NTSB Prelim. Report on Ortmayer Accident

[gyropilot]

NTSB Identification: MIA04LA058
14 CFR Part 91: General Aviation
Accident occurred Friday, March 12, 2004 in Bunnell, FL
Aircraft: Ortmayer/Parson none, registration: N69EP
Injuries: 1 Fatal, 1 Minor.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed.

On March 12, 2004, about 1830 eastern standard time, an experimental Ortmayer/Parson Gyro craft, N69EP, operated by a private individual as a Title 14 CFR Part 91 local instructional flight, had a separation of a main rotor blade during a high speed taxi at the Flagler County Airport, Bunnell, Florida. Visual meteorological conditions prevailed. No flight plan was filed. The airplane was substantially damaged. The commercial-rated/certified flight instructor (CFI) pilot reported serious injuries. The non-rated student pilot received fatal injuries.

While practicing high-speed taxi and when the speed increased, a bolt broke in the main rotor blade, and the blade separated from the hub. The blade struck the student pilot. The bolt will be examined at the NTSB Materials Laboratory, Washington, D.C. The aircraft's owner had obtained an exemption from the FAA to use the aircraft for instruction.

[automan1223]

How long does a NTSB report take ?

considering they have to do lab work now ?

Jonathan

[gyropilot]

Jonathan,

Next will come a "fact" report, which is the complete accident report submitted by the NTSB investigator. Sometime after that a "final" ruling will be posted once the NTSB decides the cause of the accident after reviewing the accident report.

From what I've seen in the past on these type of accidents, the "fact" report takes anywhere from weeks to several months. Considering lab testing is involved, I'm sure we're looking at least 2 or 3 months before we see anything new. But you never know what can happen when an energetic NTSB inspector is involved!

The "final" ruling can take a couple of months to be made after the "fact" report is submitted... assuming the report isn't lost in the NTSB bureaucracy.

Regards,

John L.

[Doug Riley]

IF they do any lab work. The bolt may have been weakened or defective, but there's likely to be some other "first cause." I don't believe NTSB knows enough about gyros to investigate whether the rotor bolt broke as a result of flapping the rotor into the tail/prop. Without investigation by some knowledgeable gyro people, we cannot expect to get to the bottom of this.

[ahancock]

I agree with you Doug, one would think that the preliminary report would at least say what bolt, (teter bolt, spindle bolt or something)
Someone with gyro experience is needed although the NTSB will probably not pay much attention to anyone who is not employed by NTSB.

[Aussie_Paul]

Guys, after rolling Raf blades into the ground, more than once unfortunately, and having seen other Raf blades that have hit the dirt and or tarmac at flight rpm, I have never seen that 1" bolt bend at all. Those bolts and the pitch adjustment mechanism are usually still perfectly operational.

The blades fail, as most rotor blades do, a few inches out from the straps.

I could not see anything that could be done to affect the integrity of that "bloody" big bolt.

Aussie Paul.

[ahancock]

Does anyone know for sure what bolt failed?

[automan1223]

Bolt failure
I spoke with an engineer who is associated with RAF. He claims they ran the numbers again and the BIG BOLT is rated for something like 54,000 lbs for millions of cycles. It is very overrated according to him. BUT and big but here if the bolt is left in an untorqued state, loose or allowed to flex for whatever reason then the numbers come down dramatically and things become educated guess's.

Again this is only speculation and he was throwing so much info at me between the different grades specs etc its hard to know what happened to the bolt. He claimed they have never had a bolt fail and they do know that this was a very old set of blades.

I can tell you first hand Ortmayer never removed or inspected the blades the whole week I trained with him back in 8/01 I can also tell you I observed an uncomfortable amount of rust on the entire rotor system. But since that was so long ago I do not know if he did any maintaince since.

Of course a picture is worth many words and I guess we will wait for the final report.

[Louis]

I don't understand how the rotor was not flung away. Did it bounce? I am not doubting that it happened, but I cannot visualize it.

[Bill Clem]

I have been told by a Florida source that the separated blade was flung several hundred feet away. It was the still attached blade that did all the damage.

