perfectionist spirit seldom follows.
old school wind turbines do also use curved blades, and at lower altitudes near trees and buildings, they are still far more efficient than modern 3-bladed wind turbines.
All modern wind turbines use curved blades. The curves are much more subtle, because the pressure differential of the air flowing over them from front to rear is much smaller than it is within a combustion gas turbine engine.
Help me think through this one....why does it take so long for a jet engine to stop spinning after you stop fuel delivery (turn engine off). If the compressor section of say the LM1500 takes 30,000 hp to turn then once you turn it off wouldn’t it come to an abrupt stop?
It's a non-linear thing. At full rpm, the compressor takes 150 lbs of air per second up to 160 psi. At zero rpm, the compressor sits there, doing nothing. Between those two data points, it's an exponential curve, not a straight line. Helpful hint: at 50% rpm, the compressor is not even at what is called flight idle... that's at 85% RPM. These are not piston engines.
The simple answer is that a jet engine rotor is effectively a stack of flywheels, rotating at several thousand rpm. The initial deceleration, caused by the compressor(s) no longer being powered by the turbine(s) is fairly rapid, but then the polar moment of inertia of the flywheel stack takes over. That engine under the hood/bonnet of your car doesn't stop turning instantly, because it has a flywheel. A Formula 1 engine does, because it doesn't.
A desk fan uses barely any power at 50% of full rpm. Same with an axial compressor: at 50% rpm it’s a nice blower but not much more. Same with any impeller water pump: the 80%-100% rpm range is 10%-100% power consumption range (ballpark numbers). As AgentJayZ said: it’s highly nonlinear.
As explained in this video, the turbine is powered by a combination of the pressure and the velocity of the gas stream going through it. The heat is just there because it is what cause the gas to expand and have velocity in the first place. The pressure was caused by the compressor... not by the heat. The heating of the air resulting from burning fuel in it does not result in a pressure rise, in a gas turbine engine.
17:40 Should be measuring perpendicular to flow direction. Any radial array of the same number of objects will just be the circumference of the circle / n parts. Easier to measure using the back side of the calipers too.
To get a precise measuring of the impulse turbine, you could stick the blades into some epoxy putty and let that cure (harden). Measure the indents in the negative now :-)
Im assuming the front and rear bearing housings stop the shaft from coming too far forward or too far rear. You mentioned before that there is about a 1/4” play because of thermal expansion/contraction with the shaft. Is this why the space is so large between the blades and stators? Closer is better for “transmission” of power i think you said before.
There is always one bearing per shaft that holds the axial position. It's a large ball bearing, and is called a thrust bearing. The other bearing(s) on the shaft use cylindrical rollers instead of balls. They allow for expansion and contraction of the shaft length, while the thrust bearing keeps it in the right location.
Impulse part of the turbine harness the kinetic energy of the gas stream while the reaction part harness the thermal energy (by allowing it to expand with the heat it carries reducing pressure, accelerate the gas further to regain the kinetic energy lost in the current impulse stage and pass it onto the next impulse stage). Am I correct?
Turbine blades do not produce thrust. They convert high speed gas flow into mechanical torque, used to turn the compressor. The high speed gas flow that gets past the turbine is then turned to thrust by the exhaust accelerating jet nozzle.
@@AgentJayZ You're right I was thinking the wrong way, Newton would be disapointed ... So blade's tip produce more torque because they have a greater arm than the root, right ?? And why the blade's tip airfoil has a higher AOA than the root airfoil ?
Hello AgentJayZ, speaking of older books the 1950's and seeing the turbine engines you usually work on, while reading I noticed that two of the most common and widely used turboprops of the day are both turboprops designed in the '50's (these being the Pratt & Whitney Canada PT6, and the Honeywell TPE331). It made me wonder, is it really such a technological feat thus such a hassle ($$$$) to research and develop new turbine engines so much so that a 1950 design is considered as good as new?
Yes. It costs billions of dollars to come up with a blank sheet new design of an airliner engine. The general aviation turboprop market might be a bit less expensive, so let's guess only a few hundred million... Better to update what we know works than go with anything totally new. Customers of the manufacturers of the engines are aircraft manufacturers, and they know their sales, reputation and survival rests on the safety and reliability of their aircraft, including the engine. The industry is very conservative, and both the engines you mentioned can rightfully say "tens of millions of flight hours". The TPE's development was funded by a US military contract, and Canada, well, we're just good at what we do! :)
@@AgentJayZ great points in regards to who the actual customers are and the US taxpayers black-hole, i.e. military budget involvement. Thanks you for your insight. Yes we are good at what we do aren't we?
So the reaction is version is more like a pelton water wheel and the impulse reaction version has more to do with the turbine blades utilizing the aerodynamic principles for lift adding to the commutation of the turbine...
So I have a question. Watching a video here on the Boeing 707 plane I noticed how long and narrow the engines are compared to the newer ones. I think I understand why the RR engines are so short because they have 3 rotating shafts. Maybe it is due to different turbine blade technology?
boomer9900 when the 707 was originally designed the engines were only low bypass turbofan engines which are small narrow engines. With the 747 a new more powerful engine was required and Pratt & Whitney gave the world the JT9 high bypass turbofan engine. In simple terms it used the basic low bypass engine, removing the small diameter inlet fan and replaced with a large diameter fan. This massively increased the amount of air being pushed rearward and thus giving the engine far more power. The American engine companies Pratt & Whitney and General Electric have developed high bypass turbofans on the twin spool model where as Rolls Royce developed the triple spool high bypass turbofans which produce the equivalent power as the Americans but with a smaller diameter engine.
So, what you’re saying is… The combustor makes the magic fairies, and the turbine slows them down thus producing energy purely from the deceleration of magic fairies
I had always thought that a gas traveling over a wing crates lift because the gas must travel a longer distance from front to rear if it goes over the top (the distances is greater) than under the bottom. If the gases arrive at the rear of the wing at the same time then the gas traveling over the top had to ‘speed up’, reducing the pressure and creating a higher pressure area at the bottom of the wing, creating lift. Since the blades are essentially wings the same principle would apply, pushing the blade in the direction of the longest surface (the top edge). Is that a bad way to think about the lift process?
I think wings produce lift in a combination of two ways: the usually mentioned Coanda effect, where the air travelling faster over the top reduces the pressure, and also by deflecting the air downward. I think turbine blades are the same. I think the deflection lift is greater than the Coanda lift. Many people think I am wrong, and I think a few of them might be right.
This is an old myth. I don't know where it originated from (but I can guess) but I do know that it was never the explanation in use by actual aerodynamicists and you can't find it in any engineering aerodynamic textbook. NASA has a nice summary of wrong ideas held by the general public: www.grc.nasa.gov/WWW/K-12/BGA/Monroe/lift_theories_act.htm. Airfoil lift was first explained by Kutta and Joukowski in 1902-1908 and that theory is what is in use to this day. It was later expanded by Prandtl in 1920 for a three dimensional wing. Lift is created as a result of a vortex motion around the airfoil - which is called circulation. This circulation causes a turning of the flow and an increase in speed above and decrease in speed below the airfoil. Thus from Bernoulli's equation there is lower pressure on top than on the bottom for a net lift.
