On T55s (on the Chinook helicopter) and TF 40 (on LCAC hoverboats) , the engines are way noisier at low power because the bleed band/valve is open .... going into higher power, the bleed is closed making them much quieter.
Uh-1 throttle like motorcycle just backward in motion. The shiny button on the box at end of the collective is idle stop, it is held down to allow fuel to be cut off when the throttle is rolled clockwise. To start the engine press the start button on the bottom of the box at end of collective watch N1 and depending on wind, roll throttle ccw to turn on ground idle fuel, watch N1 and EGT rise after stable release start and idle buttons, and slowly add fuel until full-on and governor takes over. reach up and flip start/gen switch and check for the charge. Another great video Agent J
I love it when you guys with real world experience with these things tell us your stories. You have great historical value, because those days are long gone...
And possibly the worst sounding is the Aérospatiale Alouette. I think the engineers who designed its engines went to great lengths to make sure the whine doesn't go ultrasonic so that the earthbound people for miles around it can take pleasure listening to it.
Flew in vietnam ‘68. 4am preflight. Engine start and run up. I really miss the sound and smell of the jp4. Seeing this start up took me back a long time to a different world
I have the same perception of the sound of start up. I think the frequency is very audible as the compressor spins up. It gives the illusion of high rotational speed. As it gains speed I think the frequency becomes higher than your ears can perceive. I understand his question.
Howdy Jay, Afterburner119 here. Hope all is well, maybe ACCA next year we can finally meet. In our R&D cells here, the operators and mechs are in the control room along with structures, NSMS, Op line, etc. engineers. We will bring in stand air to rotate, maybe motor to cool, then at a certain rpm the operator engages fuel and the article (engine) will light off to idle. We can even change the controls on the fly to incur a longer spool up, or shorter etc.for example if EGT Climbs too high on previous missions. Keep in mind, we are trying to break it or prove life limits. Production ATP Break in is a different ballgame set by certain regulations (as it would see in service). Modern electronics in the A320neo can even prevent the captain from starting until it “has a cool down” lol. Cheers
😂 When experts are so expert they can't remember what life is like for normies 😂..it's so obvious what the guy is asking and tbf I've always wondered the same thing. It almost sounds like a harmonic : the initial pitch of the overall sound rises fast and yeah, it's pretty "loud" as one assumes there's less power involved...which aligns well with your point about vanes (that explains why the pitch is higher than rpm). Great video despite and also thanks to the rampant pedantry 😅👌👍
Yes, the pilot uses a twist grip to bring it up from ground idle to flight idle. At that point the power turbine is up to, or near 100% RPM. It is then controlled by the governor. Increase pitch and the RPM will start to drop, the governor then tells the fuel control to put more fuel in. Of course in the past 20 years or so most helicopters and engines are FADEC. Computer controlled. Just for giggles, look up the “Thunder Screech” used a supersonic propeller. So loud it was making pilots and people on the ground sick.
I like the sound of the first start spooling up sound and I find it cool hearing that. The big click sound, spooling up, then the fuel gets added and more spooling up sounds after that. Very cool hearing those noises to me.
Perhaps a tangent, but another thing to consider is intake shape in some cases, the Olympus engines in the Vulcan would howl beautifully at a certain power setting and the F-104 used to emit a wonderful eerie set of notes whilst taxying.
T53's are both Axial and centrifugal. Different models had different numbers of axial stages but they all had centrifugal stage at end pushing air into the diffuser section.
the very first noises you hear are the sound of the straight cut gear teeth in the starter gearbox as it spins up the engine to start status, and as the speed increases? other sounds come into it such as airflow past blades and stator vanes etc
10:35 For coprime numbers (i.e. having no common divisor) you simply multiply them, i.e. 7 * 18 = 126 blade-vane interactions per revolution of the rotor, so you'd expect the strongest spectral components to be 126 * rotor frequency and multiples thereof. I wouldn't be surprised if 18 * rotor frequency also shows up in the spectrum, since the 7-fold symmetry isn't perfect (especially taking the transfer function to the listening position into account). If the rotor frequency itself shows up acoustically then there might be something to worry about, e.g. an imbalance. Of course the total number of blade-vane interactions per revolution is technically always (number of blades) * (number of vanes) since each blade passes each vane exactly once per revolution (duh), but if the numbers are not coprime then their common divisor is how many of these interactions happen simultaneously, hence in that case you need to divide the total number of blade-vane interactions by this common divider to get the number of acoustic events per revolution. With 7 and 18 the blade-vane interactions are also well distributed around the circumference. Explicitly, the distance to the next passing blade for each of the 7 vanes, as function of time, is: t=0: [0, 4, 1, 5, 2, 6, 3] t=1: [6, 3, 0, 4, 1, 5, 2] t=2: [5, 2, 6, 3, 0, 4, 1] t=3: [4, 1, 5, 2, 6, 3, 0] t=4: [3, 0, 4, 1, 5, 2, 6] t=5: [2, 6, 3, 0, 4, 1, 5] t=6: [1, 5, 2, 6, 3, 0, 4] t=7: [0, 4, 1, 5, 2, 6, 3] (sequence repeats) with time and distance both being in units of 1/126th revolution.
(a catch with this however is that this analysis assumes each blade-vane interaction sounds exactly the same, where as these events are presumably at least somewhat turbulent events which introduce wideband noise)
I'm not a regular viewer and most of the tech stuff is beyond my level of comprehension, but it is so refreshing to listen to you and hear all the gentle digs and allusions to so many other areas of knowledge. I love the 'take chances' on the Jet boat.
In designing jet engines, the blade and vane numbers are chosen primarily to avoid resonant conditions. If you are sufficiently interested (and don't want to be spoon-fed), try doing some research on Campbell diagrams (aka interference diagrams). Having said this, Noise Departments have also tried to play with blade and vane numbers for noise reduction.
@@AgentJayZ I did wonder whether the flat earth and jet fuel comments were serious, or just someone trying to wind us up. I've sailed thousands of miles, and I've seen incontrovertible evidence of the curvature of the earth. And having had a career lifetime in the design of gas turbines, including combustion systems, I know only too well that they're not powered by compressed air. I don't think I'll waste my time repeating my comment.
When I was little, my dad was a fireman at the RCAF 'air base' which is now Northern Lights College where you were filming that UH1. That was also where I had my first and only ride in a chopper. I have no idea what kind it was as I was only maybe 5 at the time. It seemed absolutely huge to me as a little kid. I remember the side door was open, and I was quite worried that I might slide across the floor and fall out.
The sound from the vanes passing by the stators is the same principal rotary sirens (like air raid and tornado) operate. They "chop" an airstream (thousands of times/second) and the pulses are what make the sound.
3 Factors cause this: 1. Sound attention is greatly helped by heat increase and humidity decreasing. 10KHz sound impact: increase temperature from 20c to 40c and humidity 70%-20% would reduce the SPL by 22DB at 100M. 2. Moving air naturally attenuates sound because moving air dilutes sound and turbulence. Once the air starts rapidly expanding and moving aft of the engine it will get quieter. 3. At the compressor the lower the pressure the harder it is to propagate noise. The faster it spins the lower the pressure (sound is non-existent in a perfect vacuum).
Some of the sound at start up of the Huey, in my opinion could be the starter generator. At startup you may hear gear noise from the Starter/Generator . It may be because the gear thrust is different at startup vs normal operation. The torsional thrust at start up is from the starter to the engine vs operation when it is from engine to generator. Gear clearance may be more during the start vs running. Also some oil coolers may add additional noise that may seem to come from the engine. and clearances in the engine may also tighten up as the engine approaches operating temperature.