And as long as I'm posting, the NTSB does ask for help. I wrote the accident report for a friend's crash, complete with the background, site findings and post-crash analysis. The NTSB investigator reworked it with NTSB language and submitted it as the final report. Good investigators know when to ask for help. But frequently they are just too busy to try and find the fatal flaw when the result was only one death in a unique aircraft. And don't forget that they are tasked to investigate train, ship and other commercial carrier accidents as well.

[KenSandyEggo]

Notice the "new" Kenny J? No ranting, or yelling or major personal opinions? Who's just trying to stay with the facts? I even stopped all my medications. When you refused to ship anymore hidden in the Twinkies and Ding-Dongs, I found this guy in Tijuana who runs an apricot juice enema clinic. He calls himself "Dr.," but I don't think he really was. He got them from a groom at the Caliente Racetrack, who got them from a vet that worked there only during the middle of the night. They were powerful and upset my stomach, and I started to grow hair on the soles of my feet, so I just decided to go cold turkey. Later. :D

[Louis]

I think that makes more sense; the flung blade radically unbalanced/destabilized the machine, it rolled and the remaining blade swung wildly (enough to hit the crew) or hit the ground and broke up (ricocheting and hitting the crew)?

[barnstorm2]

Hey Ken,

I'll take your left over twinkies and meds.. ;)

[Harry_S.]

You are somethin' K.J. Love it!!

[gyroplanes]

I read all of the early Robinson R-22 accidents and the ones involving blade to tail strikes frequently had the remaining blade come down and sweep away the left side of the cockpit, often including the left skid.
Since we like pictures I thought I'd throw this one in. It was a simple low hover, instructor inattention and student drifting to side and lowering collective. Dynamic rollover. This was a very low time R-22 Mariner (floats off on this day)

[Harry_S.]

Good info, Tom.

Thank you.

[gyroplanes]

I friend down in Florida sent me these photos of the rotor retention bolt that broke on Bill's gyro.

I saw some pictures that were going around earlier but the quality wasn't good enough to be usable.

This is all I have. No gyro pictures.

[gyroplanes]

Here is the picture of the bolt head.

[automan1223]

Tom,

Thanks for the photos, the quality is very good.

I have NEVER EVER seen anything like that in my whole automotive / gyro / marine / etc. career.

I have seen studs on exhaust manifolds break right under the nut. I am guessing that it is a similiar situation but without the high heat from exhaust manifold/expansion/contraction, also left loose when the gasket material goes away......

But to pull the head right off like that freaks me out. I cannot imagine even if the bolt was left loose how or what kind of strain could pull the head right off. The bolt does not look like it got blue or heated. It is curious how the edge of the bolt has some cruddy looking stuff, then looks like it is sawn thru like with the worlds smallest hacksawblade. You can see the grain thru most of the bolt and then you see what appears to be the final bit of tearout on the opposite side.

Was this a grade 5, 8, nas, or regular aviation bolt again ?


Thanks again

Jonathan

[Aussie_Paul]

The bolts used by Raf are 1" aviation bolts. It is surprising how the fractures have started some time earlier. I have access to a number of these bolts that have been involved in Raf rollovers so I will get a couple and cut through the section under the head.

[Mike Hook]

I have seen a lot of grade 8 bolts that have fractured in the mining equipment area and from the looks of this one is has had some stress fractures that have been there for some time. the cross sectional area of the remaining bolt just finially failed. What could have caused the initial stress is unknow to me but it was either in manufacturing or in the bolts history it has been subjected to something beyond it limits or just a combination of both. This is just one that may never be solved. If a anyalis of the bolt may be done to see it the metal was correctly manufactured then you may follow the history of the bolt back to when it was manufactured and maybe have other bolts out there also with defect.This is most important to others using the bolt.

I know everyone hates to commit on these accidents but this is a safety issue.


Mike

[Mike Hook]

Paul
After rereading all of this thread,

Guys, after rolling Raf blades into the ground, more than once unfortunately, and having seen other Raf blades that have hit the dirt and or tarmac at flight rpm, I have never seen that 1" bolt bend at all. Those bolts and the pitch adjustment mechanism are usually still perfectly operational.


Maybe we may have to rethink about the integity of these bolts after any incident. One strike and your out ( no pun intended) , just to visually inspect a bolt that is a life safety issue after any incident may not be good enough.
I dont have the answer but I am sure some of the experts do.

Just a thought and I know there will be more comment on the subject.

