@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 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 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.

Thank you for taking time out of your day to share your knowledge. It is greatly appreciated Sir.

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 👍👍👍

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!🇧🇷

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

Kudos on this video...very well explained and I understood more from your explanation than my textbook. Thanks.

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

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.

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.

Thank you for your indepth explanation, it was very interesting.

After all these years thanks to you I finally have a real comprehension of how they actually operate. Thank you !!

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 !

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 think it would be a blast to hang around your shop for a while. Seeing how stuff is done in a hands on scenario.

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.

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. :)

Fascinating and informative! I could listen to you all day talk about jets. Super fun stuff for this lowly piston flyer.

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!

Enjoyed. Nice info. Stay home stay safe. Good job.

Great explanation...great vid. Thank you, sir...and stay safe.

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!

One other note while I'm at it - love your sense of humor and delivery.

More knowledge all the time. Thank you!

This is the type of video that clarifies my questions about these engines. Great work.

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.

Great description to clear up my questions regarding hot starts. Thanks, and keep the videos going !

Beautiful vid, thanks for uploading, so I could listen to this fantastic sound.

I missed this one - superb as always and many thanks!

Your doin great work. Educate the masses!

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!

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)

Thanks for the great content!!

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.

Thank you Mr. Jetson for the video👍👍👍

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 channel is SOOO good!! Thanks for years of amazing content!!!

Got it. Thanks for an excellent explanation . Jim

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.

Great explanation. Thanks for the video.

Great video. Really enjoyed the information presented!

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.

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".

This is a topic I've been wanting to learn about. Thank you.

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. 🤣🤣🤣

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 video and explanation! Thank you!

Great video Jay, Ive always enjoyed your content so keep spreading this to the av geeks community, greetings from Mexico 🇲🇽

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.

Happy Easter Jay. Another great learning vid.

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.

I have learned lots from your videos!! Thank you!!!!

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....

Excellent description !!

Happy Easter! Stay safe and healthy!

Fascinating ,informative,, . Thank you so much .

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.

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

I still have my orenda accessory gear box cover. Cool jet city shirt!

Great video, as usual. Thanks !

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 Jay. Happy Easter to you and your family.

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🙏

Those older Engines are so cool! You can clearly see the "fire tubes" or combustion chambers! The old DeHavilland "Ghost" engines were like that! The Ghost was of course, an engine designed for military aircraft that turned out to be ideal for the Comet I commercial airliner!

Fascinating, to me, an old guy who worked only on small Continental engines.

Great video!

That was an excellent explanation.

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 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.

Great explanation. Thank you sir.

Thanks a bunch for the video. You're doing a great job. Very interesting topic and you made me buy the textbook from Jeppesen that is my buddy each evening after a hard working day.

Thank You, Have Fun & Stay Safe!!

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!

Well done!!

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 ..

Exellent video!!

Cheers, pal, Happy Easter!! :)

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.

Great video Thank you

Thankyou for everything :)

Very good sir...Thank you...!

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.

Thanks for this video

Nice work

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?

Great content squire.

Love the videos, very informative with the added bonus of giving me another way to annoy my wonderful wife!

KOOL ! I enjoyed the education

I am so glad I discovered your channel. The way you explain everything is just right for me, thanks for helping me understand a hot start. I have subscribed to your channel and will be devouring all the material it has to offer.

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.

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

I feel like ate a bowl full of fun facts to impress my friends with... yummy !

4.23 You have said it 101 times.....but keep saying it for those who are coming in late...... Thanks for the reminder. sir

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.