Accident in Namibia, SH Ventus 2cxm

Le lundi 1 février 2016 20:01:27 UTC+1, Don Johnstone a écrit*:
At 18:23 01 February 2016, Ramy wrote:
Scary! And I don't think there are that many nimbus 4DM out there.
Will be
interesting to compare this number to number of 4DM made. I
wouldn't want
to fly one myself.

Ramy

It would appear that 100 Nimbus 4D were built, of those 11 were 4DT
and 12 were 4D leaving a total of 87 DM of all types.

There is a list of 7 accidents in the previous post due to loss of control.

Just over 8% of the total built have been lost to loss of control
accidents.

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.

As the N4DM is certified, it had to be demonstrated that it will exit a spin after 3 turn at most.
Loosing 1800 m in any certified glider while trying to stop the spin is hilarious. This corresponds to something like 12-15 turns. Something has gone wrong very seriously.

Bert
Ventus cM TW

I would rather fly an L-13...

Boggs

Thanks for the detail on your accident in Namibia, Francois. It's fantastic that you are here to help us learn from it.
Quite different to intentionally spinning a training glider like ASK21.
Jim

At 20:13 01 February 2016, Tango Whisky wrote:
Le lundi 1 f=E9vrier 2016 20:01:27 UTC+1, Don Johnstone a
=E9crit=A0:
At 18:23 01 February 2016, Ramy wrote:
Scary! And I don't think there are that many nimbus 4DM out
there.=20
Will be
interesting to compare this number to number of 4DM made.
I=20
wouldn't want
to fly one myself.=20

Ramy=20
=20
It would appear that 100 Nimbus 4D were built, of those 11
were 4DT=20
and 12 were 4D leaving a total of 87 DM of all types.
=20
There is a list of 7 accidents in the previous post due to loss of
contro=
l.
=20
Just over 8% of the total built have been lost to loss of
control=20
accidents.
=20
I wonder how many other people have to die or parachute to
safety=20
before someone asks the question, should this glider be flying
at all.

As the N4DM is certified, it had to be demonstrated that it will exit
a
spi=
n after 3 turn at most.=20
Loosing 1800 m in any certified glider while trying to stop the
spin is
hil=
arious. This corresponds to something like 12-15 turns.
Something has gone
=
wrong very seriously.

Bert
Ventus cM TW

Not sure that spinning is the issue per se, it is what happens after
it stops spinning that seems to be the main issue. For whatever
reason it seems that some pilots have had difficulty stopping VNE
being exceeded in the recovery.
A test pilot might be able to demonstrate a successful recovery but
what about mere mortals?

On Monday, February 1, 2016 at 4:30:20 PM UTC-5, Don Johnstone wrote:
At 20:13 01 February 2016, Tango Whisky wrote:
Le lundi 1 f=E9vrier 2016 20:01:27 UTC+1, Don Johnstone a
=E9crit=A0:
At 18:23 01 February 2016, Ramy wrote:
Scary! And I don't think there are that many nimbus 4DM out
there.=20
Will be
interesting to compare this number to number of 4DM made.
I=20
wouldn't want
to fly one myself.=20

Ramy=20
=20
It would appear that 100 Nimbus 4D were built, of those 11
were 4DT=20
and 12 were 4D leaving a total of 87 DM of all types.
=20
There is a list of 7 accidents in the previous post due to loss of
contro=
l.
=20
Just over 8% of the total built have been lost to loss of
control=20
accidents.
=20
I wonder how many other people have to die or parachute to
safety=20
before someone asks the question, should this glider be flying
at all.

As the N4DM is certified, it had to be demonstrated that it will exit
a
spi=
n after 3 turn at most.=20
Loosing 1800 m in any certified glider while trying to stop the
spin is
hil=
arious. This corresponds to something like 12-15 turns.
Something has gone
=
wrong very seriously.

Bert
Ventus cM TW

Not sure that spinning is the issue per se, it is what happens after
it stops spinning that seems to be the main issue. For whatever
reason it seems that some pilots have had difficulty stopping VNE
being exceeded in the recovery.
A test pilot might be able to demonstrate a successful recovery but
what about mere mortals?

Hmmm.... maybe some of these pilots were taught, "Stick fully forward" in the spin recovery vs., "Get the nose below the horizon" instead. In a draggy trainer, they're slow to accelerate so not as much of an issue, in a "clean ship" speed happens very fast comparatively.
Some of this comes to, "Muscle memory" and whether or not good ideas were trained earlier.

I also agree, some ships do markedly different things depending on CG. Curious if there is a common CG (forward, aft?) on the accident ships.

PS, I know none of the involved pilots nor their experience, so I'm sorta guessing here.

