NCB From Japan, joined Jan 2008, 353 posts, RR: 1 Posted (9 months 3 weeks 1 day 16 hours ago) and read 4823 times:
The GEnx engines are expected to be 15% more efficient than actual engines on the B763/A332.
Most of that efficiency is gained thanks to the removal of the bleed air system. The bleed air system provides compressed air for cabin pressurisation, anti- and de-icing and has the merit of removing toxic ozone.
The absence of bleed air must be compensated by installing heavier electricity-hungry systems:
-air compressors causing drag at the air intake, consuming alot of electricity
-electric de-icing systems consuming alot of electricity but probably lighter than bleed air systems
-improved a/c systems
-ozone filters: actual bleed air aircraft have a couple of these installed, though most of the Ozone is eliminated through the compressors
Where the GEnx removes the need for heavy ducts, the B787 gets heavy wires and systems to compensate for it and requires more electricity to run the electric systems. More electricity and more weight means higher fuel burn and decreased aircraft efficiency.
Now let's look at it from an operating point of view:
Let's take the scenario of the B787 loosing one engine in flight. Will it be able to keep the cabin pressurized, ozone-free and anti-ice running on one engine and APU? ETOPS will certainly require a bigger and heavier APU.
The Airbus XWB design will keep the bleed air and engineers at Airbus seem to agree that it would be more efficient to do so.
Scbriml From Saudi Arabia, joined Jul 2003, 8429 posts, RR: 25 Reply 1, posted (9 months 3 weeks 1 day 16 hours ago) and read 4795 times:
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Quoting NCB (Thread starter): Most of that efficiency is gained thanks to the removal of the bleed air system.
When the bleedless engines on the 787 were first being discussed, the alleged efficiency gain was significantly over-played. I believe even the manufactures now say that there is very little difference in efficiency between bleed and bleedless versions of the same engine.
It seems clear to me, given Airbus's decision that the A350 will not be bleedless, that when considering the whole system, there is no clear operating advantage for one over the other. Bleedless proponents will claim that maintenance of a more electrical system should produce long-term maintenance savings. This is yet to be proven in large commercial passenger planes, so I guess we won't know for a while yet.
PhilSquares From Ireland, joined Mar 2004, 3741 posts, RR: 53 Reply 2, posted (9 months 3 weeks 1 day 16 hours ago) and read 4687 times:
First of all, the Airbus product doesn't have the option of having the Genx engines so they had to have a bleed system as RR was not willing to commit to a bleedless engine.
The associated weight of the pneumatic system is considerable and the offset of the additional generating capacity will still be lighter than a "conventional" system.
With respect to the electrical loads in the event of an engine failure, let's think about this. Does it make any sense for the FAA/JAA to certify an aircraft where the cabin pressure couldn't be maintained. A 777/330 with the bleed system still has the same issues with respect to bleed air and engine anti-ice. In addition, there is a APU available, plus load shedding buses. Just to make a point, on the 747-400 the APU GEN and IDG are physically the same, the IDG is rated at 60KVA while the APU Gen is rated at 90KVA. The difference is forced air cooling on the APU GEN.
The drag associated with the intakes will be no more than currently exists on the current aircraft that have the inlet/exhaust doors for the AC Packs.
Personally, I think it's great and it's a large step forward. On the aircraft I've flown, the pneumatic system has been the weakest system in the aircraft. If it's exposure can be reduced or eliminated, then I'm all for it.
Rheinwaldner From Switzerland, joined Jan 2008, 377 posts, RR: 1 Reply 3, posted (9 months 3 weeks 1 day 16 hours ago) and read 4666 times:
It seems very difficult to judge advantages for both systems from our layman's standpoint.
But still I would like to learn more about the bleed-less technology. What is driven by electric current on a 787 that uses bleed air elsewhere? The list of consumers so far mentioned in this thread:
- Cabin pressurisation
- De icing (of wings leading edge?)
Is this list complete?
General remarks:
Some time ago I searched for Boeing statements about it. I struggled to find something. Thus I wonder what does Boeing communicate about that feature? To me it seems they no longer claim better efficiency and maintenance-savings.
Advantages for bleed-less that I see:
- Electric machines always run with > 99 percent efficiency factor
- That allows power transmission nearly without energy loss
- Energy is taken directly from the engines shaft
- Maintenance checks are concentrated on some spots (where the E-machines are)
- Infrastructure that is there anyway can be used (generators)
Disadvantages for bleed-less:
- Some maintenance person here once said, the ducts are virtually "maintenance-free" while electric machines often cause troubles
- Maybe weight of electric components
- Failure rate may be higher
- Troubles in case of complete loss of electricity (as recently the Qantas Jumbo)
What is better now? I have no idea! To trade-off these these points is hardly possible. I think even Boeing will not find out before the system are operated daily for some time.
