Turbine overspeed, and inlet debris screens

[@rjtoten]

Aircraft APU inlets often have some type of screen. Story time. After arriving at JFK, a member of the ground crew came to the cockpit and told us there was a plastic bag ingested by our APU, we looked at the indications, with normal RPM, no failure messages, and a temperature within limits but probably 100C higher than normal. We dismissed his concerns but thanked him for the observation. When I performed the walk around, I came upon the APU inlet. It was protected by a large screen, and a plastic bag was covering maybe 1/4 to 1/3 of the inlet. The force of the airflow was pressing the bag 3-4 inches beyond the screen and into the duct. I went back to the cockpit, we turned off the APU, and we used a bag loader to reach the inlet and remove the bag. All good.... ready to board!

[@jmurphy1973]

I once had a part time job working in an industrial freezer that was at the magical intersection of Celcius and Farenheit: -40

[@tombrown5445]

Jay is talking and I am listening, but I'm also distracted by the Orenda behind him which looks really well finished. The black painted compressor cases and fittings are a thing to behold. If I was a customer I'd be very pleased to get my jet back looking like that.

[@kimmer6]

I worked for GE on industrial gas turbines and steam turbines. Almost every one had an ''overspeed bolt''. There is a plunger mounted radially in a threaded hole in the shaft near the journal bearing in front of the compressor on a GT and near the steam inlet section and thrust bearing on a steam turbine.. That ''bolt'' has a spring forcing it back into the shaft. Its center of mass is slightly outside the centerline of the rotor. The spring tension is adjustable by a threaded collar that is staked into place with a punch when adjustment is correct. If anything happens out of the ordinary and the shaft speed exceeds 105% operating speed, that bolt flies out by about 1/4 inch and will strike a steel trigger arm. Picture a rifle trigger...same principle. Almost always this arm dumps hydraulic oil pressure that will trip the fuel control on a gas turbine and on a steam turbine the trip throttle valve will slam the steam valve shut under spring pressure like a rat trap. The turbine hydraulic control circuit is fed by the oil pump into a header with a small orifice in one end. The hydraulic dump valve triggered by the overspeed bolt has a large area, so in effect a small overspeed bolt plunger movement causes an instant loss of hydraulic pressure operating the fuel valve on a gas turbine. Springs snap the fuel valves closed. I have tested and adjusted many overspeed bolts in my time in refineries, in power stations, and on ships.. The usual emergency trip speed is set to 105% and under no circumstance is the search speed allowed to exceed 110% rated speed. Small steam turbines driving oil pumps and small draft fans don't have overspeed bolts as the casings are built heavy to withstand a rotor failure. The GE industrial 2 shaft gas turbines have an overspeed bolt on both rotors. Overspeed is dangerous. A Frame 5 gas turbine came in to Schenectady on a flat bed rail car in 2 pieces once. The turbine was cut in half after a compressor wheel forging failed. Industrial turbines have rotating parts that weigh many tons. Although they operate much the same, I had very little contact with aircraft gas turbines so I hope this helps. Yes, every GE industrial turbine has a large inlet air filter house and debris screen.

[@allangibson8494]

A significant number of people have been killed setting overspeed bolts which is why electronic overspeed are now preferred in industrial applications.

[@SsiolisP]

Mentour pilot and blancolirio, both mention you in their videos regarding the compressor stall of the 777-200 out of LAX, which hosed a few children with fuel. I felt so proud of you! :)

[@grahamj9101]

I'm not aware of an LP or fan turbine disconnect in any of the big turbofans, resulting in an overspeed and disc burst. However, I'm acutely aware of what happened to the No.2 engine of Qantas flight QF32 in 2010, which I've discussed it the past on this channel - and someone has beaten me to it in bringing it to your attention. The IP turbine disc went into overspeed and burst, as a result of an oil fire overheating and softening its drive arm, which sheared. I'm in the snows of the French Alps, some 800 miles away from my copy of Sir Stanley Hooker's autobiography, 'Not Much of an Engineer, but it's nowhere near as cold as in Fort St John. The Proteus was SGH's project and he turned it from a 'clunker' into a great little (by modern standards) engine - and, of course, it was used as an industrial and marine engine, on which I did a little work as a very young designer at R-R IMD. I'd have to go back to the book to remind myself of the details, but my recollection is that a straight-cut pinion gear failed in fatigue because of a gear tooth resonance. The propeller turbine went into overspeed and burst, with debris puncturing a wing fuel tank. The resultant fire was in danger of taking out the wing main spar, so Bill Pegg (I think that he was the pilot), rather than try to get back to Filton, put the plane down on a mud flat in the Severn Estuary, just a few miles away from my present home. Fortunately, the state of the tide was such that there were exposed mud flats. The Severn Estuary has the second highest tide range in the world (after the Bay of Fundy) and, if had been high tide, it would have been a ditching. The solution to the problem, which was already on the drawing board, because SGH had concerns about the gears, was to introduce helical gears. After this modification, the gearbox was trouble free and, in its 1,500rpm version, drove a 4-pole alternator for 50Hz power generation. When I moved to R-R Bristol in 1982, I found myself working with a few of the old hands from that era and, as I've related before, I had the dubious privilege of letting a glass door close in Sir Stanley's face. He was well into his retirement, but was paying a visit to R-R to have lunch. PS Do you have a copy of SGH's book, AgentJayZ? I have a spare paperback that I could let you have.

[@robdoyle161]

I think, Quantas Flight 32, an Airbus A380, had a turbine disk explode from overspeed near Singapore. Quoting the FAA Airworthiness Directive dated March 18, 2011, "An uncontained engine failure has recently occurred on a Rolls-Royce RB211 Trent 900 involving release of high energy debris and resulting in damage to the aeroplane. Analysis of the available elements from the incident investigation shows that an oil fire in the High Pressure/Intermediate Pressure (HP/IP) structure cavity may have initiated a sequence of events leading to rupture of the drive arm of the IP Turbine (IPT) disc and subsequent overspeed and burst of that same disc."

[@jamesmcmanus1206]

Steam turbines used for main engines of ships have “hydraulic overspeed’s” which act as governors to throttle steam flow into the turbine. The load itself isn’t enough to keep the turbine from reaching resonance (above normal operating speeds) if steam flow in is unregulated so this feature is required.

[@mrmgreig41]

i think Qantas flight 32 was a overspeed as well. (A380 with RR trent 900) fire from oil leak caused mechanical disconnect of IP turbine from its shaft and then the disc over-sped and failed.

[@SiblingCreature]

Yep, That was my first thought as well. www.atsb.gov.au/publications/investigation_reports/2010/aair/ao-2010-089/

[@grahamj9101]

Going back to the turbojet era, there is the infamous case of a Vulcan flying test bed going up in flames at Filton back in 1962, just after I joined Bristol Siddeley as an apprentice. The LP turbine shaft of an Olympus 320 flight test engine, which was mounted under the belly of the aircraft, failed in fatigue, because of a 'bell mode' resonance. The LP turbine disc was released, but did not burst: it sliced through a fuel tank and went bowling across the airfield for several hundred yards. The pool of fuel ignited, taking with it both the plane and a brand-new fire engine. I was also told a story that an early Industrial Olympus lost an LP turbine disc, due to a bearing failure. The story goes that the disc drove itself around the reinforced concrete engine cell several times before it ran out of energy and clattered to the floor.

[@beachboardfan9544]

Daaamn I wish there was video of that Olympus failure!

[@grahamj9101]

@@beachboardfan9544 Sorry, but as far as I'm aware, there was no-one around with a film camera. However, still photos exist, which have been published: unfortunately, I can't find one on the internet.