The low pressure on top theory fails to explain downwash with helicopter rotors and wake turbulence downwash with aircraft. It’s too simplistic, but very common.
@@PattyODoors If that was aimed at the OP's post than the "equal transit time" theory as it is known can't explain anything, because it simply isn't true (air going over the top surface reaches the trailing edge much sooner than air going over the bottom surface). If it was aimed at my comment, I can assure you that circulation perfectly explains downwash in both fixed and rotary wings, and allows the calculation of it. Downwash is the Biot-Savart integration of the bound vortex (the circulation) and its wake. In a fixed wing the vortex wake is in the form of a rolling sheet and in a rotor it is in the form of a spiral.
"Patreon" is the site you're looking for. He has a second channel on that site, you pay a small subscription fee to get access to more videos than just those on RUclips.
Your videos are amazing! I have a question. I have a 1979 solar turbine generator and it was doing hot starts and also running hot. At 710 degrees f the high exhaust temp light comes on and it actually got to 800 degrees and then shut itself down. The intake had a lot of oil and dirt buildup around it which was restricting airflow and causing some of the issues. I cleaned it out and pressure washed the inlet out while it was running and I think it helped. Have you ever done a turbine wash on a running engine? It’s a 750 kw generator and the turbine probably is capable of 1200 to 1500 horsepower Also wondering how likely it is that the fuel control or fuel injectors are failing. I was thinking it could be something like that but after I saw how filthy the intake was I’m hoping that the dirt buildup is the main issue. It’s a backup generator on a dairy and has oil dripping a bit out of the front housing near the intake
You washed the compressor. Turbines are so hot that usually that crud does not effect them. It sounds like you have a front bearing seal leaking oil into the gas path, and combined with dust in the air, that makes crud that builds up on the compressor blades, making them lose efficiency. That makes the engine run hotter an produce less power. You know, we fix Solar turbine engines...
@@AgentJayZ Good morning! If we can get our hands on the needed parts we could pay for you to come down to fix it! We’re near Fresno California and with all these blackouts down here I need this running good! I may be able to get another one of these for parts or to fix. One guy said he had a hard time finding any parts and said save up for a new generator. So can you clean out the compressor section or do you fully disassemble the engine to do that? You’ll probably cringe but I pressure washed it down while it was running to try to clean up the vanes. They were filthy from that oil leak and all the dust that it sucked up. It’s probably working good and I know we got the exhaust temp to come down but with that oil leak it will gunk up again. However, this is the first time we looked at that in 12 years. Haha. It runs maybe 20 hours a year
If you want to send a bit more detail of the problem and a few pictures of the installation and engine to the email address listed on my channel page, I will try to determine if a field service would work, and help you come up with a plan. For any heavy maintenance, usually the engine requires a dedicated shop.
Question from Jacksonville Florida. Can a jet engine run away like a Diesel engine if a failure in the fuel system was to dump excessive amounts of fuel into the engine, or is the speed limited to its design? If you have covered this before, I guess I missed it. Love your videos.
I've covered it before, and many people are still arguing with me. The fuel system will not allow that to happen. I've made a video about this. Channel page has a search bar.
I was surprised that it is all impulse and reaction and there is no 'aerodynamic lift' component to the rotational force. The blades appear to have an aerofoil form. If this is correct then why do the blades have an aerofoil profile as this adds complexity (and maybe weight) to the blade?. As a sailor we use the 'slot effect' ("nozzilular") to accelerate the airflow between the sails to lower the pressure on the leeward side of the sail giving lift. A similar effect is apparent in your different entry and exit passageway measurements.
Most of the content of my edumacational videos is me relaying what the manuals ans text books say. I try to keep my opinions out of it... My controversial opinion is that wings create lift more by deflecting air down than they do by lower pressure over the top. More, not all.
@@AgentJayZ As a sideline to designing gas turbine engines (and raising a family), I flew model aircraft. As a a result, I spent years studying "how wings work", bought various books, and wrote several articles on the subject. Your opinion is not at all controversial, AgentJayZ: that is the way a wing works. However, to deflect air downwards, there is a lower pressure on the upper surface of the wing than on the lower - you can't have one without the other. Beyond that, the molecules of air flowing over the upper surface of the wing arrive at the trailing edge before the molecules flowing beneath the lower surface, which were separated at the leading edge at the same time. I wrote an article on the subject a few years ago and then found that Professor Holger Babinski of the University of Cambridge had beaten me to it with a more rigorous explanation.
I've sailed over 20,000 miles, having taken up sailing in retirement - and I had a career lifetime designing gas turbine engines. I don't like telling anyone that they don't really know what they are talking about - but I have to tell you exactly that. Don't be a smart***. Yes, most people, such as you, visualise a turbine as a series of aerofoils. However, try thinking about them as a series of curved aerodynamic passages, with a pressure gradient across each of the passages, and with complex secondary flows within those passages. Having said that, we did think in terms of a 'lift coefficient' for both turbine and compressor blades.
@@AgentJayZ Hi AgentJayZ, when I offer a comment, I think that I'm a little more tolerant than you in respect of some of your subscribers: however, I found this one rather supercilious and responded accordingly.
@Kevin Koster Sorry, but you're another one who is still getting it wrong. The greater proportion of the lift force on a wing is generated by the reduction in pressure over the upper surface. That's why on old-fashioned fabric covered wings, the fabric on the upper surface had to be securely stitched in place.
I think turbine blades can be compared with an airplane's wings: they have concave aerofoil with big curve and i suppose except deflecting of the gas flow (plane's wing deflects it too), there is difference in pressure on the concave and convex side of the aerofoil, hence lift force. Summary, i suppose in both a plane's wing and a turbine's blade, there are 2 principles of crteating force: deflecting the flow and difference in pressure because of shape. And may be I mistake), but in the first book there was a phrase that pressure and velocity of the gas flow don't change after impulse turbine, where was the energy for turbine wheel rotation taken off in this case?
The relative velocity (to the rotor) is unchanged in magnitude, but the absolute velocity drops (a lot) through the rotor. You can look for an impulse turbine velocity triangle diagram to see that clearly.
Great video. Just a simple and silly question , how is these engines different from GE FA, HA or Siemens SGT series engines. I work on Gas Turbines utilised in Power Plants.
@@AgentJayZ Thanks for the reply. I always watch the videos posted by you. I am a Loss Prevention Engineer in an Insurance Firm. So, I basically come across lot of Gas Turbine models in different Power Plants. I am just concerned whether there are any major changes in GTs installed in Power Plants compared to Aeroplane as the GT acts as a Prime Mover for the Generators in PP. Or is it only the capacity and size which is different for the ones installed in Power Plants. Thanks
Really seems that knowledge would be a critical part of doing your job. I'm really surprised you asked me that question. Seems like you need to do some background research. The internet is good for that. The books I recommend are better.
Starter air is around 250 - 350F, although that's a guess. We've never measured it, but you can't put your hands in it for more than about a half second.
The reaction is identical to a wing or airfoil. The air on 1 side of airfoil has to travel a further distance and therefore speed up causing a pressure drop , further causing that side of blade to be drawn in that direction.
