On the subject of axial vs. centrifugal compressors in small gas turbines, we touched on this a while back. As the physical size of an axial compressor is reduced, the aerofoils (ok, airfoils) have to be similarly reduced in proportion. Consequently, the blades and vanes get thinner, their leading and trailing edge radii get smaller and they have to be produced to finer tolerances. They tend to be less efficient, with increased aerodynamic losses, and are relatively more susceptible to contamination and foreign object damage (FOD). A centrifugal impeller is significantly more robust in comparison.
+grahamj9101 I think its more the blade height to clearance on the Rotors, especially the rear stages. With smaller compressors, or if you scale down a compressor your clearances don't scale down, larger clearances on smaller blades so higher losses.
+squarepusher78 I was trying to keep my comments simple and fairly brief, as AgentJayZ has implied that I can be long-winded (yes, I admit that I can be!). Stator vane to rotor drum clearance is only a little less significant than rotor blade tip clearance, in terms of leakage. Tip clearances reduce, but don't scale down in proportion, adversely affecting performance and efficiency. To counter the robustness issue, aerofoil dimensions don't normally scale down in proportion, so that surface areas tend to increase. This is compounded by the fact that, as a compressor is scaled down, there must be relatively more surface area of both aerofoil and annulus exposed to the flow. This and the effect of Reynolds Number both result in significantly increased aerodynamic losses in a smaller compressor. Going to a centrifugal stage at the rear of the compressor counters these effects to some extent, but even so, a centrifugal impeller can have its own sensitivities. I had direct experience of a performance monitoring exercise on a small engine impeller, which appeared to be sensitive to the leading edge form and profile of its inducer section. I had a large number of ex-service impellers scanned and compared with a nominal model, with the differences shown in false colour. From the results of those impellers, I was able to predict with a high degree of accuracy the performance of new impellers going into engines at repair and overhaul.
+grahamj9101 If I could give the above comment more then one thumbs up I would. This seems like the a good opportunity to ask about the RR Allison 250 ( www.enginehistory.org/GasTurbines/Allison/7_RR%20ALLISON%20250-B17F.jpg ). Unique engine reverse flow combustion chamber/turbines, combination axial and centrifugal compressor ( assets.catawiki.nl/assets/2016/3/19/6/4/c/64c2c796-ede1-11e5-881a-8682bfd04863.jpg ). Anyway some variants seem to run a solid shrouded turbine blisk (all one piece) not like the shrouded turbine blades AJZ has shown us. ( i.ebayimg.com/images/g/arYAAOSwPhdVBxFh/s-l1600.jpg ) and I've always wondered why that wasn't more common, seems like it would be more robust, reduce blade vibration concerns etc.. Is there a reason its not seen on larger engines. The only down sides I can think of would be mfg complexity. Maybe hoop strength concerns of that outer ring? Hopefully the picture links work, I wanted to include visuals for other readers that may not know what I'm asking.
Just watched your video of the J-47 assembly and test. It brought back memories of my time, 1966-1968, rebuilding and testing these engines for F-86's owned by Saudi Arabia. Unfortunately our test area was outdoors. Fortunately for use it was Southern California.
Nice mix of topics and interesting to see the tool collection. I had to have fabrication buddy whip up a spanner socket right quick for the J44 compressor stub shaft nut. We will also need to make a locking/holding fixture/tool to fix the rotor while tightening the nut. That is part of the challenge and the fun, unless it costs like Jay's AI-25 arbor! Less fun. My socket was very simple and Mark owns the $150,000 laser cutting machine, so it was 'free'. Have a great and safe trip. DD
Hi! Up front - really loving your video's! Great work and keep them coming! In this video you go on subject about the F-22 and it's start system (in brief). The puf of smoke (and occasionally a flame) you see coming out of the side of the F-22 is in fact the APU of the F-22 starting up. As far as I know it does not use a cartridge start system, unless the APU starts up with such a system, which I would find illogical. Cheers! Lukas
+MTFDarkEagle Hey, if you know, I'll respect that. I don't know, but the video shows what looks like an engine start. After the exhaust jet, there are sounds in the video of an engine winding up, not APU sounds. An APU can easily be started with a single aircraft battery. No need for pyrotechnics. Does the F-22 not have an on board battery?
+AgentJayZ The f-16's APU runs on Hydrazine, which is a really dangerous (and expensive) rocket fuel. I have no idea if the Raptor uses the same, just putting it out there.
it multiplies the force applied by 160. years ago I used a torque multiplier to install the jesus nut on UH1H helicopters, the jesus nut is what we called the nut that holds on the main rotor head. it had 650 foot pounds. you torque it and wait torque it and wait several times.
Brave video, but much appreciated. I like your custom tools. I made the mistake posting a picture of my stereo system on an audiophile polk speaker forum with my new speakers and oh how the criticism flowed... Hope you don't have a simular experience...
For protecting the arbor, you could get some Kydex sheet, and form it over a mandrel (or the actual part) It looks like it may be small enough that you can fit it in a 5 gallon bucket, and use the kydex to keep it from flopping around some desiccant or vapor corrosion inhibitor paper/tabs to keep it corrosion free.Though I'm sure you have something planned.
What generation fighter aircraft do you prefer? I like high tech, but I'm more of a 2nd generation and A-10 type of guy. My thoughts on the SR-71 are the same as yours. Thanks for the videos and the tremendous amount of knowledge you share.
Without giving too trade secrets away, on the boat, whose jet engine that you worked on, does it utilize water injection? If it does, can you provide more detail as to where the injection is inserted, amount (gpm) and shp improvement? I am familiar with Water Wash on GE Frame turbines and the water needs to be demineralized water.
Great videos (and I'm not an aero-engine nut!) Just out of curiosity has anyone tried making a centrifugal turbine on a jet engine? A sort of centrifugal compressor in reverse. I don't suppose there would be any advantages just curious.
The following occurred on a trip from Guam to Hickam AFB Hi. In 1979. This question pertains to a PW J-57-59W. This engine was installed on the KC-135-A. But first the in flight problem. The pilot summoned me to the cockpit to show me the #1 engine has low oil pressure but when he brought the engine to idle the pressure normalized. The pilot decided to fly the rest of the mission with that engine at idle. When we landed the tower controller said we had a fuel leak on number one. When we parked and shut down the engine I checked the oil on number 1. The oil tank was full of fuel. I guess fuel lubed the engine. I told the pilot we would be stuck in Hawaii until the new engine was delivered and changed. As the aircraft crew chief my job wasn’t to figure out how fuel displaced oil. My job was to change the engine. So what would you say happened? After the engine was changed and set up for an engine trim I had the honor of running all four engines under max thrust injecting water.
The only place I know of that oil and fuel come in close proximity in any quantity is the fuel cooled oil cooler. Both oil and fuel are under some pressure, and if there is a leak anywhere, the two will mix. That would be the first thing I would remove and pressure test.
I'v e only just picked up this comment: I agree. I'm reminded of the time I found lub oil in the coolant header tank of my car. The oil cooler, which was cooled not by air but by engine coolant, had failed internally.
Hey J: Specialty Tool $ in All Techie Situation's can B a Deal Breaker.Imagine a Lend/Rent Tool Distribution Center 4 Specialists.We could call it Nerd-Vain'in!!!
Hi Jay, Thanks for all your videos. I realize your job is in overhaul and maintenance. But it got me wondering if you have ever been able to go on-site with a customer and see the industrial installation for a gas turbine generator. If so, do you think a customer would ever allow you shoot some video? -Mark
The main difference in an axial compressor and a centrifugal compressor is that while the former is good at handling large amount of air for smaller pressure ratio, the later is good for giving larger pressure ratio to small amount of air. So centrifugal compressor is very compact when one wants to achieve required pressure ratio for relatively small amount of air i. e. when power output needed is relatively small. Some engines have axial LP compressors followed by one or two HP centrifugal compressor because the air volume is reduced significantly through theLP to the level where the HP centrifugal compressor can handle it. Centrifugal compressor makes small jet engines compact.
Have you ever shown a closeup of the diagram above the orange press at the bottom of the stairs? You can see it at 14:00 to the left of the screen. It looks like it shows an engine in an industrial installation.
Apropos to a previous question about what a drone strike might do to an engine, I have some stop press news. I have just picked up an online report that, earlier today, a British Airways A320, which was on approach into Heathrow, took a drone strike. Fortunately, there was no engine involvement and the aircraft was cleared to continue in service. However, it begs the question, what if ..... ? The incident is apparently the first ever drone strike on an aircraft to be reported, but I doubt that it will be the last. We've already had several near misses reported here in the UK.
+grahamj9101 Was it a bird? No! Was it a drone? No! It was a plastic bag or a bit of polystyrene! That's officially the latest. There was no blood to indicate a birdstrike and no damage to the plane.
