Fatal - TangoGyro Tango2 N8680G, near Melrose, Florida, USA 30 JUL 2022

[Abid]

Then I guess this is another one where we'll never know what happened, no one seems to have ever inspected and recorded the separated blade condition for leading edge marks or indications of rotor strike prior to crash descent...

Rotor blades should not literally separate off like that just by hitting the tail or propeller in flight. I have never come across an accident like that. Now to be honest I have never come across an accident like that except where there was fatigue cracking in the blades prior to flight which is rare but AutoGyro Gmbh and Trendak (AirGyro which is what was copied by AutoGyro) are examples of such blades.

 

[Tyger]

I feel sure we'll hear more about the condition of that separated blade in the final report, but if there is indeed a problem with fatigue cracking they really ought to let folks know ASAP.

 

[MikeBoyette]

Anyone know the alloy of these blades? Just curious might help the discussion as far as their ability to withstand many different kinds of stresses. These stresses could include trailering which dad, Chuck, and anyone I have been around since the early 90’s once the stresses were understood were warned against. If remember right some the early extruded blades were made from very soft 5053 T3 which was not very good for the stresses of flying. Not saying these are. Just curious. Chuck Beaty has many discussions about this subject of extruded blades and he has never been a fan and has stated it’s almost impossible to extrude them out of strong enough material to withstand the stress for many many hours. Most are made with 6063. I believe the ones Abid uses are the only ones that may use 6061T6. I may be wrong. Going off memory. Despite being considered the kid in the gyro world for the longest time I am getting old. I will be 51 next week. I actually knew Doctor Bensen and Ken Brock personally. Oh and that other cranky old man Ernie Boyette I kinda know that dude too. Not to brag or anything. I will write a book one day soon. Not that anyone would interested.

 

[Abid]

Anyone know the alloy of these blades? Just curious might help the discussion as far as their ability to withstand many different kinds of stresses. These stresses could include trailering which dad, Chuck, and anyone I have been around since the early 90’s once the stresses were understood were warned against. If remember right some the early extruded blades were made from very soft 5053 T3 which was not very good for the stresses of flying. Not saying these are. Just curious. Chuck Beaty has many discussions about this subject of extruded blades and he has never been a fan and has stated it’s almost impossible to extrude them out of strong enough material to withstand the stress for many many hours. Most are made with 6063. I believe the ones Abid uses are the only ones that may use 6061T6. I may be wrong. Going off memory. Despite being considered the kid in the gyro world for the longest time I am getting old. I will be 51 next week. I actually knew Doctor Bensen and Ken Brock personally. Oh and that other cranky old man Ernie Boyette I kinda know that dude too. Not to brag or anything. I will write a book one day soon. Not that anyone would interested.

I do not know the exact alloy these blades are extruded from. Russia has some alloys that we do not see in the US. Like 7050 used for aerospace but I doubt these are out of 7050. There is another alloy that kind of fits between 6061 and 7075 that is used there also. It is quite good actually. But these blades were extruded probably not by people involved in aerospace traditionally so the alloy may be something different.

The problem is not the alloy though. Well at least not the only problem. The problem is design engineering of the blade structure and lack of any steel spar. Averso has steel rods going in through all the way affixed in via a non-conducting glue that prevents galvanic corrosion while allow load paths in span to be mainly handled by the steel spar in bending loads. The other extruded blades do not have steel spars as far as I have seen. But that is also what makes Avero Stella about 15 to 18 pounds heavier than other extruded rotors.

Anyway Tango blades have a weak spot a few inches past where the clamping plates from hub bar stop. A solid rigid stiff material suddenly ends and switches to just extruded Aluminum. Bad idea. All bending loads focus right there. Same problem as in AutoGyro rotor system 1 conceptually and same problem in Aircopter rotors. It is a design of structure issue. In a Tampa North Tango accident of a recently signed off pilot when he did a bad takeoff (or was it landing), the blades grazed the ground and one blade broke off exactly around the same location as in this accident.