Most of the noise comes from the compressor, not the turbine. Each time a compressor blade passes by a stator vane, there is a small change in air pressure. These events happen at a frequency in the thousands of times per second. Sound in what we call the midrange is literally variations of air pressure at around 800 - 5000 Hz, or cycles per second. The number of blades and the number of vanes for each stage never match, and each stage is different from the other, specifically to reduce what some call the siren effect. Many techniques and designs are employed in airliner engines to reduce the noise they produce. If you compare older aircraft engines to newer ones, you'll hear how effective those improvements have been.
@@leobav2425 The 'whoosh', which is more of a roar, comes from the back end. When it comes to the whine of the compressor, I usually tell people to look at an old-fashioned siren of the kind that could be seen in old movies with police cars in hot pursuit in the States - or, of course, sirens of the same type, which are still used (eg) for tornado warnings. It's exactly the same mechanism. I have to disagree with AgentJayZ here. Jet engines of the 1940s and 50's were never designed with blade and vane numbers selected to reduce noise, although noise departments were playing with this in the 1960s and 70s. The different numbers in each stage were selected primarily to avoid blade resonances that could cause premature fatigue failures. If you want some homework, try googling Campbell Diagrams.
U making great videos, great work ! This knowledge have big supplement in particles accelerators . Also try to apply it to Tesla turbine ... We using synthesis , not only analysis ))) Thank U ! best regards from Ukraine !
There is huge torque produce by the turbine inlet guide vanes, acting on the turbine, cancelled out by the torque produced by the compressor, and acting on the compressor stators. Net torque on the engine mounts is zero. Art Arfons was misinformed, but he did hold the absolute land speed record for a while.
@@AgentJayZ I more or less know who Mr Arfons' is, but what was he misinformed about? If the turbine is quickly accelerated is there ever a reactionary torque? Been trying to remember which speed record car had a mechanical failure and made the "world's fastest turn" (right turn if I remember correctly)
@@AgentJayZ Ta Da ... found it :). I had no idea what you were referring to, but found this youtube video ( ruclips.net/video/H-2sOzDMfnw/видео.html ) where @ 2:10 he describes Art's claim that he kept repeatedly blowing his right rear tire because of the J79 producing so much torque that it overloaded that tire causing it to fail. I'm thinking that would only make sense if he was using a power turbine to drive the rear wheels through a transmission. I would assume that any overloading of that wheel would be the result of some weird non-symmetrical aerodynamic effect at high speed.
@@AgentJayZ part of my interest in "reactive torque" would be a theoretical engine of sorts. The whole thing would have to spin freely. Turbine/compressor spins one direction to create basically a gas turbine. That pushes against a final "stator" that would spin the outer parts of the engine the opposite direction. Outermost parts would be attached to a fan, similar to a turbofan system, but without the coaxial shafts. No idea if it would actually work, be practical, or even useful, just a neat thought experiment.
Both of you are referring to the Otto cycle. 4 stroke piston engine. The gas turbine does not use the Otto cycle, so everyone who says that same simple thing is wrong. The Brayton cycle for gas turbines is more like one long whoosh. Also... there is no such thing as suction. Ask your science teacher. Or read a book.
@@AgentJayZ In my second year apprenticeship schooling we were told that people might suck, but that things are drawn in, Not Sucked in!! You Are so Right
Morning! I read an accident report recently which used the term "core lock" and it's part in a double engine failure. I've never heard of this before. Have you ever seen this phenomenon?
Hi Jay; I appreciate your videos a lot. You have mentioned a number of different books, both in this video and others. As a "layman" I want to buy one to share with my kids. Ideally has good pics, older is great also. Do you have any specific recommendations? Thank you.
The nicest color diagrams are in "the Jet Engine" by RR publishing. It can be quite expensive, but if you search around, you will find it in PDF form free to download. Then it's time to push the easy button, and have it printed out, eh?
thumb up when you like when things seem simple but they are not or if this is one of your favorite channels!
Though, to be honest, that's almost every topic when you take a deeper look at it. Too many people don't learn from the bruises they received after their novel "how hard could it be"-projects.
@@Xiph1980 totally agree
I am not a jet engine technician but was curious about jet engines and how they work so I clicked on your channel. I have to say that the information and technical details you provide have increased my understanding tremendously for a lay person. Thank you sir.
Welcome to Jet City!
I mean this as sincerely and respectfully as possible; I have a profound respect and appreciate for your method of explaining the little things. "I'm not going to give you a one click link to buy, if you can't buy a book by it's name you wouldn't be able to read it anyway." Excellently put. It's why I miss the aviation maintenance field, it was full of extremely intelligent people with no nonsense attitudes. If you don't know something that you should reasonably know they're not going to spoon feed you but they'll go to great lengths to explain anything you want to know to better understand how something works. Once. (Which is perhaps the way it should be) your work and methodology is exceptional and I don't believe I've ever said it but I'm grateful for all the time you've taken out of your life to lay the stuff out barney style! Keep up the great work, eh!
Whenever I do Barney, nobody gets it. Then I sigh, and have another beer!
Strange, another beer (or two) is usually the reason anything I'm trying to explain comes out gibberish 😂
JayZ, what an educational video. I shared this with the whole aviation community in America today which was shared several times over from my FaceBook site for new A&P mechanics in training. A big pat on the back for sharing your knowledge with all of us.
Thanks AgentJayZ. Excellent presentation. There is no such thing as an unimportant question, in the quest for knowledge. I appreciate your quest to explain things to people that ask questions they can't truly understand. Back in the 50's when I was being trained on Jet Engines, my instructor substituted the word impact for impulse, just to make it more understandable. It made more sense.
Now THAT is an answer!!! You wanna know? You really wanna know?? We'll sit tight and hang on because you're about have knowledge coming your way! Way to go AgentJZ. I love these long, detailed and yet simple and easy to understand explanations.
BTW, I agree about the older manuals.
I know nothing about any of this stuff.. not my profession... But watching your passion made me want to continue to watch. I agree wanting to understand what you're going to be working on and how they work vs. "robotic" instructions. Adds more interest in your career and more likely to be happier with the work you do.
Your passion for what you do is contagious. Keep it up! Awesome videos.
Gas turbines make me think of a perpetual motion machine, when combustion happens it doesn't blow out both ends of the combustor, it only goes out the back because the compressor pushes it out the back, but the compressor only spins because the combustion being forced out the back spins the turbine, you have the energy of the fuel and at start up the engine is spun getting the air moving, it all seems like a very fine balance.
Yup, but essentially that's the same with internal combustion engines. Ignition is usually before the piston reaches the very top so if the piston, crankshaft and everything were weightless it would reverse the engine. But since the mass of the flywheel, crankshaft and piston are moving in a certain direction it overcomes that first initial pushback and keeps rotating. New engines also change the ignition point to after TDC (top dead center) while at very low rpm, as while starting, in order to make it easier to get going. Older engines using fixed ignition systems can't do that, and that actually can cause injuries when kickstarting motorcycles. 😊
Kind of how the battery supplies energy to the starter which then engages the engine which has a belt connection to turn the alternator which charges the battery which supplies energy...etc., etc. Fine balance
Have often wondered what is going on inside these engines that makes them work as they do. Not an engineer. Not a mechanic. Flew puddle jumpers for a few years in the 90s. Thanks for the insight. Absolutely fascinating, with a great presentation. You are correct. I learned something today.
