Sometimes, on a windy day, you might see an airliner that is parked and shut down, and the engines might be turning like windmills. Is it bad for the engines to be turning like that?
I just got called a huge nerd. I spent the first part of my day doing a borescope inspection on a CF6. And now in watching this on my lunch break. Now I’m getting the eye roll from the rest of the guys.
I’ve seen mil transports parked for extended periods use wooden poles made from 2x2” inserted into the compressor inlet to chock the compressor from freewheeling in the wind. The moving stage was blocked by the adjacent fixed stage, blocking rotation. I’ve seen lots of these in use with a rope and flag attached so that it would draw attention during preflight and be removed prior to engine start. My understanding is that on these engines the oil actually acts as a fluidic bearing supporting the shaft when running at high speed. When there is no oil pressure, the mechanical bearings carry the load. The compressor chock I mentioned seems like a simple fix to prevent dry running these bearings.
The sticks are a simple solution that works pretty well. The oil-supported bearings you describe sound like what RR calls a squeeze-film bearing. It's more of a vibration absorption thing, and the rollers in the bearings do the load bearing all the time. there is a very small clearance between the bearing outer race and the bearing housing, which is supplied with oil at 50 psi or so when running. When not running the oil pressure is zero, but the bearing outer race still is mounted in the bearing housing.
The bearing is supporting the shaft even if there is a very thick layer of oil between the shaft and the bearing. The forces would transfered between the shaft and the bearing through the oil. I'm not 100% in on this, just my guess. If it doesn't have oil pressure the bearing and shaft might not get adequate oil windmilling.
Thanks for the insight AJZ, much appreciated. Because I’m curious and not lazy (homage to why you don’t post links) I did look into what I thought I had learned when I worked in aerospace waaay too many years ago. It winds up that jet turbine engines indeed don’t use a fluid film bearing and rely solely on traditional roller and ball bearings as you rightly indicated, but the ACM packs do use “hydrodynamic” bearings as the principal high speed, low friction bearing and have traditional ball bearings for static support with no oil pressure and transitionally for spin up, spin down periods. I knew I had seen them used on an airframe. Much thanks for the educational videos and your suffering in the hush house. I don’t miss that or the nasty soot/mud on my car after a run. Perhaps you can do one on the immense kinetic energy stored in an operating engine and what it looks like when one lets loose. That’s a sobering sight.
The TF39 on the C5A would wind mill like crazy. The 2nd stage fan blades clanked together at the hub and would wear. There was a large fan stopper you stuck through the stators and its leather tip hit the fan blades to stop the fan. Then a padded 2x4 was stuck through the stators and in between the fan blades to stop the wind milling. At home station checks a spray was put into the platform space at the hub to help prevent wear. Running engines was fun but stopping that fan for that drill sucked.
@williammooney8499 I don't understand, how did the 2nd stage blades hit each other? Wouldn't they also do so while running the engine? Or was it a matter of thermal expansion/contraction?
I've seen C-5s at Oshkosh with sticks (painted red) inserted into the fan, presumably to stop it from windmilling. I'm guessing that this was easier than installing intake covers when you don't have the proper GSE handy. I hadn't considered the problem of inserting the sticks when the engine is already windmilling.
@@SkyhawkSteve Yep Steve, They were painted red with streamers attached as well. Its been 40 years, and i remembered after posting we sometimes opened the T/R's to slow the fans - they operated off hyd. It was rare to see intake covers installed.
Happy Sunday @agentJayZ and cheers bud…… in early GTF development I was part of an interesting test where we “reverse windmilled” an engine to failure. More interesting is the issue came up in flight test in which we did a “drag” test on an engine in flight (shut her down at altitude for a few hours/OEI testing). Later in flight, when they went to air start it, Kaplowee. Come to find out we needed a reverse windmill gear in our pumps. On the test stand we normally tie the fan down with Avis strap 😮 😊, trust the pre run FOD check 😅.