[automan1223]

My only theory or theories are

1. structrual defect from the factory,

2. Failure to torque the bolt. I flew in this machine for a week and they were not at all smooth. Who knows if this had a direct or indirect effect on the failure.

3. Florida is humid. It is concieveable to me that some corrosion could have pitted or erodded the area under the head over time and caused stress to build up and pop.

4. I would have expected the hub bar to fail way before the bolt but I am not an engineer or technically rated to offer any hard analysis.

Last thoughts. While everyone here knows I was displeased with Bill and had a bit to say about my experience with him. In no way should that be considered that I have an ax to grind with him. It is tragic that people got hurt and in no way would I want that to happen to anyone over money or even sour grapes as some might think.


I got a phone call from the widow and I did my best to reason with her and to cool down the speculation, because while I had concerns about the machine I never thought someone would get killed like this.


This is a good if not great lesson for everyone. Inspect your equipment. Know what to look for. Time wears on all parts. Never ever think you can get away with something, fix it before you regret it. Just when you think all is good, murphy throws you a surprise.

[KenSandyEggo]

Could someone post a photo or explanation as to exactly where this bolt was located on the gyro? I'm not quite placing it as to where it is. Thanks.

[quadrirotor]

KEN, what i understand is that this unique bolt (if this one...) could be subject to fatigue:

-may be an initial crack under the head of the bolt, on a blade strike (but not obligatory---> hydrogen contamination under stress? corrosion?), with a some kind of ovalisation of the hole on the hub.
-then concentration of stress on this very point and fatigue on cyclic sollicitation due to lead-lag effort...
-then a question of time and sollicitation...

a metallurgical expertise could confirm a fatigue initiation by observing the zone with some microscopic pics and craters just before the tensile zone failure (which is wavy but more smooth) ... so beware and check your bolts...

[Hognose]

"I am not a metallurgist but own and have read books on metallurgy"

Looks to me like the bolt had pre-existing fatigue cracks (the parts of the shear that look dirty) for some time, and then failed owing to fatigue. It looks like the initial fatigue cracks were jagged enough to create stress risers in the remaining material. But professional metallurgists will be able to tell NTSB if that is the case. You would be surprised what bent and broken metal can tell these guys.

I think that visual inspection in situ would not have revealed the problem with this bolt. Removal and magnafluxing or dye penetrant inspection would have done. But that isn't part of anybody's periodic maintenance programme that I am aware of.

Maybe we need to think about that sort of inspection of certain flight-critical parts. Or preventive replacement of those parts on a maintenance schedule (which might take into account flight conditions, climate, etc). What do you guys think?

As bad as this accident was, it could have been worse. Had the bolt let go at twenty feet or more of altitude, there would probably have been two killed. Small consolation to the widow, I am sure.

The sky is not our natural element. It just feels that way sometimes.

cheers

-=K=-

[MGman]

Following on Kevin's suggestion, it would seem that there would be a "typical" maintenance program for Gyros that should be used to insure safe flying. The program might well include periodic replacement of certain bolts or components that are subject to wear or continual stress. Does anyone have such a list and/or how do people check critical components, except for pre/post flight checks and visual inspection? I understand most non-experimental aircraft have periodic inspections performed by certified mechanics (Icould be wrong here - as a novice, please correct me if I have this wrong). Are gyros required to have such an inspection, or are they exempt by being "experimental", and just left to the owner's discretion.

I am not a pilot (yet), but am a mechanical engineer, and have been a maintenance manager for medical/hospital facilities for over 30 years. I have always had in place a written (and inspected) program for preventive maintenance, and daily/periodic inspection, repair and replacement of critical components of certain equipment to make sure we repaired or replaced any critical parts well before they could fail on their own. It would seem that the same would be even more critical for Gyros, since your life depends on everything working correctly while flying.

Thanks - Dave Bohler

[Aussie_Paul]

As you all know I have no "real paper qualifications" other than my pilot certificates.

I have concerns where an important bolt is used in tension, unless suitably redundant.

I prefer them in shear.

With the Bensen and the old Rotor Hawk blades, the pitch adjustment used 4, 3/8" bolts in tension and 4, 3/5" in shear. I accidentally took off with only the top 2 bolts, that are in tension, torqued. As I lifted off the rotorshake was quite strong and I suddenly realised that I had not torqued the 2 bolts under the pitch adjustment mechanism!!!!!