The 1950's G.E. stm. turbine manual is one of the best! and explains impulse and reaction forces very well and easy for a layman like me to understand!, they illustrate impulse forces with a tea cup!
Thank you for taking the time to produce these videos! They're great, very interesting and educational.
i have always liked how you dig right in. from this side of the camera it seems a conversation,,must be strange on your side,,talking to a lens. thanks for all the time you invest!
Thank you Agent JayZ . for this in-depth explanation. I am going through A&P school now. I will be showing this to other classmates when we get back to Jet engine section again.
Very true about the older service manuals! I've got a old manual of my Boeing 502-6 that goes through the theory of operation. Great videos man!!! Cheers.
I am , by no means, a specialist on Turbine. I am just someone with a physics degree. I think the reason for the name "impulse" might have something to do with the physics's definition of the concept impulse. In short: impulse in physics is defined as the instantaneous change in momentum: Delta P(P stand s for momentum). The source of thrust to push on the turbine is produced by creating a difference in momentum. Let me explain: Newton third law says momentum must be conserved. Meanwhile, the speed of gas leaving the turbine is faster than its speed entering the turbine, therefore gaining momentum in one direction(momentum is a vector). However, momentum is conserved, that means the the turbine must 'lose' the same amount of momentum( it is equivalent to gaining momentum in the opposite direction )to ensure momentum conservation. therefore, the turbine accelerates in the opposite direction of the gas leaving the turbine.
Again, I could be completely wrong here about why it is called "impulse turbine", and my explanation for newton's third law here is merely superficial.
Edit: more detailed look at the equations: www.sciencedirect.com/topics/engineering/impulse-turbine
It's ironic that in the engineering world, the older manuals, produced without sophisticated text and graphics publishing software, put so much effort into explaining the details of the product, not just how to use it.
What an eloquent and informative explanation of Newton’s laws, Aerodynamics and Jet Turbine Design to say In layman’s; “fast air pushes the windmill on the back of the jet engine and keeps the other windmills spinning” gotta love it though, lots of brilliant insight into the thought that goes into every detail of it all. Thanks mate.
The easiest example to explain the reaction turbine is the plane's wings. The same working principle of the lift caused by a plane's wing due to velocity and pressure variation.
Great session. Almost easier to visualize when you think of water hose spinning a disc. The proper angle gives higher rotation. Or toy pinwheel you find the right angle to blow on it to spin it faster
One of my first flight instructors asked me how airplanes actually fly, I scrambled to find an answer because I wasn't really sure and I was just starting with the theoretical knowledge.
After multiple tries, I gave up and he pulled out some money from his wallet and set it on the table. Nuff' said haha. AgentJayZ reminded me of that legendary moment at the beginning of the video.
Thank you Agent Jay!
Hey JayZ, been watching you for years. I became an aircraft tech and you made going through the books muuuch easier. Really surprised to see that this topic was never covered before! Anyway, I just wanted to add (and confirm whether my memory serves well...) IIRC the proportion of reaction/impulse of a turbine depends on the application, i.e. a turboshaft turbine would be more impulsive (or less reactive) than a jet turbine, since you want to maximize torque and can allow for less gas velocity exiting the turbine. And vice versa. To be honest I wasn't sure anymore and would have to go through my neato notes with the vectors and all, but since you showed the air starter turbine being purely impulsive I'm a little more confident with my memory. But this is JETcity, so sorry if it's irrelevant! Thanks, again great stuff!
Really helpful, i'm currently doing ATPL theory and these do come up in the AGK/Powerplant module, this has really helped my understanding. thanks!
An instructor of mine flew the VC10 for EAA. They went bust, and he retrained on the 707. When he returned he told me the 707 flew, due to the engines being not balanced, this caused the wings to flap, and THAT is what created the thrust..
love your passion, i retire next month....gosh where were you as a teacher back in 1977/1982....power plant operator i am , steam plant and now a ge lm6000 operator ,8 units.....but time to retire.....
How could anybody retire from running half a million horsepower?
Man, oh, man... you got the bragging rights!
I know its all not connected to one control, but jeez. A gearhead's dream.
Really well presented. Based on your accent, I suspected you were 🇨🇦Canadian🇨🇦. Then you mentioned curling and removed all doubt.
Thanks for making this video.
Hi @AgentJayZ - I have discovered your videos just recently and they're awesome! I have learned a lot from them - and that's from an Aeronautical Engineer and a 20+ years turbine engine user (pilot). One thing that I couldn't get my head around since my Uni days - how do centripetal turbines work? How do they differ from the axial ones?
3:05 Finally got an answer to that, which I actually also asked about some time ago but didn't got an satisfactory answer to. So up to 90% of the energy can be extracted, actually in the neighborhood to what I thought it had to be, good stuff.
I thought this one would be boring and basic. I was wrong.
Y'all need to hit up the patreon link: cheap. worth it.
Thank you for all the information you providing to us.
It's all the same but it is all different. :)
This is so true in a wide variaty of fields. The fundamental principles stay always the same and only the details are changing.
I also like the older books more. First you need a solid fondation, then you can start to build on it and become a specialist.
Great video as always!
Dear AgentJayZ,
You told me to send my question here rather than Facebook.
I am a self taught but very capable automobile and pickup truck mechanic. I know all the basic and some intermediate garage skills. Where would I need to start to build up my knowledge foundation if I wanted to build my own jet boat? What are the most critical things I would need to know to not die from a critical failure? If I may add this, where would someone in the USA get a hold of a New Zealand style race boat?
I cannot thank you enough for your time and for posting these videos!
There is a channel by Reagan Williamson in NZ. He owns and has built NZ 777. It is a former world champion. He knows boats, and jet boats. He also owns a mechanical shop that can make anything happen.
I would ask him a few questions...
Finding a suitable powerplant will be an adventure in itself.
You can decide for yourself if you want a professional to look it over. Jet City Turbines would be my suggestion for that... of course!
@@AgentJayZ Thank you again!
Why have I just gone onto Amazon and bought a book on Aircraft Powerplants? Ah well, no knowledge is ever wasted. 😊 Thank you for interesting me in a new subject due to all the videos of yours which I have found by chance.
Thanks for the early birthday present!
So, in the theoretical limit a pure reaction turbine would rely on aerodynamic lift only while a pure impulse turbine would rely on the deflection of mass?
The reaction that happens in the reaction turbine is the reaction force in the opposite direction of the acceleration of the gases between the blades pairs.
Curling forces...I love it. 40 years in aerospace and I've never encountered curling forces in a turbojet engine.
Really? What type of broom you using?
@@AgentJayZ My ex-wife used to fly on a broom.
June Foray was the most incredible Witch Hazel!
We did learn something from this. Very good basic stuff. Enjoyed this. If you keep making this I will keep watching
Like watching your video. I worked the assembly floor in Middletown Ct on JT8s and J59s back in the late 70s. Before that I was an avionics Tech on P3s. I went with communications. Someone once told me that being an auto mechanic was more lucrative that an A&P with all the FAA crap.