Yes. Got called to inspect a CRJ9 for a ferry flight, hopped in the inlet to check fan blades and found that the tips were bent past limits and the containment case was damaged. Containment case and fan blades were changed. Apparently happens when spins backwards with worn pins.
So how does an engine spin backwards? Are you talking about windmilling on the ground where the wind blows into the back of the engine? Wonder if that could happen? Interesting.
Very good video again. Some interesting info: On the new PW1100 family engines ( installed mainly on the A320 Neo) windmilling was an issue because of the geared fan system. Planetary gear system and using journal bearings for supporting the planetery gears instead of roller bearing, because of lack of space. As we know journal bearings need always oil, so pratt engineers constructed a special pump which always supplies oil to the journal bearings driven from the fan uib itself through a clutch system even when engine is not running. The ldesign allows the pump operating in the correct direction independently from the fan rotation. The system also retains oil for this pump after engine shutdown.
love the vid as always, great information and i love the delivery you remind me of the people who taught me everything with the way you say things that only those with motivation will look up on their own instead of blankly clicking a link 👌
Seems windmilling may, in some instances, be beneficial. Seeing this title instantly reminded me: as a kid I lived in the Town of PR beside the Forestry building which had a helo pad and more often that not there was a ranger parked on it. One summer in the mid 80s the neighborhood autistic kid Ernest was entertaining himself in the evening hours by unwrapping the strap from the tail boom and running circles around the bird with the prop, reversing direction, using the centrifugal force to hold himself aloft while jumping etc. After seeing this a couple times I told my mom (who worked as a secretary in the building) about it and asked her to tell Hank the pilot about it, I regret not ratting on him for the first instance I witnessed it. Thank you Mr. Jet City.
Anybody hanging off the rotor of a helicopter for any reason is cause for a grounding and inspection. Anybody responsible for security at that place deserved a couple weeks off without pay. Not the kid's fault. He should never have been allowed to get near the aircraft.
Thank you for posting this. I've been to airshows where C-5s are on display with their fan stages windmilling along, and often wondered if the bearings could run dry if the rest of the engine isn't running.
Even facing head-on into hurricane winds, a turbofan on a parked airliner would be turning so slow it wouldn't be any different from not turning, for the purposes of bearing wear. The pumps may not be going, but there's still oil in the bearings, it's not like it disappears when the pumps stop. And roller bearings are fine at low speed with the little bit of oil that's still coating the bearing elements -- see skateboard bearings that turn faster than a windmilling fan, are subjected to massive (for their size) off-axis forces, and they can go a long time without being oiled. That compressor fan that's lazily turning over in the wind and putting negligible loads on its bearing? It'll be fine. If anything, it's keeping the oil in the bearings from settling to the bottom.
google says a JT8D requires a bearing inspection if windmilling for more than 60 minutes in flight, it would take a lot of time standing still on the ground in normal winds to add up to that kind of wear
It would seem that windmilling in flight is probably at a much higher RPM & frontal loading all with the possibility of low RPM on the high pressure spool which drives the oil pump. Very interesting.
@@AgentJayZ What does the jingle come from, i.e. what surfaces are contacting each other? And how does that not damage the engine? (Seems like the video didn't quite touch on that.) Thanks for your work.
@@dannywilliamson3340 It would be a trivia point that doesn't give useful information to executives or pilots. An easy to digest number is percent of maximum. 100% is a limitation on this engine configuration.
I saw that older turbojet engines on early business jets can No longer be operated due to noise restrictions. One way to comply is to install a Hush kit. Can you explain how that works? Maybe a future video. If you have already explained this let me know so I can look it up.
Chapter 19 of Rolls-Royce's 'The Jet Engine' book, which AgentJayZ regularly recommends, is entitled 'Noise Suppression'. Dating back to the 1980s, it illustrates noise suppressors and explains how they work.
In the Air Force as soon as an engine cools down to a set temperature, the engine covers are put on the front and back if the engine to protect them from damage from flying from debris and any living critter from making a home inside the engine.
