another look at the AutoGyro MTOsport crash of 11 September 2016 in Germany (D-MDOZ)

Kolibri

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Before I get into the substance of this new thread, I would like at the outset to set the tone. I am not trying to "bash" a particular gyro kit manufacturer, however, looking into a 2016 fatal accident I have real concerns over the longevity of their rotor blades. I ask that those replying here constrain their remarks to the technical details, vs. "shooting the messenger". My goal here is to alert AutoGyro owners with "Rotor System 2" of a possible early fatigue point of their blades.

While posting photos of the D-MDOZ MTOsport crash in another thread, a couple of things caught my eye, so I carefully read the German BfU investigation report.


I speak, read, and write good German, and translated relevant excerpts below. (A German pilot friend of mine reviewed my work and deemed it accurate.)
Any words I thought properly inferred are [in brackets].



OVERVIEW ______________


The AutoGyro MTOsport was built in 2016, serial # M 01338
It had 333 flight hours and 1073 landings.

Two pilots, who had flown the autogyro on the day before, indicated no problems with the autogyro, the engine, or the seat-belts.

The pilot (and solo occupant) was the manager of a local gyro flight-seeing company, with approx. 110 hours total experience in the Cavalon, Calidus, MTOsport, and Xenons.

Weather: 25+ mile visibility, no clouds, wind from the north ~4-8kts

At about 1435 hours he was seen over a forest, falling from the sky in a spinning/wobbling fashion. Over 100 searchers combed the area for survivors and pieces of the wreckage. One rotor blade (never found) had broken off in flight, struck the tail, knocking it off the gyro. The pilot's seatbelt buckle may not have been fastened, as his body was found away from the gyro.




ACCIDENT WITNESSES ______________

Nach Ermittlungen der Polizei sah eine Zeugin den Tragschrauber um ca. 14:30 Uhr aus Richtung Gutach im Breisgau durch das Simonswalder Tal in Richtung Hohe Steig fliegen.

Gegen 14:35 Uhr wurde ein Zeuge in Gütenbach aufgrund plötzlich einsetzender, hubschrauberähnlicher Rotorblatt-Schlaggeräusche auf den Tragschrauber aufmerksam.

Dann habe er Teile wahrgenommen, die von diesem Flugobjekt fortfielen. Im Anschluss sei das Flugobjekt senkrecht nach unten gesunken bzw. getrudelt und habe dabei klappernde Geräusche gemacht. Zu Beginn seiner Beobachtung, noch während das Flugobjekt in der Luft stand bzw. beim ersten Trudeln, habe das Motor-geräusch aufgehört. Im senkrechten Fall habe seine Geschwindigkeit zugenommen. Unmittelbar nachdem er den Blickkontakt verloren habe, setzte er den Notruf ab. Dieser Notruf wurde um 14:36 Uhr bei der Polizei aufgezeichnet.
The police determined that a female witness saw at about 1430 hours, from the direction of Gutach in Breisgau, an autogiro in steep climb through the Simons Forest Valley.

About 1435 hours a man in Gütenbach had his attention suddenly drawn to helicopter-like rotorblade impact sounds. During questioning he indicated that he observed an aircraft, unlike autogyros he had observed in the past, [tail] spinning at a high and constant altitude.

Then he noticed parts flying off the aircraft. The aircraft fell perpendicularly, making rattling noises along the way. At the beginning of his observation, while the aircraft was first [tail] spinning, the engine sound ceased. The aircraft's velocity increased during the straight-down fall. Immediately after losing sight of it, the witness raised the alarm; police noted the emergency call at 1436 hours.
AutoGyro Rotor System 1 blade cracking.png


D-DMOZ formschlüssig.png


Das vorhandene Rotorblatt war im Nasenleistenbereich nahezu gradlinig. Das Rotorblatt war etwa im ersten Drittel im Endleistenbereich geknickt. Es wies eine Beschädigung ca. 2,6 m von der Blattwurzel auf. Die Beschädigung war formschlüssig mit der Seitenruderachse/-führung am Heck des Tragschraubers.
The existing rotor blade was almost straight along the leading edge area [but] damaged within the first third of the trailing edge. It showed [other] damage about 8.5 feet out from the root, consistent with [striking] the rudder axle/guide at the tail of the autogyro.

It is unclear if this blade struck the rudder axle/guide in the air, or upon ground impact.




