UH-60 with "bad" rotor blade

[SansAnhedral]

Official: Guard Helicopter Had Bad Rotor Blade (http://www.wltx.com/story/news/local/2014/12/04/official-guard-helicopter-had-bad-rotor-blade/19896949/)

http://www.gannett-cdn.com/-mm-/1c0052058ae80cd79cd249061d6e7d8b851a6016/c=107-0-644-404&r=x404&c=534x401/local/-/media/WLTX/WLTX/2014/12/04/635532997584344545-1495438-10202199706873557-3266696846301117291-n.jpg

Official: Guard Helicopter Had Bad Rotor Blade
2:26 p.m. EST December 4, 2014

Columbia, SC (WLTX) - The South Carolina National Guard says a Blackhawk helicopter will remain in a field off Interstate 77 for now after it had to make a precautionary landing.

The UH-60 Blackhawk had to land at the location, which is near the Cayce Water Treatment Facility, at 4:18 p.m. Wednesday after experiencing a main rotor blade malfunction. The chopper is assigned to the 1-111th General Aviation Support Battalion.

The guard says the helicopter will remain at the site until it's released by an Accident Investigation Board. Colonel James Barkley, the South Carolina State Aviation Officer, said this is the first time they've experienced an issue with the Blackhawk.

"The aircrew training and stringent standards resulted in an incredible job performed by these S.C. Army National Guard aviators. Their experience operating in a combat environment translates back to their aviation roles stateside," said Barkley. They performed in an exemplary and outstanding job. At the end of the day, they went home to their families unscathed."

"The successful emergency landing of our UH-60 Black Hawk speaks to the professionalism and skill of the aircrews in the S.C. Army National Guard," said Maj. Gen. Robert Livingston, the adjutant general for South Carolina.

The guard is determining their options for moving the aircraft.

[Mechta]

Looks like a Staffie dog got at it. I guess he left the tip as it would have made him berp... :}

[SansAnhedral]

My theory is that this was a surreptitious attempt by Sikorsky at fielding their version of a BlueEdge blade into the fleet :E

[Nubian]

Must have been some pretty unbelievable vibrations! Amazing that they could make an emergency landing in that sort of state.

Great job!:ok:

[Ian Corrigible]

I guess he left the tip as it would have made him berp...

:ugh: :D

My theory is that this was a surreptitious attempt by Sikorsky at fielding their version of a BlueEdge blade into the fleet
Also deserves a :D. Either that or the famed helicopter shark (http://en.wikipedia.org/wiki/Helicopter_Shark) finally made a kill.

I/C

[crunchingnumbers]

Must have been some pretty unbelievable vibrations! Amazing that they could make an emergency landing in that sort of state.

A pilot I fly with who also supports that Battalion sent me the pics after it happened - unbelievable. At 6000' they entered an auto and contacted approach to declare an emergency. Approach told them to squawk but the vibration was so severe that they could not get hands on to the transponder and were being thrown around the cockpit.

Kudos to the crew for getting her down and hats off to Sikorsky for keeping it together.

Well done men.:D

[Matari]

Interesting views of the recovery here:DVIDS - Images - SC National Guard recovers helicopter [Image 24 of 29] (http://www.dvidshub.net/image/1690080/sc-national-guard-recovers-helicopter#.VIZanOktAqM)

Close up of the blade:

http://d2.static.dvidshub.net/media/thumbs/photos/1412/1690080/450x300_q95.jpg

[westhawk]

Wow! That's gotta be about as damaged as 60 blade can get and still fly. It's nice to be good and it's even better to be lucky too.

Brings up some fine memories of a blade change we had to do on an A model in a field in rural West Germany back in 1987. The middle of winter as I recall. While it was often possible to make a temporary repair with speed tape after the occasional tree trimming incident, field replacement of the blade was necessary if the damage was anything more that minor. No doubt about this one!

The lateral vibration caused by that much missing material must have been pretty severe. I wonder how many IPS that would have read on the old Vibrex. I'd be concerned about the condition of the rotor hub and transmission after that. I guess they will have considered all that before flying it out of there...

