Accident in Namibia, SH Ventus 2cxm

Ailerons, flaps and mixing was rigged wrong. Once that was corrected she was a beauty. Recovered from spin entry within quarter turn of control inputs, dry. Single place Nimbus 4. I still miss that bird!

On Tuesday, February 2, 2016 at 12:58:17 AM UTC-8, wrote:
Le vendredi 15 janvier 2016 22:07:57 UTC+1, Jonathan St. Cloud a écrit :
The rigging is very important on a Nimbus and when I first got mine is was rigged horribly and flew horribly. Fixed the rigging and it was a beauty to fly.


Hi Jonathan,
Very interesting. I have a N4DM since 17 years and 2.500 hours and see no possibility at all to change any setting during rigging. I can't understand how I may "rig horribly"... Thanks for explaining to me and others.
Instead, I can change the setting of the flap angle and the force of airbrake locking by changing the extension of the controls between the fuselage and the inner wing, but this is something that takes time and attention, not simply a rigging. BTW, I actually change the airbrake locking force twice a year, for cold flights in Patagonia and warm ones in Europe. See my book "Dancing with the Wind" page 194 and following (on sale at Cumulus Soaring).
All the best
jm

This comment has nothing to do with the latest Nimbus 4DM accident:

However, in regards to some comments about a glider spin developing into a spiral. If you have not had that happen it can be a real surprise. I was spin training in a 2-32 that would do 1/2 turn in a spin and then go in spiral. The sight picture was the same, only different was rudder opposite the rotation did not work. I spotted the problem after about ¾ of a rotation but was very surprised that the spiral did not look any different than the spin I had always assumed I could tell the difference. Now picture this is a slippery modern glider of any wing length, nose 70 degrees down or more. Would very quickly go through VNE.

The most fun flying I have done is in a Nimbus 4D or ASH-25 as a shared experience is the essence of human nature. Two pilots can make one very good flight!

On Tuesday, February 2, 2016 at 5:02:50 PM UTC-5, Jonathan St. Cloud wrote:
This comment has nothing to do with the latest Nimbus 4DM accident:

However, in regards to some comments about a glider spin developing into a spiral. If you have not had that happen it can be a real surprise. I was spin training in a 2-32 that would do 1/2 turn in a spin and then go in spiral. The sight picture was the same, only different was rudder opposite the rotation did not work. I spotted the problem after about ¾ of a rotation but was very surprised that the spiral did not look any different than the spin I had always assumed I could tell the difference. Now picture this is a slippery modern glider of any wing length, nose 70 degrees down or more. Would very quickly go through VNE.

The most fun flying I have done is in a Nimbus 4D or ASH-25 as a shared experience is the essence of human nature. Two pilots can make one very good flight!

You should be able to tell the difference. Look at your airspeed indicator. In the spin the air speed will be low or at least stable and in the spiral it will be high and quickly increasing. That was the case on all gliders I spanned. Turn and bank indicator ball in the spin will be all the way to the outside of the turn.

The 2-32 is not very slippery, no need to look inside when spin recovery did not work, I recovered from the spiral. Point being, if you had not considered this possibility and are in a slippery glider you might keep this in mind. This is the only aircraft I had intentional spun that would spiral out of the spin.



On Tuesday, February 2, 2016 at 3:05:29 PM UTC-8, Andrzej Kobus wrote:

You should be able to tell the difference. Look at your airspeed indicator. In the spin the air speed will be low or at least stable and in the spiral it will be high and quickly increasing. That was the case on all gliders I spanned. Turn and bank indicator ball in the spin will be all the way to the outside of the turn.

On 2/2/2016 7:46 PM, Jonathan St. Cloud wrote:
The 2-32 is not very slippery, no need to look inside when spin recovery
did not work, I recovered from the spiral. Point being, if you had not
considered this possibility and are in a slippery glider you might keep
this in mind. This is the only aircraft I had intentional spun that would
spiral out of the spin.



On Tuesday, February 2, 2016 at 3:05:29 PM UTC-8, Andrzej Kobus wrote:

You should be able to tell the difference. Look at your airspeed
indicator. In the spin the air speed will be low or at least stable and
in the spiral it will be high and quickly increasing. That was the case
on all gliders I spanned. Turn and bank indicator ball in the spin will
be all the way to the outside of the turn.