I have never seen any other blade completely break off in just grazing the ground. I usually would have never revealed this or said anything but I know there are other people flying Tango gyroplanes and I know the real manufacturer is in Russia and I know Alex has passed away. Someone has to warn the owners. It at the least requires inspection and attention regularly.

 

[DavePA11]

I usually would have never revealed this or said anything but I know there are other people flying Tango gyroplanes and I know the real manufacturer is in Russia and I know Alex has passed away. Someone has to warn the owners. It at the least requires inspection and attention regularly.

Well, people should be more open to discuss potential issues even if they are of completing products mainly to save lives. Experimental aircraft do not require the manufacture to provide this information like certified aircraft thus there is no way to find out practical issues that come up from flying the aircraft.

 

[Aerofoam]

Anyway Tango blades have a weak spot a few inches past where the clamping plates from hub bar stop. A solid rigid stiff material suddenly ends and switches to just extruded Aluminum. Bad idea. All bending loads focus right there.

In the "Little Airplane" world, we refer to this as a "Stress Riser" and it is especially frightening with aluminum which
has a poor fatigue life at best.
I don't know if you could adequately inspect for this without doing density testing, or x-ray, or something that indicates a change that is not visually apparent.
The problem is that it can go from slightly fatigued to failure very quickly as it work hardens...

 

[Kevin_Richey]

Would the layers of plates on helicopter rotorblades we see that go from longest to shortest under the grips (preventing stress risers) be beneficial for gyroplanes?
I am assuming the hub bars that are bent upwards for the coning angle attempt to prevent this?

 

[Abid]

In the "Little Airplane" world, we refer to this as a "Stress Riser" and it is especially frightening with aluminum which
has a poor fatigue life at best.
I don't know if you could adequately inspect for this without doing density testing, or x-ray, or something that indicates a change that is not visually apparent.
The problem is that it can go from slightly fatigued to failure very quickly as it work hardens...

That's right. Aluminum of any kind has no alpha value. Any structure made of Aluminum requires proper engineering of the structural design to get proper fatigue life. You are right it is hard for normal end users to inspect for this.

 

[Aerofoam]

I'm thinking out loud here:
I think you might me able to use a contact microphone, like a Piezo transducer and record the sound from the blade root when
you whack it with a wooden mallet.
When it started to fatigue and work harden, the audio signature will change.
This would have to be quantified, but a free download "Digital Audio Workstation" like "Reaper"
would give you a visible wave form and the pitch should noticeably rise for those with a good ear....
Anyway, a method for inspecting without having to send them in for x-ray could be developed.....

 

[DavePA11]

Patten that aerofoam…

 

[Abid]

I'm thinking out loud here:
I think you might me able to use a contact microphone, like a Piezo transducer and record the sound from the blade root when
you whack it with a wooden mallet.
When it started to fatigue and work harden, the audio signature will change.
This would have to be quantified, but a free download "Digital Audio Workstation" like "Reaper"
would give you a visible wave form and the pitch should noticeably rise for those with a good ear....
Anyway, a method for inspecting without having to send them in for x-ray could be developed.....

Interesting thought. My son uses or at least used to use Reaper to record his song tracks. But there must be a smart phone app that can also record and display a wave form. Not everyone is tech savvy though. NDT approaches to finding fatigue on metal surfaces is nothing new but to develop a method to check I think is beyond the ability of Tango manufacturer of blades in Russia. They are not aviation or aerospace people to the best of my knowledge

Metal Fatigue Detection: Using Advanced NDT to Identify Failing Metals | Zetec

This article will show the best nondestructive testing methods for metal fatigue detection based on weld types and geometric patterns.

www.zetec.com

In-situ fatigue life analysis by modal acoustic emission, direct current potential drop and digital image correlation for steel

Optimizing acoustic emission (AE) is useful to understand fatigue crack growth of metal structures. Experimental investigation of fatigue in steel wit…

www.sciencedirect.com

 

[Abid]

I do not know the exact alloy these blades are extruded from. Russia has some alloys that we do not see in the US. Like 7050 used for aerospace but I doubt these are out of 7050. There is another alloy that kind of fits between 6061 and 7075 that is used there also. It is quite good actually. But these blades were extruded probably not by people involved in aerospace traditionally so the alloy may be something different.