PROBABLE CAUSE ______________

While the BfU report did not explicitly declare in-flight rotor flap as responsible for knocking off the tail, it blandly included under "
Additional Information" an English language explanation of rotor flap from 2004 Kitplanes magazine:

Rotor speed can decay rapidly when the blades are unloaded, leading to rotor instability or flap. This in turn can lead to loss of rotor control and invariably results in a blade strike where one or both blades impact the prop or tail components, further slowing the blades, not to mention the damage to blades and other parts of the airframe. In-flight rotor strikes are also typically fatal.



MY HYPOTHESIS ________________

After carefully studying the accident photos, I have strong doubts that D-MDOZ experienced rotor rpm decay and then rotor flap (striking the tail).

My hypothesis is that -- due to fatigue failure, not low rrpm rotor flap -- a blade began to tear from its outboard bolt hole, briefly went through a vigorous flapping while still tenuously attached by the bottom side, and finally broke from top to bottom as it completely tore off from front to rear.

If this is accurate, then AutoGyro's "Rotor System 2" (which uses nearly the same blades as RS1, but a different hub bar) is exhibiting similar-if-not-identical blade crack initiation to their previous "Rotor System 1".


Even if D-MDOZ had an in-flight rotor flap from decayed rotor rpm, then it remains the case that AutoGyro's "Rotor System 2" may fail catastrophically during a mid-air tail strike.
I view that as unacceptable. In my opinion, the rotor should be able to withstand a tail strike.
Even if the tail is knocked off, an intact rotor would probably allow for a non-fatal forced landing.



POSSIBLE RAMIFICATIONS FOR OWNERS _____________

D-MDOZ had 333 flight hours and 1073 landings.
Machines in excess of 200 hours may benefit from very frequent (i.e., every 25-50 hours) blade hole inspections.

Also, when taxiing over rough ground, consider having a bit of rotor rpm to alleviate some stress on the blades.

Safe flying,
Kolibri
 

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Kolibri

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An enlarged photo of the break seems to show some crystallization, which would indicate that the blade was working internally.
A metallurgical study might be warranted.


fetch?id=1143139&d=1553706478.png


AutoGyro still insists upon inspecting that bolt hole, calling it a "critical" area:

Inspect for cracks in the blade root area, especially in the area of the inner attachment bore (see Fig. 1 "Critical Area").
In case of any cracks the complete rotor system must be replaced.
AutoGyro RSII critical blade area.png
 

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Philbennett

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I think a greater understanding from the Bfu is required. I.e history of the origin of the blades (where they new, where they replacement items for example). What was the operational history, had there been multi pilots, rough landings, sporty flight, rough ground and high speed taxi, transport by road etc. When was the aircraft last serviced and so on.

ive instructed almost exclusively on autogyro product and on the RS1 blades have at least 1000hrs over 4 different aircraft all towards the upper margin of 700hrs of the rotor life. Indeed on 2 aircraft that ultimately went over that time the blades seemed fine before being destroyed to ensure no on going use. I dont believe there is a generic problem with the blades but would as always ensure my servicing, pre-flight and operational considerations were vigilant.

Kicking the tyres, taxi over a ploughed field at 30knts, lashings of wing overs, late on the round out Hoskins and road tansport will probably hurt in the long run....
 

Vance

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I find the debris field interesting.

I find the pilot being found separate from the aircraft interesting.

I find the helmet being found separate from the pilot interesting.

I find the helmet inner parts found at the beginning of the debris field interesting.

I have had clients get distracted and not fasten their helmet and/or not fasten their seat belts. These things are at the top of my pre takeoff check list because of this experience. I have had clients read these two items aloud and still not properly check their helmet and seat belts because they remember having fastened them.

I have found that a properly fastened helmet generally stays on the head of the person involved in a mishap.

I have found that even without a head in it a helmet generally retains all of its inner parts unless struck by something with considerable force.

I have found that a properly fastened seat belt generally keeps the body with the wreckage.

My hypothesis is that the pilot's helmet came off, went into the propeller and then hit the rotor. In my opinion either the rotor damage from the helmet or pilot control inputs because of the distraction of the departing helmet put the rotor into the tail.
 

Kolibri

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Phil, thanks for your comments, I applaud your ethical behavior in destroying timed-out RS1 blades. That sets a good example in the gyro community.