Since the OH6 is getting so much press in the comments maybe this is a good time to tell my little OH6 story. In the early 80s I was a Cobra crew chief and they brought us an OH6 to take "out of the mothballs". The OH6s had not been used for many years but they were starting to bring them back for special ops use. Anyway, one of the things I had to do was drain the fuel tank on this thing. I pulled the plug and drained all the fuel and took bucket by bucket to a large 100 gallon waste fuel drum on the flight line. I was finally ready to put the plug back in and fill it back up and I couldn't find the plug anywhere. I searched all over and finally had to go and stick my body down inside the opening of that waist drum and rummage around with my hand to try to find that drain plug. Now this was in the summer in Savannah Georgia and sticking your head into a old fuel drum was not a lot of fun, not to mention being dangerous. I pulled beer caps, safety wire, rocks, glass, and all sorts of stuff out of that drum but no drain plug. I was convinced that drum was completely clean on the bottom and no drain plug. Finally went back into the hangar and ran my hand through the last bucket of fuel that I had not dumped and there was the drain plug. That was an interesting day.
If I get the chance, I will try to discuss with a former colleague who, I believe, had some dealings with the Noise Department at R-R. In respect of the characteristic howl of centrifugal engines, such as the Derwent, the Nene and the Dart, the most obvious difference to consider is that they have relatively fewer things whizzing past each other. I was brought up to refer to the features on a centrifugal compressor impeller as 'vanes' - but Frank Whittle, in his book, referred to them as 'blades'. However, there are fewer of them than the equivalent number of blades in a similar sized axial compressor, and fewer pre-swirl vanes (if there are any) in front of the 'eye' of the impeller, as compared to the IGVs in a similar sized axial compressor.
JayZ, thank you for her another great video. Just relaxing after a long day. It's always a pleasure, sir! Oh, regarding lovely jet engine sounds. In the 80s I hung out with friends at MCAS El Toro. The Grey Ghosts! Nothing surpasses the woo ooo ooo of the early Phantoms! I'm sure you agree.
That little pink engine in your video.... what power does it make? Didn't realize how small it was until you stuck your hand into the compressor! It's cute!
Out of all of them the apache and long bow are the worst. Along with their rotor blades that sound like someone slapping 2 giant plastic rulers together, the apache's engine noise can be heard from 10miles away ( they overfly my house regularly), and sound like they are sheering every blade to bits while machining their gearboxes at the same time. Isis and the taliban didnt need fancy equipment to know they were coming, just a pair of ears and knowing as soon as you hear it, you have 20 to 30 minutes to get the hell out.
OMG! Charlie Lake! I'm from Dawson Creek and have been living in the USA forever. My cousins had a cabin on Charlie Lake. We used to fish there, and do donuts on the ice in the winter. Never thought I'd hear the name again!!
I can't help but LOVE the sound of a Huey or old Cobra starting up. The sound of the engine with the whop whop of the blades is music to my ears. T53's are a 50's design and the N1 speed is much slower than newer engines like a C250 or a T700 where N1, gas producer, is way higher. I'll never forget the sound of the starter, the ignition system and the 400lbs of rotor system moving. As we used to say, it's the 2 blade serenade. Ahhhh the memories!
It's also all about the 'Resonance'. Vibration through the starting phase a the mass. Until it gets into the running area of its 'happy zone' it will make weird and wonderful noises. All normal. The siren effect is what can be heard on startup. Just like the local fire siren. Google will explain the mechanics of how that works.
Probably the slowest starting turbine engine is the first gen RR RB211 that were on L-1011 Tristars. It takes forever, has a low drone heard for miles and under the right conditions turns into a fog machine when fuel is introduced. TWA had the end gates of the G terminal at the old Ohare airport and when they pushed back they blocked American and American Eagle flights in the alley fogging up both ramps the tower would lose sight of everybody for awhile...
The writer is possibly commenting on the escalating whine one hears that increases in pitch right out of the range of human hearing on start, then usually the same thing again after the engine has actually started. Multiple "whines" that start low, end high in sequence. I've always assumed it was either A) Harmonics in the noise generated by various high RPM parts that simply come in and out of the range of human hearing depending on RPM or B) Different parts of the engine producing a given pitch at different speeds because of the different number of blades on each compressor / turbine disks. Either way, I think the question is about that multi-escalating whine almost like a Shepard Tone.
10:16 And for vibration reduction, too, right? (though they are usually related, I imagine an engine designer would be more concerned about vibration than about noise) To do the arithmetic for you at 10:40 : There are lcm(7, 18) = 126 distinct sound events from an 18-bladed compressor rotating behind 7 vanes/struts, and according to an unreliable source (me trying to search through an online Allison 250 manual), an Allison 250 C18 gas generators spins at 32000 rpm (idle) to 51600 rpm (takeoff). That gives a frequency of *67.2 kHz to 108.36 kHz* , well outside the range of human hearing. So we are likely hearing some sub-harmonic (maybe generated by one blade or stator not perfectly matching the others?) or another source, for example from a different number of vanes behind the first rotor section. Also in the clip at 11:48 , I can hear all the high-pitched noises from the beginning up until the end, and a spectrum analyzer seems to confirm that the highest pitch at the start ends up at ~12kHz at the end. That's technically still in the audible range, but high-frequency hearing is known to decline with age, and I think the high-frequency tone also gets quieter as the mic adjusts to the level of the everything else, so it is quite possible you didn't hear it, while cats, dogs and young people still can. (Compare how those "anti loitering devices", or less charitably "teenager repellents" work: beeping high enough to annoy teenagers, while older people can't hear them)
The number of the struds should not really have an impact on the pitch of the sound. An odd number may be preferable because its more rigid than an even number construction. So it comes down to blades and speed, the Allison 250 runs at 51600 RPM -> 860 RPS * 16 blades = 13760 Hz. So this should be still in range depending on your hearing capabilities. Of course there will be harmonics higher than that which no human will hear.
@@AgentJayZ They do. But this is more like a parallel configuration. On each IGV the blade makes a fixed frequency sound. For a single strud the pitch is only frequency dependent, adding more struds will make more places were it will generate the same pitch. Picture it like seven engines with only one strud each, the pitch wont go any higher because of more engines(=more struds). The principle is quite the same as a air raid siren, here the pitch is only dependent on rotor ports and RPM. Adding more stator ports will make more noise, but not change the pitch. Of course you will only hear a sum of all sounds that are generated. So its like seven 13760Hz frequency generators with a 51° Phase difference which will result in some new sound.
@@Alexander470815 I disagree: there are lcm(7, 16) = 112 moments where a rotor passes a strut during a full revolution, generating 112 pressure pulses. How is an ear supposed to "know" which of the seven IGV sources it comes from? All that arrives at an ear far enough away to not be ingested is 112 pressure pulses per revolution, or a 108.36kHz, inaudible sound. Now, if one of the struts is not perfect and generates a slightly different sound, then yes, you get a 14kHz subharmonic (and in practice this will always be the case, the question is just how much), but the fundamental is at 108kHz and not audible Note also that adding up seven of sine waves with evenly spaced phases will cancel perfectly, leaving no sound at all! This is true for any number of sources larger than one. It's easiest to see in the case of two sources, for three it is well-known in electrical context (balanced three-phase power needs no ground line), and can be seen in general with complex exponentials (adding up >1 roots of unity gives zero, no matter how you rotate them).
@@hadinossanosam4459 If this would be the case sirens would not work the way they do. Lets take the in Germany common e57 siren: ruclips.net/video/hg81uavShNo/видео.html It has a (9,9) configuration giving 81 moments during a full revolution. Running at 2800 RPM. With your calculation the pitch should be: 2800/60 = 47 RPS * 81 = 3.8 kHz. Just by listening you can hear that it is much lower than that. In fact its rated frequency is 420Hz. With 47 RPS * 9 = 423Hz this is much closer. Of course there will be more harmonics with higher frequency(due to the non sinusoidal nature) My home built siren uses a (1,6) config and behaves exactly the same as the (9,9) of the e57. ruclips.net/video/zePrAI5MmHs/видео.html Motor RPS * 6 = tone pitch in my case. You are right with your second statement, they would cancel each other out and make no sound, at least in theory. There is more to it than just adding sine waves I would suspect. The chopping of the air will not give anything near a sine wave, more like a square wave. And with that many harmonics they wont cancel out anymore.