Hmm. I see the same at work. But is it really bad? Im not sure. The amount of technical knowledge has increased by something along the lines of a hundredfold just in the last 50 years. Modern technology is batshit crazy and often even the experts dont understand it, they only understand one part and 100% rely on other departments and vendors to handle the rest. Not even electronics are designed bottom up anymore, and they were until the 80s/90s. Mechanical engineering? Sheesh, carburetors, injectors, gearboxes etc have been outsourced to expert companies for like a century. Because designing carburetors is hard. Like really hard. I believe we desperately need , probably AI based, spoonfeeding courses to get young professionals up to speed faster and broader. School, university and on job training...aint matter, all of it too slow, expensive and shit.
I think the CFM56-5B is the most well known for it's windmilling fan blade noise. The midspan shrouds have a tungsten carbide coating that does eventually wear out, but of course this coating can be repaired when necessary.
Q: you can see in that technical drawing how the shaft that drives the fan runs all the way through the HP-compressor shaft. How is that fan driveshaft supported? Does it also sit on roller bearings? If yes then how is oil getting to it?
Yes it sits on bearings, and the oil is supplied via ports in the outer shaft, and flows through the gap, and lubricates and importantly cools the bearings. The outer shaft also has oil flow for the same reason, and seals to keep the oil in place. Oil feed lines come in to lubricate all the bearings, and oil return lines collect the now hot oil to go through the oil cooler, where it heats up the fuel about to be burned, and from there to the oil tanks, as a now cool oil. Hot fuel is going to vapourise easier, and thus burn more efficiently.
All the bearings for the LP shaft are axially outside the HP shaft. Sometimes there is an "intershaft" bearing. Have a look at my video called Twin Shaft Turbine Engine Bearings.
If you check closely on a cut away drawing there are roller bearings and a ball bearing per shaft. The ball bearing is generally used to hold the shaft at particular position along its axis. The fan blade shaft has a “thrust bearing” to deal with that issue. An interesting topic is how “thrust” on the high pressure spool is dealt with, it is rather counterintuitive as there should not be any or very little unbalanced thrust along the shaft. This was a topic that the engine designer from RR jumped into the comment section, huge learning experience between the video and the designer.
How does the change in temperature from ground operations (say at 60 degrees F, to 35,000 feet (air temp of - 65 degrees F) effect the engine oil viscosity and how is that handled by the formulation of the oil? Is the oil cooled by airflow or is the reserve tank insulated to reduce the cooling of high altitude flight?
The oil is capable of handling temps of up to 500F, and flows well at temps down to -65F The oil is shared through all parts of the engine, so when running, even at altitude the oil is at about 200F. It is cooling the hot parts, and heating the cold parts. The CF6 referred to in this video has a fuel cooled oil cooler, and an air cooled oil cooler in the bypass flow. Up there, it's really cold, but even at cruise throttle, the oil is flowing through all parts of an engine putting out at least ten thousand HP, so it's always plenty warm.
Jay, another outstanding presentation. always enjoy you encouraging humans to “look into it” and invest some clock cycles of discovery, while reasoning from First Principles. Mahalo! 🏄🏻♂️
Interesting that you mention intake covers. I'm halfway through reading the report on the British loss of an F-35 from a carrier two years ago on take-off; the left intake "blank" was left in, leading to the aircraft having insufficient power. I thought military jets tended to have such covers normally installed when not in use (since you mention it it occurs to me I've never seen an airliner with such covers installed), but the RN elected not to do that because they tended to get blown out on deck. They _were_ installed during port visits and the Suez transit for security reasons, but because this was unusual the procedures for removing them didn't really exist, and somehow the pilot missed it during the walk-around - I haven't got to that bit of the report yet, it's long!
Hi how are you how are you doing I hope you well thank you for giving wonderful videos please keep doing this I am raghu from India I am following almost past 10 years thank you so much for giving keep doing as good as possible
Little to no oil pressure, but the bearings won't be dry, and there's a world of difference between windmilling at **maybe** 200 RPM max and TOGA power being driven at 3600 RPM. The fact that they windmill with barely noticeable wind goes to show just how low friction those bearings really are. They'll be fine spinning on the tarmac for a bit. If the jet is going to be parked longer I imagine they'd cover up the intakes. I like it when it is windmilling backwards, and when the engine starts up the rotation slows, stops for a second, and starts turning the 'right' way.