Planemaker From Tuvalu, joined Aug 2003, 3475 posts, RR: 18 Reply 4, posted (9 months 3 weeks 1 day 16 hours ago) and read 4659 times:
I don't think that Boeing agrees with you...
While much can be said regarding the efficiency gains achieved by changing the means of extracting power for airplane systems from the engines, the 787's no-bleed architecture brings with it some significant maintenance cost and reliability advantages as well. By eliminating the pneumatic systems from the airplane, the 787 will realize a notable reduction in the mechanical complexity of airplane systems. Overall, the 787 will reduce mechanical systems complexity by more than 50 percent compared to a 767; the elimination of pneumatic systems is a major contributor.
The list below highlights just a few of the components eliminated as a result of this systems change:
Pneumatic engine and APU start motors
APU load compressor
Precoolers
Various ducts, valves, and air control systems
Leak and overheat detection systems
Auxiliary power unit. The APU provides an excellent illustration of the benefits of the more electric architecture. One of the primary functions of a conventional APU is driving a large pneumatic load compressor. Replacing the pneumatic load compressor with starter generators results in significantly improved start reliability and power availability. The use
of starter generators reduces maintenance requirements and increases reliability due to the simpler design and lower parts count. In terms of inflight start reliability, the 787 APU is expected to be approximately four times more reliable than conventional APU s with a pneumatic load compressor.
Electrical power generation. Another fundamental architectural change on the 787 is the use of variable frequency electrical power and the integration of the engine generator and starter functions into a single unit. This change enables elimination of the constant speed drive (also known as the integrated drive generator, IDG), greatly reducing the complexity of the generator. In addition, by using the engine generator as the starter motor (an approach used with great success on the Next-G eneration 737 APU), the 787 has been able to eliminate the pneumatic starter from the engine.
When compared to the more complex 767 IDG, the 787 starter generator is predicted to have a mean time between faults (MTBF) of 30,000 flight hours %u2014 a 300 percent reliability improvement compared to its in-service counterpart.
Brakes. One innovative application is the move from hydraulically actuated brakes to electric. Electric brakes significantly reduce the mechanical complexity of the braking system and eliminate the potential for delays associated with leaking brake hydraulic fluid, leaking valves, and other hydraulic failures.One innovative application of the more-electric systems architecture on the 787 is the move from hydraulically actuated brakes to electric. Electric brakes significantly reduce the mechanical complexity of the braking system and eliminate the potential for delays associated with leaking brake hydraulic fluid, leaking valves, and other hydraulic failures. Because its electric brake systems are modular (four independent brake actuators per wheel), the 787 will be able to dispatch with one electric brake actuator (EBA) inoperative per wheel and will have significantly reduced performance penalties compared with dispatch of a hydraulic brake system with a failure present. The EBA is line-replaceable enabling in-situ maintenance of the brakes.
In general, electric systems are much easier to monitor for health and system status than hydraulic or pneumatic systems; the brakes take full advantage of this. Continuous onboard monitoring of the brakes provides airlines with a number of advantages, such as:
Fault detection and isolation
Electrical monitoring of brake wear
Ability to eliminate scheduled visual brake wear inspections
Extended parking times
Because the 787 brakes can monitor the braking force applied even while parked, the electric brakes enable extended parking brake times by monitoring and automatically adjusting its parking brakes as the brakes cool.
At an airplane level, the reduction in systems parts by moving to a primarily electric architecture is significant. Overall, the 787 will reduce mechanical systems complexity by more than 50 percent compared to a 767; elimination of pneumatic systems is a major contributor. As a consequence of this reduction in complexity, airlines will experience reduced airplane-level maintenance costs and improved airplane-level dispatch reliability.
In fact, the move to electric systems is expected to cut about a third of the schedule interrupts compared to a 767 for the systems affected by the no-bleed/more-electric architecture. Other benefits include improved health monitoring, greater fault tolerance, and better potential for future technology improvements.
Moo From Falkland Islands (Malvinas), joined May 2007, 2610 posts, RR: 7 Reply 5, posted (9 months 3 weeks 1 day 16 hours ago) and read 4643 times:
Quoting PhilSquares (Reply 2): First of all, the Airbus product doesn't have the option of having the Genx engines so they had to have a bleed system as RR was not willing to commit to a bleedless engine.
Uhm, the TrentXWB is based off the Trent 1000 which is Rolls Royces offering for the 787 series, and is infact bleedless. RR were going to offer a bleed version of it for the original A350 design, in the same vein as GE offering a bleed version of the GEnx for the 747-8.
KC135TopBoom From United States, joined Jan 2005, 5566 posts, RR: 36 Reply 7, posted (9 months 3 weeks 1 day 16 hours ago) and read 4618 times:
Quoting NCB (Thread starter): The GEnx engines are expected to be 15% more efficient than actual engines on the B763/A332.
The savings don't come only from the bleedless system. These engines truely are a generation more advanced than the PW4062, CF-6-50s or RB-211s.
Quoting NCB (Thread starter): Where the GEnx removes the need for heavy ducts, the B787 gets heavy wires and systems to compensate for it and requires more electricity to run the electric systems. More electricity and more weight means higher fuel burn and decreased aircraft efficiency.
Now let's look at it from an operating point of view:
Let's take the scenario of the B787 loosing one engine in flight. Will it be able to keep the cabin pressurized, ozone-free and anti-ice running on one engine and APU? ETOPS will certainly require a bigger and heavier APU.
No, eliminating the bleed air systems and ducts will not make the airplane heavier. It will become lighter. The engines on the B-787 do sport larger generators, as far as electrical capacity goes. ETOPS should not be effected, as the B-787 is designed from the ground up to be both more effecient and ETOPS capable.
Quoting NCB (Thread starter): The Airbus XWB design will keep the bleed air and engineers at Airbus seem to agree that it would be more efficient to do so.
There is only one reason why Airbus didn't go with a bleedless system. They couldn't figuer out a way to do it around the Boeing patents. Bleedless systems promise lower cabin altitudes, with more humidity. These B-787s will not dry you out, like current airplanes, or the future A-350 will.
So, the Airbus engineers (who seem to agree using engine bleed air is efficient) are designing a modern, high tech airplane with an old low tech system.
There is a reason why Airbus decided to build the A-350 in the same class as the (by then) almost 30 year old design B-777 and A-340s. That is because they could not compete in the B-787 class, which will replace B-767s and A-330s.
PhilSquares From Ireland, joined Mar 2004, 3741 posts, RR: 53 Reply 8, posted (9 months 3 weeks 1 day 16 hours ago) and read 4617 times:
Quoting Moo (Reply 5): Uhm, the TrentXWB is based off the Trent 1000 which is Rolls Royces offering for the 787 series, and is infact bleedless. RR were going to offer a bleed version of it for the original A350 design, in the same vein as GE offering a bleed version of the GEnx for the 747-8.
But GE wasn't so they (Airbus) couldn't have two aircraft, one bleed the other bleedless. If that's not accurate, I stand corrected.
ScrubbsYWG From Canada, joined Mar 2007, 1010 posts, RR: 0 Reply 9, posted (9 months 3 weeks 1 day 16 hours ago) and read 4592 times:
Quoting NCB (Thread starter): Let's take the scenario of the B787 loosing one engine in flight. Will it be able to keep the cabin pressurized, ozone-free and anti-ice running on one engine and APU? ETOPS will certainly require a bigger and heavier APU.
Now, i'll be the first to admit that my knowledge of jet propulsion engines is little to none, but does this paragraph make sense?
The way i understand it(correct me if i am wrong), if you lose an engine on a bleed air version, your plane loses that engine's ability to keep the cabin pressurized, ozone-free and anti-ice running on one engine and APU because you can't draw the bleed air from the shut down engine. Wouldn't that mean a plane with bleedless design is better off in cases of engine failure?
However, i think you are talking about losing the engine's ability to power electrical generators or whatever is needed to power the new systems that bleed air would have taken care of in the past, correct? Well, if that is what you are asking, without knowing the systems design for the 787, i think it is very difficult to say if the 787 is worse off with a bleedless engine shut down when referring to keeping the cabin pressurized, ozone-free and anti-ice running on one engine and APU.
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Moo From Falkland Islands (Malvinas), joined May 2007, 2610 posts, RR: 7 Reply 10, posted (9 months 3 weeks 1 day 15 hours ago) and read 4550 times:
Quoting PhilSquares (Reply 8): But GE wasn't so they (Airbus) couldn't have two aircraft, one bleed the other bleedless. If that's not accurate, I stand corrected.
Actually the GEnx offering for the original A350 was also bleed, so both engine options (GE and RR) were infact bleed variants of the 787 engines - there was no particular reason why GE couldn't offer a bleed variant since they were going that way with Boeing on the 747-8.
Scbriml From Saudi Arabia, joined Jul 2003, 8429 posts, RR: 25 Reply 11, posted (9 months 3 weeks 1 day 14 hours ago) and read 4317 times:
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Quoting KC135TopBoom (Reply 7): There is only one reason why Airbus didn't go with a bleedless system. They couldn't figuer out a way to do it around the Boeing patents.
Which patents can't Airbus figure a way round?
Quoting KC135TopBoom (Reply 7): Bleedless systems promise lower cabin altitudes, with more humidity.
I don't think that has anything to do with being bleedless. The A350 also offers lower altitude cabin pressuse and higher humidity.