The problem is not the alloy though. Well at least not the only problem. The problem is design engineering of the blade structure and lack of any steel spar. Averso has steel rods going in through all the way affixed in via a non-conducting glue that prevents galvanic corrosion while allow load paths in span to be mainly handled by the steel spar in bending loads. The other extruded blades do not have steel spars as far as I have seen. But that is also what makes Avero Stella about 15 to 18 pounds heavier than other extruded rotors.

Anyway Tango blades have a weak spot a few inches past where the clamping plates from hub bar stop. A solid rigid stiff material suddenly ends and switches to just extruded Aluminum. Bad idea. All bending loads focus right there. Same problem as in AutoGyro rotor system 1 conceptually and same problem in Aircopter rotors. It is a design of structure issue. In a Tampa North Tango accident of a recently signed off pilot when he did a bad takeoff (or was it landing), the blades grazed the ground and one blade broke off exactly around the same location as in this accident.

I have never seen any other blade completely break off in just grazing the ground. I usually would have never revealed this or said anything but I know there are other people flying Tango gyroplanes and I know the real manufacturer is in Russia and I know Alex has passed away. Someone has to warn the owners. It at the least requires inspection and attention regularly.

I remembered the other alloy from Russia that I have seen used in light aircraft is D16T. I think it is similar to 2024 in US equivalent. I doubt though that either 7050 or D16T were used in this blade extrusion

 

[scottessex]

Just a note here, of the Tango's that have been rolled on runways at near rotor flight RPM, and even when Alex crashed upside down, there has been no rotor blade separation. Could these blades have been previously flapped severely? I know rotors don't like to be flapped. Just an observation,
And if I am not mistaken the Tango blades are made by a mfg that makes Russian Helicopter blades.

 

[Aerofoam]

This would do it!

 

[Abid]

Just a note here, of the Tango's that have been rolled on runways at near rotor flight RPM, and even when Alex crashed upside down, there has been no rotor blade separation. Could these blades have been previously flapped severely? I know rotors don't like to be flapped. Just an observation,
And if I am not mistaken the Tango blades are made by a mfg that makes Russian Helicopter blades.

There is a Tango at Tampa North that certainly did and it was not flapped or anything before. Alex crashed in a soft field (cotton field) not on tarmac. But one of his rotors also separated on impact as well. Of course it is hard to say what exactly happened there but impact separation still keeps things fairly close and that is the case for Alex's accident.
"One of the main rotor blades was impact separated and located about 15 ft from the main wreckage and the cap was impact separated. The separated blade exhibited impact damage, was bent in the aft direction, and rotational scoring was noted."

I do not know about the blades on this Florida fatal accident gyroplane in terms of if it was flapped before but it definitely separated in flight and it seems at the same spot as the one at Tampa North. The fact it was 300+ feet away is definitely separation in air.
Helicopter blades are not made via extrusion, are they?

The problem is now what used to be Tango and its blades (Russian) are no longer Tango and have a falling out of Alex's son who is trying to continue Tango in some fashion. Now what used to be Tango is trying to be brought in as GyroFox. They are using Tango blades and will they have any input or concern about existing Tango fleet since they are not allowed to sell Tango (brand).

 

[PJB]

Re: blades I'd like to know what work is done to establish their on going servicing requirements and longer term service lives.

Personally [and this is based upon nothing more than my own feeling based upon the documentation, the people involved, the feedback around the skill sets of people at various regulators] I do not think there is enough rigor to this. I also think that its why the AAIB report to the Cavalon crash in the UK in 2020 is so delayed because my own feeling is they [the AAIB] have asked questions or done investigations and their findings do not square or sit well. Time will tell if that "feeling" has any merit but how many times do we have to read about gyroplane blade/rotor failures across many brands and questions then come back about material, operation, suitability or maintenance?

