ACTION:of another country to identify and correct an unsafe condition on an aviation product. The MCAI identifies the unsafe condition as cracks in the connecting tube of the elevator U-bracket of the horizontal tail, which could compromise the stiffness of the
Final rule; request for comments.
SUMMARY:
The FAA is adopting a new airworthiness directive (AD) for all Schempp-Hirth Flugzeugbau GmbH Model Duo Discus and Duo Discus T gliders. This AD was prompted by mandatory continuing airworthiness information (MCAI) originated by an aviation authority
DATES:
This AD is effective February 24, 2023.
A copy of the AD is located here: https://www.federalregister.gov/documents/2023/02/09/2023-02773/airworthiness-directives-schempp-hirth-flugzeugbau-gmbh-gliders
ACTION:of another country to identify and correct an unsafe condition on an aviation product. The MCAI identifies the unsafe condition as cracks in the connecting tube of the elevator U-bracket of the horizontal tail, which could compromise the stiffness of the
Final rule; request for comments.
SUMMARY:
The FAA is adopting a new airworthiness directive (AD) for all Schempp-Hirth Flugzeugbau GmbH Model Duo Discus and Duo Discus T gliders. This AD was prompted by mandatory continuing airworthiness information (MCAI) originated by an aviation authority
DATES:One wants to speculate on the possibility that this part failed in a couple of recent fatal and non-fatal accidents. At least in one case, it would explain the known facts pretty well.
This AD is effective February 24, 2023.
A copy of the AD is located here: https://www.federalregister.gov/documents/2023/02/09/2023-02773/airworthiness-directives-schempp-hirth-flugzeugbau-gmbh-gliders
The Summary only mentions the Duo Discus and Duo Discus T. It also applies to all variants of the Arcus and Nimbus 4. It should also serve as notice to stop lifting the tail of the glider by putting your shoulder under the horizontal and picking it up.When you do that, you are loading these fittings that have the proposed AD applied to them.
Steve LeonardThanks for that Steve. Spot on!
On Friday, February 10, 2023 at 2:56:45 PM UTC-5, Steve Leonard wrote:up. When you do that, you are loading these fittings that have the proposed AD applied to them.
The Summary only mentions the Duo Discus and Duo Discus T. It also applies to all variants of the Arcus and Nimbus 4. It should also serve as notice to stop lifting the tail of the glider by putting your shoulder under the horizontal and picking it
Steve LeonardThanks for that Steve. Spot on!
I can't think of an aerodynamic or trailer storage condition that would cause the damage. Motor gliders may be at higher risk due to heavier tail weights.
KS
I have always felt that SH method of attaching the horizontal stab is on the flimsy side. Oh, it’s strong enough for vertical loads, but give it a good side load and…………not so much! I must have half a dozen of those U members in my junk box,all from ground loop accidents. They’re all bent with one elevator up and the other bent down about 15 degrees! The load path goes from the U member on the vertical fin into the elevator receiver, then through 2 little elevator bearings with 6mm bolts,
After Surgio’s accident at Truckee, I made a quick mock-up that showed a large load on one side of the horizontal stab ( like a big bird strike) would twist the U member leaving one elevator up and the other one down! This scenario also resulted inthe whole horizontal stabilizer tilted to one side and digging in (leading edge down). Would this explain the high G loops seen by some whitnesses?
So, armed with this information, what should we do? I recommend you closely inspect the U member before every assembly and inspect the bearings on both sides of the elevator and look at the bearing mounts, too. They stand off about an inch behind thespar.
Something to consider,
JJ
all from ground loop accidents. They’re all bent with one elevator up and the other bent down about 15 degrees! The load path goes from the U member on the vertical fin into the elevator receiver, then through 2 little elevator bearings with 6mm bolts,I have always felt that SH method of attaching the horizontal stab is on the flimsy side. Oh, it’s strong enough for vertical loads, but give it a good side load and…………not so much! I must have half a dozen of those U members in my junk box,
the whole horizontal stabilizer tilted to one side and digging in (leading edge down). Would this explain the high G loops seen by some whitnesses?After Surgio’s accident at Truckee, I made a quick mock-up that showed a large load on one side of the horizontal stab ( like a big bird strike) would twist the U member leaving one elevator up and the other one down! This scenario also resulted in
spar.So, armed with this information, what should we do? I recommend you closely inspect the U member before every assembly and inspect the bearings on both sides of the elevator and look at the bearing mounts, too. They stand off about an inch behind the
Something to consider,I suspect SH will beef up the design slightly and call it good. Slim chance that they will re-configure the part to be more robust (like AS?). Glider mfgs certainly can't admit the "other" guy has a better design.