I had a couple tours with Tactical Helicopter Squadrons in the Canadian Forces so a lot of time around CH-136 Kiowas & CH-135 Twin Hueys. Back then there were still some CH-118 Iroquois in service too, mainly as Base Rescue aircraft. All fine Bell products many of which are still in service in the civilian sector today ;-). To save you some searching CH-136 is equivalent to Jet Ranger, CH-135 is a Bell 212 & CH-118 is the UH-1. The CH-136 were indeed LOH (Light Observation Helicopters), CH-135 were UTTH (Utility Transport Tactical Helicopters). Throttles on both types are on the collective stick which also controls main rotor blade pitch. Once the engine(s) are started & everything's at operating temp, the throttle is essentially twisted to full on position & held there with a friction lock. Governors & other magic then take over to keep the main rotor at 100% RPM. When the pilot raises the collective stick increasing blade pitch for lift, naturally the rotor will tend to lose RPM or 'droop' as it's called. A linkage from the collective to the fuel control prevents rotor droop by dumping more fuel into the engine to maintain 100% RPM. Another tidbit of info, on helo jet engines there's no direct linkage or shaft from the 'gas producer' or hot section to the power turbine. A simple analogy is that the gas producer is blowing air over the power turbine to turn it kind of like if you were blowing air at a propeller held in your hand. The power turbine is mated to the transmission which in turn spins the rotor. The gas producer rpm varies quite a bit to keep both power turbine & rotor blades turning at a constant rpm under varying load conditions caused by pitch changes in the main rotor.
Most helicopters have free power turbine engines... but not all. Some Turbomeca engines are single shaft. You can see me demonstration of the "connection" between the gas producer and the power turbine in the T58, in the series of videos I made on that engine.
@@AgentJayZ Yes I had initially used the word 'most' but edited it out.... I'm familiar with the T58 as I finished my career in support of the Labrador CH113/113A SAR fleet. Vertol 107 or Sea Knight as the US Navy & Marines named them. The T58 also powered our recently retired Sea Kings. We finally upgraded to the -100 engines just before the Labradors were replaced by the Cormorant. Sea King fleet reaped the benefit of that for the remainder of their life in the CF. Columbia Helicopters still operates many 107's & if not mistaken they have the type certificate. The Chinook has kind of eclipsed the 107 as it's big brother... Latest versions of the CH-47 are absolute beasts, love those tandems...
Even a few minutes' research on the internet will reveal that the human ear is most sensitive to frequencies in the range 2kHz to 5kHz, with reducing sensitivity up to an audible limit of around 20kHz: however, that upper limit tends to reduce with increasing age. I've just used a tone generator, which has demonstrated that my upper audible limit is just below 9kHz: it was also noticeable that my sensitivity progressively and rapidly reduced above around 7.5kHz. The experiment also demonstrated what I'd investigated in the past: I have a low volume pure(-ish) tone tinnitus in the range 4kHz to 4.5kHz. So, doesn't this go some way towards explaining why the low-frequency howl of an engine on start-up appears to be at its loudest, with the apparent noise level reducing with increasing speed and frequency, and with the highest frequency tones rising well above the audible range?
That turned into a fascinating vid! one of those "oh, why didn't I think of that" areas. Thanks! those early centrifugal-flow engines ( Nene, etc ) also have a particular noise which I now guess is a similar interaction. I'd love to see a walkround of one of the hybrid flow helicopter engines some time - RR Gem is also iirc - seeing diagrams is ok but doesn't beat an expert's fingers. To be clear - I did enjoy the vids so far on the Allison for the boat, I'd just like to see one torn down properly & an expert go around the whole thing & talk about why it's designed how it is.
Hello Agent JayZ, I was wondering if could you explain the loud growling sound of the GE-90s (Boeing 777s) during engine startup, the fuel-burn sound. I was wondering why it is so loud compared to most other jet engines. It's also unique.
Here's an idea from left field - I'm under the impression that the screaming sound produced at the front of the J-47 is actually higher pitched than what is heard, and is red-shifted because of having to "swim upstream" against the inrushing air. :) (not worth a rebuttal, lol)
@ around 10:25, where you are talking about 7 struts/vanes and 16 blades, I wonder if that design feature has more to do with avoiding the deleterious effects of resonance on the engine, than with "noise reduction", although that could be another desirable consequence. Resonance, generally speaking, is to be AVOIDED in mechanical systems. Consider the Tacoma Narrows Bridge. In the present case, if several blades were aligning with several vanes at various points in the rotation, a shock wave would be imparted at several points round the blade and vane disks, that would not only increase it severity with speed, but far worse, could very likely take on on a resonant, self-amplifying character, when the duration of the imparted impulse was some unfortunate multiple of the time between impulses. With a 7/16 configuration, at any instant, only one blade/vane pair would be subjected to the impulse, and additionally, considering the sets of blades and vanes as wholes, no simple relationship would exist between pulse duration and time between impulses, such as can give rise to resonance and subsequent self-amplification .
@@pinkdispatcher Gee, that's funny, when I was an engineering undergrad, my Diff Eq prof used Tacoma Narrows as an example of resonance. Then, there's what others say: Galloping Gertie - Resonance and the Tacoma Narrows Bridge ruclips.net/video/l5Kt0xs_nTk/видео.html
there is alot going on there. I hear gears and a electric motor and more gears then air rushing past vanes and turbines.... most of the whine is air shrieking past sharp edges. and then the ignitors click and it starts sounding realy cool!
These are twin shaft engines, the initial noise is the compressor and turbine, the 'gas producer', the secondary increasing whine is the power turbine that's connected to the gearbox.
Nice, thank you. I remember watching some jet test videos way back when youtube was a new thing. Maybe it was your video I don't know. Anyways, it was of a large jet in just a tent and I remember the tools on the table were literally dancing from the sonic vibrations. This was not a screech, but a rumble sound at startup that went away with increasing the rpm. I always wondered what caused that phenomenon?
That was the RR Olympus in our old test cell. The Olympus is a huge engine, and created a loud bass rumble as it came up to idle rpm. This was cause by the restrictive tail cone we used for testing purposes. I still remember that being the loudest bass I've ever felt.
Hi. I have a question.. I can't understand this. Currently I'm start to work on APU engines and as far I can see fuel is injected to combustion chamber on the back then - flow/opposite direction as main flow air in engine and after that is join with main flow.. in main entry stage 1 blades.. I'm not sure is make any sense for you.? Many thanks
Just learned the other day that RUclips is cutting everything above 16KHz in audio so it might cause issues if you ever try to demonstrate this via your videos, even if you manage to actually record it.
When you run the LM2500, will you setup a spectrum analyzer app on your phone to see if it can capture the volumes at different frequencies during various operating conditions? I use a free app called dB Meter to help my deaf A&P student visualize the sound better. It would be interesting to have it running in the same frame with the camera so we can all watch the spikes at different frequencies during startup.
All the dB meters I've seen top out at 130. When I stand 20m from the start cart, those meters hit the pin as the start cart is about 60% rpm, and climbing to it's working speed of 108%. The start cart is a 90 Hp gas turbine engine. Those same phone meters are smashed flat by the LM1500 at 100m even before they get to operating power, which is 15 thousand Hp. The LM2500 we are running is a nominally rated 27 thousand Hp. You see where this is going. I have no dB readings on any of my engine test videos, and I have made a few videos explaining that there is no way to describe or record it adequately. When you are at a test of a big engine, and wearing ear defenders over earplugs... each of which claim a 30 dB reduction, your body tells you "this is very dangerous. get away". My honest estimate in numbers for the LM2500 is 175 to 180db at max. In non-numbers: take terrifyingly Earth-shaking loud, and multiply that by ten. Ok, now ten times that.
@@AgentJayZ: I have an idea! Place a wine glass near by with a camera focused on it and start up the jet engines. If the wine glass shatters, people will know that it's loud enough. 😁👍
Absolutely. Used to live on the approach path to Leeds Bradford Airport. British Airways Viscounts, Air Anglia F27s and the odd Herald and 748. Unmistakable and sublime. Not as loud as Concorde though. 12 miles from the airport but could clearly hear take off roll.
