Discussion of the purpose of the afterburner/reheat system and the variable nozzle that goes with it. Saab Draken Afterburner: • Saab Draken Afterburner Also: • Draken Afterburner to ...
My favorite internal combustion sound. Lifelong wing nut, but never in the military. I live near a SAC base (bombers) and have been to dozens of annual airshows, but getting to hear afterburners as a civilian is rare. When I do hear it, I get reminded and can't hardly believe perfect it sounds.
There is an elephant in the room: supersonic airflow. Airflow in a turbine engine is subsonic, because supersonic airfoils are basically too inefficient to use in turbine engines. Even supersonic airplanes have subsonic airflow in the compressors and turbines in their engines. There is a lot to be said about how supersonic airplanes get their intake air subsonic before it enters the compressor, but that's not the point of your video. (It's also true that some compressor blade tips are supersonic, but designers go to great lengths to avoid or reduce this, including multiple spool turbines and geared turbofans.) Air coming out of the turbines, even in supersonic airplanes, is subsonic. You might wonder how a subsonic airflow produces thrust for a supersonic airplane. Answer: the speed of sound rises as the square root of the absolute air temperature. The subsonic flow coming from a turbine on, say, the Concorde is actually faster than the colder supersonic flow going around the airplane. The job of the nozzle behind the last turbine stage is to convert pressure greater than ambient pressure into exhaust velocity. In subsonic flows, you convert pressure (and temperature) to velocity with a converging pipe. That's why all engines running without their afterburners have converging nozzles behind them. Ideally the gas exits at ambient pressure so there is no wasted pressure. In supersonic flows, you convert pressure into velocity with a diverging pipe. This makes supersonic nozzles more complex because they must have a converging section where velocity rises subsonically, a sonically choked throat where the velocity is exactly Mach 1 (at whatever the air temperature is), and a diverging section where velocity rises supersonically. If the nozzle doesn't match the condition of the gas stream, the flow won't be exactly Mach 1 at the throat and the exhaust will stay subsonic and slow down through the diverging section. That's bad. This is why optionally afterburning turbojet engines must have variable nozzles. It's not just the exit diameter that must vary, it's the throat diameter as well. Getting the throat diameter right is actually more important. All nozzles convert pressure into velocity. Afterburners don't increase the pressure after the turbine. Converting the same pressure into velocity yields more velocity when the gas starts out at higher temperature.
Sounds like that's similar to the physics going on in rocket engines where you also have a converging section (to throat as constricting element) and a diverging nozzle.
@@Martinit0 Exactly. Rocket engines have hardly any exit gas temperature fluctuation and typically don't have huge mass flow ranges -- I think the Merlin does 40-100% of full flow. And booster rocket engines typically don't even try to match their exit pressure to ambient, and just live with huge pressure losses. Jet engine gas temperature varies with throttle setting, which means sonic velocity changes. The mass flow change just from cruising altitude vs sea level is as large as rocket engines ever deal with. In short, the nozzle conditions in jet engines vary a lot more than rockets, and so they need the much more complex and heavier variable geometry nozzles.
@@IainMcClatchie Maybe you can answer this question. I know rocket engines have fuel pumps. Does the fuel pressure have to greatly exceed the combustion pressure. I'm guessing if it didn't have enough fuel pressure, it wouldn't be able to supply enough fuel for the needed combustion. I guess you can say I'm basing this question on the knowledge that jet engine fuel nozzles PSI have to exceed the air compression PSI or else that fuel wont come out.
@@TheRantingCabbie Yes, the fuel and oxidizer pressure has to significantly exceed the combustion chamber pressure so that the liquids will be forced from their manifolds into the combustion chamber through the spray nozzles. The drop is typically 20% or so, and the mechanical energy in that pressure drop is used to break the liquids up into very small droplets. The same volume of fluid broken into smaller droplets has more surface area, which speeds combustion. You need fast combustion because residence time in the combustion chamber is typically a couple of milliseconds. Note that all flows in the combustion chamber are subsonic.
I appreciate the time and effort you provide to make these videos for all of us to view. Knowledge doesn’t come cheap, so the complementary knowledge you share is truly valuable.
On the noise; I remember once after an airshow in Winnipeg, I was at 17 wing on the balcony watching the Mig-29s take off. I was just over 400m away from the runway, about 85 degrees to the side but slightly behind the first Mig, and the he took off at FULL FREAKING POWER. Sound disperses by the inverse square of the distance traveled, and it was LOUD. THUNDEROUS AND LOUD. Left a sparse black smoke trail down the runway, and I know he was using his afterburner because the other Mig's weren't anywhere near as loud as the first one!
