Bleedless Engines

BOEING747400 · Tue Feb 22, 2005 12:26 pm

Can anybody please explain the term "bleedless engines" translating from technical to layman terms? Thanks.

dl757md · Tue Feb 22, 2005 12:49 pm

A bleedless engine is one that doesn't supply air from the internal flow of the engine to the pneumatic system of the aircraft. All of the air entering a bleedless engine will be used to create thrust, excepting a small amount of air for internal cooling and engine stability. This is possible because the pneumatic system of the aircraft (787) uses electric components for heating, air conditioning, and pressurization.

Dl757Md

PhilSquares · Tue Feb 22, 2005 12:59 pm

Engine bleed is used to pressurize the pneumatic system. That system does several things. To name a few, but not all inclusive, provides air for cabin heating/cooling and pressurization via the air con packs, wing and engine anti ice, pressure to water system, head pressure on hydraulic resevoirs.

On "bleedless" engines, these functions would be replaced by electric motors. The motors would provide the air necessary to run some or all of the above systems.

The problem with having bleed air taken away from the engine is the efficiency of the engine is reduced. There is less thrust going out the back end of the aircraft. The new generation engines are designed for minimal bleed loss and maximum efficiency.

Duce50Boom · Tue Feb 22, 2005 1:35 pm

Maybe a dumb question, but is there a performance penalty by running the elec. generators and hydraulic pumps off of the engines?

dl757md · Tue Feb 22, 2005 1:42 pm

Quoting Duce50boom (reply 3):
is there a performance penalty by running the elec. generators and hydraulic pumps off of the engines?

.

Of course there is. You can't get power for free. But this is a necessary evil. And of course this power drain is considered when designing an engine.

Dl757Md

Duce50Boom · Tue Feb 22, 2005 1:59 pm

What kind of penalty is this though? My KC-10 -1 says our engines (CF-6-50C2) have an uninstalled thrust of 52.5K. Installed can you guesstimate around what that would be?

dl757md · Tue Feb 22, 2005 2:14 pm

I've never heard about an uninstalled Vs installed thrust rating. I'm not even sure what the difference would be. Are you saying that the uninstalled rating is without a generator or hydraulic pumps? I know that a Vickers engine-driven pump on a CF-6 requires about 90 HP at full flow at system pressure. This is about 40GPM at 2850 psi(the system pressure used for rating pumps).
How you would figure the loss of thrust from this I don't know other than a direct measurement on a test stand.

Dl757Md

BOEING747400 · Tue Feb 22, 2005 2:35 pm

Are there any bleedless engines around right now or not? Are the GE90s or RR Trents used on 777s bleedless or not?

Duce50Boom · Tue Feb 22, 2005 2:39 pm

My book says. "The CF-6-50C2 has an uninstalled thrust rating of 52,500 lbs thrust at sea level." I'm assuming that's on a test stand without the elec and hyd pumps and all that, versus installed on the pylon. I guess it can't be too much of a penalty, but just can't figure out how much. Thanks for your help though

dl757md · Tue Feb 22, 2005 2:44 pm

Quoting BOEING747400 (reply 7):
Are there any bleedless engines around right now or not? Are the GE90s or RR Trents used on 777s bleedless or not?

There are currently no bleedless engines installed on airliners.

Dl757Md

IFIXCF6 · Tue Feb 22, 2005 4:51 pm

Maybe a dumb question, but is there a performance penalty by running the elec. generators and hydraulic pumps off of the engines?

No, not a dumb question at all. One might think that all accessories would detract from an engines' performance, and they do. But as was hinted above, hydraulic pumps do not matter in an power assurance run (on an aircraft). Generators and bleeds do. These 2 must be off to get accurate numbers from the engine.

The KC10 CF6's that are run across the test cell at GE/Ontario do not have hydraulic pumps installed because there is no system to pressurize; generators are installed, but power nothing; and bleeds are blocked off. Pure engine giving the performance numbers.

Regards

Mike

BOEING747400 · Tue Feb 22, 2005 6:16 pm

Do bleedless engines offer any advantages over today's engines which are non-bleedless? If so, then what are they?

dl757md · Tue Feb 22, 2005 6:31 pm

Quoting BOEING747400 (reply 11):
Do bleedless engines offer any advantages over today's engines which are non-bleedless? If so, then what are they?