Not some poor kid who dropped a helium balloon then? :-) Drones are becoming a nuisance, it has happened a couple of times in Sweden that air traffic around air ports have been shut down because of a drone flying too close.
This is probably a dumb question, and I'm sure you'll light me up for it (if you even deem it worthy of response) but here goes: Looking at the super-polished compressor blades made me think of some things I've heard discussed about smooth surfaces and aerodynamic adhesion - specifically that laminar airflows like to become "unstuck" from smooth surfaces, and how this effect can increase drag. My question, therefore, is to ask if it would make sense to dimple the low-pressure faces of compressor blades and stators? The idea being that this would introduce swirling in the boundary layer and help keep it from separating from the LP surface of those airfoils (as with the vortex generators on STOL bush planes or the dimples on a golf ball). Or do the existing airflow shaping devices (VSVs and bleed air) already perform sufficiently well at this task that there would be no benefit (or, no appreciable benefit to offset the daunting task of ensuring structural integrity of such high-strain parts after introducing surface irregularities)? Thanks for reading.
I don't know if it would help to dimple the blades. That's a question for the design engineers, or even research scientists. All I know is the manufacturers spend hundreds of millions of dollars every year trying to make engines that are more efficient, more powerful, quieter, and lower in emissions every year. I've never heard of one with dimpled blades.
What is that anti-torque fitting that you mention near the end of the video? Does that connect the driver/torque-multiplier to the body of the thing the nut is attaching to, or something else?
Is there a gauge on the torque multiplier? Highest I've gone is 300 ft lbs on an axle nut. 500-1000 is getting into hand grenade territory. =8^O Also, in a reverse flow engine like a PT6, does the flow of air into the air inlet area of the engine act to increase pressure even before it reaches the first compressor stage. Part of my thinking is that a lot of energy is needed to reverse the flow of the air molecules 180 degrees, but another part thinks that the energy required to reverse the flow is recovered in the form of air at the inlet at a higher than atmospheric pressure, especially when the engine is at speed and altitude. Finally, as someone who has also "made tools," it is wrenching at a higher level than those who just use tools.
+Robert Slugg You question is really best answered in a couple chapters in a good introductory text. You cover a lot of ground and are shooting in many directions at once. The multiplier in the video goes to 3000 lb-ft. Our biggest is hydraulic, and can apply 30,000 lb-ft.
Hi, thanks for the videos it is very interesting videos, I never saw one video explaining about stators, you talk very good about blades and etc, but not so much about stators, I suppose that need the same attention like blades or not? Rgds
The video you have commented on is called Jet Questions 81. It is the 81st video in a playlist called your Questions Answered. In the index, you will find several other videos in which I discuss the function of stators.
How slow is the air moving in the engine at full compression? For the air to compress, it has to slow down correct? How slow is it going just before it hits the combustors?
+J D Notice that the ends of the compressor blades are at about the same distance from the center, but the hubs get larger from stage to stage. The air may still slow (or accelerate), I don't actually know the answer to your question... :)
+J D Interesting question, I'd be interested to hear more about this. I don't know the answer but, I can guess the velocity change from first stage to combuster inlet may stay the same or nearly the same but compression actually comes from volumetric change of the space it occupies... but Bernoulli might disagree.
Do you use any kind of sealant between the joins in engine casings, or do they fit so well that there is no call for it? another question is what sort of clips or clamps do you use between pipes and hoses. I only have experience with motorcycle engines but emit watching these jet tech videos very much, cheers.
+apx5777 No sealant is required or specified for most of the engines we work on. Sometimes engines from new customers arrive with gobs of RTV squished out of the splitlines. It adds to the work to remove it.
+apx5777 There are a lot of clamps on all the lines, to control their movement and vibration. They are made of stainless steel, are called "P-clamps", and because they are usually bent or deformed slightly...are one of the biggest pains about working on jets.
i remembered how you mentioned in various videos that the industrial gas turbines are basicaly the same as airplane engines, and that they even share same part numbers etc. my question is, a gas turbine operates without any airspeed, while an aircraft engine is moving through air at high speed and is obviously designed for such an environment. does this have any effect in the performance/efficiency of a gas turbine? i mean, the compressor blades are designed to perform properly while flying, but what happens when sitting on the ground? are they losing some of their aerodynamic properties and performance, or the "suction" itself is making up for the loss of airspeed?
+dimos k Fans and compressors are designed to operate with an air intake velocity that is the equivalent of around half the speed of sound at sea level. Assuming that the engine has a properly designed intake, such as a bellmouth, its compressors won't lose efficiency or performance when it is operating with no forward speed in an industrial application. However, when an engine is in flight at altitude, the forward speed can result in a pressure rise in the intake, which is beneficial in terms of performance relative to its performance if it had no forward speed at that altitude. Now consider what would happen if an engine is operated at a very high forward speed at ground level, possibly even at supersonic speeds. With a properly designed intake system, there will be a substantial pressure rise at the compressor front face and the engine will effectively be supercharged, possibly by as much as 20percent, relative to its 'sea level static' thrust. Can I suggest that you check out the Bloodhound Supersonic Car project?
You have shown us fuel pumps and fuel control systems for jet fuel; what about engines that run on natural gas? What type of fuel pump or control systems are required, if any?
+Mark Potts The natural gas fuel valve, and the computer(s) that control it, are part of the installation. We don't work on them, because they aren't part of the engine.
What do you think about turbine engines as range extenders for electric hybrid systems in cars to fill up the batteries? They would be small, light, smooth and since they can run at a fixed rpm number should be efficent too. Since Turbine engines are that powerful for their size: how big do you think a ~100hp turbine engine would be? Pretty small I guess. Thanks for giving me an insight in turbine-engines!
+Kalimerakis You could also do away with most of the auxiliaries - electric fuel and oil pumps, and the only thing needing to be attached to the main shaft is a generator, used as a motor to start the engine. No need for gearboxes or anything. Weight not mattering so much should mean that the construction could be cheaper, too.
Volvo built a plug in hybrid with turbine range extender in the early 90s, sadly it did not go into production. Jaguar also built one more recently. Gas turbine engine in the 100hp-range: en.wikipedia.org/wiki/Solar_T62
Another great video. Thanks. It could be a camera induced distortion I don't know. The profile of the large GE turbine with the 17 or so stages. For the first time I could see the cone shape of the hub clearly..small at the bottom and large at the top where the blades are smaller and the pressure higher. But it appears that the cone reverses shape again at the last few stages of the compressor. Is this in fact true and if so, why? My toolbox is much more of a jungle than yours, but I keep my box end wrenches just like you.
+boomer9900 You are right. This a subtlety of compressor design, so I bet we'll hear from our friendly neighborhood gas turbine engine design engineer... The tapering shape does not cause the compression of inlet air, as many mistakenly believe. It is shaped like that to maintain the velocity of the air as it moves along the length of the compressor. Air takes up less volume as it gets compressed. The last couple stages begin the transition to the diffuser, which as a divergent duct, lowers velocity and increases pressure of the air. Bonus points for you👍😊
+boomer9900 OK, I couldn't resist the temptation, but I'm not very familiar with the J79/LM1500. Yes, from the GAs that I've looked at, the compressor has a 'falling line' over the last few stages, but even so, the annulus height reduces. I certainly can't discuss the reasoning for this with any authority, but I suspect that it was done basically to improve the match with the combustion section entry and, possibly, to keep the engine that little bit more compact. If you want to see more compressors with a 'falling line', take a look at the booster stages of some of the big US turbofans. It's done in those engines to bring the annulus line down towards that of the HP compressor intake and make the duct between the two shorter and less extreme in aerodynamic terms. Take a look too at the R-R Trent series: their IP compressors have a 'falling line' over the last few stages. Again, this is to make the 'swan neck duct' of the engine's intermediate casing (mid-frame to you) less extreme.
+grahamj9101 Thanks for both your explanations. It's interesting how different people gravitate to different parts of a machine. I find the compressor section of the gas turbine most fascinating. In my earlier years I used Ansys software to do finite element analysis and played around with it's ability to do computation fluid dynamics (CFD). This work was for the semiconductor industry. We were trying to model metal migration due to electron flow in the metal interconnects. It turns out that it an art as much as a science in designing the interconnects. An analogy to the design of the compressor to the combustion section, we had to design the metal interconnects with electron flow patterns in mind to avoid crowding of the electrons at turns and bends. Most people would not realize that in semiconductor chips like a Core I7, the current densities in the interconnects far exceed 10k amps/cm2. I digress...now I just muddle around in my shop on my cars and motorcycles and have fun with the family and friends. It's still fascinating to me and I give many thanks to AgentJayZ for bringing us the unique opportunity to see inside these machines.
