On Friday, November 22, 2019 at 11:49:15 AM UTC-8, john firth wrote:
On Wednesday, October 30, 2019 at 8:49:22 PM UTC-4, wrote:
For those who haven’t seen it....

https://chessintheair.com/the-risk-o...-what-we-love/

Great piece of work which I shall read again in March!

A few comments;

"if you dread the thought of a field landing....."
then you should set up a simulation on your own field and practice till
you are confident.

No pilot should EVER be criticised for deciding on a field landing; I suppose this must happen; very immature behavior.

Duo Discus in flight wing failure.
The German report ( thanks Google) says that there was an unbonded section
on the spar some 20cm long. Surely an ultrasound scan of the spar line
would reveal this. I have no experience/ expertise in this regard.

John Firth

Thanks for pointing the Duo Discus manufacturing problem. Here is a link to the BFU report:
https://www.bfu-web.de/EN/Publicatio...ublicationFile

A couple of disturbing findings in this report:

"Manufacture of the wings was based on the knowledge of Schempp-Hirth at Kircheim which was not available as written instructions. This was true for the processes during manufacture, the specification of materical (e.g. adhesives) and the criteria for quality assurance (tolerances)."

Instead, employees from the subcontractors spent time at Kircheim to learn all of this. This system would utterly fail any quality control evaluation (e.g. CE), and is disturbing to me as a potential customer. Furthermore, this was the SECOND wing failure of an S-H product in the same year:

"The accident to the Discus CS in France revealed an even more extensive bonding defect on the wing spar."

This Discus had been in service for some time prior to the failure (900 hrs and 900 launches), so time in service is no security blanket. All Discus gliders were grounded in France after this accident:

https://groups.google.com/forum/#!to...ng/MTRTAwPn7qA

Yes, ultrasonic nondestructive testing can reveal such defects, but I don't know of any glider repair facilities that use them. I have designed such products in the past and have connections with a local NDT company. I will reach out to them to see how feasible such testing is. In the mean time, you can do a crude kind of NDT test by tapping on the surface above the bond with a metal object like a coin and listen to the sound produced. A defective bond will sound different than a good bond (less sharp and duller):

https://www.aviationpros.com/home/ar...aft-composites

Before I purchased any glider manufactured by either of these subcontractors I would insist on a full-blown ultrasonic NDT test.

Tom