ZU-DBV, ZU-RHO & RAF 2000 hub bar bolt torque Threads Merged

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ZU-DBV, ZU-RHO & RAF 2000 hub bar bolt torque Threads Merged

Postby DarkHelmet » Fri May 12, 2017 12:35 pm

Guys, on modding the forum...

The people that mod do not get paid for modding. Sometimes things slip through. All of us (you included) have hectic schedules and we cannot monitor 24/7

Please respect the decisions we make and trust that they are on behalf of the community as a whole.

If you have a problem with our actions take it up in private with the individual involve, please do not spin up new threads when something is deleted or locked. Find out what the rational was by contacting the mod.

We have always been open and honest and I know we are one of the least modded forums of any that I visit.

Also, this is in a thread that is not of interest to me so I do not know what is going on here.

I understand the thread that was deleted did contain some valid and valuable information and I apologise sincerely for its deletion. We can not mod every conversion and read through everything and selectively pick individual posts. We are putting steps in place to do that now.

Lastly, please nominate and vote for additional mods, especially for the specialized forums you follow.
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Re: RAF 2000 hub bar bolt torque over time

Postby John Boucher » Fri May 12, 2017 1:14 pm

Dave Lehr (aka Learjet) has been appointed and accepted as a MODERATOR .... welcome Dave
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Re: RAF 2000 hub bar bolt torque over time

Postby Kolibri » Fri May 12, 2017 9:29 pm

Howdy all,

I intend to stay strictly within the technical discussion of the matter, and hope others do the same.

Welcome Dave, as a new moderator.

Regards, Kolibri
RAF2000, with Boyer H-stab and Sport Copter upgrade (mast plates, rotorhead, hub bar, rotors, 4-way air-trim).
Am also a fixed-wing pilot and owner. I fly 200+ hours/year, mostly VFR x-country.
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Re: RAF 2000 hub bar bolt torque over time

Postby lion » Sat May 13, 2017 1:03 am

Welcome Dave, excellent that you are here! I have learnt a lot and some of the information is really interesting. I must say that the time and trouble that Kolibri (and others) have spent trying to educate us is appreciated. I expect that if some of his observations are considered incorrect, it would be incumbent on those that know better to set the record straight. It is a shame that some of Kolibri's previous posts where he provided technical information have been deleted.
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Re: ZU-DBV, ZU-RHO & RAF 2000 hub bar bolt torque Threads Me

Postby spinkaan » Mon May 15, 2017 9:22 am

Welcome Dave as mod on this site,glad to have you.
I am dissapointed that the previous moderators have removed the posts and threads on this accident as there were much to be learned.
Why not demand rafsa to respond directly?
Remember there are lives at stake!!!
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Re: ZU-DBV, ZU-RHO & RAF 2000 hub bar bolt torque Threads Me

Postby John Boucher » Mon May 15, 2017 9:51 am

Peter .... I think we have dealt with this matter (flogging a dead horse!)
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Re: ZU-DBV, ZU-RHO & RAF 2000 hub bar bolt torque Threads Me

Postby gyropilot » Mon May 15, 2017 10:05 am

guys it's all about SAFETY & PEOPLES LIVES!

I certainly would not want it on my conscious if I knowingly withheld or deleted vital information and another person got killed as a result!
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Re: ZU-DBV, ZU-RHO & RAF 2000 hub bar bolt torque Threads Me

Postby Kolibri » Tue May 16, 2017 2:57 am

OK, merged threads (thank you Mods), fine, back to the matter at hand.
Whatever technical stuff y'all want reposted, let me know.

The below photo is of the other RAF 2000 which popped a hub bar bolt head (AN-12) and threw a rotor (N69EP ORTMAYER).
ZU-RHO's bolt head has never been found, but it will look about like this.