The main advantage is efficiency. A lot of hot air is dumped overboard in the process of supplying pneumatic functions to an aircraft. This is wasted energy. The electrical pneumatic systems that will replace bleed air systems will be much more efficient.

Another advantage I see is lower mtc. The valves and ducting will be mostly eliminated. This will save huge amounts of labor. Weight may also be saved by eliminating these components.

Dl757Md

UAcsOKC · Tue Feb 22, 2005 11:31 pm

Weren't early generation jets bleedless? Or did they just not use bleed air for pressurization?

HAWK21M · Wed Feb 23, 2005 12:31 am

Quoting PhilSquares (reply 2):
On "bleedless" engines, these functions would be replaced by electric motors. The motors would provide the air necessary to run some or all of the above systems.

Motors or Pumps Smile

What happens in case of power loss.
And Thrust variation.
Would Bleedless Engines be sucessful.
regds
MEL

Okie · Wed Feb 23, 2005 12:41 am

In terms of efficiency,
The least is compressed air
The next would be hydraulic
The highest would be electric

The only time a generator/alternator puts a load on its power source, other than parasitic (bearings mainly), is when it is providing current to operate an electrical device. Most high energy usage systems on an aircraft other than heat/cooling/pressurization are generally very intermittent loads. Landing gear, flaps, control surfaces that can be handled by electric actuators or local hydraulic pumps for those systems. These systems are already finding there way into aircraft design piece meal albeit on many different aircraft.

Okie

2H4 · Wed Feb 23, 2005 10:15 am

Quoting Dl757md (reply 12):
The electrical pneumatic systems that will replace bleed air systems will be much more efficient.

Considering how long jet engines have been in use, why has it taken this long for this technology to be utilized in airliners?

2H4

Duce50Boom · Wed Feb 23, 2005 1:33 pm

IFIXCF6,

Thanks for the info! If you had to estimate/guesstimate, how much of a difference do you think having the generators up and running would make? Not including the bleeds of course.

pilotpip · Wed Feb 23, 2005 2:41 pm

Quoting 2H4 (reply 16):
Considering how long jet engines have been in use, why has it taken this long for this technology to be utilized in airliners?

I would assume it comes from a reliability and technology standpoint. Years ago, electrical systems were not a favorite on aircraft. These tended to have reliability issues and the generators were very heavy. The thinking has shifted in GA. In the old days, people never would have dreamed of an instrument system that was all electric with a battery for a backup. Vacuum pumps were at one time the more reliable system. Now they're being dumped left and right on new models in favor of systems like the G1000.

I think that with modern technology these systems have been miniaturized and made reliable enough that it is now a feasible and more efficient option for aircraft systems. Dl757Md hinted at a savings from an MX side. There are also other considerations like weight, as ducting that super hot air around takes lots of insulation.

2H4 · Wed Feb 23, 2005 2:58 pm

Quoting Pilotpip (reply 18):
Vacuum pumps were at one time the more reliable system.

Now THAT is a sobering thought!

2H4

Duce50Boom · Wed Feb 23, 2005 5:05 pm

Vacuum pumps were at one time the more reliable system

I don't know how reliable they are, but amongst my various and wildly creative porn spam I keep getting crap about these vacuum pumps. I'm glad Pilotpip has the inside scoop on these though Big grin

CRJ200Mechanic · Wed Feb 23, 2005 5:29 pm

Quoting Dl757md (reply 1):
This is possible because the pneumatic system of the aircraft (787) uses electric components for heating, air conditioning, and pressurization.

Is the 787 refered in the quote above. Is that the 7E7? If it is I didn't know it was given a number yet. Only seems logical since the last one was the 777. I'm alittle slow sometimes

Goldenshield · Thu Feb 24, 2005 10:55 am

When using 10th stage bleed (engine and wing anti-ice) in the CRJ-200, I've seen hits as much as 6,000 pounds.

CRJ200Mechanic · Thu Feb 24, 2005 4:40 pm

Quoting Goldenshield (reply 22):
I've seen hits as much as 6,000 pounds.

seen what hit 6000 pounds?

Goldenshield · Thu Feb 24, 2005 9:32 pm

Theoretical payload hits. It's used in dispatching to determine how much weight the plane can safely carry off a runway or during climb for obstacle avoidance, etc.

dl757md · Sat Mar 05, 2005 4:33 am

Quoting CRJ200Mechanic (reply 21):
Is the 787 refered in the quote above. Is that the 7E7?

