Eta crashed

Let's try posting that URL again, and see if I can make it not
line-break:

http://babelfish.altavista.com/babel...p=de_en&tt=url

Bob K.

Stewart,
There is no such thing as "the manufacturer" for the ETA. Instead, a group
of wealthy people financed the design and the building of the prototypes.
Several different companys contributed by building parts of the plane. The
web site www.eta-aircraft.de is run by the design bureau.

Markus



Stewart Kissel schrieb in Nachricht ...
Okay, we can call any sort of "event" we choose. According to articles I=
have read, the things cost more the $1 million US to build. Will the ma=
nufacturer be able to absorb this sort of hit?

Please explain, I do not understand.

If a 747 (just a little bit larger than the eta...) breaks up in flight
due to overloading, killing 400 passengers, it is not a an accident. So
what is it then?

Robert

Stefan wrote:
Vaughn Simon wrote:

information we have, it apparently broke up in flight, the occupants bailed
out, and then gravity took its natural course until the failed airframe
(crashed, fell, bumped, decellerated, sprinkled, oopsied) into/onto the
surface of the earth. Help me with the finer points of English please; how
is this not a crash?


Ok. Technically (and linguisitcally), it *is* a crash. Nothing wrong.

However, when I read the headline "aircraft crashed", I understand
"accident", and I guess that's what the vast majority does. My mistake,
agreed, as it wasn't written anywhere whether the plane broke up during
normal flight, did a bad landing or was destroyed voluntarily. Anyway,
"accident" ist what that headline implies.

But it wasn't an accident. It was a test flight to explore the limit,
and they found the limit, although a bit earlier than they wanted, I
guess. That's exactly what test flights are for.

So a better headline would be "eta fails spin test".

Stefan

Robert Danewid wrote:

Please explain, I do not understand.

Then read my post more carefully.

Stefan

Earlier, Stefan wrote:

...But it wasn't an accident. It
was a test flight to explore the limit,
and they found the limit, although a
bit earlier than they wanted, I guess.
That's exactly what test flights are for...

I'm not sure I completely agree with that assessment of the situation.

The way I understand it, the limits they were expecting to explore
were control and handling limits, not structural limits. The way I
read the Babel Fish translated report, they placed the aircraft into a
spin, executed a recovery, and were surprised by a structural failure
of the aft fuselage during the recovery.

I think that if they were really executing a structural test, they
probably wouldn't have had two people on board.

Going forward, it will be very interesting to follow the investigation
of why the structure failed. Did the maneuvers performed apply
loadings beyond the expected ultimate limit? Or did the structure fail
to provide the expected strength and stiffness?

And if the latter, were the stresses miscalculated or did the stucture
not perform as expected?

It's really far too early to speculate, but it will be interesting to
see if perhaps bending loads applied by the elevator plus bending and
torsional loads from the rudder combined to produce stresses in excess
of the expected maximums.

I hope that they were carrying a flight recorder, and that it (unlike
too many dented Cambridge Model 20s) yields usable data.

Anyhow, I'm glad the pilot and observer weren't injured badly. That's
what's most important.

Thanks, and best regards to all

Bob K.

18 posts on this subject line: a large portion of them debating the meaning
of the word "crash" -- yes, the season is over.

What kind of wax shall we use this year?



Jack

"Howard Franks" wrote in message
...
I have always assumed the recent (last 20 years) composite
gliders to be very robust, i.e. no issues flying right
up against placarded limitations at anytime (maybe
once or twice nipping over?).

Perhaps the Eta break-up is a sign that we are reaching
the structural/design limitations of the current materials
and the designers ability to optimise gliders for performance.
Are we at the point of diminishing returns where the
small increase in performance only comes at a far greater
risk of structural failure (similar to the Americas
Cup yachts).


This coupled with the recent Schempp-Hirth issues (agreed
manufacturing not design defects), and the AD restricting
GROB 103s is leading me to rethink just how tough these
things are.


There seems to be a prevalent attitude that all gliders are much stronger
than the POH says. At least, as a CFI-G, I have a hard time convincing
pilots that those placards mean just what they say. This is particularly a
problem when it comes to overloading 2-seaters. Exceed a placarded limit
and you become a test pilot - maybe a dead one.

I think gliders are just as strong as the manufacturer says, but no
stronger - and only then if the design and manufacturing rules are followed
to the letter. The problem with the Schempp-Hirth gliders seems to be that
the manufacturer's own procedures were not followed. The issue with the
G103's MAY be that errors in design occurred. None of this says that
composite construction is the problem, just that the process needs to be
carefully controlled and monitored. (It also says that reputable
manufacturers sometimes make mistakes that aren't found until after the
gliders are in the field.)

