wings came off

.....and none of it may bear any resemblance to the current accident.

The design of an ultralight foot-launched sailplane obviously
introduces more compromises than conventional designs. Looking at the
manufacturer's website videos shows that the rigging of the wings
seems very different from modern sailplanes, which typically use
overlapping spars. What would worry me, though, is that after one
wing separated, the second wing and tailplane rapidly followed, then
the tail boom. The glider basically disintegrated.

Mike

Don Johnstone wrote:
I think we are getting a little away from the point. The original
proposition that pulling G in any glider would result in failure. I
suggested that catostropic failure would not necessarily occur in many
gliders.

It all depends on how many Gs you pull.

Mike the Strike wrote:
What would worry me, though, is that after one wing separated,
the second wing and tailplane rapidly followed, thenthe tail boom.

I would assume that after one wing has separated, it couldn't matter
less whether the seond wing follows or not.

According to Rupport Composite, the Archaeopteryx is designed for a
maximum maneuver load of 4 g at 85 km/h. The pilot himself confirmed
that he had exceeded the allowed load by flying too fast and pulling too
hard.
Source:
http://www.ruppert-composite.ch/5312...fb06c0c01.html
(German only).

On 9/22/2010 6:13 PM, Bob Kuykendall wrote:

On Sep 22, 4:06 pm, Don wrote:

...The RAF bought 100 Grob Acros, 99 went into service and 1 went to
Slingsby for testing on a rig...

We should be cautious about confusing anecdote with data. The testing
of one relatively conservatively-designed trainer doesn't tell us much
about the strength of the average sport or racing sailplane.

Kinda-sorta related, I'll bet big bux sailplane designers (and maybe even the
JAR/FAA design criteria folks) carefully tweak their design limits to whatever
materials they're using for primary structure, too.

The 1.5 ultimate/limit load factor ratio has historical roots in the metal world.

Early glass-glider designers quickly realized the relative floppiness of 'pure
fiberglass structures' meant stiffness needed to be explicitly addressed when
it came to wing structure, hence - in spar breakage terms - 'glass gliders'
tend to be 'overstrength' simply because it's necessary in order to obtain a
useably high Vne while avoiding flutter. (How well your metal pushrods will
work/stand-up at max-load-deflections is of course a tale in itself. Joe Test
Pilot, anyone?)

Carbon fiber primary wing structure meant designers could back away from
'stiffness-influenced overstrength structures' since carbon fiber structures
(pound for pound) are so much stiffer than their fiberglass equivalents.

Is any of this relevant to the real world of Joe Pilot? Is the Pope Catholic?

Regards,
Bob W.

(How well your metal pushrods will
work/stand-up at max-load-deflections is of course a tale in itself. Joe Test
Pilot, anyone?)
Which reminds me that I've wondered WHY they're still using metal
pushrods in carbon wings, instead of pultruded carbon tubing pushrods.
Perhaps because we still don't trust the bond between a carbon tube
and the metal fitting?

On Sep 23, 5:56*pm, Grider Pirate wrote:
(How well your metal pushrods will work/stand-up at max-load-deflections is of course a tale in itself. Joe Test
Pilot, anyone?)

Which reminds me that I've wondered WHY they're still using metal
pushrods in carbon wings, instead of pultruded carbon tubing pushrods.
Perhaps because we still don't trust the bond between a carbon tube
and the metal fitting?

Cost. Open class gliders are often out of rig ;-)
Dick Butler has used carbon tubes in Concordia.

Best Regards, Dave

On Sep 23, 2:56*pm, Grider Pirate wrote:

Which reminds me that I've wondered WHY they're still using metal
pushrods in carbon wings, instead of pultruded carbon tubing pushrods.
Perhaps because we still don't trust the bond between a carbon tube
and the metal fitting?

Dave nailed it: cost, as in cost per unit stiffness. Carbon might be
stiffer per unit mass and per unit volume, but is painful in terms of
stiffness per unit paycheck.

Stan Hall wrote a great article on this that describes how Euler's law
of column buckling shows that strength cancels out of the equation; it
is dominated by the stiffness. So once you decide to use aluminum, it
pretty much doesn't matter what aluminum you use. No need for 7075-T6
or even 2024-T3, good old 6061-T6 will do just fine so that's what I
(and most European makers) use. The article is in the highly-
recommended _Collected Works of Stan Hall, Vol 1_.

Your other point is quite valid as well. Establishing a reliable high-
strength bond between a carbon fiber tube and its end features is
still a bit exotic. I've seen it done, but it's just not something I
want to do and trust my life to.

Thanks, Bob K.

Dave Nadler wrote:
Which reminds me that I've wondered WHY they're still using metal
pushrods in carbon wings, instead of pultruded carbon tubing pushrods.

Cost.

I would rather say: high cost vs. zero benefit.

On Sep 23, 3:45*pm, John Smith wrote:
Dave Nadleur wrote:
Which reminds me that I've wondered WHY they're still using metal
pushrods in carbon wings, instead of pultruded carbon tubing pushrods.
Cost.

I would rather say: high cost vs. zero benefit.

There are exceptions. Early Stemme S10-VT's used aluminum push rods
for the spoilers, which had the over center for locking the spoilers
closed in the spoiler box. Problems occurred with the differential
thermal expansion between the aluminum rods and CF wings. In cold
temperatures the spoilers could unlock without pilot input. Changing
the push rods to carbon fiber solved the problem and CF rods are used
for spoilers on Stemmes now.

bumper
MKIV and QV
Minden