N69EP failed during an instructional flight, and in a bizarre fluke the separated rotor whipped back and brained the student.
The CFI/owner had run the rotor set past the 500 hour RAF designated life span, to ~900 hours.
Nonetheless, why can't RAF/RAFSA make a hub bar without a tensile bolt under improper bending loads which will fail <1000 hours?
An aeronautical engineer commented about N69EP's RAF hub bar, calling it "a bad design, poorly executed."

______
Have any of you RAF 2000 owners taken up my suggestion of checking your hub bar bolt torques?
Please report back to this thread with your results.
Meanwhile, I urge you all to check your hub bar/winglets like a hawk, with a 10x loupe pre- and post-flight.
Also, don't fly too aggressively, as the RAF rotor system is not robust (to put it kindly).

Regards, Kolibri
Attachments
N69EP ORTMAYER bolt head.jpg
N69EP ORTMAYER bolt head.jpg (81.21 KiB) Viewed 265 times
RAF2000, with Boyer H-stab and Sport Copter upgrade (mast plates, rotorhead, hub bar, rotors, 4-way air-trim).
Am also a fixed-wing pilot and owner. I fly 200+ hours/year, mostly VFR x-country.
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Re: ZU-DBV, ZU-RHO & RAF 2000 hub bar bolt torque Threads Me

Postby Kolibri » Tue May 16, 2017 3:08 am

Below are my excerpts from the SACAA Accident Report on ZU-RHO.

http://www.caa.co.za/Accidents%20and%20 ... s/9462.pdf

I've not quoted the full report, but only the most relevant excerpts. Bold emphasis is mine.

Regards, Kolibri


Synopsis

During take off from Avontuur, The pilot reported that he felt a vibration and he was unable to control the aircraft. After climbing to a height of approximately 3.2m above ground level, the aircraft sank without warning and struck the ground, sustaining substantial damage. Both pilot and passenger suffered minor injuries.

It was determined during the investigation that the aircraft experienced a rotor hub bar assembly failure during take-off. The bolt installed between the rotor hub bar and winglet broke. Both rotor blades separated and were flung several metres to the left and right of the runway some distance from the main wreckage.

The rotor hub bar assembly was taken for metallurgical examination. The metallurgist’s report concluded that the bolt had broken due to fatigue and repeated exposure to reverse bending loads in the horizontal/lead-lag operational plane.

Probable Cause
Loss of control during take-off due to fatigue failure of the Hex head high-strength shear bolt.

Contributing factor: Improper maintenance due to the failure to replace old bolt with a new one.



1.5.2 Approved Person (AP)

1.5.2.1 AP no. 246 had maintained the aircraft over the previous two years (2014 and 2015), carrying out the annual and 25-hour maintenance inspections.

1.5.2.2 The AP received his accreditation from Recreation Aviation Administration of South Africa (RAASA) on 15 July 2015. According to his AP certificate, he fulfilled the technical approved person scheme requirements. The AP certificate was valid until 31 July 2017. He was approved to carry out maintenance on non-type certificated aircraft (NTCA) and was rated on the RAF 2000, Ela gyroplanes, Xenon and ZEN 1. The certificate was valid until 31 July 2017.

1.6 Rotor Assembly
1.6.6 The rotor hub bar assembly maintenance was inspected during the investigation. The logbook entry in the scheduled inspection record states that “the rotor winglet (blade) with s/n B.A.A.S 6006.2 and s/n B.A.A.S 6001.2 was replaced” on 23 July 2012. The reason for the replacement is not written down. Another entry dated 5 November 2013 was recorded as an “inspection for ATF” where the work performed was “done complete roll-over replacement as per manufacturer’s requirements”. The above winglets were exchanged with S/N B.A.A.S 6036.2 and S/N B.A.A.S 6038.2.

1.6.6.1 The owner/pilot stated that after the aircraft had been rebuilt by RAF and transported from Upington in the Northern Cape by road to Avontuur. The winglets were removed for the road trip and installed by the AP on arrival in Avontuur.

