@20:20 "Realize that this is a real world test situation and-ah ... your criticisms of our ineptitude and stupidity are welcome and cause a great deal of humor in the shop ... so thank you" An engineer myself (albeit in a very different discipline), that line cracked me up so much. Plus, I once again learned new things about the fascinating tech and operation of jet engines. Much appreciated. Thank you.
Served in the Air Force, and US Army. Run qualified on KC-135’s. The only difference between hung starts and hot starts in the US Army is, Hot Starts are recorded for record and carried forward on helicopters, hung starts were not. In 20+ years Army Aviation never seen a hot start recorded. In the Air Force we didn’t keep a record of hot starts, but we made an entry in the log book for further examination. On KC-135 back in mid 70’s QC checked you out being run qualified. Hung starts we shut down. Hot starts requiring shut down of fuel, leaving starter engaged to help cool down within starter limits, record hot start in log book. Then after a cooling period, attempt restart. As part of a OMS ground crew we had to run engines to get special oil samples, or if someone forgot to get them after landing. Engine replacement to reach, military rated power. Or run one engine to defuel from alert status to ground status. Best one was to check the water injection system. You knew it when you flipped that switch, always waiting for it (KC-135) to jump chocks. A real rush! KC-135’s with original turbojets were loud, water injection switched on they were screaming. On takeoff 670 gallons were good for about 90 seconds.
Why did I subscribe? To learn more about jet engines! I was a US Navy avionics tech way back in the '80s. Just the thought of a jet engine turning sends thrills up my old Jolly Roger. I'll never forget the mind-blowing awe I felt as a young plane captain the first time I stood on 'the hot pad' within a few feet of a chained down Tomcat in full afterburner... Thank you for sharing your work.
10:30, when starting a twin engine helicopter, that's exactly what happens. The first engine to start, starts hot asf! (Within allowable limits of course) but once she's up and running, the second engine will start with an EGT (T4) of 150DegC or more cooler. That's why on odd days, we start ENG1 and even days we start ENG2 so we keep the LCF numbers in phase with each other.
Great Video! Your explanations are wonderful, you do a great job. It's a big job you have taken on, education of the unwashed masses (of which I am a part) but you do it with flare and enthusiasm. We applaud you, Sir. Well done. Understanding jet engines was unthinkable until you appeared on my screen. Now it gets clearer with every episode. Thank You.
I thought I understood jet engines before I started watching these videos. Turns out that much of what I “knew” was wrong. Thank you for making these programs.
I used to do a lot of maintenance ground runs on the De havilland Buffalo. During one start, apu was on, I started opposite engine from apu then did a cross bleed start from the running engine to the engine being started and noticed the ng was hung but the temp was taking off like crazy. I killed the fuel and motored the engine with bleed air to cool it down. Next attempt went off without a hitch. I miss those days, well not the night shift part.
I don’t know why people want to criticize your video I have learned so much about jet engines from you I’m very appreciative that you provide this to viewers.im a current pilot flying the Hawker 800 XP and I always remember the points you make about hot and hung starts. Most of the times when I’m in the Simulator I have to recognize a hot start, and resolve by doing two things, 1. Shut fuel, 2 Abort the start. It’s simple, but recognize it before damage happens is the trick, it’s just a sustained sudden high rise in temperature with no N1 response. Thanks again.
A little story, I'm from 63 I have not traveled much in my life but recently I was flying in an airliner for the first time, I was sitting so I could see the jet engine out of the window and it was really cool, I had a reasonable good insight in what was going on in the engine thanks to you that was awesome, thanks for the videos 👍👍👍
Excellent video! About 20 years back, I built a couple of turbocharger-based GTs and in a couple of hundred successful starts, I got to observe a hung start twice. Kind of amazing just how fast the temperature climbs if fuel is added when the engine won't spool up to match. It's really instinctive to continue adding more fuel at just the wrong time. Oops.
You have to be one of the best teachers I know... I am right now getting my A & P licenses and tbh my teachers don’t even explain it like how you do. It’s like they don’t even know what they are teaching.. I wish there was more folks like you in the world actually being able to educate those that are interested in such a AWESOME and BADASS career XD
Thanks for explaining a hot start. I'd never heard of it until Mike Patey mentioned it recently after having a catastrophic engine failure in Turbulence. He said that engine never had one but he didn't explain what it was.
I too heard of hot starts from Patey. I've read about turbines for decades and knowing liners and airflow were milestones in the development... But ONE hot start can kill an engine!
@@dousiastailfeather9454 Yeah, I'm looking forward to an analysis of what happened with Turbulence. Obviously, I'm glad Mike and his passenger are OK but I'm also glad that amazing plane only needs a new engine.
Thank you for making these videos, I have been following you for years. When I applied for an aviation job selling Hamilton APU parts and PW turboprop parts- I was mainly accepted for knowing what I know on Jet engines, and all I know I learned from your videos. Keep it up
I am lawyer with previous electrical engineering schooling and job experience and really enjoy watching the videos of this channel, learning about the challenges of really intelligent human beings. Thanks for posting.
That oxy-acetylene mixed flame is almost the closest you can get to burning pure gaseous carbon - a hypothetical substance which doesn't really exist on earth (though arguably does in some parts of outer space). No matter how much oxygen you cram into the flame, the temperature is limited by the water vapour present, a result of burning the small amount of hydrogen in the acetylene, which has the formula C2H2. Adding more hydrogen (and hence more water vapour) into the flame cools it off, so a flame burning ethylene (C2H4) is cooler, and burning ethane (C2H6) is cooler still. The hottest steady state flame burning oxygen with a gaseous fuel uses dicyanoacetylene (C4N2), which burns at almost 5000 degrees C (9000 F), a result of there being no hydrogen present at all, and therefore no water vapour in the flame. The only way to go any hotter is to start getting super-exotic with your fuel-oxidiser combination, such as burning rolled aluminium or magnesium foil tubes with fluorine gas. A thermic lance using that combination can slice through concrete like a hot knife through butter.
This was brilliant ! Really great Information for those getting into aviation to understand and really puts into perspective the real side to the operation of these amazing engines ! Love all the content you make it really helps. :)
Very interesting. And as always, a little touch of your subtile humour, now and then, makes this lesson on hot-starts delightful. Stay healthy, Happy Easter to you and family, salutations from Quebec City !
The exhaust temperature trend during start up has less to do with the cooling air in the combustor, but more to do with the fact that compressor and turbine airfoil are running at an extreme off-design condition and do not transfer work to air and extract air work from air effectively. If the turbine does not extract the heat energy from combustion effectively, exhaust temperature goes up, even if the combustion flame temperature is the same. A typical hot start, especially the newer engine that starts on automatic control, happens when the turbine is not extracting enough work (could be many reasons, most common on is a fouled/degraded turbine) causing the RPM increases to be slower than acceleration schedule prescribed in the control, then the controller add more fuel to compensate -- not the right thing to do, exactly as you said, but the controller just follows what is programmed and cannot make decision on the fly like humans do, yet. This is why the book said it's fuel rich, in the sense that additional fuel was added than should be. In manual control, if all other systems are functioning normally, yes, you can put too much fuel and potentially have a hot start, but that's really rare occurrence in professional hands like yours. A hung start happens when the torque received by the shaft (in its entirety, including compressor and turbine) was too little to accelerate. This could be due to turbine's failure to extract enough work (this will also be a hot start), but it could also be because a fouled/degraded compressor that needs extra torque to overcome air resistance, or a starter that is not producing its speced torque. The fouled compressor and starter failure do not automatically create a hot start, especially in the higher RPM region right before starter cut-off where the turbine is extracting reasonable amount of heat energy. Again, if in an automatic control and acceleration schedule takes over the fuel flow control, it will do the dumb thing and add more fuel to try to accelerate, then it can become a hot start. In short, a hot start does not necessarily means a hung start -- the engine could still accelerate to idle, but just transiently has extraordinary exhaust temperature excursion. A hung start also doesn't necessarily equals to a hot start, but tends to do so in automatic control before human intervention.