Besides the noise from back stages being chopped up by blades as it tries to come toward the front the sound waves from the back would also be cancelled out by sound waves heading toward the rear from the front stage (I remember seeing on TV how sound wave canceling is built into automotive exaust mufflers).
Would love a turbine engine in my truck, but settled for a turbodiesel lol. I’ve always both turbochargers and jet engines just sounded like massive vacuum cleaners. Being they “suck” by using centrifugal turbines its not too surprising.
No such thing as suction. Turbines do not move air. They are moved by air. What you are thinking of is a compressor. at the inlet they create an area of lower pressure. The air rushes in towards this area of lower pressure. That's how a vacuum cleaner works. Air can never be pulled, only pushed.
@@AgentJayZ True, but I don't know what to say a vacuum cleaner does other than suck, saying inhale or take in like I would for an engine just seems strange to say about what the vacuum's motor does. And to be technical, like with suction, a vacuum cleaner doesn't create anything close to a vacuum, it's just a low pressure pocket of air inside it.
Morning! Just want to say, thanks for these videos they've honestly really helped to keep me motivated in my area of study. By the way, anything new going on with the Orenda Iroquois? I sure would love to hear that one running one day.
Seems as if curved blades would maybe mitigate this some? Perhaps even improve efficiency? Curved in the direction perpendicular to the rotational axis. In the plane of rotation. With the stator blades curved the other direction. Somewhat like the fan on a high bypass turbo fan. Apply a bit of that tech to the compressor. Well hell, apply some of that to all of it really. Dont let the air slide off the end so much.
All compressor blades, and all stator vanes... in every engine ever created since Sir Frank and Hans von Ohain did it in the 1930s... ... ... have been of compound curvature in all three dimensions. It's why and how they work. Your comment is so great! It's like you are suggesting that light bulbs might work better if we made an electric current flow through the filament. Even better: just think how much better a camp fire would be if the wood was actually burning! ... although I'm actually sighing... ... ... LOL.
Sorry, but you're decades too late in suggesting this. Compressor aerofoils with so-called 'end bend', or 'three-dimensional geometry', have been around for years. If the technology had obviously been applied to large fan blades, hadn't it occurred to you that the same brains might have applied it to the compressors, where you couldn't see it and where the application wouldn't be so obvious?
@@AgentJayZ Lol1 on the other hand light globe filaments seem to last longer when the current flows around the filament.Mind you the fittings and wires for them don't seem to last anything like as long as they should and the smoke leaks out of them.
I service gas turbine generators. our engines operates at 750hz. I've been around a few that have suffered F.O.D. to the compresor. omg they it becomes soooooo much louder!
Hello sir, I have a question, If the turbine use Starter Machine permanently during the fuel firing burn, is it stronger than not use Starter Machine permanently?
The starter has no way of reaching the working rpm of the main engine, its main role is to get the rpm up to a level where the combustion can start being effective and then it gradually looses efficiency up to idle rpm (at most). So keeping the starter running would mean absolutely nothing for the output (except a draw on the generator if it's powered by internal batteries).
If a starter (whether electric, air turbine or gas turbine) remained connected to the engine up to maximum engine speed, there would be a major failure of the starter. Starters are designed to run up to a speed (with a safety margin) sufficient to start the engine and no more. I have direct experience of an air starter running up to overspeed in flight, as a result of an electrical fault. The starter suffered a disc burst, the debris punctured a fuel tank, there was a major fire and the aircraft had to ditch.
Seems like every engine has an initial low-order(2X), 4X, 8X, 16X are naturally less(intense) noisy harmonic sound...usually a howl kinda thing at 2X and increases to a whine at higher multiples. The higher the harmonic, the less energy(I think). Engine has no choice but to pass through that harmonic band as it speeds up. Interesting
When I read the title and saw the Huey I thought is was going to be about the rotor. It has a very distinctive sound at least when coming towards you. That must be some interaction effect right? The rotor and the tail rotor maybe? Or is the rotor somehow very different from that of other helicopters?
The diffent sound is because it's a two bladed prop (more blades at equal rpm means more pulses per second = higher pitch and harder to distinguish individual blade whumps)... All two blade props sound like that. There are also different types of hub but I don't think they affect sound per se).
@@nonsequitor The Bell Jet Ranger also had a 2 blade rotor. I don't remember it sounding like that but I haven't seen one in a long time so I might not remember. And it's a bit smaller too.
On T55s (on the Chinook helicopter) and TF 40 (on LCAC hoverboats) , the engines are way noisier at low power because the bleed band/valve is open .... going into higher power, the bleed is closed making them much quieter.
Uh-1 throttle like motorcycle just backward in motion. The shiny button on the box at end of the collective is idle stop, it is held down to allow fuel to be cut off when the throttle is rolled clockwise. To start the engine press the start button on the bottom of the box at end of collective watch N1 and depending on wind, roll throttle ccw to turn on ground idle fuel, watch N1 and EGT rise after stable release start and idle buttons, and slowly add fuel until full-on and governor takes over. reach up and flip start/gen switch and check for the charge. Another great video Agent J
I love it when you guys with real world experience with these things tell us your stories. You have great historical value, because those days are long gone...
The sound of a turbine engine firing up is one of the most satisfying sounds in the world and the rotor spin up only adds to it.
The cobra and the UH1 are some of the best sounding whirlybirds out there. Love that rotor slap.. they're the bass guitarists of the heli world.
And possibly the worst sounding is the Aérospatiale Alouette. I think the engineers who designed its engines went to great lengths to make sure the whine doesn't go ultrasonic so that the earthbound people for miles around it can take pleasure listening to it.
YES!
Flew in vietnam ‘68. 4am preflight. Engine start and run up. I really miss the sound and smell of the jp4. Seeing this start up took me back a long time to a different world
I have the same perception of the sound of start up. I think the frequency is very audible as the compressor spins up. It gives the illusion of high rotational speed. As it gains speed I think the frequency becomes higher than your ears can perceive. I understand his question.
Howdy Jay, Afterburner119 here. Hope all is well, maybe ACCA next year we can finally meet.
In our R&D cells here, the operators and mechs are in the control room along with structures, NSMS, Op line, etc. engineers. We will bring in stand air to rotate, maybe motor to cool, then at a certain rpm the operator engages fuel and the article (engine) will light off to idle. We can even change the controls on the fly to incur a longer spool up, or shorter etc.for example if EGT Climbs too high on previous missions. Keep in mind, we are trying to break it or prove life limits.
Production ATP Break in is a different ballgame set by certain regulations (as it would see in service). Modern electronics in the A320neo can even prevent the captain from starting until it “has a cool down” lol. Cheers
😂 When experts are so expert they can't remember what life is like for normies 😂..it's so obvious what the guy is asking and tbf I've always wondered the same thing. It almost sounds like a harmonic : the initial pitch of the overall sound rises fast and yeah, it's pretty "loud" as one assumes there's less power involved...which aligns well with your point about vanes (that explains why the pitch is higher than rpm). Great video despite and also thanks to the rampant pedantry 😅👌👍
Yes, the pilot uses a twist grip to bring it up from ground idle to flight idle. At that point the power turbine is up to, or near 100% RPM. It is then controlled by the governor. Increase pitch and the RPM will start to drop, the governor then tells the fuel control to put more fuel in.
Of course in the past 20 years or so most helicopters and engines are FADEC. Computer controlled.
Just for giggles, look up the “Thunder Screech” used a supersonic propeller. So loud it was making pilots and people on the ground sick.
I like the sound of the first start spooling up sound and I find it cool hearing that.
The big click sound, spooling up, then the fuel gets added and more spooling up sounds after that.
Very cool hearing those noises to me.
Perhaps a tangent, but another thing to consider is intake shape in some cases, the Olympus engines in the Vulcan would howl beautifully at a certain power setting and the F-104 used to emit a wonderful eerie set of notes whilst taxying.