[@n6mz]

Awesome channel awesome video as usual. As you note, the Connie series (L-049 through L-1649 "Starliner") had various dash numbers of the highly problematic Wright R-3350 which was two rows of nine (18 cylinders). Beginning with the L-1049 "Super Constellation" the powerplants were R-3350 Turbo Compounds which had 3 "power recovery turbines" (PRTs) each extracting power from the exhaust of 6 cylinders, delivering an additional 400HP or so mechanically to the crankshaft at takeoff power via fluid couplings, quill shafts and gearing. Although more reliable than the early 3350s (my dad was lucky to survive his combat tours in the B-29, he said the Migs didn't have to shoot at them, just wait for the engines to fail) the Super Connie still had a derogatory nickname, "the most beautiful tri-motor in the sky" and I've heard that the PRTs were called "parts recovery turbines." Those engines were the most efficient production aircraft recips, I think the BSFC was something like 0.4 pounds per HP-hour when properly leaned-out and spark-advanced by the most important crew member on any 3350-powered a/c, the FE. Try to visit one of the cutaways if you have time (SAC Museum, Omaha NE has one I think), they really are a work of art internally. BTW there's a reason the Connie series is so spectaculary beautiful, it was from the drafting pen of Kelly Johnson.

[@AgentJayZ]

Cool info. We actually own two scrapped R3350-TC engines. The turbines are about 18 inches in diameter, and quite heavy. They seemed to be worth it though, weight-wise.

[@jimmypetrock]

JayZ, always a pleasure to watch your videos! Makes me miss my days wrenching on aircraft. We had a JT8D on a C-9B (military version of a DC-9) that ingested a taxi light that broke off from the front landing gear on takeoff. Despite being a low bypass, the fan ate the light, peppered the intake duct with debris, but the engine kept running and the flight crew experienced zero indications or reductions in power. The only way they knew something had happened was the crew in the cabin saw and heard the event, and ground crews found debris on the runway after the plane took off. Engines are far more robust than most people realize. oh, and the hair, we would call that a "high speed, low drag style" LOL

[@sorgfaeltig]

On overspeed, catastophic overspeed and disintegration of an LP turbine happened on Qantas A380 in climb out of Singapore. The cause was an oil fire in the hot section near the LP turbine disc that heated up the bell-shaped interface between the LP turbine disc and the LP shaft. The softened, orange-glowing metal sheared under the torque load and the LP turbine disc RPM went up until the disc disintegrated into three main sectors crippling the aircraft when the fragments were transiting the wing and the lower fuselage of the A380.

[@AgentJayZ]

Yes, thank you for being the hundredth person to "notify" me of this.

[@billdennis2993]

Agent Jay Z thx for another great informative video. FWIW on power turbine over speed I was on a Patrol Gun boat in USN in '70s which had an LM1500 gas turbine along with diesels which drove 2 6' dia. variable pitch props at max of 720rpm. Once during a mock attack on the Cruiser Chicago which resulted in a power turbine overspeed and trip as pitch came off the screws before the pneumatic control backed off the fuel control. I remember this very clearly as I was the engineman (lowest ranking) that had to go into the hot stack to reset it while still hotter than an oven. Just another day on a gunboat.

[@clayz1]

-19C is -2F so ... cold. Yes stupid cold. Thanks for the 1AM lecture. I never wondered about turbine overspeed but am happy to have a 20% boost in my level of jet turbine knowledge. Great channel.

[@Kebnes89]

For industrial applications overspeed is a real concern. For example if you have a blackout, the breakers for your generator will open. Hence you will lose all load on your power turbine, that will cause a overspeed. However systems are built in that will shut down the entire engine as fast as possible if that happens. But failures have still occurred.

[@jamespohlmann3246]

I don't know of any LPT overspeed events due to a dropped load, but I do know that a lot of turbofans have a row of vanes in the LPT that are bowed at their midspan and protrude axially forward (appropriately called "banana vanes"). The idea is that if the LP shaft is severed, the LPT will no longer be connected to the locating ball bearing at the front of the engine and will be allowed to translate aft. When this happens, the row of blade immediately forward of the banana vanes will crash into the forward protrusion of the banana vanes absorbing kinetic energy as bits of blades and vanes are sheared off and mangled (hopefully slowing/binding the rotor).

[@rwbishop]

Out of passing interest, one of our A&P instructors (c.early 70's) once mentioned one reason for engines slung under/forward of wings was for them to also act as damper weights; to aid in wing flutter mitigation.

[@WranglerSlim]

I’ve also heard that putting the engines below the aircraft’s center of mass helps to make the aircraft handle more predictably. Increasing the power makes the aircraft to pitch up slightly, while decreasing the power-or suffering a sudden loss of power-causes the nose to drop, which makes the aircraft avoid stalling all by itself. There was an incident a few years ago where a cargo plane in the middle east was hit by AA and lost all hydraulics, but the pilots were able to land safely on a runway using nothing but throttle manipulation for pitch control and differential thrust for steering.

[@lewiscole5193]

I'm not an aircraft designer and I don't play one on TV, but I suspect that the main reason why engines are placed below the wing is that this gets them lower to the ground where they can gotten to (and therefore serviced) easier. From the aerodynamic point of view, putting the engines on a pylon or mounted just below the wing is a wonderful way of increasing interference drag from conflicting airflows around the wing and pylon/engines. You can reduce said drag a lot with proper design, but it would be better if they weren't there at all As for acting as dampeners, I suppose that's possible, but given that you want to put the engines as close to the center line as possible to reduce the adverse effects of an engine-out condition, the result is that the engines ended up being placed closest to the thickest part of the wing where I suspect dampening would be less effective.

[@lewiscole5193]

@@WranglerSlim Many (most) airfoil sections that make up a wing have a nose-down pitching moment (i.e. those that aren't zero pitching moment airfoil sections) which is what down force generated at the tail (elevators) is supposed to cancel out in level flight. Placing the engines below the wing will tend to produce a moment that would also counter this pitching moment, but while I'm sure is something that real live aircraft designers have to take into consideration, I doubt that it's a big factor in why the engines end up below the wings. After all, the nice thing about swept back wings is the cummulative effect of the pitching moment can be reduced to the point where you don't even need a tail (i.e. you can have a flying wing).

[@Not-C-418]

I dont have any relationship with jet engies but i really enjoy with your way to explain things and you inspire me to read and look about these amazing machines . Good luck for you

[@michaelogden5958]

I have an old windmill on my ranch. The sucker rods have long since deteriorated, so there is no load on the "compressor". I have the "stator vane" set so that the "compressor" is in a permanent stall. :-)

[@captainmidnite93]

Walked away from a compressor stall (FOD unknown) in a PHI 302 at couple hundred feet over McMoRan platform in High Island Alpha field GOM. Kudos to pilot Ken that put us back down on that postage stamp with only starboard skid tip overhanging chain link fence deck skirt. He was breathing hard and could not stand upright or talk for a minute or 2. I thought the luggage had fallen over from the big 'Thump', whilst the old seasoned diesel mechanic in the back roared out this was his 3rd time and at least this time the landing gear did not curl up like a stepped on beer can around your foot and prevent egress... Love your channel as this electrician has taken an interest in such matters since then!

[@alisonfox7318]

In the late 1970's or early 1980's the RB211 on a Tristar had a fan shaft failure allowing the entire fan assembly to break from the engine. It was caused by an oil fire in the rear bearing which led to softening of the fan shaft causing it to fail.

[@ValExperimenter]

Qantas QF32, An airbus A380 with an RR trent suffered a turbine overspeed when torque arm failed with similar results to the Bristol plane you mentioned. one part of the turbine wheel cut all the redundant control lines to part of the plane another punctured the wing and the third part went through the roof of an Indonesian school missing everbody inside. Only one turbine disk failed

[@skyhawknz6204]

the QF32 was not an over speed it was a failure caused by restricted oil flow to the turbine bearing resulting in the Bering over heating and failing

[@NoisyPlaces]

skyhawknz6204 Disagree. From the ATSB report. The turbine disk separated from the shaft and overspeed. www.atsb.gov.au/publications/investigation_reports/2010/aair/ao-2010-089/ The thin wall section significantly reduced the life of the oil feed stub pipe on the No. 2 engine so that a fatigue crack developed, ultimately releasing oil during the flight that resulted in an internal oil fire. That fire led to the separation of the intermediate pressure turbine disc from the drive shaft. The disc accelerated and burst with sufficient force that the engine structure could not contain it, releasing high-energy debris.