Awesome response thanks! Next question, as for bleed air scavenging off a compressor section, what does that system look like? Every manual or handbook has described it as being "taken off a compressor section" and I imagine a hole in the engine near one of the compressor sections that allows presssurized air to flow off the engine?
It is definitely never called scavenging. Could say tapping, but usually called bleeding, or bleed air. It is taken off... through a hole in the compressor case... Have a look at my video called Bleed Air, because it means a few different things, and as always, it's more complicated than you might first think.
In the terminology that I was familiar with at R-R, the term 'bleed air' was typically used for compressor handling bleeds, ie, from bleed valves (aka blow-off valves for those of the Bristol persuasion). Air for (eg) cabin services or otherwise externally ducted elsewhere on the engine was usually termed 'offtake air'. Rather than being taken from a single "hole" in the compressor casing, there would normally be a manifold arrangement, with multiple ports or slots between stator vane platforms.
I'd consider two things on wind induced rotation and that's the case of lubrication issues if it goes on for too long and then when it's windy there might be objects flying around that can cause damage. But those concerns are outliers.
So would this excellent explanation apply to a turbofan engine shutdown in flight for an extended period of time...? Just curious, no plans regarding this.
Well, during flight the wind will be about 300 mph, and the long duration will be no longer than 180 minutes. I think an inspection of the thrust bearing would be a good idea. The thrust on the bearing would be in the opposite direction of what it would be in normal operation. This of course is all secondary to finding the cause of shutdown of the engine.
@@AgentJayZ Actually, the 180 duration is well surpassed nowadays. EDTO has been increased to 330min and beyond! I recall a precautionary shut down of a RB211 a long time ago, due to low oil quantity. Windmilled it for over 7 hours on three engines without any damage. Enroute checked with RR and they advised no restriction on doing so, even if quantity went to zero! As it happened, the cause was immediately known to us. Hyd system MEL required EDP to be depressed in previous transit. Incorrect procedure caused the oil loss.
Starting protocols specifically prohibit use of an underpowered starter, and specifically include limits for wind direction and wind velocity. So no, and also yes!
Dear AgentJayZ, I do not believe you have no idea what you talking about :), so I am not going to say this in the comment...:)); on the contrary, I believe you have very much a very good idea what you are talking about and I appreciate you educational work being done and put here for all to see (and learn) - I am a big fan of yours. I have a question, though... What about windmilling restart? On an airliner, in some circumstances - certain wind speeds / altitudes, and maybe even angles of attach, as they also might be a factor - a "windmill restart" of an engine is achievable: no APU, no power from another source other then the RAT and the engine can turn enough that it is in a condition capable of being reignited. So does the engine then turn so fast, windmilling only, that it has enough RPM and airflow, even to the core, not only LP-fan shaft , that the air mass in the combustion zone is sufficient? And oil / fuel pumps / accessories, etc. are being driven to sufficient condition for the engine start? If yes ... then ... wow... that's quite neat!!
Hello Jay, At 8:23 we can see two supports in the base of the CF6 blade. Do you have the manufacturer name and / or part number for those? I have a fan blade from a CF6-50C2 (Airbus A300B2 - MSN 205) which I want to use as a decorative item in my living room and I'm having difficulties finding a support like this online. Thank you for all those years of high quality technical content.
Question here: thinking about how the bearings need to withstand the gyroscopic forces on a jet engine, given the big mass spinning at high speeds, is it a correlation between the bearings life expectancy and the movement on an airplane, specially pitch (the fastest vector-changing maneuver)? It would be interesting to learn wether the engine manufacturer gives any advise on pitching speeds. Moreover, you have mentioned that bearings that are no longer airworthy, are still used in ground based jet engines, does this factor have anything to do or is just a design margin? And lastly, are military fighter jet engine's bearings and casings stronger due to the ability of the airplane to make much faster movement changes than airliners? Or the lack of a big diameter fan makes it easier for the bearing to withstand the loads with a comparable overall structure? I got here trying to find a way to explaining my toddlers about gyroscopic effect. Perhaps in a couple of years.