The 700 hour lifespan was largely due to the Cranfield study (attached below).

View attachment Cranfield rotorsportuk_report_v2_compressed.pdf

I've no doubt that some RS1 blades (with a gyro history of gentle handling) could exceed that, while other machines roughly treated wouldn't make the 700 hours.

Regarding RS2 blades I presume that they're an improvement over the RS1, but I've heard of none having yet reached their declared service life of 2500 hours.
I'd be surprised if the RS2 could last that long. The blade design is still essentially the same as RS1: to my knowledge, the root section is still hollow, and the doubler I doubt sufficiently compensates.
My skepticism is based on the fact that any company which had the crack-prone RS1 should be scrutinized on their subsequent blade designs.
The engineering reports used by the CAA to approve the RS2 do not seem to be available online, and neither does the university study claiming a 2500 hour service life.



CAA 29247000202.pdf.png


Finally, what concerns me is that the hassle of inspecting the six bolt holes per blade will dissuade many owners from doing so, especially more often than 100 hours.

I've previously read of AutoGyro defenders quoting the strength of the blade material vs. 3.5g at max gross weight, and while those simplistic numbers would seem to betoken a safety margin, the Cransfield study of RS1 makes the important point that fatigue cracking could occur well within normal flight loads, and very early on:


It is unlikely that the stresses measured fully reflect the extremes of loading placed on the failed blades, as a maximum stress of 179MPa has been recorded. This is insufficient to cause plasticity and permanently bend the blade. The 6005 alloy has a specified minimum proof strength of 240MPa, possibly the blade strength level is greater still, and stresses larger than this will be required to cause plastic deformation.

Nevertheless, the recorded fatigue cyclic stresses [within normal flying and inside material proof strength] are sufficient to cause very early crack initiation in fretting. Data developed in Cranfield fatigue laboratories suggest that only a few hundred cycles of stresses of this range would be necessary to create a fatigue crack in aluminium alloys under fretting conditions. (my emboldened emphasis)


Regards,
Kolibri
 

Kolibri

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My hypothesis is that the pilot's helmet came off,
That's possible, Vance, and the debris field seems to support the early loss of helmet.

However, if the blade/tail strike occurred first, then the sudden and massive imbalance could have shaken off a helmet which was not fastened (or fastened too loosely).
Regarding the helmet's interior parts found separately, such could have come out during its free fall.
I've seen helmets with very lightly attached components (usually from worn out Velcro) which dropped out from merely setting it down on a table.


__________
. . . went into the propeller and then hit the rotor.
In my opinion either the rotor damage from the helmet
I just gave it another read, and apart from the debris field map, the helmet was not mentioned at all. (Open the pdf and search for "Helm".)
I think such helmet damage would have been observed and remarked on, especially from a severe impact.


Regarding the propeller, here is what the report stated:

Am Dreiblattpropeller war ein Propellerblatt am Blattgriff abgerissen. Der abgerissene Teil war entlang der Halbschalenverklebung in Ober- und Unterschale zerbrochen und lag ca. 80 m vom Hauptwrack entfernt. Ein zweites Propellerblatt war geknickt und steckte bis zum Blattgriff im Erdreich an der Unfallstelle. Das dritte Propellerblatt war nahezu unbeschädigt.
Of the three-bladed propeller, one blade was torn off at the mount. The torn off part had broken along the half-shell [glue] bond and lay about 80m from the main wreckage.
A second prop blade was found at at the accident scene, bent and stuck up to the mount in the soil.
The third prop blade was virtually unscathed.

________
I have found that a properly fastened seat belt generally keeps the body with the wreckage.

Reading about the seat-belt, it apparently had not been fastened. It showed no overload stress or failure.
It seems that the 110 hour gyro pilot was sloppy that day.


or pilot control inputs because of the distraction of the departing helmet put the rotor into the tail.
That certainly could have been the case; a credible scenario.

However, in my opinion that still leaves the issue of either an already compromised blade (at the outboard bolt hole), or a design so weak that it cannot withstand a tail strike.


Thanks for contributing some good ideas.

Regards,
Kolibri
 

Kolibri

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Here are some GoogleMap photos with my interpretation.
First, an overview of his apparent flight path.


