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.

" BERP Plate "
 

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.

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.

Tip Cap
 

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.

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!

Definition
 

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

Basically everything aft of the aft spar wall.

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

Tip
 

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.

Tip cap attachment
 

Rotor Blade Balancing - Rotor & Wing Aviation Services - Rotor Track - Static and Dynamic Balance

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

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

BERP
 

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.

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/501...a-photo-2.html

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.

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