Having never spun anything more slippery than a 2-32 (at least four of which
have been spun into the ground from well aloft), but having many times
incipiently-spun a 15-meter glass bird, and having thoroughly spun a 1-26 (in
both directions) for up to 17 turns (in one direction only), and having gained
a modicum of knowledge concerning aeronautical industry practices and war
stories related to spinning, I long ago concluded several things about spins:
1) they were then (and remain) beyond mankind's computational skills regarding
"absolutely-predictable behavior," and (along with flutter testing) rightfully
are one of the reasons within industry that test-piloting remains a
well-respected, and reasonably well-paying occupation; 2) anyone who treats
them complacently is either seriously ignorant or willfully blind; and 3) just
because a bird is certified is no reason to complacently bet your life on the
*next* spin behaving identically to past spins. I'm not trying to be dramatic
here, just trying to convey the very real complexity of spinning aerodynamics.

My present working conclusion is big, heavy, clean sailplanes (e.g. ASH-25,
Nimbus 4DM) may well (likely do, for cleanliness & inertial reasons) have less
"ham-fisted margin" between the time of stopping rotation and returning to
level flight than "the rest of the glider fleet." Thoughtful pilots will fly
them accordionly...

As to "looking inside at ASI/needle-ball" to verify whether one is in a spin
or spiral dive, I'd hesitate to make a sweeping claim one does or does not
have to, but - assuming for the sake of discussion that ground clearance isn't
an issue - if you choose wrongly as to which methodology to apply first in the
face of "WTF is the ship doing?" I know I'd rather apply spiral dive
corrective action *before* anti-spin corrective action, simply because being
late on the former includes dire structural implications. Best, of course, to
have confirmed what the ship is doing before attempting corrective action, and
instruments are (used to be, anyway) a part of every instructors' teaching
toolkit.

I could never get that (still in the flying fleet) 1-26 I spent so much time
with investigating its spinning behavior, to remain in a spin in one direction
(I've forgotten which) for more than 5 (sometimes less than 3) turns;
throughout it "hunted up/down in pitch" in phase with decreasing/increasing
spin rate until on one of its downward-pitching excursions, it always exited
in a skidding diving turn which showed every indication was about to become a
spiral dive if left unaddressed. It spun rock-steadily in the other direction,
but required ailerons to be strictly neutralized to avoid more or less
instantly exiting in either a nose-low slipping turn (aileron out of the spin)
or a nose-low skidding spiral dive (aileron into the spin). The transition
from spinning flight to non-spinning flight was attention grabbing in that
aerodynamically dirty bird. Quite audible and accompanied by obvious lateral
accelerations. I never could convince myself to permit the skidding spiral
dive entry aft-stick recovery to continue to nose level without quickly
neutralizing the ailerons so cautious was I of spiral dive possibilities,
though I think it would have safely recovered at that early stage of things.
My "spin-now-stopped" recoveries involved rapidly neutralizing ailerons and
maintaining full aft stick. I never managed to induce a secondary stall under
those circumstances in that docile, forgiving, ship.

The transition from spinning to non-spinning flight may well *not* be obvious
in some other ship. You pays your money and takes your chances with spin
behavior, ideally treading thoughtfully, cautiously and preparedly...

Bob - so call me overcautious - W.

As glider pilots there are many things we do which are familiar to
us, we deal with these events very quickly, the so called muscle
memory. If we are prudent we practise, on a regular basis so
emergency situations, such as launch failures and every one we
practise increases the chance of recognition and proper recovery
action.

As regards spinning we may practise in a glider cleared for
intentional spinning but we seldom if ever practise a spiral dive
which is uncontrolled, we have no experience of such an event. We
may have been told that it can happen, briefed on the symptoms
and warned of the consequences but never actually seen it and
recovered unless we are one of the very few test pilots.

The difference between a spiral dive and a spin may be bleedin
obvious to a few but for most of us it is a situation which requires
the processing of information which is completely unfamiliar.

Some gliders are prohibited from deliberate spinning so we never
have the opportunity to practice, it is likely therefore that the first
time we see an event be it spinning or spiral dive is when it occurs
unintentionally. One of the symptoms which distinguishes a spiral
dive from a spin is the already high and increasing airspeed. To
recognise the difference you have to see it. The problem is that the
increase in airspeed, the acceleration, is very high, maybe
approaching 18kts per second per second (32fps/ps). If we take
just 3 seconds to see that the speed is in fact increasing we will
have added 57kts and we still have to decide how to correct that
and take the appropriate action. If we take a further 3 seconds to
decide on and start to carry out the appropriate recovery we are
already through VA, approaching or exceeding VNE and headed for
the scene of the accident. It has been said that recovery will result
in uncommanded airbrake deployment which transfers and
increased load to the outer wing panels, which are likely to fail.