D-M-DOZ - Freiburg Airport, Gutach, Gütenbach.png.jpg

Here is looking WNW:

D-MDOZ looking 290 toward Gütenbach.png

Here is a view to the WSW showing an estimated altitude with approximate Gütenbach line of sight, and the debris field.
The Gütenbach witness reported first hearing the blade impact sounds, which from his 5000+ feet distance would have occurred several seconds earlier. Yet he still managed to see a portion of the fall before losing sight of it (behind terrain). That means the gyro was at significant AGL, and not ridge running. Since an earlier witness in the valley saw the gyro in a steep climb, I wanted to understand how high above he was to the crash site.

The debris field was rather long; some 513 yards, and the pilot's body was farther still. This indicates the gyro's ample forward motion at time of tail strike,
perhaps cruise speed. This incident was likely not attributable to rotor decay/flap following a steep climb with low ground speed.


D-MDOZ looking 160 - 500 AGL approach.png
D-MDOZ looking 160 - 750 AGL approach.png
D-MDOZ looking 160 - 1000 AGL approach.png

Looking due south, the debris field and my translated nomenclature in order of direction of debris travel:

D-MDOZ wreckage overview pointed south in direction of travel.png



I've been thinking about Vance's departing helmet theory. The snag I see is that the helmet was found near the
main wreckage, near the end of the debris trail, not at the beginning. The helmet inner part (purple circle) was farthest away.
If the pilot lost his helmet before the blade/tail strike, it seems that the helmet wouldn't have fallen so far south.

I'm thinking that the lighter elements of book pages and presumably helmet foam liner (purple and gray circles) fluttered,
and thus landed behind the heavier parts. I don't quite see the helmet having caused (directly or indirectly) the tail strike
since it landed near the gyro and past the tail parts. To me, this suggests that the blade/tail strike occurred before anything
to do with the helmet.

Regards,
Kolibri
 

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Philbennett

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Good morning. I get confused with the motivations to some of these posts vis a vis what on earth is / was the mindset that leads one to an old German accident report?

Never the less whilst i have have absolute confidence in our own UK AAIB, French BEA or German Bfu there is no doubt when they investigate these sporting aviation accidents they seldom come to definitive conclusion because the aircraft do not have systems that can be interrogated after the fact.

However regards AutoGyro product. Im not their PR but i think this particular accident (unless there is something to be learnt from translating the entire German text) from the info you've highlighted - I can't draw a link between this accident and a wider blade problem.

if nothing else in EU countires we dont see blades failing with any frequency and aircraft falling from the sky.

The Cranfield study is further support to my view because it doesnt really highlight issue with the blades as much as it does the method of securing them to the hub bar. If you see RS1 v RS2 rotors then youll see the hub bar evolution.
 

Kolibri

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Never the less whilst i have have absolute confidence in our own UK AAIB, French BEA or German Bfu there is no doubt when they investigate these sporting aviation accidents they seldom come to definitive conclusion because the aircraft do not have systems that can be interrogated after the fact.
Good morning, Phil.
If you mean Cockpit Voice Recorders and the like, I'm not sure how much help such would have been in this crash.

In my opinion, national aviation safety boards rarely go in much depth to analyze possible material failures in gyro crashes.

A notable exception was the
5 August 2016 takeoff crash in Greenland of an ELA 07, tail number OY-1027.
It was theorized that the nosewheel fork broke during the T/O roll, and the Danish report was remarkably thorough, including electron microscope material analysis.

ELA 07 OY-1027.png
In my layman's opinion, the rotor blade stub remains of D-MDOZ should have been similarly analyzed.
Such could have determined if the blade had been working and tearing at the bolt hole before striking the tail.



The Cranfield study is further support to my view because it doesnt really highlight issue with the blades as much as it does the method of securing them to the hub bar.
If you see RS1 v RS2 rotors then youll see the hub bar evolution.
Phil, I've handled both hub bars and understand the design change.
However, the hollow extruded 6005 blades were not much changed in RS2, so I've not that faith in them that AG owners have.
What supports my skepticism are the number of broken RS2 blades from mere taxi tip-overs at less than flight rotor rpm.
Also, AutoGyro GmbH themselves continue to require owners to check for bolt hole cracks and linearity, while prudent, suggests to me a lack of engineering confidence.