[@russianslender3624]

The MiG-29 has the best debris protection in my opinion, closed while on the ground (allowing it to take off from rougher runways) and a whole of sorts opens on the top of the aircraft, and open while in the air.

[@barek257]

As others already described here, a broken LP turbine shaft downed one of 2 identical Ilyushin Il-62M planes in Poland, in 2 nearly identical high-profile air disasters in the 1980's. This particular crash was LOT flight No. 7 from New York to Warsaw, in March 1980. The plane was christened Mikolaj Kopernik (Nicolaus Copernicus) and it went down 1 minute before landing in Warsaw, with 87 souls on board. The shaft had manufacturing defects, including a ridge with sharp edges, which concentrated stresses just in front of turbine support bearing. There were various other design flaws and, on the maintenance side, the plane was regularly used despite unusual vibration produced by this particular engine and attempts to mitigate it. It is described in much detail in Polish version of the Wiki article, which I give below: Original: pl.wikipedia.org/wiki/Katastrofa_lotnicza_na_Okęciu_(1980)#Śledztwo Translated: translate.google.com/translate?sl=auto&tl=en&u=https%3A%2F%2Fpl.wikipedia.org%2Fwiki%2FKatastrofa_lotnicza_na_Okęciu_%281980%29 Quote: "[...] the shaft of the low-pressure turbine of engine No. 2 broke, and the turbine rotating freely in the stream of gases accelerated to a speed causing its explosive tearing into three parts, completely destroying engine No. 2. [...] The official announcement stated that the reason for the crack were material and technological defects of the No. 2 engine shaft. [...] the engine shaft, [...] contained [a] so-called notch which causes the accumulation of stress and fatigue of the material , as a result of which the motor shaft has broken. This engine showed increased levels of vibration during operation, despite being still operated." Unfortunately the English Wiki gives a slightly different (aka "politically correct") view, blaming the turbine disc and other factors. I can only imagine who made these edits in the international version of Wiki and why, but I do not want to comment, nor enter Eastern politics: Quote: "disintegration of one of the turbine discs in one of the plane's engines, leading to uncontained engine failure [...] the low-pressure turbine of the number 2 engine disintegrated after 9 seconds" According to Polish press, the turbine disk ruptured as a result of the shaft failure, not the opposite. Maybe we will never know the real reason, but you should have your own opinion. Especially that the second crash, a 1987 disaster of flight LO 5055 from (yep, you guessed) Warsaw to New York, where an identical Il-62M christened "Tadeusz Kosciuszko" crashed into the Kabaty Woods / Forest just 6 km from the Warsaw runway , was caused by nearly the same mechanical causes. Despite effort by the Polish maintenance crews through the 1980's to make Russian-made Il-62M's more safe. That second plane was downed because the roller bearing near the (yep, you guessed) LP turbine section was - for economic reasons - changed by the manufacturer, during the production run, from a 26-roller to a weaker 13-roller one, unbeknownst to the quality control, as well as the end Customer (Polish airlines). In addition, no less than 3 holes were drilled vertically, straight in the face of the bearing's outer race, presumably to supply more oil to the weakened bearing, which caused further premature wear. It should never be done, as it causes severe vibration and direct abrasion of the rollers... Again, you should rather read the Polish Wiki translated to English, not the English one, as there are subtle "political" differences: pl.wikipedia.org/wiki/Katastrofa_lotnicza_w_Lesie_Kabackim translate.google.com/translate?sl=auto&tl=en&u=https%3A%2F%2Fpl.wikipedia.org%2Fwiki%2FKatastrofa_lotnicza_w_Lesie_Kabackim en.wikipedia.org/wiki/LOT_Polish_Airlines_Flight_5055 As a kid, growing up in poor communist Poland at the time, I remember the jolt that both these accidents caused in the Polish society. Both crashes were widely covered in the media, including the resulting high-level investigations and the clashes with the Soviets about the real causes of the technical failures. Both crashes, together with the Challenger disasters, also had profound impact on me. Many people died in both crashes, including no less than 22 members of US National amateur boxing Team and the famous & very popular young Polish singer Anna Jantar, who orphaned her small daughter (who also became a famous singer). It is just enough to say that the quality of Soviet hi-tech production was decreasing in the 1980;s, in par with the collapse of the empire. And, although the technology was almost in par with the Western one, the quality, materials & workmanship were not anymore. Tragic. As for other issue from the KZbin clip, a low mounted wing with jet engine nacelles hung beneath and in front of them (in order to avoid turbulence & stalling the inlets), was introduced by the Germans in the pioneering Messerschmitt Me-262 Schwalbe jet fighter during the wartime, I think. Introduced very late during the war, it nevertheless downed no less than 542 Allied planes. It first flew in 1943, almost 15 years before the first flights of jet powered Boeing 367-80 (Dash 80) in 1954 and 707 in 1957. Anyway, wonderful channel, lot of information, and skilled, joyful workmanship. Great Canadian KZbin channels, such as this one and Cold War Motors keep us entertained & happy for years. And, although no pilot license here, Your channel and the channels of Blancolirio or Mentour Pilot keep me flying virtually, just as my father did in real life in his gliders :-) Keep on the good work!

[@abarratt8869]

@AgentJayZ, the Bristol Britannia Proteus failure was, according to Stanley Hooker's book, entirely down to himself failing to properly understand and heed the advice of a junior engineer. The reduction gears were straight cut - easy and strong to make, but this engineer warned that they'd be prone to resonating at certain speeds, risking gear failure. Had they used helical cut gears, which mesh a whole lot more smoothly, it would never have happened. They moved to helical cut gears thereafter! A sobering moment for Hooker no doubt.

[@cg9952]

The Soviets (and others) used gear spats/fenders to reduce FOD into engines. The A-10 and others just put the engines up high to avoid FOD. FOD prevention walks are an everyday thing on US Carriers and several other aircraft operational areas.

[@GeoffTV2]

I worked for a company (many years ago now) that did a safety assessment on an RR Olympus engine and I know that one thing that was looked at was the mechanism that deals with the potential of shaft failure between the compressor and turbine. The factors that might cause a shaft failure are many and varied (e.g. Bearing failure/degradation causing contact with a static engine component, imbalance caused by blade failure, vibration from gas flow instability, fire, loss of lube etc.). As far as I know engine manufacturers cannot get an engine certified unless they can demonstrate that a shaft failure (leading to turbine overspeed) is sufficiently mitigated. So I'm surprised that this seems like a foreign concept (see 1:25). If memory serves, the Olympus had a mechanically actuated emergency fuel shut-off valve as part of it's overspeed protection.

[@nullpointer1]

A different realm, but in aging, light helicopters we unload the PT with every power reduction, flirting with the N2 limits. (The PT governor has significant lag). Several scenarios could lead to real overspeeds. In the Bell 206, the PTG has overspeed protection (primary pneumatic, secondary electronic). 1) Practice autorotations and real autorations (if engine is still running) risk overspeeding N2 because the collective pitch needs to be dumped ASAP. 2) The PTG controls the N1 governor with compressor bleed air, filtered and applied to a diaphram - multiple opportunities for runaway. 3)The accessory gear box is linked to the main rotor geabox via a freewheel unit and a flexible "short shaft". Oil starvation of the freewheel can prevent the cams from engaging on power application -> initial overspeed. Then they'll likely grab and shear off the short shaft or the main rotor mast. That's when you get the classic broken-shaft overspeed. If you ever get to NorCal and you're not too scared, let's do some autos!

[@KozmykJ]

When I was a kid we had a school trip in an airliner that took us for ride along the South Wales coast. Organised by the geography teacher. Rhoose airport to St Davids and back. Us kids were hoping it would be a Bristol Britannia but we got a Vickers Viscount instead. A little smaller but still a 4 engined turbo-prop and most exiting for a bunch of kids. Not too disappointing ...

[@odbo_One]

I work close proximity to military jets most of my career (20 years), no matter how much or advanced hearing protection we have I have developed a ringing noise for about 2 years now. Last year I had failed my hearing test and had to get a new baseline and I am due for another test next month; might have to retire soon. Anyways, love your videos and apologize for being off topic.

