Not a question... just a massive thank you for what you do. I'm just a regular guy with a passing interest, and wanted to know how a jet engine works. I've now watched loads of your videos and I find them absolutely fascinating. Even though I'm a novice, I think that you explain the very technical terms as clearly, concisely and as understandable as possible. Thank you sir!
You know what's interesting, while some of us have a higher level of engineering experience or just mechanical knowledge and what he says lines up with established knowledge, if you didn't know any of that base material you'd just have to take his word that he knows/knew what he's talking about and not showboating as a guy who pushes a broom around a jet engine shop. =D
Thank you so much for doing these videos and answering questions. I am learning so many things about jet engines that have been on my mind for a number of years. I Have always been interested in this subject but being a big dummy do not know the correct question to ask or things get real complicated real fast and other commentators seem to be all over the place. You have a wonderful, natural gift. Teaching seems to be in your genes. It is also very obvious how much joy you feel when the word turbine is mentioned. You absolutely love your job.
this guy and his videos are awesome. the bleed valves are like a compression release in older, bigger motorcycle engines that you couldn't kick over unless you released some combustion pressure
thank you for the information regarding the bleed air. I'm working as a process control tech, one day we had a problem in one of the power generators. They were GE gas turbines with GE redundant control system mark VI. Operations couldn't start the generator because of a problem in the bleeding valves, there were only two bleed valves. After tracing back inside the turbine compartment, we have noticed that the bleed valve actuators are operated by the turbine's compressor output and this compressed air was controlled by a solenoid valve located in the accessory compartment where you will find the lube oil system ad the started motor with. After testing the solenoid alone by forced signal through the control system, we have found it functional and healthy. We asked the operation to try the generator for another start " cool down between every start was set at 30 minutes". Again another failure in the bleed valves. At the end we had managed to test the valves actuators alone together at the same time by using an external source of air supply and found a big deviation in time, about a 22 seconds difference. It was confirmed that this wasn't normal, and the main issue was in the second valve actuator leakage. It has been replaced and the deviation was set to be less than 3 seconds after the second startup of the gas turbine. The limit switches on every valve actuator was the main reference to us, because it was unsafe to start the turbine while the doors of the compartment were open. My questions: Are aircraft engines equipped with the same setup? Is this a real issue in aircraft engines? Are the bleed valves in the aircraft engines designed to also be used as a surge protection when startup? sorry for the long story, thank you again for your explanation.
We used bleed air on our ships for a lot of various things. Masker air was used to make the ship sound like a rainstorm to submarines. Prairie air to come out of the leading edge of the prop to change the signature of the ship. Anti-icing air for our intakes when it gets below icing conditions. We could also do cross bleed starts to start other turbines.
AgentJayZ I've been Netflix style binge watching your videos. My question is about the bleed air valves. Is the purpose of the valves to unload the compressor to allow for it to reach the target rpm unimpeded by compression resistance? Thanks
Bleed air valves are for air start purposes. Bleed air from the 13 stage or whatever the manufacturer deems is for deciding and air conditioning packs. On the Lockheed C 130 I worked on, you start #1 engine then open bleed air valve so the manifold is filled with bleed air to start #2,3,4 engines. Great video! (You must start the APU to utilize it's bleed air to start #1!)
Ive always had the understanding that "bleed air" had 3 types (as you said). Starting purge, running balance/cooling (the air sent to the center bearing is also needed for air flow stability along with cooling), and service air (used for running services outside the engine.
Funny you should know I grew up in rural Manitoba... my first jobs were all farm related. When I was a teen we flew Cessnas and Cubs like motorcycles and snowmobiles. Later working with the turbine crop dusters they always had trouble with bleed valves and shut downs. I've never flown an actual jet but the few times I flew those planes I was told if you can't land it you'll die and if you hurt it, the owner will kill you instead.
Great video. You opened up a can of worms with this subject. There are so many different uses for bleed/discharge air. You have everything you talked about plus more depending on the engine. There is labyrinth seal pressurization, engine anti-icing, aircraft inlet anti-icing, fuel system purge, emergency oil pressurization, balance piston seal pressurization and much more.
In my previous experience bleed valves were called "blow off valves" in industrial centrifugal compressors. Those would be open until the compressor reached operating rpm and would slowly close after the VIGV reached maximum opening perecentage. Then the VIGV would close slowly and modulate as per requirement. That was done to prevent the compressor to go from idle to load all of a sudden which can cause surging.
Jay, several military helicopters use turbine engines that use a bleed air system you may not be aware of. These engines include the T53 (all models), L-712 (to include the L-11 or L-7-11and all following models). There are many more gas turbine engines that we use in the military that use the same bleed air system. However, none of these same type systems use the air... for ANYTHING. These engines produce an excess amount of compressed air by the time it reaches the centrifugal compressor. So, to control over compression in the outer combustion chamber there is a system of bleed air that is comprised of a large vacuum operated bleed valve that in turn opens a bleed band that surrounds the case halfs usually just after the second last axial compressor stage. The band is a stainless steel band that when tightened it prevents bleed air. Whan the actuator is in open position the band allows a specific amount of air to escape right to the atmosphere as directed by several other system.... such as the fuel control, the torque sensor and for some a few other sensors. This bleed air system was the real first coined 'bleed air' because it is what it is, just bleed air, not 'service air'. But service air didn't sound right so any system using the name calls it bleed air. A truly well engineered turbine engine shouldn't need that kind of bleed air system... but it does. For ninety percent of all other engines... that's wasted service air. PS: Also, these same engines use a separate bleed air system that actually is used for service air. Most are just used for 'anti-icing' around the intake cowling. This air is of the highest pressure as it comes from what we call the 'hot air gallery'... and yes, after being squashed as it does in a turbine engine... it really does get hot. This gallery sits right over the blades of the centrifugal compressor. The point at which the air is at it's hottest. As we techs know... hot is bad, even for intake air. The hotter the intake air is... the less expansion it is capable of during combustion.
Cool, I was about to ask what exactly it was. When he said that it was a single-spool turboshaft engine I figured it had to be a mechanical load. Neat idea to use what you already have and where you have a good idea about its power consumption. But sucking/blowing air through these sharp-edged variable holes is certainly going to make a huge noise. I was aware of all the different kinds of "bleed air", but never thought about the possible confusion. Another major use for "customer bleed air" is wing de-ice/anti-ice in most jet airliners.
I want to thank you for this and all your videos, this is good infromation about the air bleed valves. When the engines starts, it makes easier to turn the engine and other reason is to cool down other componets of the engine. There is on point, the turbo prop entgine, this one doesn;'t use the power turbine. Thanks a lot. Please send some snow to here.
JORGE E Thomas they are there to prevent destructive compressor surge in axial flow compressors...they require minimum flow .....all other uses of bleed or recycling valves is sympathetic....
Hi Jay, Thanks for the full explanation of 'bleed air'; it seem all kinds of systems like to suck air off of the compressor! Please note that I placed 'air' in between 'suck' and 'off'!! That homemade load machine is interesting & sounds like it would work to me, however most likely very noisy! I'll be watching for that video... Darren
On the R.R. Alison turbine engines Ive worked on, for helicopters, the bleed air port has 2 functions. When the engine is at 60% or idle, air blows out of it back into the atmosphere so that the compressor doesn't blow the flame out in the combustion chamber. at 100% the airflow reverses to help feed the compressor and keep the engine cool. It all happens with no moving parts, its just part of the design of the compressor fan (13:1) in this case.
One part you may or may not have mentioned on here what bleed air is used for besides a/c, cabin pressurization. It's is also used for de-ice on the leading edges of the wings, vertical & horizontal stabs, windscreen and engine inlets. Also engine starting either from an APU or ground start cart like you use to start your engines at the test cell and to help pressurize hydraulic systems. I work on KC-135's and seen the different ways bleed air is used. There are great videos on RUclips that go over the bleed air systems of many different aircraft types like from 737 to a 747.
Jay, at 3:53 you talk about cooling the sump. Is there also a rotary pump that draws the air and oil out of the sump? Also, tell your developer to build a heat sink and install it around the ad on compressor. Have the working engine draw air through the heat sink. (naturally the heat sink needs to be configured right.) When the pressure drops around the heat sink, heat will be forced into the air. You will yield more psi and the process will be much more efficient.
The scavenge pumps on this engine are gear pumps, and they are designed to handle a mixture of oil and air. Most of the cooling air exits out of the sump vent, but some of it is in the form of bubbles in the oil drawn out by the scavenge pump. The scavenge pump has a greater capacity than the amount of oil being pumped in.
... and for the heat sink idea... I think I'll leave the design just the way it is, the way the hundreds of professional engineers working for years on this project intended it to be. No matter what anyone thinks about their "innovative" or "game changing" idea... they have to remember the ability and talent they are attempting to improve upon. I do, and so do all the rest of us. Cheers !
I know that you are somewhat sensitive about answering questions that have already been answered.....completely understandable. However I have been trying to find the answer to this question in your videos and I have not yet had any luck. So....I will ask: Is there a quantifiable limit as to how much bleed air an engine can divert away from the combusters without effecting the performance of the burning of the fuel? A large commercial jet obviously uses vast quantities of compressed air to run various systems....is there a practical limit as to how much can be used without effecting thrust characteristics? Thanks much!
Bleed air is bled from the compressor to be used for a lot of different purposes. If air was bled from the combustors, there would be a lot of extremely hot and high pressure air and burning fuel that would ruin various engine and airframe accessories and components. Hope that helps.
Holy balls, that thing is going to be putting out a lot of air. I love it! I assume the goal is to get the company more involved with rebuilding and testing those -501 engines?
We share our test cell with Maddex Turbines, and they already do a lot of 501 work. This new setup will allow us to measure torque on the output shaft under full power. It is a specific request made by an important customer that uses these engines to produce electricity. And yes, we will have a 3,500 Hp air compressor on our hands...
