Plane wings

"Stubby" wrote in message
. ..


Matt Whiting wrote:
Stubby wrote:
What is the point of that extreme testing?

To confirm the design calculaions and assumptions before placing human
life at risk.

Is it even possible to operate an airframe in a way that will produce
wing-bending of that degree? If so, I believe human life will have
already been in risk long before.

True, but people do accidently wander into thuderstormsm and it would be
nice to come out the other side with the wings still attached.

It's unrealistic and I believe the
value of "accelerated testing" was debunked about 30 years ago.

That is news to me. Someone better tell the big aircraft manufacturers
about that, as well as the big auto makers. They ALL participate in
accelerated testing.
--
Jim in NC

Stubby wrote:



Matt Whiting wrote:

Stubby wrote:

What is the point of that extreme testing?


To confirm the design calculaions and assumptions before placing human
life at risk.


Is it even possible to operate an airframe in a way that will produce
wing-bending of that degree? If so, I believe human life will have
already been in risk long before. It's unrealistic and I believe the
value of "accelerated testing" was debunked about 30 years ago.

Generally, the answer is yes. I don't know what G loading the test was
at when the wing broke, but at typical cruise speeds, a very abrupt
control input or very strong wind gust can generate loads that exceed
the design limits of the airplane.

Your second sentence makes no sense. No structure is 100% safe.

This isn't accelerated testing, this was simply a load test to failure.


Matt

My favorite was the tail skid test. Apparently some airline pilots are
quite ham-fisted and are known to over rotate on take off, dragging the
tail on the ground. The test is that the plane can still take off under
the drag of the tail sliding on the ground. It was pretty awesome to
watch this thing draggin its butt down the runway!!

-Robert


Roy Smith wrote:
In article . com,
Robert M. Gary wrote:
One of the other fun tests was the maximum effort braking test. They
take a real production 777 (not yet certified), load it up, and go
barrelling down the runway at full speed, then slam on the brakes for
an emergency stop. Tires pop, and the brake drums are glowing red
hot, but the plane comes to a safe stop. Part of the certification
test is that the wheels have to withstand this for a certain amount of
time without catching fire. The fire & rescue guys are all standing
around with fire hoses counting down the time on their watches until
they're allowed to turn on the water to cool things off. Wait too
long, and you risk destroying a perfectly good airplane. Jump in too
soon, and you invalidate the test.

Stubby

Was flying a F2H3 (Banshee) and dive bombing. Dropped and pulled it in
to 6 G's for recovery. 'G' suit was inflated to max and I was grunting
like a stuck pig to stay awake when I hit the jet wash of the bird
ahead of me. G meter went to over 14 G's but bird stayed together
thank god.

Flew home very straight and level and when parked ground crew found
loose rivets all over the bird.

Sure glad they built some extra into that bird and used at least the
1.5 criteria as I was near the ultimate.

Just another day at the office )

Big John
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On Sat, 18 Feb 2006 12:12:44 -0500, Stubby
wrote:



Matt Whiting wrote:
Stubby wrote:
What is the point of that extreme testing?

To confirm the design calculaions and assumptions before placing human
life at risk.

Is it even possible to operate an airframe in a way that will produce
wing-bending of that degree? If so, I believe human life will have
already been in risk long before. It's unrealistic and I believe the
value of "accelerated testing" was debunked about 30 years ago.

My favorite was the tail skid test. Apparently some airline pilots are
quite ham-fisted and are known to over rotate on take off, dragging the

tail on the ground. The test is that the plane can still take off under

the drag of the tail sliding on the ground. It was pretty awesome to
watch this thing draggin its butt down the runway!!

That's the Vmu test (minimum unstick speed) or the minimum airspeed the
plane will fly with. Naturally it requires a high AOA so they attach
blocks to the skid on the tail and watch the sparks fly. Not sure if
it's because of ham-fisted pilots; I think it's just part of normal
certification.

This ultimate test isn't done on a virgin airframe. Rather it is done
after the prototype airframe has been subjected to a very extensive
random fatigue spectrum using typically a hundred or more hydraulic
actuators, which simulates the design life inputs to the airframe.

This fatgue test will include taxi loads, ground-air-ground loads,
pressurizations, power up and power down, turbulence - the whole gamat
of what an airframe sees in its life. This test may go on for years to
verify the desiign life of the airframe. During the fatigue test,
cracks will be encountered in the test airframe, and a fix will be
engineered to repair the crack, and the test continues. Meanwhile
later production airframe versions are put in service, but the
operators are careful to follow the service and crack etc history and
the repair of each airframe to make sure they do not get ahead of the
lab test airframe.

It is important in fatigue testing (whether cars or airplanes) to
maintain some semblance of the randomness of the loading, otherwise the
test specimen will give a wildly optimistic picture of the fatigue
life. The ground-air-ground cycles have to be randomly interspersed
with flight loads and pressurizations etc for an accurate test. Hence
this is a big test facility involving a lot of people.