When a test pilot carries out his tests he deliberately does so, he
knows what to expect and has already decided on his recovery
action, his recovery is likely to be close to optimum. He is likely to
guard the airbrake control. I would suggest that anyone, including
our test pilot might have difficulty if the event was completely
unexpected.

Even if the acceleration is only 90% of the maximun in a Nimbus
4DM, the speed will increase by 100kts in the 6 seconds. Assuming
we started with 50kts the recovery will go through VNE (177kts).
Max manouvering speed (VA) for a Nimbus 4 is 100kts, so full
control deflection is not available after 3 seconds. It seems to me
that if it happens unexpectedly it is not going to end well however
lighting fast our reactions might be.

Don,

the answer is simple. Don't fly a Nimbus 4 if you do not feel competent to
do so.

There is a sh1t load of opinions in this thread and some frankly outlandish
comments from people (most of whom) have not flown the aircraft.

"I wonder how many other people have to die or parachute to safety
before someone asks the question, should this glider be flying at all"

A knee jerk response to a factually correct but ill-informed statement
which lacked all of the information.

So far as I can see, there are two people on this thread who has
constructively contributed. JMC and Francois.

I would happily fly a Nimbus 4DM with either of these people.




At 11:05 03 February 2016, Don Johnstone wrote:
As glider pilots there are many things we do which are familiar to
us, we deal with these events very quickly, the so called muscle
memory. If we are prudent we practise, on a regular basis so
emergency situations, such as launch failures and every one we
practise increases the chance of recognition and proper recovery
action.

As regards spinning we may practise in a glider cleared for
intentional spinning but we seldom if ever practise a spiral dive
which is uncontrolled, we have no experience of such an event. We
may have been told that it can happen, briefed on the symptoms
and warned of the consequences but never actually seen it and
recovered unless we are one of the very few test pilots.

The difference between a spiral dive and a spin may be bleedin
obvious to a few but for most of us it is a situation which requires
the processing of information which is completely unfamiliar.

Some gliders are prohibited from deliberate spinning so we never
have the opportunity to practice, it is likely therefore that the first
time we see an event be it spinning or spiral dive is when it occurs
unintentionally. One of the symptoms which distinguishes a spiral
dive from a spin is the already high and increasing airspeed. To
recognise the difference you have to see it. The problem is that the
increase in airspeed, the acceleration, is very high, maybe
approaching 18kts per second per second (32fps/ps). If we take
just 3 seconds to see that the speed is in fact increasing we will
have added 57kts and we still have to decide how to correct that
and take the appropriate action. If we take a further 3 seconds to
decide on and start to carry out the appropriate recovery we are
already through VA, approaching or exceeding VNE and headed for
the scene of the accident. It has been said that recovery will result
in uncommanded airbrake deployment which transfers and
increased load to the outer wing panels, which are likely to fail.

When a test pilot carries out his tests he deliberately does so, he
knows what to expect and has already decided on his recovery
action, his recovery is likely to be close to optimum. He is likely to
guard the airbrake control. I would suggest that anyone, including
our test pilot might have difficulty if the event was completely
unexpected.

Even if the acceleration is only 90% of the maximun in a Nimbus
4DM, the speed will increase by 100kts in the 6 seconds. Assuming
we started with 50kts the recovery will go through VNE (177kts).
Max manouvering speed (VA) for a Nimbus 4 is 100kts, so full
control deflection is not available after 3 seconds. It seems to me
that if it happens unexpectedly it is not going to end well however
lighting fast our reactions might be.

At 11:05 03 February 2016, Don Johnstone wrote:
The difference between a spiral dive and a spin may be bleedin
obvious to a few but for most of us it is a situation which requires
the processing of information which is completely unfamiliar.

The instruction standard I teach by mandates spiral dive and spin recovery
prior to first solo. Common sense dictates that if you can't distinguish
between the two in your day-to-day glider (and their very different
recoveries), you shouldn't fly solo IMHO. Granted, the differences are a
lot more subtle in an advanced (open class) glider (and time to react a lot
shorter), but it still suprises me how often students confuse the two and
put in the wrong control inputs.