As for the Eta, this may turn out to be an intriguing case. At 31 meters it
is certainly pushing the limits. Bob K. perceptively speculated about
bending and twisting loads on the tailboom. It could also be that the spin
recovery has to be performed exactly right of the airspeeds get way, way out
of hand. I would expect that the Eta will be placarded against intentional
spins for this reason.

Bill Daniels

Bill Daniels wrote:

I think gliders are just as strong as the manufacturer says, but no
stronger

Most Gliders are built in JAR country and are certified by JAR rules.
For the utility category, JAR requires an allowed load of 5.3g at Vne
and 4.0g at Vm. JAR further requires that the break load be no lower
than 1.5 times the allowed load.

Since every extra strengh comes at a price in weight and money, the
break load of most gliders acually *is* 1.5 times the allowed load. This
is when the glider is new. Take some turbulence, and the safety cusion
is rather small.

As for the Eta, this may turn out to be an intriguing case. At 31 meters it
is certainly pushing the limits.

Actually this is the whole idea of the Eta project: pushing the limits.
Remember that the first prototype was too heavy and extra work was
required to bring the take off mass down to 850 kg! (The 850 kg limit is
again required by JAR as well as by contest rules.)

Stefan

Never assume the glider is stronger than the placarded
limits. As quite rightly stated earlier, exceed them
and you become a test pilot - especially so on excess
speed where there is little margin.

A friend of mine broke the boom on a SF34 (best thing
to do to the beast, some might say;-) recovering from
an intentional spin. He's a Chief Flying Instructor
and engineer so one presumes he knows what he's doing
but even he was caught out. These things are not unbreakable
in flight.

The loads on spin recovery can be quite unpredictable,
especially if the recovery pull-up is done with some
twisting moment still present on the tail - hence we
are trained to stop the spin, unstall the wings, recover,
not one 'pot-stirring', stress-inducing manoeuvre.

Rob

At 09:12 03 October 2003, Stefan wrote:
Bill Daniels wrote:

I think gliders are just as strong as the manufacturer
says, but no
stronger

Most Gliders are built in JAR country and are certified
by JAR rules.
For the utility category, JAR requires an allowed load
of 5.3g at Vne
and 4.0g at Vm. JAR further requires that the break
load be no lower
than 1.5 times the allowed load.

Since every extra strengh comes at a price in weight
and money, the
break load of most gliders acually *is* 1.5 times the
allowed load. This
is when the glider is new. Take some turbulence, and
the safety cusion
is rather small.

As for the Eta, this may turn out to be an intriguing
case. At 31 meters it
is certainly pushing the limits.

Actually this is the whole idea of the Eta project:
pushing the limits.
Remember that the first prototype was too heavy and
extra work was
required to bring the take off mass down to 850 kg!
(The 850 kg limit is
again required by JAR as well as by contest rules.)

Stefan

On 2 Oct 2003 15:36:37 -0700, (Bob Kuykendall)
wrote:

Earlier, Stefan wrote:

...But it wasn't an accident. It
was a test flight to explore the limit,
and they found the limit, although a
bit earlier than they wanted, I guess.
That's exactly what test flights are for...

I'm not sure I completely agree with that assessment of the situation.

The way I understand it, the limits they were expecting to explore
were control and handling limits, not structural limits. The way I
read the Babel Fish translated report, they placed the aircraft into a
spin, executed a recovery, and were surprised by a structural failure
of the aft fuselage during the recovery.

I think that if they were really executing a structural test, they
probably wouldn't have had two people on board.

Going forward, it will be very interesting to follow the investigation
of why the structure failed. Did the maneuvers performed apply
loadings beyond the expected ultimate limit? Or did the structure fail
to provide the expected strength and stiffness?

And if the latter, were the stresses miscalculated or did the stucture
not perform as expected?

It's really far too early to speculate, but it will be interesting to
see if perhaps bending loads applied by the elevator plus bending and
torsional loads from the rudder combined to produce stresses in excess
of the expected maximums.

I hope that they were carrying a flight recorder, and that it (unlike
too many dented Cambridge Model 20s) yields usable data.

.....and that the rate was set high enough to show anything.

Last time I flew I had a logger running at its usual 4 second
recording interval. On the way back to the field I remembered I hadn't
stalled or spun in quite a while, so I ran through a HASSEL check and
then a couple of stalls and 4-5 incipient spins, always recovering
after 1/4 - 1/3 turn. I was surprised to see just how little of this
appeared in the trace; the 4 sec interval was enough to average the
series of maneuvers out into 2-3 wide turns combined with a fairly
constant high descent rate. I suspect the Eta logger would need
sub-second sampling to show anything useful al all.

Anyhow, I'm glad the pilot and observer weren't injured badly. That's
what's most important.

Agreed.


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :