wings came off

I'm pretty sure a hard pull at VNE in just about any glider (Swift or
Fox excepted, maybe) has a good chance of causing catastrophic
failure.

Pretty sure a hard pull at VA+ is all that is needed...

-Paul

Don Johnstone wrote:
I think you might find that most of the modern gliders we fly are capable
of withstanding more "G" than the human body can take.
Overstressing a modern glider is unlikely to result in a catastrophic
failure unless there is already damage.

If you want to go up and verify this in real, then please be so kind and
do so without an innocent passenger on board!

Modern gliders tend to be certified to JAR-22. Non-acro gliders are
certified in the utility category which means a max. load factor of
+5.3G at maneuvre speed and +4G at Vne. Safety factor ist 1.5 (for a new
glider, probably less for a worn-out one!). Since gliders tend to be
constructed to the minimum requirements, because more strength means
more material, hence more cost and less payload, both not desirable,
chances are you will break a glider when pulling 8G at Vne. 8G are
perfectly standable (albeit for most peoole not enjoyable).

BTW, for aero-reated gliders, JAR-22 requires a load factor of 7G at
Vne. Earlier certified gliders are rated for less, only few gliders
(Swift, Fox) are rated for a higher load factor.

Don Johnstone wrote:
[lots of yadda yadda snipped]
G-LOC was reported most frequently between +5 to +5.9 Gz.

You completely forgot to mention the time factor. G-Loc needs at least 4
seconds to occur. No glider aerobatic maneuvre will give you a high G
load of more than 4 seconds, it's simply not possible, energeticwise.
(Except with a spiral, of course.)

Read for example: http://aeromedical.org/Articles/g-loc.html

On Sep 22, 6:54*am, Don Johnstone wrote:

Studies have shown that prone positioning has little effect...

Prone, as in a Horton? Yes, that would be as expected.

As for the rest, many small aircraft have been shed of their wings in
circumstances where the only possible explanation was deliberate
though injudicious pilot input. So I don't think anybody should doubt
that it is well within the realm of possibility.

Thanks, Bob K.

Max. g is not a structural issue with several modern gliders. Other design
requirements result in a structure that by far surpasses the certification
requirements.

Andor

On Wed, 22 Sep 2010 17:30:25 +0200, John Smith
wrote:


Modern gliders tend to be certified to JAR-22. Non-acro gliders are
certified in the utility category which means a max. load factor of
+5.3G at maneuvre speed and +4G at Vne. Safety factor ist 1.5 (for a new
glider, probably less for a worn-out one!).


chances are you will break a glider when pulling 8G at Vne. 8G are
perfectly standable (albeit for most peoole not enjoyable).

Should I read 6G, I guess.

aldo

On Sep 22, 8:54*am, Don Johnstone wrote:

*Prevalence of G-induced loss of consciousness (G-LOC)in the United
Kingdom Royal Air Force (RAF) was found to be 19.3% in 1987. With the
introduction of the Typhoon, a fourth generation aircraft, the prevalence
of G-LOC has been re-assessed to determine the effectiveness of current G
tolerance training. *Method: *A survey was sent to 4018 RAF aircrew,
irrespective of their current role. Information was requested on G-LOC,
role and aircraft type, experience, and attitudes toward G-LOC prevention..
*Results: *Responses were received from 2259 (56.2%) individuals, 882 (39%)
of whom were current fast jet aircrew. At least one episode of G-LOC was
reported by 20.1% of all respondents. In front line aircraft, prevalence
of G-LOC among the 882 fast jet aircrew who responded was 6%. In the whole
group, G-LOC was reported most commonly in aircrew under training (70.9%),
and was most prevalent in training aircraft (77.4% of G-LOC events). At
the time of the G-LOC, 64% of aircrew had less than 100 h total flying
time. G-LOC was reported most frequently between +5 to +5.9 Gz, and
“push-pull” maneuvers were associated with 31.3% of G-LOC events. *

G-LOC was reported most frequently between +5 to +5.9 Gz.

Studies have shown that prone positioning has little effect, the only
remedy is a G suit and training, not often found in gliders.
The USAF require F16 pilots to demonstrate an ability to withstand a
maximum of 9 Gz and this can only be achieved through training and the
wearing of a G suit.