Excellent description of a complex subject. Those two side by side bleed valves...can I think of them as a sort of "Compression Release" for startup purposes ? They let air bleed out during startup, to allow things to get up to a self sustaining speed more easily, without so much resistance? The other types I understand from your description...
+SquillyMon The bleed valves prevent aerodynamic stall of the compressor blades at lower rpm, allowing the compressor to function. It would be more accurate to say that they increase compression. It helps to ignore everything you know about piston engines.
There is also a bleed air exit (I guess from the 4th stage of the Compressor for this case) that is used for anti-icing of the inlet guide vanes, am I wrong?
I realize it been almost 5 years since this video was posted but Back in the late 60's when in the USAF I ran the P&W J52 P3 in combined systems test cell of the AGM28B Hound Dog Missile and it had a series of bleed Valves around the compressor case at about the No 5 or 6 compressor wheel. I remember I had to check them when activated from the control room during the engine check portion of the combined systems check. What was the function of these bleed valves on the J52 P3? Any Ideas?
I have a question for you ? I am a AD in the Navy i work on the T-56A-14 or 501. Why is it that that you guys are taking the air on the old compressor section from the bleed valves on the 5th and 10th stages vs the 14 stage on the diffuser section, wouldn't you rather have 14 stage bleed air?
Regarding cabin bleed air (air passing from the compressor directly into the cabin) is it safe to assume that the smells of fuel inside the cabin, are from worn bearing seals, or from jet fuel that somehow flows in that direction? I travel a lot and some planes smell more that others. I love your efforts here and actually bought the gas turbine book that you showed us. Keep up the good work!!!
Fuel is introduced well downstream of any compressor bleed. A leaking front bearing seal may allow oil into the bleed air, but usually bleed air does not directly pressurize the cabin. It is used to run a small compressor, much like an automotive turbocharger, so that there is no way engine air can get into the cabin. That's as far as I can go, because I'm not a plane guy.
I have been studying the dynamics of internal shockwaves ( Mach+). Do you know of any good material on this as it pertains to turbine engines? Can you explain any of it in layman's terms? Thanks JayZ for all the knowledge you share!
Most airflow within a standard jet engine is subsonic, remembering that the speed of sound is not constant, rather a function of fluid temperature. So throughout the core of the engine, the speed of sound varies due to temp differential. Once outside, however, it's a function of the ambient temp. This also applies to the inlet. That's why variable geometry intakes are required for high performance aircraft. As AgentJayZ mentions, down below, have a gander at the Rolls Royce book "The Jet Engine". It's basically the sumpy's bible.
I have one for you JayZ. On a recent trip to the UK from Tampa I flew on a British Airways 777. At ground idle the RR Trents moaned so loud it was unpleasent. It was the sound turbpprops and jets make when they go through the startup procedure but didn't go away until takeoff power was applied. Any ideas?
Coulda been bleed valves. The RB211, which is an early design that was developed into the Trent series, has three stages of bleed valves. Once the last stage has closed, the engine begins making serious power. Could also be resonance of the fan. Like everything else in a jet engine, it's designed to work best at its rated output. At idle it's not exactly happy.
Agent Jay z... I have a question but it's not about the bleed valves/ air. where do carbon deposits on the main oil filter come from specifically for PT6A-27?
Is the cooling air that cools the bearing also what pressurizes around the bearing inclosure to keep oil that gets past the seal out of the engine? what would the range of air pressure and what temps would you see when engine is at operating power? Is the air that is used by the plane systems closed circuit like when a car uses vacuum servos where there is no leak of pressure or vacuum in cars and just the pressure itself is doing the work? Thanks for the hard work you have a first rate site.
Yeah the internal cooling air is also used for seal pressurization, in both labryinth seals and pressurizing some carbon seals. The pressure depends on the engine type, engine compressor ratio and where in the compressor the air is taken from. The bleed air used in aircraft systems like air conditioning, anti-ice, cabin pressurization is exhausted overboard once it's been used, so it's not a closed circuit.
The big disadvantage I see with the single shaft systems is the power needed for starting. You've mentioned the LM1500 and LM2500 are started with about 100hp, can you give an indication of how much hp this engine needs to start? I imagine it would be quite a bit higher than engines producing thrust or powering a free power turbine. It also looks like this load system wouldn't produce much load until the engine got to running RPM. I imagine that would make starting easier than normal, right?
Jay you have gone over several bleed air, on different engines, but can you find or create a video that shows how the two different systems work (Bleed Band System, Bleed Valve System). I have scoured FAA.gov, 8083, and jeppessen books and the best i can find are some poor drawing diagrams that don't explain or show their functions well at all. thank you.
Here is a quick wiki explenation on tip clearence. I'm sure AJZ will be able to explain this better with drawings and actual engines with this feature. By reading this, it seems it is related to the bleed air system. I'm going to search for some schematics and see where some engines have this system mounted. Wiki- Active clearance control (ACC) is a method used in gas turbines to improve fuel efficiency. This is achieved by controlling the tip clearance. It is particularly effective on turbofans since they are required to respond quickly to changes of the thrust setting. The active clearance control consists of the ACC valve which receives the air from the bypass duct and routes the air to flow over the pipes surrounding the turbine casing which in turn reduces the thermal expansion of the turbine case and maintains the accurate clearance between the turbine case and the blade tip. This clearance should be maintained accurately which is essential for the engine efficiency and its performance. The ACC valve opening is adjusted automatically by the FADEC system depending on the throttle position.
Alfredo Pacheco Jr hey Alfredo thanks for the response, I still don't get it does the bleed air mass flow control the width of the case opening, so shouldn't the thermal expansion and contraction reduce the life of the turbine, how does the FADEC know the initial expansion of the engine if it was thermally deformed completely in the first place.
I saw a NASA or theory paper on this. The amount of formulas used was mind boggling. For the FADEC to be able to control tip clearence by controling thermal expansion, all the variables would have had to be programmed into the system. So engineers have plugged in all the formulas to monitor outside air temp, inlet temp, compressor speed/temp, thrust settings, etc. These calculations would be done at lightning speed with every change of the thrust lever. I'm sure they came to an average setting that gave the best results for tip clearance as each and every use of the engine is always different. As for the control, it just sends the "right" amount of air over the case to try and maintain as level of a temp as possible to reduce thermal expansion. Again, the formula for that was so long, I feared trying to copy and paste it. So I'm not even going to try and think what the hell it means.
Here is the NASA paper with the formulas: Dynamic Turbine Tip Clearance Model for Clearance Control Prototyping mece.utpa.edu/Kypuros/publications/NASA_TM_Kypuros03v2.pdf
Thx for this once again! 3500 HP compressor? Hook this up to your engine-lift-thing :-) (Maybe open the roof first...) I would like to wish you a powerfull pre-christmas time! Can't wait for the next vid!
another great video thank you for the effort just to educate us very selfless on your part and I appreciate it. question for you the bleed air you called customer bleed air for systems on plane is this the same one planes use to start other engines with or is that a different bleed air outlet? looks small for the size of hose starters use but I don't know. Thanks again Jay
Jay, On the Spey bleed valves, are they not also used beyond startup? I thought they were operated through the intermediate percent range and closing up at high power? Fully/partially open at idle? Do they not kinda mirror the function of VSV's? Thanks as always, hope we all get to see the Allison run! That should be a noisy and breezy test cell!
The Spey has bleed valves for both the LPC and the HPC. By the time the engine gets to what might be considered the bottom of its working range of rpms or power settings, all bleed valves are closed. Bleed valves are there to help get the engine started, and also to get the engine from idle to significant power... You are right: there are two ways to avoid stall in a high-performance compressor - bleed valves and variable stators. Variable pitch compressor blades would also work, but nobody has done that yet.
hi sir.. thank u for ur nice efforts. I have a question about ,is there a difference between compressor bleed valve which is used to avoid compressor stall and surge and a bleed valve from which bleed air is usually taken for the purpose of de-iceing,cabin pressurisation,etc
Regarding the bleed air uses, what kind of pressure(psi) and air movement(cfm) run through the bleed air systems?(as in the Orenda engine I figured that the different uses of it require different amounts of air and use "restrictions" in some fashion. Love the channel Jay!
For the internal engine air bleeds for cooling... I have no idea; the rates of flow are not listed in the engine information manuals, and the pressures will depend on engine rpm. The customer bleed air is variable on demand, and it's pressure will depend on what stage of the compressor it is sourced from. Different designs for different engines. The airflow through the bleed valves depends on when they close, which is different in different engines, but it is very large.
I've always wondered what compressor stall is, ive read descriptions but they are all a bit abstract so hard to get my head around. Especially when the air reverses flow and flames come out the front, i really don't get how that happens.
Stall/surge is primarily an axial flow problem (tho not exclusively so, I should add). It's because an axial compressor works thru a series of convergent (accellerating) and divergent (pressure recovery) ducts. A divergent duct works closely to its designed airflow limits. Outside of this, the airflow becomes turbulent and stagnates. However, the compressors in front of the stagnated section are still compressing so all of a sudden that air can no longer pass thru the engine and must go out the only way it can...thru which it came. And BOY do you need a change of undies if you hear one up close! I should mention this is a rather simplistic explanation, but I hope it helps.
ajz - understand the air systems, but im curious what type of alignment is used between the engine and your test/load cell - obviously the turbine will heat up as load is increased so was just curious what alignment considerations were taken while bolting these two units together
The coupling shaft is splined on both ends, allowing for axial movement. The forward compressor is rigidly mounted. The engine has one fixed mount to secure its location, and three floating mounts to allow for axial and radial changes in size.