The ultimate test is done after the design fatigue life has been
reached in the lab. I suspect much champagne is popped when it reaches
150%. The Airbus A-380 just had its very recent ultimate test (per
Wall Street Journal) and only made something less than 150% so there
wasn't much champagne popped after that one.

This system broke down in the case of the DC-10 at Chicago because a
very damaging prying load was input to the engine mount through a jury
rigged maintenance procedure that of course was not anticipated in the
fatigue test.

I'm not an expert in this, maybe others posters are. I know Boeing is
very good at predicting the fatigue life of structures.

nrp wrote:

I'm not an expert in this,

Yes, that is apparent.

Matt

Airbus A380 test wing breaks just below ultimate load target
Flight International 02/16/06

The wing of the Airbus A380 static test specimen suffered a structural
failure below the ultimate load target during trials in Toulouse
earlier this week, but Airbus is confident that it will not need to
modify production aircraft.

The airframer has been running load trials on a full scale A380 static
test specimen in Toulouse since late 2004 (pictured below). After
completing "limit load" tests (ie the maximum loads likely to
experienced by the aircraft during normal service), progressively
greater loads have been applied to the specimen towards the required
1.5 times the limit load. Engineers develop finite element models (FEM)
to calculate the load requirements.

"The failure occurred last Tuesday between 1.45 and 1.5 times the limit
load at a point between the inboard and outboard engines," says Airbus
executive vice president engineering Alain Garcia. "This is within 3%
of the 1.5 target, which shows the accuracy of the FEM." He adds that
the ultimate load trial is an "extremely severe test during which a
wing deflection of 7.4m (24.3ft) was recorded".

The European Aviation Safety Agency (EASA) says that the maximum
loading conditions are defined in the A380 certification basis. "The
aircraft structure is analysed and tested to demonstrate that the
structure can withstand the maximum loads, including a factor of safety
of 1.5. This process is ongoing and will be completed before type
certification."

However Garcia says that the failure of the wing below the 1.5 target
will require "essentially no modifications" to production aircraft:
"This static test airframe has the first set of wings built, and we
have refined the structural design for subsequent aircraft due to
increased weights etc. We will use this calibration of the FEM to prove
the adequacy of the structure on production aircraft."

EASA says that it is aware of the structural failure but "cannot make a
statement about the specific failure as it has not been officially
briefed by Airbus on what the cause was, and the certification process
is ongoing".

Garcia says that the FEM calculations had already established that the
A380's wing had "no margin at ultimate load. We had a weight saving
programme and `played the game' to achieve ultimate load." However in
earlier briefings, Airbus structural engineers had stated that it
planned to carry out "a residual strength and margin research test" in
2006 after completing ultimate load trials.

The results gleaned from the static testing will be extrapolated for
the future aircraft developments over the next 40 to 50 years says
Garcia. "It is normal to refine and strengthen the structure of new
heavier or longer range variants," he says.

Before purchasing the B-747 for AF ONE, Boeing had to do a highspeed
heavy weight abort. The aircraft stopped. The brakes eventually caught
fire and they let it cook for about 12 minutes. Result was the
fuselage was entact and never really threatened during the 12 minutes.
The damaged parts were replaced and the aircraft was flown again.
There are films of the event. Our part 121 carrier shows the film in
recurrent training.

Evacuation tests require all the evacuatees to be out of the aircraft
in 90 seconds or less. This is done in darkered conditions, with some
exits blocked. FAR PArt 121-291
http://www.flightsimaviation.com/data/FARS/part_121-291.html will
give the details and criteria for a evacuation certification.

I'm not familiar with that plane, but why did you exceed its ratings?
14 Gs is a lot and I'm not surprised there were some loose rivits but I
am surprised you survived without damage to your body!



Big John wrote:
Stubby

Was flying a F2H3 (Banshee) and dive bombing. Dropped and pulled it in
to 6 G's for recovery. 'G' suit was inflated to max and I was grunting
like a stuck pig to stay awake when I hit the jet wash of the bird
ahead of me. G meter went to over 14 G's but bird stayed together
thank god.

Flew home very straight and level and when parked ground crew found
loose rivets all over the bird.

Sure glad they built some extra into that bird and used at least the
1.5 criteria as I was near the ultimate.

Just another day at the office )

Big John
```````````````````````````````````````````````

On Sat, 18 Feb 2006 12:12:44 -0500, Stubby
wrote:


Matt Whiting wrote:
Stubby wrote:
What is the point of that extreme testing?
To confirm the design calculaions and assumptions before placing human
life at risk.
Is it even possible to operate an airframe in a way that will produce
wing-bending of that degree? If so, I believe human life will have
already been in risk long before. It's unrealistic and I believe the
value of "accelerated testing" was debunked about 30 years ago.