- Boeing's new 787 Dreamliner is the first plane from the
company to be almost entirely made of carbon composites. The first delivery
was recently made to one of their customers in Asia. Carbon-composite material
is far lighter than aluminum. I for one am gravely concerned about the
heavy use of carbon composites, all in the name of better fuel mileage.
-
- I learned from NASA engineers first hand about an experiment
they performed. Some years ago, NASA/Langley did a real-world test on an
aircraft and carbon composites. To do the test, engineers removed a small
area of aluminum on the upper wing surface from one of their resident test
aircraft. An identical size carbon-composite panel was installed to fill
the opening flush with surrounding wing metal to prevent any change in
flight characteristics. Then the plane was intentionally flown through
a lightning storm to attract several strikes. Several lightning strikes
hit the plane. Where lightning hit aluminum surfaces nothing happened.
Aluminum is a good conductor of electricity and any powerful strikes were
quickly dissipated.
-
- When lightning struck the carbon composite test panel
it blew a large hole in the panel several feet across, much to the surprise
of engineers and scientists. This happened because carbon-composite materials
have far electrical higher resistance than aluminum. It is the same property
which causes electric heaters and light bulbs to become hot when electricity
is applied. It will be the integrity of this material which keeps all such
aircraft flying.
-
- High voltage will find a electrical path through even
the smallest pinhole. Power company line-man who work on power lines leak-test
their gloves every day for pinholes or cuts to protect their lives. Conductive
paint or coatings is one avenue that has been explored to prevent lightning
damage. But whether the final material used is a good conductor or a new-tech
insulator, both must remain in perfect condition for many years outside
in the elements to protect the aircraft.
-
- There are many commercial aircraft already flying around
the world which use some carbon-composite panels. Airline companies have
a long-standing habit of continuing to fly aircraft long past design lifetimes.
When a large section of the top half of the fuselage suddenly blew off
a commercial plane at high altitude some years ago, some of the passengers
fell several miles to their deaths into the ocean. Fortunately the plane
managed to land safely in Hawaii. Only passengers who were wearing their
seatbelts at the moment the top half of the fuselage blew off had any chance
to survive. For surviving passengers it was the worst flight of their lives
- all of them were completely exposed to the icey, 500MPH blast of wind
until the plane could decend and land. Imagine being strapped to a rocket
sled at the North Pole in winter which never stops for more than an hour.
This was a good example of what can happen when an aircraft is flown well
past it's design lifetime - the fuselage failure was pinpointed to metal
fatigue cracks.
-
- What will happen to carbon-composites when today's new
commercial planes around the world are flown well past their design lifetimes?
-
- Below is an unedited excerpt from a NASA article stating
what they found about carbon-composites back in June 2009:
-
- "Boeing 787 aircraft is one recent example, and
there has been a strong move toward composites in new general aviation
and business jet aircraft. One disadvantage of this new direction is that
the aircraft are far more vulnerable to lightning strikes. The energy deposited
in a typical lightning strike involves tens of KV and 10,000-200,000 amperes,
occurring in a fraction of a second. Without some type of shielding, or
conductive path, the electrically insulated carbon fiber/ epoxy composites
can be damaged, particularly at the entry and exit points for the strike.
The aircraft instrumentation can also be damaged in such an event and extra
shielding is often necessary for composite aircraft." [1]
-
- Let's put this into perspective. If we consider a modest
lightning strike with 100,000 amperes at 20,000 volts (based on the above
statement) this represents 2 BILLION WATTS of power striking the aircraft.
A typical home uses about 5,000 watts, so to consume two billion watts
you will need 400,000 homes.
-
- This also confirms my concerns (and likely the concern
of others) that perfect shielding is paramount to maintaining aircraft
safety. How can anyone really 100% check the integrity of aircraft shielding
material? They cannot because it's buried under the paint.
-
- For additional info, there is also an in-depth technical
paper about lightning effects on digital systems in aircraft at [2].
-
- Only time will tell about aging and element effects on
carbon-composites used beyond their design lifetimes - which are fabricated
with glue.
-
- SMALLER SIZE OF THE 787
-
- While aircraft size is a bit off-topic, it's interesting
that while some new jet planes are getting bigger others are getting smaller
like the 787.
-
- Boeing 787 Dreamliner in foreground is dwarfed by a older
legacy Boeing 747 some distance away in the background. You can tell
- the rear plane is most likely a 747 by the hump on top
which houses the upper passenger deck.
-
-
-
-
- Photo Credit - http://english.pravda.ru/photo/album/6504/2/
-
- Ted Twietmeyer
- tedtw@frontiernet.net
-
- [1] - http://www.techbriefs.com/component/content/article/5358
- [2] - http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810010479_1981010479.pdf
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