I once saw an F 8 Crusader light it’s afterburner as it was taking off. I’ll absolutely never forget it. It lighted with a very loud boom and a tremendous roar.
Don't argue with Jay. Because 99.999% of the time, his answers are accurate and correct. Probably the only, occasional time Jay doesn't care to prove someone wrong, is when he doesn't want to blow up the test engine cell, his camera, the shop or himself up. This is a great explanation of how afterburners work. When I flew B-707s with water injection JT3Ds, we had to monitor EGTs like a hawk during hot day takeoffs from any airport in Southeast Asia. On occasion, this was also true for some U.S. airports including Love Field (Dallas) because the runway simply wasn't long enough for the limited amount of thrust the JT3Ds would make when it was over 105 - 110 F OAT. There were days we simply could not takeoff until outside air temperature dropped late in the evening - with water injection. Even Phoenix with its 10,000'+ runways could be dicey if it was really hot outside. We were instructed the sole purpose of water injection was simply to avoid melting parts by reducing EGTs which allowed the JT3Ds to maintain up to 95% of maximum rated thrust (18,000 lbs) depending on OAT. Even on newer model B-707s with JT4As, I can't tell you how many countless times we wished we had the military version, the J75 with afterburner (and optional water injection for 26,000+ lbs thrust) mounted on the pylons - just to get off the ground in 9,500' or less and clear the approach lights.
The reason these engines make that crackling sound is that atmosperic air on Earth (sea level) can only support sound up to 196 db. Sound is an oscillating wave, and 196 db is the highest the high side of the oscillation can be without the low side hitting zero pressure. Since pressure cannot be less than zero, sounds louder than 196 db are "clipped" on the bottom of the oscillation, causing distortion.
Once again, an extremely insightful and well explained video. My dad had Reheat on his 57 Bel Air. The carbs were so rich that raw fuel would run out the exhaust. So he put a spark plug in the exhaust pipe near the end of the pipe and a on/off switch on the console. At a stop light he would rev the engine, getting lots of raw fuel in the exhaust, press the spark plug ignition, and flames would some shooting out the tail pipe. He says 3', but I think is was probably more like 1 foot. I would have to say that the reheat added about 1/2 pound of thrust, but it was a magnet for the police.
At work we have two Rolls Royce Trent60 Industrial gas turbines witb afterburners... Well they work like afterburners but are in fact just propane burners installed in the exhaistpipe of the engine to increase the temperature of the exhaust gas, wich then heats water to power a steam turbine and/or heat water for distant heating. We call those afterburners "Zusatzfeuer" wich literally translates to additional fire
I can still vividly recall the first time I experienced a B1B taking off with the burners lit. I was prob a mile & half from the runway & fueling up my truck when this enormous roar and the gas pumps started shaking then noticed that everything was vibrating and the roar was growing when the B1B rose above the buildings with beautiful yellow/blueish cones of thrust. It was amazing, not to long after that I became part of the team of the worlds fastest jet Limousine.
B1’s used to be stationed in my city in the 80s and 90s during war time and they were insane. Especially at night jet after jet in full afterburner taking off.
Being stationed at fighter bases in my Air Force days working around the end of the runways at times, I can assure anyone that doubts AgentJayZ description of afterburner effects up close he is spot on. It is incredibly powerful and noisy as noise can be.
Worked at EOR while stationed at MHAFB. A pair of 111's pushing up to light the AB's on take off could rattle the fillings out of your teeth while you went crosseyed!
During my basic training we often camped and trained in the bushes at the end of the runway, beyond the airfield area. It was funny when jets were taking off, nobody could hear what the sarge was shouting, it was absolutely useless to try to communicate in any way. And this always went on for a while as fighters were taking of in groups.
@@gearloose703 There was a phrase we learned in the Air Force very quickly especially when talking with someone on the phone, "Standby, I have a jet in my ear". Worst thing though was trying to have any kind of a conversation while launching aircraft or during engine runs.
I've got some epic video of a Strike Eagle at the trim pad at MHAFB. Double burner at night. You can see the full range of colours and 9 rings inside the flame.