I am confused. My prof told us that bleed valves, or what he called them, bleed hatches are used to bleed off the excess air in order to avoid surge of the compressor. Though, maybe he was right partially, since the only showpieces we have in our uni are the vintage soviet engines, and their age vary from 40 to 60 years or even more, and the older the engine, the more unorthodox it's construction is.
Great vid, once again, thanks (missing playing with donks). Now with regards the inlet appertures on your load compressor. What's the risk of inducing compressor stall on the load unit? It must surely induce majorly turbulent airflow onto the first stage, doesn't it? Have you done a video of the unit running? I'd love to see the results. Thanks, once again.
I noticed you said that the bleed valves open on the 501 because the high pressure section can't handle the air from the low pressure section on start. That makes sense but I guess I am confused because you later said the 501 was a single shaft engine. Why are the bleed valves needed on a single shaft engine lacking an HP system? Thanks!
Dan8432 I meant the lower pressure stages at the front of the single shaft compressor are more efficient at low rpms than are the later, higher pressure stages on the same rotor. It does get confusing sometimes.
Hi Jay thanks for the video. I'll bet with very little effort that restrictor plate could be turned into the world's loudest whistle if it isn't already. On a more serious note though, regarding alignment of that load to the main engine: in prior videos you've said that for the engine it is the rigidity of the individual sections that forces the alignment to be perfect during assembly. Is it the same for that forward extension out to the load compressor some feet away? (I know you said you're just a bystander, but I'm wondering just same - how do you get that load perfectly aligned with the jet so it all won't be out of balance and shake apart).
Amazing video! So that is basically the same concept as an engine dynamometer used to produce a variable and measurable load to test the performance? How is the output tq being measured by the driven compressor? Is this as simple as psi air to percent aperture will equal tq required to produce and how are these numbers determined or is there some type of load sensor directly attached to measure output? Thank you for the great videos!
Hi Jay, thank for your work in the videos. Question, does that load compressor for the turbine have any clutch system or just adjusting the air intake you can put no load bellow IDLE?
@@AgentJayZ thank you very much. How you will measure the load? Sorry the questions. I develope a turboprop and i want to make a non regular dyno and this is awesome
What I would like to know is the history of the use of compressor bleed for customer pneumatic power. What was the first engine to be designed with a system specifically to tap air off the compressor for airframe pneumatic power? What was the first aircraft, military or civil to use compressor bleed for pneumatic power? I'd also like to know what the first aircraft was to use an air cycle machine or pack for environmental control.
hey sir, do you know why one of the air vent, 9 0'clock position from aft looking forward, is pointing down and other one, 3 o'clock position, is pointing up on the diffuser section? thank you.
AJZ, Good video about bleed air. In an airliner does the cabin ventilation and pressure come from bleed air? If so, what is the proximate cost in loss of engine efficiency ? The reason I ask, in the early days of jet airliners there seemed to be never a lack of cool air in the cabin but now you get baked until you have reached 10,000 feet or so. I think cabin air is being recirculated to cut down on the use of bleed air off the engines to save fuel. Thanks for you time, John Valos
In airliners, it all comes from the bleed air. As for the A/C, the bleed air will cause parasitic power loss. It all depends on the many factors to determine the amount of loss. One method to help ease the use of bleed air for cabin cooling/heating is the use of the "Recirculation Fan". Larger engines don't experience as much power loss as would smaller engines. If you look at the King Air 350, when you apply prop and anti/deice heating, you get a significant loss of power. The more equipment/systems that demand for bleed air, the more the engine must work to compensate for the loss of air flowing through the engine. If you want to get more in-depth, I'd suggest checking this site out to get all the technical info: www.b737.org.uk/index.htm
Also, in regards to the loss of engine efficiency question, it all depends on the ITT (Inlet Turbine Temp). When you use bleed air, your taking away cooling air for the turbine. The more or higher demand for bleed air, the less cooling air you will have. This will cause higher ITT's. So, to prevent this pilots will lower thrust settings to compensate for the increase in ITT. Most of today's engines have an updated FADEC that can do this automatically. Some, however, must be monitored manually (like the CRJ). So the "loss of power" that an engine will have with the use of bleed air is based off how much cooling air is lost and how much less the engine must operate to not exceed ITT limits.
Here is a forum discussion about bleed air and power loss in turbofan engines. forums.jetcareers.com/threads/turbofan-power-vs-bleed-air-extraction-the-mechanics.86319/
I think you are right, John. You can feel nowadays that the A/C doesn't come on until takeoff, and the engines are really working. As with any business these days, penny pinching is the whole strategy, and any bleeding of air from the compressor of a turbine engine reduces the power output, so for a given power, it costs more fuel. Aircraft designers and engine engineers are fine with that, but it really bothers the accountants, and they control the world, don'tchya know...
Some turboprops, like those using a P&W PT6, have the prop on the turbine side rather than the compressor side. Is there any advantage pointing one engine end forward over the other?
Actually, the differences are deeper than that. The PT6 has a free power turbine driving the prop reduction gearbox, while the T56 is a single-shaft engine. The relative merits of each design as an aircraft engine is a subject beyond the scope of this discussion.
Erik Pearson The reasoning I have heard for having the PT6 pointing "backwards" is that the shaft from the free power turbine to the prop reduction gearbox can be made shorter and lighter.
I saw your video while I was searching for an explanation about active clearance control(ACC) but the video was about bleed valve and bleed air .it would be helpful if u could explain about ACC in modern tubofan engine such as ge90/genx.
Do you know why that compressor used for load has 8 bleed air "points" attached in groups of 4, where the first group doesn't have any valve, does that just produces drag? Thank you
The engine has 8 bleed ports, each of which has a bleed valve attached. The "extra" compressor, attached to the driveshaft coming out the front of the engine, is of identical design, but the bleed valves are not there. We've connected the ports with tubing, and installed manually controlled valves on the tubing manifolds.
It's more complicated than that. The bleed valves are not there to unload the compressor at design speed. They are there to increase air speed through the compressor at lower rpm to prevent stalling. When a compressor stalls, it stops working, and it requires less power to turn it. So... at operating speeds, opening the bleed valves would unload the compressor, but they are not used that way. At lower rpm, the bleed valves must be open to allow the compressor to work; closing them would cause a stall, which is not good for it, but also technically unloads it. I suggest you watch my video about compressor stall.
Great Videos and something i like to watch. I have one question i.e. you said the HBV assist in starting? I thought they are there to help in surge operation to release the pressure from compressor.
+Ninety Nine They help the engine to run at very low rpms without having the compressor experience aerodynamic stall. That region of operation includes starting.
I was wondering if you could explain how blow off valves (or BOVs) function? It is my understanding they are operated not just during startup and are activated somehow by a pitot tube measuring airflow velocity and are hydraulically opened/ closed. Is there some sort of control unit in between? Could you clear this up?
On the bleed valves in the beginning of the video, how is it that they assist in starting and allow the compressor to function, if the air is coming out of the engine? Thanks!
Great video Jayz, well explained. On the topic of engine loads, I assume if you translate this to a turboprop, the prop being the load. On turboprops I usually see that the prop itself starts turning a short while after you hear the turbine start up? Is this because as the engine rises in RPM the prop starts to turn because of the reduction gearbox? Or is the prop on some sort of clutch that engages at a certain engine RPM speed? I notice this when flying in the De Havilland DASH 8 aircraft quite a lot. I hear the engines wind up and finally the prop starts to turn. If anyone knows the answer I would really like to know as I have searched the web and not found a definitive answer on this one. the same happens on helicopters. The turbine starts and then slowly the blades start to turn. Many thx
The Dash 8 uses the P&W PW100 series turboprop engine, which has a separate "free" power turbine, connected via a reduction gearbox to the prop. That is quite different from the T56, which does not have a separate power turbine. Both engine types have their advantages and disadvantages...a discussion of which would require pages of text, or a few pints at the Flying Beaver.
AgentJayZ In the Aurora/P3 (T56), the turbine output is fed to a 13:1 (roughly) gearbox that translates the 13000 engine rpm down to a useful 1000 rpm prop speed. There's also generators (on 2, 3,4) and compressors (2,3) that suck power from the engines but provide useful things like electrical power and pressurization. At flight idle, the engine turns at full speed (100% rpm +/- a couple %) and the prop is at flat pitch... no thrust...more or less. As the power levers are increased by the pilots, the prop pitch increases and they try to slow down, but the fuel flow is increased in response to keep the props/engines turning at 100% rpm. Max thrust/power is determined by the TIT (Turbine Inlet Temp). Higher temp=more power (up to a limit of course)=shorter engine life. You can pull more power if you have to (bagging an engine at take off), but at the expense of reducing engine life. Engine/prop RPM deviation (more than a few %) in flight is a real problem and indicative of something going bad somewhere.... as is the "chips" light for the gearbox which indicates the gears are starting to come apart.... Flying Beaver Jay?!?! LOL... let me know the next time you're in town and I'll buy the first round!
CP140405 Thanks for the info Jay and CP140405. When on the ground and starting up one of these turboprops, does the prop start to move freely at a given turbine RPM or is it "engaged " by the pilots? Jay mentioned a "free" turbine. I am just trying to understand the process by which the prop starts to turn as the turbine increases in rpm, I assume it is connected direclty via the gearbox to the turbine with no clutch or device that can "release" the prop. Wish I could join you at the Flying Beaver, but its just a tad far for me being in OZ otherwise I would shout you all a cold one. cheers
Hotdogger808 Well, one of "these" turboprops has the propeller directly connected to the main and only shaft in the engine, through a reduction gearbox, but no sort of clutch. So the prop moves as soon as the starter begins to move the engine. But... there are two types of turboprops.... Other engines, like the P&W PW120 series, have a free power turbine, which means the prop is not mechanically connected to the engine shaft. The coupling is aerodynamic, and gets more effective as it reaches its operating speed. On these engines, the prop sometimes takes a few seconds before it moves. The T58 is a free power turbine engine, and we look at the "coupling" in Pt 8. of the series.