Can you show high pressure and low pressure turbines and why they use the combination?
"The pressure and speed of the gases passing through the impulse turbine remains essentialy the same, the only change begin in the direction of flow. The turbine absorbs the energy required to change the direction of the high-speed gases".
In my opinion, while the pressure does not change significantly, the speed decreases.
I agree. I'm thinking that's the reason almost all gas turbines are designed as a mixture of impulse and reaction. To keep the velocity up for the next stage...
Thank you for this.
You didn't seem all that excited with my promise. How'd I do?
I'm confused right now, if you mean the video in general it answered my question well, and I'm sorry for taking up your time.
just like my old mentor said to me when i still work as a automotive helper mechanic. all engine are the same and have the same priciples on how it works. its just the technology and application that is diffrent. from an automotives perspective
Hi JayZ, ex RAF propulsion tech here. In your experience, are there any turbines that use pure reaction, ie, straight NGVs?
Thanks a lot for this informative video , you make things easy to understand, great channel.
Great video, thanks a lot. Best regards from Brazil!!!
I am getting a good understanding of this technology and love it
Always have
Thanks again for teaching us
And for your time
Sir, Thankyou for the information. Please upload a similar video for compressor. What is surging in compressor and what could be its impact?
I have done that. Maybe try searching my channel. Perhaps you will find my video called "Compressors", or one of the other ones.
'if you can't look up a book by it's name you probably can't read it anyway' - legendary
Facts aren't always pretty!!
Please do a video explaining the progress the newer engines have made and perhaps what the next generation might look like.
“If you can’t look up a book and find it by it’s name, you probably won’t be able to read it.” Never heard any truer words. Great video and content like always.
Impulse turbines extract the most power per turbine stage, theoretically up to twice the power of the very common 50% reaction turbine. Therefore ideally they could be used in jets, and could cut the turbine's length and weight by a big factor. The reason that they are not used in jets is that there are severe issues with leading edge heating in these turbines. In effect they can't be cooled around the leading edge, which is also where heating is maximal. They are very commonly used in water and steam turbines where heat is not a problem. It is also common in cold air starter turbines (cold being the operative word), like the one shown here, where this design can result in the lightest possible starter turbine.
On the other hand, a reaction-impulse turbine can be cooled, due to the comparatively "fat" leading edge, so it is suitable for gas turbines. A 50% reaction turbine also offers the least frictional loses.
Schmerrr.... if they were better, they would be used. Military fighter jet engines make no compromises, and leave nothing on the table. Performance above all.
@@AgentJayZ As an aerospace engineer I have to disagree with you on that. Military fighter jets are nothing but a series of compromises that as a whole are what the engineers think is best for a specific applications's constraints, limitations and requirements.
Impulse turbines can't be used in a gas turbine application because the sharp leading edge can't be cooled effectively. That is straight from the mouth of a professor (who's an expert in gas turbine combustion) who was my teacher in a jet propulsion class, a class that later on as a graduate student I was the TA in. A simple analysis shows that an impulse turbine can extract twice the power of a 50% reaction turbine. That was also taught in class, and as a TA I taught it to students. You can also see it for example in "Mechanics and thermodynamics of propulsion" by Hill and Peterson, chapters 8, 12. From this it is obvious why for a required power output an impulse turbine can be made shorter and lighter than a reaction-impulse turbine, and that can obviously be desirable in a fighter jet. Problem is, such a turbine is guaranteed to overheat, so a different compromise must be made.
I actually don't enjoy arguing, so I'm going to fold.
@@AgentJayZ Fair enough, though I really wasn't trying to argue.
Hi! Enjoying you're an expert in the field, one question: I've studied that an impulse blade is that where degree of reaction is zero -hence the blade geometry, from the symmetrical velocity triangles- and that other blade where R > 0 is working as a reaction one. What is then a reaction-impulse turbine?
Regards
Many thanks for not going into high & low pressure like they do with lift of a wing. Once someone explained to me that the reason a wing creates lift is simply because more atoms are hitting the bottom of the wing than the top, it made it more real than talking in terms of pressure.
2:45 Also, "If you can't look up and find a book by it's name, you probably won't be able to read it anyway". Brutal (but true)!
I had a career lifetime in the design of gas turbine engines and I'm sorry, but I have to tell you that the "more atoms hitting the bottom of the wing" is not the way a wing (or a turbine blade) works. Pressure difference between the 'pressure surface' (the concave side) and the 'suction surface' (the convex side) is a fact.
I agree. I think the pressure on the "pressure surface" is raised, much more than it is lowered on the "suction surface". I guess the debate is about how the difference is created...
In my tiny brain, anyway!
@@AgentJayZ The opposite is actually true - pressure drop on the suction side is much greater than pressure rise on the pressure side. As a reference, see for examples measurements in this NASA paper: ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19870016600.pdf.
In page 26 there is a graph of the pressure distribution over an airfoil. Pressure is displayed as a coefficient, which is the change in pressure from ambient relative to dynamic pressure. So in this graph, the peak pressure drop on top is 3.7 times the dynamic pressure (Cp = -3.7). On the bottom however, pressure rise at its highest is exactly equal to the dynamic pressure (Cp = 1). It can also never be more than 1 because at that point all of the airflow speed was traded for pressure. In this example the top ("suction") surface is responsible for 80% of the total lift, 4 times more than the bottom ("pressure") surface.
Note too how well theoretical calculations (using circulation theory) match with measurements.
@@ASJC27 Thanks for setting that straight, most folks don't want to get their heads round it. Sad really
That was enlightening
thank you for this great channel
It's not supposed to be fun? See, this is why I prefer a person that does something passionately vs as a job. For instance the countless parts changers in any mechanical industry, that only change parts, but cannot troubleshoot or design a simple tool to get the job done. There is a huge diffrence when you can visualize in your minds eye how and why something is done, instead of just doing it for the sake of getting it done. As soon as you start doing something without a pssion for it, that certain perfectionist spirit seldom follows.
old school wind turbines do also use curved blades, and at lower altitudes near trees and buildings, they are still far more efficient than modern 3-bladed wind turbines.
All modern wind turbines use curved blades. The curves are much more subtle, because the pressure differential of the air flowing over them from front to rear is much smaller than it is within a combustion gas turbine engine.
In goes air, magic happens, then fire comes out, makes it easier for my brain 😂😂😂😂
Help me think through this one....why does it take so long for a jet engine to stop spinning after you stop fuel delivery (turn engine off). If the compressor section of say the LM1500 takes 30,000 hp to turn then once you turn it off wouldn’t it come to an abrupt stop?
It's a non-linear thing. At full rpm, the compressor takes 150 lbs of air per second up to 160 psi. At zero rpm, the compressor sits there, doing nothing. Between those two data points, it's an exponential curve, not a straight line.
Helpful hint: at 50% rpm, the compressor is not even at what is called flight idle... that's at 85% RPM.
These are not piston engines.