I lived 6 miles east of Fightertown, USA in the 70's and 80's. F-4's and F-14's were making afterburner takeoffs by the dozens, everyday and into the night during the cold war. Even at that distance and over a couple hills, it was just routine to hear the rumble, on and off. At that distance, the crackling sound became a muffled rumble in the background. I could feel the vibration in my house walls and windows. It could make certain things rattle or buzz from the low frequency vibrations. Likewise, watching rocket launches on RU-vid, such as the Falcon9, you can hear that crackling sound. Supersonic exhaust flow punching its way into the ambient air. Rocket engines use convergent-divergent nozzles, too. Only, the divergent part is much longer. The chamber pressure is higher, and the flame is very long...about 250 feet (75m) long...and bright yellow-white from burning kerosene and pure oxygen.
I work on the F100 that's in the F15 and a burner run goes like this: The engine gets pretty loud, the nozzle closes all the way, and it gets kinda windy. Once that throttle grip goes over the hump into burner it gets so loud it seems quiet somehow. It's starts in your feet. The vibrations work their way all the way up to your chest where it resonates freedom throughout the rest of your body and you realize you have a stupid grin on your face. All of your senses narrow to this beautiful glowing stream coming from the nozzle, and the nozzle begins to open. All of a sudden you realize the air around you is moving 3 times as fast toward this flame that is pushing air well over 600 miles per hour. If you're within 20 feet you can easily feel the heat radiating from the flame, and for some reason you want to get closer, but your body is screaming no. When you come out of burner its as if everything that just happened floods from your body and is gone in an instant. Imagine a tornado ending in an instant as if it was never there.
Being a former eagle keeper. Having stood under a jet in the hush house. You see the flame. You kind of feel it. Yes it's loud. But what you really notice is the volume of air moving around you. It's almost undescribable. And at the trim pad. Standing 30-40 ft next to and aft of the jet. You can not breath. Your chest and sinuses are vibrating so much. There is no way to truely explain what you are feeling. Just that you want to do it again.
Loved this video, thank you for the relatively easy to understand way you present things. I also very much appreciated your comments on resourcefulness, a very good point for any mechanic. It's a long way from the Cessnas and Pipers that I work on, but jet engines fascinate me!
Super good explanation on afterburner function. And the cooling effect that is needed in afterburner function. I'm a BC auto mechanic with a journeyman ticket. And have been following your channel for some time and find it amazingly informative. And the way you explain stuff makes it easy for a mechanically focused journeyman to understand. Thanks a lot.
I know nothing about these engines but now that I've found your channel I feel the urge to come there, put down a bed and live in your shop. Learn everything there is to learn from you about them! And I'm not even kidding.
You bring up a great point I was just talking about a few days ago. How "quiet" airports are nowdays. I started flying in the early 70's. I used to fly in and out of the old Denver Stapleton airport quite a bit. On a hot day, when the 2nd gen jets were having to launch out with high density altitude, I can't think of a more "noisy" airfield back then. Every take off was a full power and in some instances you'd hold the brakes to about 80% and then let go. 707's, 727's and DC'8s were loud but nothing compared to the Convair's(880's). Now...you can live under the corridors and get "used to it" pretty quickly.
12:12 Very excellent Jay. Back around '65 Dad and I were at Wright Patterson air show and thank you for the explanation. An F-101 VooDoo made 2 sub sonic low level runs (cool as hell) about a 1000 feet in front of us and then just as he pulled hard into vertical a chest pounding double Boom...Boom as he would go perfectly straight up and in about 6 seconds disappear in a small white poof.
They do powerplants the last year, that sucked but the best is saved for the last. You'll have to start a jet engine in a test cell, I helped with a J100 (I think it was called) on 100/130 aviation gas. Coolest stuff ever!!
...have to confess, totaly captivated...I like big engines, power and heavy metal, I know the difference between Capirotti(S?) and Walcherts(S?) valve gear and I understand the Bernoulli(S?!) equation so I don`t watch your channel to be educated as such, I enjoy the footage of big power units running and some of the more arcane bits of technology that you come up with but most of all I just revel in your style...mate, you would be a nightmare for most students as a technical college lecturer but the way you communicate your vast, precise and detailed knowledge and understanding is an absolute joy...I am a particular enthusiast when it comes to the English language (I`m Welsh but that`s a whole other thing) especially in terms of idiosyncratic utility and your unique didactic eloquence is a constant source of delight to me, a spark of light in the dark mundanity that sometimes threatens to overwhelm...thank you, carry on, that man...