AgentJayZ It's true... on the T56, the prop starts turning as soon as the starter is engaged. I remember the "chatter" over the intercom quite well... "Clear to start One" "Selecting One" "Starting One" "One's turning" (pause) "Ignition" "Fuel Flow" "Light Off" "Temperature Rise"....
AJZ, if there is no load on that engine for some reason due to a failure of the props or shaft, you said it would not be a good thing, would the engine be damaged? Is there a way the engine powers down automatically if this were to happen?
Answer to question 1: It will overrev, i. e. turn to fast and ultimatly disassemble itself because the centrifugal force is too strong. (Yes I know that the centrifugal force is a phantom force percieved in a rotating reference frame, all ya screaming physicists) Answer to question 2: I don't know. But you'd have to react major fast.
saxonlight what he was referring to was the load on the shaft. Because this particular engine is a single shaft, it must have a load on it. If the engine did not have a load, the engine would continue to spin, beyond its designed limits, and eventually destroy itself. All aircraft engines can not automatically shutdown. This is for the safety of the crew. You don't want a computer malfunction and it kills the engine right in the middle of takeoff. The pilot is the only one capable of shutting down an engine. But there are turboprop and turboshaft engines that can run without a load. These have separate or dual shafts. One for the gas generator and compressor, the other for the power turbine. However, this specific engine can be shutdown in-flight. There are videos of C-130's and P-3's with an engine off and the prop lock engaged.
Alfredo Pacheco Jr Yes mate. And he referred to a scenario where the load would become 0 suddenly. And if this engine has no load it overrevs and rips itself apart into it's own components like the compressor blades, the stators, the turbine blades...
Disassemble is a nice way of saying destroy itself. To see what happens to turbine discs when they overspeed, google "turbine engine failure" and look at the wikipedia article. At the bottom there are notable uncontained engine failure incidents. It's very nasty business but fortunately it happens extremely rarely. Multiple things need to go wrong (or need to be manufactured wrong) in order for an over speed to happen
Agent... are these "bleed valves" similar to a surge valve on a JT8D? Id like to see a surge valve and how it actuates/commonly fails to modulate closed on a JT8D
Hello sir, can I ask a question? I had a problem from 2 months ago about bleed air temperature out of limits. Until now, I did'nt understand the problem. Hopefully you give an answer to this question. thank you.
so there is customer "bleed air" for aircraft usage, and then there is internal cooling air, that's the air ducted thru the engine thru pipelines and valves used to cool certain parts of the engine most specifically, the combustion section and the turbine section. But what about the external cooling you were talking about? like I know that it mixes with the gas path downstream of the exhaust, but what does it specifically do?
@@AgentJayZ I've just recently found out your channel, kinda nervous about an upcoming exam so yeah :) what books would you suggest? I'm really sorry for these urgent questions.
why don't they call the bleed valves compression release? also, on the engine "dyno" don't you need a valve on the exhaust side of the compressor more than the inlet or is there enough restriction in the end plate that the bleed air system will do? i assume the intake restriction is for unloading the engine at startup. if you were to shut the intake valve quickly while the "dyno/load" was at high load, would it attempt to stall the compressor?
+jon “tweakit” spon 1) because that's not a good description of what they do 2) restricting the inlet is more effective than restricting the outlet. Where is the throttle plate for a piston engine? 3) that is the basic idea, although we may need to restrict both the inlet and discharge...
I never thought about how the engineers would have had to make so many provisions for air...like the blanket of air that surrounds the flame to cool it... No wonder jet engines can handle such an enormous flame within!!! Prior...I just thought it could handle those temps magically...and i was correct to always question that in my mind... AWESOME!!! Not understanding something mechanical, and knowing that I don't, bothers me, seriously.
I have a little CAE-140 engine from a MA-1 GPU and I see a compressor bleed air path for a couple more functions. One assists in the actuation of the butterfly valve for the main compressor bleed (from the start cart), and the other leads, via a filter, to the hydromechanical fuel control unit. But maybe these aren't considered 'bleed air' because there is very little actual flow of air?
They will, most likely, be servo or sensing pressures as opposed to bleed air. Though I am unfamiliar with the type of donk you're referring to, this is pretty standard for most turbines.
Of the three types of "Bleed Air" discussed; which is responsible for Engine Surge and how does clearing a surge (throttling back) prevent an engine from destroying itself?
The bleed valves are the ones you mean. They help offload the diffuser at lo-rpms because the engine compressor is so efficient. With regards stall/surge conditions. once established, the bleed valves have no control over them (as far as I know...certainly not from the ones I've worked on, anyway). That is purely a function of offloading the engine, either thru decreasing the RPM on a variable speed engine or thru offloading engine pressure with a constant speeder such as the 501. However, sometimes this just isn't possible, especially if the engine has suffered a mechanical failure. In which case, it's time to reach for the yellow and black painted handles and hope for the best.
MrShobar The compressor has 10 stages, and at full rpm, the compressor ratio is 5 to 1. The temperature of the air discharged from the compressor at 100% rpm is roughly 245C.
So does anti-icing fit somewhere into this? I remember seeing in another video where bleed air was routed to the cowling to prevent icing so would there be any other parts of the engine like maybe the inlet guide vanes that would require that? Thx for the vid!
Hi... Not sure if this is a 'dumb question' as you say... but here goes anyway... Is this not a super complicated way of putting a load on a turbine under power. Maybe I'm oversimplifying things here... but could you not just strap a variable pitch prop (via reduction gearbox) to provide the load then increase or decrease the pitch to vary the load?
+Mac Anix That's a lot of machinery, and the prop would be mounted high up in the air. The mount for the prop would need to handle the torque produced by the prop, and the thrust of it. It would not be simpler, and require a lot of setup time.
I'm guessing, based on your avatar pic, that you are a professional. So let me start by apologizing for your having to see those... Those flow pipes are "home made" out of regular automotive exhaust system tubing. They were welded by a well meaning technician who is not employed as a welder. I think those are MIG welds. They are prototype test cell equipment, and would never be used for any length of time on an industrial working engine. The thought of using them for an aircraft engine has never occurred to anyone ever. Thanks for not throwing tomatoes at your screen.
AgentJayZ. Haha thank you for taking the time to reply. I am a professional doing some indep. research on bleed valves and Titanium bleed ducts. Found your video helpful and was just curious about the piping system you used.
Hello! I was wondering if there are any concerns of adverse affects to a compressor when airflow is restricted? Will the compressor be more likely to stall?
Anything that reduces the axial velocity of airflow through the compressor can cause it to stall. It's a common misconception that the IGVs control the amount of airflow... I used to think that way. They only control the angle of the air, and therefore the angle of attack of the blades. Under normal operation, air flow is never restricted at the inlet of a subsonic compressor.
Thank you for your quick response, your videos are excellent! The first sentence of your response was what I was thinking about, in regards to the Iris system for controlling inlet airflow. I hope the test went well, seems like an ingenious solution for loading an engine!
The air dyno will be compressing air and releasing it through restricting orifices. This will cause the air which passes through the dyno to be at a higher temperature as it comes out.
Not a question... just a massive thank you for what you do. I'm just a regular guy with a passing interest, and wanted to know how a jet engine works. I've now watched loads of your videos and I find them absolutely fascinating. Even though I'm a novice, I think that you explain the very technical terms as clearly, concisely and as understandable as possible. Thank you sir!
Hes the master
John Clarkson right on
You know what's interesting, while some of us have a higher level of engineering experience or just mechanical knowledge and what he says lines up with established knowledge, if you didn't know any of that base material you'd just have to take his word that he knows/knew what he's talking about and not showboating as a guy who pushes a broom around a jet engine shop. =D
This is the best explanation anywhere. Thanks! I teach at FSI and I have guided many low time pilots to this video.
Thank you so much for doing these videos and answering questions. I am learning so many things about jet engines that have been on my mind for a number of years. I Have always been interested in this subject but being a big dummy do not know the correct question to ask or things get real complicated real fast and other commentators seem to be all over the place. You have a wonderful, natural gift. Teaching seems to be in your genes. It is also very obvious how much joy you feel when the word turbine is mentioned. You absolutely love your job.
this guy and his videos are awesome. the bleed valves are like a compression release in older, bigger motorcycle engines that you couldn't kick over unless you released some combustion pressure
thank you for the information regarding the bleed air. I'm working as a process control tech, one day we had a problem in one of the power generators. They were GE gas turbines with GE redundant control system mark VI. Operations couldn't start the generator because of a problem in the bleeding valves, there were only two bleed valves. After tracing back inside the turbine compartment, we have noticed that the bleed valve actuators are operated by the turbine's compressor output and this compressed air was controlled by a solenoid valve located in the accessory compartment where you will find the lube oil system ad the started motor with. After testing the solenoid alone by forced signal through the control system, we have found it functional and healthy. We asked the operation to try the generator for another start " cool down between every start was set at 30 minutes". Again another failure in the bleed valves. At the end we had managed to test the valves actuators alone together at the same time by using an external source of air supply and found a big deviation in time, about a 22 seconds difference. It was confirmed that this wasn't normal, and the main issue was in the second valve actuator leakage. It has been replaced and the deviation was set to be less than 3 seconds after the second startup of the gas turbine. The limit switches on every valve actuator was the main reference to us, because it was unsafe to start the turbine while the doors of the compartment were open.
My questions:
Are aircraft engines equipped with the same setup?
Is this a real issue in aircraft engines?
Are the bleed valves in the aircraft engines designed to also be used as a surge protection when startup?
sorry for the long story, thank you again for your explanation.