I don't know about gyroscopic forces affecting bearing life, but I know the bearings and their housings are hugely strong. They appear to this layman to be over engineered. The standards for serviceability in industrial engines are the same as for flight, but there are almost no laws requiring the owners of these engines to follow them. Most operators maintain their gas turbine engines to these standards, but some run their multi-million dollar engines the same way most people run their cars: run to failure, then fix.
12:33 When you say “makes no power up to 85% RPM”, is that in reference to an industrial version that is used as a gas generator for a low pressure turbine power takeoff (or the item that you have shown that is used to measure power) and is the “POWER” you talk about measured via this? If I remember correctly, your mentioned some terminology like “ground idle RPM” and “flight idle RPM” that are reasonable high but are not producing much thrust?As a reminder, how high is the “flight idle RPM”? Many thanks, I have really learned a lot from your channel.
ground idle is roughly 40% of max rpm, makes zero power, and takes about 10 seconds to get up to full power, even if the throttles are slammed open. flight idle is roughly 85% of max, makes almost no power, and takes a couple of seconds to ramp up to full power if throttles are slammed to max. 90% rpm will give you maybe 40% of full power, and might be called cruise. One second or less to get to full. 95% rpm might get you 60 to 70% of full power. Only at 100% rpm does the power match the rpm. Otherwise, turbine engines do not respond like piston engines.
Great quality video as per usual, thanks for sharing. Since I was a kid, about half a century ago, I've always wondered what causes the acoustic 'tink-tink or clank-clank' noise when a jet engine windmills. In my naivety I thought that such a marvel of precision engineering would windmill silently. Do you know what causes the noise? Thanks.
The fan and compressor blades are held relatively loosely in their slot mounts in the fan and compressor hubs...the blades are meant to slide in and out of their dovetail mounts relatively easily when not held in place with a set screw. They only firm up in their mounts when the engine is running and centripetal force holds the blades firmly in place. The tinkling sound when windmilling occurs when gravity is stronger than the centripetal force and the blade slightly jiggles in its mount. I believe the exact cause of the sound is the blade itself acting like a tuning fork when given a slight excitation energy from the movement within its mount.
I think the blades are a little bit loose on purpose to help dampen harmonic resonation in them when the engine is running. Too tight and they can start to vibrate. Also some engines have a starter turbine. They blow the high pressure air into that when starting. that is connected to turn the main engine by a kind of ratchet thing. It disengages from the main engine when the engine is up to speed, but you can hear it clicking like a ratchet when the engine is freewheeling slowly as it shuts down or is turned by the wind. The sound could be caused by either or both of those things.
If you follow my recommendations in this video, and watch my vid called Turbofan 1, the clanking is explained. Another good one is my old vid called jet engine turbine blade noise... or something like that.
@@ewanrollo5562 If I remember correctly from the NTSB video on the Southwest Airlines Flight 1380 where a contained fan blade failure occurred on a CFM56-7B-series engine that the blade containment slot actually have requirements for repeated lubrication and maybe even need some special Anti-Seize coatings. I was interested in what happened as my daughter flew on the same flight the day before and sat in the next row behind where the window was broken.
Are the oil pumps run from the N2 since that gets up to operating speed sooner? Could running the hydraulic pumps from the N1 add enough drag to make windmilling much less likely?
1) Yes, the N2 in a two spool turbofan IS the operation. 2) Making windmilling less likely is not even on the list of things that are important in designing an airliner engine. But it could be done. However, the engine running controls must be attached to the fuel burning core, so your idea would require two transfer gearboxes, two radial drives, and two accessory gearboxes. That's a lot of expensive, heavy stuff to carry around and maintain. All for microscopically minimal benefit.
could some turning be an advantage in some cases, equaling the forces on the shaft so it doesn't bend and the bearings doesn't sit on the same spot for a long time?