Excellent talk. Thank you. I have probably read all of those books when I was a kid, should really get my hands on those again. I feel sad in this time and part of the world seeing and hanging around airplanes and airfields has gotten a lot more difficult. Military never flies low and fast anymore and only uses afterburner at sea. I really want my kids to see all that like I did.
Not around here. National guard does short and low afterburner over my town often. They are so low sometimes you can see the pilot and it shakes the house. We have the latest and greatest Military jets at McEntire and Shaw AFB. Airport access in general is not like it used to be. Now you have to look through a fence to see anything. When I learned to fly you could go and talk to the pilots, sit in the planes, kick the tires and possibly get a ride. I can still do that, but most people can't because of the stupid Guvment access rules. Military Airshows are the best places to see it but they aren't that frequent anymore. My son couldn't care less about flying. lol
and yet there is no end the discussions here about how many of the neigherbours should be compensated for the increase in noise from the F-35 vs. the old F-16
Excellent content! I live/work at a Church Camp about 10 miles off the end of a B-1 base, and can testify that when they do afterburner takeoffs, buildings rattle and conversation ends
Excellent explanation of after-burners and why the variable area exhaust pipes are opened to the max, when they are used.... A very good explanation of the increased 'ripping-crackling' sound as after-burners are used also...
While ALL of your content is amazing those are spot on comments about resourcefulness, such a great nugget of wisdom. I see this all the time across various disciplines and hobbies and it is so true. I've pissed off a few people because I've told them that if they can't take the initiative to figure out X they don't need to be in this hobby/play this deep computer strategy game/etc etc. Sound Advice, sir, well done.
Great vid. You haven't felt power until you've been a few feet from a jet in full AB. It'll really rock you. Incidentally, the only instrument indications in the cockpit from mil power to AB is fuel flow increase & nozzle position change. RPM, FTIT, & oil pressure remain the same as mil power (speaking F100/F110 engines). All of the fun happens in the augmenter.
We had a pair of B1B's here at Oshkosh a few years ago. My house was approx 3 mi away from the approach end of Rwy 18...the runway they were using to depart. Anyhoo...when each pulled out and lit the blowers, the windows in my house started rattling. Now...there are many trees, houses and buildings between the two and even with all of that deflection, they were still pounding away. Also, having spent some time on aircraft carriers, I can tell you that nothing compared to launching F-14A's at full throat. The later models didn't require AB on takeoff so weren't as impressive.
Very nice video. Thank you very much! So many things in life that I see without contemplating. After watching your awesome video, I "realized" that the additional thrust provided by the afterburner is transmitted into the engine structure by way of the nozzle attachment mechanism. That mechanism is apparently quite robust! I'm in electronics, not propulsion. I particularly liked your attempt to get across the experience of being in the vicinity of an active afterburner. Thanks again.
I saw an English Electric Lightning when I was a teen. It did a low pass down the runway and then stood on its tail and lit the reheat. The noise was phenomenal, the ground shook and it made me feel sick. Wonderful. BTW it's pronounced Darbyshire.
I literally found your channel yesterday and subscribed, this is the best video you could have possibly uploaded! From an engine nerd, this is the perfect channel.
Dear Export Man... there are much better videos than this one, but I forget where they are. I have about 575 uploads. Your mission, if you choose to accept it, is to watch them all, pick out your faves, and report back. You will be allotted 30 days, so get crackin'!
If the nozzle didn't open the extra pressure would mean the turbines wouldn't be so happy about that. I'd have never thought of that. I always imagined the screech pipe going from high velocity to rapid expansion, but the big question always remained why the nozzle opened up. I did guess on the extra kaboomness overtaking the cooling air and possibly overheating the pipe if the nozzle didn't open. I've been searching for concise answers for a while why nozzles open in AB. Thanks for the video.
Yes, I think you are right. The J57s were used on the Gs, which did use W. I. I was an Avionics guy at Barksdale in 1981-1985! I wondered about the H models... they do not smoke near as much.
I miss the 707, DC-8, DC-9 etc. The original old main terminal in Toronto, long gone now, used to have open balconies by the departure lounges as well as a rooftop parking lot with a fantastic 360 degree view. You could spend all day there listening to those aircraft thundering.
