MesaMXORD From , joined Dec 1969, posts, RR: Posted (8 years 10 months 1 week 1 day 5 hours ago) and read 7655 times:
I was reading the website and it said that it has Starter Gens that start the engine and then provide electrical power to supply the A/C and ECS. I'm still confused on how the 787 A350 747-8 bleeds will work or is the APU running all the time? Will this be an issue in service with this new technology? I am still stuck on the conventional APU supplies air the the ATS then motor supplies bleed air to ACM etc, etc......
There are going to be no "bleeds" in 787 except for engine nacelles anti-ice, period. Based on what I read the apetite of 787 for electricity will therefore be 4 times higher than other conventional aircraft with engine bleeds. So yes, it needs generators, generators and more generators.
Aviator27 From , joined Dec 1969, posts, RR:
Reply 2, posted (8 years 10 months 1 week 1 day 5 hours ago) and read 7595 times:
The conventional systems that use bleed air will be replaced by electrical air pumps. For example, the bleed air that is used for air conditioning and pressurization will not be "bled" off the engines, but instead be generated by an electrically powered air pump.
The APU also will not provide bleed air because it won't be needed for Air Conditioning or Engine Start. Engine start will be provided by an electrical motor (similar to your car's starter) as opposed to an pneumatic air starter currently in use. An APU will still be needed to provide electrical power while on the ground with the engines not running.
Energy is energy and you have to get it from somewhere. Boeing believes they can gain greater efficiency by using electrical energy instead of pressurized air energy (bleed air from engines). Airbus believes its a net zero sum gain (or close to it).
Airbus tried to put bleed-less engines on the A330/A340 about 20 years ago but the engines were not available at the time. Jump to 2006 and now they don't want to use bleed-less engine technology. Perhaps its a case of them trying to avoid "monkey see-monkey do". Then again, Boeing is switching to "Airbus style" assembly of airplanes.
If it works, then it works and eventually the technology will be incorporated in all future transport airplanes. If it flops, then it flops. Only the future holds the truth.
Saturn5 From United States of America, joined Apr 2006, 313 posts, RR: 0
Reply 3, posted (8 years 10 months 1 week 1 day 4 hours ago) and read 7572 times:
Quoting Aviator27 (Reply 2): Boeing believes they can gain greater efficiency by using electrical energy instead of pressurized air energy (bleed air from engines). Airbus believes its a net zero sum gain (or close to it).
Boeing actually admits that this is close to net zero sum gain or that savings won't be significant. But their main motivation behind this bleedless technology is that they had reached conclusion that pneumatics technology won't advance much further whereas they expect further significant advances in the electrics - this was they will have a ready aircraft that can utilize even more efficient electrical components that will apparently be coming in the following years (lighter, more efficient, etc.).
Atmx2000 From United States of America, joined Oct 2004, 4576 posts, RR: 37
Reply 4, posted (8 years 10 months 1 week 1 day 4 hours ago) and read 7561 times:
Quoting Aviator27 (Reply 2): Energy is energy and you have to get it from somewhere. Boeing believes they can gain greater efficiency by using electrical energy instead of pressurized air energy (bleed air from engines). Airbus believes its a net zero sum gain (or close to it).
Boeing has argued that there are weight, maintenance and procurement advantages for other systems if you go bleedless. If it were just an energy issue, it might not be worth the effort.
ConcordeBoy is a twin supremacist!! He supports quadicide!!
MesaMXORD From , joined Dec 1969, posts, RR:
Reply 5, posted (8 years 10 months 1 week 1 day 4 hours ago) and read 7541 times:
Well the less bleed air lines the better ripping apart the A/C to find A bleed leak (whether a bad detection loop or actual leak) Is no fun! Nor is isolating a problem from the APU to engine with a start issue (LCV to ISOL Valve to the ATS). Also what will all those generators be like for dispatch ex: MEL, ETOPS, etc.
Okie From United States of America, joined Jul 2003, 3251 posts, RR: 3
Reply 7, posted (8 years 10 months 1 week 7 hours ago) and read 7339 times:
Thanks for the link ReidYYZ.
I had to search to find it.
The article answers a lot of questions an engineer has been wondering about.
They are bringing quite a bit of industrial bread and butter to the table for aircraft after a decades of R & D on the industrial side. Up until about 10 years ago reliability, size and weight would have been major issues of the electrical devices mentioned in the article.
Okie From United States of America, joined Jul 2003, 3251 posts, RR: 3
Reply 9, posted (8 years 10 months 5 days 11 hours ago) and read 7219 times:
One thing I noticed in the article ReidYYZ had linked was the use of "air foil" bearings on the "ACM's"
While not a new technology, I would am not so sure it is a mature technology. What little information I could gather quickly, mentioned the use of air foil bearings in ACM's but I do not know if they were referring to ACM's used in the 787 or if this has been used in ACM's for some period of time.
Maybe some Mx could give a little insight.
The article stated that the compressors for the ACM's turned at a whopping 42,000 rpm with a 12" diameter wheel with a 100 hp motor. That has got to be heavy. I don't think "Tiny" is going to be lifting one up in the wing root with one hand while he bolts it in with the other.
ReidYYZ From Kyrgyzstan, joined Sep 2005, 536 posts, RR: 0
Reply 10, posted (8 years 10 months 5 days 10 hours ago) and read 7211 times:
Quoting HAWK21M (Reply 8): Gearbox driven Pneumatic Air Pumps for each Engine.
Not sure if this is a question or spontaneous outburst. However, another benefit and great weight savings is the running of wiring for the operation of the elex compressors (which are an integeral part of the pack as show in a figure in the magazine, not the e-article) versus the routing of pneumatic ducting, monitoring equipment and subsequent time lost to maintenance of said ducting and other components. Also as stated in the article, pneumatic technology is at a maturity that probably would not go much further. As opposed to electrics, with broader industrial use and great R&D $ going into it. It has a greater future for exploration.
Quoting Okie (Reply 9): I would am not so sure it is a mature technology.
Air bearings have been in use since at least the dawn of the B757/767 program, maybe even early A300's (not sure). Occasionally, with certain conditions in place, the ACM's will seize in its last place. First step in the TSM is to pull out the ACM. While holding it down, check break away torque to free it up. 9 out of 10 times it was within limits and throw it back on. With no re-occurrence of snag.