Heckuva good outcome. Pilots and Sikorsky engineers did well.

westhawk

[dangermouse]

well there IS an argument that some Sikorsky engineers didn't 'do well' as the blade fell apart!!, not so much for the rest of the aircraft.

The report on this one will be interesting, hopefully not a systemic MRB issue, probably quality control or an unreported incident some time in the past

congrats to the crew though, couldnt have been much lift off that blade.

DM

[Peter-RB]

Well it could be said the entire crew..Won the lottery, perhaps they should now try the next ticket sale.
That must be one hell of a strong Heli..! :D

[Boudreaux Bob]

Think about being at 6,000 feet when it happened and how long it took to land.

It seemed the older I got....the lower I flew for some unfathomable reason.:uhoh:

[JohnDixson]

On Aug 9, 1976 at about 2315 hrs, an Army evaluation crew* with a 101st Airborne squad/weapons aboard were flying low level at 145 KIAS when a similar looking blade cover problem took place.

* Boeing and SA both trained 10 operational pilots in their respective aircraft for the op eval at FT Campbell. They were chosen to represent the range of experience and rank within a unit. Serendipity stepped in here, and just a few moments prior to the event, one of the brand new aviators handed over the controls to one of the most experienced.

The cause of the cover peel was determined fairly quickly. There are three wraps of skin bonded on at either 30 or 45 degree angles ( can't recall ). At the outboard edge of the blade, the skins were cut straight along the chordwise edge. Evidence at that edge indicated that the bond was not perfect, air got into the open edge and an unpeeling proceeded. The fix was to eliminate the open edge of the skins by changing the design to provide for the upper skin to wrap around the others at this edge ( i.e., tuck it around and in ).

Looking into the history of this blade and inspecting it is no doubt job one in Stratford at the moment.

The reason I know the details as to this event was that shortly before midnight my phone rang and a few hours later a corporate aircraft departed for Ft Campbell with a small team of the UTTAS senior talent.

The young aviators doing the flying were faced with very very high 1P vibratory excitation ( remember, this was at low level BEFORE NVG ) and decided to slow it up and land. They did that and made a rather excellent vertical landing thru the FT Campbell pine trees, trimming quite a few**. There was one injury: upon landing the squad leader gave it a follow me order and stepped out, travelling about 1-2 feet before getting a bloody nose on a 5 inch pine tree the trunk of which tree was right outside the door.
** You could see how vertical the landing was by looking at a tree just beside the tail rotor. That tree showed damage from up high to a point even with the tail rotor as it was after landing. So the tail rotor just chipped away at this one tree trunk as they descended.

I have a few pictures but they are large and probably too big for this site. Send me a PM with your email and I will get them to you.

On Aug 10th we looked over the aircraft and finding it just needed blades, the Army brought in chainsaws, and cleared a bit larger LZ, so to speak. Put a new set of mains and tail paddles on, and the next morning an Army crew flew it out and back into the competition. BTW, the UTTAS came with a portable maintenance crane which hooked onto the side cabin floor and the Army troops assigned to maintain the ships for the eval got some realistic practice in changing out the blades.

[SansAnhedral]

Ah, the true story behind the "lumberhawk" incident.


Is it true that this exact airframe (73-21650) was the accident aircraft in the Stratford crash in 1978?

[JohnDixson]

It was either 650 or 651. 652 went to Ft Rucker as a flying trainer for the Aviation School Maintenance Dept. It probably was 650, now that I think of it, because it was best instrumented for structural/vibration work and that was what we were going to do with it. That day of that crash, it was to do a demo for a senior DOD visitor, after which it was to be ferried to the West Palm flight test facility.