Your first paragraph is accurate. It has everything to do with cooling air. It cools the flame to a point where it becomes hot air that isn't so hot as to damage the engine. If you don't cool it down, it's too hot. "A failure to establish sufficient cooling air flow", whatever the underlying mechanism.
Um, I think we are talking two different things, one is the root cause of a hot start, the other is what is the prime path to cause damage, or failure mode, to the engine in a hot start. If more fuel is applied than what cooling airflow can cool, absolutely, the resulting temperature will damage the engine, especially stage 1 turbine components. There are, however, other bad things that can damage the engine, such as airfoil vibratory crossing in a hung start. On the other hand, why would more fuel than cooling airflow can support be commanded in the first place, that's a completely different story and what I was trying to describe.
I used to run J-33 engines. Coming over the horn was always a time to eyeball the EGT. I think it was 799 C but long time. If it was going to hot start on that engine you basically had to pull back to cutoff before it took off. Hot start was very quick. Thanks for great vids!
I must respectfully disagree, a hot start is not the same as a hung start. The difference is where to apply the blame for the anomaly. Hot Start - If the starter is generating energy to spec, but the fuel control is not (too much fuel for that rpm), then you could have a hot start as the fuel control continuously delivers higher than required fuel flow at that rpm so the starter is unable to break the cycle, and egt increases above spec without increase in rpm. Hung Start - If the fuel control is delivering fuel per spec, and the starter is not delivering enough energy, then the engine rpm will "hang" and not accelerate to idle while the fuel control schedules fuel per spec resulting in high egt. If the starter is anemic then the fuel at that rpm will create too much pressure for the starter to overcome, and the engine rpm will not increase while egt goes out of spec. Both instances are caused by too much fuel, not enough rpm. The difference is in why. Case in point: J79-GE-17A cartridge starts are a fine example. Sometimes the cartridge would burn fast enough to start the engine, often the engine would start relatively normally. But you had to really watch for a hot start in that scenario because the cartridge burn rate could be insufficient for a start and you had to know when that was. Key indicator was rpm vs egt out of spec. The same engine would start perfectly fine with a working start cart, sometimes it would start with a cartridge, sometimes not. If you weren't paying attention the engine could have a bad day. I suspect the difference between "hot start" and "hung start" meant more in the past and was due to trying to differentiate between blaming the starting system or the fuel system including the fuel control for insurance or warranty or maintenance tracking. Things like cleaning fuel nozzles and swirl guides used to matter. Great videos. Thank you very much.
Yes. They are different, and they are the same. This is why I prefer to use my definition, which avoids the cause issue. "A hot start occurs when there is a failure to establish sufficient cooling air flow during the start sequence of a gas turbine engine."
Jay, I've always thought of it like this - a Hung Start can become a Hot Start but a Hot Start can never be a Hung Start. Also, a Hot Start is more likely to be caused by environmental conditions (i.e. trying to start a jet with an out-of-limits tailwind) than a mechanical condition (i.e. starter or battery failure). You avoid Hung Starts by ensuring your batteries are in good shape or use of a start assist (i.e. GPU or APU), especially when it's cold outside. You avoid Hot Starts by making sure the plane is positioned properly and you allow the starter to accelerate to full speed prior to the introduction of fuel in the engine (on non-AutoStart engines). You might use a GPU to help with abating a Hot Start on an extra hot day as well, but that's secondary to the first 2 items.
Here's how my powerplant teacher explained it to me: hot start IS a hung start with the possibility of a fire due to high EGT and extra fuel left in the engine. A hung start is just that; EGT did not reach a high enough temp to accidentally light any extra fuel before you blow it out. Furthermore, as it was explained to me, a "rich" mixture simply meant too much fuel for the combustible air. That is why hot starts are so dangerous; hot EGT and no accelerated air with extra fuel after cutoff. I was always told to wait 1 minute then dry crank.
On an F15C fitted with F100PW220, hot start and hung start can be two very different conditions. A hung start can and would most likely turn into a hot start rapidly, but has its own criteria. I have seen often a tail wind cause a hung start, which is aborted prior to it becoming a hot start as the stert criteria has a time to rpm limit. I have also seen motors that come from engine backshop pickled hot start even though the rpm is climbing normally. What I *assume* happens is the storage oils are burning on the combustors / liners. 3 or 4 start attempts usually allows for a complete start and the greatest fog machine ever made.
Really good breakdown of what goes on during a hot/hung start. I used to be really heavy into DCS: World with the Ka-50, and every now and then i would grenade the engines on the pad by screwing up the start sequence - usually by introducing fuel too LATE, which always confused me.... Now I understand why that is: by introducing fuel too late, combustion starts right as the engine controller decides "this start is going nowhere, close the starter valve" and so i end up with combustion happening at too low of an RPM for the engine to spool up on its own right as the start valve closes....
I am reposting this because it seems you did not realize I was trying for humour. Nice analogy with the acetylene torch. I liked the picture you drew of the PISTON ;) Edit. To be clear it is a joke (Piston)
I love watching this stuff. I have nothing to do with your industry. But my father was a USAF B47 crew chief and he created a curiosity in me about such things.
After watching the very intensive and meticulous process of building these engines, I don’t think I would be able to be on the start controls without having an anxiety attack. Especially when the temperatures climb so fast beyond the limit. I guess with experience you get the “fadec” feel for how far you can go before shutting down!
Jim Goff - It’s not hard to deal with a hot start. You watch the needle and if it looks like it will exceed the limit, you kill it. Rarely are you close to the limits with modern FADEC engines as they will generally control the acceleration. The last hot start I prevented was when the start surge control valve failed at the same time as a FADEC channel. What you don’t do is exceed the start limit otherwise you have a potential pile of scrap on the wing.
My father was an airline pilot, and a former Air Force fighter pilot in Vietnam. Back in the late 90s, he was explaining the progression from analog to digital flight controls. When he was younger, the pilot was in control of the aeroplane. Good ol' stick and rudder. But with the advent of FADEC and fly-by-wire setups, the pilot makes suggestions to the computer, and the computer controls what happens. He said that it's safer, but not as much fun. And by fun, I think he meant dangerous. 🤣🤣🤣
Was ground man on one hot start on a j 57 ( KC-135A) fuel was on before ignition, could see fuel out the tailpipe for a second or or two then a flame growing stronger untill engine rotation blew it out maybe 5 or 10 seconds, was quit a sight. It was 48 yrs ago
Thank you for that video. I always wondered how the older engines functioned, and how the startup procedures were done in order. Well versed, and explained very well. I appreciate that.
Thank You Jay: Every episode is a true learning experience, especially this one. Even though I have operated turbine engines, Your explanation provides a technical support for the real world operating experience, and therefore a greater understanding of what the instruments are showing (or not showing). My question from today's class is ... why doesn't the manufacturer / engineer place the ITT sensor in the combustor rather than the tailpipe? We know there are mountings in the combustor (igniter), so why not place one for a sensor that would give the operator a dynamic and instantaneous reading, which from a user perspective would be beneficial?
The reason a sensor is placed downwind of the turbine is because the actual temperature at the turbine inlet, or TIT, is so high that the thermocouple has a very short life. So think of it: we use EGT as an indicator, knowing the actual critical temp, TIT is several hundred degrees higher. The actual critical variable we don't see, but infer from another, lower observed indicator. It would be great if a sensor could be made that would survive the job of actually measuring Turbine Inlet Temp.