My brother And I flew the a BRITISH AIR CONCORD FROM HEATHROW TO DULLES,, that thing roared , Those days before they were allowed in to JFK.Cheers From NJ.. USA🇬🇧🇺🇸
BA would do 90 minute Concorde 'Round the Bay' (of Biscay) flights out of Filton, where UK Concordes were built. The take-off could clearly be heard at my home over 3 miles away on the other side of low hills. When a Concorde took off from LHR, it would routinely set off the car alarms on a car park at the end of one of the runways.
I like what you said about being serious about learning aviation and not needing a link. I firmly believe a good pilot shows up to training knowing the material already. You gotta be a self starter. So many accident via pilot error were preventable by self study. Know your systems know your aircraft
I recall the earsplitting sound of the Rolls Royce Spey powered BAC 111s back in the day, a stark contrast to modern Rolls Royce Trent XWBs on the Airbus A350 which is a much larger airliner.
I stumbled on your channel after Juan Browne made a reference on the Blancolirio channel to your videos. Your content selection matches my interests and I am enjoying your deep dives into the hardware. It is great stuff that is only hinted at in the press. I'd like to pay you back with a J79 afterburner story. A good friend of mine was an electronics tech on an aircraft carrier during the Vietnam war. The flight deck on an aircraft carrier during wartime flight ops is a very dangerous place to be. You had to be very careful. One day Jim P. and 3 other techs were tasked with a mission critical task. It seems that the electronic displays that guide pilots to the deck were down. The carrier was performing very active flight ops with flagmen. Jim and his companions were hunkered down behind a blast shield waiting for an opening; they hoped to sprint to the island and begin repairs. They were watching over the top of the blast shield as an F4 was landing. At this point Jim always explains that the F4 Phantoms landed with the afterburners lit, developing lots of power in case they missed the hook. As they watched, a F4 landed and blew a tire. He and his companions were hit by the thrust of two J79s on full afterburner. They were blown off the deck into the ocean. They survived a 70 foot drop into the ocean; some of the guys had minor injuries but Jim was okay. A man over board call when out. Carriers stop for no one during flight ops but a net with rafts and such was opened and dumped into the ocean. A helicopter was always running during flight ops. It rescued Jim and his mates in short order. It is a great story. After watching your afterburner videos and seeing a J79 ravage the Canadian countryside, I cannot imagine what Jim felt when the F4 swept both its afterburners at him.
Nice video, just like always! Concerning the water injection, even new cars use this system to decrease air temperature after compression, and thus enhance engine efficiency. For the books that don't talk about pressure, it turns out that velocity is always inverse proportional to pressure, but I think that you know that. When you get to supersonic jet engine there's a more beautiful pattern that comes out of the engine, the shock diamond, which owes to pressure drop after post combustion. Hope that you'll make a video about that. Cheers and keep it going Jay's! Really nice channel
I gathered a bit more of the concept thanks to your montage of explanations. Thanks again! I have told this story before but to support your claim of "Just had to be there in person to understand...", I have see F-4s flying about at air shows & a 'Centennial' celebration: They are very loud! How many ever thousands of feet away from me they were, it was freakin' loud! A good part of it you FEEL, no just 'hear'. It is true white noise (or is it pink?), with all frequencies, at a high amplitude! Thanks Jay for the info & illustrations.
The original Orion programme (as proposed in the 50's) used small nuclear charges to push a rocket into space and beyond orbit. A small hatch would open at the back of the rocket, and the charge would be pushed out behind. The rocket had a spring loaded pusher plate which would absorb the energy of the nuclear explosion and push the rocket forwards. All the small scale tests were performed with conventional explosives, and the scheme was proven effective and realistic. In the most general sense, an afterburner is the same deal. By creating a small explosion behind the engine, one creates a "wall" of expanding gas which pushes the engine forward, and gives the conventional output of the engine something to push against.
As an addendum to my previous comment: I went into the the R-R Heritage Trust at Bristol on Tuesday and was in conversation with John A****, a former combustion engineer, who showed me a report, dated 1955. This summarised experiments with the use of 'wee-heat' in the exhaust of a DeHavilland Ghost. The engine had a fixed nozzle and the dry thrust was compromised by the larger nozzle area required for the reheat system. The thrust augmentation was small, hence the system being colloquially called 'wee-heat'. John also showed me a report containing an analysis of the performance of the wartime German axial flow engines in comparison to the British centrifugal engines. The German engines were characterised as "crude", with greatly inferior performance and reliability. Yes, they established the future 'architecture' of the axial flow turbojet - but so did Metrovick in the UK with their series of engines, culminating in the Sapphire. I will be seeing John again in a couple of hours' time and will ask him whether he worked on Plenum Chamber Burning (PCB) in the Pegasus. PS: The answer was 'no', but he had some interesting stories about the people who did. I knew some of them in their later years at R-R Bristol. PPS: The 20percent thrust augmentation of the Olympus 593 in Concorde was locally and colloquially referred to as 'wee-heat' at R-R Bristol.