1) bending due to gravity? Don't be ridiculous. 2) bearings damaging their races? It's an appealing thought, but if the bearing race can support the load for a microsecond, it can support it for a month. However, I do agree that some occasional slow movement might be a good idea if the engine is to be stored for years. I've seen perfect bearings inside engines taken out of decades of storage, so It may not be that important.
@@AgentJayZ I just read that many engines need "debowing" by motoring before startup under certain conditions, but apparently it is caused by thermal effects during shutdown, so it is in the core and windmilling wouldn't help
Many people talk of "rotor bow". You know who doesn't? The engineers who design these things. My opinion is that "rotor bow" is an old timey fallacy. It's based on the assumption that when the rotor stops moving, it sits in an environment where the thermal gradient is large from the bottom of the engine to the top. I believe this assumption is erroneous, and rotor bow is made-up quackery, from people who think too much without thinking enough.
@@AgentJayZ I respectfully disagree with you. Rotor Bow is 100% real, however it is more noticeable on some engine types than others. The evidence for this is during start-up of an engine that has been recently run (ballpark shutdown time of 45mins for example), the N2 vibrations will be initially much higher, for example around 4 times higher than after the engine thermally stabilizes at idle. Also, and I'm being picky here, but engine fans can windmill in either direction - it depends on whether the wind is blowing from in front of or behind the engine. The direction of windmilling makes no difference to your assessment of whether windmilling is bad for engines though. Big Thanks for all your thought provoking content 👍
Agent JayZ Sir . I was wondering if the manufactures use Asian bearings, USA, Canadian, German made bearings in remanufacturing? We use to test in NDT bearing failures. What is your favorite manufacturer?
The engine manufacturer assigns a part number to the bearing, and sources it from more than one bearing maker. We do not select bearing makers, we just make sure it's the right part number.
My experience at R-R ( and I've just celebrated the 20th anniversary of my retirement) was that mainshaft bearings from different manufacturers were allocated different part numbers.
As to your statement that windmills are turbines, many of the old windmills found on farms etc., were advertised as, and some called, “wind turbines”, as part of a brand name. Getting what you’re saying regarding duty cycle of bearings, running vs. windmilling, I’m left wondering about the of the long term affect of the “clinking”, for the lack of centrifugal loading / locking of the blades, at the dovetail blade / hub, for long term fretting action. Yeah, I’m guessing we’d be talking years, but… Regarding engine covers and parking, in Army aviator, the main concern was for FOD, and the potential for injury from rotating components. I believe that it can be reasoned, that for the infrequent use of engine covers on commercial ramps for quick turn arounds, the covers aren’t immediately available, for the risk of the presence covers, and the additional time required to remove and secure them. That said, it does seem that many operators / companies do have engine covers available for parking aircraft during inclement weather, etc., but availability for all types and numbers of airframes, in situations like diverted flights, would leave ramp crews going, “Oh well, no covers for you…”.😊 As usual another insightful and informative video. Thanks for sharing.
Seen them being stored using what is basically a large length of pallet wrap, that is placed over the inlet, then held fast with a few turns over the cowl, and the same for the rear. Most issues would come with needing to strap the aircraft down during high wind speed events, though there you will find them playing Jenga in hangers to fit all the planes in, or flying them out to safer climes, as after all you do not want your multi million dollar aircraft being blown over, and either damaged, or landing on somebody else's property.
keeping in mind that airlines want those planes in the air making$$, so, maybe a few hours between flights? As stated, when "parked"( extended /days long) the inlet/exhaust covers will be installed. Great video,,
No, I think he meant that when windmilling the fan gets pushed from the front, while in normal operation the fan is "pulling". So the direction of the load on the bearings is the opposite. But like you said, a fraction of a percent of the load.
