As an Aerospace Engineering student, this is a very well thought out and well executed lesson in jet engines. Thank you for getting this out to the world.
@343jonny Johnny, you need to do a bit of research into just what a diffuser is. I'm hoping to do a video on the subject soon, but an introductory text like "the Jet Engine" by Rolls Royce publishing will do a much better job explaining it. ..Also, the PT6 has the coaxial and concentric shafts. They just don't pass thru each other, because to the normal way of looking at things, the engine is "backwards". Check out "aircraft gas turbine powerplants" by Jeppesen.
@343jonny The older engines were the basis for the first generation of industrial engines. The fighters are retired, but the industrial versions are still running strong. We help keep them going.
@343jonny Several possible reasons to do that. One is to increase the length of the gas path in which combustion takes place without making the engine longer. This allows lower burn temps and lower NOx emissions . It is usually a newer, longer combustor design retrofitted to an existing engine design, like an upgrade. It is also a way to initially design an engine to be as physically short as possible, and is how many helicopters engines are made.
@Fierobsessed Well, it was still early days for hi-bypass engine design, and also I think you got it right: an extra turbine stage would be heavier and would have involved a lot more redesigning than using a nozzle to harness any leftover energy in the exhaulst stream. There is a sharp turn for the air to make as it heads into the core. It works as an inertial particle separator, protecting the core from FOD ingestion.
@tranceaddict704 That's only half the question: there are many benefits - ideally each and every stage of compression would turn at its own most efficient speed all the time. But that brings up the other half: the disadvantages, which are mechanical complexity, cost, and weight. The RB211 is more compact, arguably more powerful, and arguably more efficient than its two-spool rivals, but it was a hugely expensive engine to design, and very expensive to maintain.
Thank you very much for that fine explanation, Jay! I've been interested in aircraft engine technology for a long time and this is the best comparison I've ever seen!
@tranceaddict704 The RB211 bankrupted RR, which went into recievership and was run by the government for 16 years, and it may have been the last completely new engine the company will ever develop. The Trent is simply an new name applied to the continually improving, evolving and expanding line of engines that started with the original RB211. I believe that any totally new engines in the future will be joint ventures between several large manufacturers.
@LinnaeusRC The JT8D is a turbofan with a bypass ratio of about 1:1 I don't work on them, but I'm fairly sure both the HP and LP system rotate in the same direction. When you want me to compare turbojet with turbofan... that's not two engines, it's two classes of engines. I'm flattered you ask me, but I don't know everything :) I know GE makes a new engine that has contra-rotating turbines, so the answer to your question is : "in some cases" (pun intended !)
@blampa The ebb and flow of projects. Today we recieved an engine for overhaul, and the Spey is in the test cell awaiting its chance to roar to life...
@joelvh1 I like the look of the bike, and I like the engineering it took to make it. We have a RR250 C-18 in a box, the same engine as Y2K. Not a very practical bike, but if I owned one I'd be heading to Bonneville for a run. There must be a land speed category for showroom stock motorcycles...
@Fierobsessed I noticed that too. From the back you can see the output of the second stage going through a smaller duct. 7:30 shows it. You can see all the way from the spinner back.
You need to do a bit of background reading. The answers will only confuse you more until you gain some understanding of how these things work. So, here are the technically correct answers: the two shafts are mechanically independent, but aerodynamically coupled... no gears. Secondly, it really depends on how fast you spin it. Turning the outer, LP shaft is unlikely to turn the inner HP shaft. In operation, the exhaust of the HP turns the LP. "the Jet Engine" by Rolls Royce is a great book.
In commercial aircraft, the bypass engines are vital, more efficient fuel engines and reliable. There was a confused situation with piston type engines and turbo jet engines. The fuel for piston type engines are LL100 AVgas, and re-fuelers were confused with those decals. the decals in those engines was modified and turbo was changed. Turbo charger is not the same as turboprop, or jet engine. I do love your videos, it is like going back to training classroom.Thanks for sharing all these ones.
Thanks for your suggestion to check this one out. Answers a question I should not have had... got tripped up on 'terminology'! Good work, teach'... keep it up!!
@tranceaddict704 you're going to have to do some research, and find that there is no unbiased source for an answer. Other maunufactureres will claim it is a waste of complexity and unnecessary... but then they don't make three-shaft engines. Rolls-Royce, in the corporate history : "the Magic of a Name", claim it is a superior way to design an engine. It's an engine out there competing with others, and you'll have to decide for yourself which type you would spend millions on...
A turbojet is used as a gas generator to turn a power turbine which then turns a generator. A turbofan includes an integral power turbine... which is used then to drive the fan. Instead of a fan, we want to drive a generator.
I watched the first episode of Canadian Corner, and I only sound like those guys if I try to. I have one remaining AgentJayZ toque, which I wear in my winter vids.
About the CF6. It appeared that the second stage was only in the bypass duct at 7:12, you can see straight through. I don't see the core intake. I'm also curious as to why the CF6 isn't exactly like the LM2500, It seems it would be more efficient to use the excess exhaust flow to drive an extra LP turbine stage to run a larger or stronger first stage rather then constricting it down to produce a little more thrust. Maybe it's just that a nozzle is just lighter then a turbine stage? I don't know.