[@uploadJ]

I find the more chilled I get, the worse the tinnitus gets, and for me it's mostly a low-level background ringing ... in the morning, after a good sleep, the ringing is at a minimum.

[@Lycras]

0:13 I remember back in 2012 february there was -36,7 °C at my premises. It was a sunny day and 50 cm of snow. Me, my wife and kids went outside had a snowball battle and than drove to Uniejów hot springs and had a good swim in outside pool with 38°C water when there was -36 outside. I do not know how we survived it, but no one caught a cold. Now in 2020 we have no winter. Until today there was no snow and temps are 8 during day, 4 during night, occasionally dropping to -4 at night.

[@48306jw]

Some Russian fighters, Mig 29 and Su35 have intake screens which retract as soon as the front wheels leave the ground. Their theory being that in a real world environment, their may be damaged runways, but in a real conflict, the show must go on, so to speak.

[@lloydevans2900]

The Wright R-3350 is an 18 cylinder twin row radial, one of the most powerful aircraft piston engines ever used in active service - the Boeing B29 flew with 4 of them, with the P&W R4360 Wasp Major being the direct competitor. Anyway, the R-3350 is one of my favourite radial engines because of the way it used turbo-compounding: It had 3 blowdown turbines on its exhausts, each one being fed by 6 of the cylinders, and these were coupled to the main driveshaft by fluid couplings. It's interesting because the extra power generated by these 3 blowdown turbines was in the 400 to 500 HP range - which isn't much more than some early 1930s aircraft engines had in total. Really shows you how the power production of aircraft engines shot up over just a few decades, until the late 1940s when jets took over.

[@AgentJayZ]

We've got two of them in our back lot. 3350 TC's in very rough condition. The power recovery turbines have been removed, and they may have escaped the scrap bin. This is a turbine channel, so I'll see if I can find them.

[@lloydevans2900]

@@AgentJayZ I think the turbines used were single stage axial flow. Not sure what they were made of, but the piston engine exhaust probably wasn't as hot as the air jet turbines deal with. I was wondering if one of these turbines could be re-used in a jet application, but it would be interesting to see if either the blade design or the material they are made from would tolerate that. I'm guessing the answer to both would be no, but I don't know for sure either way.

[@georgegonzalez2442]

Stanley Hooker worked on that Britannia engine and describes that overspeed incident in his book. He already had a newer design for the gear that failed as he didn't like the primitive straight-cut gears of the original design. Smart guy, the straight-cut gears were prone to resonate and fail. There also was that A-380 where oil leaked and oversped the middle turbine causing it to fly apart.

[@threeparots1]

Hi AgentJayZ. QF32, the Qantis A380 that blew an engine did have its intermediate shaft separate from the disk due to an internal engine oil fire and the weakening of the shaft leading to the intermediate compressor. While not a fan unloading, the disk did over speed a tad and “liberated” itself from the engine. I am sure you are aware of this tho.

[@raymondgoff9983]

Thanks for sharing your experience on jet engines Agent Jay

[@Flyingscotsman79]

Excellent channel, was catching up and thought it about time tou had a scottish flag on the wall, ironically I was thinking about it literally minutes before you received one! Anyway greetings from Scotland and from a Solar Turbines Gas Turbine Engineer (your channel helped me push for a job working with turbines)

[@IGCameron]

Always good to watch your videos. Maybe I wrote to you about this before so apologies if I write it here again. When I was a Rolls-Royce aero apprentice in 1967 part of my education/training was in the jet engine test facility. I remember well when a fitter had forgotten to remove a few of his tools in front of the engine (maybe 6 ft away) and there was no cross-check by his supervisor or workmates. The engine was started to run through the load performance checks and during the run, there was a big loss of power and heavy vibration of the engine. When the engine was recovered to the engine strip bay at the factory and then pivoted vertically on its end most of the compressor blades fell onto the floor. After inspection the fitter stripping the engine recovered a few of the tool fragments that had been ingested and the installation fitter's name was etched on the parts. The cost to Rolls-Royce was a new engine to the client and, needless to say, the fitter no longer worked for then after that.

[@vrendus522]

On overspeed the only thing that comes to mind, is the high flight testing of the Convair B-36 engine test at altitude. Gave a lift to an engineer who worked on that project for the Air Force. General called him early one morning and asked how his life insurance was. They took off and flew that 36 up to the fifty, think he said sixty thousand foot level. This was for an assessment of the Wood ward's overspeed governors on the B-36.Liked this fellow. He said he looked out the 36e's side blister and up above them the sky was jet black and you could see meteors coming in. Overspeed unit worked fine. This guy was on the begining crew of what was to become Sustrand Woodard Company.I think and I get this mixed upped that this was Sustrand tool and die company during that era. Guy was a millionaire, but you'd never know it. Was one of the most blessed rides I ever gave to anyone in need. Could not belive what he said, but here it is.en.wikipedia.org/wiki/Convair_B-36_Peacemaker Thanks

[@vrendus522]

@@SlocketSeven Yeah, but they somehow flew.Thnaks for the return comment. :)

[@joemeyer6876]

I was taught by an old head to put a clean shop rag or handkerchief in my mouth (as well as wearing earplugs and a headset) while trimming an engine. It keeps the head from being a resonant cavity. Oh the nights laying on my back on the ground under a fresh engine with a screwdriver and flashlight. It’s good to be retired.

[@CStuartHardwick]

Overspeed is a problem mostly with large steam and hyroelectric turbines. If a grid problem causes sudden load loss, destructive overspeed can occur quickly, destroying the entire building. Multiple systems are therefore used to prevent that, and such events are exceedingly rare. Also, my father flew B-47s. The plan was fine, but in order to deliver the H-bomb, had to perform an Immelmann maneuver to lob the bomb "overhand." After a couple of years of training sortees, cracks were found in the wing roots and the planes were quickly phased out.

[@JAMESWUERTELE]

I run lm600’s and lms100’s. An over speed can certainly happen, and I have been at the control when an over speed has happened. It’s called load rejection. When a gas turbine generator trips at full load (40 mw, and 92mw respectfully) the gas turbine has milliseconds to close fuel valves and or trip. I have seen it and been around it. It immediately makes the unit unavailable, and a boroscope is preformed.

[@MikeSiemens88]

I fondly recall the inlet screens on the Rolls Royce Nene 10 installed in our venerable Canadair CT-133! Some are still flying today with civilian registration. Being a fan of the Bristol Britannia, perhaps you already know this, but the RCAF had Canadair license build them as transports, CC-106 Yukon. My 1st ever flight was as a young kid from Germany to Trenton in an RCAF Yukon. Another real cool thing is that the Britannia was the basis for the CP-107 Argus Maritime Patrol Aircraft. Redesigned & built by Canadair to use radial engines vs the turboprops. Range & endurance at low altitude being key, the radials were much better suited at the time. The aircraft could stay aloft close to 24 hrs if not longer. Canadair was a busy outfit back in the day.

[@atsdroid]

20:00 (roughly) discussion reminds me of the "inertial separator" feature on the Cessna Grand Caravan, to prevent ice ingestion to the gas generator for this turboprop. Very clever. And, it reduces the power of the engine too. The force of the incoming airstream being bent around a curve permits the small particles to continue out a reject duct due to their own inertia, bypassing the core.

[@WayneHauber]

FWIW, I watched your videos showing the retracting wind screens on a J-47 a few weeks ago. It reminded me of a similar retracting feature used in the 1950's . Both the B-36 and the Lockheed Neptune had jet engines that were added to later variants to assist with take off. Once altitude was reached, the engines were shutdown and two louver doors closed to block the inlet. The B-36 had four J-47's and the Neptune had two J-34's. You can see these doors on the nacelles at museums such as the Pima Air Museum in Arizona. I always thought that these doors were closed to reduce drag. Now, I wonder if the louver doors also protect the engines. An RB-36 was capable of missions longer than 40 hours. While I don't think that this is an overspeed issue, I wonder what would happen to a J-47 freewheeling at 300 knots for 40 hours? Maybe the oil pumps would passively run and protect the bearings but I'll bet nothing good would come from the story. I have a book that describes flight operations on an RB-36 in detail but no mention is made about the funky inlet doors.