Thank you for that explanation! I hear a lot about hot starts and hung starts in the vids I watch. But not being a jet engine guy it was very educational for me. I am very grateful!! Thanks for your time and work on this video!
thank you so much, no one in the flight school teach you that topic, thanks for knowledge, is going to help me a lot for my future as a airline pilot thanks again.
O don't know why i am so curious about these engines ,and watching your vedios, since i have no connection with the engineering studies, but as a ley man ,i am grasping quite well what you explains , means you are very brilliant in teacher.
Thank you. I have always been fascinated by jet engines.. I could never work on one because I would be afraid of error and problems. But I learn as I go from you and others. So please keep us flying.
Oxyacetylene welding. For complete combustion the gasses need to be mixed in the correct ratio to achieve what's called a neutral flame. Too much acetylene results in a carbonizing flame: contains unburned carbon (soot). Too much oxygen results in an oxidizing flame: contains unburned oxygen (ruining the ability of the exhaust gas to shield molten metal from atmospheric oxygen).
I've seen pilots with PT6s and a week battery move to cut off just prior to max temp., then adding fuel again, repeating until they get a successful start. Anyone think that's acceptable? In the middle of no where, no battery or external power was available. One thing that helps alot is to not attempt to start any turbine engine with any significant tailwind. Single engine taxi starts create this issue quite often as well because you are usually starting in a tailwind. Even when you allow the engine to max motor before adding fuel.
Once again, Thank you. This time I had a pretty good understanding of the subject, so your video was confirmation. I had a jumpseat ride in a Fokker F28 jet with Spey engines. After we passed 10,000 feet the FO asked me what questions I had, and I asked why I hadn't seen the spike in temperature at start. I think I was looking at the wrong gauge. That moved the conversation to a whole new level. On FADEC Newer cars have Electronic Throttle Control, I think the idea is similar. Anyway when the pedal is pushed the computer is informed and adjust the throttle and so on to accommodate.GM calls it a "Torque request".
You can think of an open camp fire where the heat carries the flame snd smoke high in the sky but there's no pressure increase. In fact for a couple of reasons like Mr. Bernoulli and low density the pressure is lower than ambient.
Sorry but I disagree with a hung and hot start being the same thing. A Hung start is when you get normal light off but rpm stays low usually with increasing EGT but not always exceeding EGT limits (normally due to low starter power). A Hot start occurs with normal engine rotation but EGT limits are exceeded (can be due to fuel control malfunction).
Hmmm... didn't I say that exact, exact, exact same thing somewhere in this, this, this very actual video? I do think I did... Yeah, I did. I'm sorry, but I disagree with your contention that you disagree with me. Me thinks you agree, and I agree with that. Yo!
Simply here because I love your channel .. Hnmmm.... Lemme rephrase that, I love your personality, adored your knowledge and cherish your sense of or ability to teach or your teaching sense... Now as an automobile tech wt 32 yrs of practice .. Now hearing you described combustion in piston and jet engine... And you was perfectly right, I realized " why am I here " You have to respond to console me because am heartbroken right now.. .. Maybe I should start working on equipping auto-crafts wt JET engines or something ..
I wanted to say thank you for a fantastic explanation of what a "hot start" is and how it can be so damaging to the turbine of a turbojet engine. New sub here. Previously I did not understand why a longer hot start event would require inspection prior to use.
Do single spool engines still exist? Back in the 1960 I think the Brits made a small portable genset powered by a jet engine but sadly these things never took off commercially.
I always considered a hung start as one where there is an issue with the starting fuel schedule where perhaps the secondaries don't kick in. But I see that there may be other causes for lack of acceleration. Thanks for the video.
Fascinating stuff! Three questions: 1. A high percentage of energy coming out of the combustors goes back to the compressor, but also a large amount of air coming out of the combustors is unburnt - for ease of explaining - "untouched" compressor air (=energy [not really but kind of]). Is there energy being "recycled"? If the compressor were to spin by itself at max rpm how much energy in % would it put out in comparison with fuel and without it? Might be in a theoratical dead end with this tought, and I know that ALL energy comes from fuel beeing burnt. Still "untouched" compressor discharge air is hitting and spinning the turbines, so to a degree spinning itself; so that makes the energy consumed by the compressor less than it might seem at first. The other two are easier: 2. Is the EGT-temperature that limits the maximum power the same as the max tempertature at startup? In my mind it should be less as it is continuous. 3. Planes are marked where the turbine disks are in case they come apart (i know extremely rare); is that something you take into consideration in the test cell? Especially since these engines are run for the first time. Thanks for sharing your knowledge! Stay safe
The compressor rotor of this engine needs 20 thousand Hp to turn at 7800 rpm. The load it puts on the turbine is evident whenever an engine is shut down... the rpm drops rapidly when no fuel is being burned. The max power EGT limit for this engine is around 1300 F The max starting EGT limit is 1560 F The red markings on airliner nacelles are more for guidance of personnel on the ground as the limits of approach areas, to avoid exhaust blast, or inlet wind pressure. Our test cell is designed so that the control room is well forward of the plane of rotation of the turbines of the engines.
The turbine is designed to extract power from hot combustion gases, mixed with cooling and dilution air. If the fuel is shut off at maximum engine RPM, the volumetric flow instantly reduces. This results in the turbine becoming instantly so far off design that it is not being spun by by the relatively cold air from the compressor and it just adds to the power absorption from the inertia of the decelerating rotor.
@@AgentJayZ thanks for your answer! you broke it down to the essence. my curiosity was: If now one were to take the turbine out and spin the compressor on its own how much more power would it take to spin it?
I think I need a cigarette now. I'm pretty sure my testosterone level increased as the RPM's spooled up on that jet engine. I'm gonna go to my shop and be with my weak power tools for awhile. Maybe read some engine repair manuals. This guy really has the goods where gas-turbine hot starts are concerned.
jay, wouldn't the fuel control schedule prevent "excessive" fuel input based on rpm/ discharge pressure? in 8 years in USAF i can only recall 2 "hot/ hung" starts, they were performed on alert pad and with prevailing winds up the butt.[no blast fences there]thank you for another informative video.
The computer screen when you are running the engine has a plethora of data showing all at once. Are you able to process that all at once because you are well practiced, or do you only focus on a few select pieces of the most important data?
I spent years making Spey "scoops" whilst at the same time having no clue as to what they did. I do know that they are as hard as hell. Tapping them was a nightmare. I can't remember if they were tapped to accept a wire insert or not. As you know, a lot of RR parts have wire inserts fitted from new, which surprised me at first. In some instances the guys that fitted the inserts had to collect the little "tangs" that you break off during fitting. They were sealed in a bag and went along with the delivered part to be counted and verified at RR. I guess that there must have been a "foreign body" issue in the past.
With the Orenda engine, you often find those little wire tangs left "unremoved" in the bottom of holes in the cases, still attached to the insert. Somebody thought that was safer. It seems to have worked, as they are still there after 65 years.
At first I imagined the air and exhaust flow in your cross section traveling away from the viewer. But when you showed the inside of the combuster can aft end toward the viewer, thought maybe gasses coming toward us. But because of all I’ve learned from your great videos, I’m guessing for the purposes of this discussion the flow could be going toward or away from the viewer 🤔. Thank you, I really needed this tonight🙏
I wander if the wind direction and how you are parked could play a factor. Maybe parking facing the wind might help the airflow and assist the starter.!