+boomer9900 Thanks for your interest in a technology that is not related to your professional experience. CFD is indeed used extensively nowadays in the design of gas turbine engines, resulting in the complex aerofoil shapes that you see, for example, when looking at the latest design of fans. Of course, CFD was way in the future when the J79 and all of the other engines that AgentJayZ works on were designed. I'm fairly sure that the J79 compressor could have been designed with a constant outer annulus diameter over the last few stages. However, to have the diffuser section lined up on the centre line of the heads of the individual combustors, they would have had to be canted outwards and the outer casing enlarged to accommodate them. This would have resulted in a 'bulge' in the profile of the outer casings. Having said this, there might also be another benefit in the 'falling line', as, for the same annulus area, the blades would be relatively longer. This would result in the blade tip clearance being a smaller proportion of the blade height and the overtip leakage slightly less, with some benefit in terms of efficiency and surge margin.
Hey Jay. The start carts I've worked with in the USAF with centrifugal compressors use radial turbines. Not axial turbines. I'm assuming your start cart is the same. We would have to take a peak at the case and would probably be able to tell.
Beach&BoardFan The combustion chamber is usually perpendicular to the rest of the engine. It kind of protrudes out of the plenum and the combustion gases are directed toward the outer edge of the turbine wheel. Look up "air start cart" here in youtube.
+goutvols103 Even in the case of the electrical grid which contains paralleled generators, if the energy input from the fuel exceeds the electrical power demand from the consumers the frequency goes up. Disconnecting the load of a power station will cause it to shut down to prevent damage from over speeding generators/turbines. The same principles apply to other mechanical loads.
Now we are talking about parallel generators, iso synch or droop and getting away from his original comment on increasing/decreasing fuel changes frequency. It has been my experience that disconnection load or load shedding will bring down all parallel gens by same amount - down to spinning reserve. A turbine will protect itself by opening the 52G breaker and going to Full Speed No Load before tripping the unit.
goutvols103 My argument is that the generating capacity of a country basically acts as a single generator, if the generated output(or fuel/energy put into system) exceeds the demand from the customers the frequency goes up. They have national control centre's and strict regulation to try and make sure supply and demand match. You sound like you have expertise in this field and understand the control systems used to make sure the correct amount of fuel/or steam etc is fed into turbines/engines to get the desired output frequency and power. There are plenty of video's of diesel generators hunting around and shutting down because their controls systems are set incorrectly on TH-cam.
+illidur A great deal of cleaning of parts. Not much polishing at all. Parts have to be perfectly clean to function as new, but they do not necessarily need to look good.
I bet that when a new guy starts working at a jet shop...that is when the compressor blades get polished to a gleam...once you work there for a while you probably don't go quite as crazy on the ultra fine detail that ultimately doesnt affect the overall performance or durability...
+grahamj9101 Pretty sure on this channel any process that uses the word super needs to be elaborated on. Vibratory media polish, drag polish, tumbler... etc.? What level of surface smoothness is considered super polished?
+Beach&BoardFan You're asking me to cast my mind as far back as the 1990s. From memory, the process involved tumbling the blades and vanes in revolving drums with an abrasive medium. The processing time had to be closely controlled, to avoid the aerofoils losing chord width and leading/trailing edge radius definition. I can't remember with any certainty the surface finish that was stated on the drawings, but I'm thinking in terms of 16 micro-inches or better.
There are a couple of videos on You-tube of the B-57 Canberra that uses cartridge starting. The amount of smoke in incredible. Well worth doing a search for. Not the most stealthy was to start a Turban (ha got you, Gas Turbine Engine) Can I assume that on a turbo fan gas Turbine Engine, that it is just called the fan, or is it one of the stages of the compressor as it does do some compression? Along those lines, on a turbo prop, I would assume that the propeller is not considered as a compressor stage as it is either connected by a gearbox, or it can be connected to the second spool in a two spool turbine engine, but does not really compress any air (other than through ram effect due to the increased air flow from the propeller.)
+Todd Dembsky The single-stage fan of a high bypass turbofan engine is commonly just referred to as the 'Fan'. Depending on the nomenclature of the manufacturer, it may also more formally be referred to as the LP Fan or Compressor, LP, Stage 1. From memory, the blading in the IAE V2500 engine followed P&W practice, numbering up from Stage 1 for the fan, through the booster stages to the HP compressor, the first stage of which was Stage 6 and the last, Stage 15. In my experience, a propeller has never been counted as a compressor stage. You make a valid point though, as there must be a small pressure rise from the root section of a propeller blade. However, it will be very small as compared to the pressure rise from the root section of a fan blade.
grahamj9101 Thank you Graham. Are are things doing across the pond? Is spring finally arriving there? I was thinking that that with the propeller that the only compression you would really get would be from ram air compression due to flight air speed. From my Cessna days, the blade root on a 172 propeller is more rounded than airfoil.
+Todd Dembsky As you were referring to a turboprop (or propeller gas turbine engine - mustn't forget that "engine" word, eh, so as not to upset AgentJayZ?), I was thinking in terms of altogether bigger props with the cylindrical section of the blades faired by the spinner. Check out the T56 or the Tyne, or more recently, the AE2100 or TP400.
Because the blades in a gas turbine are arranged radially, is the distance between each blade different from the root of one blade to the root of the one next to it, versus the distance from the tip of the same blade to the the tip of the one next to it? The circumference of the compressor shaft (or turbine shaft) of the engine is less than the diameter of the outer case. This would be true of the stators as well. Are the blades shaped to compensate for this difference so a consistently sized space is created between the blades or does the space get larger as you move from roots to tips?
+Rob Oakman Take a close look at the Spey LP compressor, rotor, which AgentJayZ is showing us in this video. The blade aerofoils are 'stacked' on a radial line (well, not quite - but that's another story) and the aerofoils reduce in thickness from root to tip. This means that the circumferential gap between each and every aerofoil increases from root to tip. If the gap were to be made constant, the blades would have a reverse taper on their thickness and the tip sections would be impossibly thick (and heavy).
+grahamj9101 do you know how the engine would be affected if the gap could be made constant? Say a material were created that was somehow strong and lite enough for this. Would it create more or less flow...if you know what I mean? Is there a trade off being made here because of the limitations of the materials?
Sorry, but it would be pointless to try to make the circumferential gap constant. Even if the excessive mass of material at the tip of the blade could be discounted, the excessive volume would make it quite impossible to create a satisfactory aerofoil form, and the increase in 'blockage' would compound the impossibility.
+Rob Oakman OK, you have effectively identified for yourself that the space/chord ratio (aka, the pitch/chord ratio) of the aerofoils does have a significant effect on performance and efficiency . A ratio of about 0.7:1 occurs to mind as an optimum: too few blades wouldn't work. Nevertheless, If the circumferential gap at the blade tips could magically be made the same as that at the roots (without changing the existing aerofoil sections), then it might well give a small improvement - but that's not possible!
+Derrick Moyer We've discussed this a few times in the Q series. At the time of its introduction, the J79 was a vastly superior engine than anything else being produced. It was smokey, but that was the price for nearly double the power. The updated low-smoke combustor liners have eliminated most of the black smoke of the original design.
Hi AgentJayZ! It is I again, matching your pedantry in respect of a "gas turbine engine". I must admit that I sometimes say "gas turbine" and omit to add "engine" - and so did/does the industry more widely. I once worked for Bristol Siddeley Engines, Industrial and Marine Gas Turbine Division, before it magically metamorphosed into the Industrial and Marine Division of Rolls-Royce. And yes, you were touching a first stage blade of the 5-stage LP compressor of that Industrial or Marine(?) Spey engine. The first stage rotor is overhung in front of the front bearing housing, which is supported by the first stage stator vanes, forming the 'front frame', in N American gas turbine (engine) speak. Is there any chance of showing us one of the combustion liners from the engine? That might determine whether it is a liquid-fuelled (I spell 'fuelled' with two 'l's) marine engine or a gas-fuelled industrial engine.
+grahamj9101 It's a liquid fuelled marine Spey. I'll be in Victoria, BC for a week. I can almost guarantee you'd love the place. PS: my spell check redlined "fuelled" !
So, if it's a liquid fuelled Marine Spey, does it have the reflex airspray burner (RAB) standard of combustor? If so, the dome of the can will have a mushroom-shaped device into which the fuel is injected. This is effectively an annular version of the hockey stick or candy cane vaporiser. OK, I'll give you one guess as to who designed it - admittedly in accordance with the principle proposed by our tame combustion engineer at IMD. PS I have an old school friend in that neck of the BC woods, but I haven't heard from him for a year or two.