[@lancer2204]

"freewheeling at 300 knots for 40 hours" And given the altitude I can only guess that the oil would cool down, lose it's lubricity and ... then things get ugly inside (unless there was a heater for the oil.)

[@AgentJayZ]

Turbine engine oil is just fine at -50F, and if the rotor is turning, the oil pump is pumping. About the speed attained by unpowered rotation in a 300 knot wind, I can't say, but I would bet it would be less than operating rpm.

[@WayneHauber]

@@AgentJayZThanks for the opinion of the environment a non-operating engine would be subject to. It is neat to know that the oil would be pumped passively if the engine is freewheeling. I wouldn't feel to bad about a free wheeling engine then. However, I wonder about the folks who designed the B-36 and their thinking. I have a book called RB-36 Days at Rapid City which I picked up at the EAA store (ISBN 0-9637909-1-9). It is a book of personal anecdotes by everyone who worked on or flew the RB-36. I got the impression that the J-47's were not run very much during flight. They were used to take off and reach altitude and if extra power was needed during flight...say to climb over a storm. The jet techs had so little work that they were reassigned to work in the rebuild shop. The piston engines failed all of the time at 40,000 feet; Rapid City had a small rebuild factory pumping out rebuilt engines. I found a good photo of the J-47 doors I mentioned. To me, the doors look like a way to provide in-flight storage of the J-47 and may reflect the same mentality as the retracting screens.

[@WayneHauber]

My question/comment was answered on page 41 of the book I mentioned. The jets were not used in long range cruise and the pod doors were closed. "They (the doors) were open just enough for low rotational speed, for lubrication, with minimum drag". They were fully open when the engines were run for take off, climb or high speed cruise. The B-36 jet pods were nearly identical to the B-47 inboard jet pods, except one used AC power and the other used DC power.

[@mrstyles9999]

there is a story similar i can think of with quantis flight 32. the rolls royce trent 900 engine had a fault across all released engines of that type whereby an oil stub pipe over time wore thin and in the case of quantis flight 32, the pipe ruptured and caused an oil fire inside the engine core that caused the engine to spool up uncontrolably, the fadec could not give any less fuel to stop the spool up and the engine cointinued to accelerate untill the intermediate pressure turbine disc failed due to the stresses amd sent out debris that knocked out many major systems on the aircraft. thankfully the aircraft was able to make a safe landing and the fault was discovered and the entire fleet using that engine had to be retrofitted with a better stub pipe. hope this is helps everyone

[@jacobpoucher]

almost maybe like a diesel run-away kinda

[@whatsit52]

Is it clear as to how the oil fire caused the engine to continue accelerating? I could see how loss of oil lubrication and runaway temps could cause bearing failure and subsequent turbine disk destruction. I'd be interested in hearing more details about this accident.

[@grahamj9101]

A while back, I promised to provide some information about engines with LP turbine overspeed protection devices: belatedly, here it is. The Olympus 593 in Concorde had a mechanical device that would (might is probably a better word) cut off the fuel in the event of an LP turbine disconnect. A secondary centre tube, which ran through the LP turbine drive shaft, connected the LP turbine stubshaft to the LP compressor rear stubshaft. In the event that there was any relative rotational movement between the LP turbine disc and the LP compressor, a ring nut would be driven rearwards. This would move a bellcrank, which would pull a cable, which would actuate a fuel shut-off valve. Calculations showed that it would prevent a potentially dangerous overspeed at subsonic flight conditions, but not at supersonic cruise. The ‘last ditch’ protection was that, as the LPT disc overspeeded (oversped?) and was near to burst, its dilation would release the LP turbine blades. While this would prevent the disc from bursting, it would have resulted in blades coming out through the turbine casing. Thank goodness, it didn’t ever happen. I was very familiar with the 593, but I also have recollections of seeing GA drawings of a Trent engine, possibly the Trent 500 in the A340, which had a similar arrangement. In this case, if there was relative rotational movement between the fan and the LP turbine, a ‘hook’ would be projected outwards from the LP turbine rear stubshaft. This would catch in a ring on the end of a cable, which would wrap around the stubshaft, which would actuate a fuel shut-off valve. It all looked rather like an old-fashioned lavatory chain! This particular mark of Trent had such an arrangement because it had a secondary or auxiliary thrust bearing at the rear of the LP turbine. This was probably because there was a thrust reversal on the LP spool in the running range. The bearing would prevent the LP turbine moving rearwards in the event of a disconnect and, consequently, the LPT blades could not “tangle”. “Tangling” of the LPT blades in the event of an LPT shaft failure in a big turbofan is the common method for preventing an LPT overspeed. As the turbine moves rearwards, the blades come into contact with the following NGVs and mutual destruction occurs, providing a very crude but effective braking mechanism.

[@cck0728]

Thank you sir for the excellent piece of knowledge . Please keep on sharing your valuable expertise.

[@gordonfreeman1915]

Thank you sir!

[@ronaldmulligan4329]

Customer Abuse permalink

[@joansmith8215]

Great video as usual. I’m an auto engine reconditioner but love to watch the big toys you play with. Also, you seem to have developed a sense of humour lately, you cracked some good funnies in this one. Also, first time I’ve seen that cap come off. Was expecting a tied bunch of dreadlocks beneath but now know you’re as bald as me. Good work my friend. Gerry from the U.K.

[@JPTV-eu7xs]

Enjoy your videos on jet engines. In A&P school or Chuck Yeager's book learned another reason that inlet screens are not used. They would become work hardened, fail and be ingested into the powerplant causing major FOD. The worst damage I saw to a jet engine in my career was when the N1 turbine shaft broke while the engine was operating. All of the blades and vanes of the JT8D were missing, you could look in at the inlet and see out the exhaust section. It was determined that the low turbine shaft was not heat treated.

[@geoffpyne4766]

N1 overspeed can occur on a low bypass turbofan engine with a variable exhaust nozzle if the nozzle unexpectedly opens too much at high power ie. mil power or above. In that case the engine will automatically shut down.

[@itsmewillempy]

One of the first documentary of the qantas a380 engine failure. they show a animation and explain. when the oil pipe leaks. the oil ended up in the combustion chamber. thereby increasing the engine power. and overspeed the turbine.

[@grahamj9101]

That is incorrect. The leak was from the HP/IP turbine bearing housing. The oil could not possibly have found its way to the combustion chamber. The oil spontaneously ignited, resulting in a major fire in the bore of the IP turbine disc, which overheated and softened the integral drive arm of the disc, which then sheared. In 200 milliseconds or less, the turbine went up to 140percent overspeed, at which speed it was bound to burst. PS As I've said elsewhere, there have been various incorrect explanations of the failure. The only authoritative explanation of the event is contained in the official report of the Australian Transport Safety Bureau.

[@micstonemic696stone]

you taught me to have a pretty good understanding of the Gas Turbine, you also have taught me had to learn, by using multiple source's one problem there are no other AgentJayZ's like you, who is a real Jet Tech who shows us these multiple source's book's scale diagrams and white board image's, with all my heart thankyou Sir. Mikey d

[@jmorales68]

Thanks a lot for sharing knowledge. May I suggest for you to make a video explaining all the sources of noise produced, and what is the physics behind that noice being produced. Greetings from Chihuahua.

[@eadohayut214]

I was in the Israeli Air Force as ground crew on active F16s, and birds just sat there 50 feet from idling and revving engines like it was a nice quiet day. I don’t know how they do it

[@charlesthomas7970]

One thing not many consider is that all turbines have potential for overspeed but thankfully it isn't too common, but probably more so Steam turbines, especially ones in power plants, have huge risk. I saw a lightning strike cause the switchgear to open which removes the load from the turbine and generator rotors. This was on an 1100 MwE unit and thankfully the overspeed protection caught it in time. You should see the actuators on the inlet valves that trip, absolutely massive to shut the valves in time. And the steam blow that ensues is deafening. One of my family members is a consultant in the industry and showed what a 500 MwE turbine did in an overspeed. Imagine what a few hundred tons of rotating mass slinging blades and discs with enough force to pierce several inches of casing can do. Scary stuff, indeed. Cost to repair: starting in the 10's of millions

[@circusmime]

Thats crazy

[@stormeagle28]

These very large turbines have massive inertia, so that fast closing steam valves are fast enough to cut the power to the turbine when the load gets disconnected. I've read an article about such an incident where a power generating turbine rated for 3000 rpm reached speeds in the range of 3400..3600 rpm after a loss-of-load condition and was shut down safely without damage to the unit.