That is definitely a concern, mentioned in the pilot operation handbook for the Canadair Sabre. "Ensure the aircraft is parked facing into the wind before attempting a start".
I used to start Rolls Royce darts at work, and they were prone to hot start.....you had to be quick on the condition lever to get it to accelerate through the hot part of the start.....noisy as hell those things
Yeah, when I saw that I wondered about the guys outside the control room, and Jay when he was standing downwind of a running engine! Ma goom ba! Of course, he did say it was LOUD.
Thanks for the video. Like playing your stuff on lunch at school. We work on gasoline piston engines. I like the thought process and the attention to detail. Along with the content of course. But when we start talking about exhaust and especially turbos. I can't stress enough how heat translates to velocity.
Great info & something I can relate to; I need a bit more starter voltage the J44. You mentioned that it seemed a tad too flamey for your taste & I think getting the speed up quicker is a good start towards reducing the thermal stresses on the poor old thing! Thanks, stay safe, & good to see Pink Dispatcher is back. Cheers. DD
Before this video I watched another on the PT 6 engine When talking about the air flow he mentioned suck squeeze bang blow I enjoy his videos and also being that tea is a captain I have too much respect to say anything, Intake squeeze burn and blow, like mentour pilot and 74 Gear they know vastly more than I, I am now watching your hot start video, take care now
I work on SCADA systems that interface with the beasts. So, I've been in plenty of test cells. You've likely answered this question before. But gonna ask anyway. What is the story with that "resonant" sounds that seems to occur on every turbine slightly before it goes live? Love hearing the sound but don't understand it. Thanks. Gear-head here.
Officially and technically, it's known as "one of those things". A complex resonance due to the interaction of the engine speed being out of the operation band, the exhaust heat, and the ducting? We have a few exhaust ducts that we have made for various engines, and they make thundering and howling sounds on startup that the engines normally never make.
@@AgentJayZ Ha! It is a comforting and expected howl. Perhaps ducting designed so it happens only once on spool up(out of normal operating range). The howl would be a very unwelcome characteristic if didn't go away. Thanks. Makes me think of my '90 GSXR 750. It resonated in 6th gear at about 63mph. Despised that bike for that. I owned it for just about 1000 miles. Irritating piece of machinery it was.
Awesome bike. you had it in too high a gear for that speed. You were operating the engine outside of it optimal range. That bike is designed for ripping, not cruising. You would really like something torquey-er, like a VFR, maybe? I ride a big V-four now, but I once had an 86 Gsxr 750. It was so manic, shrieking through the Yosh 4 into 1 towards redline. It always seemed to me I was riding a rabid wolf... if given the chance it would hurt me, but If I paid attention and always used firm, controlled inputs, it would do amazing things for me!
@@AgentJayZ I'd love a VFR. I've had these: GS550ES, FJ1100, ZX7, V-Rod, CBR600RR(track bike), ZX9, '06 YZFR1(the only bike I still have) Was getting into racing and the '08 recession put the kabosh on that. That Suzuki was my least favorite of the bunch. Nothing like a numb arm to make you fall out of love with a visibly beautiful machine. I'm 51 now so getting a little long in the tooth to resume the passion. It was and is fun. The BMW R1000 is so damned attractive right now at least to me. Will I be practical and not buy one just because? TBD. Damned sexy motorcycle though.
With respect to a fellow experienced motorcyclist, you may enjoy a sport touring frame fitted with an engine with a meatier mid-range than the (great) inline fours you have been riding. The V-rod has the right engine, but the wrong frame. I would suggest you take a test ride on a strong middleweight sport tour, naked, adventure, or what used to be called a standard bike. Cheapest option would be any of the SV650 models. Most satisfying engine I have ever experienced. Most enjoyable might be the KTM 790, in any of its forms. Also, if you can find one: the Triumph Sprint ST. Sport tourer with a 1050cc triple. They don't make em any more, and you don't see many for sale... there's a reason for that. If I was going to try a BMW 1000, I would look at the XR first, and probably move more towards the new 900XR. Anyway, now I've got bike fever a few weeks too early in this part of the world.
The rotational speed of the engine must be sufficient enough to supply air for combustion and cooling. You can under-speed with enough combustion air to ignite the fuel, but will not have enough cooling air, and cause a hot/hung start.
Love your videos, particularly the depth into which you explain things, I thought I had a reasonably good gasp of how turbine engines functioned but thanks to you I'm learning there's a whole lot more to the story. If you get a chance at some point could you do a clip on cartridge starters?
When we rebuilt a J-79 out of a Phantom II, I made a series of videos about it. It's a playlist called Working on a J79 turbojet engine. One of the series is a video about the cartridge starter, which is also a pneumatic starter. Put the title in the search bar on my channel page, and try watching all 18 vids!
@@AgentJayZ cool thanks for that... One more question if I might, I love the sound of turbine engines starting (who doesn't I guess) I've noticed on some start ups, (not all) that occasionally there's an accompanying deep rumbling / growling sound Russian engines seem to be prone to it and I'd always wondered what it was that caused it?
A lot of people ask that. I ask that. The best answer is: it's part of the start up that really isn't that important, and nobody has really looked into it. Maybe we will get a visit from our friendly gas turbine design engineer, and he can give us his opinion.
@20:20 "Realize that this is a real world test situation and-ah ... your criticisms of our ineptitude and stupidity are welcome and cause a great deal of humor in the shop ... so thank you"
An engineer myself (albeit in a very different discipline), that line cracked me up so much. Plus, I once again learned new things about the fascinating tech and operation of jet engines. Much appreciated. Thank you.
Served in the Air Force, and US Army. Run qualified on KC-135’s. The only difference between hung starts and hot starts in the US Army is, Hot Starts are recorded for record and carried forward on helicopters, hung starts were not. In 20+ years Army Aviation never seen a hot start recorded. In the Air Force we didn’t keep a record of hot starts, but we made an entry in the log book for further examination. On KC-135 back in mid 70’s QC checked you out being run qualified. Hung starts we shut down. Hot starts requiring shut down of fuel, leaving starter engaged to help cool down within starter limits, record hot start in log book. Then after a cooling period, attempt restart. As part of a OMS ground crew we had to run engines to get special oil samples, or if someone forgot to get them after landing. Engine replacement to reach, military rated power. Or run one engine to defuel from alert status to ground status. Best one was to check the water injection system. You knew it when you flipped that switch, always waiting for it (KC-135) to jump chocks. A real rush! KC-135’s with original turbojets were loud, water injection switched on they were screaming. On takeoff 670 gallons were good for about 90 seconds.
Always great to hear from you guys who worked with these engines in their element, doing what they were meant for. Welcome to Jet City!
I did not know that there was a water injection system for jet engines…do they still use them today?
Why did I subscribe? To learn more about jet engines!
I was a US Navy avionics tech way back in the '80s. Just the thought of a jet engine turning sends thrills up my old Jolly Roger. I'll never forget the mind-blowing awe I felt as a young plane captain the first time I stood on 'the hot pad' within a few feet of a chained down Tomcat in full afterburner...
Thank you for sharing your work.
10:30, when starting a twin engine helicopter, that's exactly what happens. The first engine to start, starts hot asf! (Within allowable limits of course) but once she's up and running, the second engine will start with an EGT (T4) of 150DegC or more cooler. That's why on odd days, we start ENG1 and even days we start ENG2 so we keep the LCF numbers in phase with each other.
Great Video! Your explanations are wonderful, you do a great job. It's a big job you have taken on, education of the unwashed masses (of which I am a part) but you do it with flare and enthusiasm. We applaud you, Sir. Well done. Understanding jet engines was unthinkable until you appeared on my screen. Now it gets clearer with every episode. Thank You.