Astuteman From United Kingdom (England), joined Jan 2005, 4919 posts, RR: 69 Reply 12, posted (9 months 3 weeks 1 day 14 hours ago) and read 4256 times:
Is it April 1st already?
Quoting NCB (Thread starter): Most of that efficiency is gained thanks to the removal of the bleed air system
Not correct - at all.
Quoting KC135TopBoom (Reply 7): The savings don't come only from the bleedless system. These engines truely are a generation more advanced than the PW4062, CF-6-50s or RB-211s.
Correct. I'd venture to suggest that the SFC efficiency gains from "bleedless" (which isn't really fully bleedless anyway, in the same way that Airbus's "bleed-air" isn't fully bleed air either) is minimal. I can buy a maintenance saving through life, though , though
Quoting PhilSquares (Reply 2): First of all, the Airbus product doesn't have the option of having the Genx engines so they had to have a bleed system as RR was not willing to commit to a bleedless engine.
Quoting PhilSquares (Reply 8): But GE wasn't so they (Airbus) couldn't have two aircraft, one bleed the other bleedless. If that's not accurate, I stand corrected
I know Moo's answered these, but the old A350 was offered with both the GEnx, AND the T1000, EXACTLY the same as the 787 - only bleed-air. And GE were first on the platform, by a long way.
Quoting KC135TopBoom (Reply 7): There is only one reason why Airbus didn't go with a bleedless system. They couldn't figuer out a way to do it around the Boeing patents
That sounds plausible
Quoting KC135TopBoom (Reply 7): There is a reason why Airbus decided to build the A-350 in the same class as the (by then) almost 30 year old design B-777 and A-340s. That is because they could not compete in the B-787 class, which will replace B-767s and A-330s
This doesn't, though.
I can more readily accept that they saw that the 788 had already gobbled up a large share of the 250 seat segment, and also realised that the A340NG was on life-support.
Aiming at a range greater than 250 up to 360 therefore made sense.
It does to me (although of course the 250 seat gap is still there).
Aerosol From Germany, joined Oct 2000, 483 posts, RR: 0 Reply 13, posted (9 months 3 weeks 1 day 14 hours ago) and read 4183 times:
Quoting KC135TopBoom (Reply 7):
There is only one reason why Airbus didn't go with a bleedless system. They couldn't figuer out a way to do it around the Boeing patents. Bleedless systems promise lower cabin altitudes, with more humidity. These B-787s will not dry you out, like current airplanes, or the future A-350 will.
Moo From Falkland Islands (Malvinas), joined May 2007, 2610 posts, RR: 7 Reply 14, posted (9 months 3 weeks 1 day 13 hours ago) and read 4147 times:
Quoting KC135TopBoom (Reply 7): There is a reason why Airbus decided to build the A-350 in the same class as the (by then) almost 30 year old design B-777 and A-340s. That is because they could not compete in the B-787 class, which will replace B-767s and A-330s.
Firstly, the market the XWB is aimed at is the 777 and A340-500/600 market, neither of which are '30 years old' - 13 at best (first 777 entered service in 1995), and secondly the reason I see Airbus as not competing directly with the 787 is not because they can't (Airbus is perfectly able to produce quality aircraft), but because Boeing has the short term orders in that market sewn up - Airbus would have to suffer a longer break even period as they would not enjoy the short term orders necessary to make that period shorter, so why enter that market at all currently?
Airbus thus decided the best market to go for is the next oldest they could offer a solution for - the lower end 777-200 market which is destined to see a renewal spate in the next 5 to 10 years, and later on the higher end 777-300/A340-500/600 market with a stretch. Also by aiming their offering at a larger base version, they have the potential to serve better economics on future large stretches of the same type.
Moo From Falkland Islands (Malvinas), joined May 2007, 2610 posts, RR: 7 Reply 15, posted (9 months 3 weeks 1 day 13 hours ago) and read 4110 times:
Quoting KC135TopBoom (Reply 7): There is only one reason why Airbus didn't go with a bleedless system. They couldn't figuer out a way to do it around the Boeing patents.
I'm sorry, but thats complete crap. Unless Boeing has a patent on 'Using electrical systems in place of air blown hydraulics in an aircraft' (which is an unbelievably broad patent and would almost certainly be thrown out if challenged), theres no reason Airbus could not find a way around it as patents under US law cover specific concepts and the specific application of that concept - you cannot patent an concept (bleedless system) in its entirety.
After all, Boeing uses composites for many of the same parts that Airbus has patents for....
BlueSky1976 From Poland, joined Jul 2004, 1057 posts, RR: 3 Reply 17, posted (9 months 3 weeks 1 day 13 hours ago) and read 4005 times:
Quoting KC135TopBoom (Reply 7): Bleedless systems promise lower cabin altitudes, with more humidity. These B-787s will not dry you out, like current airplanes, or the future A-350 will.
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