The simple answer is that a jet engine rotor is effectively a stack of flywheels, rotating at several thousand rpm. The initial deceleration, caused by the compressor(s) no longer being powered by the turbine(s) is fairly rapid, but then the polar moment of inertia of the flywheel stack takes over.
That engine under the hood/bonnet of your car doesn't stop turning instantly, because it has a flywheel. A Formula 1 engine does, because it doesn't.
A desk fan uses barely any power at 50% of full rpm. Same with an axial compressor: at 50% rpm it’s a nice blower but not much more. Same with any impeller water pump: the 80%-100% rpm range is 10%-100% power consumption range (ballpark numbers). As AgentJayZ said: it’s highly nonlinear.
Agent JayZ,thanks for the wonderful explanation,what is more of the driving force for that extra oomphh on the turbines,pressure or temperature?
As explained in this video, the turbine is powered by a combination of the pressure and the velocity of the gas stream going through it.
The heat is just there because it is what cause the gas to expand and have velocity in the first place. The pressure was caused by the compressor... not by the heat.
The heating of the air resulting from burning fuel in it does not result in a pressure rise, in a gas turbine engine.
17:40 Should be measuring perpendicular to flow direction. Any radial array of the same number of objects will just be the circumference of the circle / n parts. Easier to measure using the back side of the calipers too.
I was wondering the same, he noticed some times after.
sir AGENT JAYZ, can you make videos about small Gas turbine engine starter specs.?
A video about specs? Just look them up.
Sheer force of pilot will makes the turbine spin.
To get a precise measuring of the impulse turbine, you could stick the blades into some epoxy putty and let that cure (harden). Measure the indents in the negative now :-)
Easier to measure blades directly than indirectly.
Ever used epoxy? It does not release things.
So, unworkable idea.
Im assuming the front and rear bearing housings stop the shaft from coming too far forward or too far rear. You mentioned before that there is about a 1/4” play because of thermal expansion/contraction with the shaft. Is this why the space is so large between the blades and stators? Closer is better for “transmission” of power i think you said before.
There is always one bearing per shaft that holds the axial position.
It's a large ball bearing, and is called a thrust bearing. The other bearing(s) on the shaft use cylindrical rollers instead of balls.
They allow for expansion and contraction of the shaft length, while the thrust bearing keeps it in the right location.
Impulse part of the turbine harness the kinetic energy of the gas stream while the reaction part harness the thermal energy (by allowing it to expand with the heat it carries reducing pressure, accelerate the gas further to regain the kinetic energy lost in the current impulse stage and pass it onto the next impulse stage). Am I correct?
21:33 so there are a jet engines inside of a jet engine :D
Which part of the turbine blades produces more thrust ? the root or the tip ? and why the tip airfoil has a greater angle than the root ?
Turbine blades do not produce thrust. They convert high speed gas flow into mechanical torque, used to turn the compressor.
The high speed gas flow that gets past the turbine is then turned to thrust by the exhaust accelerating jet nozzle.
@@AgentJayZ You're right I was thinking the wrong way, Newton would be disapointed ... So blade's tip produce more torque because they have a greater arm than the root, right ?? And why the blade's tip airfoil has a higher AOA than the root airfoil ?
You need to do a bit of homework on velocity triangles for yourself: it's basic turbine theory. This will help you to understand.
@@grahamj9101 Could you name a book or web page where I could find velocity triangles explaination & turbine theory ?
I have not seen a high bypass engine on any of your videos. Do you work on them and will we see one in a future video?
Did a few videos on the CF6-6 being disassembled for parts.
Hello AgentJayZ, speaking of older books the 1950's and seeing the turbine engines you usually work on,
while reading I noticed that two of the most common and widely used turboprops of the day are both turboprops designed in the '50's
(these being the Pratt & Whitney Canada PT6, and the Honeywell TPE331).
It made me wonder, is it really such a technological feat thus such a hassle ($$$$) to research and develop new turbine engines so much so that a 1950 design is considered as good as new?
Yes. It costs billions of dollars to come up with a blank sheet new design of an airliner engine. The general aviation turboprop market might be a bit less expensive, so let's guess only a few hundred million...
Better to update what we know works than go with anything totally new. Customers of the manufacturers of the engines are aircraft manufacturers, and they know their sales, reputation and survival rests on the safety and reliability of their aircraft, including the engine. The industry is very conservative, and both the engines you mentioned can rightfully say "tens of millions of flight hours".
The TPE's development was funded by a US military contract, and Canada, well, we're just good at what we do! :)
@@AgentJayZ great points in regards to who the actual customers are and the US taxpayers black-hole, i.e. military budget involvement. Thanks you for your insight. Yes we are good at what we do aren't we?
I love these videos!
amazing information, thank you sir
Hi,l,m still alive and still have dyslexa,could you please do one on hellicopter roter jet enghines, thanck you.
I've got a whole series on the T58, which is a helicopter turboshaft used in the racing jet boats.
Why are the turbine blades jagged on the outer edge? Is that from scraping or are they made like that on purpose?
From touching.. or scraping the turbine shrouds. Tighter clearance means less air leakage, and less wasted power.
So the reaction is version is more like a pelton water wheel and the impulse reaction version has more to do with the turbine blades utilizing the aerodynamic principles for lift adding to the commutation of the turbine...
Sort of, but exactly the opposite. Impulse: stuff bounces off. Reaction: stuff squirts out.
All turbines are a combination of both designs.
@@AgentJayZ yeah, I wanted to flip it around after posting...thanks for replying. I enjoy your channel and have the utmost respect for what you do.
So I have a question. Watching a video here on the Boeing 707 plane I noticed how long and narrow the engines are compared to the newer ones. I think I understand why the RR engines are so short because they have 3 rotating shafts. Maybe it is due to different turbine blade technology?
Answer: Turbine blade technology has indeed advanced in the last 65 years, but that is not why the engines have become larger in diameter.
boomer9900 when the 707 was originally designed the engines were only low bypass turbofan engines which are small narrow engines. With the 747 a new more powerful engine was required and Pratt & Whitney gave the world the JT9 high bypass turbofan engine. In simple terms it used the basic low bypass engine, removing the small diameter inlet fan and replaced with a large diameter fan. This massively increased the amount of air being pushed rearward and thus giving the engine far more power. The American engine companies Pratt & Whitney and General Electric have developed high bypass turbofans on the twin spool model where as Rolls Royce developed the triple spool high bypass turbofans which produce the equivalent power as the Americans but with a smaller diameter engine.
@@ianobiwan Not necessarily smaller diameter, but very definitely shorter.
So, what you’re saying is… The combustor makes the magic fairies, and the turbine slows them down thus producing energy purely from the deceleration of magic fairies
If it was necessary to drug me with truth serum to assist my remembrance of what I said... I would agree to what you said. Yeah... I think so.
Not magic fairies,ANGRY PIXSIES.
I had always thought that a gas traveling over a wing crates lift because the gas must travel a longer distance from front to rear if it goes over the top (the distances is greater) than under the bottom. If the gases arrive at the rear of the wing at the same time then the gas traveling over the top had to ‘speed up’, reducing the pressure and creating a higher pressure area at the bottom of the wing, creating lift. Since the blades are essentially wings the same principle would apply, pushing the blade in the direction of the longest surface (the top edge). Is that a bad way to think about the lift process?