I was past the point of landing and had to fly a very gentle low,10', circuit to get back into the wing and land. I don't believe I breathed during that circuit. The not even finger tight nuts has gone and one of the bolts was able to slide out.

What this means is that I flew with only the top 2 bolts holding, and that allowed the blade to cone up extra. I now know that the blade did find its own coning amount.

Sheez, owning up to that. Gee, I hate being human!!!!!!! LOL

Bills Raf blades on his tandem would have had qhite a solid stick and or airframe shake. The trouble is that we can get used to something like that and maybe not even realise that it is getting worse.

Aussie Paul.

[KenSandyEggo]

I'm getting close. Is it the big, fat bolt that runs longitudinally with the blade that basically holds the 2 parts of the hub-bar together....if I'm recalling correctly. I don't have an RAF hub-bar anymore to see.

[mceagle]

A fatal accident in Oz may put some light on the subject. It concerned the failure of the two AN4 bolts that hold the cross bar to the torque tube on the rotor head. A spring mount was bolted under the two nuts and the bolts were facing downwards. The spring mount extended back a further 8” to gain extra leverage because of the heavier than usual spring tension required for these blades. This spring applied considerable tension to the bolts. The blades apparently had a vibration problem that the pilot could not eliminate, and supplied considerable feedback through the stick. This constant movement caused the torque tube to distort requiring re-tensioning of the bolts. At the time of the accident, the torque tube was further distorted and the heads had popped off both bolts, causing complete dislodging of one of the bolts and half dislodging of the other. The missing bolt and one bolt head was located back along the flight path and the other bolt head was never found. At the time of impact, the cross bar had swung around on the remaining bolt and was lying against the universal block, making control impossible. On re-assembly, it was evident that the bolt heads were up against the torque tube at a slight angle causing a bending moment under the head of the bolt. This, combined with the high spring tension and the shaking of the rotors, was enough to fatigue the bolts at the weakest point close to the head and cause failure. The fatigue fractures looked very close to those in the above photo.
I did several tensile tests on identical AN4 bolts and there was no way that I could break the heads off the bolts. They either stripped the threads from the nut or from the bolt (or both). I came to the conclusion that it must have been local fatigue that caused the failure.
Back to Bill’s bolt failure. 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.

[Hognose]

[QUOTE=KenSandyEggo]

Is it the big, fat bolt that runs longitudinally with the blade

[QUOTE]

Exactimundo.

In responce to Dave Bohler, who asked about inspections, all experimental aircraft must have an annual condition inspection. But there are few specific guidelines as to what that entails, and the wide variety of experimental gyroplanes precludes a one-fits-all checklist.

However, I believe that kit vendors do generally provide suggested inspection protocols. And they do listen to their customers, and watch accident investigations closely.


cheers

-=k=-

[quadrirotor]

Can we use a RAF rotor with other than a very flexible mast??? :confused:

[Aussie_Paul]

I wouldn't.

Aussie Paul.

[MGman]

Thanks Kevin - I should have realized the manufacturers should have maintenance recommendations.

Dave

[GyroRon]

I just don' like the idea of the blades being held together with one bolt the way the RAF blades are done. I also had rotorhawk blades just like Paul was talking about, and I didn't like that either.

[KenSandyEggo]

"However, I believe that kit vendors do generally provide suggested inspection protocols. And they do listen to their customers, and watch accident investigations closely."

Excuse me, Kevin, but...........BWAAAAHAAAAAHAAAAAHAAAAA!!

I think you should have added "some." :rolleyes:

[mceagle]

Chuck,
Is there any way that the strength requirement for such a bolt can be calculated? I realise that there is no such thing in a gyro as "under normal operating conditions" but I suppose we would have to be looking at the worst possible scenerio.

[C. Beaty]

The specified tensile strength of a 3/4" AN bolt is 43,494 lb, Tim, certainly adequate for retaining RAF blades.

In tension, a bolt will always fail by shearing of threads or breaking at the minor diameter. But I'm told by people who have more experience with such things than I that it's not unusual to pull the valve cover on an automobile engine and find the head of a cylinder head bolt lying on top of the cylinder head surface. Fatigue failure no doubt but still puzzling why the head fails rather than the minor diameter.