Thank you for the kind words. And by kind words, I mean not calling me an idiot.(!)
I thought I understood jet engines before I started watching these videos. Turns out that much of what I “knew” was wrong. Thank you for making these programs.
I used to do a lot of maintenance ground runs on the De havilland Buffalo. During one start, apu was on, I started opposite engine from apu then did a cross bleed start from the running engine to the engine being started and noticed the ng was hung but the temp was taking off like crazy. I killed the fuel and motored the engine with bleed air to cool it down. Next attempt went off without a hitch.
I miss those days, well not the night shift part.
Good call.
I don’t know why people want to criticize your video I have learned so much about jet engines from you I’m very appreciative that you provide this to viewers.im a current pilot flying the Hawker 800 XP and I always remember the points you make about hot and hung starts. Most of the times when I’m in the Simulator I have to recognize a hot start, and resolve by doing two things, 1. Shut fuel, 2 Abort the start. It’s simple, but recognize it before damage happens is the trick, it’s just a sustained sudden high rise in temperature with no N1 response. Thanks again.
I am a commercial pilot students and a mechanical engineer it gave me a way more better understanding that any other lecture .
I have never worked on a gas turbine
I will never work on a gas turbine
But I sure do love to learn about gas turbines.
Sir kindly make a video of replacement of LSGI soleniod on T56-A-15 engine which is usually used on c 130 air craft.
A little story, I'm from 63 I have not traveled much in my life but recently I was flying in an airliner for the first time, I was sitting so I could see the jet engine out of the window and it was really cool, I had a reasonable good insight in what was going on in the engine thanks to you that was awesome, thanks for the videos 👍👍👍
Thank you for taking time out of your day to share your knowledge. It is greatly appreciated Sir.
Your channel is fantastic! I'm an airline pilot here in Brazil, right now at home due to the Corona virus. I learn a lot from you. Thank you!🇧🇷
Excellent video! About 20 years back, I built a couple of turbocharger-based GTs and in a couple of hundred successful starts, I got to observe a hung start twice. Kind of amazing just how fast the temperature climbs if fuel is added when the engine won't spool up to match. It's really instinctive to continue adding more fuel at just the wrong time. Oops.
You have to be one of the best teachers I know... I am right now getting my A & P licenses and tbh my teachers don’t even explain it like how you do. It’s like they don’t even know what they are teaching.. I wish there was more folks like you in the world actually being able to educate those that are interested in such a AWESOME and BADASS career XD
Thanks for explaining a hot start. I'd never heard of it until Mike Patey mentioned it recently after having a catastrophic engine failure in Turbulence. He said that engine never had one but he didn't explain what it was.
I too heard of hot starts from Patey. I've read about turbines for decades and knowing liners and airflow were milestones in the development... But ONE hot start can kill an engine!
@@dousiastailfeather9454 Yeah, I'm looking forward to an analysis of what happened with Turbulence. Obviously, I'm glad Mike and his passenger are OK but I'm also glad that amazing plane only needs a new engine.
Thank you for making these videos, I have been following you for years. When I applied for an aviation job selling Hamilton APU parts and PW turboprop parts- I was mainly accepted for knowing what I know on Jet engines, and all I know I learned from your videos. Keep it up
Hey, send me a hat or something, OK?
Kudos on this video...very well explained and I understood more from your explanation than my textbook. Thanks.
I am lawyer with previous electrical engineering schooling and job experience and really enjoy watching the videos of this channel, learning about the challenges of really intelligent human beings. Thanks for posting.
Not everybody is a Luddite!
That oxy-acetylene mixed flame is almost the closest you can get to burning pure gaseous carbon - a hypothetical substance which doesn't really exist on earth (though arguably does in some parts of outer space). No matter how much oxygen you cram into the flame, the temperature is limited by the water vapour present, a result of burning the small amount of hydrogen in the acetylene, which has the formula C2H2. Adding more hydrogen (and hence more water vapour) into the flame cools it off, so a flame burning ethylene (C2H4) is cooler, and burning ethane (C2H6) is cooler still.
The hottest steady state flame burning oxygen with a gaseous fuel uses dicyanoacetylene (C4N2), which burns at almost 5000 degrees C (9000 F), a result of there being no hydrogen present at all, and therefore no water vapour in the flame. The only way to go any hotter is to start getting super-exotic with your fuel-oxidiser combination, such as burning rolled aluminium or magnesium foil tubes with fluorine gas. A thermic lance using that combination can slice through concrete like a hot knife through butter.
After all these years thanks to you I finally have a real comprehension of how they actually operate. Thank you !!
Thank you for your indepth explanation, it was very interesting.
Enjoyed.
Nice info.
Stay home stay safe.
Good job.
This was brilliant ! Really great Information for those getting into aviation to understand and really puts into perspective the real side to the operation of these amazing engines ! Love all the content you make it really helps. :)
Great explanation...great vid. Thank you, sir...and stay safe.
Very interesting. And as always, a little touch of your subtile humour, now and then, makes this lesson on hot-starts delightful. Stay healthy, Happy Easter to you and family, salutations from Quebec City !
The exhaust temperature trend during start up has less to do with the cooling air in the combustor, but more to do with the fact that compressor and turbine airfoil are running at an extreme off-design condition and do not transfer work to air and extract air work from air effectively. If the turbine does not extract the heat energy from combustion effectively, exhaust temperature goes up, even if the combustion flame temperature is the same.
A typical hot start, especially the newer engine that starts on automatic control, happens when the turbine is not extracting enough work (could be many reasons, most common on is a fouled/degraded turbine) causing the RPM increases to be slower than acceleration schedule prescribed in the control, then the controller add more fuel to compensate -- not the right thing to do, exactly as you said, but the controller just follows what is programmed and cannot make decision on the fly like humans do, yet. This is why the book said it's fuel rich, in the sense that additional fuel was added than should be. In manual control, if all other systems are functioning normally, yes, you can put too much fuel and potentially have a hot start, but that's really rare occurrence in professional hands like yours.
A hung start happens when the torque received by the shaft (in its entirety, including compressor and turbine) was too little to accelerate. This could be due to turbine's failure to extract enough work (this will also be a hot start), but it could also be because a fouled/degraded compressor that needs extra torque to overcome air resistance, or a starter that is not producing its speced torque. The fouled compressor and starter failure do not automatically create a hot start, especially in the higher RPM region right before starter cut-off where the turbine is extracting reasonable amount of heat energy. Again, if in an automatic control and acceleration schedule takes over the fuel flow control, it will do the dumb thing and add more fuel to try to accelerate, then it can become a hot start.
In short, a hot start does not necessarily means a hung start -- the engine could still accelerate to idle, but just transiently has extraordinary exhaust temperature excursion. A hung start also doesn't necessarily equals to a hot start, but tends to do so in automatic control before human intervention.
Your first paragraph is accurate.
It has everything to do with cooling air.
It cools the flame to a point where it becomes hot air that isn't so hot as to damage the engine.
If you don't cool it down, it's too hot.
"A failure to establish sufficient cooling air flow", whatever the underlying mechanism.
Um, I think we are talking two different things, one is the root cause of a hot start, the other is what is the prime path to cause damage, or failure mode, to the engine in a hot start.
If more fuel is applied than what cooling airflow can cool, absolutely, the resulting temperature will damage the engine, especially stage 1 turbine components. There are, however, other bad things that can damage the engine, such as airfoil vibratory crossing in a hung start.
On the other hand, why would more fuel than cooling airflow can support be commanded in the first place, that's a completely different story and what I was trying to describe.
