Archived from groups: comp.sys.ibm.pc.games.flight-sim (
More info?)
On Mon, 2 May 2005 at 00:13:58 in message
<hidb71hqcqehkai94g0kfip4cspnt2knhu@4ax.com>, PAPADOC
<PAPADOC@jimbobs.drive.by> wrote:
>Absolutely the problem from my standpoint is that Denial is not just a river in
>Egypt. Airbus advocating visual inspections for possible delamination problems
>is almost laughable...almost. Having the NTSB color their final report on an
>aircrash to not scare off anyone is not funny at all.
>
I remember looking as carefully as I could at the photos of the crash
that were published. It looked pretty clear that the lugs and joints at
the bottom of the fin had failed. No obvious signs of delamination. If
the NTSB did colour their report than that would be unforgivable and
would call into question their entire usefulness. The lugs appear to be
the main failure point and are laminates themselves. However a quick
glance at:
http://www.ntsb.gov/publictn/2004/AAR0404.pdf
seems to show that the lugs more than withstood their maximum design
load even one that had slight damage.
Looks like a very serious read for anyone who wants to find out more.
Try section 1.16.4.2 on page 67
Here is the last paragraph of that section:
~~~start quote~~~~
NASA's and Airbus' FEA models determined that failure of the right
rear main attachment lug was the most probable initial failure. The FEA
models and NASA's PFA model also determined that the failure initiated
at the final observed maximum vertical stabilizer root bending condition
during the accident flight, when the vertical stabilizer was subjected
to a global root bending moment of more than two times the value defined
by the limit load design envelope. (As previously stated, for
certification, the vertical stabilizer is only required to support loads
of 1.5 times limit load without catastrophic failure.)
The structural analyses showed that the large aerodynamic loading
produced by the accident scenario would result in the right rear main
attachment lug experiencing reaction forces and associated stresses that
were equivalent to those that produced lug fractures in the Airbus
full-scale certification test (lateral gust condition) and the Safety
Board's static lug tests. Figure 16 compares the resultant lug forces
at the time of fracture for the tests and analyses that were pertinent
to the flight 587investigation.
~~~~end quote~~~
>The final recommendation that it was the pilot who broke off that tail over New
>York is also not very funny. The pilot did not break off the tail...the
>combination of oversensitive controls married to a delaminated tail broke off
>that tail.
>
A reasonable hypothesis to test. However I would myself ask some more
questions. Like: Was the yaw damper engaged and functioning? Were the
measured lateral accelerations greater than the maximum design load?
What does analysis show of the failure mode of the fin? How many control
reversals were applied and how much yaw was generated at each reversal?
Maybe there are other failure modes that need attention.
Yaw damping is important to large commercial aircraft with their very
large moments of inertia about the Z axis and their potentially very
powerful fin and rudder combination.
--
David CL Francis
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