The head of a bolt is formed by an upsetting operation; the blank is gripped in dies and a projecting end is squashed down, exactly the same as forming the head on a nail. The metal normally flows evenly without folds or creases. All forming operations with the exception of thread rolling are completed prior to heat treatment.

There is a radius between head and shank that must be protected by use of the prescribed AN washer which has an ID slightly larger than the bolt shank diameter.

Where there is no redundancy and life hangs from a single bolt, its integrity should be verified by Magnefluxing or some other equally reliable means. Probably the best way of verifying integrity is x-ray inspection using a radioactive cobalt source.

I don't know any of the details surrounding Bill Ortmeyer's accident so anything I say from now on is conjecture.

I'm told the blade that separated was flung several hundred feet and the one that remained attached flailed around, took off the prop tips and mauled the occupants. It's hard to imagine the rotor was running near flight rpm; had it been, the unbalance would have ripped off the rotorhead at the very least.

Why would the bolt fail at some speed lower than flight rpm (centrifugal force increases as the square of rpm)? Perhaps there was blade flap and the rotor tagged the runway, completing a process that had been in the making for some time.

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.

Rigid mast machines such as Parsons trainers invariably ride like jackhammers from violent rotor shake. Perhaps the biggest surprise is that the bolt didn't break sooner.

With so many unknown variables, it is futile even to speculate on the life span of the retention bolt.

[raghu]

Why would the bolt fail at some speed lower than flight rpm (centrifugal force increases as the square of rpm)? Perhaps there was blade flap and the rotor tagged the runway, completing a process that had been in the making for some time.



Chuck,
I am by no means well versed in matters of fracture mechanics ( though my dad is, perhaps should have a chat with him) but the way I understand fatigue it is all a case of number of cycles, if enough damage has been accumalated then even a lower than usual load will tip the balance and cause failure- essentially the crack will grow till it reaches a critical length and then failure occurs. So I am not sure about the rotor having to tag the runway scenario.

The bolt photographs does quite clearly shows striations indicating fatigue failure.

Also, usually if bolts are used in tension and subject to cyclic loads then PRELOADING the BOLTS is strongly recommended. This will reduce the cyclic component of the load and greatly increase fatigue life. Was the bolt in question required to be preloaded?

[C. Beaty]

Below a certain stress level, Raghu, steel will have infinite fatigue life. Off the top of my head, the endurance limit for most alloy steels is ~50,000 psi. Probably the RAF rotor as used their machine with rubber flex mast operates below the endurance limit.

I don't know what value of torque RAF specifies for the retention bolt but expect they follow the published guidelines which ensure considerable preload.

The reason for my speculation about blade flap is that full flight rpm of a fixed pitch rotor can't be achieved until several seconds after liftoff. If a rotor flies at 340 rpm, it will break ground at 300 rpm or so. Simply an attempt to rationalize why the rotor broke on the ground rather than in the air.

[automan1223]

During my daily work load there are 2 instances where bolt preload cannot be under estimated, and then check it a 3 & 4th time. My case in point. I had to replace an axle assy on my wifes 93 Jeep Cheorkee. The the wheel is attached to the hub with 5 studs that are pressed thru the back of the axle hub. I did the usual, torque to specs, drive the car, get the brakes hot, recheck / retorque the bolt load and you are done. Big surprise yesterday I was installing new tires on the vehicle and the axle was replaced over new years time. I went to zip off the lug nuts with my impact gun and to my surprise the lug nuts came off of that wheel with half the effort that the other ones did. I had checked the torque when it was new at least 2 maybe 3 times. Over so many heat and drive cycles the assy must have seasoned itself and loose nuts were the result. Thankfully there was no damage or noticable trouble but the fact that the nuts were considerabllylose from where they were previously it really startled me.

The second important thing was with trailer hitches. anytime you install a trailer ball check it 2-3 4 times until it seats itself in on the hitch bar, and also the attaching hardware on the hitch to the frame.

Jonathan

[Hognose]

\BWAAAAHAAAAAHAAAAAHAAAAA!!

I think you should have added "some." :rolleyes:

Hey buddy.

I said they watched accident investigations closely -- some of them to learn, and some of them to steer their mechanisms of denial!