T53's are both Axial and centrifugal. Different models had different numbers of axial stages but they all had centrifugal stage at end pushing air into the diffuser section.
the very first noises you hear are the sound of the straight cut gear teeth in the starter gearbox as it spins up the engine to start status, and as the speed increases? other sounds come into it such as airflow past blades and stator vanes etc
10:35 For coprime numbers (i.e. having no common divisor) you simply multiply them, i.e. 7 * 18 = 126 blade-vane interactions per revolution of the rotor, so you'd expect the strongest spectral components to be 126 * rotor frequency and multiples thereof. I wouldn't be surprised if 18 * rotor frequency also shows up in the spectrum, since the 7-fold symmetry isn't perfect (especially taking the transfer function to the listening position into account). If the rotor frequency itself shows up acoustically then there might be something to worry about, e.g. an imbalance.
Of course the total number of blade-vane interactions per revolution is technically always (number of blades) * (number of vanes) since each blade passes each vane exactly once per revolution (duh), but if the numbers are not coprime then their common divisor is how many of these interactions happen simultaneously, hence in that case you need to divide the total number of blade-vane interactions by this common divider to get the number of acoustic events per revolution.
With 7 and 18 the blade-vane interactions are also well distributed around the circumference. Explicitly, the distance to the next passing blade for each of the 7 vanes, as function of time, is:
t=0: [0, 4, 1, 5, 2, 6, 3]
t=1: [6, 3, 0, 4, 1, 5, 2]
t=2: [5, 2, 6, 3, 0, 4, 1]
t=3: [4, 1, 5, 2, 6, 3, 0]
t=4: [3, 0, 4, 1, 5, 2, 6]
t=5: [2, 6, 3, 0, 4, 1, 5]
t=6: [1, 5, 2, 6, 3, 0, 4]
t=7: [0, 4, 1, 5, 2, 6, 3] (sequence repeats)
with time and distance both being in units of 1/126th revolution.
(a catch with this however is that this analysis assumes each blade-vane interaction sounds exactly the same, where as these events are presumably at least somewhat turbulent events which introduce wideband noise)
Hey man I just came here for the cool sounds and odd humor. I don't need your math.
I'm not a regular viewer and most of the tech stuff is beyond my level of comprehension, but it is so refreshing to listen to you and hear all the gentle digs and allusions to so many other areas of knowledge. I love the 'take chances' on the Jet boat.
In designing jet engines, the blade and vane numbers are chosen primarily to avoid resonant conditions. If you are sufficiently interested (and don't want to be spoon-fed), try doing some research on Campbell diagrams (aka interference diagrams). Having said this, Noise Departments have also tried to play with blade and vane numbers for noise reduction.
My apologies, Graham. I mistakenly deleted your most recent comment, and there is no way to undo that. It was a response to a flat earther...
@@AgentJayZ I did wonder whether the flat earth and jet fuel comments were serious, or just someone trying to wind us up.
I've sailed thousands of miles, and I've seen incontrovertible evidence of the curvature of the earth.
And having had a career lifetime in the design of gas turbines, including combustion systems, I know only too well that they're not powered by compressed air.
I don't think I'll waste my time repeating my comment.
I sure will. Thanks!
When I was little, my dad was a fireman at the RCAF 'air base' which is now Northern Lights College where you were filming that UH1. That was also where I had my first and only ride in a chopper. I have no idea what kind it was as I was only maybe 5 at the time. It seemed absolutely huge to me as a little kid. I remember the side door was open, and I was quite worried that I might slide across the floor and fall out.
250 series manufactured by both Alison and RR were used in both the OH-6 (H369) and the early Kiowas OH-58 (B206A).
The early C18's had about 320 shp.
Awesomeness 👍🏻 any updates on the Iroquois?
Ditto 😍. I have been wondering myself.
12:25 It probably also becomes quieter for animals because attenuation of sound waves in air very strongly increases at ultrasonic frequencies.
The sound from the vanes passing by the stators is the same principal rotary sirens (like air raid and tornado) operate. They "chop" an airstream (thousands of times/second) and the pulses are what make the sound.
3 Factors cause this:
1. Sound attention is greatly helped by heat increase and humidity decreasing. 10KHz sound impact: increase temperature from 20c to 40c and humidity 70%-20% would reduce the SPL by 22DB at 100M.
2. Moving air naturally attenuates sound because moving air dilutes sound and turbulence. Once the air starts rapidly expanding and moving aft of the engine it will get quieter.
3. At the compressor the lower the pressure the harder it is to propagate noise. The faster it spins the lower the pressure (sound is non-existent in a perfect vacuum).
Some of the sound at start up of the Huey, in my opinion could be the starter generator. At startup you may hear gear noise from the Starter/Generator . It may be because the gear thrust is different at startup vs normal operation. The torsional thrust at start up is from the starter to the engine vs operation when it is from engine to generator. Gear clearance may be more during the start vs running. Also some oil coolers may add additional noise that may seem to come from the engine. and clearances in the engine may also tighten up as the engine approaches operating temperature.
Since the OH6 is getting so much press in the comments maybe this is a good time to tell my little OH6 story. In the early 80s I was a Cobra crew chief and they brought us an OH6 to take "out of the mothballs". The OH6s had not been used for many years but they were starting to bring them back for special ops use. Anyway, one of the things I had to do was drain the fuel tank on this thing. I pulled the plug and drained all the fuel and took bucket by bucket to a large 100 gallon waste fuel drum on the flight line. I was finally ready to put the plug back in and fill it back up and I couldn't find the plug anywhere. I searched all over and finally had to go and stick my body down inside the opening of that waist drum and rummage around with my hand to try to find that drain plug. Now this was in the summer in Savannah Georgia and sticking your head into a old fuel drum was not a lot of fun, not to mention being dangerous. I pulled beer caps, safety wire, rocks, glass, and all sorts of stuff out of that drum but no drain plug. I was convinced that drum was completely clean on the bottom and no drain plug. Finally went back into the hangar and ran my hand through the last bucket of fuel that I had not dumped and there was the drain plug. That was an interesting day.
If I get the chance, I will try to discuss with a former colleague who, I believe, had some dealings with the Noise Department at R-R.
In respect of the characteristic howl of centrifugal engines, such as the Derwent, the Nene and the Dart, the most obvious difference to consider is that they have relatively fewer things whizzing past each other.
I was brought up to refer to the features on a centrifugal compressor impeller as 'vanes' - but Frank Whittle, in his book, referred to them as 'blades'. However, there are fewer of them than the equivalent number of blades in a similar sized axial compressor, and fewer pre-swirl vanes (if there are any) in front of the 'eye' of the impeller, as compared to the IGVs in a similar sized axial compressor.
JayZ, thank you for her another great video. Just relaxing after a long day. It's always a pleasure, sir!
Oh, regarding lovely jet engine sounds. In the 80s I hung out with friends at MCAS El Toro. The Grey Ghosts! Nothing surpasses the woo ooo ooo of the early Phantoms! I'm sure you agree.
7:20 Isn't that pretty much the noise generation in a WW air raid siren?
yes if you watch the video(s) by Matthias Wandel, he makes one out of wood and you can see how it works
I like the Doppler Effect at the end. To me, Doppler Effect gets more of your attention, for coolness awards.
The T-53 does have variable inlet guide vanes.
Could you take a video of engine start and identify each of the sounds?
It all happens so fast it can't really be narrated without stopping the vid several times.
I have an idea, though...
@@AgentJayZ I think there are some of the noises that if not present means or indicates a problem
9:00 Are you thinking of the Hughes OH-6?
You know why it’s so noisy, it beats the air into submission. That’s why!
Ten thousand moving parts seeking to do you bodily harm.
Would you please tell us about lubricating system of a jet engine?
He’s done videos about it, use the search.
The mechanical siren used on fire engine makes a loud and similar sound, on the same principal. Only about the size of a football.
love the clip of the Hornet overhead! What a great sound!
That little pink engine in your video.... what power does it make? Didn't realize how small it was until you stuck your hand into the compressor! It's cute!
Allison 250 C-18.
320 Hp.
Not just the turbine is noisy, but the blades as in a class of themself!