I used to run J-33 engines. Coming over the horn was always a time to eyeball the EGT. I think it was 799 C but long time. If it was going to hot start on that engine you basically had to pull back to cutoff before it took off. Hot start was very quick. Thanks for great vids!
I must respectfully disagree, a hot start is not the same as a hung start. The difference is where to apply the blame for the anomaly.
Hot Start - If the starter is generating energy to spec, but the fuel control is not (too much fuel for that rpm), then you could have a hot start as the fuel control continuously delivers higher than required fuel flow at that rpm so the starter is unable to break the cycle, and egt increases above spec without increase in rpm.
Hung Start - If the fuel control is delivering fuel per spec, and the starter is not delivering enough energy, then the engine rpm will "hang" and not accelerate to idle while the fuel control schedules fuel per spec resulting in high egt. If the starter is anemic then the fuel at that rpm will create too much pressure for the starter to overcome, and the engine rpm will not increase while egt goes out of spec.
Both instances are caused by too much fuel, not enough rpm. The difference is in why.
Case in point: J79-GE-17A cartridge starts are a fine example. Sometimes the cartridge would burn fast enough to start the engine, often the engine would start relatively normally. But you had to really watch for a hot start in that scenario because the cartridge burn rate could be insufficient for a start and you had to know when that was. Key indicator was rpm vs egt out of spec. The same engine would start perfectly fine with a working start cart, sometimes it would start with a cartridge, sometimes not. If you weren't paying attention the engine could have a bad day.
I suspect the difference between "hot start" and "hung start" meant more in the past and was due to trying to differentiate between blaming the starting system or the fuel system including the fuel control for insurance or warranty or maintenance tracking. Things like cleaning fuel nozzles and swirl guides used to matter.
Great videos. Thank you very much.
Yes. They are different, and they are the same.
This is why I prefer to use my definition, which avoids the cause issue.
"A hot start occurs when there is a failure to establish sufficient cooling air flow during the start sequence of a gas turbine engine."
Jay, I've always thought of it like this - a Hung Start can become a Hot Start but a Hot Start can never be a Hung Start. Also, a Hot Start is more likely to be caused by environmental conditions (i.e. trying to start a jet with an out-of-limits tailwind) than a mechanical condition (i.e. starter or battery failure). You avoid Hung Starts by ensuring your batteries are in good shape or use of a start assist (i.e. GPU or APU), especially when it's cold outside. You avoid Hot Starts by making sure the plane is positioned properly and you allow the starter to accelerate to full speed prior to the introduction of fuel in the engine (on non-AutoStart engines). You might use a GPU to help with abating a Hot Start on an extra hot day as well, but that's secondary to the first 2 items.
I think it would be a blast to hang around your shop for a while. Seeing how stuff is done in a hands on scenario.
More knowledge all the time. Thank you!
Fascinating and informative! I could listen to you all day talk about jets. Super fun stuff for this lowly piston flyer.
Here's how my powerplant teacher explained it to me: hot start IS a hung start with the possibility of a fire due to high EGT and extra fuel left in the engine. A hung start is just that; EGT did not reach a high enough temp to accidentally light any extra fuel before you blow it out.
Furthermore, as it was explained to me, a "rich" mixture simply meant too much fuel for the combustible air. That is why hot starts are so dangerous; hot EGT and no accelerated air with extra fuel after cutoff. I was always told to wait 1 minute then dry crank.
Great again, as usual. Thanks. I'm glad you can still do your work, I guess most of it can be done without a lot of social interaction. Stay healthy!
On an F15C fitted with F100PW220, hot start and hung start can be two very different conditions. A hung start can and would most likely turn into a hot start rapidly, but has its own criteria. I have seen often a tail wind cause a hung start, which is aborted prior to it becoming a hot start as the stert criteria has a time to rpm limit. I have also seen motors that come from engine backshop pickled hot start even though the rpm is climbing normally. What I *assume* happens is the storage oils are burning on the combustors / liners. 3 or 4 start attempts usually allows for a complete start and the greatest fog machine ever made.
Correct. A 'hung start' and a 'hot start' are two different things. A hung start can progress into a hot start... if not recognized and terminated.
Really good breakdown of what goes on during a hot/hung start.
I used to be really heavy into DCS: World with the Ka-50, and every now and then i would grenade the engines on the pad by screwing up the start sequence - usually by introducing fuel too LATE, which always confused me....
Now I understand why that is: by introducing fuel too late, combustion starts right as the engine controller decides "this start is going nowhere, close the starter valve" and so i end up with combustion happening at too low of an RPM for the engine to spool up on its own right as the start valve closes....
One other note while I'm at it - love your sense of humor and delivery.
I am reposting this because it seems you did not realize I was trying for humour.
Nice analogy with the acetylene torch.
I liked the picture you drew of the PISTON ;) Edit. To be clear it is a joke (Piston)
I love watching this stuff. I have nothing to do with your industry. But my father was a USAF B47 crew chief and he created a curiosity in me about such things.
สุดยอด
After watching the very intensive and meticulous process of building these engines, I don’t think I would be able to be on the start controls without having an anxiety attack. Especially when the temperatures climb so fast beyond the limit. I guess with experience you get the “fadec” feel for how far you can go before shutting down!
My video called Sabre Jet Engine: first start, is about the first time I went through this experience. I talk about the anxiety a bit.
Jim Goff - It’s not hard to deal with a hot start. You watch the needle and if it looks like it will exceed the limit, you kill it. Rarely are you close to the limits with modern FADEC engines as they will generally control the acceleration. The last hot start I prevented was when the start surge control valve failed at the same time as a FADEC channel. What you don’t do is exceed the start limit otherwise you have a potential pile of scrap on the wing.
My father was an airline pilot, and a former Air Force fighter pilot in Vietnam. Back in the late 90s, he was explaining the progression from analog to digital flight controls. When he was younger, the pilot was in control of the aeroplane. Good ol' stick and rudder. But with the advent of FADEC and fly-by-wire setups, the pilot makes suggestions to the computer, and the computer controls what happens. He said that it's safer, but not as much fun. And by fun, I think he meant dangerous. 🤣🤣🤣
Your doin great work. Educate the masses!
Was ground man on one hot start on a j 57 ( KC-135A) fuel was on before ignition, could see fuel out the tailpipe for a second or or two then a flame growing stronger untill engine rotation blew it out maybe 5 or 10 seconds, was quit a sight. It was 48 yrs ago
Love me a good tailpipe fire...
Thank you for that video. I always wondered how the older engines functioned, and how the startup procedures were done in order.
Well versed, and explained very well. I appreciate that.
Thank You Jay: Every episode is a true learning experience, especially this one. Even though I have operated turbine engines, Your explanation provides a technical support for the real world operating experience, and therefore a greater understanding of what the instruments are showing (or not showing). My question from today's class is ... why doesn't the manufacturer / engineer place the ITT sensor in the combustor rather than the tailpipe? We know there are mountings in the combustor (igniter), so why not place one for a sensor that would give the operator a dynamic and instantaneous reading, which from a user perspective would be beneficial?
The reason a sensor is placed downwind of the turbine is because the actual temperature at the turbine inlet, or TIT, is so high that the thermocouple has a very short life. So think of it: we use EGT as an indicator, knowing the actual critical temp, TIT is several hundred degrees higher.
The actual critical variable we don't see, but infer from another, lower observed indicator.
It would be great if a sensor could be made that would survive the job of actually measuring Turbine Inlet Temp.
Thank you for that explanation! I hear a lot about hot starts and hung starts in the vids I watch. But not being a jet engine guy it was very educational for me. I am very grateful!! Thanks for your time and work on this video!