Agent JayZ, it appears that the 5 stage compressor rotor behind you that is suspended is being supported by a few blades from the straps. should the straps not be placed around the rotor to prevent damage to the rotor blades?
Those first stage blades are immensely strong. We could have slung it the way you suggest, but didn't for two reasons. We wanted to have the points of support as far apart as possible to balance the load. Between each stage there is a labyrinth seal, and the knife edges on the 1-2 seal are quite long and thin. If they were bent or crushed, the seal would need replacing, which would require rotor disassembly and a very expensive part. This compressor is now running in one of the Speys we successfully tested a couple months ago.
Interesting to see the high solidity, lack of blade lean and sweep on those guys, especially R1. Open up a modern compressor and you'll see low aspect ratio low solidity, 3d features to the nth degree.
+squarepusher78 The first three stages are of significantly lower aspect ratio than the TF41blades from which they were derived, no longer requiring snubbers/clappers/mid-span shrouds (choose your term). They were, of course, designed long before CFD came along, but they still look good to me. Keith O** and his designers did a good job on them back in the 1970s.
+Aidan Brown Thrust2 used an Avon. Thrust SSC had a total of four engines throughout its development and then setting the record. 10 years ago, S&S Turbines purchased two of them, and used them for parts. Records weren't kept, so we don't know if we got the trainers or the runners. My guess is: the trainers.
+AgentJayZ I can't be certain, but I think that Thrust SSC still has its record-breaking run engines fitted. I must go back to Cov (Coventry to you) sometime and visit the new building at the Museum of Transport, in which (I was told only yesterday) Thrust 2 and Thrust SSC are now housed.
+AgentJayZ I saw Thrust SSC at R-R Bristol when it did a tour of the UK, immediately after it set the world record. I saw it (and Thrust 2) again at the Coventry Museum of Transport a couple of years ago, when I attended a conference there. I've just found photos and video clips that show the intakes prettily illuminated and the front faces of the two Speys can be seen quite clearly. I can't imagine that anyone bothered to change out the engines after it set the record.
Hi AgentJay. Given the critical safety aspect of working on jet engines, what if a Jet Engine Mechanic had a niggling concern about a job he/she did after servicing an engine (e.g. not reattached a part correctly) and decided to tell the manager and the jet owner had to be contacted. Would he/she be rewarded, disciplined or the issue shrugged off? What do you think the ethos of aircraft serving community is in a situation like this, if it can be generalised? Thanks for the vids.
+Richard E The person who would get in trouble is the chief engineer who signed off on the job, but as AgentJayZ said, there is so many controls, procedures and independent inspections it's pretty well impossible to make those mistakes. As for the second part of your question, you can be forgiven for a mistake if you own up to it. Hiding your mistake will get you fired or maybe imprisoned (if someone is injured/killed).
+Android811 So it's a system of first taking responsibility self and thereafter responsibility rests with 'oversight', like in most companies. I guess in this vocation engineers must have high confidence in their training and be self confident.
Regarding the F-22 "cartridge starter". I was going to bring the question up in the last video about that video you mention thinking it was a starter cartridge, but I do believe that was the F-22's APU starter not a cartridge starter. You can hear the apu running and at about 2:12 the main engines are then brought to ground idle. This is the video I am talking about th-cam.com/video/VAFUo0gmVG8/w-d-xo.html . The apu is actually a 450hp gas turbine engine system. www.globalsecurity.org/military/systems/aircraft/f-22-fcas.htm The F-35 also uses a similar system according to several of my engineering friends, but like most defense workers they will not reveal too much about those systems.
May I ask why the pitch of the compressor (mistakenly written as "turbine" before the edit) blades (shown in the beginning of this video) increases outwards, as opposite to propellers? I understand the goal of propeller pitch design is to produce uniform thrust throughout the length of a blade. I guess the compressor blades are meant to compress the air instead of to push them. How does the pitch design help to achieve that? Thanks.
+Yaofu Zhou I would guess because a propeller is not in a case, so that decreases turbulence at the tip. A compressor tip is very close to its case so they add pitch for more flow without tip turbulence. That's just my guess though
+Yaofu Zhou First off: you mean compressor blades ;). Second the blades actually have decreasing pitch angle from the hub to the tip. You might misinterpret the rotors turning direction? Using 5:01 as reference, the blades are turning upwards.
+TheDotango I had this thought for a bit... forgive my wording but I guess the dominant component of the velocity of air flow is in the rotational direction, rather than along the shaft (we want this component small, right?), and this is why the pitch measurement does not start with the shaft direction, but 90 degrees from the shaft direction...
+Yaofu Zhou The blade pitch angles and many many more things of jet engine are referenced to the shaft axis (direction of main flow for axial machines). As this is a common reference point for design considerations between the relative (rotors) and absolute (stators, case) systems.
+TheDotango Alright I guess I understand your point now. Allow me to rephrase myself - the angle of attack of the the blades against the air flow decreases outwards along the blade.
Each stage of an axial flow compressor has pressure ratio of about 1.1 or 1.15 to 1. To get more compression, more stages are added, and the effect is multiplicative, not additive. A J79 has a CDP of about 150 to 160 psi. If each compressor stage has a pressure ratio of 1.15 to 1, then together the 17 stages have an overall pressure ratio of 10.76 to 1. Multiply 10.76 by one Bar, or 14.7 psi, and we get 158.2 psi. I think we just estimated the average per stage pressure ratio of a J79 compressor, eh?
thank you, its easier to understand now i still wondering why jets now mostly used axial compressor rather than centrifugal compressor, i think the centrifugal compressor has fewer moving parts
why the homebuilt tools? can you not get the "official" tools from the producer? it strikes me as odd that they sell parts that have no tool to fit them. or is it simply cheaper to make them yourself?
Looking for you for 3 years, and now finally found you. I used to write emails to your company, but there was no response. You are my teacher, my team and I now in the production of 300 mm jet engines. In Chinese folk get jet engine knowledge is too difficult, Accurately, it is difficult to see a real jet engine 。thanks to you for helping me, I beg you to give me your email address, I hope can give you Chinese feature gift, to express my gratitude. Thank God let me meet you
Disparity definition: lack of similarity or equality. Why discuss semantics anyway, literally 1 minute before you're saying easy it is to make mistakes when discussing a topic outside your field of expertise. You answered his question when you said "It's easier to collect energy from a high pressure exhaust stream than it is to shove air in to the engine".
On the subject of axial vs. centrifugal compressors in small gas turbines, we touched on this a while back. As the physical size of an axial compressor is reduced, the aerofoils (ok, airfoils) have to be similarly reduced in proportion. Consequently, the blades and vanes get thinner, their leading and trailing edge radii get smaller and they have to be produced to finer tolerances. They tend to be less efficient, with increased aerodynamic losses, and are relatively more susceptible to contamination and foreign object damage (FOD). A centrifugal impeller is significantly more robust in comparison.
+grahamj9101 I think its more the blade height to clearance on the Rotors, especially the rear stages. With smaller compressors, or if you scale down a compressor your clearances don't scale down, larger clearances on smaller blades so higher losses.
+squarepusher78 I was trying to keep my comments simple and fairly brief, as AgentJayZ has implied that I can be long-winded (yes, I admit that I can be!). Stator vane to rotor drum clearance is only a little less significant than rotor blade tip clearance, in terms of leakage. Tip clearances reduce, but don't scale down in proportion, adversely affecting performance and efficiency. To counter the robustness issue, aerofoil dimensions don't normally scale down in proportion, so that surface areas tend to increase. This is compounded by the fact that, as a compressor is scaled down, there must be relatively more surface area of both aerofoil and annulus exposed to the flow. This and the effect of Reynolds Number both result in significantly increased aerodynamic losses in a smaller compressor. Going to a centrifugal stage at the rear of the compressor counters these effects to some extent, but even so, a centrifugal impeller can have its own sensitivities. I had direct experience of a performance monitoring exercise on a small engine impeller, which appeared to be sensitive to the leading edge form and profile of its inducer section. I had a large number of ex-service impellers scanned and compared with a nominal model, with the differences shown in false colour. From the results of those impellers, I was able to predict with a high degree of accuracy the performance of new impellers going into engines at repair and overhaul.
+grahamj9101 If I could give the above comment more then one thumbs up I would. This seems like the a good opportunity to ask about the RR Allison 250 ( www.enginehistory.org/GasTurbines/Allison/7_RR%20ALLISON%20250-B17F.jpg ). Unique engine reverse flow combustion chamber/turbines, combination axial and centrifugal compressor ( assets.catawiki.nl/assets/2016/3/19/6/4/c/64c2c796-ede1-11e5-881a-8682bfd04863.jpg ). Anyway some variants seem to run a solid shrouded turbine blisk (all one piece) not like the shrouded turbine blades AJZ has shown us. ( i.ebayimg.com/images/g/arYAAOSwPhdVBxFh/s-l1600.jpg ) and I've always wondered why that wasn't more common, seems like it would be more robust, reduce blade vibration concerns etc.. Is there a reason its not seen on larger engines. The only down sides I can think of would be mfg complexity. Maybe hoop strength concerns of that outer ring?