[John Eacott]

Another view of the blade from this report: Army Times (http://www.armytimes.com/story/military/guard-reserve/2014/12/10/guard-pilot-blackhawk-crash/20160877/?sf34537477=%5B%271%27%5D)

http://www.gannett-cdn.com/-mm-/f38a9e39dabcdcb5b7c422e4ba9825f9b41bca89/c=204-0-3396-2400&r=x404&c=534x401/local/-/media/2014/12/09/GGM/MilitaryTimes/635537578713275128-ARM-Guard-pilots-rotor-fail-3.jpg

(I'll put up JohnDixson's photos of the old incident later)

[John Eacott]

JohnDixson's photos: I'll leave him to tell the stories that go with the event :cool:

http://www.eacott.com.au/gallery/d/7061-2/Leoni+Hi+Res_0009x.jpg

http://www.eacott.com.au/gallery/d/7064-2/Leoni+Hi+Res_0010x.jpg

http://www.eacott.com.au/gallery/d/7067-2/Leoni+Hi+Res_0011x.jpg

http://www.eacott.com.au/gallery/d/7070-2/Leoni+Hi+Res_0016x.jpg

[JohnDixson]

Thanks to John Eacott for sizing the pictures.

First picture is typical of the trees that were trimmed, and is also the culprit causing the only injury: the tree that the squad leader ran into egressing into the night.

Next shot is the portable maintenance crane being used to R/R the main blades. You can see the type trees that were hit by the blades during descent.

3rd shot is the ship as it looked in the morning after the landing. The greater amount of blade core that is missing on the South Carolina ship compared to this one is obvoius. I remember that the amount of core that was missing on this blade was 10-12 feet,and that was all out toward the tip cap. Hard to see that in this picture.

The last photo is the Army crew flying the ship out, after the young troopers with the chainsaws had done their work. Getting the machine back to the cornfield used by the 101st for the evaluation and ready for missions so quickly surprised a few people, but probably shouldn't have. The design spec requirements for that aircraft, in particular the basic structural standards, the crashworthy requirements and the ballistic survivability requirements blended to make a very tough machine.

[birrddog]

JohnDixon: Sounds like a story out of "Chicken Hawk"

[JohnDixson]

There is a connection, though slim:

( Chicken Hawk refers to a book by Robert Mason, a slick pilot in B/229 in the 1st Cav at An Khe in 65-66 )

The US Army Colonel running the Op Eval at Ft Campbell was Ron Perry, who was a Captain flying an ARA * UH-1B in the 1st Cav at the same time. Ron flew three tours in Vietnam, getting shot down seven times. Last one was during the LamSon 719 operation up in I Corps, and he spent a week walking out. He ran the UTTAS Op Eval pretty much like a real tactical operation. In fact, there is a story here:

* ARA. Aerial Rocket Artillery. UH-1B with a 6 x 4 tube 2.75 rocket pod on each side. With the larger warheads, each one was about the same as a 105mm wowitzer round in terms of effect. There were also flechette rounds.

After the blade peel landing, Army regulations required that the accident pilots get a checkride before return to flight duties. Army didn't yet own any IP's etc, so I got the task. Like I said, everything was being run like a war, so up we went in the other SA UTTAS at around midnight, the following night. The two pilots were just fine but that ship had way too much 4P vibration, and upon return, I wrote it up and went over the machine with a SA crewchief who was there to assist the 101st maintenance if needed. Not finding anything major using flashlights, I told them we would give it a good look in the morning. Col. Perry comes up and says " Are you grounding this aircraft? " I told him " No, but we just had one event and it seems prudent to make absolutely certain the other ship is 100%. He says: " OK, you grounded the aircraft ". We went round and round until I said something to the effect of " Fine, have it your way ". It ws 2 AM by then and I really didn't give a you know what.

Bright and early we went out to the cornfield and found that the nose absorber bushings were shot and started replacing them. Field phone rings and Bill Paul, SA Engr VP is on the line. I could hear Bill holding the phone 3 ft from my ear. Was he upset? The message I was listening to started out with " John, the name of the company is not The Dixson Aircraft Corporation, it is Sikorsky Aircraft...." and went downhill from there. Anyway, by the time he was finished talking the absorber was fixed and bottoned up and the ship was ready to fly.

Teaser: Ron Perry was running Cobra Hall ( AH-1 school )at Ft Stewart in 1971 when we took the S-67 around the USA on tour and was the second guy I rolled that machine with.