I sat on the shelter floor under an F-111E just forward of the exhaust about 5' away during a ground run. I got Roy boy to crack zone 1 burner for me. Yes it's very loud. Louder than anything I've ever experienced. The starting line of a Top Fuel drag race is not as loud. You can feel your bones.
Standing 10 feet away to see the pit crew member squrit fuel into the blower then BAM it started with all the fury of a top fuel dragster. Then the driver gives it a blip of the throttle and I had no idea it could get so much louder, chest rattling waves! But not face ripping, you win.
As a former eagle keeper, I've stood next to 2 P&W F-100-229 after burning engines. I'll do my best to describe it. Working ground gaurd, standing about 15 ft to the side and underneath the a/c at times. Double hearing protection mandatory. You don't feel anything underneath the jet or right next to it. You start walking aft. 5ft-nothing. 10ft-still nothing. 15ft-you start to feel it in your chest. 18ft-you feel it in your sinuses. 20ft-you literally can't breath it's so loud. I couldn't go past that point. The sound is incredible but the pressure difference is just as amazing. The 229s spit out a 30+ foot flame. It's extremely hard to describe. I do have some amazing video of this particular event. If your interested, pm me.
In england they called the little nozzles on the Harrier puffa jets they use to say at airshows they ran from bleed air from the engine to help turn and move the jet in the hover and indeed you could here what sounded like high pitched whistling as the jet maneuvered which i always believed to be the air exhausting from these nozzles.
At 7:25, you talk about fresh air being introduced into the reheat stream instead of the hot air from the core. I may be wrong but I believe this is what the SR71 engine did. I think it bypassed air from the compressor stage to the after burner stage and made the jet engine into a hybrid ram jet coaxial jet.. love your channel.. learend so much
The J58 engine is off limits... out of bounds for any discussion of simple turbojet engines. Let's not endlessly distract ourselves by getting lost in a sea of irrelevant details, OK?
Great video, thanks! Do you have any idea why the Draken exhaust nozzle uses the 'eyelid' shutter? Fewer moving parts when compared to the American/British variable area nozzle flaps? I know the Concord used 'eyelid' type nozzles, but I think they were part of the thrust augmentation system (in non-afterburning mode) in supersonic cruise, where air was ducted around part of the engine and reinjected before the buckets, as well as for reverse thrust, important for its use as a commercial airliner.
Went TDY to CFB Cold Lake in the early 80's for Maple Flag. Great base and a great bunch of people there! Halloween at the NCO Club was a blast! (From what I can remember of the night.)
Good video. afterburners aren't really my thing but I do hope your videos end up leading to some better homebuilt turbocharger videos on RU-vid with better afterburners.
@AgentJayZ : in modern afterburning engines, is there a time lag between the throttle position demand, and the time it takes the engine to get to the desired power setting? and when a pilot dials back from full power to idle, is there also a lag between the throttle position and actually feeling the thrust reduce? In an airliner, I can see that going from idle to takeoff thrust takes some time for the engines to catch up with throttle position, but not so much when going from what seems like 80% to idle during landing.
Afterburner can only be activated when the engine is at 100% rpm and power, so it becomes fully activated an a second or so. With airliner engines, a reduction in power is felt much more quickly than an increase. That's the nature of engines of all types.
Agent JZ The reason for the delay is the engine fuel controller that limits the engine acceleration to prevent exceeding the allowable turbine inlet temperature. This is done by following an acceleration schedule determined during engine development test. Also there is a deceleration schedule to prevent flame out. These override the power lever angle coming from the thrust lever. I know because I designed the mechanism implementing this limiter for the P&W turbofan engine at Hamilton Standard In those days the engine fuel controllers were hydromechanical and we just started on the electronic controllers, which now integrate many functions hence 'FADEC's.
re: the explanation of the exhaust sound: tbf to the asker, you mostly hear the turbine whine when not in reheat. But watch video of a rocket launch (or better yet, go see one on person). Sounds like popcorn popping, almost.