1.17 Organisational and Management Information

1.17.1 Owner/pilot and Approved Person:

1.17.1.1 The role of the owner/pilot was investigated. The evidence showed that he operated the aircraft privately (Part 24). He was responsible for the continued airworthiness of the aircraft and was required to ensure that it was operated safely. He was also required to ensure that it was maintained in accordance with applicable regulations. The logbooks show that he took the aircraft to RAFSA for maintenance in 2013. The aircraft had being involved in a roll-over accident and needed repairs. RAFSA completed these and the aircraft was returned to the owner/pilot. He appointed AP 246, who had the responsibility of continuing maintenance on the aircraft.

1.17.1.2 The role of the AP was investigated. It was deemed important to review his accreditation to carry out maintenance on the type, and RAFSA was requested to provide information in this regard. RAFSA stated that it was company policy to provide training in-house, and for this reason they had not issued training accreditation to any institution. In addition, they preferred gyroplane owners to bring their aircraft to Upington, where their facility was located, for maintenance. RAFSA records show that the last training was presented to the industry in 2014. RAFSA had no record of AP 246 attending any of their training sessions. RAFSA were unable to say where AP 246 had received the ratings authorising him to carry out maintenance on the aircraft. According to RAFSA, the only way the AP could have been issued with the rating was on the basis of an approval letter issued by the company. SACAA, Recreation Aviation Administration – South Africa (RAASA), Aeroclub and the South African Gyroplane Association (SAGPA), had been informed of this requirement. RAFSA had also written to the SACAA to make them aware of the fact that AP 246 had been servicing and certifying maintenance on RAFSA aircraft without having attended the required training.

1.17.1.3 For the purpose of the investigation, it was important to establish if AP 246 had been taught the technology of the gyroplane and trained to perform maintenance. In particular, it was important to know whether he had been trained on rotor balancing and approved to carry it out. RAFSA stated that they did not allow owners or APs to carry out any adjustments to the aircraft rotors, as they considered it a critical component that required special tools for adjustment. In order to carry out rotor balancing and tracking, sophisticated equipment was required, and this was only in RAFSA’s possession in Upington. This meant that if an AP were to carry out field maintenance of balancing himself, he would most likely have done so with unapproved special tools. In this case, if carried out incorrectly, the consequence could be that the vibration had lessened, but the actual problem would be worse, putting the aircraft and its occupants in danger.

1.17.1.4 The AP’s licence was obtained from RAASA. It indicated that he had fulfilled the requirements as set out by the technical approved person’s scheme and thereby approved to carry out inspections on the RAF 2000. Thus, he was formally authorised to carry out maintenance as per the licence conditions.


2.9 (i) S/n B.A.A.S 6038.2) was inspected visually to determine the cause of failure. It was found was that the bolt (p/n AN12-34A) installed between the hub bar and winglet had failed. The broken bolt was recovered and examined by a metallurgist to determine the cause of the failure.

(ii) According to the metallurgist’s report, the failure of the bolt was associated with fatigue fractures after exposure to reverse bending loads in the horizontal/lead-lag operational plane. The primary cause can be attributed to operational exposure or assembly/design issues, or both. More significantly, the metallurgist found that the washer installed at the bolt head end exceeded the dimensions of the slotted sections in the hub bar. This might have resulted in a false torque value during fitment of the bolt. Thus, when exposed to normal centrifugal loads during operation, this washer mechanically interacted with the hub bar, as seen by the resulting bending damages. This might have led to lowering the applied torque, with resultant movement of the hub bar/bolt assembly in the shear direction (horizontal/lead-lag) as well as the inducement of excessive forces on the fracture-prone bolt head radius.

(iii) The winglet S/N B.A.A.S 6036.2 was also inspected visually. It was found that its bolt (p/n AN12-34A) installed between the hub bar and winglet was still intact. However, this bolt revealed indications of fracture initiation that bore similarities with the bolt of winglet s/n B.A.A.S 6038.2.