It's hard to make a comment since I don't know which engine you are talking about. Not all industrial gas turbine engines have an aviation equivalent.
We used bleed air on our ships for a lot of various things. Masker air was used to make the ship sound like a rainstorm to submarines. Prairie air to come out of the leading edge of the prop to change the signature of the ship. Anti-icing air for our intakes when it gets below icing conditions. We could also do cross bleed starts to start other turbines.
veyly intalesting ...
You Sir, are a super stud jet turbine bleed air expert. Thank you for a bit of your knowledge!
My school uses your videos all the time! Your going to be the reason I pass my powerplants classes haha
Thanks, dude, but always remember, I supply infotainment, which is only the starting point for your journey...
AgentJayZ I've been Netflix style binge watching your videos. My question is about the bleed air valves. Is the purpose of the valves to unload the compressor to allow for it to reach the target rpm unimpeded by compression resistance? Thanks
Bleed air valves are for air start purposes. Bleed air from the 13 stage or whatever the manufacturer deems is for deciding and air conditioning packs. On the Lockheed C 130 I worked on, you start #1 engine then open bleed air valve so the manifold is filled with bleed air to start #2,3,4 engines. Great video! (You must start the APU to utilize it's bleed air to start #1!)
We call that a crossbleed start, airlines do it a lot on start to save the starters and apu
I could listen to you all day long...
Ive always had the understanding that "bleed air" had 3 types (as you said). Starting purge, running balance/cooling (the air sent to the center bearing is also needed for air flow stability along with cooling), and service air (used for running services outside the engine.
Funny you should know I grew up in rural Manitoba... my first jobs were all farm related. When I was a teen we flew Cessnas and Cubs like motorcycles and snowmobiles. Later working with the turbine crop dusters they always had trouble with bleed valves and shut downs. I've never flown an actual jet but the few times I flew those planes I was told if you can't land it you'll die and if you hurt it, the owner will kill you instead.
a cowboy from the wild west...yeehaaa
Great video. You opened up a can of worms with this subject. There are so many different uses for bleed/discharge air. You have everything you talked about plus more depending on the engine. There is labyrinth seal pressurization, engine anti-icing, aircraft inlet anti-icing, fuel system purge, emergency oil pressurization, balance piston seal pressurization and much more.
Oh, I know it... and thank you very much for even mentioning balance air... way to go, dude !!
Thanks. I figured I'd stir the pot a little with some of these.
In my previous experience bleed valves were called "blow off valves" in industrial centrifugal compressors. Those would be open until the compressor reached operating rpm and would slowly close after the VIGV reached maximum opening perecentage. Then the VIGV would close slowly and modulate as per requirement. That was done to prevent the compressor to go from idle to load all of a sudden which can cause surging.
Thank you very much for explaining different types of bleed air and what they are for. also for addressing the load.
Jay, several military helicopters use turbine engines that use a bleed air system you may not be aware of. These engines include the T53 (all models), L-712 (to include the L-11 or L-7-11and all following models). There are many more gas turbine engines that we use in the military that use the same bleed air system.
However, none of these same type systems use the air... for ANYTHING.
These engines produce an excess amount of compressed air by the time it reaches the centrifugal compressor. So, to control over compression in the outer combustion chamber there is a system of bleed air that is comprised of a large vacuum operated bleed valve that in turn opens a bleed band that surrounds the case halfs usually just after the second last axial compressor stage. The band is a stainless steel band that when tightened it prevents bleed air. Whan the actuator is in open position the band allows a specific amount of air to escape right to the atmosphere as directed by several other system.... such as the fuel control, the torque sensor and for some a few other sensors.
This bleed air system was the real first coined 'bleed air' because it is what it is, just bleed air, not 'service air'. But service air didn't sound right so any system using the name calls it bleed air.
A truly well engineered turbine engine shouldn't need that kind of bleed air system... but it does.
For ninety percent of all other engines... that's wasted service air.
PS:
Also, these same engines use a separate bleed air system that actually is used for service air. Most are just used for 'anti-icing' around the intake cowling.
This air is of the highest pressure as it comes from what we call the 'hot air gallery'... and yes, after being squashed as it does in a turbine engine... it really does get hot. This gallery sits right over the blades of the centrifugal compressor. The point at which the air is at it's hottest.
As we techs know... hot is bad, even for intake air. The hotter the intake air is... the less expansion it is capable of during combustion.
Good Afternoon Jay!! You Grew A Beard Mate! Keep Up The Good Work Brother!!!
Thank you 😊 boss🤝👍..simple but yet easy to visualise and understand.
Cool, I was about to ask what exactly it was. When he said that it was a single-spool turboshaft engine I figured it had to be a mechanical load. Neat idea to use what you already have and where you have a good idea about its power consumption. But sucking/blowing air through these sharp-edged variable holes is certainly going to make a huge noise. I was aware of all the different kinds of "bleed air", but never thought about the possible confusion. Another major use for "customer bleed air" is wing de-ice/anti-ice in most jet airliners.
I wish you lots of luck, since I would very much like to see that thing run :)
I want to thank you for this and all your videos, this is good infromation about the air bleed valves. When the engines starts, it makes easier to turn the engine and other reason is to cool down other componets of the engine. There is on point, the turbo prop entgine, this one doesn;'t use the power turbine. Thanks a lot. Please send some snow to here.
JORGE E Thomas they are there to prevent destructive compressor surge in axial flow compressors...they require minimum flow .....all other uses of bleed or recycling valves is sympathetic....
Sir thank you so much for your good works I am learning alot
Man your videos are awesome! It's sad you hadn't reached yet the 100k subscription mark.
Hi Jay,
Thanks for the full explanation of 'bleed air'; it seem all kinds of systems like to suck air off of the compressor! Please note that I placed 'air' in between 'suck' and 'off'!! That homemade load machine is interesting & sounds like it would work to me, however most likely very noisy! I'll be watching for that video...
Darren
On the R.R. Alison turbine engines Ive worked on, for helicopters, the bleed air port has 2 functions. When the engine is at 60% or idle, air blows out of it back into the atmosphere so that the compressor doesn't blow the flame out in the combustion chamber. at 100% the airflow reverses to help feed the compressor and keep the engine cool. It all happens with no moving parts, its just part of the design of the compressor fan (13:1) in this case.
The Heisenberg of engines.
Ha! Thanks for the compliment !
... but it could also mean that i am also uncertain about everything turbine related ...
I was leaning more towards the fact that you deserve a nobel prize
Runduh R You got my say on that case as well. i cant agree with you more . this guy needs appreciation for what he is doing
One part you may or may not have mentioned on here what bleed air is used for besides a/c, cabin pressurization. It's is also used for de-ice on the leading edges of the wings, vertical & horizontal stabs, windscreen and engine inlets. Also engine starting either from an APU or ground start cart like you use to start your engines at the test cell and to help pressurize hydraulic systems. I work on KC-135's and seen the different ways bleed air is used. There are great videos on RUclips that go over the bleed air systems of many different aircraft types like from 737 to a 747.
Cool. All of these uses are indeed mentioned in this very video. "Customer bleed" is the term I use...
thank you so much for this amazing informations they help me a lot on my research
Jay, at 3:53 you talk about cooling the sump. Is there also a rotary pump that draws the air and oil out of the sump?
Also, tell your developer to build a heat sink and install it around the ad on compressor. Have the working engine draw air through the heat sink. (naturally the heat sink needs to be configured right.) When the pressure drops around the heat sink, heat will be forced into the air. You will yield more psi and the process will be much more efficient.
The scavenge pumps on this engine are gear pumps, and they are designed to handle a mixture of oil and air. Most of the cooling air exits out of the sump vent, but some of it is in the form of bubbles in the oil drawn out by the scavenge pump.
The scavenge pump has a greater capacity than the amount of oil being pumped in.
... and for the heat sink idea... I think I'll leave the design just the way it is, the way the hundreds of professional engineers working for years on this project intended it to be.
No matter what anyone thinks about their "innovative" or "game changing" idea... they have to remember the ability and talent they are attempting to improve upon.
I do, and so do all the rest of us.
Cheers !
such nice clarification ! thanks from Brazil !
This one was particularly interesting.
thanks agent jay z for all your videos very cool to learn about jet engines
Another fabulous video! Thanks.
I know that you are somewhat sensitive about answering questions that have already been answered.....completely understandable. However I have been trying to find the answer to this question in your videos and I have not yet had any luck. So....I will ask: Is there a quantifiable limit as to how much bleed air an engine can divert away from the combusters without effecting the performance of the burning of the fuel? A large commercial jet obviously uses vast quantities of compressed air to run various systems....is there a practical limit as to how much can be used without effecting thrust characteristics? Thanks much!
Bleed air is bled from the compressor to be used for a lot of different purposes. If air was bled from the combustors, there would be a lot of extremely hot and high pressure air and burning fuel that would ruin various engine and airframe accessories and components. Hope that helps.
Holy balls, that thing is going to be putting out a lot of air. I love it! I assume the goal is to get the company more involved with rebuilding and testing those -501 engines?
We share our test cell with Maddex Turbines, and they already do a lot of 501 work. This new setup will allow us to measure torque on the output shaft under full power. It is a specific request made by an important customer that uses these engines to produce electricity.
And yes, we will have a 3,500 Hp air compressor on our hands...
Nice... Wish I could change professions this late in the game.
Excellent description of a complex subject. Those two side by side bleed valves...can I think of them as a sort of "Compression Release" for startup purposes ? They let air bleed out during startup, to allow things to get up to a self sustaining speed more easily, without so much resistance? The other types I understand from your description...
+SquillyMon
The bleed valves prevent aerodynamic stall of the compressor blades at lower rpm, allowing the compressor to function.
It would be more accurate to say that they increase compression.
It helps to ignore everything you know about piston engines.