It has been very beneficial to me to learn from your experience over the years. Not to mention less costly than experience of my own would have been.

cheers

-=K=-

[Hognose]

Below a certain stress level, Raghu, steel will have infinite fatigue life. Off the top of my head, the endurance limit for most alloy steels is ~50,000 psi.

But of course, the endurance limit speaks to single loads in intact metal. Things like reversing or alternating loads (probably not a factor for this bolt, loaded in tension), corrosion & pitting (possibly a factor), surface finish, previous overloads (who knows?) can alter the properties of the metal.

Only microscopic examination of the bolt can tell for sure, but those photos sure look like there was a partial crack (actually a pair of cracks centred 180 degrees apart from one another around the circumference of the bolt) for some time in the bolt. The crack exemplifies a stress riser. (A "stress riser" is a something that alters the properties or a material to make it more vulnerable to stress. The little notch in a restaurant packet of ketchup is a deliberately built-in stress riser, which makes it easy for you to tear into the foil packet). The crack, if crack it is, in the rotor retention bolt could have been caused by overload or corrosion. A corrosion pit is often the launchpad for a fatigue crack. Microscopic examination can tell the tale: an overstressed bolt will have deformed (gone ductile) before failing, unless the onset of the overstress was extremely violent.

I'm pretty sure that Chuck knows this already, but nonferrous metals don't have this endurance-limit property -- which is one of the many good reasons we don't attach our rotors with aluminium bolts. Aluminium alloys fatigue more or less linearly with increasing stress loads (amplitudes) and cycles. The behaviour of irons and steels is linear until the endurance limit is passed.

cheers

-=K=-

[GyroRon]

Imagine how spooky it would be to take out that same bolt a few weeks ago and see a crack on either side!!! Too bad that very thing wasn't done.

One more weird thing I haven't seen anyone bite on yet - or maybe I missed it - Jonathan Weis who posts here as Automan 1223 was contacted by the widow of the student who died in this accident. She says that her husband was struck in the LEFT side of his head by the blade not the right side as you would imagine with the direction the blades turn in flight... Now I might be wrong since this was heresay at this point - maybe he was hit in the right side and Jonathan got bad info??? - But how could the blade hit him on the left when they should have hit him on the right?

[Aussie_Paul]

Ron you would be surprised where rotor blades go during an accident. I have seen a video of a guy landing very nose high and the rotors touched the groud at the back and the machine rolled to the left. Slowing the video down the blades go to all sorts of places that you would nopt think possible and back again.

Tim McEagle, may have that video. Tim I can convert it to digital if you had a spare copy.

Aussie Paul.

[automan1223]

To re verify what Ron A said, when he quoted me. The widow did contact me after finding my web page in google. Just go in and type Bill. O. gyro training or something close to it and my flight training page comes up close to the top. The widow did tell me that her husband suffered a fatal impact on the LEFT side of the helmet thru his head. I can only guess he looked right and the remaining blade came down and over. Other than that I can only guess it was a mistake on the report or something really unconventional happened.

Bolt question for Chuck. On race engines we use studs on hi po apps. Head bolts are traded for a studded block. I am guessing for the reason that a the threaded part of the fastener is stronger than the head of the bolt ? Yes ?

Would the Raf design benefit from a stud with 2 nuts on each end ?
or a material of titanium or grade 9 ? I know nothing is unbreakable but I would want the very best bolt available to increase my safety factor due to possible defects.

I was shopping last night in Lowes and looked in the hardware section of grade 8 bolts. All are made in the far east and look considerably cheaper than they should. I noted numerous visible defects in the overly shiny plated hardware. Grade 8 my foot.

Thats a sick joke.

Jonathan

[C. Beaty]

Ordinarily, Jonathan, one wouldn’t expect threaded shanks to be more fatigue resistant than the head junction but evidently it is because the threads are rolled on after heat treatment.

Thread rolling work hardens the surface, something akin to shot peening a crankshaft.

Cut threads would surely fail from fatigue before the head.

I expect RAF blade attachment bolts are fine as is on an RAF airframe. But I'd be reluctant to use an RAF rotor on a jackhammer gyro.

[automan1223]

So then why has everyone jumped on the stud bandwagon. I know companies like ARP put a lot of money and flash into their products. Personally I have never studded a block and I have run 200 hp NOS on warmed over chevy 350 engines with 2 bolt mains and never had a problem. I guess I am old school.