Out of all of them the apache and long bow are the worst. Along with their rotor blades that sound like someone slapping 2 giant plastic rulers together, the apache's engine noise can be heard from 10miles away ( they overfly my house regularly), and sound like they are sheering every blade to bits while machining their gearboxes at the same time.
Isis and the taliban didnt need fancy equipment to know they were coming, just a pair of ears and knowing as soon as you hear it, you have 20 to 30 minutes to get the hell out.
It all depends on the conditions and your location in relation to the bird. I had some hovering just over a hill and never heard then many times
Yikes. I would be so nervous starting her up. Greetings from Nova Scotia. 2nd class marine engineer here.
OMG! Charlie Lake! I'm from Dawson Creek and have been living in the USA forever. My cousins had a cabin on Charlie Lake. We used to fish there, and do donuts on the ice in the winter. Never thought I'd hear the name again!!
I can't help but LOVE the sound of a Huey or old Cobra starting up. The sound of the engine with the whop whop of the blades is music to my ears. T53's are a 50's design and the N1 speed is much slower than newer engines like a C250 or a T700 where N1, gas producer, is way higher. I'll never forget the sound of the starter, the ignition system and the 400lbs of rotor system moving. As we used to say, it's the 2 blade serenade. Ahhhh the memories!
OH6 cayuse was the observation helicopter.
That CF-18 zoom over was cool. Thanks for the info
It's also all about the 'Resonance'. Vibration through the starting phase a the mass. Until it gets into the running area of its 'happy zone' it will make weird and wonderful noises. All normal. The siren effect is what can be heard on startup. Just like the local fire siren. Google will explain the mechanics of how that works.
Same principle is why air raid sirens.
It was a 0H6a Cayuse made by Hughes also known as the Hughes 500
@Stephen Hudson :
Also known as "Little Bird" to some people.
The Kiowa was the OH-58, which is what is commonly called a Bell Jet Ranger in civilian models.
Yes I've had a ride in both the OH58 and the OH6a but my main aircraft was the Huey uh1 Iroquois I was a door gunner
I've ridden in the UH-1 Iroquois, and the UH-60 Blackhawk.
I've even rappelled from the Iroquois.
I didn't get a chance to repel and the Blackhawk was after I got out of the army
20k cycles per sec is about the limit for human hearing.The blade/vane interaction is very interesting.
Air starter on a J79 at startup makes a loud noise ,or is it the start cart making the noise.
They both are very loud.
Probably the slowest starting turbine engine is the first gen RR RB211 that were on L-1011 Tristars. It takes forever, has a low drone heard for miles and under the right conditions turns into a fog machine when fuel is introduced. TWA had the end gates of the G terminal at the old Ohare airport and when they pushed back they blocked American and American Eagle flights in the alley fogging up both ramps the tower would lose sight of everybody for awhile...
I would be very interested to see the noise on a spectral analyzer as the engine increases in rpm.
So do that.
The writer is possibly commenting on the escalating whine one hears that increases in pitch right out of the range of human hearing on start, then usually the same thing again after the engine has actually started. Multiple "whines" that start low, end high in sequence.
I've always assumed it was either A) Harmonics in the noise generated by various high RPM parts that simply come in and out of the range of human hearing depending on RPM or B) Different parts of the engine producing a given pitch at different speeds because of the different number of blades on each compressor / turbine disks.
Either way, I think the question is about that multi-escalating whine almost like a Shepard Tone.
Is that commentor a DOG? If it's outside of human decibels, he'd have to be to hear it.
Just kidding. 😁
Why is it so noisy at low rpm for the same reason an air raid siren is so noisy at very slow rpms
Pity the poor bat.
Interesting discussion of how sound is produced by "jet" engines
10:16 And for vibration reduction, too, right? (though they are usually related, I imagine an engine designer would be more concerned about vibration than about noise)
To do the arithmetic for you at 10:40 : There are lcm(7, 18) = 126 distinct sound events from an 18-bladed compressor rotating behind 7 vanes/struts, and according to an unreliable source (me trying to search through an online Allison 250 manual), an Allison 250 C18 gas generators spins at 32000 rpm (idle) to 51600 rpm (takeoff). That gives a frequency of *67.2 kHz to 108.36 kHz* , well outside the range of human hearing. So we are likely hearing some sub-harmonic (maybe generated by one blade or stator not perfectly matching the others?) or another source, for example from a different number of vanes behind the first rotor section.
Also in the clip at 11:48 , I can hear all the high-pitched noises from the beginning up until the end, and a spectrum analyzer seems to confirm that the highest pitch at the start ends up at ~12kHz at the end. That's technically still in the audible range, but high-frequency hearing is known to decline with age, and I think the high-frequency tone also gets quieter as the mic adjusts to the level of the everything else, so it is quite possible you didn't hear it, while cats, dogs and young people still can. (Compare how those "anti loitering devices", or less charitably "teenager repellents" work: beeping high enough to annoy teenagers, while older people can't hear them)
it's an air raid siren but multiplied many times over
Great video 👍🏻
Any update on the the Iroquois?
What is the loud screaming noise at the beginning of startup?
It sounds like a turbo to me!
it's a gale banks turbo
lovely engine
That collage I hear has a great cultural venue nearby , I hear they have a popular "ballet" thats attended by many daily right next door.....
The number of the struds should not really have an impact on the pitch of the sound. An odd number may be preferable because its more rigid than an even number construction.
So it comes down to blades and speed, the Allison 250 runs at 51600 RPM -> 860 RPS * 16 blades = 13760 Hz. So this should be still in range depending on your hearing capabilities.
Of course there will be harmonics higher than that which no human will hear.
Need to remember that each of those blades passes 7 IGVs in each revolution...
@@AgentJayZ They do. But this is more like a parallel configuration. On each IGV the blade makes a fixed frequency sound.
For a single strud the pitch is only frequency dependent, adding more struds will make more places were it will generate the same pitch.
Picture it like seven engines with only one strud each, the pitch wont go any higher because of more engines(=more struds).
The principle is quite the same as a air raid siren, here the pitch is only dependent on rotor ports and RPM.
Adding more stator ports will make more noise, but not change the pitch.
Of course you will only hear a sum of all sounds that are generated.
So its like seven 13760Hz frequency generators with a 51° Phase difference which will result in some new sound.
@@Alexander470815 I disagree: there are lcm(7, 16) = 112 moments where a rotor passes a strut during a full revolution, generating 112 pressure pulses. How is an ear supposed to "know" which of the seven IGV sources it comes from? All that arrives at an ear far enough away to not be ingested is 112 pressure pulses per revolution, or a 108.36kHz, inaudible sound. Now, if one of the struts is not perfect and generates a slightly different sound, then yes, you get a 14kHz subharmonic (and in practice this will always be the case, the question is just how much), but the fundamental is at 108kHz and not audible
Note also that adding up seven of sine waves with evenly spaced phases will cancel perfectly, leaving no sound at all! This is true for any number of sources larger than one. It's easiest to see in the case of two sources, for three it is well-known in electrical context (balanced three-phase power needs no ground line), and can be seen in general with complex exponentials (adding up >1 roots of unity gives zero, no matter how you rotate them).
@@hadinossanosam4459 If this would be the case sirens would not work the way they do.
Lets take the in Germany common e57 siren: ruclips.net/video/hg81uavShNo/видео.html
It has a (9,9) configuration giving 81 moments during a full revolution. Running at 2800 RPM.
With your calculation the pitch should be: 2800/60 = 47 RPS * 81 = 3.8 kHz.
Just by listening you can hear that it is much lower than that. In fact its rated frequency is 420Hz.
With 47 RPS * 9 = 423Hz this is much closer.
Of course there will be more harmonics with higher frequency(due to the non sinusoidal nature)
My home built siren uses a (1,6) config and behaves exactly the same as the (9,9) of the e57.
ruclips.net/video/zePrAI5MmHs/видео.html
Motor RPS * 6 = tone pitch in my case.
You are right with your second statement, they would cancel each other out and make no sound, at least in theory.