JJ
lørdag den 11. februar 2023 kl. 20.51.56 UTC+1 skrev Craig Reinholt:box, all from ground loop accidents. They’re all bent with one elevator up and the other bent down about 15 degrees! The load path goes from the U member on the vertical fin into the elevator receiver, then through 2 little elevator bearings with 6mm
I have always felt that SH method of attaching the horizontal stab is on the flimsy side. Oh, it’s strong enough for vertical loads, but give it a good side load and…………not so much! I must have half a dozen of those U members in my junk
in the whole horizontal stabilizer tilted to one side and digging in (leading edge down). Would this explain the high G loops seen by some whitnesses?After Surgio’s accident at Truckee, I made a quick mock-up that showed a large load on one side of the horizontal stab ( like a big bird strike) would twist the U member leaving one elevator up and the other one down! This scenario also resulted
the spar.So, armed with this information, what should we do? I recommend you closely inspect the U member before every assembly and inspect the bearings on both sides of the elevator and look at the bearing mounts, too. They stand off about an inch behind
Correct, but in aviation, there are limits to that, unless you are designing a flying tank.These models presents such a discomforting number of cases of poor design and poor manufacturing quality. Yet, it doesn't seem to affect the number of buying customers.Something to consider,I suspect SH will beef up the design slightly and call it good. Slim chance that they will re-configure the part to be more robust (like AS?). Glider mfgs certainly can't admit the "other" guy has a better design.
JJ
In our country there's reason to believe, that identified faults reported to our authority won't systematically find it's way to the manufacturer.
Look out for yourself out there.
A good design is resilient towards foreseeable unintended (ab)use.
Who would ever consider lifting up a 40 kg plus tail by lifting under the tailplane? Apparently foreseeable.
A good design is resilient towards foreseeable unintended (ab)use.<<
Have seen it time and again! Same with turning the glider on the main wheel w/o a tail dolly installed by just yanking on the wing tip. Just because you have the dough to own a nice, shiny toy doesn't mean you have the brain power to understand theWho would ever consider lifting up a 40 kg plus tail by lifting under the tailplane? Apparently foreseeable.<<
On Sunday, February 12, 2023 at 5:54:29 AM UTC-5, Per Givskov wrote:box, all from ground loop accidents. They’re all bent with one elevator up and the other bent down about 15 degrees! The load path goes from the U member on the vertical fin into the elevator receiver, then through 2 little elevator bearings with 6mm
lørdag den 11. februar 2023 kl. 20.51.56 UTC+1 skrev Craig Reinholt:
I have always felt that SH method of attaching the horizontal stab is on the flimsy side. Oh, it’s strong enough for vertical loads, but give it a good side load and…………not so much! I must have half a dozen of those U members in my junk
resulted in the whole horizontal stabilizer tilted to one side and digging in (leading edge down). Would this explain the high G loops seen by some whitnesses?After Surgio’s accident at Truckee, I made a quick mock-up that showed a large load on one side of the horizontal stab ( like a big bird strike) would twist the U member leaving one elevator up and the other one down! This scenario also
the spar.So, armed with this information, what should we do? I recommend you closely inspect the U member before every assembly and inspect the bearings on both sides of the elevator and look at the bearing mounts, too. They stand off about an inch behind
mechanics of things!These models presents such a discomforting number of cases of poor design and poor manufacturing quality. Yet, it doesn't seem to affect the number of buying customers.Something to consider,I suspect SH will beef up the design slightly and call it good. Slim chance that they will re-configure the part to be more robust (like AS?). Glider mfgs certainly can't admit the "other" guy has a better design.
JJ
In our country there's reason to believe, that identified faults reported to our authority won't systematically find it's way to the manufacturer.
Look out for yourself out there.
A good design is resilient towards foreseeable unintended (ab)use.
Who would ever consider lifting up a 40 kg plus tail by lifting under the tailplane? Apparently foreseeable.
Have seen it time and again! Same with turning the glider on the main wheel w/o a tail dolly installed by just yanking on the wing tip. Just because you have the dough to own a nice, shiny toy doesn't mean you have the brain power to understand theA good design is resilient towards foreseeable unintended (ab)use.<< Correct, but in aviation, there are limits to that, unless you are designing a flying tank.
Who would ever consider lifting up a 40 kg plus tail by lifting under the tailplane? Apparently foreseeable.<<
I am sure these sort of things are covered in the 'Feeding & Care' manual, as in 'Do not ....'
Uli
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