2.11
While RAFSA was preparing to comply with the requirements, they continued supplying and giving support to gyroplane owners. It took them eight years – from 2007 until March 2015 – before the SACAA eventually found them to be compliant and issued them with a manufacturing/assembly approval.

2.14
The investigators spoke to AP 246 on several occasions during the investigation, questioning him about the maintenance activities certified by him in the aircraft logbooks. Due to the fact that the winglets separated from the aircraft, the investigation deemed it important that he should clarify certain issues about their installation. He admitted reinstalling the two rotor blades on the aircraft after they were removed by RAFSA, but apparently did not carry out any rotor balancing or tracking tests afterwards. The owner of the gyroplane confirmed that the AP had reinstalled the winglets. RAFSA emphasises that in order to carry out balancing and tracking, the AP needs special tools and testing equipment. The company does not allow any AP to carry out the tests themselves, as they are not trained for this nor have the required test equipment.

2.15
The above indicates why RAFSA issued Product Notice 51. However, the company singled out the winglets received from 1 April 2013. This does not make sense, considering that Rotary Air Force, Ref. W/Product Notice 39 refers to hub bar winglets and AN12 bolts dated 15 December 2004. The product notice indicates that another but similar incident occurred where the AN12 bolt suffered a catastrophic failure at the head. . . .

2.16
It is evident from the above that it is incumbent on RAFSA to use the date of 15 December 2004 instead of 1 April 2013. The reason is that the bolt failure problem remains unresolved: the new RAF NAS bolt, like the AN12 bolt, also failed due to fatigue, this time as a result of the washer combined with the stress loads acting on it. The product notice should have been a recall of all the rotor head hub bar assemblies worldwide to urgently inspect for damage and carry out non-destructive testing (NDT) examination for fatigue on each one. RAFSA should go back to the drawing board to revisit their design standard of the rotor hub bar winglets and bolts installation, specifications and limitations.


3. CONCLUSION
3.1 Findings

3.1.12 The NAS bolt that broke was recovered for further investigation by a metallurgist, who concluded that it had failed as a result of fatigue due to reverse bending loads in the horizontal/lead-lag operational plane.

3.1.13 The other NAS bolt was also examined by the metallurgist, who found that it had indications of fracture initiation similar to bolt No. 1.

3.1.15 The metallurgist’s report indicated that closer inspection of the NAS hex head, high-strength shear bolt, heat-treated washer and attachment bracket interface revealed extensive mechanical interaction at opposite positions.

3.1.16 Rotor hub bar assembly installations are carried out exclusively by the manufacturer, Rotary Air Force South Africa Pty Ltd (RAFSA). The industry is not authorised or approved to carry out the installation. If for any reason a defect is experienced with the rotor hub bar assembly, the gyroplane should be returned to RAFSA for the required repairs.

3.1.17 The gyroplane was involved in a roll-over accident in 2013 and all repairs were carried out by RAFSA. After the repairs were completed, the gyroplane was returned to the owner/pilot without rotor blades installed. These were later installed by AP 246.

3.1.18 AP 246 was responsible for carrying out maintenance on the gyroplane. There was no anomaly identified with the AP’s accreditation issued by RAASA and it had the gyroplane rating endorsed on it. This was despite the fact that he did not attend any of RAFSA’s prerequisite training.

3.1.19 The evidence was that the AP was also an owner/pilot of his own gyroplanes and familiar with RAFSA’s maintenance requirements and documentation. He performed all the maintenance on ZU-RHO.

3.2 Probable Cause/s
3.2.1 Loss of control during take-off due to fatigue failure of the Hex head high-strength shear bolt.

Contributory Factors
3.2.2 Improper maintenance due to the failure to replace old bolt with a new one.


4. SAFETY RECOMMENDATIONS
4.1 It is recommended that SACAA conduct similar research to that carried out by the University of Glasgow, on gyroplane aircraft registered in South Africa. Alternatively, it should adopt its research findings and conclusions.

