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

We've seen this type of cracking in blades other than all-extruded ones. It can happen in old-school tin-and-spar blades, too.

It's fine to put a life limit on blades. It's even better also to look for the forces that lead to cracking.

Most of us know that the developer of the 2-blade teetering rotor, Bell Helicopter, mounts its engine, transmission and mast/driveshaft on a vertically-oriented shock mount similar to a Dynafocal engine mount on a FW plane. This allows the whole mast-engine-tranny unit to deflect in any direction, and also to hop up and down a bit. Such a setup is expensive and adds weight. Bell (and Robinson, who uses a similar arrangement) must feel that it's necessary, though.

When Igor Bensen adopted a simplified, Bell-style underslung teetering rotor for his gyro, he judged that he could get away with omitting the complex, soft mast mount in his tiny rotorcraft, with its 75-pound engine and light 20-foot rotor. He cautioned us repeatedly NOT to brace the mast any more rigidly than shown on the plans. Even the 2-tube "redundant" mast increases the transmission of 2-rev vibes through the frame.

What worked on a 450lb. GW Bensen does NOT necessarily work on a heavier gyro with a longer rotor. We periodically get into trouble when we transfer Bensen's "calculated informalities" straight onto heavier, faster gyros carrying two passengers and a 4-stroke engine on a steel mast. What works for the little guys does not necessarily work for the big guys.

IMHO, we need to move at least partway back toward the Bell approach to mast suspension. In fact it wouldn't hurt a bit to go whole hog (see the R-22 pic) -- but at least use sliders, the RAF magic mast, or something that works the same way. An overly rigid rotor suspension puts all the lag-lead stress on the blades and hub.

All aluminum alloys, not just 6063 vs. 6061, have relatively poor fatigue performance. Strength-to-weight ratio is so important in aircraft that we put up with aluminum's shortcomings. But we can't pretend they don't exist.

Pardon my interjection but if this rotor was at 4000 hours when life limit by manufacturer is 2400 hours, I think they would say to you rightly that they don't need to do anything. What needs to be done is by German authorities to find out how an annual was signed off without replacement of rotors on that gyroplane.
 
Hello,

I ran this through google translate and I also edited the very drastic accident overview image with English tags.
Thomas Kiggen probably didn't trailer much, Hildesheim is is home airport. As you can tell by the huge amount of hours, he worked day in, day out as instructor, most flight instructors in Germany went through his school at some time. He had hangar-space. This whole thing is stil a mystery to all of us. It seems like the familiarity breed contempt applied here, after so many hours and landings, rules and regulations seem optional. I have seen more accidents of over-confident, highly experienced pilots, but never such a bad maintenance. I assume, as he himself was a certified tester, he may have "done" the annual inspections himself, taking shortcuts.

Kai.
 

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Yeah but if the rotors were almost at 4000 hours who cares. They are well past their 2400 hour life limit. This then becomes a maintenance and owner/operator issue.
No, Fara. That photo of the broken off rotorblade was from a set that only had 333 hrs. on them (Crash of D-MDOZ in a forest in Germany), not the Hildesheim (D-MTMZ) crash in 2021:
That figure of 333 hrs. is in the first post on that thread.

Also, where is the 2,400 hrs. limit coming from that you quote repeatedly? I read 2,500 hrs., for their 2nd generation rotors, both on the British Rotorcraft statement as well as Autogyro of Germny's website under their page "Safe Life Limits".
The BRA states only 700 hrs. life limit on the 1st generation rotors.
 
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In response to the lifespan of any rotor:

Do not neglect the fact that not all rotors are properly maintained with respect to proper track and balance throughout their lifespan. Many pilots are unaware of the actual state of track and balance other than a very subjective seat of the pants feel for it.

I doubt any gyroplane rotor manufacturer can give accurate derating curves for various magnitudes of out of track and/or balance vs. rotor life-span, although there is most certainly a relationship between the two.
 
How does the pilot's body end up so far away from the wreckage? Both should logically be near each other. Both don't have any airfoils to cause them to land far away from where they should be, straight down along the flight path, taking into account any forward momentum from engine thrust.
"The seat belts were intact. The flight instructor's belt was open at the buckle."

It sounds like the buckle somehow popped open, or... he never put the seatbelt on. Given what Gyro_Kai just said, I wonder which is more likely.
 
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In response to the lifespan of any rotor:

Do not neglect the fact that not all rotors are properly maintained with respect to proper track and balance throughout their lifespan. Many pilots are unaware of the actual state of track and balance other than a very subjective seat of the pants feel for it.

I doubt any gyroplane rotor manufacturer can give accurate derating curves for various magnitudes of out of track and/or balance vs. rotor life-span, although there is most certainly a relationship between the two.


Yes .... vibrations are usually the main culprit ... strength of blade secondary.

This can be seen in the early days of Enstrom Helicopters .... they used 3 very strong metal blades .... hinged at the hub for flapping ..... but did not know they also needed a lead-lag hinge .... lead-lag is the small amount of back and forward movement of the blade as it "hunts" for its comfort zone .... makes a very smooth system that relieves stress on the blade root.