On this point, I believe the 2011 Service Bulletin issued by RotorSport UK Ltd regarding RS1 to be either naive or disingenuous:


SB No.: 040 issue 1
Problem description & cause of problem if known

A recent comprehensive study on the flight loading conditions of the rotor system used on both Calidus and the MT-series
has shown that, whilst the [RS1] rotor system is safe and robust, the system can be significantly improved.
A complete new rotor system [RS2] has now been developed and approved by CAA.

No crack-prone rotor blade deemed nonairworthy by 700 hours is safe or robust to my reckoning.
I think that the gyro market (and perhaps also your own CAA) gave AutoGyro a virtual "hall pass" on the RS2. Time will tell.


if nothing else in EU countires we dont see blades failing with any frequency and aircraft falling from the sky.
Had their weakness not been discovered in time, the same could have been said in 2008 before many RS1 rotor blades would have consequently failed in flight.

I can't draw a link between this accident and a wider blade problem.
Really? You've no qualms flying a gyro which has rotor blades incapable of withstanding a tail strike?
Especially a tail so flimsy as on AG machines?


AG tail separation-1.png
AG tail separation-2.png
Auto-Gyro MTOsport D-MFWA  - 5.png


I get confused with the motivations to some of these posts vis a vis what on earth is / was the mindset that leads one to an old German accident report?
Why, Phil, I thought it obvious: to possibly save your neck.

Regards,
Kolibri




21 APRIL REPLY TO PHIL _________________


but aside from a view that suggests blades should be able to survive a tailstrike i dont see any other real evidence that these things arent suitable.
I think that alone should be enough to warrant real skepticism, especially since their first rotor system would have failed in flight had the issue not been caught when it was.
The RS2 seems an improvement, but I distrust it as a credible 2500 hour component.



but that just seems to be the natural focal point of stress
I mulled over that aspect myself; i.e., if an AutoGyro blade were to break, where would it likely break but there?
But just because it would break there does not justify that it does break there (and in comparatively mild incidents).

Without metallurgical analysis, it cannot be known for certain if fatigue failure was present.
However, that is meanwhile moot as no 333 hours blade should have snapped off like that, even after striking fiberglass or carbon tail pieces.

Ease of manufacture, financial economy, and weight reduction seem the hallmarks of the RS1 and RS2, not strength. They break off fairly commonly.
I don't even fly those machines, yet that concerns me.

The data and studies supporting the longevity of the RS2 are not readily available, so I doubt that AG owners have read such themselves.
Have you, Phil?
Meaning, their faith on the 2500 hour service life claim is based on generic CAA approval and marketing prose.
I question the prudence that the same CAA which approved the crack-prone/unsafe RS1 is subsequently given full faith about RS2.

My strong suggestion for AG owners is to not handle their gyros roughly, to be gentle with their blades (hangaring, taxiing, flying), and to inspect them more often than every 100 hours.
If anybody discovers an RS1-like crack in their RS2, please publicly inform the gyro community as well as AutoGyro.



Without real evidence [on] what basis do you go to a national authority?

The family of the deceased pilot could have the blade root analyzed by a private firm.
Any results pointing to material fatigue would be then sent to the BfU for a reevaluation of the case.

Rotor flap or not, blade strike or not: your blades should be strong enough to remain attached to the hub bar.
This is not an impossible engineering feat to achieve, and at a reasonable cost. I fly such blades every week.
It saddens me that such is not the norm for everyone else. I just want all our machines to be robust and safe.

Regards,
Kolibri
 

Philbennett

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Well of course one appreciates the concern for my neck but aside from a view that suggests blades should be able to survive a tailstrike i dont see any other real evidence that these things arent suitable.

yes the german accident aircraft displays similar failure point to the blades in Cranfield study but that just seems to be the natural focal point of stress.

Without real evidence one what basis do you go to a national authority?
 

Kolibri

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but aside from a view that suggests blades should be able to survive a tailstrike i dont see any other real evidence that these things arent suitable.
I think that alone should be enough to warrant real skepticism, especially since their first rotor system would have failed in flight had the issue not been caught when it was.
The RS2 seems an improvement, but I distrust it as a credible 2500 hour component.



but that just seems to be the natural focal point of stress
I mulled over that aspect myself; i.e., if an AutoGyro blade were to break, where would it likely break but there?
But just because it would break there does not justify that it does break there in comparatively mild incidents.

Without metallurgical analysis, it cannot be known for certain if fatigue failure was present.
However, that is meanwhile moot as no 333 hours blade should have snapped off like that, even after striking fiberglass or carbon tail pieces.