Yes. Boeing announced last month that the 7E7 would be called the 787.

Quoting HAWK21M (reply 14):
Motors or Pumps

I think the most accurate term would be electric motor driven pneumatic pump. So...yes and.........yes.

Dl757Md

Jetlagged · Tue Mar 15, 2005 2:26 pm

Quoting Dl757md (Reply 12):
The main advantage is efficiency. A lot of hot air is dumped overboard in the process of supplying pneumatic functions to an aircraft. This is wasted energy.

I'm not sure that much hot bleed air is dumped overboard on current aircraft, apart from thermal anti-ice. All the air bled from the engine flows through the pneumatic ducts to the cabin. Only ram air used in pack heat exchangers is returned to the atmosphere.

I vaguely recall the VC10 had bleedless engines in that the air for pressurisation was ram air pumped by mechanically driven compressors. The turbo-compressors on the 707 and DC-8 were driven by bleed air, so in that case the bleed was dumped overboard.

I understand the 787 is less than an all electric airplane now. Whether it will still use bleedless engines remains to be seen.

HAWK21M · Tue Mar 15, 2005 7:02 pm

Quoting Jetlagged (Reply 26):
understand the 787 is less than an all electric airplane now. Whether it will still use bleedless engines remains to be seen.

Thats correct.Will it be used.
regds
MEL

lehpron · Wed Mar 16, 2005 3:33 pm

Quoting Dl757md (Reply 1):
A bleedless engine is one that doesn't supply air from the internal flow of the engine to the pneumatic system of the aircraft. All of the air entering a bleedless engine will be used to create thrust, excepting a small amount of air for internal cooling and engine stability. This is possible because the pneumatic system of the aircraft (787) uses electric components for heating, air conditioning, and pressurization.

Hold up, that's it?! How exactly is that a big deal for 787 then? How much 'thrust' was lost before? Does this contribute to the Trent 1000's fuel efficiency?

Okie · Thu Mar 17, 2005 2:15 am

Quoting Lehpron (Reply 28):
Hold up, that's it?! How exactly is that a big deal for 787 then? How much 'thrust' was lost before? Does this contribute to the Trent 1000's fuel efficiency?

It is not exactly 'thrust' but the additional amount of excess compressor capacity from the appropriate turbines sections that required additional fuel to be burned in the hot section to supply the energy for the excess compressed air.

So if you believe the touted 15-20% fuel savings, and deduct the additional weight of the air piping, controls, etc, vs the electric the you would have to estimate using the SWAG (Scientific Wild A$$ Guess) method that maybe 12-17% of the fuel burn was to provide compressed air. Even a 10% would be a major fuel/cost savings with $50+ per barrel of oil.

Okie

sonic67 · Thu Mar 17, 2005 2:06 pm

Is the gearing in the gearbox the same as other engines and will the electric generator still be gear driven off the fan on the 787?

GS
biggrin

Okie · Fri Mar 18, 2005 2:57 am

I have not seen any diagrams of the new engines but I would guess you will see rare earth permanent magnets mounted in a hub on the N1 turbine. The starter/alternator will be a combined unit there would be no needed lubrication or mechanical losses incurred in a gear drive as everything will be electrically driven.

Starter/Alternator with RE magnets embedded in the flywheel of an automobile is common on electric/gasoline powered automobiles as well as some test engines with automotive manufacturers. It will just bring the technology up a notch to include aircraft.

But I am just guessing.

Okie

dl757md · Fri Mar 18, 2005 5:58 am

Quoting Sonic67 (Reply 30):
Is the gearing in the gearbox the same as other engines and will the electric generator still be gear driven off the fan on the 787?

I haven't seen any diagrams on the engine either. AFAIK all generators are mounted to the accessory gearbox which in a dual spool engine is driven by the N2 section. The reason that N2 drives the gearbox is because that except for at the fan and N1 turbine the N1 shaft is surrounded by the N2 shaft. The N1 shaft is a concentric shaft within the N2 shaft. There is a bevel gear on the N2 shaft that drives a tower shaft at a right angle to N2 which in turn drives the gearbox

Quoting Okie (Reply 31):
I have not seen any diagrams of the new engines but I would guess you will see rare earth permanent magnets mounted in a hub on the N1 turbine

Unlikely. The turbine area of a jet engine is too hot for this. In fact anywhere internal to the engine wouldn't make much sense as MX of it would be uneconomical.