As the N4DM is certified, it had to be demonstrated that it will exit a spin after 3 turn at most.
Loosing 1800 m in any certified glider while trying to stop the spin is hilarious.

Maybe not if you in it. But I do see your point, was a spiral mistaken for a spin?

Cheers

Paul


This corresponds to something like 12-15 turns. Something has gone wrong very seriously.

Bert
Ventus cM TW

The very long wing open class gliders have a bad record on spin recovery.
They will generally transition to a spiral dive quite early in a spin,
but will accelerate very rapidly on the exit.
If they do get into a stable spin, the momentum in the wings is a problem.

If you have water in the wings, or fuel, then you are a test pilot.
Certification is done dry.

There are at least five Nimbus 4D accidents I am aware of where recovery
was past Vne and the glider broke up on recovery. Ash25 - same story.

Bruce

On 2016-02-02 08:12, Paul B wrote:

As the N4DM is certified, it had to be demonstrated that it will exit a spin after 3 turn at most.
Loosing 1800 m in any certified glider while trying to stop the spin is hilarious.

Maybe not if you in it. But I do see your point, was a spiral mistaken for a spin?

Cheers

Paul


This corresponds to something like 12-15 turns. Something has gone wrong very seriously.

Bert
Ventus cM TW


--
Bruce Greeff
T59D #1771

On Tuesday, February 2, 2016 at 3:41:35 AM UTC-5, BruceGreeff wrote:
The very long wing open class gliders have a bad record on spin recovery.
They will generally transition to a spiral dive quite early in a spin,
but will accelerate very rapidly on the exit.
If they do get into a stable spin, the momentum in the wings is a problem.

If you have water in the wings, or fuel, then you are a test pilot.
Certification is done dry.

There are at least five Nimbus 4D accidents I am aware of where recovery
was past Vne and the glider broke up on recovery. Ash25 - same story.

Bruce

Bruce Greeff
T59D #1771

"Certification is done dry..." No. Current CS-22 Amendment 1:

"CS 22.221 General
(a) Compliance with the following requirements must be shown in all configurations and, for a powered sailplane, with the engine idling.
For sailplanes equipped to carry water ballast, the demonstrations of sub-paragraphs (b) to (g) must also be made for the most critical water ballast asymmetry that might occur due to any single malfunction or due to lateral accelerations during a spin."

Then, in spin testing (later in CS22 AL1):
"AMC 22.221(b)
Spinning
General
It will normally be sufficient to conduct a number of spins of about two turns in each of the conditions of CS 22.221(b) and subsequently to conduct spins of five turns in the most adverse cases."

You may recall the ETA spin test with one wing full/one empty led to a crash. Both CS-22 AL1 and the ETA test are available by mr. google.

Le mardi 2 février 2016 13:41:43 UTC+1, Dan Daly a écrit*:

You may recall the ETA spin test with one wing full/one empty led to a crash. Both CS-22 AL1 and the ETA test are available by mr. google.

No. The Eta crashed when trying to recover from a spiral dive (dry). The load on the rudder simply snapped the tail boom.

The ASH25 did crash during flight testing when spinning with water in only one wing. The centrifugal force of the water made the wing skin pop, and Martin Heide had to parachute down. He had been suspicious about this outcome beforehand and had tried to talk authorities into dropping this part of the test, but to no avail. So he did the test starting at 10'000 ft.

On Tuesday, February 2, 2016 at 8:48:43 AM UTC-5, Tango Whisky wrote:
Le mardi 2 février 2016 13:41:43 UTC+1, Dan Daly a écrit*:

You may recall the ETA spin test with one wing full/one empty led to a crash. Both CS-22 AL1 and the ETA test are available by mr. google.

No. The Eta crashed when trying to recover from a spiral dive (dry). The load on the rudder simply snapped the tail boom.

The ASH25 did crash during flight testing when spinning with water in only one wing. The centrifugal force of the water made the wing skin pop, and Martin Heide had to parachute down. He had been suspicious about this outcome beforehand and had tried to talk authorities into dropping this part of the test, but to no avail. So he did the test starting at 10'000 ft.

******
According to the Oct 2009 BFU Investigative report 3x221-0/05, the test was a spinning trial with asymmetric fuel (not water as I said - you are correct on that) - page 1 (History of the flight). According to the conclusions, the spin changed to a spiral dive and the use of rudder for recovery broke the tail (page 5). I guess we are both right, and both wrong in some parts! The asymmetric condition was not noted in conclusions, so probably not critical in comparison to the engineering conclusions.

I didn't say anything about ASH25 but it sounds interesting... I did a brief search but couldn't find it online. When did it happen?

Thank you for the correction.