AgentJayZ
Oh Jeez... LOL
There is also a bleed air exit (I guess from the 4th stage of the Compressor for this case) that is used for anti-icing of the inlet guide vanes, am I wrong?
Another great video, thanks!
I relly learn too mutch from ur vids
Thankyou
Thank you sir
Greetings to you from Algeria
I realize it been almost 5 years since this video was posted but Back in the late 60's when in the USAF I ran the P&W J52 P3 in combined systems test cell of the AGM28B Hound Dog Missile and it had a series of bleed Valves around the compressor case at about the No 5 or 6 compressor wheel. I remember I had to check them when activated from the control room during the engine check portion of the combined systems check. What was the function of these bleed valves on the J52 P3? Any Ideas?
Bleed valves are usually used for anti stall. Please watch my video called compressor stall, then the follow up vid for it.
I have a question for you ? I am a AD in the Navy i work on the T-56A-14 or 501. Why is it that that you guys are taking the air on the old compressor section from the bleed valves on the 5th and 10th stages vs the 14 stage on the diffuser section, wouldn't you rather have 14 stage bleed air?
Regarding cabin bleed air (air passing from the compressor directly into the cabin) is it safe to assume that the smells of fuel inside the cabin, are from worn bearing seals, or from jet fuel that somehow flows in that direction? I travel a lot and some planes smell more that others. I love your efforts here and actually bought the gas turbine book that you showed us. Keep up the good work!!!
Fuel is introduced well downstream of any compressor bleed. A leaking front bearing seal may allow oil into the bleed air, but usually bleed air does not directly pressurize the cabin.
It is used to run a small compressor, much like an automotive turbocharger, so that there is no way engine air can get into the cabin.
That's as far as I can go, because I'm not a plane guy.
What is the typical temperature and pressure of bleed air for customer utilities?
I have been studying the dynamics of internal shockwaves ( Mach+). Do you know of any good material on this as it pertains to turbine engines? Can you explain any of it in layman's terms? Thanks JayZ for all the knowledge you share!
Most airflow within a standard jet engine is subsonic, remembering that the speed of sound is not constant, rather a function of fluid temperature. So throughout the core of the engine, the speed of sound varies due to temp differential. Once outside, however, it's a function of the ambient temp. This also applies to the inlet. That's why variable geometry intakes are required for high performance aircraft. As AgentJayZ mentions, down below, have a gander at the Rolls Royce book "The Jet Engine". It's basically the sumpy's bible.
Thank you sir for the video
I have one for you JayZ. On a recent trip to the UK from Tampa I flew on a British Airways 777. At ground idle the RR Trents moaned so loud it was unpleasent. It was the sound turbpprops and jets make when they go through the startup procedure but didn't go away until takeoff power was applied. Any ideas?
Coulda been bleed valves. The RB211, which is an early design that was developed into the Trent series, has three stages of bleed valves. Once the last stage has closed, the engine begins making serious power.
Could also be resonance of the fan. Like everything else in a jet engine, it's designed to work best at its rated output. At idle it's not exactly happy.
Agent Jay z... I have a question but it's not about the bleed valves/ air. where do carbon deposits on the main oil filter come from specifically for PT6A-27?
is bleed air hot? is it because of compressing the air?
Is the cooling air that cools the bearing also what pressurizes around the bearing inclosure to keep oil that gets past the seal out of the engine? what would the range of air pressure and what temps would you see when engine is at operating power? Is the air that is used by the plane systems closed circuit like when a car uses vacuum servos where there is no leak of pressure or vacuum in cars and just the pressure itself is doing the work? Thanks for the hard work you have a first rate site.
Yeah the internal cooling air is also used for seal pressurization, in both labryinth seals and pressurizing some carbon seals. The pressure depends on the engine type, engine compressor ratio and where in the compressor the air is taken from. The bleed air used in aircraft systems like air conditioning, anti-ice, cabin pressurization is exhausted overboard once it's been used, so it's not a closed circuit.
The big disadvantage I see with the single shaft systems is the power needed for starting. You've mentioned the LM1500 and LM2500 are started with about 100hp, can you give an indication of how much hp this engine needs to start? I imagine it would be quite a bit higher than engines producing thrust or powering a free power turbine.
It also looks like this load system wouldn't produce much load until the engine got to running RPM. I imagine that would make starting easier than normal, right?
Jay you have gone over several bleed air, on different engines, but can you find or create a video that shows how the two different systems work (Bleed Band System, Bleed Valve System). I have scoured FAA.gov, 8083, and jeppessen books and the best i can find are some poor drawing diagrams that don't explain or show their functions well at all. thank you.
Dear AgentJayZ awesome videos as always, could you explain active tip clearance and low density nickel blades
Here is a quick wiki explenation on tip clearence. I'm sure AJZ will be able to explain this better with drawings and actual engines with this feature. By reading this, it seems it is related to the bleed air system. I'm going to search for some schematics and see where some engines have this system mounted.
Wiki-
Active clearance control (ACC) is a method used in gas turbines to improve fuel efficiency. This is achieved by controlling the tip clearance. It is particularly effective on turbofans since they are required to respond quickly to changes of the thrust setting.
The active clearance control consists of the ACC valve which receives the air from the bypass duct and routes the air to flow over the pipes surrounding the turbine casing which in turn reduces the thermal expansion of the turbine case and maintains the accurate clearance between the turbine case and the blade tip. This clearance should be maintained accurately which is essential for the engine efficiency and its performance. The ACC valve opening is adjusted automatically by the FADEC system depending on the throttle position.
hyronov here is a crazy video showing tip clearance measurements via a boroscope and some insane software.
Blade Tip Clearance Measurement
Alfredo Pacheco Jr hey Alfredo thanks for the response, I still don't get it does the bleed air mass flow control the width of the case opening, so shouldn't the thermal expansion and contraction reduce the life of the turbine, how does the FADEC know the initial expansion of the engine if it was thermally deformed completely in the first place.
I saw a NASA or theory paper on this. The amount of formulas used was mind boggling.
For the FADEC to be able to control tip clearence by controling thermal expansion, all the variables would have had to be programmed into the system. So engineers have plugged in all the formulas to monitor outside air temp, inlet temp, compressor speed/temp, thrust settings, etc.
These calculations would be done at lightning speed with every change of the thrust lever. I'm sure they came to an average setting that gave the best results for tip clearance as each and every use of the engine is always different.
As for the control, it just sends the "right" amount of air over the case to try and maintain as level of a temp as possible to reduce thermal expansion. Again, the formula for that was so long, I feared trying to copy and paste it. So I'm not even going to try and think what the hell it means.
Here is the NASA paper with the formulas:
Dynamic Turbine Tip Clearance Model for Clearance Control Prototyping
mece.utpa.edu/Kypuros/publications/NASA_TM_Kypuros03v2.pdf
Thx for this once again! 3500 HP compressor? Hook this up to your engine-lift-thing :-) (Maybe open the roof first...)
I would like to wish you a powerfull pre-christmas time! Can't wait for the next vid!
another great video thank you for the effort just to educate us very selfless on your part and I appreciate it. question for you the bleed air you called customer bleed air for systems on plane is this the same one planes use to start other engines with or is that a different bleed air outlet? looks small for the size of hose starters use but I don't know. Thanks again Jay
Jay, On the Spey bleed valves, are they not also used beyond startup? I thought they were operated through the intermediate percent range and closing up at high power? Fully/partially open at idle? Do they not kinda mirror the function of VSV's?
Thanks as always, hope we all get to see the Allison run! That should be a noisy and breezy test cell!
The Spey has bleed valves for both the LPC and the HPC. By the time the engine gets to what might be considered the bottom of its working range of rpms or power settings, all bleed valves are closed.
Bleed valves are there to help get the engine started, and also to get the engine from idle to significant power...
You are right: there are two ways to avoid stall in a high-performance compressor - bleed valves and variable stators. Variable pitch compressor blades would also work, but nobody has done that yet.
hi sir.. thank u for ur nice efforts. I have a question about ,is there a difference between compressor bleed valve which is used to avoid compressor stall and surge and a bleed valve from which bleed air is usually taken for the purpose of de-iceing,cabin pressurisation,etc
Regarding the bleed air uses, what kind of pressure(psi) and air movement(cfm) run through the bleed air systems?(as in the Orenda engine I figured that the different uses of it require different amounts of air and use "restrictions" in some fashion. Love the channel Jay!
For the internal engine air bleeds for cooling... I have no idea; the rates of flow are not listed in the engine information manuals, and the pressures will depend on engine rpm. The customer bleed air is variable on demand, and it's pressure will depend on what stage of the compressor it is sourced from. Different designs for different engines.
The airflow through the bleed valves depends on when they close, which is different in different engines, but it is very large.
I've always wondered what compressor stall is, ive read descriptions but they are all a bit abstract so hard to get my head around. Especially when the air reverses flow and flames come out the front, i really don't get how that happens.
Stall/surge is primarily an axial flow problem (tho not exclusively so, I should add). It's because an axial compressor works thru a series of convergent (accellerating) and divergent (pressure recovery) ducts. A divergent duct works closely to its designed airflow limits. Outside of this, the airflow becomes turbulent and stagnates. However, the compressors in front of the stagnated section are still compressing so all of a sudden that air can no longer pass thru the engine and must go out the only way it can...thru which it came. And BOY do you need a change of undies if you hear one up close!
I should mention this is a rather simplistic explanation, but I hope it helps.
Why the air bleed band can prevent engine surge?
ajz - understand the air systems, but im curious what type of alignment is used between the engine and your test/load cell - obviously the turbine will heat up as load is increased so was just curious what alignment considerations were taken while bolting these two units together
The coupling shaft is splined on both ends, allowing for axial movement. The forward compressor is rigidly mounted. The engine has one fixed mount to secure its location, and three floating mounts to allow for axial and radial changes in size.