Ought to add that one might get the wrong impression from this short anecdote. Over many years following, I counted myself very lucky to be working for Bill Paul and working with Ron Perry. Still think that Ron Perry would have made a terrific General.

[Peter-RB]

Could this very sad looking r/b have been held together by the leading edge( is it all one piece) plus the Berp Plate, so that even though under extremis of Vibes it held it together long enough so the pilot could get down ?

[SansAnhedral]

Being an old pre-AWC blade (Sans anhedral :} or taper) , the main pickled titanium spar was left intact (doesn't even look that the BIM blanket was exposed or that they popped the schrader valve) and the leading edge sheath assembly (nose taco shell, heater blanket, and abrasion strip) looks to be fully intact as well.

Once the skin+core afterbody departed, theres really not much left to come apart, other than the sheath-spar bondline, which is sized pretty stoutly.

Had they flown for much longer I am quite sure they would have lost the Sikorsky (patented) removable blade tip assembly as those fasteners are already a fatigue issue.

[JohnDixson]

Peter, you made me " burp " with that one! The S-67 swept tip first flew in 1970, long before the BERP blade flew. The UTTAS tip was pretty much a copy of that idea, and applied to the UTTAS design for generally the same considerations, and also in consideration of a bit higher tip speed as well.

Sans, cannot concur with the assumption that had they flown much longer the tip assembly would have departed. That assembly stands on its own structurally and has been flight tested to 3.53 G and a free stream mach number of 1.0. Auto Nr to 125%. The structure was initially designed to be field replaceable ( rather than run a spar all the way to the tip as in the UH-1 ) as it was accepted that the Army tactical environment would inevitably lead to tree strikes. ( Subject of an intense internal trade-off during UTTAS design phase in-house ). Never say never in aviation discussions, but the background indicates the tip cap wasn't going anywhere in the immediate future.

[Lonewolf_50]

John, I am digging into memory and cannot remember if the aircraft remains controllable if the tip cap departs from one of the blades.
I am sure the balance is shot, and vibes would go up significantly. Would the blade go divergent in that case? (My brain thinks is would flap too much and hit something, but I don't recall why I think that.)
Has anyone had one leave in flight?
I should have some data points on this in my memory, but it's been enough years since I was operating that class of helicopter that it's been pushed out of long term memory by other less important details.

[JohnDixson]

LW, I cannot recall a specific design requirement spec there, but one assumes that making the tip cap replaceable due to expected tree strikes indicates an aero assessment of the impact upon rotor stability was made to support the design feature. In any case the loss of that outer 10-12 ft of blade at 145 KIAS at Ft Campbell answers the question, as that impact on blade pitching moment had to exceed the tip cap contribution.

Now that I think of it, there was one time during the pre fly-off testing when we found a longish crack in one tip cap skin, like 10-12 inches. Engr evaluated it and ok'd it for flight. I asked about the impact of the failure progressing to failure, they said not to worry, but in the end decided to replace it prior to flight anyway.* Torsional stiffness of the UTTAS Ti spar blades was higher than the previous Al spar machines. ( not the only factor of course, but an important one, in getting to the free stream Mach 1.0 point with not a hint of a rotor stability issue ).

*In reading how this sounds, it seems to indicate a rather snap decision making process. Actually we had a few serious discussions before proceeding.

[SansAnhedral]

With the missing afterbody, would you not expect in-plane chordwise oscillatory forces at the cap to increase dramatically?

With the TE wedge long gone, the skins are no longer contributing to a "torque box" at the attachment location for the cap.

I don't doubt in testing the cap would survive a plethora of overspeed and other conditions...but that is with, at worst, and intentionally placed flaw within the laminate on a fatigue test - not missing an entire afterbody!

[JohnDixson]

Sorry, Sans. When you refer to afterbody, what are you referring to?

[SansAnhedral]

Basically everything aft of the aft spar wall.

Upper skin, lower skin, core, and trailing edge wedge insert.