[@dtiydr]

I push thumbs up right away, then I watch the video since the content is top notch all the time.

[@express3158]

There are huge opposite aerodinamic forces acting on fan and free turbine. So besides torque there is axial force that stretches the shaft. If shaft breaks the fan and turbine will both fly away in opposite directions.

[@mikus4242]

Double plus un good - Orwell’s book is still so relevant today.

[@grahamj9101]

"It was a bright cold day in April and the clocks were striking thirteen."

[@sixstringedthing]

More relevant to today than to the era in which it was published. ;)

[@eddean6663]

You ought to see what a fiberglass and aluminum ladder that was left in a test cell by mistake will do to a CFM-56-3. Two million dollar mistake.

[@richardgreen7811]

Have you seen the Ytube video where a plane-handler inspected the port intake of an A6 Intruder (engine running)? He was lifted from the carrier deck, sucked through the intake, fortunately went through the bypass duct, and was spit out. He reportedly survived.

[@bbman_01]

I've seen power generators with free power turbines are fitted with over-speed protection devices. Generally the argument to have a protection system has been due to the length of time the gas generator will operate for (generally online for months unlike aircraft). The throttle valve normally remains in a fairly consistent position, due to the normally constant power demand, there's been instances where the throttle cannot fully close when there is a sudden loss of load (normally when the generator is disconnected from the power grid if its protection activates when a short or under-frequency on the power grid is detected) resulting in an uncontrolled speed increase. There are also oil production platforms where they take gas fuel from different sources with significantly different calorific contents, the fuel control systems are often are pre-programmed with the calorific value of gas for each source and rely on a signal from the platform's control system to tell them which source is in use. There have been cases where these signals have failed to function and the turbine has over-sped when the platform has started to provide them with the higher calorific value gas. Though in all these cases, as far as I know, one of several layers of protection, if not the over-speed unit, has kicked in and closed high speed fuel isolation valves to cut fuel flow to the engine well before it exceeded the maximum power turbine speed. These protection systems are something I wouldn't expect to have on an aircraft due to their over-sensitivity and that an aircraft engine will be maintained far more often.

[@AgentJayZ]

The only time an over speed condition should appear is when the mechanical connection to the load fails. Any decent fuel control system is measuring the actual load, and adjusting the fuel going to the gas generator based on the load. If the turbine is connected to the load, even if the load fluctuates wildly, and if an over speed condition occurs, there is a failure in the fuel control, or with a sensor somewhere.

[@bbman_01]

AgentJayZ the control systems I’ve seen generally infer load like in the helicopter example. Given they are operated at a fixed speed they will either operate under N3 speed control until the turbine T48 temperature limiter takes over and begins to cut fuel when the machine is operating at its limit. I’ve seen torque meters on turbine driven gas compressors with gearboxes though I think they were used to limit acceleration to protect the gearbox. In some higher powered Aeroderivative generators the load can drop around 30 - 45MW within a couple of seconds if disconnected by electrical protection. You’re right though, in pretty much all cases there has been another system failure that leads to over speed unless the system design is poor. You’ll probably find US patent US4998949A of interest, it was submitted by rolls Royce in 1988 detailing intermediate turbine over speed when the engine experiences IGV failure during acceleration from idle. I would guess this relates to the RB211. They have also had shaft separations within some variants of the Trent engines due to internal fires cause by high pressure oil feeds cracking. The fires have compromised IP turbine disc drive arm causing separation of the IP turbine disk from the shaft resulting in over speed and blade ejection. They have rolled out a software update to the engine control unit which monitors for excessive temperatures and sudden drops in compressor speed, I’m contradicting myself here but the fuel system response is to shut down the engine

[@nalamobil]

Jay, the first Plane with sweptback wings and engines below the wings I can think of is the ME-262. Although a lot smaller, the same concept.

[@richglenn3729]

Jay said 1st. airliner. As in a commercial passenger plane.

[@kinsley2108]

@AgentJayZ at 14:00, funny you say that. I went through the catalogue of an engine I work on (turboshaft) and the most expensive single component in the whole engine is the power-shaft. An eye watering amount of money I won't bother mentioning. We've seen them pretty messed up with coking and corrosion but never anywhere near to failure. Makes me wonder what the heck they're made of, imagine the quality control on them.

[@whawaii]

I don't remember where I was taught this, but it was explained to me that the enlargement of the "fan nose-cone", which you refer to at 24:34, is what helps eject large amounts of water (& hail) away from the intake of the core. If I remember correctly, I think it was because of TACA Flight 110 in 1988 that it became more prominent.

[@shawnmulberry774]

Yes I think you are right. The pilot accidentally flew into a hailstorm and both engines were shut down. He was able to glide to a safe landing. Masterful pilot.

[@notyou6950]

Soviets learned about the overspeed on the Mig25 Foxbat going over mach3. Engines were shot. The discs grow and blades cut the casing. That's how they seal compressors on the inside.

[@621Tomcat]

It was mostly the oncoming air at those speeds wrecking the engines if memory serves edit: no wait I was being a doofus

[@johncashwell1024]

The only intake screens I am aware of are on the Russian Mig-29, Su-27 and Su-30m fighters. With the Mig actually using a solid intake door with louvers on the upper surface of the intake. The Sukhois used a mesh screen in basically the same position with later Migs reportedly replacing the solid doors with mesh screens. Russia and its predecessor, the Soviet Union, are renowned for the rough state of their airfields plus the fighters were designed to use unprepared runways. These screens were necessary to keep FOD out of the engines and were only used while on the ground. Once in the air, the screens/ doors are opened so as to not restrict the airflow in any way. Great video!

[@michaelpdallas]

Messerschmidt 262 had podded engines. Not entirely in front of the wing but that's just semantics surely.

[@AgentJayZ]

That one does count, but it's not an airliner. Still, thanks for the reminder.

[@mytmousemalibu]

There was a 1 or 2 instances of an IL-62 having an overspeed and turbine disk exploding. They had left a sharp step instead of a smooth radius on the turbine shaft that failed. Unfortunately it crashed killing all onboard. It was a Polish airline, LOT. The Pratt 308's I work on have a cut off system should the compressor and turbine become disconnected!

[@pizzagogo6151]

I got that book on your recommendation and it was definitely helpful in improving my knowledge in the area. Mr Gunston wrote so many excellent aero books over his long career and I didn’t know about this one until you mentioned it- thanks! Regarding the shape of commercial jet, I assumed under the wing also allowed upgrades to engines with minimum design changes ( yes the 737max is a very tragic attempt at this). I liked the fairly unsuccessful convair 990 commercial jet, they were very fast and looked cool!

[@chemistryinstruments7156]

Interesting one, learned a bit more. Really lucky to get these, thanks.

[@PODHERECOMESTHEBOOM]

I have known of one. 4 C-17 engines flamed out due to water ingestion. Good engineering allowed two of the four engines light back off. The EECs logic could not control the engine any longer so the fuel controls took over "sec mode" with that, the pilots pushed the throttles up. N2 was only controllable through the throttle. So the pilots overshot the limits and over speeded the engine.

[@whatsit52]

This techno-geek likes the idea of your functional section tutorial series! I'd also be interested in seeing some installations! Perhaps it wouldn't be practical for you in terms of your work, travel time cost etc. Maybe some of your customers would be interested in sending you some vids that they generate..The mutual PR could be a good thing!