I think wings produce lift in a combination of two ways: the usually mentioned Coanda effect, where the air travelling faster over the top reduces the pressure, and also by deflecting the air downward.
I think turbine blades are the same.
I think the deflection lift is greater than the Coanda lift. Many people think I am wrong, and I think a few of them might be right.
This is an old myth. I don't know where it originated from (but I can guess) but I do know that it was never the explanation in use by actual aerodynamicists and you can't find it in any engineering aerodynamic textbook. NASA has a nice summary of wrong ideas held by the general public: www.grc.nasa.gov/WWW/K-12/BGA/Monroe/lift_theories_act.htm.
Airfoil lift was first explained by Kutta and Joukowski in 1902-1908 and that theory is what is in use to this day. It was later expanded by Prandtl in 1920 for a three dimensional wing.
Lift is created as a result of a vortex motion around the airfoil - which is called circulation. This circulation causes a turning of the flow and an increase in speed above and decrease in speed below the airfoil. Thus from Bernoulli's equation there is lower pressure on top than on the bottom for a net lift.
The low pressure on top theory fails to explain downwash with helicopter rotors and wake turbulence downwash with aircraft. It’s too simplistic, but very common.
@@PattyODoors If that was aimed at the OP's post than the "equal transit time" theory as it is known can't explain anything, because it simply isn't true (air going over the top surface reaches the trailing edge much sooner than air going over the bottom surface).
If it was aimed at my comment, I can assure you that circulation perfectly explains downwash in both fixed and rotary wings, and allows the calculation of it. Downwash is the Biot-Savart integration of the bound vortex (the circulation) and its wake. In a fixed wing the vortex wake is in the form of a rolling sheet and in a rotor it is in the form of a spiral.
What's your another RUclips channel?
Something pattren page.... I don't get. Can u help me with that?
"Patreon" is the site you're looking for. He has a second channel on that site, you pay a small subscription fee to get access to more videos than just those on RUclips.
Your videos are amazing! I have a question. I have a 1979 solar turbine generator and it was doing hot starts and also running hot. At 710 degrees f the high exhaust temp light comes on and it actually got to 800 degrees and then shut itself down. The intake had a lot of oil and dirt buildup around it which was restricting airflow and causing some of the issues. I cleaned it out and pressure washed the inlet out while it was running and I think it helped. Have you ever done a turbine wash on a running engine? It’s a 750 kw generator and the turbine probably is capable of 1200 to 1500 horsepower Also wondering how likely it is that the fuel control or fuel injectors are failing. I was thinking it could be something like that but after I saw how filthy the intake was I’m hoping that the dirt buildup is the main issue. It’s a backup generator on a dairy and has oil dripping a bit out of the front housing near the intake
Love to see a video of it running!
You washed the compressor. Turbines are so hot that usually that crud does not effect them. It sounds like you have a front bearing seal leaking oil into the gas path, and combined with dust in the air, that makes crud that builds up on the compressor blades, making them lose efficiency.
That makes the engine run hotter an produce less power.
You know, we fix Solar turbine engines...
@@AgentJayZ Good morning! If we can get our hands on the needed parts we could pay for you to come down to fix it! We’re near Fresno California and with all these blackouts down here I need this running good! I may be able to get another one of these for parts or to fix. One guy said he had a hard time finding any parts and said save up for a new generator. So can you clean out the compressor section or do you fully disassemble the engine to do that? You’ll probably cringe but I pressure washed it down while it was running to try to clean up the vanes. They were filthy from that oil leak and all the dust that it sucked up. It’s probably working good and I know we got the exhaust temp to come down but with that oil leak it will gunk up again. However, this is the first time we looked at that in 12 years. Haha. It runs maybe 20 hours a year
If you want to send a bit more detail of the problem and a few pictures of the installation and engine to the email address listed on my channel page, I will try to determine if a field service would work, and help you come up with a plan.
For any heavy maintenance, usually the engine requires a dedicated shop.
@@joewiddup9753 maybe I’ll get a video on an upcoming load test.
What makes a turbine turn? The same thing that makes congress, (or parliament) go. Hot air!
Question from Jacksonville Florida. Can a jet engine run away like a Diesel engine if a failure in the fuel system was to dump excessive amounts of fuel into the engine, or is the speed limited to its design?
If you have covered this before, I guess I missed it.
Love your videos.
I've covered it before, and many people are still arguing with me.
The fuel system will not allow that to happen.
I've made a video about this.
Channel page has a search bar.
I was surprised that it is all impulse and reaction and there is no 'aerodynamic lift' component to the rotational force. The blades appear to have an aerofoil form. If this is correct then why do the blades have an aerofoil profile as this adds complexity (and maybe weight) to the blade?. As a sailor we use the 'slot effect' ("nozzilular") to accelerate the airflow between the sails to lower the pressure on the leeward side of the sail giving lift. A similar effect is apparent in your different entry and exit passageway measurements.
Most of the content of my edumacational videos is me relaying what the manuals ans text books say. I try to keep my opinions out of it...
My controversial opinion is that wings create lift more by deflecting air down than they do by lower pressure over the top. More, not all.
@@AgentJayZ As a sideline to designing gas turbine engines (and raising a family), I flew model aircraft. As a a result, I spent years studying "how wings work", bought various books, and wrote several articles on the subject. Your opinion is not at all controversial, AgentJayZ: that is the way a wing works.
However, to deflect air downwards, there is a lower pressure on the upper surface of the wing than on the lower - you can't have one without the other. Beyond that, the molecules of air flowing over the upper surface of the wing arrive at the trailing edge before the molecules flowing beneath the lower surface, which were separated at the leading edge at the same time.
I wrote an article on the subject a few years ago and then found that Professor Holger Babinski of the University of Cambridge had beaten me to it with a more rigorous explanation.
I've sailed over 20,000 miles, having taken up sailing in retirement - and I had a career lifetime designing gas turbine engines. I don't like telling anyone that they don't really know what they are talking about - but I have to tell you exactly that. Don't be a smart***.
Yes, most people, such as you, visualise a turbine as a series of aerofoils. However, try thinking about them as a series of curved aerodynamic passages, with a pressure gradient across each of the passages, and with complex secondary flows within those passages. Having said that, we did think in terms of a 'lift coefficient' for both turbine and compressor blades.
@@AgentJayZ Hi AgentJayZ, when I offer a comment, I think that I'm a little more tolerant than you in respect of some of your subscribers: however, I found this one rather supercilious and responded accordingly.
@Kevin Koster Sorry, but you're another one who is still getting it wrong. The greater proportion of the lift force on a wing is generated by the reduction in pressure over the upper surface. That's why on old-fashioned fabric covered wings, the fabric on the upper surface had to be securely stitched in place.
I think turbine blades can be compared with an airplane's wings: they have concave aerofoil with big curve and i suppose except deflecting of the gas flow (plane's wing deflects it too), there is difference in pressure on the concave and convex side of the aerofoil, hence lift force. Summary, i suppose in both a plane's wing and a turbine's blade, there are 2 principles of crteating force: deflecting the flow and difference in pressure because of shape.