 

[Abid]

Re: blades I'd like to know what work is done to establish their on going servicing requirements and longer term service lives.

Personally [and this is based upon nothing more than my own feeling based upon the documentation, the people involved, the feedback around the skill sets of people at various regulators] I do not think there is enough rigor to this. I also think that its why the AAIB report to the Cavalon crash in the UK in 2020 is so delayed because my own feeling is they [the AAIB] have asked questions or done investigations and their findings do not square or sit well. Time will tell if that "feeling" has any merit but how many times do we have to read about gyroplane blade/rotor failures across many brands and questions then come back about material, operation, suitability or maintenance?

Well it seems like there are a couple of different reasons

1) AutoGyro. A structural design issue between hub bar and blade

2) AirCopter. Same. Both these are copies of each other

3) Trendak. It’s an AirCopter rotor as well

4) TAG. It was a construction and quality control issue where balancing rods were not properly secured in composite blade and came out

5) Tango. It’s a structural design issue I suspect

6).ELA. I am not quite sure why but I have seen a few composite blades with cracks starting

I decided to go with Averso because Dominator did not at the time have appropriate blades for a 2 seater. Averso in my research had a lot of rotors out since 2004 and there were no reports of in flight failures or cracking and generally no negatives I could find. I did not want to get into figuring out how to manufacture the rotors when there was plenty else to figure out.

I know that Averso was of the opinion that AutoGyro's 2400 hours life for their rotors was not appropriate given that Averso rotors are about 20 pounds heavier because of having that much more metal and structure and they are lower lifetime.

 

[Tyger]

And then there's Magni:

The Magni composite rotors avoid the traditional fatigue-life issues of many rotors. There are Magni rotor blade assemblies that have flown in excess of 3000 hours – most of those in rugged training hours with students. There have never been any reported rotor failures or even structural cracks with Magni rotors – other than obvious rotor strikes with hard objects. Magni does, however, require replacement of rotor blades at 2500 operational hours. This is mostly so that the factory can evaluate such high time rotors to see if there are any issues developing, and to eventually determine if the 2500 hour lifetime limit can be extended.

Full composite material construction is a major reason for the long, trouble-free life of Magni rotor blades. But the Magni hub-bar attachment, with large lateral bolts rather than vertical bolting, avoids top side and bottom side stressor points at the bolt holes and hub-bar tips that would focus the fatigue stress at those most critically stressed root attachments points. With the high stress concentration points unavoidable with common vertical attachment bolts and holes, extruded spars and even full extrusions may be prone to stress fatigue cracks at or near these stressor points – often difficult to observe internally. Magni simply avoids all of these issues with use of a full carbon-fiber spar and fiberglass construction.

The Magni rotor spar consists of a large number of unidirectional carbon-fiber strips, routed tip to root through a rounded window in a massive, aluminum attachment hub block at the root of each blade. The horizontal configuration attachment bolts – two very large bolts that sandwich the aluminum attachment hub between the hub bar's steel plates – avoid the stressor points created by vertical bolt holes and the tip of the hub bar on standard-configuration rotors.

Magni is the only producer that uses this entire rotor and hub-bar configuration. As far as we know, there have been no normal-use failures of Magni rotors or hub bars in the [30+] years that this design has been in operation. Even a popular fiberglass rotor blade that employed an aluminum spar and standard vertical blade attachment bolts had severely limited life and experienced numerous cracking issues.
If there is one issue that really takes the fun out of flying, it is probably having doubts about the structure and reliability of the rotor!

– Greg Gremminger

 

[GyrOZprey]

4) TAG. It was a obstruction and quality control issue where balancing rods were not properly secured and came out

For full disclosure (for newcomers here) on the 2018/19 TAG rotor problem ...(carbon composite matched with carbon spar design)
Rotor blades serial # 1-20 = mark1
Original leading edge weights were leadshot in resin ...moulded sticks! .....tricky to handle & labor-intensive to place in rotor mold!