4.2 It is recommended that the SACAA Certification Department assist RAFSA to correct the designs and manufacturing issues relating to the rotor hub bar bolts that caused it to fail. This intervention is required urgently, as all indications show that over last few years RAFSA has been unable to get it right themselves.


6. INVESTIGATION
6.1 The visual inspection revealed a fractured attachment bolt of the No 1 Main Rotor blade (Photo 3, red arrow).

The fracture surface showed clear indications towards fatigue as the primary failure mode (Photo 4) while the direction of fracture progression (red dashed arrows suggests exposures to bending loads in the horizontal/lead-lag plane of MR (Main Rotor) operation. This was affirmed by orientating the remainder of the No 1 bolt similar to the still attached No 2 bolt, assuming corresponding fitment techniques.


7. DISCUSSION AND CONCLUSIONS
The conclusions are based on the investigation results obtained from the supplied parts/components only. The following assumptions have references:

1. All parts supplied conforms to OEM specifications.
2. Applied torque values conforms to OEM specifications.
3. Aircraft was operated within OEM/Authority set limits.

7.1 The investigation results revealed fatigue to be the No 1 MR blade attachment bolt primary fracture mode while exposed to reverse bending loads in the horizontal/lead-lag MR operational plane.

7.2 The No 2 MR blade attachment bolt revealed comparitive indication of fracture intiation relative to position and orientation with bolt No 1.

7.2.2. Assembly/Design. The investigation results have shown that the washers (No1 and No 2) at both the bolt head ends dimensionally exceeds the slotted sections in the MR blade attachment brackets. During fitment this may render a "false" torque value. When exposed to normal centrifigual loads during operation, the washer mechanically interact with the MR blade attachment bracket with resulting bending damages noted. This may lead to lowering the applied torque with resultant movement of the bracket/bolt assembly in the shear direction (horizontal/lead-lag) as well as the inducement of excessive forces on the fracture prone bolt head radius.


8. RECOMMENDATIONS

8.1.2 Revisting the design of the MR blade attachment bracket.
Attachments
RAF2000  ZU-RHO.jpg
RAF2000, with Boyer H-stab and Sport Copter upgrade (mast plates, rotorhead, hub bar, rotors, 4-way air-trim).
Am also a fixed-wing pilot and owner. I fly 200+ hours/year, mostly VFR x-country.
Kolibri
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Re: ZU-DBV, ZU-RHO & RAF 2000 hub bar bolt torque Threads Me

Postby Kolibri » Sat May 20, 2017 1:37 am

N69EP Ortmayer used the RAF hub bar/winglets, and it failed on 12 March 2004.
(The still-attached rotor blade struck student Ashley Godeaux in the left side of his skull with a fatal blow.)
There were two contributing factors to the failure:

1) The Parsons trainer type of gyro has a rigid mast, and thus vibrated quite a lot.

2) The CFI/owner Bill Ortmayer was apparently rather lax on preventative maintenance, and allowed the bolts to remain in his machine for a total of 930 hours (430 hours of which were airtime). There was reportedly significant rust throughout his rotor system according to a previous student.

So, it was a mere AN (not NAS) bolt, not enjoying the smoother 2-part RAF mast and its rubber bushing, which was left installed for nearly twice the published 500 service life. The worst of all possible conditions.

Comparatively, a NAS bolt on an RAF 2000 which is replaced every 500 hours (along with the entire rotor system, as RAFSA insists in PN33) will probably serve the average owner well enough . . . provided that all goes right during those 500 hours.

The bolt failures of N69EP and ZU-RHO occurred when they did due to extraordinary (although different) circumstances. However, those circumstances merely accelerated the timing of failures. They did not cause the failures. The inherent design did. The ¾" bolt (regardless of AN or NAS spec) so improperly used in a such a dynamic joint must fail eventually. It's only a matter of time, and I suspect that it will occur far before the 2000+ hour service life of the gyro itself.