Ease of manufacture, financial economy, and weight reduction seem the hallmarks of the RS1 and RS2, not strength. They break off fairly commonly.
I don't even fly those machines, yet that concerns me.

The data and studies supporting the longevity of the RS2 are not readily available, so I doubt that AG owners have read such themselves. Have you, Phil?
Meaning, their faith on the 2500 hour service life claim is based on generic CAA approval and marketing prose.
I question the prudence that the same CAA which approved the crack-prone/unsafe RS1 is subsequently given full faith about RS2.

My strong suggestion for AG owners is to not handle their gyros roughly, to be gentle with their blades (hangaring, taxiing, flying), and to inspect them more often than every 100 hours.
If anybody discovers an RS1-like crack in their RS2, please publicly inform the gyro community as well as AutoGyro.



Without real evidence [on] what basis do you go to a national authority?

The family of the deceased pilot could have the blade root analyzed by a private firm.
Any results pointing to material fatigue would be then sent to the BfU for a reevaluation of the case.

Rotor flap or not, blade strike or not: your blades should be strong enough to remain attached to the hub bar.
This is not an impossible engineering feat to achieve, and at a reasonable cost. I fly such blades every week.
It saddens me that such is not the norm for everyone else. I just want all our machines to be robust and safe.

Regards,
Kolibri
 

Philbennett

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Kolibri - im not sure why but your reply to me is out of sequence, no matter.

ok ultimately you have now descended into a personal view based on nothing scientific just conjecture.

have you taken your concerns to the UK CAA? Have you raised them with the FAA who seem to accept RS2 in much the same way? Have you done some analysis on the blades of these many rolled aircraft where the failure mode is equally concerning?

i suspect the answer to all the above is no. Therefore this concern for peoples neck can also be mis interpreted as fear mongering .

I think i am right in saying that the German aircraft was crashed in 2016. In the next 3 years i know of no in flight blade failures. I do not think it un reasonable to suspect that if there were real issues that wouldn't be the case.

with respect to you i dont think you do yourself any favours peddling such (what increasingly seems like) nonsense. That isnt putting a head in the sand its merely asking you to give some facts. I mean why should a blade survive a tail strike? Dont you really need to give a load factor it must withstand??
 

Brent Drake

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Iv'e heard amny times, that extruded blades are subject to fail. There is no way of inspecting the interior of the blade as it's being made. Cracks won't be found until catostraphic.
 

WaspAir

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Philbennett;n1143879 said:
. I mean why should a blade survive a tail strike? Dont you really need to give a load factor it must withstand??
Quite right.
They are called "blades" because of their long narrow thin shape, not because they are meant to cut through anything, and the strength necessary for safety of flight is that required to support lift-borne loads, not endure solid impacts. One needs an airfoil that can move easily through air and unavoidable airborne contaminants such as dust / water / bugs / etc., but not something to mow your lawn, prune tree branches, or chop off major components of the airframe while remaining intact. Competent pilots in competently designed and constructed aircraft simply don't lob off their own tails, and if one is nonetheless concerned about surviving such an event, maybe investing in a parachute is prudent.
 

Kolibri

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im not sure why but your reply to me is out of sequence
Phil, it was a forum glitch which occasionally prevents new posts, so I meanwhile revised my previous reply.

a personal view based on nothing scientific just conjecture
The beginning of a scientific argument is conjecture.

have you taken your concerns to the UK CAA? Have you raised them with the FAA who seem to accept RS2 in much the same way?
Have you done some analysis on the blades of these many rolled aircraft where the failure mode is equally concerning?

i suspect the answer to all the above is no. Therefore this concern for peoples neck can also be mis interpreted as fear mongering .
A fallacious argument, Phil, especially at the outset of my discussion about this.

Besides, I've put more time into this than many AG owners combined.
How about one of those tip-over pilots send out their RS2 blade stub out to a metallurgical lab to determine if the part had been working at the outboard bolt hole?



I mean why should a blade survive a tail strike?
So that a mid-air tail strike is not inevitably a fatal crash.
The sine qua non of gyros is their autorotating rotor. It's supposed to be the "parachute".
As long as they remain intact, an uncontrolled descent may be survivable.

Compromise that with cheap and weak construction, and you've gutted the only inherent safety feature of the aircraft.


