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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 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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