Do you have a video where you explain how the different chaising parts are held toghether?
If that's not a typo for casing, I don't know what you mean.
@@AgentJayZyes, it's my fault. It should be casing. (My native language is not english so I apologize for spelling mistakes)
I am confused. My prof told us that bleed valves, or what he called them, bleed hatches are used to bleed off the excess air in order to avoid surge of the compressor. Though, maybe he was right partially, since the only showpieces we have in our uni are the vintage soviet engines, and their age vary from 40 to 60 years or even more, and the older the engine, the more unorthodox it's construction is.
Agent Jay, Did we ever get a video of this thing running?
We did
:) Thx.
Great vid, once again, thanks (missing playing with donks). Now with regards the inlet appertures on your load compressor. What's the risk of inducing compressor stall on the load unit? It must surely induce majorly turbulent airflow onto the first stage, doesn't it? Have you done a video of the unit running? I'd love to see the results.
Thanks, once again.
I noticed you said that the bleed valves open on the 501 because the high pressure section can't handle the air from the low pressure section on start. That makes sense but I guess I am confused because you later said the 501 was a single shaft engine. Why are the bleed valves needed on a single shaft engine lacking an HP system? Thanks!
Dan8432 I meant the lower pressure stages at the front of the single shaft compressor are more efficient at low rpms than are the later, higher pressure stages on the same rotor. It does get confusing sometimes.
Thank you ! A very informative video!
Hi Jay thanks for the video. I'll bet with very little effort that restrictor plate could be turned into the world's loudest whistle if it isn't already. On a more serious note though, regarding alignment of that load to the main engine: in prior videos you've said that for the engine it is the rigidity of the individual sections that forces the alignment to be perfect during assembly. Is it the same for that forward extension out to the load compressor some feet away? (I know you said you're just a bystander, but I'm wondering just same - how do you get that load perfectly aligned with the jet so it all won't be out of balance and shake apart).
Fancy coupling being made as we speak.
AgentJayZ Will be interesting to see it all.
Amazing video!
So that is basically the same concept as an engine dynamometer used to produce a variable and measurable load to test the performance? How is the output tq being measured by the driven compressor? Is this as simple as psi air to percent aperture will equal tq required to produce and how are these numbers determined or is there some type of load sensor directly attached to measure output?
Thank you for the great videos!
The T56 aircraft turboprop has a torque meter on the drive shaft, and we will be using that.
Hi Jay, thank for your work in the videos. Question, does that load compressor for the turbine have any clutch system or just adjusting the air intake you can put no load bellow IDLE?
The air dyno presents a load that rises exponentially from zero as the rpm rises. No need for a clutch.
@@AgentJayZ thank you very much. How you will measure the load? Sorry the questions. I develope a turboprop and i want to make a non regular dyno and this is awesome
What I would like to know is the history of the use of compressor bleed for customer pneumatic power. What was the first engine to be designed with a system specifically to tap air off the compressor for airframe pneumatic power? What was the first aircraft, military or civil to use compressor bleed for pneumatic power? I'd also like to know what the first aircraft was to use an air cycle machine or pack for environmental control.
hey sir, do you know why one of the air vent, 9 0'clock position from aft looking forward, is pointing down and other one, 3 o'clock position, is pointing up on the diffuser section? thank you.
I don't see what you are seeing. It helps if you give me a time in the video concerning your comment.
Awesome video. Could you explain about free turbine engine ?
I have several videos about power turbines. Search bar on my channel page.
AJZ,
Good video about bleed air.
In an airliner does the cabin ventilation and pressure come from bleed air?
If so, what is the proximate cost in loss of engine efficiency ?
The reason I ask, in the early days of jet airliners there seemed to be never a lack of cool air in the cabin but now you get baked until you have reached 10,000 feet or so. I think cabin air is being recirculated to cut down on the use of bleed air off the engines to save fuel.
Thanks for you time,
John Valos
In airliners, it all comes from the bleed air. As for the A/C, the bleed air will cause parasitic power loss. It all depends on the many factors to determine the amount of loss. One method to help ease the use of bleed air for cabin cooling/heating is the use of the "Recirculation Fan".
Larger engines don't experience as much power loss as would smaller engines. If you look at the King Air 350, when you apply prop and anti/deice heating, you get a significant loss of power. The more equipment/systems that demand for bleed air, the more the engine must work to compensate for the loss of air flowing through the engine.
If you want to get more in-depth, I'd suggest checking this site out to get all the technical info:
www.b737.org.uk/index.htm
Also, in regards to the loss of engine efficiency question, it all depends on the ITT (Inlet Turbine Temp).
When you use bleed air, your taking away cooling air for the turbine. The more or higher demand for bleed air, the less cooling air you will have. This will cause higher ITT's. So, to prevent this pilots will lower thrust settings to compensate for the increase in ITT.
Most of today's engines have an updated FADEC that can do this automatically. Some, however, must be monitored manually (like the CRJ).
So the "loss of power" that an engine will have with the use of bleed air is based off how much cooling air is lost and how much less the engine must operate to not exceed ITT limits.
Here is a forum discussion about bleed air and power loss in turbofan engines.
forums.jetcareers.com/threads/turbofan-power-vs-bleed-air-extraction-the-mechanics.86319/
I think you are right, John. You can feel nowadays that the A/C doesn't come on until takeoff, and the engines are really working.
As with any business these days, penny pinching is the whole strategy, and any bleeding of air from the compressor of a turbine engine reduces the power output, so for a given power, it costs more fuel.
Aircraft designers and engine engineers are fine with that, but it really bothers the accountants, and they control the world, don'tchya know...
AgentJayZ
Thanks for your quick reply.
John
Some turboprops, like those using a P&W PT6, have the prop on the turbine side rather than the compressor side. Is there any advantage pointing one engine end forward over the other?
Actually, the differences are deeper than that. The PT6 has a free power turbine driving the prop reduction gearbox, while the T56 is a single-shaft engine.
The relative merits of each design as an aircraft engine is a subject beyond the scope of this discussion.
Erik Pearson The reasoning I have heard for having the PT6 pointing "backwards" is that the shaft from the free power turbine to the prop reduction gearbox can be made shorter and lighter.
I saw your video while I was searching for an explanation about active clearance control(ACC) but the video was about bleed valve and bleed air .it would be helpful if u could explain about ACC in modern tubofan engine such as ge90/genx.
Do you know why that compressor used for load has 8 bleed air "points" attached in groups of 4, where the first group doesn't have any valve, does that just produces drag?
Thank you
The engine has 8 bleed ports, each of which has a bleed valve attached. The "extra" compressor, attached to the driveshaft coming out the front of the engine, is of identical design, but the bleed valves are not there. We've connected the ports with tubing, and installed manually controlled valves on the tubing manifolds.
On the load for the allsion, I am assuming that closing the valves on that compressor increases the load since the air has now where to go.
It's more complicated than that. The bleed valves are not there to unload the compressor at design speed. They are there to increase air speed through the compressor at lower rpm to prevent stalling.
When a compressor stalls, it stops working, and it requires less power to turn it.
So... at operating speeds, opening the bleed valves would unload the compressor, but they are not used that way.
At lower rpm, the bleed valves must be open to allow the compressor to work; closing them would cause a stall, which is not good for it, but also technically unloads it.
I suggest you watch my video about compressor stall.
Great Videos and something i like to watch. I have one question i.e. you said the HBV assist in starting? I thought they are there to help in surge operation to release the pressure from compressor.
+Ninety Nine They help the engine to run at very low rpms without having the compressor experience aerodynamic stall. That region of operation includes starting.
I was wondering if you could explain how blow off valves (or BOVs) function? It is my understanding they are operated not just during startup and are activated somehow by a pitot tube measuring airflow velocity and are hydraulically opened/ closed. Is there some sort of control unit in between? Could you clear this up?
None of the engines I have worked on have a mechanism called a Blow Off Valve. After you mention that term, nothing makes any sense at all. Sorry.
Is the dynamometer configured to measure torque directly (e.g., using a suitable transducer) or are the air properties measured to infer this?
MrShobar Torque is measured by angular deflection between two spinning shafts; one loaded, and one along for the ride.
On the bleed valves in the beginning of the video, how is it that they assist in starting and allow the compressor to function, if the air is coming out of the engine?
Thanks!
***** We'll get to that in the compressor video(s)... coming soon.
Great video Jayz, well explained.
On the topic of engine loads, I assume if you translate this to a turboprop, the prop being the load. On turboprops I usually see that the prop itself starts turning a short while after you hear the turbine start up? Is this because as the engine rises in RPM the prop starts to turn because of the reduction gearbox? Or is the prop on some sort of clutch that engages at a certain engine RPM speed? I notice this when flying in the De Havilland DASH 8 aircraft quite a lot. I hear the engines wind up and finally the prop starts to turn.
If anyone knows the answer I would really like to know as I have searched the web and not found a definitive answer on this one. the same happens on helicopters. The turbine starts and then slowly the blades start to turn. Many thx
The Dash 8 uses the P&W PW100 series turboprop engine, which has a separate "free" power turbine, connected via a reduction gearbox to the prop.
That is quite different from the T56, which does not have a separate power turbine.
Both engine types have their advantages and disadvantages...a discussion of which would require pages of text, or a few pints at the Flying Beaver.
AgentJayZ
In the Aurora/P3 (T56), the turbine output is fed to a 13:1 (roughly) gearbox that translates the 13000 engine rpm down to a useful 1000 rpm prop speed.
There's also generators (on 2, 3,4) and compressors (2,3) that suck power from the engines but provide useful things like electrical power and pressurization.
