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dl757md
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7E7 Radical Changes

Mon Jun 21, 2004 9:53 am

Found this article on the 7E7 which details some of the radical approaches Boeing is using to achieve their efficiency goals.

http://seattlepi.nwsource.com/business/174159_electric20.html

What I was wondering is, with such a heavy reliance on electric power, are the weight savings realized by the elimination of pneumatics and switch to a 5000psi hyd system somewhat offset by the considerably larger and heavier electrical power busses required and much larger standby electric system? I realize the elimination of the pneumatics was primarily for engine efficiency with weight reduction being a secondary benefit.

In any event it looks like we're all going to have to learn a lot of new stuff for this one. Should really keep the avionics guys busy.
757 Most beautiful airliner in the sky!
 
LMP737
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RE: 7E7 Radical Changes

Mon Jun 21, 2004 11:36 am

Evidently Boeing is going to use the VSCF system on the 7E7 to cut down on weight. Hopefully they will have learned the lessons of the MD-90 program and design the system that will not latch onto every little fault.
Never take financial advice from co-workers.
 
dl757md
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RE: 7E7 Radical Changes

Mon Jun 21, 2004 12:00 pm

Yeah, it sounds like the VSCF system but with the added complexity of using the generators as starters. Sounds fun. As for not latching every nuisance fault.....we can only hope.
757 Most beautiful airliner in the sky!
 
lehpron
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RE: 7E7 Radical Changes

Wed Jun 23, 2004 12:06 pm

Pardon my ignorance, I do not see what is so radical about using more than usual, or any at all, electrical components. According to the tone in the article, it has never been done before, hence a big deal. Shall I ask, how those systems ran in the first place and on what power source; a weed-wacker motor perhaps?

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dl757md
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RE: 7E7 Radical Changes

Fri Jun 25, 2004 1:36 am

Lephron

A large part of what makes air travel so safe are the conservative engineering methods used to design aircraft and their systems. Change is evolutionary rather than revolutionary. That is why we see many radical designs never progress beyond wind tunnel models or drawings. Think sonic cruiser, Boeing BWB, etc..

Jet transport AC systems, with the exception of avionics, have changed very little since the 707 and DC-8. Pneumatics, electrical, and hydraulics have seen the least change. The changes in hydraulics will be the most evolutionary. I'm not sure but I think the military already uses some 5000 psi systems and the A-380 will too.

The complete change from pneumatics to electrical for anti-ice, pressurization, back-up hydraulics, engine starting, hydraulic resevoir pressurization, and potable water pressurization is a paradigm change. You are eliminating an entire ATA system chapter and requiring another to take over it's functions as well as perform those it already has. One reason this hasn't been tried already is that having seperate systems share tasks gives you built in redundancy. Reducing the number of systems requires that more redundancy be engineered into the remaining systems.

None of this is impossible. It's just a large departure from standard aircraft design and one that is entirely neccessary to achieve the design efficiency goals that Boeing has for The 7E7.

Dl757md
757 Most beautiful airliner in the sky!
 
lehpron
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RE: 7E7 Radical Changes

Sat Jun 26, 2004 8:08 am

So it will be an unseen change to the plane as view throughout it's performance lifetime, hardly radical, more like a well deserved change in the category of "it's about time"

>> "A large part of what makes air travel so safe are the conservative engineering methods used to design aircraft and their systems. Change is now evolutionary rather than revolutionary" <<

You missed a word, I threw it in as bold. If the industry was following a standard business cycle, then we are in the mature stage, it's is not conservative, rather traditional. We had an introduction cycle and a growth cycle. I would hate to figure what a decline cycle would involve...

Those concepts you spoke of are far from radical, lack of interest was what killed one and the other is simply early (they are no supposed to fly any time soon anyway), their shape only has to do with the word radical as it varies by perception from person to person. I would not consider the modern aerospace industry as invoking a conservative engineering perspective by a long shot. They do not call the shots, their bosses do, people who know costs rather than engineering. Modern engineers' imaginations are being restricted, aside from the fact that there are more than just one solution to every problem. This industry was built on risk-taking and now the business folks have taken it over by making risk-taking bad.

Hopefully another introduction or growth cycle will appear, i do not trust prolonged maturing of technology (past 35 years), it is almost like people would be willing to take things for granted to such an enormous degree that they would be will to give up things they enjoyed before.

The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
LineMechQX
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RE: 7E7 Radical Changes

Wed Jun 30, 2004 3:48 pm

Dl757md-
Starter/Generators are DC not AC, as the big generators are going to be. More then likely these engines will have a completely separate starter. That's not even starting on the subject of the historical reliability of starter/generators on the smaller turbine DC aircraft that use them everyday (think the Dash family)

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kalakaua
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RE: 7E7 Radical Changes

Wed Jun 30, 2004 9:30 pm

This table is interesting.

Gravity explains the motions of the planets, but it cannot explain who set the planets in motion.
 
lehpron
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RE: 7E7 Radical Changes

Sun Jul 04, 2004 12:47 pm

>> "Each of the two engines will have 225-Kilowatt generators to produce electrical power" <<

I am thinking of either a hybrid car's braking system or a desiel train engine, that's what came to mind anyway. Almost sounds as if they are doing away with the APU.

As a whole it is an improvement, but far from radical. Big grin

[Edited 2004-07-04 05:48:08]
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
meister808
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RE: 7E7 Radical Changes

Sun Jul 04, 2004 1:03 pm

Regarding the generators:

What is the difference, either positive or negative, between the theoretical thrust 'lost' by bleed air and the theoretical thrust 'lost' to turning the generators in a theoretical engine where there were identical versions, one to be mated to a bleed-air system and the other to be bleedless and turning generators such as the proposed 225kW ones for the 7E7?

-Meister
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
 
lehpron
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RE: 7E7 Radical Changes

Sun Jul 04, 2004 3:56 pm

An engine with a bleed air system may have to do slightly more work just to maintain flight thrust and force the air to be ducted elsewhere whereas a generator may run with the engine (either same shaft or a gearbox) so .... hmm.... it would have to do slightly more work too...darnnit. It may be negligible just like the weight savings claims. Big grin

Ignore my response unless I was on the right track. Embarrassment
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Klaus
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Lehpron

Sun Jul 04, 2004 9:31 pm

The problem is probably in the engine operating outside of its optimal airflow regime.

There are more efficient and less efficient combinations of thrust and N1, N2 and bleed air volume/pressure. Optimizing an engine to just produce the right amount of thrust at the best possible efficiency is complicated, but when you add every conceivable combination of bleed air requirement at every possible thrust setting to the equation, I´m sure it gets even more complicated. And I guess some of those combinations are not quite as efficient as others, thus reducing average efficiency.

It may be less problematic to extract rotational energy from the N2 or N3 shaft than to extract compressed air which would skew the combustion mix. (Which would force the developers to provide a significant potential of excess airflow for the "worst case" which is not needed most of the time. For the "electrical" engine, you´d need additional torque potential in case the generators increase their load.)

I´m just guessing, but it seems somewhat plausible...

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