[@h0ll1s]

My favourite quote, let's play a game of what hits what? 'You're a duck, your going at 28mph flapping through the sky, and here comes something doing 180... what hits what?' XD so good!! Hahaha

[@grahamj9101]

This is your friendly (well, most of the time) neighbourhood gas turbine design engineer (retired) here: I'm sitting in the French Alps with a glass of French beer (6.7percent alcohol) to hand. I've been taken to task for denying someone the right to have an "opinion" about the Trent engine failure on Qantas flight QF32. So let me say that opinions about such things as what is the best airliner, what is the best engine (etc, etc) are fine: we can put forward differing opinions and even have an argument. However ..... to continue to express "opinions" about how and why the No.2 engine of QF32 failed, which are at variance with the facts, is unreasonable and unacceptable. The event was investigated by the ATSB, who (much to R-R's embarrassment) published regular updates on their website. Almost within hours of the event, a photo of a 120deg segment of the failed disc was published worldwide: to anyone who had been involved in the design and development of jet engines, this gave some obvious clues. Then, quite early on in the investigation, the ATSB published a photo of an oil tube end fitting that had failed in fatigue: this had a counterbore that been machined slightly offset. The Bureau's investigations and findings were published in a very detailed and authoritative report, which has been in the public domain for years. And yet there are people out there who, with too little understanding and knowledge, and without any reference to the facts, continue to tell us what happened. Is it any wonder that I get a bit unfriendly? Nevertheless, I will accept that perhaps they are being misled by the media, who don't want to let the facts get in the way of a good story. PS I promised you some more info about engines with LP turbine overspeed prevention or protection devices and how a disconnected multi-stage fan turbine can be prevented from overspeeding. Sorry, but you will have to wait until after I get home tomorrow: I think that I will have another glass of beer.

[@AgentJayZ]

... You people need to realize that when your version of events differs from a professional engineer who spent a career designing jet engines... maybe you should stop and listen for a bit. And by You People, I mean everybody... myself included.

[@micstonemic696stone]

I know the Bristol Britannia quite well, and from the pilot's perspective he absolutely made the right decision the RR Proteus's gas turboprop's look like they are the width of the wing's and it's both it's wing spars must have got pretty hot, there would be no warning before they broke send the aircraft spiralling to it's doom, so putting off a couple possible customers, the loss of an aircraft would have been far worse, MUD, there alive aren't they, I also a US engine maker say that RR always had good names for it's engine's, the Rolls Royce Proteus Turbo-Prop

[@johncashwell1024]

AgentJayZ , please forgive me if you have already covered this, but I was recently looking at a diagram/drawing of a purported turboshaft that, frankly, confused me to no end. This particular example showed the intake on the left with the air moving through the compressors from left to right. The next item in this basic example (moving from left to right) was the gearbox shaft intersecting at a 90° angle with the shaft that runs through the engine. The next item we come to is the exhaust outlet. Then, again from left to right, we come to the N2 turbine and after that, the N1 turbine. The shaft was shown to be connected to the compressors, gearbox and turbines with no separation like you show in the video. Next up is the combustion chamber and lastly we have the ignitor and fuel jet followed by the outer casing and that's it. The example does show a tiny pathway for the compressed air to flow through, from left to right, but it just doesn't look like it could possibly get enough air to cool the engine, let alone run it. Anyway, thank you in advance for any light you could shed on this. I would also like to thank you for teaching me so much about jet engines.

[@AgentJayZ]

I am not going to try to figure out your description. The term N is math-speak for rpm of shaft #, so if you have two things labelled N1 and N2, they are turning at different speeds. Maybe tell me the name of the engine you're looking at...?

[@butchsmith1140]

Love your videos. I know nothing about jet engines but am learning by watching. Thanks.

[@thomasaltruda]

There was a Saab 340 with the GE helicopter engine I believe, had the propeller come off! I imagine the rpm oversped before the governor pulled it back down..

[@AgentJayZ]

Maybe, But when the T58 powered jet boats come out of the water at high speed, the PT does not over rev. The fuel control is vary good at its job.

[@juliussokolowski4293]

Prop overspeed is a bigger issue I would say on turboprops. On a PW150 (Q400) the prop OSG will kick in at 1071 RPM if my memory serves me (normal max Np is 1020). The OSG will basically start driving the prop towards coarse pitch to increase the load and bring the Np down. There is a second level protection as well through restricting the FF (or I might be mixing it up with the Allison 2100... been a while since I taught this stuff. Anyways, the funny thing is the Np underspeed protection on the PW150, if your Np goes low the PEC (Prop Electronic Controller) will just drive the props towards fine until it hits min pitch (limited by the beta valve) or the OSG kicks in. You will still have control of the thrust but you wont be able to select Np. Funny solution - protect against underspeed (and possibly over-torque) by deliberately creating an prop overspeed...

[@brbroberts1]

"Makin' the grid vibrate!" Outstanding!

[@cg9952]

Stay warm Buddy. I always enjoy your vids.

[@williamswenson5315]

Ah, minor point. The B-47 (and the aircraft that followed it) had its engines mounted on pylons, not pods. I believe the term pod would refer to the dual engine nacelle of which there were four as in the B-52 which had a total of eight engines. Enjoying the channel so far.

[@AgentJayZ]

Minor? Get outta here. The B47 had two "pods" with two engines each, mounted on you precious pylons. Then outside of that it had another one engine per side ( am I allowed to say were single engine "pods"?), also on your pylons. Jeez. I just wasted my time Thank you.

[@SuburbAllied]

I believe there's an another aspect to add when talking about not having a protection screen in front of a jet engine, whether its turbofan or an engine for an aircraft without the fan. If something (a foreign object) where to hit the protection screen, and assume it didn't disintegrated into small bits, it would obviously get stuck on that grill - and further disrupt the airflow into the engine, so it literary goes from an air dynamic problem that the screen itself is a part of to an air dynamic nightmare when you suddenly have a big lump of solid object in front of the intake. Secondly (I don't know how about fighter jets), but with those huge airliner engines, a screen would make it harder to control the icing factor, just as the MD80 experienced; and then that clear ice wasn't even in the very inlet of the engine, it was on the front wing and pieces of ice debris was sucked in to the engine. Also, regarding the airliner type of engines, that screen isn't bulletproofed from mishaps, so then you have the fact that you've got a large structure just in front of the very intake which could, if damaged badly enough, cause some serious problem to the engine if the screen where to fail somehow. All those considerations, including the reasons already mentioned in the video, I believe counts for the fact why we don't see those protection screens mounted on the engines of today's modern airliner and perhaps even the fighter jets and engines that doesn't use a fan.

[@grahamj9101]

As someone who had a career lifetime in the design of gas turbine engines, I agree in principle with all you say. In particular, the risk of debris stuck on the screen producing a strong first engine order excitation of the first and early stage compressor blades fills me with dread.

[@grahamj9101]

As someone who had a career lifetime in the design of gas turbine engines, I agree in principle with all you say. In particular, the risk of debris stuck on the screen producing a strong first engine order excitation of the first and early stage compressor blades fills me with dread. PS And as I've pointed out before, a mid-sized high bypass engine, such as the CFM56, will, in one second, take in a volume of air greater than that of my modest-sized home here in the UK. Industrial engines, with much smaller mass flows, have intake screens and filters that are the size of the side of a house.

[@stevewilcoxson7173]

Excellent video. Very informative. Was curious about bird strikes. Thanks.

[@Flightstar]

Nothing like a stout direct drive tube for transmitting immense power reliably. With the advent of large gear drive turbo fans. It must be a challenge to design a light weight compact robust gear drive to handle the torque to spin such a large mass and load. If a gear fails in that system the engine would most likely grenade instantly at take off power. KZbin propeller failure air race and hear what an engine sounds like when it loses its load at high power setting. Yes its a piston engine, but the results are pretty much comparable.

[@AllanMain]

JayZ, perhaps in a future video could you explain how the turbine in the Harrier has the compressor spinning in reverse to the turbine. I understand this was done to counter the torque effect and make the thing controllable in a hover but that must have taken some tricky engineering in the guts of the thing.

[@AgentJayZ]

The Pegasus is a turbofan, with the HP system turning in the opposite direction of the LP system. The only way to make a turbine go the opposite of its compressor is to put a gearbox somewhere, and a high speed, high torque, lightweight gearbox as always two of three things: heavy, expensive, and unreliable... maybe all three.