_______

and the strength necessary for safety of flight is that required to support lift-borne loads, not endure solid impacts.
So, WaspAir, rotor blades should not be expected to withstand even a bird strike?

The designers of turbofan blades have a minimum standard they adhere to, and even test with dead geese.
Yes, within limits, they are meant to "
endure solid impacts".

I find it interesting that it's axiomatic with some here that a gyro rotor may be permitted to detach if it strikes a glued together flimsy vertical stab.



Competent pilots in competently designed and constructed aircraft simply don't lob off their own tails
Then, who was the incompetent party of this crash?
The moderately experienced gyro tour owner/operator pilot flying over a familiar route in non-turbulent air?

Or the market leader which didn't know how to design a quality rotor system the first time -- affecting hundreds of gyros -- and may not have done so their second time?


________
Finally, my hypothesis here is not generic rotor flap/then tail strike, but, rather, that the blade was already failing which caused the flap.
The BfU photo of the blade stub shows apparent crystallization of the aluminum.

It would be encouraging if even one AG owner replied something to the effect of:


Well, Kolibri, while I don't think you've conclusively proven your point, you have given me enough to warrant more caution. I've also wondered why our blades often break off in mere ground incidents. Maybe you're on to something. I'll start checking my RS2 blades for bolt hole cracks more often than AG's schedule of 100 hours. A case of beer for you if I ever find one.

Regards,
Kolibri
 

loftus

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Kolibri, your points are well taken. Nevertheless it's important to put things in perspective. Autogyro has sold more than 2500 aircraft - more than any other manufacturer of gyros, and actually more than many aircraft manufacturers even in the FW world.
Even if this were a case of blade failure - and it is only speculation on your part - it's really a stretch to insinuate that Autogyro rotor components - particularly in their present form, are a cause for concern for in flight failure particularly if manufacturer service bulletins are followed. The data considering the number of flight hours flown, simply do not support it, irrespective of what happens to th blades on impact with the ground.
 

Kolibri

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Hi loftus, thanks.

it's really a stretch to insinuate that Autogyro rotor components - particularly in their present form, are a cause for concern for in flight failure particularly if manufacturer service bulletins are followed.
Hmmmm, I don't know if you meant it in such a slippery way. :)
I.e., if SBs are followed, crack propagation will be found in time before in flight failure.
(One arguably could have claimed the same with the cracking RS1 blades.)

Well, lol, that's not what I meant, as such is still an untenable scenario.
Gyro rotor blades shouldn't crack at their mounting holes. RS1 did, and it's prudent to view RS2 as "guilty until proven innocent".



The data considering the number of flight hours flown, simply do not support it, irrespective of what happens to th blades on impact with the ground.
It's a large fleet out there, and x machines times 50-600 [email protected] won't indicate presence of any impending fatigue failures which may manifest at 700+ hours.

I'd concede your point if there were hundreds -- or even dozens -- of RS2 bladed machines with 1000+ or 1500+ hours of crack-free service.
However, I doubt there's even a single example of one reaching their vaunted 2500 hours.
That figure is a projection, and, in my opinion, a suspect one (with its very high, yet nicely rounded, number).

Regards,
Kolibri
 

loftus

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You may or may not be correct that these blades may not reach 2500 hours, there are probably not many known examples for any gyro reaching that number - considering that at an average of 100 hours per year, that's 25 years. My understanding of manufacturers providing a lifespan on any component is related to the fact that the component has been bench tested to that number of hours, similar to a TBO provided by Rotax. Autogyro being a manufacturer of certified aircraft is probably bound legally to provide guidelines like these whereas others are not. Personally if I were a betting man I'd guess that Magni blades would last longer than MTO blades, but I'm not sure what the upper limit on Magni blades has been shown to be. Nevertheless I'd be comfortable flying either. This is similar to the expiry date on medications - usually does not mean that that the medication will not work after the expiry date, but only that the manufacturer has tested the medications and can vouch for their efficacy for a certain period of time only.
Certified aircraft manufacturers are generally required to provide lifetime limits on major components, particularly as any components are found to fail over time. Robinson for example require almost total rebuilds at 3000 hours I believe, I'd be interested to know if there are maximum blade times provided by other manufacturers, or can they guarantee their blades will last forever? Interestingly I myself had someone crash into my MTO on the ground at a fly-in a few years ago - I believe they were Dominator blades. My one blade was bent slightly about a third the way down due to multiple strikes from the spinning blade, the other blades were truly like a pretzel afterwards. I really don't think that would allow me to make any adverse comments about Dominator blades vs MTO blades, neither would it make me uncomfortable to fly either. Clearly they can both fail (they both needed replacement), but they failed quite differently, arguably the Dominator much more dramatically.
It's also quite likely, again due to number of aircraft out there, that there are more Autogyro aircraft with more hours on their blades, than most other manufacturers, except possibly Magni can document.
 

