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  (Source: Boeing)

  (Source: Boeing)
Boeing glides along with Dreamliner development

Boeing has a lot riding on its 787 Dreamliner program, and after a two-year delay, things appear to be panning out nicely for the Seattle-based company. The first 787 Dreamliner made its maiden flight on December 15, 2009 and stayed aloft for roughly three hours.

The second 787 Dreamliner took to the air a week later featuring the markings of the first customer which will receive the new planes: All Nippon Airways (ANA). In total, 15 flights (totaling nearly 60 hours) have been made so far using the first two aircraft.

Another milestone was reached late last week; the 787 Dreamliner achieved "initial airworthiness" status. This milestone allows Boeing to open up the testing phase to more aircraft. Boeing flight engineers will also be allowed on the flight deck now according to the Associated Press.

"This is an important step forward," said Boeing Commercial Airplanes VP Scott Fancher. "We are very pleased with the results we have achieved so far. The airplane has been performing as we expected."

The previous test flights have seen the 787 Dreamliners reach a top speed of Mach 0.65 and an altitude of 30,000 feet. In the coming weeks, Boeing test pilots will take the aircraft to Mach 0.85+ and in excess of 40,000 feet.

"The pilots have told me the results we are seeing in flight match their expectations and the simulations we've run. That's a real tribute to Boeing's expertise and the international team that helped develop and build the airplane," Fancher added.

ANA is expected to receive its first 787 Dreamliners during the fourth quarter of 2010. The Japanese airliner has ordered 55 of the aircraft.



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RE: Conventional looking now
By Amiga500 on 1/19/2010 9:06:07 AM , Rating: 2
Yes, it is quite funny.

Not many would believe you if you pointed out an isotropic lay-up Carbon Fibre composite will be heavier than an equivalent strength titanium component.


RE: Conventional looking now
By Spacecomber on 1/19/2010 10:26:08 AM , Rating: 2
I assume the advantage is in ability to more easily shape the part to a specific purpose. This makes it easier to make do with less; so, you may end up with a weight savings in the final product. Carbon fiber composite bikes have pretty much replaced everything metal at the high-end, for example. (On the other hand, I'd never trade my titanium frame for a composite, in part, because of its durability. No one will be giving a me new frame if I break this one, unlike for the professional riders.)


RE: Conventional looking now
By stromgald30 on 1/19/2010 12:18:29 PM , Rating: 2
Yes, most people don't know the details of composites and would make that mistake.

However. . . who uses isotropic lay-ups? I doubt more than 5% of composites on the 787 are isotropic. You're basically comparing one of the structurally weakest composite designs with a metal that's good in any direction. Of course it'll be inferior.


RE: Conventional looking now
By Amiga500 on 1/19/2010 3:22:14 PM , Rating: 2
You'd be very surprised at how close everything is to a balanced laminate. It has to be for a myriad of other reasons (which I'm guessing you are somewhat familiar with).

Orientate more than 30-40% of your lamina in any one direction and your laminate will start to become weaker, not stronger. That it accentuated when a hole exists (such as bolt hole).

Oh, and the metal has good through thickness strength - a composite will never have that without 3D weaving - which isn't used in the aerospace industry.


RE: Conventional looking now
By Keeir on 1/19/2010 6:56:29 PM , Rating: 2
Err... I guess that all depends on your notion of "balanced laminate". Also, I am fairly sure your assertion is primarly true for tensile or axial compression type loads.

Even a "Balanced" Laminate is significantly less dense than Titanium. Also significantly less expensive. A Balanced Composite comes down as in general significantly stronger per dollar than titanium in all but a few applications.

Not that I like composites, expecially due to as you mentioned the through thickness strength


RE: Conventional looking now
By Amiga500 on 1/20/2010 5:41:35 AM , Rating: 2
A balanced laminate has the same density as an unbalanced laminate...

What I was saying is that you can make a lighter titanium component to do the same job as a isotropic composite lay. That is not the same as saying less dense. The component dimensions will be different, hence the different weights.


RE: Conventional looking now
By Solandri on 1/20/2010 4:46:59 PM , Rating: 2
It's been over a decade since I did directional strength calculations for composite lays. But for most applications a 0-60-120 lay ends up pretty close to isotropic properties (except perpendicular to the panel of course).

CF has about 7x the tensile strength of titanium
Titanium is about 4.5 g/cc, CF about 1.75 g/cc, epoxy about 1.0 g/cc
Figure a 60/40 ratio of epoxy to CF

For a load in the 90 degree direction (its weakest orientation), the 3 layers end up contributing 0%, 86.6%, and 86.6% of their strength, for an average of 57.7%, knocking the 7x down to 4.039x. The 60/40 ratio knocks this down further to 1.6156x.

The weight of the 60/40 composite would be .6*1+.4*1.75 = 1.3 g/cc.

So for the same weight, the isotropic composite lay would have 1.6156*4.5/1.3 = 5.6x the strength of titanium for the same weight. Obviously the composite is a weaker perpendicular to the panel (no fibers oriented in that direction). Which is why you use them where loads are primarily within the panels like aircraft skin.

For applications where true isotropy in all three axes is required, I could see titanium being superior. But I'm pretty sure that would be because your specifications are deflection-limited, not strength-limited. CF is so flexible that if you need it to stay within a specified maximum deflection, it often ends up being several times stronger (and heavier) than it needs to be to withstand the load.


RE: Conventional looking now
By Amiga500 on 1/21/2010 8:17:08 AM , Rating: 2
quote:
CF has about 7x the tensile strength of titanium


With regards aerospace, CF plies have at best around 2.75x the ultimate tensile strength of Titanium. The densities are around 1600 kg/m^3 (CF) and 4500 kg/m^3.

That is AS4-8552 compared to Ti-5Al-2.5Sn.

So you can recalc that. Using your approach CF will still work out lighter if you've managed to confine the loading to in-plane only.

[FYI, compared to Al2024-T3, aligned CF is about 6.25x stronger, and 1.75x lighter]

Although it is all irrelevant as best practice is to design CF for max strain allowable (typically < 0.4%), not stress. The equivalent max "stress" of that is only 560 MPa or so... quite a ways short of Ti's 830 MPa yield strength. That is before you start to consider ply alignment!


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