[@BigBoy4005]

Look up the various documentaries about Qantas Flight 32 (2010). Not only was it an example of a very modern airliner engine failing, the true story rivals Apollo 13 - no joke! That A380 lost more systems than the 6 pilots were ever trained for when that turbine disk (they found it in a field) exploded.

[@rodgerball6149]

Now, now Agent JZ. You are all about accuracy, which I love. So the correct statement isn't "I can't help you." more like "I'm not going to help you." (Just some giggles for your chilly day.)

[@HoundDogMech]

Back in the late 60's while in the USAF I Rn what what was referred to as the HI Bay (test Cell) for the AGM28B Hound Dog Missile. It had a J52P3 Turbo Jet Engine That we ran during a complete Combined Systems check where all systems were checked out before the Missile was hung on the B-52H. I installed an inlet screen made of heavy wire cloth about 4' long cone shaped with an opening that fitted over the outside of the engine inlet to prevent FOD. en.wikipedia.org/wiki/AGM-28_Hound_Dog

[@otm646]

Any idea how much performance was lost to that intake screen?

[@jurypl]

PLL LOT flight nr 7, LP shaft failed in engine no.2, that caused LP turbine to overspeed and disintegrate, en.wikipedia.org/wiki/LOT_Polish_Airlines_Flight_7 as for PLL LOT flight no.5055 mentioned by myoniwy, faulty bering overheated what caused turbine shaft failure leading to turbine overspeed and disintegrate

[@pstav1]

You're forgetting the ME-262 as far as a low wing, wing mounted engines, intakes in undisturbed air.

[@MrMrMeile]

Hello, Qantas-Flight 32 An oil leak caused an fire on the coupling of intermediate pressure turbine disk to its shaft, its overheated the connection and the turbine disk loosened, over-speeded and did explode. it was only 10 years ago and was on an A380 en.wikipedia.org/wiki/Qantas_Flight_32

[@AgentJayZ]

Yes, many people have pointed this out. It is so memorable precisely because it is such an exceedingly rare event.

[@willandersen3319]

What hits what? Probably the best statement ever!

[@TheLastDay-BobReese]

YES! The Grand Ole B-47 STRATOJET! 6 glorious GE J47's with 7200lbs. of thrust each (with water injection at takeoff). 17,000 gallon fuel capacity. 3500nm flights with inflight refueling - 36 hour missions! A total of 2039 made for the Air Force -14 years of service and best of all featured in the movie "Strategic Air Command" (1954) with Jimmy Stewart & June Allyson - the best video ever of the B-47's flying in SAC at that time! Hope you get another J47-GE-25A in for service. I would really like to see that little beast dissected!

[@stormeagle28]

@AgentJayZ On May 9, 1987 an IL-62M on LOT flight 5055 suffered an uncontained engine failure due to LP turbine overspeed after the fan drive shaft of its Soloviev D-30KU engine broke because of incorrectly assembled roll bearings. Rotating without load (the aircraft was climbing shortly after takeoff) the first LP turbine disc disintegrated into three fragments. One fragment left the engine without further damage, a second piece set fire to engine number 1 (the failed engine was number 2, inner left side), the last fragment caused severe damage in the aircraft's tail (elevator control, electric wires and a fire in the cargo hold), leading to a fatal crash which killed all 183 people on board.

[@AgentJayZ]

Yes, I have become familiar with this incident, as a few people have mentioned it. The story behind it is the inspiration for my next video.

[@juliane__]

AFAIK, turbines overspeeded in the early days when run in testbeds. Btw. one could argue the very first series production jet airccraft originated the swept wing, pod mounted und and before the wing design. Although it looks like the pods are inbetween clear pods and wing integrated, they are clearly pods under and the wing. Sorry in advance, the B-47 might be your emotionally attached first aircraft to start your business, but not in history to combine these aspects. 24:25 Very interesting explanation for the bulgy fan node. I guesstimate the angeled outwards compressor blades of the PW4000 are designed to deflect unwanted debris or whatever comes across the fan? Or is itfor more airflow from the fan stage? If you have seen people on the airport placing things into the fanhousing and forget it or use it as a litter box and throwing stuff into it for "good luck", i guess there are the questions coming from.

[@AgentJayZ]

Not talking about research engines here. You're right. The B-45 had engine pods, but I think The B-47 is the most familiar plane from that era, because there were so many of them. Whatever you mean by angled outwards compressor blades... not sure what.

[@lkw6640]

I know this isn't the same but, in HVAC, a screen like that would reduce the airflow by about 30-40%

[@shadowbanned69]

Must be the same principle as a txv or a tev screen...you agree?

[@lkw6640]

lutes workshop gener'al I was talking about outside air screens used to prevent birds and critters from getting inside the ductwork, but the same thing applies to any kind of screen. Although, since the screens come with the expansion valves, I'd expect the engineers would've accounted for the loss of flow even if it's going directly into a small metered orifice in a clean system. What can really affect the flow are filter dryers that are too small or haven't been changed after a burnout and/or water contamination especially if it wasn't, leak checked, triple evacuated, purged with nitrogen each time and pulled into a deep vacuum for at least 24hours. Some of the replaceable filter cores aren't made to be installed permanently. After cleaning up the system, they are meant to be replaced with permanent ones otherwise they break down over time and the pieces plug up the screen. Thankfully the units are usually a little forgiving if you go a bit larger on capacity for filter dryers. Sorry, I know it's a bit long winded lol

[@southjerseysound7340]

On a stationary engine chances are the losses would be higher like you have seen in HVAC stuff. But on a plane the losses are lower because of the ram air effect at speed. But like Jay explains they are still massive losses all things considered. I once asked my uncle when I was a kid why there's no screen and he basically said that it's many times cheaper to lose an engine every 5-10 years from fod damage than it was to protect the engine and use more fuel.

[@jamesfackenthal]

The Wright R3350 had 2 rows of 9 cylinders, for a total of 18 cylinders. Named the Cyclone by Pratt & Whitney. The R4360 had 4 rows of 7 cylinders, for a total of 28 cylinders. Named the Wasp Major by Pratt & Whitney. The Convair Constellation had Cyclone engines.

[@AgentJayZ]

How could an engine built by Wright be named by P&W? I get what you mean. Thanks for telling us all what we already knew.

[@thomasaltruda]

A couple of years ago, I think it was in NYC, there was a helicopter that appears to have broken a shaft and crashed. You hear the rpm go to the moon! It’s on KZbin somewhere.. not sure of the details..

[@High_Alpha]

QF32 sheared an IPT shaft and the subsequent IPT overspeed caused a disk burst and the resultant damage. The Trent now has a software fix that will auto shutdown the engine if it detects a IPT overspeed. Given the processing speeds of modern FADEC it happens long before the crew knows what is happening. I believe it's now on all three shafts.

[@AgentJayZ]

Shoulda been there from day 1...

[@allangibson8494]

Better quality tube fittings would have helped too. (A tube fitting broke and starved the shaft bearing of oil, the bearing then overheated and the shaft failed). Newer turbofans have gearboxes on the fan stage (like the 737Max and A320Neo). Power gas turbines overspeed about once in 50,000 hrs if separate overspeed protection is not provided. Containment of an overspeed failure requires about 20mm of mild steel.

[@grahamj9101]

@@AgentJayZ But there were tens of millions of hours when it wasn't needed. The problem was down to someone changing a manufacturing process, which resulted in an oil tube end fitting being machined with an offset counterbore. Somehow, it reminds me of the old proverb that ends with, "for want of a horseshoe nail, a kingdom was lost." Hindsight is the only 100percent accurate science ..... so they say.

[@homeworxchannel4120]

There was an engine explosion on a southwest 737 that killed one passenger. Might look into that for an engine that has come apart.

[@AgentJayZ]

The incident I remember was nothing like that. A part of the cowling ripped off, entered the engine, cause a blade loss, and a hole was put into the fuselage. One cabin crew was killed. Nothing exploded.