Have a look at a vid I made that also covers the subject. It's called the Turbojet Start Sequence.
thank you so much, no one in the flight school teach you that topic, thanks for knowledge, is going to help me a lot for my future as a airline pilot thanks again.
I wish you much success in the future. Welcome to Jet City!
Got it. Thanks for an excellent explanation . Jim
Thanks for the great content!!
O don't know why i am so curious about these engines ,and watching your vedios, since i have no connection with the engineering studies, but as a ley man ,i am grasping quite well what you explains , means you are very brilliant in teacher.
Thank you. I have always been fascinated by jet engines.. I could never work on one because I would be afraid of error and problems. But I learn as I go from you and others. So please keep us flying.
Oxyacetylene welding. For complete combustion the gasses need to be mixed in the correct ratio to achieve what's called a neutral flame. Too much acetylene results in a carbonizing flame: contains unburned carbon (soot). Too much oxygen results in an oxidizing flame: contains unburned oxygen (ruining the ability of the exhaust gas to shield molten metal from atmospheric oxygen).
I've seen pilots with PT6s and a week battery move to cut off just prior to max temp., then adding fuel again, repeating until they get a successful start. Anyone think that's acceptable? In the middle of no where, no battery or external power was available. One thing that helps alot is to not attempt to start any turbine engine with any significant tailwind. Single engine taxi starts create this issue quite often as well because you are usually starting in a tailwind. Even when you allow the engine to max motor before adding fuel.
Once again, Thank you. This time I had a pretty good understanding of the subject, so your video was confirmation. I had a jumpseat ride in a Fokker F28 jet with Spey engines. After we passed 10,000 feet the FO asked me what questions I had, and I asked why I hadn't seen the spike in temperature at start. I think I was looking at the wrong gauge. That moved the conversation to a whole new level.
On FADEC
Newer cars have Electronic Throttle Control, I think the idea is similar. Anyway when the pedal is pushed the computer is informed and adjust the throttle and so on to accommodate.GM calls it a "Torque request".
You can think of an open camp fire where the heat carries the flame snd smoke high in the sky but there's no pressure increase. In fact for a couple of reasons like Mr. Bernoulli and low density the pressure is lower than ambient.
Sorry but I disagree with a hung and hot start being the same thing.
A Hung start is when you get normal light off but rpm stays low usually with increasing EGT but not always exceeding EGT limits (normally due to low starter power).
A Hot start occurs with normal engine rotation but EGT limits are exceeded (can be due to fuel control malfunction).
Hmmm... didn't I say that exact, exact, exact same thing somewhere in this, this, this very actual video? I do think I did...
Yeah, I did.
I'm sorry, but I disagree with your contention that you disagree with me.
Me thinks you agree, and I agree with that.
Yo!
@@AgentJayZ
Sorry maybe I missed that...kinda hard to hear with screaming kids stuck in the house going stir crazy.
Now where's my gaffer tape. 😏
silence is golden, but duct tape is silver!
Simply here because I love your channel .. Hnmmm.... Lemme rephrase that, I love your personality, adored your knowledge and cherish your sense of or ability to teach or your teaching sense...
Now as an automobile tech wt 32 yrs of practice .. Now hearing you described combustion in piston and jet engine... And you was perfectly right, I realized " why am I here "
You have to respond to console me because am heartbroken right now.. ..
Maybe I should start working on equipping auto-crafts wt JET engines or something ..
Sometimes, when trying to make a hydro-mechanical fuel control work right, all you wish for is a magic wand!
I still have my orenda accessory gear box cover. Cool jet city shirt!
I wanted to say thank you for a fantastic explanation of what a "hot start" is and how it can be so damaging to the turbine of a turbojet engine. New sub here. Previously I did not understand why a longer hot start event would require inspection prior to use.
Do single spool engines still exist? Back in the 1960 I think the Brits made a small portable genset powered by a jet engine but sadly these things never took off commercially.
There are many single shaft industrial engines in use, while almost all aviation engines are using two or even three shafts,
Thank You, Have Fun & Stay Safe!!
Great description to clear up my questions regarding hot starts. Thanks, and keep the videos going !
Happy Easter! Stay safe and healthy!
Fascinating, to me, an old guy who worked only on small Continental engines.
I feel like ate a bowl full of fun facts to impress my friends with... yummy !
I always considered a hung start as one where there is an issue with the starting fuel schedule where perhaps the secondaries don't kick in. But I see that there may be other causes for lack of acceleration. Thanks for the video.
This is the type of video that clarifies my questions about these engines. Great work.
Fascinating stuff!
Three questions:
1. A high percentage of energy coming out of the combustors goes back to the compressor, but also a large amount of air coming out of the combustors is unburnt - for ease of explaining - "untouched" compressor air (=energy [not really but kind of]). Is there energy being "recycled"? If the compressor were to spin by itself at max rpm how much energy in % would it put out in comparison with fuel and without it?
Might be in a theoratical dead end with this tought, and I know that ALL energy comes from fuel beeing burnt. Still "untouched" compressor discharge air is hitting and spinning the turbines, so to a degree spinning itself; so that makes the energy consumed by the compressor less than it might seem at first.
The other two are easier:
2. Is the EGT-temperature that limits the maximum power the same as the max tempertature at startup?
In my mind it should be less as it is continuous.
3. Planes are marked where the turbine disks are in case they come apart (i know extremely rare); is that something you take into consideration in the test cell?
Especially since these engines are run for the first time.
Thanks for sharing your knowledge!
Stay safe
The compressor rotor of this engine needs 20 thousand Hp to turn at 7800 rpm. The load it puts on the turbine is evident whenever an engine is shut down... the rpm drops rapidly when no fuel is being burned.
The max power EGT limit for this engine is around 1300 F
The max starting EGT limit is 1560 F
The red markings on airliner nacelles are more for guidance of personnel on the ground as the limits of approach areas, to avoid exhaust blast, or inlet wind pressure.
Our test cell is designed so that the control room is well forward of the plane of rotation of the turbines of the engines.
The turbine is designed to extract power from hot combustion gases, mixed with cooling and dilution air. If the fuel is shut off at maximum engine RPM, the volumetric flow instantly reduces. This results in the turbine becoming instantly so far off design that it is not being spun by by the relatively cold air from the compressor and it just adds to the power absorption from the inertia of the decelerating rotor.
@@AgentJayZ
thanks for your answer!
you broke it down to the essence. my curiosity was:
If now one were to take the turbine out and spin the compressor on its own how much more power would it take to spin it?
at 7800, twenty thousand horses...
@@AgentJayZ so you are saying there would be no difference between a compressor with and without a turbine attached?
I think I need a cigarette now.
I'm pretty sure my testosterone level increased as the RPM's spooled up on that jet engine. I'm gonna go to my shop and be with my weak power tools for awhile. Maybe read some engine repair manuals. This guy really has the goods where gas-turbine hot starts are concerned.
jay, wouldn't the fuel control schedule prevent "excessive" fuel input based on rpm/ discharge pressure? in 8 years in USAF i can only recall 2 "hot/ hung" starts, they were performed on alert pad and with prevailing winds up the butt.[no blast fences there]thank you for another informative video.
Yes, you are correct. Hot starts of an engine that has been tested, accepted, and installed in an aircraft are rare, mysterious events.
Great explanation. Thanks for the video.
Love the videos, very informative with the added bonus of giving me another way to annoy my wonderful wife!
Hey, annoying women is one of my special skills. Just ask airplane girl!
You probably don't need any special skills or techniques to annoy your wonderful wife. Just act natural.
The computer screen when you are running the engine has a plethora of data showing all at once. Are you able to process that all at once because you are well practiced, or do you only focus on a few select pieces of the most important data?
