Fatal - AutoGyro MTOSport D-MTMZ, near Hildesheim airfield, Germany 21 JUL 2021

Uncle Willie

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If you are reusing a Ny-Loc Nut and you can turn it with your fingers, it needs to be replaced.
If it needs to be wrenched on the whole way and feels like new, it is OK to be reused.
Use common sense.

Loctite 242 and its close cousins are Not recommended for use with "Plastics". Read the package.
It may be called a "Nylon" Locking Nut, but do you truly know what plastic really is used?

Loctite 425 is intended for use on Plastic parts. Not Cheap!!! ~$25 per half-ounce.
It is labeled as "Low Strength", But don't assume that means you won't need tools.
It is more like Super Glue Strength than Red Loctite Strength.
 

Abid

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I read (or was told), Loctite is not good for Nyloc nuts - use either Loctite or use Nyloc nuts.

Was it wrong advice?

No. Not bad advice. You should only use it on deformed metal lock nuts (which also should not be used if they cannot hold prevailing torque) or on multi used nylock nuts if you cannot or somehow are not able to get new ones for the moment and they are not holding prevailing torque. Usually a nylock nut will hold minimum prevailing torque for 5 to 10 times of reuse.
At the end of the day Loctite or Permatex are anaerobic compounds with their base being saccharin. They will play havoc on thermoplastics. Nylon 66 should not be effected by them but if you are looking at metric nuts or SAE nuts (not something like AN365, 364 nylock nut), you probably don't have Nylon 66 alone lining the nut for locking. Most likely use Zytel resin inserts which is based on Nylon 66. Anyway, better to be safe.
 
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JETLAG03

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@fara Whilst I accept your comments re nyloc can be re-used on the same bolts, for the cost, I will continue to use only once.

thanks

phil
 

Abid

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No. Not bad advice. You should only use it on deformed metal lock nuts (which also should not be used if they cannot hold prevailing torque) or on multi used nylock nuts if you cannot or somehow are not able to get new ones for the moment and they are not holding prevailing torque. Usually a nylock nut will hold minimum prevailing torque for 5 to 10 times of reuse.
At the end of the day Loctite or Permatex are anaerobic compounds with their base being saccharin. They will play havoc on thermoplastics. Nylon 66 should not be effected by them but if you are looking at metric nuts or SAE nuts (not something like AN365, 364 nylock nut), you probably don't have Nylon 66 alone lining the nut for locking. Most likely use Zytel resin inserts which is based on Nylon 66. Anyway, better to be safe.


Here is the official engineering advice on Loctite 242 from Loctite team

Question asked:
"Hi
I wanted to know if Loctite 242 will dissolve or make brittle nylon insert in a Nylock locking nut or not?
Thanks"

Answer by Loctite:

"Thank you for contacting us.

LOCTITE Threadlocker 242 is a medium strength threadlocking adhesive offering general
purpose qualities. The product provides quick fixture times on steel, brass and stainless steel
of 5, 15 and 20 minutes respectively.

Please refer the link for more product details and description :
https://www.tryloctite.in/estore/threadlockers-loctite-242-AD.TH.333219/

Hence the above Loctite Threadlocker 242 will not dissolve or brittle the nylon insert in the
nylock locking nut , it will simply secures and seals bolts, nuts and studs to prevent loosening
due to vibration."
 

Uncle Willie

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It doesn't look like the Loctite rep reads their own literature ...
- - -
Directly from the Loctite 242 FAQs ...

Can I use anaerobics where one or both parts are made of plastic?
Anaerobics are generally not recommended for use with plastics as they might result in stress cracking or softening.
In such cases, cyanoacrylates are recommended.
- - -

The Loctite 425 I mentioned earlier is a Cyanoacrylate Thread Locker for use on Plastics.
242 may be OK if the Locknut is truly Nylon and not something else.
The wise man would test for compatibility before committing the whole assembly.
 

Abid

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It doesn't look like the Loctite rep reads their own literature ...
- - -
Directly from the Loctite 242 FAQs ...

Can I use anaerobics where one or both parts are made of plastic?
Anaerobics are generally not recommended for use with plastics as they might result in stress cracking or softening.
In such cases, cyanoacrylates are recommended.
- - -

The Loctite 425 I mentioned earlier is a Cyanoacrylate Thread Locker for use on Plastics.
242 may be OK if the Locknut is truly Nylon and not something else.
The wise man would test for compatibility before committing the whole assembly.