Kolibri

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My understanding of manufacturers providing a lifespan on any component is related to the fact that the component has been bench tested to that number of hours, similar to a TBO provided by Rotax. Autogyro being a manufacturer of certified aircraft is probably bound legally to provide guidelines like these whereas others are not.
loftus, I've not read anything to indicate that AutoGyro actually tested their RS2 under simulated flight loads for 2500 hours (i.e., 15 weeks continuous).
All that I and others have heard of is a vague reference to a curiously unavailable "university study". (Lives depend on the data; why not publicize the document?)

____________
Here's a human medical analogy which may help illustrate the nature of my concern.

The most common bone fracture is a distal radius fracture, or Colles' fracture, often suffered when trying to stop a fall with outstretched arm.
That the arm bone breaks there from a heavy fall does not mean that the bone is inherently weak. Excessive stress is concentrated on it, and it breaks.
A strong and healthy person will not suffer a Colles' fracture from anything but an extreme fall.

However, if the bone typically breaks during much less severe events, it may point to a personal issue such as osteoporosis.
(Example: "Mr. Glass" from the movie Unbreakable.)

There are rotor blades which have been on the market for over a decade which not only do not break off from from <flight rrpm taxi tip-overs,
but they stay intact at 300+ rrpm ground impacts. These same blades are used well past 2000 hours ("on condition"), and some have 4000+ hours.
They do not develop bolt hole cracks along the way. In my opinion, all gyro rotor blades should provide such robust service.

However, instead of Sport Rotors being the standard, some/many gyro owners act as if tip-over breaking RS2 blades are an acceptable standard
(which implicitly implies that Sport Rotors are somehow outside the norm as freaks, and thus irrelevant).

To me, this is akin to the osteoporosis crowd claiming that their bone breakages betoken no health challenges.

Back to AutoGyro. To recap:

1) AutoGyro is not a deeply experienced gyro kit manufacturer. They began by making copies of an ELA (which was essentially a copy of a Magni).
To my knowledge, the owner is not an engineer, nor even a gyro pilot with a lifetime of gyro fabrication history and gyro piloting.

2) Even though they have received type certifications, their Rotor System 1 was a bad design -- manifesting inexcusable engineering ignorance --
which would have soon enough killed people with mid-air blade separations.

3) Their Rotor System 2, while a likely improvement of RS1, has a claimed service life of 2500 hours, apparently on the basis of a university study
of questionable objectivity since it was commissioned by AutoGyro themselves.

4) RS2 blades have often shown to break off at the outboard bolt hole from much lower rotor rpm than flight speeds.
They shouldn't break off like that. Other rotor blades do not.

5) Considering the above, logical prudence indicates the very often and careful inspection of these blades.


_______
As Thelma counseled Louise in the movie: "
You get what you settle for."

Regards,
Kolibri
 

WaspAir

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stopped caring at 1000
Loftus, here's one example. Blades on the Standard Airworthiness A&S18A are "on condition", meaning no specific life limit so long as they continue to pass inspection, which could be a very, very long time if the aircraft is properly stored and cared for. I don't expect to be replacing any in my lifetime. In certified aircraft, it is not uncommon for a conservative initial life limit to be set, and then extended as the fleet gains experience (the J-2 was initially set at 300 hours for rudder cables and 1200, if memory serves, for blades, but unfortunately, the company went under before fleet experience could have shown that higher limits were appropriate and there was nobody left with the data to press for the extension). Helicopter blades with 5000 hour limits are not uncommon. My Bell 47 has different limits for the tail rotor and main rotor blades.

Last I heard, the Robinson cycle for factory rebuild was 2200 hours, extended from 2000. I suppose it could have been extended again since I last noticed.

Some life limits run by the calendar as well, as in "12 years or 2000 hours, whichever comes first", which I have also encountered on TBO for engines for fixed wing twins.
 
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