There is more to it than just adding sine waves I would suspect.
The chopping of the air will not give anything near a sine wave, more like a square wave.
And with that many harmonics they wont cancel out anymore.
I had a couple tours with Tactical Helicopter Squadrons in the Canadian Forces so a lot of time around CH-136 Kiowas & CH-135 Twin Hueys. Back then there were still some CH-118 Iroquois in service too, mainly as Base Rescue aircraft. All fine Bell products many of which are still in service in the civilian sector today ;-). To save you some searching CH-136 is equivalent to Jet Ranger, CH-135 is a Bell 212 & CH-118 is the UH-1.
The CH-136 were indeed LOH (Light Observation Helicopters), CH-135 were UTTH (Utility Transport Tactical Helicopters). Throttles on both types are on the collective stick which also controls main rotor blade pitch. Once the engine(s) are started & everything's at operating temp, the throttle is essentially twisted to full on position & held there with a friction lock. Governors & other magic then take over to keep the main rotor at 100% RPM. When the pilot raises the collective stick increasing blade pitch for lift, naturally the rotor will tend to lose RPM or 'droop' as it's called. A linkage from the collective to the fuel control prevents rotor droop by dumping more fuel into the engine to maintain 100% RPM.
Another tidbit of info, on helo jet engines there's no direct linkage or shaft from the 'gas producer' or hot section to the power turbine. A simple analogy is that the gas producer is blowing air over the power turbine to turn it kind of like if you were blowing air at a propeller held in your hand. The power turbine is mated to the transmission which in turn spins the rotor. The gas producer rpm varies quite a bit to keep both power turbine & rotor blades turning at a constant rpm under varying load conditions caused by pitch changes in the main rotor.
Most helicopters have free power turbine engines... but not all.
Some Turbomeca engines are single shaft.
You can see me demonstration of the "connection" between the gas producer and the power turbine in the T58, in the series of videos I made on that engine.
@@AgentJayZ Yes I had initially used the word 'most' but edited it out.... I'm familiar with the T58 as I finished my career in support of the Labrador CH113/113A SAR fleet. Vertol 107 or Sea Knight as the US Navy & Marines named them. The T58 also powered our recently retired Sea Kings. We finally upgraded to the -100 engines just before the Labradors were replaced by the Cormorant. Sea King fleet reaped the benefit of that for the remainder of their life in the CF. Columbia Helicopters still operates many 107's & if not mistaken they have the type certificate. The Chinook has kind of eclipsed the 107 as it's big brother... Latest versions of the CH-47 are absolute beasts, love those tandems...
I keep telling my psychiatrist just because you can’t see or hear it, it doesn’t mean it’s not there.😏
Even a few minutes' research on the internet will reveal that the human ear is most sensitive to frequencies in the range 2kHz to 5kHz, with reducing sensitivity up to an audible limit of around 20kHz: however, that upper limit tends to reduce with increasing age.
I've just used a tone generator, which has demonstrated that my upper audible limit is just below 9kHz: it was also noticeable that my sensitivity progressively and rapidly reduced above around 7.5kHz. The experiment also demonstrated what I'd investigated in the past: I have a low volume pure(-ish) tone tinnitus in the range 4kHz to 4.5kHz.
So, doesn't this go some way towards explaining why the low-frequency howl of an engine on start-up appears to be at its loudest, with the apparent noise level reducing with increasing speed and frequency, and with the highest frequency tones rising well above the audible range?
That turned into a fascinating vid! one of those "oh, why didn't I think of that" areas. Thanks! those early centrifugal-flow engines ( Nene, etc ) also have a particular noise which I now guess is a similar interaction.
I'd love to see a walkround of one of the hybrid flow helicopter engines some time - RR Gem is also iirc - seeing diagrams is ok but doesn't beat an expert's fingers. To be clear - I did enjoy the vids so far on the Allison for the boat, I'd just like to see one torn down properly & an expert go around the whole thing & talk about why it's designed how it is.
Hello Agent JayZ, I was wondering if could you explain the loud growling sound of the GE-90s (Boeing 777s) during engine startup, the fuel-burn sound. I was wondering why it is so loud compared to most other jet engines. It's also unique.
Big blades man 😁🤠
Here's an idea from left field - I'm under the impression that the screaming sound produced at the front of the J-47 is actually higher pitched than what is heard, and is red-shifted because of having to "swim upstream" against the inrushing air. :) (not worth a rebuttal, lol)
@ around 10:25, where you are talking about 7 struts/vanes and 16 blades, I wonder if that design feature has more to do with avoiding the deleterious effects of resonance on the engine, than with "noise reduction", although that could be another desirable consequence. Resonance, generally speaking, is to be AVOIDED in mechanical systems. Consider the Tacoma Narrows Bridge.
In the present case, if several blades were aligning with several vanes at various points in the rotation, a shock wave would be imparted at several points round the blade and vane disks, that would not only increase it severity with speed, but far worse, could very likely take on on a resonant, self-amplifying character, when the duration of the imparted impulse was some unfortunate multiple of the time between impulses. With a 7/16 configuration, at any instant, only one blade/vane pair would be subjected to the impulse, and additionally, considering the sets of blades and vanes as wholes, no simple relationship would exist between pulse duration and time between impulses, such as can give rise to resonance and subsequent self-amplification .
Tacoma Narrows was *NOT* resonance. It was flutter.
@@pinkdispatcher Gee, that's funny, when I was an engineering undergrad, my Diff Eq prof used Tacoma Narrows as an example of resonance.
Then, there's what others say:
Galloping Gertie - Resonance and the Tacoma Narrows Bridge
ruclips.net/video/l5Kt0xs_nTk/видео.html
The odd even odd thing applies to steam turbines also for the same reasons as well as preventing axial hammering of the thrust bearings.
there is alot going on there. I hear gears and a electric motor and more gears then air rushing past vanes and turbines.... most of the whine is air shrieking past sharp edges. and then the ignitors click and it starts sounding realy cool!
These are twin shaft engines, the initial noise is the compressor and turbine, the 'gas producer', the secondary increasing whine is the power turbine that's connected to the gearbox.
Also, BEARINGS make a high pitched whine. The faster they spin, the higher the pitch.
Thanks for the school day Prof!
Loach and early jetrangers used the C18 engine
I don't know what that is. The first model of the Allison 250 that I know of is the C-18.
T63
@@AgentJayZ typo yep c18
Love the videos as always. Thanks. I have always wondered how much startup "noise" was gearbox related vs air flowing
Nice, thank you. I remember watching some jet test videos way back when youtube was a new thing. Maybe it was your video I don't know. Anyways, it was of a large jet in just a tent and I remember the tools on the table were literally dancing from the sonic vibrations. This was not a screech, but a rumble sound at startup that went away with increasing the rpm. I always wondered what caused that phenomenon?
That was the RR Olympus in our old test cell. The Olympus is a huge engine, and created a loud bass rumble as it came up to idle rpm. This was cause by the restrictive tail cone we used for testing purposes. I still remember that being the loudest bass I've ever felt.
Nice Doppler effect at the end!
Hi. I have a question.. I can't understand this. Currently I'm start to work on APU engines and as far I can see fuel is injected to combustion chamber on the back then - flow/opposite direction as main flow air in engine and after that is join with main flow.. in main entry stage 1 blades.. I'm not sure is make any sense for you.? Many thanks
Just learned the other day that RUclips is cutting everything above 16KHz in audio so it might cause issues if you ever try to demonstrate this via your videos, even if you manage to actually record it.
When you run the LM2500, will you setup a spectrum analyzer app on your phone to see if it can capture the volumes at different frequencies during various operating conditions? I use a free app called dB Meter to help my deaf A&P student visualize the sound better. It would be interesting to have it running in the same frame with the camera so we can all watch the spikes at different frequencies during startup.
All the dB meters I've seen top out at 130. When I stand 20m from the start cart, those meters hit the pin as the start cart is about 60% rpm, and climbing to it's working speed of 108%.
The start cart is a 90 Hp gas turbine engine.