This wasn't a Loctite Rep. It was Loctite technical support from Henkel.
Plastics is a large wide thing. The stress cracks and brittleness would happen in certain thermoplastics like Plexiglass/acrylics, polycarbonate/lexan etc.
Nylon should be ok. If we are using cheap Chinese nuts, God help us because no telling what exactly was used. But generally good quality industrial nylock nuts (including those made to spec in China or Taiwan) and MS or AN nuts will use Nylon resin to make the locking mechanism. Easy enough test though to do
 
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rcflier

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Wondering why I had seen no official explanation of the crash by now, I did a search.

And found this: https://www.ndr.de/nachrichten/nied...he-fuer-Gyrocopter-Absturz,gyrocopter108.html

It's just 3 weeks later, but according to the NDR article, a blade broke off and the engine tore off.

A Google translation :

"Experts had examined the wreck and found that there were signs of corrosion at the point where the rotor blade broke off at a height of around 50 meters, as reported by the Federal Bureau of Aircraft Accident Investigations on NDR request. A detailed interim report from the federal agency is expected at the end of September."

I remember I went ballistic over everyone judging the maintenance as faulty, because DULV wrote "pictures are shown as examples".
Meaning they weren't from the actual crash. But the NDR article may suggest the pictures being of the actual Type2 rotor?

Erik
 

Kevin_Richey

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Chilling to see the close-up photo showing rotorblade hub bar w/ the bolts still present, but no trace of the rotorblade attached to it, unlike the other end. Photo is a different angle than the original photo we saw, where vegetation blurred the hub bar end.

Google translate rendition:
 
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Tyger

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So did a blade come off the prop too? What on earth made the engine separate in the air?
 

Abid

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So did a blade come off the prop too? What on earth made the engine separate in the air?

When a whole rotor blade breaks off, whatever is the weakest point will go next due to extremely violent shaking. In this case it was the engine mount with a 155 pound engine hanging off it. All they have there is laser cut and bent plates welded to round rings for engine rubber mounts. The plate probably broke right off the mast with such shaking and that's really not important because its a consequence of the rotor blade coming off and causing extremely violent shaking. If engine didn't break off, the mast would have broken off
The rotor blade was clearly fatigued and probably accelerated fatigue due to corrosion from what I could see. The bolt was rusted badly. I would have never flown on seeing a bolt like that on a rotor system. Don't know how it got so rusted and corroded.
 

rcflier

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It seems strange, that anyone would've let the bolts corrode that far.

On the other hand, it wasn't that visible from the outside. But that's what inspection is for.

I suppose when rust forms, it takes up more space than the fresh steel did
(adding oxygen) and thus causes stress in the aluminum.

I haven't heard of this happening to any other Type2 rotor (corrosion, grass and dirt from crash),
so... But there may be - I don't have great connections.
 

Martin W.

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The amount of corrosion on that bolt is bizarre .
It is like it was coated with a corrosive liquid when installed.
 

Tyger

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I imagine water got in there on a semi-regular basis and, not being very exposed to the air, it probably almost never fully dried out...
 

Abid

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It seems strange, that anyone would've let the bolts corrode that far.

On the other hand, it wasn't that visible from the outside. But that's what inspection is for.

I suppose when rust forms, it takes up more space than the fresh steel did
(adding oxygen) and thus causes stress in the aluminum.

I haven't heard of this happening to any other Type2 rotor (corrosion, grass and dirt from crash),
so... But there may be - I don't have great connections.

If you look at the design of the hub bar from AG and how it "mates" to the blade profile, it never really seats and spreads the load evenly but instead only touches in certain spots causing localized stresses and risers. I don't like it but it seems to work. Extremely important to keep proper torque specially with that design on clamping bolts. I can't explain the rust on the bolt but the blade was fatigued which suggests there was movement of blade metal there somehow but that's my guess. We have to get the report.
 

Kevin_Richey

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Reiterating from my post (#38 in this thread) from last July (2021):

..."I shudder to see photos of departed rotorblades, because 15+ years ago, Jim Vanek was emphatically telling us in PRA Chapter 73 that extruded rotorblades aren't strong enough because of insufficient strength of 6063 architectural-grade aluminum that is extruded (screen doors & railings stuff).

He added that we would hear about extruded blades coming apart IN FLIGHT because they do not have the necessary strength/margin of safety for flying, & that it had already happened, but has been kept quiet. Criminal for those who did so."
 
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Kevin_Richey

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I received the following from a gyroplane-knowledgable person Re: this accident:

"...the rotor blade separated first, and the violence then shook off the Rotax.

Although the bolt is badly corroded, it neither failed nor was the cause of the departed blade. (The corrosion does indicate that no regular inspection disassembly had occurred, apparently not even during the annuals.)