First high speed test flight developed a severe vibration .... pilot managed to land ... all 3 blades looked like they came from a noodle factory.

After installing the lead-lag hinge , and 50 years later , the Enstrom , is still renowned for having one of the best and strongest rotor systems

2 blade gyroplanes should have either a flexible mast ... a rubber mounted mast .... elastomerics .... or a slider affair to absorb the pulses . Surprisingly many manufactures do not realize it even today.

.
 
No, Fara. That photo of the broken off rotorblade was from a set that only had 333 hrs. on them (Crash of D-MDOZ in a forest in Germany), not the Hildesheim (D-MTMZ) crash in 2021:
That figure of 333 hrs. is in the first post on that thread.

Also, where is the 2,400 hrs. limit coming from that you quote repeatedly? I read 2,500 hrs., for their 2nd generation rotors, both on the British Rotorcraft statement as well as Autogyro of Germny's website under their page "Safe Life Limits".
The BRA states only 700 hrs. life limit on the 1st generation rotors.

It is 2500 hours lifetime for Rotor System 2. I thought it was 2400.

Now regarding you pointing to Kolibiri's analysis. I had assumed this thread was about this accident not the one Kolibiri posted about. That whole accident sounds very much like a rotor flap not cracking. Cracking came as a result of flap. Chicken came before the egg. Always look at who is saying what.
Kolibiri is a fan and now an associate of Sport Copter. I never considered Kolibiri "objective". It was very evident to me that he had an agenda. AutoGyro are my competitors as well but I cannot blame them based on Kolibiri's "expert" analysis of that accident. I know personally of a dozen AutoGyro products with Rotor System 2 that have well in excess of 335 hours that Kolibiri claims that fatigue set in in that rotor. It simply does not jive with facts otherwise known. I have personally performed annual inspections on a MTO Sport 2017 with about that many hours. They have issues but they aren't anything like this. I would choose AutoGyro's Aluminum blades over ELA's composite blades any day.
 
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Martin W, you may have already heard it, but Enstrom just filed for Chapter 7 bankruptcy. That means it's being liquidated.
 
I hope somebody picks up the parts and support business from the Chinese owners.
 
Yes .... vibrations are usually the main culprit ... strength of blade secondary.

This can be seen in the early days of Enstrom Helicopters .... they used 3 very strong metal blades .... hinged at the hub for flapping ..... but did not know they also needed a lead-lag hinge .... lead-lag is the small amount of back and forward movement of the blade as it "hunts" for its comfort zone .... makes a very smooth system that relieves stress on the blade root.

First high speed test flight developed a severe vibration .... pilot managed to land ... all 3 blades looked like they came from a noodle factory.

After installing the lead-lag hinge , and 50 years later , the Enstrom , is still renowned for having one of the best and strongest rotor systems

2 blade gyroplanes should have either a flexible mast ... a rubber mounted mast .... elastomerics .... or a slider affair to absorb the pulses . Surprisingly many manufactures do not realize it even today.

.

But yet we are here discussing an accident with 4000 hours on blades when they finally gave up.
The reality is that the masts do flex a little and are made of steel or SS and have an Alpha value where that flex is not critical to their fatigue life. There is no triangular capture of the mast to stop the top from flexing a bit. Trendak was forced by Polish CAA to make a stiffer mast in order to get certification that too from Aluminum alloy which has no Alpha value. That results in blades taking the brunt of the fatigue and premature cracking. Polish CAA may have thought they were doing a good thing because they did not understand this
 
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It seems like the familiarity breed contempt applied here, after so many hours and landings, rules and regulations seem optional. I have seen more accidents of over-confident, highly experienced pilots, but never such a bad maintenance.
I assume, as he himself was a certified tester, he may have "done" the annual inspections himself, taking shortcuts.
"The flight instructor concerned was the managing director and head of training. According to the information provided by the operator, the necessary technical maintenance and control measures were carried out by the flight instructor concerned. The airworthiness of the affected autogyro was certified annually by one and the same class 5 inspector"
It's a bit ambiguous, but it sounds to me like "one and the same" means that the same person (the flight instructor who was killed) did both the maintenance and inspections. Perhaps someone with a good understanding of the original german can clarify that?

The report then quotes this rule (from Ordinance on the Inspection of Aviation Equipment): "It is not permissible for an inspector to carry out the necessary maintenance and repair work and then inspect the microlight as part of a re-inspection. It is not permissible for an examiner to examine work carried out by himself."

But of course the elephant in this room remains the blades having been used for nearly 4000 hours, or 1.6 times their life limit. They're also supposed to be disassembled and inspected every 500 hours. Judging from those rusty bolts, I'd be suprised if that happened even once.
 
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Exactly, Abid. Aluminum lacks any "unlimited life" endurance limit, while steels generally have one. This makes Al. less than ideal for aircraft (which are vibe-prone) -- but strength-to-weight trumps just about everything else, so we use it anyway.

My point about lead-lag (or in-plane, if you prefer) stresses is broader than this accident. We've seem similar vibe damage from in-plane bending of blades at quite low hours. Such damage was turning up in RAF blades on non-RAF gyros, and also in one or more Aussie designs, IIR.