Hopefully the picture links work, I wanted to include visuals for other readers that may not know what I'm asking.
Just watched your video of the J-47 assembly and test. It brought back memories of my time, 1966-1968, rebuilding and testing these engines for F-86's owned by Saudi Arabia. Unfortunately our test area was outdoors. Fortunately for use it was Southern California.
I hope you have a great trip. Thanks for showing us around your shop o/
The best channel when it comes on jet engines , I do already learned a lot further here so greetings from Bavaria
Cool seeing your custom tools! Some of them look a lot like the sockets we use for the landing gear wheels on our jets.
Hi Jay. Loved your 'Tool Tour'!
Rich.
Nice mix of topics and interesting to see the tool collection. I had to have fabrication buddy whip up a spanner socket right quick for the J44 compressor stub shaft nut. We will also need to make a locking/holding fixture/tool to fix the rotor while tightening the nut. That is part of the challenge and the fun, unless it costs like Jay's AI-25 arbor! Less fun. My socket was very simple and Mark owns the $150,000 laser cutting machine, so it was 'free'. Have a great and safe trip.
DD
Thanks for another awesome vid Jay!
awesome tour thanks for video jay
17:25 describing my life in auto dealer parts. Thanks for the great videos
Once again very informative video, thanks!
With the stage 0 and 00 it's just like Phillips screwdrivers sizes 2-1-0-00-000 I guess
Love the tour of your toolbox. I drew all sorts of conclusions about you.
+Dawn Alderman Uh oh...
Love the tools (I'm a big rig mech and a gear head). Show us some more specialty stuff in use.
Awesome video.
Smoking green wrapped with agentJayZ makes for very interesting information 👍
Hi!
Up front - really loving your video's! Great work and keep them coming!
In this video you go on subject about the F-22 and it's start system (in brief). The puf of smoke (and occasionally a flame) you see coming out of the side of the F-22 is in fact the APU of the F-22 starting up. As far as I know it does not use a cartridge start system, unless the APU starts up with such a system, which I would find illogical.
Cheers!
Lukas
+MTFDarkEagle You're right, going back to the F-15 APU's have been used on US fighters.
+MTFDarkEagle Hey, if you know, I'll respect that.
I don't know, but the video shows what looks like an engine start.
After the exhaust jet, there are sounds in the video of an engine winding up, not APU sounds.
An APU can easily be started with a single aircraft battery. No need for pyrotechnics.
Does the F-22 not have an on board battery?
+AgentJayZ I'm fairly certain the APU on the F-22 is started via compressed air, I do not believe pyro is used at all during engine start.
+AgentJayZ The f-16's APU runs on Hydrazine, which is a really dangerous (and expensive) rocket fuel.
I have no idea if the Raptor uses the same, just putting it out there.
it multiplies the force applied by 160. years ago I used a torque multiplier to install the jesus nut on UH1H helicopters, the jesus nut is what we called the nut that holds on the main rotor head. it had 650 foot pounds. you torque it and wait torque it and wait several times.
Brave video, but much appreciated. I like your custom tools.
I made the mistake posting a picture of my stereo system on an audiophile polk speaker forum with my new speakers and oh how the criticism flowed... Hope you don't have a simular experience...
For protecting the arbor, you could get some Kydex sheet, and form it over a mandrel (or the actual part) It looks like it may be small enough that you can fit it in a 5 gallon bucket, and use the kydex to keep it from flopping around some desiccant or vapor corrosion inhibitor paper/tabs to keep it corrosion free.Though I'm sure you have something planned.
+CKOD A plastic bucket is an excellent idea!
What generation fighter aircraft do you prefer? I like high tech, but I'm more of a 2nd generation and A-10 type of guy. My thoughts on the SR-71 are the same as yours. Thanks for the videos and the tremendous amount of knowledge you share.
Without giving too trade secrets away, on the boat, whose jet engine that you worked on, does it utilize water injection? If it does, can you provide more detail as to where the injection is inserted, amount (gpm) and shp improvement? I am familiar with Water Wash on GE Frame turbines and the water needs to be demineralized water.
The steering wheel analogy 😄
Great videos (and I'm not an aero-engine nut!)
Just out of curiosity has anyone tried making a centrifugal turbine on a jet engine? A sort of centrifugal compressor in reverse. I don't suppose there would be any advantages just curious.
The F22 cannot be cartridge started, those videos with the flame and smoke are from the APU starting.
The following occurred on a trip from Guam to Hickam AFB Hi. In 1979. This question pertains to a PW J-57-59W. This engine was installed on the KC-135-A. But first the in flight problem. The pilot summoned me to the cockpit to show me the #1 engine has low oil pressure but when he brought the engine to idle the pressure normalized. The pilot decided to fly the rest of the mission with that engine at idle.
When we landed the tower controller said we had a fuel leak on number one. When we parked and shut down the engine I checked the oil on number 1. The oil tank was full of fuel. I guess fuel lubed the engine. I told the pilot we would be stuck in Hawaii until the new engine was delivered and changed.
As the aircraft crew chief my job wasn’t to figure out how fuel displaced oil. My job was to change the engine. So what would you say happened?
After the engine was changed and set up for an engine trim I had the honor of running all four engines under max thrust injecting water.
The only place I know of that oil and fuel come in close proximity in any quantity is the fuel cooled oil cooler. Both oil and fuel are under some pressure, and if there is a leak anywhere, the two will mix.
That would be the first thing I would remove and pressure test.
I'v e only just picked up this comment: I agree. I'm reminded of the time I found lub oil in the coolant header tank of my car. The oil cooler, which was cooled not by air but by engine coolant, had failed internally.
I had no idea the F-22 was cartridge started. VERY interesting!
It isn't.... It has an APU that uses Hydrazine.
'The Scales of a dragon or the teeth of a shark'... nah, just the Axial LP compressor from an RR marine SPEY.
Hey J: Specialty Tool $ in All Techie Situation's can B a Deal Breaker.Imagine a Lend/Rent Tool Distribution Center 4 Specialists.We could call it Nerd-Vain'in!!!
Hi Jay,
Thanks for all your videos. I realize your job is in overhaul and maintenance. But it got me wondering if you have ever been able to go on-site with a customer and see the industrial installation for a gas turbine generator. If so, do you think a customer would ever allow you shoot some video?
-Mark
The main difference in an axial compressor and a centrifugal compressor is that while the former is good at handling large amount of air for smaller pressure ratio, the later is good for giving larger pressure ratio to small amount of air. So centrifugal compressor is very compact when one wants to achieve required pressure ratio for relatively small amount of air i. e. when power output needed is relatively small. Some engines have axial LP compressors followed by one or two HP centrifugal compressor because the air volume is reduced significantly through theLP to the level where the HP centrifugal compressor can handle it. Centrifugal compressor makes small jet engines compact.
Have you ever shown a closeup of the diagram above the orange press at the bottom of the stairs? You can see it at 14:00 to the left of the screen. It looks like it shows an engine in an industrial installation.
+compactc9 It looks like a Cooper-Rolls Coberra power turbine, powered by an Industrial Spey, to me.
Apropos to a previous question about what a drone strike might do to an engine, I have some stop press news. I have just picked up an online report that, earlier today, a British Airways A320, which was on approach into Heathrow, took a drone strike. Fortunately, there was no engine involvement and the aircraft was cleared to continue in service. However, it begs the question, what if ..... ? The incident is apparently the first ever drone strike on an aircraft to be reported, but I doubt that it will be the last. We've already had several near misses reported here in the UK.
+grahamj9101 Was it a bird? No! Was it a drone? No! It was a plastic bag or a bit of polystyrene! That's officially the latest. There was no blood to indicate a birdstrike and no damage to the plane.
Not some poor kid who dropped a helium balloon then? :-) Drones are becoming a nuisance, it has happened a couple of times in Sweden that air traffic around air ports have been shut down because of a drone flying too close.
This is probably a dumb question, and I'm sure you'll light me up for it (if you even deem it worthy of response) but here goes:
Looking at the super-polished compressor blades made me think of some things I've heard discussed about smooth surfaces and aerodynamic adhesion - specifically that laminar airflows like to become "unstuck" from smooth surfaces, and how this effect can increase drag.