The only head bolts I see broken are on aluminum heads on higher mileage vehicles that were most likely running hot or low on coolant. They usually break at the ends of the cylinder heads, not in the middle. Again, heat and pressure, gasket failure, or lack of retorque has to be the deciding factor in these failures. The trend in most rebuilds now is to NOT reuse the head bolts as they strech to a limit and are used only once. Torque wrenches have given way to angle torque specs. I will admit I actually dont know why as I never had a problem with the old ways. Reinventing the wheel, etc.

Jonathan

[Plato]

I am the widow of Ashley Godeaux, who was the student pilot killed in the accident on March 12 in which Bill Ortmayer was the CFI. I can assure you that the wound to my husband's head was indeed on the left side of his skull.

Very shortly I will be selling the Dominator single-seat gyro Ashley was building from a kit. If anyone is interested in buying it, I will post info and pictures. He put a lot of extremely careful, conscientious work into (for example) torquing the bolts properly.

[Plato]

Jonathan suggested that I leave contact info for anyone who might want to contact me, so will do so. I am the widow of Ashley Godeaux, the student pilot killed in the gyro accident March 12 with Bill Ortmayer as pilot and CFI. My name is Ellen Wagner and my email is ewagner@unf.edu. If anyone wants to contact me, I'd be glad to talk--or you can certainly reach me on the forum. I am interested in understanding just how this terrible accident occurred, and would like to know if or how it could have been prevented. Needless to say, I miss my husband very much and think that any of you on the list, male or female, would not want to be in my shoes right now. It would be comforting to some degree to be instrumental in preventing another such tragic loss of life.

Thanks.
Ellen

[Hognose]

There is a radius between head and shank that must be protected by use of the prescribed AN washer which has an ID slightly larger than the bolt shank diameter.



Chuck and all,

I wonder if that washer was present in this installation. If it was not, that radius could have been damaged. A nick in there is all the stress riser that would be needed to lead to this mishap.

Another possibility to consider is this: what if, instead of being torqued up against the hub bar (and not having RAF rotors for comparison, I have no idea what the torque specs are), the bolt was a little loose. It would have pivoted about the axis of the bolt as it moved around from retreating side to advancing side. This would have left a lot of physical evidence, and so far there is no report of such evidence, but it's a possibility, I think. Chuck?

cheers

-=K=-

[Hognose]

Duh. Chuck already said:


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.



So disregard my last...

cheers

-=K=-

[Heron]

Ellen:
your post made my heart shrink to the size of a pea . . .
I know that words are just a little balm on this occasion but, have a good and warm hug and just brave this moment.
God bless and comfort you.
Heron

[Brennen]

Maybe there was some serious blade flapping that happened with these blades and that led up to the bolt head shearing off. Since this is a student pilot craft maybe it happened more than once. Maybe just a little crack appeared and then the rust started. That's just my guess.

[Hognose]

I thouight I had seen some metal failures that looked like that bolt head somewhere in rotor land and then it struck me -- Rotorway Exec secondary shafts. Here are two sites which discuss the metallurgy and the mechanics of these failures. Pay particular attention to the appearance of the sheared area, and to the table showing what happens to the strength of a piece of ferrous alloy that has been subjected to corrosion and fretting. Finally, the corrosion can cause the fretting so any rust on metal-to-metal mating surfaces on your machine is to be (1) prevented; (2) cured; or at least (3) watched like a hawk.

http://www.epi-eng.com/RW-BendFatigue.htm

http://www.flyapro.com/SSTheProblem.htm

Pay particular attention to Fig. 2 and Fig. 4 in the second link.

Do these or do these not resemble the bolt-head failure from the mishap aircraft (as posted earlier in this thread)? Other engineers, what say ye?

Disclaimer -- I am not a metallurgist, and I don't play one on TV (can you imagine a TV show about a metallurgist? Maybe when the public gets sick of lawyers).

cheers

-=K=-

[Doug Riley]

I'm sorry that we don't yet have more definite information that might ease Ellen's pain a little. When I lost my best gyro-flying friend in an ultralight sailplane crash some ten years ago, the need to know why-and-how burned for a very long time.

My guess (nothing more than that) about this accident is that on-ground flapping had to be involved. It's extremely unlikely that a rotor would happen to fail in pure tension on the ground at partial RPM when it had just been flying around at full RPM for some time. More likely it flapped, collided with something in the rear of the craft and consequently experienced an in-plane bending load that finished the job of cracking the bolt. 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.