And may be I mistake), but in the first book there was a phrase that pressure and velocity of the gas flow don't change after impulse turbine, where was the energy for turbine wheel rotation taken off in this case?
The change of direction... hence the name impulse.
The relative velocity (to the rotor) is unchanged in magnitude, but the absolute velocity drops (a lot) through the rotor. You can look for an impulse turbine velocity triangle diagram to see that clearly.
@@ASJC27 thanks!
@@marklundeberg7006 thanks too!
@@AgentJayZ thank you
The video is great but I couldn't hold my laugh at 4:10.
Great video. Just a simple and silly question , how is these engines different from GE FA, HA or Siemens SGT series engines. I work on Gas Turbines utilised in Power Plants.
Did you watch this actual video? What type of work do you do on these engines?
@@AgentJayZ Thanks for the reply. I always watch the videos posted by you. I am a Loss Prevention Engineer in an Insurance Firm. So, I basically come across lot of Gas Turbine models in different Power Plants. I am just concerned whether there are any major changes in GTs installed in Power Plants compared to Aeroplane as the GT acts as a Prime Mover for the Generators in PP. Or is it only the capacity and size which is different for the ones installed in Power Plants. Thanks
Really seems that knowledge would be a critical part of doing your job. I'm really surprised you asked me that question. Seems like you need to do some background research. The internet is good for that. The books I recommend are better.
@@AgentJayZ Thanks. I already ordered the book you suggested. You are doing great job. Much appreciated
What is the starter turbine made of? Steel or something lighter?
It's quite heavy. It feels like stainless steel.
So it can handle a bit of temperature. How warm is the air coming from the start cart?
Starter air is around 250 - 350F, although that's a guess. We've never measured it, but you can't put your hands in it for more than about a half second.
That is a really effective hand drier :-) And too hot to be comfortable for aluminium.
The reaction is identical to a wing or airfoil. The air on 1 side of airfoil has to travel a further distance and therefore speed up causing a pressure drop , further causing that side of blade to be drawn in that direction.
There is no physical law that demands a fluid to go faster because it has a longer distance to go. That is not the reason for the speed up.
There is no such thing as suction.
Great video
Great video like Great explanation but already know basic physics
It's for everybody
What causes the high pitch whine on a turbine ?
Most of the noise comes from the compressor, not the turbine. Each time a compressor blade passes by a stator vane, there is a small change in air pressure. These events happen at a frequency in the thousands of times per second.
Sound in what we call the midrange is literally variations of air pressure at around 800 - 5000 Hz, or cycles per second.
The number of blades and the number of vanes for each stage never match, and each stage is different from the other, specifically to reduce what some call the siren effect. Many techniques and designs are employed in airliner engines to reduce the noise they produce.
If you compare older aircraft engines to newer ones, you'll hear how effective those improvements have been.
@@AgentJayZ that's interesting. One would think it would sound like whooshing air running through the engine, not a whine. Thanks for the explanation.
@@leobav2425 The 'whoosh', which is more of a roar, comes from the back end. When it comes to the whine of the compressor, I usually tell people to look at an old-fashioned siren of the kind that could be seen in old movies with police cars in hot pursuit in the States - or, of course, sirens of the same type, which are still used (eg) for tornado warnings. It's exactly the same mechanism.
I have to disagree with AgentJayZ here. Jet engines of the 1940s and 50's were never designed with blade and vane numbers selected to reduce noise, although noise departments were playing with this in the 1960s and 70s. The different numbers in each stage were selected primarily to avoid blade resonances that could cause premature fatigue failures. If you want some homework, try googling Campbell Diagrams.
U making great videos, great work ! This knowledge have big supplement in particles accelerators . Also try to apply it to Tesla turbine ... We using synthesis , not only analysis ))) Thank U ! best regards from Ukraine !
Is there a opposing torque on the stators? Something measurable in your dyno cell?
There is huge torque produce by the turbine inlet guide vanes, acting on the turbine, cancelled out by the torque produced by the compressor, and acting on the compressor stators.
Net torque on the engine mounts is zero. Art Arfons was misinformed, but he did hold the absolute land speed record for a while.
@@AgentJayZ I more or less know who Mr Arfons' is, but what was he misinformed about? If the turbine is quickly accelerated is there ever a reactionary torque?
Been trying to remember which speed record car had a mechanical failure and made the "world's fastest turn" (right turn if I remember correctly)
@@AgentJayZ Ta Da ... found it :). I had no idea what you were referring to, but found this youtube video ( ruclips.net/video/H-2sOzDMfnw/видео.html ) where @ 2:10 he describes Art's claim that he kept repeatedly blowing his right rear tire because of the J79 producing so much torque that it overloaded that tire causing it to fail. I'm thinking that would only make sense if he was using a power turbine to drive the rear wheels through a transmission. I would assume that any overloading of that wheel would be the result of some weird non-symmetrical aerodynamic effect at high speed.
... and... was he using a PT?
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@@AgentJayZ part of my interest in "reactive torque" would be a theoretical engine of sorts. The whole thing would have to spin freely. Turbine/compressor spins one direction to create basically a gas turbine. That pushes against a final "stator" that would spin the outer parts of the engine the opposite direction. Outermost parts would be attached to a fan, similar to a turbofan system, but without the coaxial shafts. No idea if it would actually work, be practical, or even useful, just a neat thought experiment.
i want to work under you sir
Hi jay theory of operation,I think your looking for.
most combustion engine will have this cycle on them or process on them
1 Intake
2 Compression
3 Combustion / power
4 Exaust
man I just miss working
I just heard a guy refer to it as: Suck...Squeeze...Bang...Blow :)
Both of you are referring to the Otto cycle. 4 stroke piston engine.
The gas turbine does not use the Otto cycle, so everyone who says that same simple thing is wrong.
The Brayton cycle for gas turbines is more like one long whoosh.
Also... there is no such thing as suction. Ask your science teacher. Or read a book.
@@AgentJayZ In my second year apprenticeship schooling we were told that people might suck, but that things are drawn in, Not Sucked in!! You Are so Right
Morning! I read an accident report recently which used the term "core lock" and it's part in a double engine failure. I've never heard of this before. Have you ever seen this phenomenon?
I've only seen core lock in the initial run-in of an industrial RB211.
@@AgentJayZ That comment takes me back to 1974 and R-R IMD.
@@AgentJayZ It happened to a pair of GE CF34 engines fitted to the aircraft involved in the Pinnacle Airlines flight 3701 incident.
Read about it, but I wasn't there, so I never saw it.
Hi Jay; I appreciate your videos a lot. You have mentioned a number of different books, both in this video and others. As a "layman" I want to buy one to share with my kids. Ideally has good pics, older is great also. Do you have any specific recommendations? Thank you.
The nicest color diagrams are in "the Jet Engine" by RR publishing. It can be quite expensive, but if you search around, you will find it in PDF form free to download.
Then it's time to push the easy button, and have it printed out, eh?
Thank you!
Is possible to use a milk tine to make jet engine
A book in my collection { Gas Turbine Theory - 7th Edition By H.I.H. Saravanamuttoo, G.F.C. Rogers) good basics