I recently found your channel and have been watching whenever I can. My dad was an A&P for Allegheny Airlines in the 70s and worked on JT8Ds and JT9Ds. I took a different career path to a locomotive engineer but still love learning about turbine engines. Off topic from the video ,but I bought some compressor blades off ebay years ago. Is there any database to find out which engine they're from? Thanks!
There is no master database. Just like car parts, the first thing you need to know is what car it is from. Then a parts list will help. Somebody needs to first recognize the part, and what it came out of.
Having beer and fun with a gas generator! In one of your videos, of which I forget the title, described how essentially every gas generator could be made in to a 'jet engine' by adding a propelling nozzle to the exhaust gas stream. I have a GTCP85 APU from a 727 airliner (similar to your start cart), I placed it on a stand and have run it up many times. Why? Because as you said, its fun and why not! I want to add a jet nozzle to the exhaust, because again, why not?! Its a 2 stage radial compressor, single stage turbine. My question is, can you explain in simple ish terms how a backyard guy can figure out the optimal converging nozzle angle and end opening, while keeping EGTs and backpressure in a comfortable range? Long time subscriber, first time commenter, keep up the no nonesense content 🍻
Sorry. If you want to design an appropriate jet nozzle for that engine, you need to do some engineering and some math. If you are not interested in maximizing thrust, then any old thing will do. Even the introductory text books I recommend don't get in to nozzle area calculations, but they will list sources that do.
This guy amazes me!!! Im not smart enough to be considered an "engineering geek" or anything remotely close! I know enough to know i dont know $hit compared to 99% of the people who follow these videos! But I am curious enough, and motivated enough and have loved aviation since i was old enough to look up in the sky and recognize a plane! And, I'm grateful that I have that much curiosity at least!!! At least I'll look stuff up!
It seems to me that low RPM windmilling would not create enough centrifugal force to seat the blades which would cause them to rattle around in their mounts.
You are correct, they absolutely do, depending on the engine of course, and how the blades are fastened to the hub. A Rolls Royce Tay, for example, makes quite a racket when the fan windmills. So does a GE CF34, P&W JT15D, among others.
If jet engines would use pressurized bearings like the crankshaft main bearings in a car engine, they'd get damaged pretty quickly windmilling along for awhile due to the large contact/friction surface pressurized bearings have. Roller and ball bearings have a much lower friction surface and can handle wind milling much better.
Of course you did not clarify what kind of engine, so I will pick one. And you did not specify what size of bird, so I will pick one. For a large airliner turbofan, any bird up to the size of a seagull, if hit by the engine in operation, will not cause any damage to the engine. The shape of the inlet spinner deflects the bird outward, towards the bypass flow. The fan slices up the bird and flings it further outward. Basically none of the debris enters the compressor, or flows through the combustor. For larger birds, like the Canada goose, you'll have to ask Sully.
@@AgentJayZ Is that not part of the testing of a new design engine? I thought I saw testing where a chicken sized bird was propelled towards a running engine on a test stand to validate the fan blade design. Maybe this was a one off research project.
Around the 20 minute mark when you're explaining how the core works, that brings up one question. Pardon my ignorance here, but since the front fan is "free-wheeling," what exactly causes it to turn under power?
In a two shaft engine like the CF6, the LP compressor is driven by the LP turbine. The fan is the first stage of the LP compressor, which has been greatly enlarged in diameter to move much more air than the core needs. This extra air goes around the outside of the core, so it's called bypass air flow.
@@captaincurle4529 No. the Low Pressure (LP) section is driven by hot gas produced by and in the High Pressure (HP) section flowing through the Low Pressure turbine after it has already passed through the High Pressure Turbine.
You need to watch my vid called turbojet or turbofan. Also, you might enjoy my vids on power turbines. Just type that into the search box on my channel page.
Jay, where do you go about buying new bearings for these engines? You obviously cant just open a catalogue and match the numbers? Is it manufacturer only or are there other companies that specialise in these bearings?