[JohnDixson]

I looked in vain for a drawing that shows how the tip cap is attached, but its pretty simple, thus easily replaced. Anyhow, in the two incidents to date, the tip cap has survived ( I think the Ft campbell tip cap had some tree dings ). The tip cap on the South Carolina Guard blade will get a thorough inspection, and that will answer your question. Be happy to post the findings. I am betting that the tip cap is good for much more than the max duration of fuel incl the outboard 230's if one has the ESSS.

[ring gear]

Rotor Blade Balancing - Rotor & Wing Aviation Services - Rotor Track - Static and Dynamic Balance (http://www.rwas.com.au/blade-balancing.html)

John, See the attached link for a pictorial view of the tip cap attachment screw holes and underlying span tip weights. It can be seen that the tip cap could be conceivably lost in a tree strike and the tip weights not be affected….another great design feature:)…. obviously a lateral would develop in such an incident but certainly remain quite flyable.

cheers
RG

[Peter-RB]

John,
My mistake, I thought the angled tip and the Berp were a universal sort of design with the Berp being a more modern piece of kit having seen it up close on the Speed record Lynx, but the question was answered in reading on through the next posts.
But still one hell of a strong helicopter to take that sort of breakdown/vibration and still recover from such height.

PB

[JohnDixson]

Peter, no apology necessary: I was just kidding anyway.

Ring Gear: thanks for the drawing link. The point you noted re the tip weight attachment being separate from the tip cap is important. The tip cap itself is extremely light. Might be kevlar now (?), but it started out as Al sheet and even that was really light. Point is that from a balance point of view, if the tip ( or tips, more likely ) get smashed on some tree limbs the resultant mass/aero imbalance won't be such as to create a more serious difficulty.

[Matari]

Different failure mode, I'm sure, but I can't help but think of this blade failure. You'll probably have to scroll down a bit to see the photo.
http://www.pprune.org/rotorheads/501843-r-22-rotor-separation-florida-photo-2.html

[Greg Mellema]

There are some wrong accounts here. To set the record straight, that blade and two others (similar events) were only about 200 hours out of CCAD and where the aft fairing skin meets the fwd skin over the spar, some bonehead took heat lamps and lined them up to cure EA 9309 epoxy as a "filler" used to fill & fair the gap at depot. The skin was badly discolored indicating they had exposed it to roughly 600degrees F. That all but destroyed the aft fairing skin-to-spar bond every 14 inches along most of the spar.

So, one good flex up put that skin in compression and a single portion of the skin popped loose. At that point, it's essentially a parachute and off she came. The U.S. Army sucks at repairing blades and composite structures. Both at the technician AND (especially) engineering level.

[blakmax]

Greg M

Do you have first hand knowledge of the use of 9309 as a "filler"? Was it used to fill dents or was it used as effectively an "injection" repair to repair disbonds?

I actually conduct courses on adhesive bond failure forensics and with better close up photos I could probably provide a more reasoned assessment. However, the different colour on the core at the outer end would make me suspect moisture ingress, and the absence of core separation towards the leading edge would make me suspect adhesion (interfacial) failure. The change in colour of tyhe leading edge bond is probably a transition from weak adhesion failure at the leading edge to mixed mode failure aft of the leading edge. Such failures are typical of hydration of the metal oxides on the leading edge due to hydration in service. This does not necessarily match with the overheat theory, but that could be verified by metallurgical analysis of the metal in the region.

I suggest you look at this file

I agree totally that the vast number of technical and engineering personnel in many organsations including OEMs do not have even a modest level of competency in management of heat distribution in complex structure during repair processes, especially using point source heating devices such as heat lamps. As a simple demonstration of this assertion, there is a common perception that because an arbitrarily located thermocouple reaches a designated set point temperature, then the repair has been adequately heated. Reality: move the sensor or change the location of the heat source, the result will be totally different.

Heat sources must be configured to match the individual structural heat sinks, the sensors must be located to measure the hottest point under each heat source to prevent overheat damage, but they also must be located where the anticipated COLDEST point will occur so that there is assurance of full adhesive cure.

Happy to accept PMs to discuss this further.

My name is on the attached document.

Regards

Blakmax