It's a problem that rears its head unexpectedly in various circumstances, with various blade designs. It may be difficult to predict because different mast lengths, materials, upper-mast weights (such as prerotator upper units) and engine weights change the resonant frequency of the whole system. You may have the bad luck to end up with a setup that happens to resonate at 2/rev. That's bound to crack the blades sooner than would otherwise be the case.

I'd like to see manufacturers of gyros in the "Bx2 to BX4" weight range (GW = Bensen times two or four) deal more formally with these vibes than merely using Igor's "flexible mast" approach.

A smoother ride would be an additional benefit in many cases.

Some people want a brutally strong mast, to provide a crash-resistant roll bar (maybe that's what the Polish CAA had in mind with Trendak). The two goals for the mast are apt to clash, though. Better to build a separate, dedicated roll bar if you want one, and let the mast wave about to relieve in-plane rotor bending.
 
Trendak was forced by Polish CAA to make a stiffer mast in order to get certification that too from Aluminum alloy which has no Alpha value. That results in blades taking the brunt of the fatigue and premature cracking. Polish CAA may have thought they were doing a good thing because they did not understand this
Trendak's masts are aluminum??
 
Exactly, Abid. Aluminum lacks any "unlimited life" endurance limit, while steels generally have one. This makes Al. less than ideal for aircraft (which are vibe-prone) -- but strength-to-weight trumps just about everything else, so we use it anyway.

My point about lead-lag (or in-plane, if you prefer) stresses is broader than this accident. We've seem similar vibe damage from in-plane bending of blades at quite low hours. Such damage was turning up in RAF blades on non-RAF gyros, and also in one or more Aussie designs, IIR.

It's a problem that rears its head unexpectedly in various circumstances, with various blade designs. It may be difficult to predict because different mast lengths, materials, upper-mast weights (such as prerotator upper units) and engine weights change the resonant frequency of the whole system. You may have the bad luck to end up with a setup that happens to resonate at 2/rev. That's bound to crack the blades sooner than would otherwise be the case.

I'd like to see manufacturers of gyros in the "Bx2 to BX4" weight range (GW = Bensen times two or four) deal more formally with these vibes than merely using Igor's "flexible mast" approach.

A smoother ride would be an additional benefit in many cases.

Some people want a brutally strong mast, to provide a crash-resistant roll bar (maybe that's what the Polish CAA had in mind with Trendak). The two goals for the mast are apt to clash, though. Better to build a separate, dedicated roll bar if you want one, and let the mast wave about to relieve in-plane rotor bending.

Yes I got you. You have to find the natural frequency of your structures and tail and make sure its not in the 5.8 - 6 or 11.5 to 12.5 Hz range because that is where rotor RPM is generally. Its not too difficult to do today. There are even phone apps that allow you to record them. In most structures like Magni, AutoGyro, us; the mast, the tail keel are at clearly higher frequencies than 1/rev or 2/rev. We had to modify our tail to make it have a different frequency range naturally.
There is even another strange phenomenon that has to do with airflow around a body causing a pulse. We had to deal with that. At 65 to 70 mph with a 3 blade prop with no passenger in the back seat in open cockpit AR-1, it would set off a shake in the tail. We kept looking for structural resonant frequencies and trying to figure out which RPM is setting it off and it wasn't any rotary motion doing it. It was this Vortex Shedding phenomenon. It happened when we made the tail out of Carbon Fiber first.

Crash resistant mast is actually fine with 2 inch square 4130 or 304 tubing. It bends but does not break off. Unfortunately have seen this with some customers flipping over or flapping the rotors. Aluminum masts may not be able to do that.
 
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Excellent app for detecting vibrations and resonant frequency vibrations
Only available for android but one never knows maybe the future will bring apple apps.
 
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Trendak's masts are aluminum??
The older ones were 2.9mm wall thickness IIRC The newer one is 3.2 I think ..I removed one or two in my time and fitted the new thicker mast, the effect was a more pronounced stick shake as the mast could not absorb the 2 in one …with my own xenon I have retained the older thinner mast and just fitted the doubler kit as described in the SB easy upgrade and great instruction and drawings from AT web site
 
Terrible, ideed.

The autogyro was optically in a neat condition. The high number of operating hours could not be seen from the seat cushions, the joysticks or any other traces.

It seems they took care to make sure it looked good, cosmetically, but yet never took a look at the most important components...

The affected autogyro had a comparatively high total operating time. Due to the permanent use as a training device, it is very likely that an exceptionally high number of take-offs and landings, with corresponding speed changes in the rotor system, were carried out.
Due to the unladen weight of the autogyro and the masses of the occupants, it was constantly operated above the maximum permissible operating mass during training...
It was only possible to find out that the operating hours counter had been changed and that the actual total operating time was approx. 3,940 hours by looking at old on-board documents from before 2018. The operating hour counter in the cockpit and the operating time noted in the onboard documents
gave a student pilot a completely wrong impression of the total operating time of the gyroplane, the age and the wear and tear of the components.

The poor student had no idea he was getting into a deathtrap.
 
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