Dl757Md

Pihero · Fri Mar 18, 2005 6:16 am

A question for you engineering types :
I was taught that there is something akin to energy conservation. So, a given power requirement like cabin pressurisation and air conditionning through air-cycle machines would remain the same,whether it comes from bleeding the compressor cycle or powering air pumps to the packs.
So, my question is : in the end, is not the power->energy->fuel burn the same ?
But as someone remarked, does the weight saving on pipes and ducts warrant that solution?
As far as can guess,the main gain could come from aerodynamics ,both external (more sreamlined cowling) and internal (better airflow control inside the compressor)

Am I right ?

Okie · Fri Mar 18, 2005 6:46 am

Quoting Okie (Reply 15):
In terms of efficiency,
The least is compressed air
The next would be hydraulic
The highest would be electric

Without numbers in front of me, lets just say from my past experience that you will only receive about 20-25% of the initial energy input at the work end with compressed air at around 80 psi. The efficiency will increase at lower pressures but will still be low.

On the other hand electrical resistance heating, as proposed for anti-icing on the 787 is one of the most inefficient uses of electricity. One would have to assume that the infrequent use of the need for anti-icing offsets that inefficiency in the long run.

Okie

Okie · Fri Mar 18, 2005 9:12 am

Quoting Dl757md (Reply 32):
I haven't seen any diagrams on the engine either. AFAIK all generators are mounted to the accessory gearbox which in a dual spool engine is driven by the SA de CV (Mexico)">N2 section

Again I am guessing that the magnets will be embedded in the first N2 section blade hub with stator windings around it which may make the first compressor section a little larger in diameter. As far as heat is concerned that term would be relative as massive amounts of air will passing by for cooling.

Again that is a guess.

Okie

[Edited 2005-03-18 01:40:19]

HAWK21M · Fri Mar 18, 2005 12:53 pm

Has there been any Sucessfull Aircraft with Bleedless Engines in the past.
regds
MEL

NDSchu777 · Fri Mar 18, 2005 1:11 pm

Okie,

From what I have heard the Starter/Generators will be mounted to the Accessory Gearbox of the engine and extract power the traditional way.

I can see where having the generator directly mounted on the spool would be efficient since you have no losses through a gearbox. However, the big negative I see is that the generator would be deep within the engine and inaccessable. I'm sure the generator is a very complicated unit and if you had a generator failure, it would not be replaceable on-wing, and would require the entire engine to be changed and a shop visit for repair. Mounting the generator on the gearbox makes it a line replaceable unit and if that component were to fail, it would be easy to just remove and replace and dispatch the airplane.

I can't speak for the engineers designing the engine, but that's why I think they're mounting the Starter/Generators on the AGB.

Nick

EconoBoy · Fri Mar 18, 2005 11:43 pm

Here's a link to a related topic:
https://www.airliners.net/discussions/tech_ops/read.main/84340

Jetlagged · Sun Mar 20, 2005 3:49 am

Quoting HAWK21M (Reply 36):
Has there been any Sucessfull Aircraft with Bleedless Engines in the past.
regds

Vickers VC10 (still a some flying with the RAF). Air conditioning source is mechanically pumped ram air.

Not that successful in terms of numbers built, but still operational after all these years.

astuteman · Mon Mar 21, 2005 3:03 am

You'll find an excellent article on the Trent 1000 bleedless engine in the January 14th - 27th issue of the Engineer Magazine (haven't got a link just now - only hard copy).

RR quote up to 20% of airflow in the HP CCOMPRESSOR section of the engine can be lost trying to balance airflows as a result of bleed. (I don't think this means 20% losses for the whole engine - just a few % I would guess).

One of the biggest efficiency gains RR do quote is new fan aerodynamics resulting in the fan being run 10% slower for a given thrust than in the Trent 900.

The other gain is - what power they do take off is coming off the IP compressor, and not the HP compressor. Apparrently an unexpected benefit of this is:- power off the HP compressor destabilises the compressor flows, whereas power off the IP compressor actually STABILISES the flow better.

Read the article if you can - some of it was over my head, but it was informative. I'll look for a link.

