2009 Lawsuit

BobW:

Assuming a condition where the C of G is out of limits, how would that affect the flight characteristics in a way that would result in the accident as it played out (unintentional stall-spin transforming into a spiral dive which then wound up tight enough to generate g-forces sufficiently high so as to break the wings)? - I'm currently going through the reference material I have on hand as I found, to my embarrassment, that I wasn't at all certain about the various effects of C of G on flight characteristics.

I assume that only a too far aft C of G could be a problem in this case. An aft C of G makes a stall-spin easier to get into and can result in the spin being unrecoverable in extreme situations correct? I would think that an aft C of G would also make it easier to induce positive g's with the elevator and would make the elevator control lighter and "twitchier" making it easier to overstress the glider during the subsequent spiral. I can't see how the C of G would lead to the spiral dive being unrecoverable though.

I recall a Nimbus 4DM accident in which it was suggested that after a certain number of turns in a spiral dive when g forces and airspeed had built up high enough that it would be impossible to roll level and recover - I wonder if the lawsuit was suggesting something similar about the 29? It doesn't seem too likely that that would be the case though.

Not knowing the C of G position for sure, especially in a glider which lets you alter wing loading and tail weight to the degree a modern competition ship would seem to be a prerequisite for flight to me. Even my old 15b (without ballast bags) has been up on the scales, leveled and weighed during an annual just to put my mind at ease. (it was imported from Germany to Canada in 1998 and the German records indicate that it was reweighed every 48 months when it was there!)

Many flight manuals of newer gliders say that a spin will turn in to a spiral dive on its own after a few turns. Spin and spiral dive recovery are, of course, quite different. If you've lost situational awareness enough to inadvertently spin, not noticing the subtle transition from spin to spiral dive might happen too. Also, reading flight manuals, a few of them recommend somewhat different recovery than "standard" that we were all taught.

This has little to do with speculation about this accident, but it's an interesting related fact. Reading the flight manual about spins is a useful winter pastime.

John Cochrane

On Thursday, January 16, 2014 10:28:12 AM UTC-5, wrote:
Many flight manuals of newer gliders say that a spin will turn
in to a spiral dive on its own after a few turns.
Spin and spiral dive recovery are, of course, quite different.

Please note this probably has NOTHING to do with Tim's accident:
Experienced pilots have become confused and thought they were
in a spin when in fact they were in a spiral dive.
IIRC a prominent example was the crash of an Eta during
a spin test...

Quick:
- how do you tell the difference?
- recovery technique?

Hope that helps,
Best Regards, Dave

On Thursday, January 16, 2014 10:28:12 AM UTC-5, wrote:
Many flight manuals of newer gliders say that a spin will turn in to a spiral dive on its own after a few turns. Spin and spiral dive recovery are, of course, quite different. If you've lost situational awareness enough to inadvertently spin, not noticing the subtle transition from spin to spiral dive might happen too. Also, reading flight manuals, a few of them recommend somewhat different recovery than "standard" that we were all taught. This has little to do with speculation about this accident, but it's an interesting related fact. Reading the flight manual about spins is a useful winter pastime. John Cochrane

Also worth noting is that T tail sailplanes commonly do surprising(to those not familiar)things in pitch during spin recovery. Commonly, as the stick is moved forward to unstall, the nose will pitch down, followed by pitching up a bit as the horizontal tail goes through the wake, followed again by pitch down(sometimes a LOT) as the tail comes out of the wake and becomes more effective pushing the nose way down. This easily leads to a very low nose with speed building at a very high rate. Add to this the autorotation associated with the spin entry and you have a very disorienting situation. You are in a high speed spiral before you know it.
This is why many flight manuals, and I directly quote the ASW-27 manual, say to apply opposite rudder and ease the stick forward until the rotation stops.
Jamming the stick full forward, as some pilots have been incorrectly taught, makes the end of the recovery much more difficult due to the behavior described above.
FWIW
UH

Jamming the stick full forward, as some pilots have been incorrectly taught, makes the end of the recovery much more difficult due to the behavior described above.