The most expensive option is to purchase from the engine manufacturer. Sometimes they do that, but they generally don't like aftermarket service providers. Next there are many companies in what you might call the component aftermarket. You can buy new parts from them at whatever price they want to charge. There are also specialist bearing manufacturers who will build anything you have the blueprints for, but they usually have a minimum quantity. We only deal with the industrial variants of these big engines, so a good source of parts are retired aircraft versions. The CF6-6 featured in this video donated turbine blades and bearings to the rebuilding of an LM2500, used to generate electricity.
Engine driven pump - If the oil pump is gear driven off the accessory gear box - The main shaft - If HP compressor shaft vs. LP diving gearbox - Interestingly if windmilling in reverse - Would the accessory box turning in reverse cauing the oil pump to turn in reverse - Would this pull air into the system?
I heard from @gregmink that another reason you want to put the covers on your engines is to prevent insect damage. Bees love the smell of jet fuel, and they will build a nest inside your engine, even if it's parked for a day or two.
I choose not to use the subtitle generator, because it is so inaccurate, it only causes confusion. My channel is about information, and the RU-vid subtitle generator is unable to perform to a satisfactory level of accuracy.
Function of Oil: Shock Absorption. It probably doesn't need shock absorption on a gas turbine engine. But on reciprocating piston engines, the oil between the bearings and journals will absorb the shock such as the start of the power stroke. Also, I have heard that PT-6 engines need to have the propellers secured to prevent windmilling, because just a few hours of windmilling can destroy the bearings on the power section of that engine. Also the oil pump on the PT-6 is on the compressor section of that engine and not on the turbine or power side of the engine. At least that is what I have heard about the PT-6 always secure the props from windmilling.
Yes, that is why the props on PT6's, and other free power turbine engines, are always secured by a strap-like thing... a prop immobilizer. And... shock absorption is power transmission.
We need to teach the concept of “orders of magnitude” to ALL incoming high school freshmen. It would solve many of our societal/political (and RU-vid question) problems. E.g. a jet engine in its operational range is operating at many orders of magnitude than a cold jet engine windmilling in the weather. I only learned of orders of magnitude in high school precalculus, then college calculus and computer science. I still use these concepts in my job many decades after.
What does the clank come from, i.e. what surfaces are contacting each other? And how does that not damage the engine? (Seems like the video didn't quite touch on that.)
Dear blah blah blah. If you follow the suggestions, and go watch the video I talk about in this video... called Turbofan 1, I talk about exactly where the clanking noise is coming from.
When you take the time and make the effort to look things up for yourself you are far more likely to retain the information that you sought. So, let your curiosity help put you on the path to learning all you can. Sure, it may never help you in a financial sense or a life or death situation, but 'curiously enough', it does "exercise" your brain, so it does help your intelligence.
Ah, yes… yet another ‘born-knowing-everything’ who complains that people asking questions are ‘lazy’ and won’t do ‘research’. Isn’t ‘asking questions’ the BASIS of research????? What it boils down to is your attitude of ‘don’t bother ME with those questions, go bother SOMEONE ELSE with your silly questions’.
Well it was a simple "NO" answer really, if he was so narcissistic he wouldn't have made a 27min crash coursing of 30yrs experience film to say the same thing.
Dear Ernest. Thank you for ranting on, and missing the point entirely. I am referring to information I have already provided, and is literally a mouse click or two away. Your use of five question marks indicates your understanding of curiosity and resourcefulness is lacking. Your assumptions are incorrect, and your judgement is unwarranted. Please find someone else to complain about.
@ernestgalvan9307 I'm pretty sure that he was referencing people who, probably much like you, might be curious, but, lamentably, completely and totally lack the ambition to put forth any effort at all to try to find any answer themselves, and instead demand that the presenter spoon feed all the information to them in entirety or else be labelled "yet another 'born-knowing-everything' who complains that people asking questions are 'lazy' and won't do research"...
BKD70: Yes. The people who I know in the biz I'm in... figure out what they need, find it, and get it. No maps, no menus, no easy answers, no giving up because it's "too hard". So... if I show a book, and say the title, but somebody needs a clickable link to find it... well, they aren't going to make it, captain...