The sub-contacted composite manufacturer of TAG rotors... changed the leading edge weight to a steel rod. = mark2. serial#21-89

A new hire ...incorrectly supervised/trained ...evidently did not clean the steel rods on 2 blades that were manufactured consecutively!

2 blades had leading edge steel-rod weights that were not bonded to the encasing matrix. These blades ended up on 2 different rotors.

Both rotors ended up on folding-mast design machines. The first accident review initially focused on the folding mast plates! The rotor was buried in an asbestos landfill and never able to be re-examined after the second accident 3 months later when the rod was determined to be missing in one blade!

Extensive testing on sacrificial blades showed it impossible to pound out or draw out that rod with forces FAR ABOVE flight forces.

ASRA officials refused to accept all the engineering evidence & research on the static & dynamic testing on the engineered modification to install a safety-mod to that group of rotors! (those rotors are not approved to be used in Australia!)

Neil personally travelled in July/August 2019 to his international TAG owner's in Israel,USA & South Africa to install the safety mod! EVERY single rotor opened up proved to have SOLID well -fixed leading edge balance rods that were then modified with addition of 150% of the engineer approved glass plugs& heavier-duty end-caps!

Several months PRIOR to either accident ...TAG Aviation had redesigned the leading edge weight ...returning to the leadshot encased in resin concept ...only now the shot is encased in a fiber open weave stocking ...and resin poured ...in the mold! =Mark 3/ current rotor design serial # 90+
Since 2020 ... the rotor mold was relocated from the WA Composite sub-contractor to TAG factory in NSW ...and rotor blades NOW MADE IN HOUSE ...personally by Neil!

 

[GyrOZprey]

And then there's Magni:

The Magni composite rotors avoid the traditional fatigue-life issues of many rotors. There are Magni rotor blade assemblies that have flown in excess of 3000 hours – most of those in rugged training hours with students. There have never been any reported rotor failures or even structural cracks with Magni rotors – other than obvious rotor strikes with hard objects. Magni does, however, require replacement of rotor blades at 2500 operational hours. This is mostly so that the factory can evaluate such high time rotors to see if there are any issues developing, and to eventually determine if the 2500 hour lifetime limit can be extended.

Full composite material construction is a major reason for the long, trouble-free life of Magni rotor blades. But the Magni hub-bar attachment, with large lateral bolts rather than vertical bolting, avoids top side and bottom side stressor points at the bolt holes and hub-bar tips that would focus the fatigue stress at those most critically stressed root attachments points. With the high stress concentration points unavoidable with common vertical attachment bolts and holes, extruded spars and even full extrusions may be prone to stress fatigue cracks at or near these stressor points – often difficult to observe internally. Magni simply avoids all of these issues with use of a full carbon fiber spar and fiberglass construction.

The Magni rotor spar consists of a large number of unidirectional carbon fiber strips, routed tip to root through a rounded window in a massive aluminum attachment hub block at the root of each blade. The horizontal configuration attachment bolts – two very large bolts that sandwich the aluminum attachment hub between the hub bar's steel plates – avoid the stressor points created by vertical bolt holes and the tip of the hub bar on standard configuration rotors.

Magni is the only producer that uses this entire rotor and hub-bar configuration. As far as we know, there have been no normal-use failures of Magni rotors or hub bars in the [30+] years that this design has been in operation. Even a popular fiberglass rotor blade that employed an aluminum spar and standard vertical blade attachment bolts had severely limited life and experienced numerous cracking issues.
If there is one issue that really takes the fun out of flying, it is probably having doubts about the structure and reliability of the rotor!

– Greg Gremminger

DITTO for the Mark3 TAG rotors!!! Tevermaki design Hub-bar & blade attachment. Full Carbon composite on CARBON (NOT AL ) SPAR!