Really? Recovering from an inverted loop sounds easy...

John Cochrane

BobW:

Assuming a condition where the C of G is out of limits, how would that
affect the flight characteristics in a way that would result in the
accident as it played out (unintentional stall-spin transforming into a
spiral dive which then wound up tight enough to generate g-forces
sufficiently high so as to break the wings)? - I'm currently going through
the reference material I have on hand as I found, to my embarrassment, that
I wasn't at all certain about the various effects of C of G on flight
characteristics.

Good on you for refreshing your CG-related book knowledge! General reply to
your 1st-sentence-question below next paragraph...


I assume that only a too far aft C of G could be a problem in this case. An
aft C of G makes a stall-spin easier to get into and can result in the spin
being unrecoverable in extreme situations correct? I would think that an
aft C of G would also make it easier to induce positive g's with the
elevator and would make the elevator control lighter and "twitchier" making
it easier to overstress the glider during the subsequent spiral. I can't
see how the C of G would lead to the spiral dive being unrecoverable
though.

You seem to've sussed out the correct (as I understand things) general answer
to your lead-in question...based on what's expressed in sentence 1 of the
immediately-preceding paragraph. Same comment applies to the second sentence
of para. 2.

As the CG is shifted aft, the aircraft stability decreases until
(definitionally) when the CG and ship/pilot neutral point coincide, the ship
is "neutrally stable." With a CG aft of the neutral point, the ship is
definitionally (stick-free) unstable. "Unstable" doesn't mean "instant
uncontrollability and certain death" but it DOES have sufficient import that
designers almost certainly define their ships' POH's aft CG limit "somewhat
forward" of the neutral point. You'd have to know the ship's designer to know
for certain how he addressed this aspect of the ship's design.

Ease of/possibly inadvertent entry to the spin, non-pilot-commanded transition
from a (generally recoverable) nose-down spin to a (sometimes not recoverable)
not-so-nose-down "flat spin", "twitchy" pitch characteristics...that about
covers the broad brush downsides to "too far aft" CG considerations.

Considering the topic of a glider transitioning from a spin to a spiral dive
greatly complicates an already complex situation (i.e. spin dynamics), and my
general response to the implicit question in para. 2's final sentence is, "The
devil is in the details/it just depends (on the ship, the air, on the system
CG, on pilot input, on LOTS of things)." There are reasons every glider POH
(of which I'm aware) limits their spin recovery verbiage "simply" to spins,
and don't consider aspects extending to botched or delayed spin recoveries. (A
line has to be drawn somewhere...)

Every pilot is free to explore those limits on their own, ideally in an
intentional manner, as opposed to doing so unintentionally. Not that I've
flown a wide variety of gliders, but I have flown or taken BFRs in 3 different
ATC-ed gliders approved for spins, spun each, and noted each had widely
varying spin characteristics and (to a lesser extent) varying recommended (and
actual) spin recovery techniques. The single-seater in that mix actually had
completely different spin characteristics in opposite spin directions...yet
was the most eager to recover "on its own" in either direction.

I've also flown 3 1st-generation high performance single seaters, none of
which I ever spun, each of which I intentionally and fairly extensively
explored departure (from controlled flight) characteristics as part of
"routine self-education." One of those 3 I know had been spun (not my
particular ship, though) during factory test flying, so I'd reason to expect
my example would spin/recover similarly...but I never wanted to put that clean
a ship that nose down out of simple (unpaid!) curiosity, given that my example
gave all sorts of aerodynamic warnings - long before departure - that if Joe
Pilot continued to do as he was, ship departure was nearing. Simply exploring
"near-departure" flight characteristics at my normal CG location satisfied my
curiosity in that particular ship. Never experienced an unexpected departure
from controlled flight in any ship (yet)...


I recall a Nimbus 4DM accident in which it was suggested that after a
certain number of turns in a spiral dive when g forces and airspeed had
built up high enough that it would be impossible to roll level and recover
- I wonder if the lawsuit was suggesting something similar about the 29? It
doesn't seem too likely that that would be the case though.