My question, therefore, is to ask if it would make sense to dimple the low-pressure faces of compressor blades and stators? The idea being that this would introduce swirling in the boundary layer and help keep it from separating from the LP surface of those airfoils (as with the vortex generators on STOL bush planes or the dimples on a golf ball). Or do the existing airflow shaping devices (VSVs and bleed air) already perform sufficiently well at this task that there would be no benefit (or, no appreciable benefit to offset the daunting task of ensuring structural integrity of such high-strain parts after introducing surface irregularities)?
Thanks for reading.
I don't know if it would help to dimple the blades. That's a question for the design engineers, or even research scientists.
All I know is the manufacturers spend hundreds of millions of dollars every year trying to make engines that are more efficient, more powerful, quieter, and lower in emissions every year.
I've never heard of one with dimpled blades.
2:08 Honeywell makes automotive turbochargers with axial flow turbines, see DualBoost.
awesome thanks.. did you modify the bent handled needle nose pliers?
+thomas m. tordel jr. No, they are a standard set of MAC pliers. Quite handy sometimes.
13:52
Am I the only one who noticed the turboshaft diagram hanging on the wall? just a pointless detail I'm bringing up.
What is that anti-torque fitting that you mention near the end of the video? Does that connect the driver/torque-multiplier to the body of the thing the nut is attaching to, or something else?
+Steven Ziuchkovski This question will be answered in a future video, because it requires me talking and moving my hands at the same time...
Is there a gauge on the torque multiplier? Highest I've gone is 300 ft lbs on an axle nut. 500-1000 is getting into hand grenade territory. =8^O Also, in a reverse flow engine like a PT6, does the flow of air into the air inlet area of the engine act to increase pressure even before it reaches the first compressor stage. Part of my thinking is that a lot of energy is needed to reverse the flow of the air molecules 180 degrees, but another part thinks that the energy required to reverse the flow is recovered in the form of air at the inlet at a higher than atmospheric pressure, especially when the engine is at speed and altitude. Finally, as someone who has also "made tools," it is wrenching at a higher level than those who just use tools.
+Robert Slugg You question is really best answered in a couple chapters in a good introductory text. You cover a lot of ground and are shooting in many directions at once.
The multiplier in the video goes to 3000 lb-ft.
Our biggest is hydraulic, and can apply 30,000 lb-ft.
Hi, thanks for the videos it is very interesting videos, I never saw one video explaining about stators, you talk very good about blades and etc, but not so much about stators, I suppose that need the same attention like blades or not?
Rgds
The video you have commented on is called Jet Questions 81. It is the 81st video in a playlist called your Questions Answered. In the index, you will find several other videos in which I discuss the function of stators.
thanx
How slow is the air moving in the engine at full compression? For the air to compress, it has to slow down correct? How slow is it going just before it hits the combustors?
+J D Notice that the ends of the compressor blades are at about the same distance from the center, but the hubs get larger from stage to stage. The air may still slow (or accelerate), I don't actually know the answer to your question... :)
+J D Interesting question, I'd be interested to hear more about this. I don't know the answer but, I can guess the velocity change from first stage to combuster inlet may stay the same or nearly the same but compression actually comes from volumetric change of the space it occupies... but Bernoulli might disagree.
Do you use any kind of sealant between the joins in engine casings, or do they fit so well that there is no call for it? another question is what sort of clips or clamps do you use between pipes and hoses. I only have experience with motorcycle engines but emit watching these jet tech videos very much, cheers.
+apx5777 No sealant is required or specified for most of the engines we work on.
Sometimes engines from new customers arrive with gobs of RTV squished out of the splitlines.
It adds to the work to remove it.
+apx5777 There are a lot of clamps on all the lines, to control their movement and vibration.
They are made of stainless steel, are called "P-clamps", and because they are usually bent or deformed slightly...are one of the biggest pains about working on jets.
i remembered how you mentioned in various videos that the industrial gas turbines are basicaly the same as airplane engines, and that they even share same part numbers etc.
my question is, a gas turbine operates without any airspeed, while an aircraft engine is moving through air at high speed and is obviously designed for such an environment.
does this have any effect in the performance/efficiency of a gas turbine? i mean, the compressor blades are designed to perform properly while flying, but what happens when sitting on the ground? are they losing some of their aerodynamic properties and performance, or the "suction" itself is making up for the loss of airspeed?
+dimos k If you check the playlist index for Inlet Bellmouth, you will find this question discussed in several videos
+dimos k Fans and compressors are designed to operate with an air intake velocity that is the equivalent of around half the speed of sound at sea level. Assuming that the engine has a properly designed intake, such as a bellmouth, its compressors won't lose efficiency or performance when it is operating with no forward speed in an industrial application. However, when an engine is in flight at altitude, the forward speed can result in a pressure rise in the intake, which is beneficial in terms of performance relative to its performance if it had no forward speed at that altitude. Now consider what would happen if an engine is operated at a very high forward speed at ground level, possibly even at supersonic speeds. With a properly designed intake system, there will be a substantial pressure rise at the compressor front face and the engine will effectively be supercharged, possibly by as much as 20percent, relative to its 'sea level static' thrust. Can I suggest that you check out the Bloodhound Supersonic Car project?
grahamj9101 thx for the response :)
More close up look please!
You have shown us fuel pumps and fuel control systems for jet fuel; what about engines that run on natural gas? What type of fuel pump or control systems are required, if any?
+Mark Potts The natural gas fuel valve, and the computer(s) that control it, are part of the installation. We don't work on them, because they aren't part of the engine.
What do you think about turbine engines as range extenders for electric hybrid systems in cars to fill up the batteries?
They would be small, light, smooth and since they can run at a fixed rpm number should be efficent too.
Since Turbine engines are that powerful for their size: how big do you think a ~100hp turbine engine would be?
Pretty small I guess.
Thanks for giving me an insight in turbine-engines!
+Kalimerakis You could also do away with most of the auxiliaries - electric fuel and oil pumps, and the only thing needing to be attached to the main shaft is a generator, used as a motor to start the engine. No need for gearboxes or anything.
Weight not mattering so much should mean that the construction could be cheaper, too.
Volvo built a plug in hybrid with turbine range extender in the early 90s, sadly it did not go into production. Jaguar also built one more recently.
Gas turbine engine in the 100hp-range: en.wikipedia.org/wiki/Solar_T62
Kalimerakis better to use a turbodiesel tuned for a fixed speed, turbines are less fuel efficient.
Another great video. Thanks. It could be a camera induced distortion I don't know. The profile of the large GE turbine with the 17 or so stages. For the first time I could see the cone shape of the hub clearly..small at the bottom and large at the top where the blades are smaller and the pressure higher. But it appears that the cone reverses shape again at the last few stages of the compressor. Is this in fact true and if so, why? My toolbox is much more of a jungle than yours, but I keep my box end wrenches just like you.
+boomer9900 You are right. This a subtlety of compressor design, so I bet we'll hear from our friendly neighborhood gas turbine engine design engineer...
The tapering shape does not cause the compression of inlet air, as many mistakenly believe.
It is shaped like that to maintain the velocity of the air as it moves along the length of the compressor.
Air takes up less volume as it gets compressed.
The last couple stages begin the transition to the diffuser, which as a divergent duct, lowers velocity and increases pressure of the air. Bonus points for you👍😊
+boomer9900 OK, I couldn't resist the temptation, but I'm not very familiar with the J79/LM1500. Yes, from the GAs that I've looked at, the compressor has a 'falling line' over the last few stages, but even so, the annulus height reduces. I certainly can't discuss the reasoning for this with any authority, but I suspect that it was done basically to improve the match with the combustion section entry and, possibly, to keep the engine that little bit more compact. If you want to see more compressors with a 'falling line', take a look at the booster stages of some of the big US turbofans. It's done in those engines to bring the annulus line down towards that of the HP compressor intake and make the duct between the two shorter and less extreme in aerodynamic terms. Take a look too at the R-R Trent series: their IP compressors have a 'falling line' over the last few stages. Again, this is to make the 'swan neck duct' of the engine's intermediate casing (mid-frame to you) less extreme.
+grahamj9101 Thanks for both your explanations. It's interesting how different people gravitate to different parts of a machine. I find the compressor section of the gas turbine most fascinating. In my earlier years I used Ansys software to do finite element analysis and played around with it's ability to do computation fluid dynamics (CFD). This work was for the semiconductor industry. We were trying to model metal migration due to electron flow in the metal interconnects. It turns out that it an art as much as a science in designing the interconnects. An analogy to the design of the compressor to the combustion section, we had to design the metal interconnects with electron flow patterns in mind to avoid crowding of the electrons at turns and bends. Most people would not realize that in semiconductor chips like a Core I7, the current densities in the interconnects far exceed 10k amps/cm2. I digress...now I just muddle around in my shop on my cars and motorcycles and have fun with the family and friends. It's still fascinating to me and I give many thanks to AgentJayZ for bringing us the unique opportunity to see inside these machines.