It would be helpful to see the top of the head of the bolt, to see who made it. A bogus bolt might also be involved.

In blade strikes, it's not unusual for a blade to end up quite near the occupants on the left side, even though North American rotors usually turn counter-clockwise. I understood that Bill also received an injury to his left side. When I had a blade strike in my Dominator a few years ago, one blade bent enough that it sailed right by my (left side) throttle arm and hit that arm quite hard. I got a severe bruise, a nasty cut and permanent dent in my forearm muscle at that spot.

[CLS447]

Doug, What size prop are you using on your 912(s)? What pitch are you running? What is your full throttle RPM? What is the max RPM that Rotax recommends? What ratio is your redrive?

[rfonseca]

Dear Ellen,

I am sad for you and for the lost of your husband. I never met him but as a fellow gyro pilot I consider him part of some loose fraternity where we all, crazy gyro fans, belong. I hope that you will be able to recover.

[Rotorhead]

I don't like to think about to much, In my early years in rotorcraft during the training phase
We were testing a new prop and engine configuration when the pilot couldn’t generate enough
Rotor rpm at the point of no return, he tried to horse it into the air needless to say we didn’t fly for
Long as the aircraft listed to the left, I heard 4 distinct rotor strikes as the aircraft tumbled 4 or
5 times something struck me in the head and I actually saw the rotorblade slice thru the fiberglass
enclosure why it didn’t nail my feet, I can’t explain but in the end I had a compound break of my left wrist
primarily because the pilot fell on my elbow on one of the rolls in the side by side configuration each occupant
Should have there own restraint system otherwise this injury would have never have occurred as for head strike
Those of you using military helmets, they do not meet DOT regs biggest piece of the helmet was the size of
A quarter this was a most serious accident and the outcome could have been similar to this one .

Ellen Prayers

[Doug Riley]

Chris Spadafora, I'll reply to your questions about my gyro in the "Dominator" section of this forum.

[Ron Marlett]

[QUOTE=automan1223]So then why has everyone jumped on the stud bandwagon. I know companies like ARP put a lot of money and flash into their products. Personally I have never studded a block and I have run 200 hp NOS on warmed over chevy 350 engines with 2 bolt mains and never had a problem. I guess I am old school."


As I understand the use of studs over bolts in automotive applications, When you torque a headbolt you apply a lot of twisting force to the shank of the bolt in order to rotate the threads down in the block. This distorts the bolt and applies additional stresses to it, twisting stresses not encountered in normal operation. With studs, a great deal of the twisting forces that would be applied to the shaft are avoided during the torque process. This saves wear on the studs making them more reliable and reuseable. Since the torque errors resulting from bolt twist are removed from the equation, it makes the torque settings more precise also.

Ron

[lanichol]

[ A corrosion pit is often the launchpad for a fatigue crack. Microscopic examination can tell the tale: an overstressed bolt will have deformed (gone ductile) before failing, unless the onset of the overstress was extremely violent. ]

Some thoughts; I work with natural gas pipelines. The gas flowing through the pipeline sets up a current. Pipeline companies install ground beds so the corrosion will occur in the metal of the ground beds and not on the pipeline.

The whole goal in the pipeline industry is to prevent corrosion. If a pipeline is sealed from air or water, and no current, it will last a very long time. Most corrosion is external. If corrosion occurs it is often where you have two different materials as is the case for ground beds.

I know this is silly, but I saw in a movie where a guy getting transfer from a helicopter to a ship had to discharge the static electricity first. I would expect the amount of static electricity would depend on the contruction material in the blades (alum vs fiberglass).

I am not a corrosion engineer, but I can sure find a couple to get an opinion.

[automan1223]

You are not being silly. I have seen on many programs where a rescue chopper is hovering over the target and the jolt from static electricity can be stunning. Rescue divers, and others that are suspended on the cable talk about this every so often on tv programs.

It would be interesting to see if there was any way a rotor was generating and electric current and transfering it to / thru the airframe. You might be on to something. ECR occurs inside engine blocks with antifreeze. Damage to radiators, heater cores, hoses etc can be startling if electro galvanic action starts.

Jonathan