Now — and this is the point which is crucial for you all to understand — such guaranteed failure cannot likewise be said of a properly designed hub bar with multiple bolts used properly in shear. Those bolts are not subjected to the RAF's bending lead/lag loads, and the hub bar is not jointed. Steel has an infinite service life if never stressed beyond its fatique point.

RAFSA can bloviate all they wish about their NAS bolt's tensile strength, as if the only forces acting upon the bolt were centrifugal, and as if these hub bar bolts were pulled apart. This is like a defensive attorney claiming that his client must be innocent of murder because he's never been convicted of theft. The RAF hub bar is not on trial for tensile failure.

My RAF's hub bar had only 234 hours on it, and both NAS bolts had fracture initiation rings at the head/shank corner.
Could my bolts have lasted another 266 hours? Sure, theoretically, but I wasn't going to keep flying it to find out.

Here is its broken AN12-34A bolt shank, protruding through the separated winglet.
The bolt head suffered bending forces in the lead/lag horizontal plane, just as ZU-RHO did (shown in the CrashLAB photo).

Both bolt heads were pried off in the same direction, by the same forces.
Nobody else in the industry manufactures gyro hub bars of this vulnerable design.

The NTSB Material Laboratory Factual Report states the [N69EP] bolt that retains the hub bar wing to the hub bar was fractured in the radius between the shank and the head. Presence of fatigue arrest marks covering approximately 90 percent of the cross-sectional area. The fatigue cracks initiated from multiple origins all the way around the outer diameter surface at the bases of the radius with the head.
http://www.ntsb.gov/ntsb/brief.asp?ev_i ... 0373&key=1
I just reread the 2004 Rotary Wing Forum posts concerning N69EP. Commentators back then were beginning to question the RAF hub bar design, and several warned that any reduction of bolt torque would intensify the back-and-forth prying forces on the bolt head:
If the picture shows the bolt in its original location, then it would appear to have fatigued in the fore and aft positions. The only thing that surprised me about this accident is that it has not happened sooner. The single bolt under massive tensile loads and subject to large alternating bending moments every revolution, would surely be a recipe for disaster. I am not an engineer, - hopefully someone who is can do the sums and tell us what the safety margin is in such a blade mounting. Even so, I would suggest that the safety margin would diminish very quickly if the blades were not smooth.
I have seen a RAF show up after a reasonable flight and seen black powder coming from the join line at this point. This suggests movement under stress that was not evident by the tension of the bolt.
A possible reason for fatigue failure is that the bolt wasn't properly torqued down, permitting movement of the mating parts and causing severe shock and cleavage loads.
(Chuck Beaty)
The bending load on a single, centered bolt would produce a prying action that would be very effective at popping the head off if the bolt were the least bit loose.
The bolt could have started its life quite tightly torqued and still ended up loose. Without some fore-aft mast flexibility, the rotor would be experiencing two-per-rev in-plane bending loads. These loads pound away at the airframe, but the airframe of a big, heavy double-masted gyro does not readily get out of the way. As a result, much of load concentrates right in the rotor head and hub. This action could eventually cause the aluminum of the hub itself under the bolt head to squish out and away from the bolt, loosening the fit.
(Doug Riley)
The squished hub bar and resulting loosened fit is precisely what I've been warning the RAF owners about.
It was happening to my hub bar, and I didn't realize it until I'd removed/disassembled it for my Sport Copter upgrade.

How many of you have yet checked your NAS bolts for 180 ft/lbs of torque?
Confirmed that your hub bar and winglets are not deformed under the washers?
Please have a look, ASAP.


Regards, Kolibri
Attachments
N69EP ORTMAYER bolt shank.jpg
ZU=RHO CrashLAB photo 4.jpg
RAF hub bar bolt fracture initiation after only 234 hours.jpg
RAF2000, with Boyer H-stab and Sport Copter upgrade (mast plates, rotorhead, hub bar, rotors, 4-way air-trim).
Am also a fixed-wing pilot and owner. I fly 200+ hours/year, mostly VFR x-country.

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