The bolt’s original zinc plating acted as a sacrificial anode to the more cathodic 6005A aluminum, and the zinc was eaten away over time through galvanic corrosion. That left bare steel, which itself then corroded badly.

Aircraft hardware should be AN-spec, as its cadmium-plating has nearly zero galvanic corrosion potential with aluminum.
AutoGyro has yet to figure this out.
Magni did, though."

Summation: "...the poor design of the AutoGyro blades and hub bar, with proclivity for early failure."

Seeing photos of the root end of the departed rotorblade would be interesting.
 

Abid

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Reiterating from my post (#38 in this thread) from last July (2021):

..."I shudder to see photos of departed rotorblades, because 15+ years ago, Jim Vanek was emphatically telling us in PRA Chapter 73 that extruded rotorblades aren't strong enough because of insufficient strength of 6063 architectural-grade aluminum that is extruded (screen doors & railings stuff).

He added that we would hear about extruded blades coming apart IN FLIGHT because they do not have the necessary strength/margin of safety for flying, & that it had already happened, but has been kept quiet. Criminal for those who did so."

That is a very generalized statement and untrue. It is the design of the hub bar that I don't know which engineer did for both AirCopter as well as AutoGyro rotors that has a propensity to create stress risers, movement and fatigue prematurely. I would like to see what engineering analysis makes Jim come to that conclusion. I suspect, its garage banter not based on any engineering. You design with materials keeping their properties in mind. It is true that 6061-T6 has a higher yield point (20 to 25%) and fatigue strength (35 - 40%) than 6063 Aluminum.
Averso uses 2004 series Aluminum for Stella blades whose yield strength and fatigue strength is even higher than 6061. It is however more prone to corrosion so it has to be "clad" or anodized nicely. Somehow Averso blades are heavier than AutoGyro blades of the same size and yet their lifetime is listed at less than claimed AutoGyro Rotor System 2 rotors. This obviously does not make sense. Averso being of a material much stronger with more yield and fatigue strength than material used by AutoGyro and being heavier (meaning there is more metal being used) should have a higher claimed lifetime than AG blades but they don't. So it comes down to engineering analysis and design of who is doing it for AG. Averso had told me that if AutoGyro rotors have a lifetime of 2400 hours claimed than Averso should be 3000 but of course they won't do that because they don't believe that lifetime in typical usage. There in lies the rub.
 
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Gyro_Kai

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Although the bolt is badly corroded, it neither failed nor was the cause of the departed blade. (The corrosion does indicate that no regular inspection disassembly had occurred, apparently not even during the annuals.)

The bolt’s original zinc plating acted as a sacrificial anode to the more cathodic 6005A aluminum, and the zinc was eaten away over time through galvanic corrosion. That left bare steel, which itself then corroded badly.

Aircraft hardware should be AN-spec, as its cadmium-plating has nearly zero galvanic corrosion potential with aluminum.
AutoGyro has yet to figure this out.
Magni did, though."

Summation: "...the poor design of the AutoGyro blades and hub bar, with proclivity for early failure."

Seeing photos of the root end of the departed rotorblade would be interesting.
very interesting and helpful infomration!

Kai.
 

Abid

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I received the following from a gyroplane-knowledgable person Re: this accident:

"...the rotor blade separated first, and the violence then shook off the Rotax.

Although the bolt is badly corroded, it neither failed nor was the cause of the departed blade. (The corrosion does indicate that no regular inspection disassembly had occurred, apparently not even during the annuals.)

The bolt’s original zinc plating acted as a sacrificial anode to the more cathodic 6005A aluminum, and the zinc was eaten away over time through galvanic corrosion. That left bare steel, which itself then corroded badly.

Aircraft hardware should be AN-spec, as its cadmium-plating has nearly zero galvanic corrosion potential with aluminum.
AutoGyro has yet to figure this out.
Magni did, though."

Summation: "...the poor design of the AutoGyro blades and hub bar, with proclivity for early failure."

Seeing photos of the root end of the departed rotorblade would be interesting.

Bottom line is rusting of clamping bolts to that level create space (minor diameter). When that happens, it allows for slight movement and loss of clamping force. That in turn accelerates fatigue as the system is not working as a single unit. Nothing can stand that for too long. Its a design issue that in turn requires more frequent and more thorough inspections to get things right to prevent this from happening. When the rust isn't there it will likely not happen. I do not personally care for the design of that hub bar as I stated earlier but inspections carried out at prescribed intervals (annuals) to catch it before getting too far will probably keep things from getting to this point. I am a bit surprised that being at the same airport as the factory this instructor did not take advantage of the resources available to him to get more thorough inspections done.
 
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