A380 and Glare
Frank Jenkins
ago: A drawing showed where the "stronger, lighter" Glare material was
being used on the A380. However, the one place it was *not* used was in the
center fuselage area above the wing, which would seem to be a place where it
would be advantageous.
Does anyone out there know why this is so? Is there some negative property
of Glare (other than, presumably, cost)?
Frank
George William Herbert
I should qualify this comment with, I am not qualified/educated in
engineering with glare.
I hear that it only takes to curves in a single dimention
well, which explains why the fuselage tail and nose are in
aluminum (well... the ribs, stiffeners, stringers, etc are aluminum
anyways) but only the relatively circular cross section body areas
are glare.
I don't know for sure why it's not used above the wing on A380.
I was wondering about its elastic modulus and ability to be
joined with an aluminum sheet in a lap riveted structure.
But I don't know.
-george william herbert
gher...@retro.com
Frank Jenkins
panel in question looks to be constant cross section (i.e., simple
curvature).
And since the elastic modulus and thermal-expansion coefficients are likely
to be different between Glare and "regular" Aluminum alloy, it seems doubly
curious that Glare is not used on the entire fuselage.
The only explanation I can think of is that, since Glare has to be made in
an autoclave, that fuselage panel is too large to fit in any
commercially-available autoclave. But with the money spent on the A380
development, a specially-large autoclave wouldn't seem to be that big a
deal.
Or, did I possibly misinterpret the drawing in AW&ST?
--
Frank
"George William Herbert" <gher...@retro.com> wrote in message
news:421b07fc$0$46567$c0de...@dsl.net...
> Frank Jenkins <sava...@sbcglobal.net> wrote:
>[snip]
>
> I hear that it only takes to curves in a single dimension
matt weber
<sava...@sbcglobal.net> wrote:
>Actually, several of the Glare fuselage panels have compound curves. The
>panel in question looks to be constant cross section (i.e., simple
>curvature).
>
>And since the elastic modulus and thermal-expansion coefficients are likely
>to be different between Glare and "regular" Aluminum alloy, it seems doubly
>curious that Glare is not used on the entire fuselage.
>
>The only explanation I can think of is that, since Glare has to be made in
>an autoclave, that fuselage panel is too large to fit in any
>commercially-available autoclave. But with the money spent on the A380
>development, a specially-large autoclave wouldn't seem to be that big a
>deal.
>
>Or, did I possibly misinterpret the drawing in AW&ST?
I'll give you another possibility, and i admit to being none to
comfortable about using Glare in the Fuselage. I'd be very cautious
about using it in load bearing structures.
Glare is a multilayer sandwich of alumining and glass/resin, which is
all well and good, but one of the things you have to plan for is can
your material handle the current density of a lightening strike?
You'd be amazed at the amount of copper mesh buried inside the
composite fuselage of a V22 Osprey!
What concerns me about glare is the possibliity of explosive
de-lamination in the event of a lightning strike. it isn't all that
unusual for a lightning strike to burn a hole at the entry or exit
point in the aluminum skin. On most aircraft, you just patch the
alumiun skin, and you are done. On glare, the vaporized aluminum is
likely to delaminate, and resin are huge producers of gas when
overheated, to the point that they are used in blow up protectors to
protect high voltage lines. The strike flashes over the blowout
protector, which is lined with resin. The resin just about explodes
from the heat, and literally blows out the arc. It is very impressive
to watch.
Explosive de-lamination in the area of the wing box is likely to have
very unpleasant consequences because of the loads being carried.
Same problem on the wings. The further you get away from the wing box,
the smaller the loads being carried, and the less of a concern the
delamination is likely to be.
That is an opion, no more, no less. I am electrical engineering by
education, with some specialized education in high voltage and
lightning protection.
Rock Ayers
The benefits of Glare unfold in areas where tension loads are
predominant. Hence its use on the upper side of the forward and rear
fuselage.
Due to the presence of the wing, the center fuselage section has to
cope with shear loads, hence a different material is used here.
Some ventral sections of the A380 fuselage use yet something different
- welded aluminum shells, which favourably lend themselves to
compression loads.
Generally spoken, if you take any aircraft and have a look at the
materials and construction principles used throughout the fuselage,
you'll find just the same patchwork the A380 is. Nothing peculiar
about it.
Regards,
Rock
Frank Jenkins
In addition to the possible vaporization of the resin, the
negatively-charged aluminum "plates" would be electrostatically repelled
from each other.
OTOH, it's inconceivable to me that lightning strikes weren't considered by
the A380's design engineers. And airliner certification requires extensive
lightning-strike testing. However, it's possible that the mix-and-match of
aluminum and Glare on the A380 is related to lightning tolerance.
Be interesting to see if Boeing has some clever (i.e. lightweight) way of
handling the lightning issue on their 787, other than by embedding a metal
mesh.
--
Frank
"matt weber" <matth...@cox.net> wrote in message
news:ja0o1150lkrpin97a...@4ax.com...
[snip]
Rock Ayers
<sava...@sbcglobal.net> wrote:
>Interesting comment on the welded shells, since it implies that a
>lower-strength weldable alloy is actually a better choice in some locations.
>Or does the A380 use friction-stir welding?
The lower lobe section environment rather implies a material that has
superior characteristics in terms of corrosion and fatigue.
Lower lobe skin panels with laser-beam welded stringers were
introduced with the A318.
Friction stir welding is primarily an option for joining panels.
Regards,
Rock
Rock Ayers
<sava...@sbcglobal.net> wrote:
>You make an interesting point: Glare is built like a multi-layer capacitor!
>In addition to the possible vaporization of the resin, the
>negatively-charged aluminum "plates" would be electrostatically repelled
>from each other.
>
>OTOH, it's inconceivable to me that lightning strikes weren't considered by
>the A380's design engineers. And airliner certification requires extensive
>lightning-strike testing. However, it's possible that the mix-and-match of
>aluminum and Glare on the A380 is related to lightning tolerance.
>
>Be interesting to see if Boeing has some clever (i.e. lightweight) way of
>handling the lightning issue on their 787, other than by embedding a metal
>mesh.
The 787 is going to use lightning strike protection appliqué (adhesive
thin foils) in places, e.g. the wing box upper and lower surfaces.
An interesting point is how far Boeing will stretch that technology.
The JSF was to make extensive use of paint replacement appliqué, and
the foils may as well bestowed with tiny streamwise grooves (riblets)
for a benefit in skin friction drag. So far, Boeing only makes mention
of the lightning strike protection function.
Regards
Rock