+boomer9900 Thanks for your interest in a technology that is not related to your professional experience. CFD is indeed used extensively nowadays in the design of gas turbine engines, resulting in the complex aerofoil shapes that you see, for example, when looking at the latest design of fans. Of course, CFD was way in the future when the J79 and all of the other engines that AgentJayZ works on were designed. I'm fairly sure that the J79 compressor could have been designed with a constant outer annulus diameter over the last few stages. However, to have the diffuser section lined up on the centre line of the heads of the individual combustors, they would have had to be canted outwards and the outer casing enlarged to accommodate them. This would have resulted in a 'bulge' in the profile of the outer casings. Having said this, there might also be another benefit in the 'falling line', as, for the same annulus area, the blades would be relatively longer. This would result in the blade tip clearance being a smaller proportion of the blade height and the overtip leakage slightly less, with some benefit in terms of efficiency and surge margin.
Hey Jay. The start carts I've worked with in the USAF with centrifugal compressors use radial turbines. Not axial turbines. I'm assuming your start cart is the same. We would have to take a peak at the case and would probably be able to tell.
+MrBen527 I think you are right.
AgentJayZ
Yeah, the start cart turbines look and operate exactly like a turbo charger turbine for a piston engine.
+MrBen527 Interesting, so where is the combustion chamber? I was under the impression they used centrifugal compressors and axial turbines.
Beach&BoardFan
The combustion chamber is usually perpendicular to the rest of the engine. It kind of protrudes out of the plenum and the combustion gases are directed toward the outer edge of the turbine wheel.
Look up "air start cart" here in youtube.
In an industrial unit, increasing or decreasing fuel flow will only effect the MegaWatt (MW) output and not the frequency.
+goutvols103 Maybe if it's turning a generator electrically locked to the grid frequency :-)
Most industrial units are synched to a grid generating power except, say the ones turning a mechanical load (e.g. compressor).
+goutvols103 Even in the case of the electrical grid which contains paralleled generators, if the energy input from the fuel exceeds the electrical power demand from the consumers the frequency goes up. Disconnecting the load of a power station will cause it to shut down to prevent damage from over speeding generators/turbines. The same principles apply to other mechanical loads.
Now we are talking about parallel generators, iso synch or droop and getting away from his original comment on increasing/decreasing fuel changes frequency. It has been my experience that disconnection load or load shedding will bring down all parallel gens by same amount - down to spinning reserve. A turbine will protect itself by opening the 52G breaker and going to Full Speed No Load before tripping the unit.
goutvols103 My argument is that the generating capacity of a country basically acts as a single generator, if the generated output(or fuel/energy put into system) exceeds the demand from the customers the frequency goes up. They have national control centre's and strict regulation to try and make sure supply and demand match. You sound like you have expertise in this field and understand the control systems used to make sure the correct amount of fuel/or steam etc is fed into turbines/engines to get the desired output frequency and power. There are plenty of video's of diesel generators hunting around and shutting down because their controls systems are set incorrectly on TH-cam.
Are the zero stages you talked about added by the maker or can they be added as an "upgrade" is shops like yours?
+Robert Albert I think I explained that very clearly in the video
Does repairing jet engines involve a lot of polishing and cleaning?
+illidur A great deal of cleaning of parts. Not much polishing at all. Parts have to be perfectly clean to function as new, but they do not necessarily need to look good.
I bet that when a new guy starts working at a jet shop...that is when the compressor blades get polished to a gleam...once you work there for a while you probably don't go quite as crazy on the ultra fine detail that ultimately doesnt affect the overall performance or durability...
+Gary Ferguson Jr In my time at R-R, we started 'super polishing' of compressor aerofoils for improved efficiency and performance.
+grahamj9101 Pretty sure on this channel any process that uses the word super needs to be elaborated on. Vibratory media polish, drag polish, tumbler... etc.? What level of surface smoothness is considered super polished?
+Beach&BoardFan You're asking me to cast my mind as far back as the 1990s. From memory, the process involved tumbling the blades and vanes in revolving drums with an abrasive medium. The processing time had to be closely controlled, to avoid the aerofoils losing chord width and leading/trailing edge radius definition. I can't remember with any certainty the surface finish that was stated on the drawings, but I'm thinking in terms of 16 micro-inches or better.
There are a couple of videos on You-tube of the B-57 Canberra that uses cartridge starting. The amount of smoke in incredible. Well worth doing a search for. Not the most stealthy was to start a Turban (ha got you, Gas Turbine Engine) Can I assume that on a turbo fan gas Turbine Engine, that it is just called the fan, or is it one of the stages of the compressor as it does do some compression? Along those lines, on a turbo prop, I would assume that the propeller is not considered as a compressor stage as it is either connected by a gearbox, or it can be connected to the second spool in a two spool turbine engine, but does not really compress any air (other than through ram effect due to the increased air flow from the propeller.)
+Todd Dembsky It's called the LP (low pressure) compressor.
Android811 Thank you
+Todd Dembsky The single-stage fan of a high bypass turbofan engine is commonly just referred to as the 'Fan'. Depending on the nomenclature of the manufacturer, it may also more formally be referred to as the LP Fan or Compressor, LP, Stage 1. From memory, the blading in the IAE V2500 engine followed P&W practice, numbering up from Stage 1 for the fan, through the booster stages to the HP compressor, the first stage of which was Stage 6 and the last, Stage 15. In my experience, a propeller has never been counted as a compressor stage. You make a valid point though, as there must be a small pressure rise from the root section of a propeller blade. However, it will be very small as compared to the pressure rise from the root section of a fan blade.
grahamj9101 Thank you Graham. Are are things doing across the pond? Is spring finally arriving there?
I was thinking that that with the propeller that the only compression you would really get would be from ram air compression due to flight air speed. From my Cessna days, the blade root on a 172 propeller is more rounded than airfoil.
+Todd Dembsky As you were referring to a turboprop (or propeller gas turbine engine - mustn't forget that "engine" word, eh, so as not to upset AgentJayZ?), I was thinking in terms of altogether bigger props with the cylindrical section of the blades faired by the spinner. Check out the T56 or the Tyne, or more recently, the AE2100 or TP400.
I have a question how many gallons of fuel. Does a jet engine burn per mille?
That is not the way it's measured for aircraft. Industrial engines don't move, so they are not measured that way either.
Because the blades in a gas turbine are arranged radially, is the distance between each blade different from the root of one blade to the root of the one next to it, versus the distance from the tip of the same blade to the the tip of the one next to it? The circumference of the compressor shaft (or turbine shaft) of the engine is less than the diameter of the outer case. This would be true of the stators as well. Are the blades shaped to compensate for this difference so a consistently sized space is created between the blades or does the space get larger as you move from roots to tips?
+Rob Oakman Take a close look at the Spey LP compressor, rotor, which AgentJayZ is showing us in this video. The blade aerofoils are 'stacked' on a radial line (well, not quite - but that's another story) and the aerofoils reduce in thickness from root to tip. This means that the circumferential gap between each and every aerofoil increases from root to tip. If the gap were to be made constant, the blades would have a reverse taper on their thickness and the tip sections would be impossibly thick (and heavy).
+grahamj9101 do you know how the engine would be affected if the gap could be made constant? Say a material were created that was somehow strong and lite enough for this. Would it create more or less flow...if you know what I mean? Is there a trade off being made here because of the limitations of the materials?
Sorry, but it would be pointless to try to make the circumferential gap constant. Even if the excessive mass of material at the tip of the blade could be discounted, the excessive volume would make it quite impossible to create a satisfactory aerofoil form, and the increase in 'blockage' would compound the impossibility.
+Rob Oakman OK, you have effectively identified for yourself that the space/chord ratio (aka, the pitch/chord ratio) of the aerofoils does have a significant effect on performance and efficiency . A ratio of about 0.7:1 occurs to mind as an optimum: too few blades wouldn't work. Nevertheless, If the circumferential gap at the blade tips could magically be made the same as that at the roots (without changing the existing aerofoil sections), then it might well give a small improvement - but that's not possible!
+grahamj9101 That's really cool. Thank you.
why did the j79 burn so dirty compared to some other jets?
+Derrick Moyer We've discussed this a few times in the Q series.
At the time of its introduction, the J79 was a vastly superior engine than anything else being produced. It was smokey, but that was the price for nearly double the power.
The updated low-smoke combustor liners have eliminated most of the black smoke of the original design.
can u please give some brief knowledge about cfm 56 engine
I have done that in a few videos. Also there are many good websites describing two spool high bypass turbofans engines.