In theory, I’m assuming from your video, you can greatly increase the turbo jets Efficiency by increasing the length of the ‘exhaust stream section’ of the engine. Are there any know working examples or concept/ designs of this? It seems like an engine like that could be put to good use on smaller jets.
The length of the jet pipe has no practical effect on engine efficiency. Here is an answer I gave to another question about the jet pipe length a day before. The jet pipe length is determined by making a compromise between several competing needs. The CG of the aircraft is affected by where the engine is, and that can be changed by, well, you get the idea.
@@jameya5007 Depends, with an afterburner (and-or aftercooler) you definitely can get between 17-40+% increase in power, but fuel and-or water expensive. In military jets the increase in speed can be upwards of 50-70% more boost, but that includes fancy variable nozzles and such.
@AgentJayZ Not at all, you presented the information in a way that clearly and concisely outlined the differences and similarities between the different engine types. Keep up the good work.
Blah. If you are able to recognize that "all the information was there", why do you need an explanation? I've covered the subject of noise in other videos. No matter what I do, somebody always bitches about it.
@AgentJayZ Ok. Cool! Sorry for all the questions Jay. I just grew up fascinated by all this stuff (my dad even had to give me a limit on the number of questions I was allowed to ask him per day about stuff like this hehe). Thanks for answering my questions!
I seen jet engines used for tractor pulls. I always wondered how does the power of the jet engine get transferred into mechanical power of the transmission?
I also noticed that some engines use a centrifugal diffuser. Could you maybe talk about these and which engines they get used in?.....and last question hehe: i noticed some turbines use two separate non-concentric shafts (a power turbine shaft and a compressor turbine shaft like a PT6 turboprop) and that the first turbine turned by exhaust gases is a single stage of the compressor turbine. I didn't know if S&S worked on those types, but thought that would be interesting. Thanks!
A power turbine is designed to extract as much energy as possible from the gas stream generated by the gas generator. Many power turbines have more than one stage, but they are all on the same shaft and turn at that speed. I do not know of any multi-shaft power turbines.
@AgentJayZ Right! I was just looking at the PT6 manual in simcom's king air c90a book and saw that it had 2 separate shafts...didn't know if you guys worked on anything like that. I will definitely look into that text though! Last thing: Just curious why you guys are working on 1950's engines which belong in extinct aircraft like the starfighter and phantom? Are there private owners which have need of them or does the military still use these in aircraft?
Hi Jay ! Again thank you very much for your work and again i need your help to understand: what is the main PRACTICAL difference between the IMPULSE type turbine and the REACTION type turbine. Beause in theory the main difference is that P,T DECREASE thourgh out the stator and remain CONSTANT through out the rotor, and in the REATION type we have also the DECREASE in P,T through the stator but in this time we will have a DECREASE also in P,T through the rotor. Is it possible to have an exemple ?? Thanks very much for your help ! With P=pressure T= Temperature.
What about the Rb-211, it was a triple spool engine with a low,intermediate,and high pressure spool. What benefits are there from having the third spool?
When I say any other engines, I mean other manufacturers, GE and P&W use two spools so if you can produce the same thrust with two instead of three why manufacture the more expensive/ complex engine?
Do turbofans, with the fan still attached, have any industrial use? I suppose you could harness the energy of the fan bypass airflow, but would there be any sense in that?
Hey Jay, I just watched a youtube video where a guy explained a GE frame 5 gas turbine. I noticeed that after the compressor, the air makes a weird trun 180 degrees to flow axially towards the compressor, and then makes the turn into the combuster burner can. After watching your videos I can't help but wonder if the J79 or CF6 or any of your engines use this same curved path. It seemed like the ones on your vids go straight from the LP compressor to the swirler. Could you explain? Thanks Jay!
The best way to make a super simple summary: The Turbojet is a gas generator fitted with a jet nozzle. The turbofan is a gas generator fitted with a power turbine that drives a bypass fan. The turboprop is a gas generator fitted with a power turbine that drives a reduction gearbox that drives a propeller.
Like asking why do some trucks use gas V8s and why do some use diesel inline 6s. The size of the plane and the desired speed has a lot to do with it, as does initial cost of construction. All the books I mention in Jet Questions 96 will go into this subject in detail.
AgentJayZ lol no what I meant is that the way you drew it on the board shows it not interacting with the compressor or the combustion chamber. So i was just wondering if it was just used as bleed air or does it just pass through without any interaction. lol whatever happened to no stupid questions haha. I'm just a pilot who wants to learn more about engines.
@AgentJayZ Hmmm. Well it's actually the opposite. My brain runs at twice the speed of my mouth. Kinda like a reduction gearbox on a turbine engine i guess. hehe
I love your videos! Could you explain differences in turbofans; low pass ratio vs hIgh pass ratio, how fast they perform at take off. Please could you compare JT8D with GE90 in terms of acceleration.