The discussion is moving into an arena well beyond what most average glider
pilots might consider "routine flight"...but that's never a bad thing, IMHO.
In any event, as complex an aerodynamic condition as is a "simple spin," I
consider the dynamics of "an extending-in-time spiral dive" well into the
nether regions of paid test flying. Simply pondering those same dynamics might
be considered an exercise in "around the campfire engineering"...caveat
emptor? Anyhow...

Clean gliders - when seriously nose down - pick up speed rapidly, and as
"structurally overbuilt" as are "pure glass" gliders and as strong as are
"post-pure-glass gliders" (i.e. those incorporating carbon/possibly-et-al
fibers), I think trying to define (say) time limits beyond which, or speeds
above which, spiral dives might be "problematically recoverable" is
essentially an 0'-beer thirty consideration, akin to pondering how many angels
can fit atop the head of a pin. Point being that spiral dives are known to be
"quickly problematic" for every type of airplane/glider construction whether
considering: 1) exclusively construction (tube-n-rag, wood, all metal,
composite), or 2) documented accident history. Whether the failure mode
initiates with the structure breaking before the pilot even has a chance to
recognize and respond, or structural failure occurs after the pilot recognizes
and responds (even if properly) but for (say) G-load reasons cannot transmit
his response from hands/feet to aerodynamic controls doesn't matter...at least
not given today's state-of-the-art in glider construction material technology.
He's still likely to die in a broken-before-the-ground ship.

I'd put practicing recoveries from developed spiral dives in the same category
as practicing departures from controlled flight in the landing pattern or
practicing playing on the freeway. :-)


Not knowing the C of G position for sure, especially in a glider which lets
you alter wing loading and tail weight to the degree a modern competition
ship [permits] would seem to be a prerequisite for flight to me.

Methinks you intended to write the preceding sentence w/o the "Not..." and if
you did, then we're in 100% agreement!!! That was my essential point in an
earlier "little Red Worry Flag" post.

Bob W.

Well, ya better duck, cause pigs are now flying and they do sh++t. Yes, it was dropped against the Dealer, but best to remember that attorney fees can be very expensive. Settlement out of court for...1.1m US bucks.

While not as sad as seeing a good friend lose his life, this is pretty sad. Unfortunately in today's litigious environment, it probably made sense, as trial costs could have run far higher.

2C

BobW:

Yeah, I didn't start that last paragraph with the right word did I :-)

Thanks for the response - it answered a lot of questions I had!

Personally I practice spin and spiral recovery every year but I've never experienced an unintentional stall or spin in over 1000 hours of soaring. That is probably a result of the vast majority of those hours being spent ridge soaring very close to the mountains around Hope BC. Not much height for recovery if it happens so one tends to keep the airspeed higher than would be normal when thermalling with a few thousand feet between the glider and the ground.

On Saturday, January 11, 2014 7:31:18 PM UTC-8, wrote:
Not looking to open old wounds. One question.

Was the case against Eastern Sailplane ( Tim Donovan 2009 ASG-29 accident) successful?



Rick Lake

Not wishing to muddy the water any further, but we had a 29 with jammed ailerons out here. Thankfully, it was found on the ground. My understanding is a glob of goo from the wing mating process ended up stuck to one of the aileron pushrods.
JJ

On Friday, January 17, 2014 6:55:06 PM UTC+1, JJ Sinclair wrote:
On Saturday, January 11, 2014 7:31:18 PM UTC-8, wrote:

Not looking to open old wounds. One question.



Was the case against Eastern Sailplane ( Tim Donovan 2009 ASG-29 accident) successful?







Rick Lake



Not wishing to muddy the water any further, but we had a 29 with jammed ailerons out here. Thankfully, it was found on the ground. My understanding is a glob of goo from the wing mating process ended up stuck to one of the aileron pushrods.

JJ

Hello JJ, and that happened after some flights were made or before first flight?