Bullshit. At military dry power, these things thunder the earth with an unimaginable roar. The only whining coming from this engine is from the front, and that's the compressor. Rockets are even louder, agreed.
Good evening, I was wondering if you'll be starting a custom project and will be looking for a (Probably vintage over production turbine blade that is not to expensive) what will be the one that you will go for!! I'm trying to make a small size turbine no more than 10 inches turbine wheel. "To be converted as been refine & tuned into a small turbofan" your advice and your knowledge will be greatly appreciated...
@@AgentJayZ -Thank you, Sir. Amazing how a skinny rotating cable can be used to prevent those hydraulic actuators (capable of many thousands of pounds of force) from getting out of step. The inventors deserve more recognition, IMO.
Excellent videos, AgentJayZ! I very much like the way how you are presenting and also the insights (literally) you give into engines. Have a question about function of nozzles in supercruise (flying greater Mach 1 without keeping afterburner on): is the nozzle open or closed in supercruise? What I understood: In order to produce thrust engines need to throw something aft. This is usually air (with some fuel). GE-79 class of engine throws around 75 kg / s aft. Amount of thrust depends on how much air and how fast the air is thrown aft. Max speed an aircraft can achieve depends on the speed of the exhaust. E.g. if air is pushed out at 300 m/s you cannot accelerate beyond 300 m/s (no matter if you throw 1 kg / s or 1 ton / s); you would be probably slower than 300m/s because of drag etc). Non afterburner engines seem to have a convergent nozzle only. Max exhaust speed inside the engine / inside the nozzle can be max Mach 1 only since anything higher would cause a shock wave (and after the shock front the speed would be always < Mach 1; same principle use by engine intakes to slow down airspeed to subsonic for the compressor). Since mach value primarily depends on temperature and since exhaust gas is hot the exhaust speed can go much higher than the 300m/s at 30k (where air is at around -40°C). So even a non afterburner aircraft can reach almost Mach 1 (300 m/s at 30k) because it can still throw air aft fast enough (e.g. maybe 450 m/s inside the engine nozzle, which would be still < Mach 1 for the hot gas). Now if a F-104 / F4 would supercruise (fly at Mach 1.5 without afterburner = around 450 m/ s) I assume the nozzle is closed (because afterburner is off) but engine gas is still hot enough to be pushed out at more than 450 m/s (= closed nozzle = convergent nozzle which would not allow exhaust speed greater than M1, but due to the temperature local M1 INSIDE the nozzle would be much higher than 300m/s). Or would the nozzle open (at least a bit) to further allow the exhaust gas to exceed local M1 inside the nozzle? I mean if the gas is hot enough after the turbine it could make sense to (partially) open the nozzle even though the gas is not as hot as in afterburner mode.
I think I seriously missed my calling. I am a turbine engine fanatic, I even did my 8th grade report on the history and origins of the jet engine with Frank Whittle and the mechanics of a LB turbofan engine complete with a hand drawn cutaway 3D model in colors to represent the air flow. I've seen Iron Eagle 47 times, watched every episode of Air Crash Investigation/Mayday, Air Disasters, Seconds From Disaster, etc. I love commercial grade mechanical things and engineering, and I'm constantly reading and looking online at turbine engines, mostly aircraft engines, but anything that spins along a shaft is fair game....from steam turbines to APUs to water turbines. Earning a decent paycheck wouldn't have felt very much like work. 🤔
"What causes the crackling sound of an afterburner?" The same reason you hear a crackling sound on a rocket launch, especially the space shuttle and even more so on the Saturn V. And if you think a jet engine with the afterburners on is loud, a rocket engine is on a league of its own. Even when wearing protection, the sound can actually kill you by destroying your internal organs, if you're close enough.
Re water injection on the B52s, I used to live right by the Lockheed facility in Fort Worth. There were still some aircraft using WI at the time and they could roll coal like no other. On your comment there (weight of water, usage, etc.), I think that use case was only practical because it was used only for heavy takeoff. So they didn't have to carry around much. I would imagine your counterparts maintaining those engines at the time would have had a lot of fun dealing with whatever hell those particulates unleashed on the hot sections.