Those same phone meters are smashed flat by the LM1500 at 100m even before they get to operating power, which is 15 thousand Hp.
The LM2500 we are running is a nominally rated 27 thousand Hp.
You see where this is going.
I have no dB readings on any of my engine test videos, and I have made a few videos explaining that there is no way to describe or record it adequately.
When you are at a test of a big engine, and wearing ear defenders over earplugs... each of which claim a 30 dB reduction, your body tells you "this is very dangerous. get away".
My honest estimate in numbers for the LM2500 is 175 to 180db at max.
In non-numbers: take terrifyingly Earth-shaking loud, and multiply that by ten.
Ok, now ten times that.
@@AgentJayZ: I have an idea! Place a wine glass near by with a camera focused on it and start up the jet engines. If the wine glass shatters, people will know that it's loud enough. 😁👍
Were you talking about MD-500 HELICOPTER? The little bird?
yep. Known as the OH-6 too. en.wikipedia.org/wiki/Hughes_OH-6_Cayuse Looks like a lot of fun to fly!
Horsepower is a noisy business. The "little bird" you're thinking of is the AH6/MH6.
What about that loud whirrring noise on some turbines that happens seemingly right before it reaches idle speed?
what about your mom?
He literally explained it in great detail.
Does the dash on that boat say drive fast take chances?
It's a proven winning formula.
I was surprised to hear that any centrifigul engines still exxisted?
I believe the JT15D found on many bizzjets have a centrifugal compressor, very rare on a turbofan engine.
@@SOUTHENDAVIATION Yes sir that is one for sure.
well done!! and if you want a screech er try the Dart on a Viscount. i heard that the Kuznetsovs on the Tu95 are painful but never had that pleasure.
Absolutely. Used to live on the approach path to Leeds Bradford Airport. British Airways Viscounts, Air Anglia F27s and the odd Herald and 748. Unmistakable and sublime. Not as loud as Concorde though. 12 miles from the airport but could clearly hear take off roll.
Besides the noise from back stages being chopped up by blades as it tries to come toward the front the sound waves from the back would also be cancelled out by sound waves heading toward the rear from the front stage (I remember seeing on TV how sound wave canceling is built into automotive exaust mufflers).
If you look closely, you may be able to see this is not an automotive exhaust muffler.
@@AgentJayZ hahahaha good point
Axial flow jets are designed to eliminate this standing waves on their compressor or turbine stages during their normal operation.
I love the smell of burning jet fuel in the morning
We had French built Fuga as trainer jets. At idle their 2 tiny engines were a screeming whistle.
Would love a turbine engine in my truck, but settled for a turbodiesel lol. I’ve always both turbochargers and jet engines just sounded like massive vacuum cleaners. Being they “suck” by using centrifugal turbines its not too surprising.
No such thing as suction.
Turbines do not move air. They are moved by air.
What you are thinking of is a compressor. at the inlet they create an area of lower pressure. The air rushes in towards this area of lower pressure. That's how a vacuum cleaner works.
Air can never be pulled, only pushed.
@@AgentJayZ True, but I don't know what to say a vacuum cleaner does other than suck, saying inhale or take in like I would for an engine just seems strange to say about what the vacuum's motor does. And to be technical, like with suction, a vacuum cleaner doesn't create anything close to a vacuum, it's just a low pressure pocket of air inside it.
@@AgentJayZ "Air can never be pulled, only pushed."
THIS helps makes sense of the concept.
Morning! Just want to say, thanks for these videos they've honestly really helped to keep me motivated in my area of study.
By the way, anything new going on with the Orenda Iroquois? I sure would love to hear that one running one day.
why does AgentJayZ, with his experience, even entertain such sloppy questions
Just trying to share knowledge with the curious...
Seems as if curved blades would maybe mitigate this some? Perhaps even improve efficiency? Curved in the direction perpendicular to the rotational axis. In the plane of rotation. With the stator blades curved the other direction. Somewhat like the fan on a high bypass turbo fan. Apply a bit of that tech to the compressor. Well hell, apply some of that to all of it really. Dont let the air slide off the end so much.
All compressor blades, and all stator vanes... in every engine ever created since Sir Frank and Hans von Ohain did it in the 1930s... ... ... have been of compound curvature in all three dimensions. It's why and how they work.
Your comment is so great! It's like you are suggesting that light bulbs might work better if we made an electric current flow through the filament.
Even better: just think how much better a camp fire would be if the wood was actually burning!
... although I'm actually sighing... ... ... LOL.
Sorry, but you're decades too late in suggesting this. Compressor aerofoils with so-called 'end bend', or 'three-dimensional geometry', have been around for years. If the technology had obviously been applied to large fan blades, hadn't it occurred to you that the same brains might have applied it to the compressors, where you couldn't see it and where the application wouldn't be so obvious?
@@AgentJayZ Lol1 on the other hand light globe filaments seem to last longer when the current flows around the filament.Mind you the fittings and wires for them don't seem to last anything like as long as they should and the smoke leaks out of them.
they do not make noise, the make great sound...the Huey noise is a combination of starter, turbine
I service gas turbine generators. our engines operates at 750hz. I've been around a few that have suffered F.O.D. to the compresor. omg they it becomes soooooo much louder!
Hello sir, I have a question,
If the turbine use Starter Machine permanently during the fuel firing burn, is it stronger than not use Starter Machine permanently?
The starter has no way of reaching the working rpm of the main engine, its main role is to get the rpm up to a level where the combustion can start being effective and then it gradually looses efficiency up to idle rpm (at most).
So keeping the starter running would mean absolutely nothing for the output (except a draw on the generator if it's powered by internal batteries).
@@sharg0 I appreciated sir, thanks, I am planning to build mini turbine to test 🥰🥰👌 from Cambodia, thanks you!!!!
@@khmertopposter Best of luck! It's not an easy project :-)
If a starter (whether electric, air turbine or gas turbine) remained connected to the engine up to maximum engine speed, there would be a major failure of the starter. Starters are designed to run up to a speed (with a safety margin) sufficient to start the engine and no more.
I have direct experience of an air starter running up to overspeed in flight, as a result of an electrical fault. The starter suffered a disc burst, the debris punctured a fuel tank, there was a major fire and the aircraft had to ditch.
@@grahamj9101 thanks so much , I really appreciate it sir, thanks
Are starter motors loud?
Seems like every engine has an initial low-order(2X), 4X, 8X, 16X are naturally less(intense) noisy harmonic sound...usually a howl kinda thing at 2X and increases to a whine at higher multiples. The higher the harmonic, the less energy(I think). Engine has no choice but to pass through that harmonic band as it speeds up. Interesting
Bell 212 noise doesn't go away, you can hear that bugger 10 miles out
When I read the title and saw the Huey I thought is was going to be about the rotor. It has a very distinctive sound at least when coming towards you. That must be some interaction effect right? The rotor and the tail rotor maybe? Or is the rotor somehow very different from that of other helicopters?
i forgot the exact reason but is has to do that hueys only have two rotors, compared to 99% of all other helicopters out there
The diffent sound is because it's a two bladed prop (more blades at equal rpm means more pulses per second = higher pitch and harder to distinguish individual blade whumps)... All two blade props sound like that. There are also different types of hub but I don't think they affect sound per se).
@@otherw1s3 that's exactly the reason. Two things swooshing past sounds different to three four or more
@@nonsequitor And seven, like the big'uns the Marines have, is just a high-pitched roar.
@@nonsequitor The Bell Jet Ranger also had a 2 blade rotor. I don't remember it sounding like that but I haven't seen one in a long time so I might not remember. And it's a bit smaller too.
For the little pink engine : frequency (Hz) = 7 * 18 * rpm/60
Yes, that makes it go ultrasonic at about 9000 RPM.
Where is that UH-1H located now? ... somewhere in Canada?
In the hangar at Northern Lights College, as explained in the video. Did you watch it?
@@AgentJayZ Jay, I did watch it, but I obviously missed it!
@@AgentJayZ: Are you a licensed pilot, do you get to fly any jets, or helicopters to test them out? 🙂