I spent years making Spey "scoops" whilst at the same time having no clue as to what they did. I do know that they are as hard as hell. Tapping them was a nightmare. I can't remember if they were tapped to accept a wire insert or not. As you know, a lot of RR parts have wire inserts fitted from new, which surprised me at first. In some instances the guys that fitted the inserts had to collect the little "tangs" that you break off during fitting. They were sealed in a bag and went along with the delivered part to be counted and verified at RR. I guess that there must have been a "foreign body" issue in the past.
With the Orenda engine, you often find those little wire tangs left "unremoved" in the bottom of holes in the cases, still attached to the insert.
Somebody thought that was safer.
It seems to have worked, as they are still there after 65 years.
At first I imagined the air and exhaust flow in your cross section traveling away from the viewer. But when you showed the inside of the combuster can aft end toward the viewer, thought maybe gasses coming toward us. But because of all I’ve learned from your great videos, I’m guessing for the purposes of this discussion the flow could be going toward or away from the viewer 🤔. Thank you, I really needed this tonight🙏
I wander if the wind direction and how you are parked could play a factor. Maybe parking facing the wind might help the airflow and assist the starter.!
@@ohwell2790 is rude.!
That is definitely a concern, mentioned in the pilot operation handbook for the Canadair Sabre. "Ensure the aircraft is parked facing into the wind before attempting a start".
I used to start Rolls Royce darts at work, and they were prone to hot start.....you had to be quick on the condition lever to get it to accelerate through the hot part of the start.....noisy as hell those things
Great video and explanation! Thank you!
I have learned lots from your videos!! Thank you!!!!
Very good sir...Thank you...!
So FADEC pretty much eliminates all posiblities of a hot start/hung start. Technology is marvelous.
It just shuts things down before it gets out of hand. I've still had hot starts in a fadec controlled pt6
You know its loud when you have in-ear foam AND over the ear muffs.
Yeah, when I saw that I wondered about the guys outside the control room, and Jay when he was standing downwind of a running engine! Ma goom ba! Of course, he did say it was LOUD.
I missed this one - superb as always and many thanks!
Thank you Mr. Jetson for the video👍👍👍
Great video. Really enjoyed the information presented!
Thanks for the video. Like playing your stuff on lunch at school. We work on gasoline piston engines. I like the thought process and the attention to detail. Along with the content of course. But when we start talking about exhaust and especially turbos. I can't stress enough how heat translates to velocity.
Great video!
Like after you eat a big Thanksgiving dinner.
Your fuel/air mixture is too rich and you need to shut off and restart after a period of rest.
4.23 You have said it 101 times.....but keep saying it for those who are coming in late...... Thanks for the reminder. sir
Great info & something I can relate to; I need a bit more starter voltage the J44. You mentioned that it seemed a tad too flamey for your taste & I think getting the speed up quicker is a good start towards reducing the thermal stresses on the poor old thing! Thanks, stay safe, & good to see Pink Dispatcher is back. Cheers.
DD
Great video Jay, Ive always enjoyed your content so keep spreading this to the av geeks community, greetings from Mexico 🇲🇽
Before this video I watched another on the PT 6 engine
When talking about the air flow he mentioned suck squeeze bang blow
I enjoy his videos and also being that tea is a captain I have too much respect to say anything,
Intake squeeze burn and blow, like mentour pilot and 74 Gear they know vastly more than I,
I am now watching your hot start video, take care now
I work on SCADA systems that interface with the beasts. So, I've been in plenty of test cells. You've likely answered this question before. But gonna ask anyway. What is the story with that "resonant" sounds that seems to occur on every turbine slightly before it goes live? Love hearing the sound but don't understand it. Thanks. Gear-head here.
Officially and technically, it's known as "one of those things". A complex resonance due to the interaction of the engine speed being out of the operation band, the exhaust heat, and the ducting?
We have a few exhaust ducts that we have made for various engines, and they make thundering and howling sounds on startup that the engines normally never make.
@@AgentJayZ Ha! It is a comforting and expected howl. Perhaps ducting designed so it happens only once on spool up(out of normal operating range). The howl would be a very unwelcome characteristic if didn't go away. Thanks. Makes me think of my '90 GSXR 750. It resonated in 6th gear at about 63mph. Despised that bike for that. I owned it for just about 1000 miles. Irritating piece of machinery it was.
Awesome bike. you had it in too high a gear for that speed. You were operating the engine outside of it optimal range. That bike is designed for ripping, not cruising.
You would really like something torquey-er, like a VFR, maybe?
I ride a big V-four now, but I once had an 86 Gsxr 750. It was so manic, shrieking through the Yosh 4 into 1 towards redline. It always seemed to me I was riding a rabid wolf... if given the chance it would hurt me, but If I paid attention and always used firm, controlled inputs, it would do amazing things for me!
@@AgentJayZ I'd love a VFR. I've had these: GS550ES, FJ1100, ZX7, V-Rod, CBR600RR(track bike), ZX9, '06 YZFR1(the only bike I still have) Was getting into racing and the '08 recession put the kabosh on that. That Suzuki was my least favorite of the bunch. Nothing like a numb arm to make you fall out of love with a visibly beautiful machine. I'm 51 now so getting a little long in the tooth to resume the passion. It was and is fun. The BMW R1000 is so damned attractive right now at least to me. Will I be practical and not buy one just because? TBD. Damned sexy motorcycle though.
With respect to a fellow experienced motorcyclist, you may enjoy a sport touring frame fitted with an engine with a meatier mid-range than the (great) inline fours you have been riding.
The V-rod has the right engine, but the wrong frame.
I would suggest you take a test ride on a strong middleweight sport tour, naked, adventure, or what used to be called a standard bike.
Cheapest option would be any of the SV650 models. Most satisfying engine I have ever experienced.
Most enjoyable might be the KTM 790, in any of its forms.
Also, if you can find one: the Triumph Sprint ST.
Sport tourer with a 1050cc triple. They don't make em any more, and you don't see many for sale... there's a reason for that.
If I was going to try a BMW 1000, I would look at the XR first, and probably move more towards the new 900XR.
Anyway, now I've got bike fever a few weeks too early in this part of the world.
Fascinating ,informative,, . Thank you so much .
Great video Jay. Happy Easter to you and your family.
@17:35 I always thought all full size jet engines use FADEC control systems..Model turbine engines uses fadc control for starting.
This is a topic I've been wanting to learn about. Thank you.
Beautiful vid, thanks for uploading, so I could listen to this fantastic sound.
The rotational speed of the engine must be sufficient enough to supply air for combustion and cooling. You can under-speed with enough combustion air to ignite the fuel, but will not have enough cooling air, and cause a hot/hung start.
Love your videos, particularly the depth into which you explain things, I thought I had a reasonably good gasp of how turbine engines functioned but thanks to you I'm learning there's a whole lot more to the story.
If you get a chance at some point could you do a clip on cartridge starters?
When we rebuilt a J-79 out of a Phantom II, I made a series of videos about it. It's a playlist called Working on a J79 turbojet engine. One of the series is a video about the cartridge starter, which is also a pneumatic starter.
Put the title in the search bar on my channel page, and try watching all 18 vids!
@@AgentJayZ cool thanks for that...
One more question if I might, I love the sound of turbine engines starting (who doesn't I guess) I've noticed on some start ups, (not all) that occasionally there's an accompanying deep rumbling / growling sound Russian engines seem to be prone to it and I'd always wondered what it was that caused it?
A lot of people ask that. I ask that.
The best answer is: it's part of the start up that really isn't that important, and nobody has really looked into it.
Maybe we will get a visit from our friendly gas turbine design engineer, and he can give us his opinion.