dear jay in some of the engines in england the had what they call the "blue note" this is when the afterburner is on the whole tube vibrates like an organ pipe.. which in turn can cause things to beak up so they discovered that the gases were whirling round. so some one solved this problem by showing the powers that be,,, take a cup ,half fill it with water the spin it up with a spoon, take the spoon out and the liquid will keep spinning and slowly stop spinning.. .... but put a circle of corrugated card board in the cup spin it up with a spoon take the spoon out it will not spin ,,, they did this on the engine where the afterburner fuel rings are , and magic no blue note the corrugated steel section is only 18" long and must not go forward of the fuel rings.. "simple "
So, in regards to the sound question, is it safe to say that the bi-pass air that flows around the turbine core exhaust also helps make the engine system quieter, kind of like splitting those 2 pressure differences (between the still air and the turbine core air) with a buffer (the bi-pass air)? Such as the sound created between the exhaust of a turbojets exhaust air and still air, would be more than the total sound created from the air speed differences of engine core air to bi-pass air plus bi-pass air to still air combined, from a turbofan (hope that makes sense). If bi-pass air can create a buffering, has there ever been an afterburning turbofan built for application requiring a quieter engine?
The Harrier/Pegasus use water also during engine borne (hover) flight. Cooling and thrust. You're lucky you contacted that library, SIS were closing in on you!
Correction: I've posted this information previously. The Harrier II uses water injection for a 'Short Lift Wet' rating maximum weight rolling takeoff, with a full load of underwing stores and external fuel tanks. My recollection is that the capacity of the water tank gives only 90 sec duration of water injection. With nothing hanging under the wings, the Harrier has no need of water injection in the hover: its thrust:weight ratio is greater than one.
Hi AgentJayZ. I've been slow in viewing this video and someone else has already mentioned Plenum Chamber Burning in the Pegasus engine, which I will expand on (pun quite unintentional!). But firstly, a correction: there was never any combustion in what were colloquially called the 'puffer jet' nozzles of the Harrier 'jump jet'. However, extensive development work on so-called Plenum Chamber Burning (PCB) was carried out at R-R Bristol before my time there. This was effectively reheat (afterburning, if you must) in the front nozzles of the Pegasus engine. A considerable amount of development ground running was carried out, even to the extent of installing an engine with PCB in a Kestrel/Harrier airframe. This was mounted in a huge gantry, in order to experiment with the effect of using PCB for vertical take-off. I've seen video clips of this in the past, but I can't find one on RU-vid. PCB would have gone into the BS100 engine, to power the P.1154, a supersonic development of the Harrier, which, of course, was one of those British projects that got cancelled. PS You really need a copy of 'Pegasus: the Heart of the Harrier' to add to your library: I've just placed an order with Amazon.
I trust your info on everything RR to be the gold standard. Somewhere, years ago, I saw a diagram showing grids inside the wingtip jets of a Harrier that were labeled as a system called In Duct Burning. Must have been a non-RR publication.
@@AgentJayZ There wouldn't have been any real benefit in 'reheat' in the puffer jets - and the fuel supply and control systems would have been fiendishly complicated. The PCB in the Pegasus 'cold' nozzles had a grid arrangement for fuel injection and flame stabilisation. Perhaps you saw an illustration of that. PS It was called 'Plenum Chamber Burning' because the grid arrangements were in the transition sections between the annular plenum chamber at the fan exit and the 'cold' nozzles.
@@AgentJayZ I couldn't find a film clip on RU-vid. However, try googling 'Images of Pegasus Plenum Chamber Burning.' There are quite a few still photos of interest.
Another question, again from reading the development of the Lockheed blackbird, sometimes the P&W engine would allow thrust to leek out the front of the jet engine but this was corrected with re-engineering. Was there a miscalculation in the pressure levels at different compressor stages?
i'm lucky to live near civilian airport that also has air force base. So it is easy and legal to go watch f18 hornets while they are taking off and landing, also had opportunity to see F35, eurofighter and super hornets with full afterburners. For that reason i can tell that with full afterburners, sound is so loud that car alarms go off around the airport, ground and buildings are shaking. You simply have to feel and hear it in real life.
JZ, That Draken AB video was awesome! Because of the extremely high temps, are the nozzles and connecting parts ever lubricated or do they just rub together? Thanks as always for your dedication and willingness to educate.
Second the question about lubrication :#) I'm proud Swede and grow up close to Säve airport, Gothenburg, Sweden and fortune to see SAAB Draken and -Viggen flying above on dayli bases. The engines was from Volvo(!) Aero, but licence built GE.
Anecdotal: when I was 17 yo I drive past the Säve landing strip on moped and a Gripen was starting, - I feelt the warm air from it pushing on me. Exited feeling :-)