I am left wondering how sufficient acceleration could be maintained in a
LS6 to load the aircraft, in controlled flight, to sustain 9 G or indeed
more than 6G, ignoring that the pilot is going to become rapidly
unconsious if it were to be achieved. I am at a loss to understand why
anyone would want to do that anyway.- Hide quoted text -

- Show quoted text -

At the time (many years ago) I was active and current in F-4s, and we
had to undergo centrifuge training to identify G-LOC causes and
prevention. Centrifuge was with a G-suit, and gradually ramped up to
determine relaxed G tolerance, G-tolerance with proper straining
maneuver and G-suit, and time of useful consciousness at 9 Gs while
performing a tracking exercise in the centrifuge (simple video game
type thing). At the time (I was in my late 30s, smoked, partied, NOT
a marathon runner!), I could function at 4 to 5 Gs relaxed, 6 Gs with
simple straining, and 20 - 30 seconds at 9 Gs with everything working
(tight G-suit, straining, breathing, etc). 9 Gs is rough, and the
penalty of any relaxation was immediate GLOC (fun to watch the "fit"
skinny non-smoking runners pass out at 8 Gs!).

I'm surprised about the comment that position had little effect - that
goes counter to my experience and to the physiology of G-effects on
the human body. Bloody boffins, probably asked the wrong questions...

The thing about G-LOC is that it is not so much a matter of the peak G
load, but is more a function of the rate of onset of the Gs. If you
are expecting the Gs, then you can prepare; but a snatch pull to 5 Gs
when not expecting it (which happened frequently when you were in the
back seat of an F-4, for example, looking in the radar or checking 6)
could definitely put you in a world of hurts!

But Gs is like any physical activity - you have to do it a lot to
maintain your acclimitization. I enjoy acro up to 3-4 gs nowadays,
but would not like to try 5 sustained anymore! Fortunately, glider
acro is not only low peak but also short sustained Gs.

My LS6 has a pretty small elevator but at redline is real sensitive in
pitch, I think the instantaneous G that could be generated with a hard
pull would not be good for the airframe, to say the least! And it's
the instantaneous G that is what is going to break the wings, not the
sustained G (which is always going to be low in a glider).

Cheers,

Kirk

cernauta wrote:
On Wed, 22 Sep 2010 17:30:25 +0200, John Smith
wrote:


Modern gliders tend to be certified to JAR-22. Non-acro gliders are
certified in the utility category which means a max. load factor of
+5.3G at maneuvre speed and +4G at Vne. Safety factor ist 1.5 (for a new
glider, probably less for a worn-out one!).


chances are you will break a glider when pulling 8G at Vne. 8G are
perfectly standable (albeit for most peoole not enjoyable).

Should I read 6G, I guess.

Of course, my mistake. I had it correct, then reviewed it, mixed up the
Gs at Va and Vne and "corrected" it. Oh well.

At 21:33 22 September 2010, John Smith wrote:
cernauta wrote:
On Wed, 22 Sep 2010 17:30:25 +0200, John Smith
wrote:


Modern gliders tend to be certified to JAR-22. Non-acro gliders are
certified in the utility category which means a max. load factor of
+5.3G at maneuvre speed and +4G at Vne. Safety factor ist 1.5 (for a
new
glider, probably less for a worn-out one!).


chances are you will break a glider when pulling 8G at Vne. 8G are
perfectly standable (albeit for most peoole not enjoyable).

Should I read 6G, I guess.

Of course, my mistake. I had it correct, then reviewed it, mixed up the
Gs at Va and Vne and "corrected" it. Oh well.

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. The certified load factors do not necessarily indicate the actual
load factor that an airframe can sustain. The RAF bought 100 Grob Acros, 99
went into service and 1 went to Slingsby for testing on a rig. It was as
the result of this testing that the spigot problem was indentified. After
the airframe had been tested beyond the expected life by a considerable
margin Slingsbys were asked to apply loads sufficient to break the
airframe. They were unable to do so, and after breaking the rig several
times trying, gave up.

On Sep 22, 4:06*pm, Don Johnstone 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.

It may be that this one example tells us more about Slingsby's welding
than about Grob's composites.

Thanks, Bob K.