Astuteman

RR quote this as a unique advantage of their 3 spool design

astuteman · Mon Mar 21, 2005 3:13 am

Link to The Engineer article is at:-

www.theengineer.co.uk/articles/266429/Flight+fan-tastic.htm

Hope this works.

Only problem is You'll need to subscribe in order to view.

A

PW100Testpilot · Sun Mar 27, 2005 4:04 am

Quoting IFIXCF6 (Reply 10):

When testing a PW-100 turboprop we have nothing installed on the (accessory) gearbox accept for a starter and the fuelpump/fuelcontrol. All the other accessories like the AC generator, Hydraulic pump, Prop Control Unit, Overspeed governor are not neccesary to test an engine (we don't have a prop and we don't need electrical power from a generator etc.)
So, according to IFIXCF6, what we 'measure' is pure engine power (torque in SHP) without the loss of power to drive certain accessories.
Bleed air is not always blocked off, it depends on the powersetting if the Handling Bleed Valve is open or not (testing also includes bleed valve adjustment)
Oh and in comparison with all you jetfreaks, 'our' PW-100 can deliver 325 lbf Jet Thrust when in full take off (2750 SHP for a PW-127B) Smile

Btw this is my first post, I hope you enjoyed it Smile

PW100Testpilot · Sun Mar 27, 2005 4:13 am

Quoting NDSchu777 (Reply 37):
From what I have heard the Starter/Generators will be mounted to the Accessory Gearbox of the engine and extract power the traditional way.

I can see where having the generator directly mounted on the spool would be efficient since you have no losses through a gearbox. However, the big negative I see is that the generator would be deep within the engine and inaccessable. I'm sure the generator is a very complicated unit and if you had a generator failure, it would not be replaceable on-wing, and would require the entire engine to be changed and a shop visit for repair. Mounting the generator on the gearbox makes it a line replaceable unit and if that component were to fail, it would be easy to just remove and replace and dispatch the airplane.

I can't speak for the engineers designing the engine, but that's why I think they're mounting the Starter/Generators on the AGB.

I've also heard that you have to place generator on a gearbox otherwise the RPM at which the generator would turn would be way to high for it... And yes it is far easier to replace a unit installed on a (accessory) gearbox.

darkblue · Sun Mar 27, 2005 1:38 pm

One thing I haven't seen discussed yet in this thread is bleed resets. Taking bleeds off the compressor will not directly effect thrust because at high power the engine is controlled to either N1 or EPR. Using bleed air will only force the core to work harder to get the same work out of the low pressure turbine (to power the fan). This will impact fuel consumption not thrust directly. This impact on fuel consumtion is why Boeing has requested bleedless engines.

Now, back to bleed resets for engines that actually have to provide bleed air to the aircraft. When the core is forced to work harder, the result is higher temperatures in the turbine. To protect the turbine, bleed resets are included in the power management that pull the engine back in power whenever bleed is increased. This all occurs transparent to the pilot.

For example, when the pilot turns on the anti-ice system, an increase of bleed is pulled off the engine. The engine reacts by lowering the N1 the engine is run to. However, the indicated N1 in the cockpit is unchanged. So indirectly, thrust will decrease due to bleeds.

Klaus · Mon Mar 28, 2005 10:17 pm

DarkBlue: For example, when the pilot turns on the anti-ice system, an increase of bleed is pulled off the engine. The engine reacts by lowering the N1 the engine is run to. However, the indicated N1 in the cockpit is unchanged. So indirectly, thrust will decrease due to bleeds.

But only if the core is already at its limit, right? Unless it was for that, why burden the pilot with a loss of net thrust to worry about?

darkblue · Tue Mar 29, 2005 1:04 am

Quoting Klaus (Reply 45):
But only if the core is already at its limit, right? Unless it was for that, why burden the pilot with a loss of net thrust to worry about?

Yes, the bleed resets are designed to pull back the engine only at conditions of high EGT. However, it's not perfect so I'm sure there are plenty of conditions where engines still have margin but N1 is still decreased.

However, remember that the only time when more thrust is not going to be available is when full rated takeoff is required. During derated takeoffs turning bleed on only means that less derate is used. I'll let the pilots on this board respond to this, but I believe they have special rules when using bleeds at full rated takeoff (no derates). I think they're allowed to use the APU for longer durations if needed.

Who is online

Popular Searches On Airliners.net