At flight idle, the engine turns at full speed (100% rpm +/- a couple %) and the prop is at flat pitch... no thrust...more or less. As the power levers are increased by the pilots, the prop pitch increases and they try to slow down, but the fuel flow is increased in response to keep the props/engines turning at 100% rpm.
Max thrust/power is determined by the TIT (Turbine Inlet Temp). Higher temp=more power (up to a limit of course)=shorter engine life. You can pull more power if you have to (bagging an engine at take off), but at the expense of reducing engine life.
Engine/prop RPM deviation (more than a few %) in flight is a real problem and indicative of something going bad somewhere.... as is the "chips" light for the gearbox which indicates the gears are starting to come apart....
Flying Beaver Jay?!?! LOL... let me know the next time you're in town and I'll buy the first round!
CP140405
Thanks for the info Jay and CP140405. When on the ground and starting up one of these turboprops, does the prop start to move freely at a given turbine RPM or is it "engaged " by the pilots? Jay mentioned a "free" turbine. I am just trying to understand the process by which the prop starts to turn as the turbine increases in rpm, I assume it is connected direclty via the gearbox to the turbine with no clutch or device that can "release" the prop. Wish I could join you at the Flying Beaver, but its just a tad far for me being in OZ otherwise I would shout you all a cold one. cheers
Hotdogger808 Well, one of "these" turboprops has the propeller directly connected to the main and only shaft in the engine, through a reduction gearbox, but no sort of clutch. So the prop moves as soon as the starter begins to move the engine.
But... there are two types of turboprops....
Other engines, like the P&W PW120 series, have a free power turbine, which means the prop is not mechanically connected to the engine shaft.
The coupling is aerodynamic, and gets more effective as it reaches its operating speed. On these engines, the prop sometimes takes a few seconds before it moves.
The T58 is a free power turbine engine, and we look at the "coupling" in Pt 8. of the series.
AgentJayZ
It's true... on the T56, the prop starts turning as soon as the starter is engaged. I remember the "chatter" over the intercom quite well...
"Clear to start One"
"Selecting One"
"Starting One"
"One's turning"
(pause)
"Ignition"
"Fuel Flow"
"Light Off"
"Temperature Rise"....
AJZ, if there is no load on that engine for some reason due to a failure of the props or shaft, you said it would not be a good thing, would the engine be damaged? Is there a way the engine powers down automatically if this were to happen?
Answer to question 1: It will overrev, i. e. turn to fast and ultimatly disassemble itself because the centrifugal force is too strong. (Yes I know that the centrifugal force is a phantom force percieved in a rotating reference frame, all ya screaming physicists)
Answer to question 2: I don't know. But you'd have to react major fast.
saxonlight what he was referring to was the load on the shaft. Because this particular engine is a single shaft, it must have a load on it. If the engine did not have a load, the engine would continue to spin, beyond its designed limits, and eventually destroy itself.
All aircraft engines can not automatically shutdown. This is for the safety of the crew. You don't want a computer malfunction and it kills the engine right in the middle of takeoff. The pilot is the only one capable of shutting down an engine.
But there are turboprop and turboshaft engines that can run without a load. These have separate or dual shafts. One for the gas generator and compressor, the other for the power turbine. However, this specific engine can be shutdown in-flight. There are videos of C-130's and P-3's with an engine off and the prop lock engaged.
Alfredo Pacheco Jr
Yes mate. And he referred to a scenario where the load would become 0 suddenly. And if this engine has no load it overrevs and rips itself apart into it's own components like the compressor blades, the stators, the turbine blades...
Disassemble is a nice way of saying destroy itself. To see what happens to turbine discs when they overspeed, google "turbine engine failure" and look at the wikipedia article. At the bottom there are notable uncontained engine failure incidents. It's very nasty business but fortunately it happens extremely rarely. Multiple things need to go wrong (or need to be manufactured wrong) in order for an over speed to happen
There is a governor on the fuel control, and it would attempt to bring the engine to idle.
Agent... are these "bleed valves" similar to a surge valve on a JT8D? Id like to see a surge valve and how it actuates/commonly fails to modulate closed on a JT8D
Never worked on a JT8D
Hello sir, can I ask a question? I had a problem from 2 months ago about bleed air temperature out of limits. Until now, I did'nt understand the problem. Hopefully you give an answer to this question. thank you.
As I try to explain in this video, the term "bleed air" can mean many things.
There is not enough information in your question.
@@AgentJayZcopy that, thank you sir.
so there is customer "bleed air" for aircraft usage, and then there is internal cooling air, that's the air ducted thru the engine thru pipelines and valves used to cool certain parts of the engine most specifically, the combustion section and the turbine section. But what about the external cooling you were talking about? like I know that it mixes with the gas path downstream of the exhaust, but what does it specifically do?
"cooling air"... and if you read the chapter on combustors in any of the books I recommend, you would become enlightened.
@@AgentJayZ I've just recently found out your channel, kinda nervous about an upcoming exam so yeah :)
what books would you suggest? I'm really sorry for these urgent questions.
Thank You, I wish that when I was young I could have learned about the systems on a jet engine. Thank Geo
why don't they call the bleed valves compression release? also, on the engine "dyno" don't you need a valve on the exhaust side of the compressor more than the inlet or is there enough restriction in the end plate that the bleed air system will do?
i assume the intake restriction is for unloading the engine at startup.
if you were to shut the intake valve quickly while the "dyno/load" was at high load, would it attempt to stall the compressor?
+jon “tweakit” spon
1) because that's not a good description of what they do
2) restricting the inlet is more effective than restricting the outlet. Where is the throttle plate for a piston engine?
3) that is the basic idea, although we may need to restrict both the inlet and discharge...
I never thought about how the engineers would have had to make so many provisions for air...like the blanket of air that surrounds the flame to cool it... No wonder jet engines can handle such an enormous flame within!!! Prior...I just thought it could handle those temps magically...and i was correct to always question that in my mind... AWESOME!!! Not understanding something mechanical, and knowing that I don't, bothers me, seriously.
I have a little CAE-140 engine from a MA-1 GPU and I see a compressor bleed air path for a couple more functions. One assists in the actuation of the butterfly valve for the main compressor bleed (from the start cart), and the other leads, via a filter, to the hydromechanical fuel control unit. But maybe these aren't considered 'bleed air' because there is very little actual flow of air?
They will, most likely, be servo or sensing pressures as opposed to bleed air. Though I am unfamiliar with the type of donk you're referring to, this is pretty standard for most turbines.
Of the three types of "Bleed Air" discussed; which is responsible for Engine Surge and how does clearing a surge (throttling back) prevent an engine from destroying itself?
The bleed valves are the ones you mean. They help offload the diffuser at lo-rpms because the engine compressor is so efficient. With regards stall/surge conditions. once established, the bleed valves have no control over them (as far as I know...certainly not from the ones I've worked on, anyway). That is purely a function of offloading the engine, either thru decreasing the RPM on a variable speed engine or thru offloading engine pressure with a constant speeder such as the 501. However, sometimes this just isn't possible, especially if the engine has suffered a mechanical failure. In which case, it's time to reach for the yellow and black painted handles and hope for the best.
Is eighth-stage air from the Orenda adjacent the combustion section? Also, hot hot is the eighth-stage air typically?
MrShobar Should be "how hot". Sorry.
MrShobar The compressor has 10 stages, and at full rpm, the compressor ratio is 5 to 1. The temperature of the air discharged from the compressor at 100% rpm is roughly 245C.
So does anti-icing fit somewhere into this? I remember seeing in another video where bleed air was routed to the cowling to prevent icing so would there be any other parts of the engine like maybe the inlet guide vanes that would require that? Thx for the vid!
+Mike O'Brien Yes, anti-icing uses compressor bleed air.
+AgentJayZ thx!
Hi... Not sure if this is a 'dumb question' as you say... but here goes anyway... Is this not a super complicated way of putting a load on a turbine under power. Maybe I'm oversimplifying things here... but could you not just strap a variable pitch prop (via reduction gearbox) to provide the load then increase or decrease the pitch to vary the load?
+Mac Anix That's a lot of machinery, and the prop would be mounted high up in the air. The mount for the prop would need to handle the torque produced by the prop, and the thrust of it.
It would not be simpler, and require a lot of setup time.
+AgentJayZ Cool... thanks... And thanks for all your informative videos btw...
What kind of welds are on the air flow pipes from the bleed valves?
I'm guessing, based on your avatar pic, that you are a professional.
So let me start by apologizing for your having to see those...
Those flow pipes are "home made" out of regular automotive exhaust system tubing.
They were welded by a well meaning technician who is not employed as a welder. I think those are MIG welds.
They are prototype test cell equipment, and would never be used for any length of time on an industrial working engine.
The thought of using them for an aircraft engine has never occurred to anyone ever.
Thanks for not throwing tomatoes at your screen.
AgentJayZ. Haha thank you for taking the time to reply. I am a professional doing some indep. research on bleed valves and Titanium bleed ducts. Found your video helpful and was just curious about the piping system you used.
Hello! I was wondering if there are any concerns of adverse affects to a compressor when airflow is restricted? Will the compressor be more likely to stall?
Anything that reduces the axial velocity of airflow through the compressor can cause it to stall. It's a common misconception that the IGVs control the amount of airflow... I used to think that way. They only control the angle of the air, and therefore the angle of attack of the blades.
Under normal operation, air flow is never restricted at the inlet of a subsonic compressor.
Thank you for your quick response, your videos are excellent! The first sentence of your response was what I was thinking about, in regards to the Iris system for controlling inlet airflow. I hope the test went well, seems like an ingenious solution for loading an engine!
Amazing!
Where does the energy on the load get channel to, and doesn't eventually turn into heat?
The air dyno will be compressing air and releasing it through restricting orifices. This will cause the air which passes through the dyno to be at a higher temperature as it comes out.