Hi AgentJayZ! It is I again, matching your pedantry in respect of a "gas turbine engine". I must admit that I sometimes say "gas turbine" and omit to add "engine" - and so did/does the industry more widely. I once worked for Bristol Siddeley Engines, Industrial and Marine Gas Turbine Division, before it magically metamorphosed into the Industrial and Marine Division of Rolls-Royce. And yes, you were touching a first stage blade of the 5-stage LP compressor of that Industrial or Marine(?) Spey engine. The first stage rotor is overhung in front of the front bearing housing, which is supported by the first stage stator vanes, forming the 'front frame', in N American gas turbine (engine) speak. Is there any chance of showing us one of the combustion liners from the engine? That might determine whether it is a liquid-fuelled (I spell 'fuelled' with two 'l's) marine engine or a gas-fuelled industrial engine.
+grahamj9101 It's a liquid fuelled marine Spey.
I'll be in Victoria, BC for a week. I can almost guarantee you'd love the place.
PS: my spell check redlined "fuelled" !
So, if it's a liquid fuelled Marine Spey, does it have the reflex airspray burner (RAB) standard of combustor? If so, the dome of the can will have a mushroom-shaped device into which the fuel is injected. This is effectively an annular version of the hockey stick or candy cane vaporiser. OK, I'll give you one guess as to who designed it - admittedly in accordance with the principle proposed by our tame combustion engineer at IMD.
PS I have an old school friend in that neck of the BC woods, but I haven't heard from him for a year or two.
Agent JayZ, it appears that the 5 stage compressor rotor behind you that is suspended is being supported by a few blades from the straps. should the straps not be placed around the rotor to prevent damage to the rotor blades?
Those first stage blades are immensely strong. We could have slung it the way you suggest, but didn't for two reasons.
We wanted to have the points of support as far apart as possible to balance the load.
Between each stage there is a labyrinth seal, and the knife edges on the 1-2 seal are quite long and thin. If they were bent or crushed, the seal would need replacing, which would require rotor disassembly and a very expensive part.
This compressor is now running in one of the Speys we successfully tested a couple months ago.
That makes a lot of sense. Thanks AgentJayZ
Interesting to see the high solidity, lack of blade lean and sweep on those guys, especially R1. Open up a modern compressor and you'll see low aspect ratio low solidity, 3d features to the nth degree.
+squarepusher78 The first three stages are of significantly lower aspect ratio than the TF41blades from which they were derived, no longer requiring snubbers/clappers/mid-span shrouds (choose your term). They were, of course, designed long before CFD came along, but they still look good to me. Keith O** and his designers did a good job on them back in the 1970s.
Yes good point. Part span shroud is what i'd call them.
I found out a few days ago that thrust 2 and thrust ssc were rolls Royce Spey and Avon (don't know which is which)
+Aidan Brown Thrust2 used an Avon.
Thrust SSC had a total of four engines throughout its development and then setting the record.
10 years ago, S&S Turbines purchased two of them, and used them for parts.
Records weren't kept, so we don't know if we got the trainers or the runners.
My guess is: the trainers.
+AgentJayZ I can't be certain, but I think that Thrust SSC still has its record-breaking run engines fitted. I must go back to Cov (Coventry to you) sometime and visit the new building at the Museum of Transport, in which (I was told only yesterday) Thrust 2 and Thrust SSC are now housed.
+AgentJayZ wow, thanks!
+AgentJayZ I saw Thrust SSC at R-R Bristol when it did a tour of the UK, immediately after it set the world record. I saw it (and Thrust 2) again at the Coventry Museum of Transport a couple of years ago, when I attended a conference there. I've just found photos and video clips that show the intakes prettily illuminated and the front faces of the two Speys can be seen quite clearly. I can't imagine that anyone bothered to change out the engines after it set the record.
billynomates :)
Hi AgentJay. Given the critical safety aspect of working on jet engines, what if a Jet Engine Mechanic had a niggling concern about a job he/she did after servicing an engine (e.g. not reattached a part correctly) and decided to tell the manager and the jet owner had to be contacted. Would he/she be rewarded, disciplined or the issue shrugged off? What do you think the ethos of aircraft serving community is in a situation like this, if it can be generalised? Thanks for the vids.
+Richard E There are systems in place that render the first part of your question not applicable.
+Richard E There are systems in place that render the first part of your question not applicable.
+Richard E The person who would get in trouble is the chief engineer who signed off on the job, but as AgentJayZ said, there is so many controls, procedures and independent inspections it's pretty well impossible to make those mistakes.
As for the second part of your question, you can be forgiven for a mistake if you own up to it. Hiding your mistake will get you fired or maybe imprisoned (if someone is injured/killed).
+Android811 So it's a system of first taking responsibility self and thereafter responsibility rests with 'oversight', like in most companies. I guess in this vocation engineers must have high confidence in their training and be self confident.
Richard E I wouldn't say confident, at least in my case (I'm just starting out as an AME). It's more about honesty and taking pride in your work.
Combotion chembar one more video 📸📷📷
Regarding the F-22 "cartridge starter". I was going to bring the question up in the last video about that video you mention thinking it was a starter cartridge, but I do believe that was the F-22's APU starter not a cartridge starter. You can hear the apu running and at about 2:12 the main engines are then brought to ground idle. This is the video I am talking about th-cam.com/video/VAFUo0gmVG8/w-d-xo.html . The apu is actually a 450hp gas turbine engine system. www.globalsecurity.org/military/systems/aircraft/f-22-fcas.htm The F-35 also uses a similar system according to several of my engineering friends, but like most defense workers they will not reveal too much about those systems.
May I ask why the pitch of the compressor (mistakenly written as "turbine" before the edit) blades (shown in the beginning of this video) increases outwards, as opposite to propellers? I understand the goal of propeller pitch design is to produce uniform thrust throughout the length of a blade. I guess the compressor blades are meant to compress the air instead of to push them. How does the pitch design help to achieve that? Thanks.
+Yaofu Zhou I would guess because a propeller is not in a case, so that decreases turbulence at the tip. A compressor tip is very close to its case so they add pitch for more flow without tip turbulence. That's just my guess though
+Yaofu Zhou First off: you mean compressor blades ;). Second the blades actually have decreasing pitch angle from the hub to the tip. You might misinterpret the rotors turning direction? Using 5:01 as reference, the blades are turning upwards.
+TheDotango I had this thought for a bit... forgive my wording but I guess the dominant component of the velocity of air flow is in the rotational direction, rather than along the shaft (we want this component small, right?), and this is why the pitch measurement does not start with the shaft direction, but 90 degrees from the shaft direction...
+Yaofu Zhou The blade pitch angles and many many more things of jet engine are referenced to the shaft axis (direction of main flow for axial machines). As this is a common reference point for design considerations between the relative (rotors) and absolute (stators, case) systems.
+TheDotango Alright I guess I understand your point now. Allow me to rephrase myself - the angle of attack of the the blades against the air flow decreases outwards along the blade.
"Mechanical Pornography" yes, exactly!
why axial compressor has stage compression why dont just make nozzle from the first compressor blade?
Each stage of an axial flow compressor has pressure ratio of about 1.1 or 1.15 to 1. To get more compression, more stages are added, and the effect is multiplicative, not additive. A J79 has a CDP of about 150 to 160 psi.
If each compressor stage has a pressure ratio of 1.15 to 1, then together the 17 stages have an overall pressure ratio of 10.76 to 1. Multiply 10.76 by one Bar, or 14.7 psi, and we get 158.2 psi.
I think we just estimated the average per stage pressure ratio of a J79 compressor, eh?
thank you, its easier to understand now
i still wondering why jets now mostly used axial compressor rather than centrifugal compressor, i think the centrifugal compressor has fewer moving parts
You may want to check the index of my playlist of videos called Your Questions Answered...
AgentJayZ have my question answered... thanks AgentJayz!
why the homebuilt tools? can you not get the "official" tools from the producer? it strikes me as odd that they sell parts that have no tool to fit them. or is it simply cheaper to make them yourself?
this is the dark side. I don't know why I brought you here :)
F4 phantom cartridge start:
th-cam.com/video/rodPPrpAqVQ/w-d-xo.html
Damn, that is some smoke!
Looking for you for 3 years, and now finally found you. I used to write emails to your company, but there was no response. You are my teacher, my team and I now in the production of 300 mm jet engines. In Chinese folk get jet engine knowledge is too difficult, Accurately, it is difficult to see a real jet engine 。thanks to you for helping me, I beg you to give me your email address, I hope can give you Chinese feature gift, to express my gratitude. Thank God let me meet you
Disparity definition: lack of similarity or equality.
Why discuss semantics anyway, literally 1 minute before you're saying easy it is to make mistakes when discussing a topic outside your field of expertise.
You answered his question when you said "It's easier to collect energy from a high pressure exhaust stream than it is to shove air in to the engine".