US Koala crash

[flygunz]

Would appreciate any information on the recent Koala crash in the US. Initial reports suggest a tail rotor related incident.
Thanks.

[Heliport]

flygunz
This link may be what you're looking for ........ Tail rotor, gearbox fall off new Air-Rescue 1 (http://www.tcpalm.com/tcp/trib_local_news/article/0,1651,TCP_1107_1206283,00.html )

[flygunz]

Thanks for this, trying to get to the bottom of it all.

[Autorotate]

Talk to Careflight in Sydney, Australia as well. They had major problems with their tail rotor cracking and it got to the stage where they voluntarily grounded it until Agusta got their act together and sorted it out.

:confused:

[flygunz]

As of today, Agusta have issued a 5 hour inspection of the new tail rotor blades fitted to the A119. The crash in the US has been attributed to a T/R blade fracturing in flight. Having done a number of EOLs in the Koala I know the pilot did very well getting it down.

[Autorotate]

Doesnt surprise me. They released some new blades not that long ago and told Careflight and others that it would solve all the problems. Looks like that was shortlived. I sent them some emails asking a whole bunch of questions about the problem and surprise surprise, not one of them was answered.

[Lu Zuckerman]

NTSB Identification: MIA02TA109

Accident occurred Wednesday, June 12, 2002 at Okeechobee, FL
Aircraft:Agusta 119, registration: N911SL
Injuries: 3 Uninjured.

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 June 12, 2002 about 1615 eastern daylight time, an Agusta 119 helicopter, N911SL, registered to and operated by the St. Lucie County Sheriff's Office, impacted with the ground during a forced landing near Okeechobee, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 training flight. The helicopter was substantially damaged. The commercial-rated pilot, and two other occupants reported no injuries. The flight was originating from the Raulerson Hospital helo-pad, Okeechobee, Florida, at 1614, and was en route to Fort Pierce, Florida.

The helicopter's crew stated they were training and practicing landings at a hospital's landing facility. On takeoff from the hospital, at an altitude of about 250 feet, the pilot reported hearing a bang, and elected to autorotate into a field about 1/2 mile from the hospital. After touchdown the helicopter skidded several feet, and nosed down in the dirt, resulting in the main rotor making contact with the tailboom and subsequently separating the tailboom from the fuselage. Preliminary examination of the tailrotor 90-degree gearbox showed that the gearbox had failed.

:eek:

[flygunz]

Thanks Lu, thats more informative than the FAA initial report on their website. Agusta have isued a bulletin where they say quite clearly that the a tail rotor blade fractured in flight. This no doubt brought the gearbox of its mountings.
The 111 blade was supposed to fix the blade cracking problem and it will be interesting to see why the blade failed.

[Capn Notarious]

LU Shawn Nick and all of you other rotorheads.
How are T/R and M/R blades tested.
Does vertical forward motion of a T/R blade cause delamination faster that an M/R blade: given that air flow and lift are compressing the layers of Main Rotor blades in the vertical plane and that the chopping action of a T/R blade into the down wash of a Main Rotor blade meets an area of air which is condensed.Am I writing a load of rubbish and mentally out of depth. Be genorous to an English man, we lost a football match.
Question No TWO(0h crikey here he goes again) Do the blades of a fenestrated tail rotor, a la dauphin; last longer than blades not protected by a fuselage?

[CRAN]

The way blades are inspected depends on there construction. Thermographics is frequently used with glass fibre blades for inspection of laminate integrity. This method has recently been extended to carbon-fibre blades too. This method heats up the surface using a hot air blower and then use an IR camera to measure the emission of IR from the surface. Characteristic faults can be picked up in this manner. X-raying is also applied to blades of various materials. Carbon fibre composite blades are frequently inspected using ultrasonic’s. This is an ingenious process in which a scanner moves methodically over the blade surface and a ultrasonic transducer sends and receive ultrasonic signals to and from the blade via a jet of water (carrier). The returned signal is processed by some wizzy software and a permanent graphical record (+ hard data) of the blade is created by the post-processing software. Looks a bit like an MRI scan but more colourful!

There are a whole host of techniques applied to this critical role, that come under the heading non-destructive testing and/or non destructive inspection. Various manufacturers will select the techniques based on the particular needs of their specific applications. The three techniques that I have mentioned are techniques that I have seen used on production aircraft blades in service around the world today, but is by no means an exhaustive list.

With regards the operating environment of the TR, it certainly does operate in a much more unsteady regime than the MR does. In forward flight the main rotor wake is skewed backwards by the forwards velocity and engulfs the TR. The exact nature of the flow field cannot be accurately calculated (we have the techniques but computers are not powerful enough), therefore the true oscillating aero-loads that cause fatigue failures are difficult to predict. Composite materials can be designed to be very resilient to fatigue indeed, so something must have really caught Agusta by surprise.

As to whether TR blades will fail sooner than MR blades - you can't really answer that question from the general point of view because it depends heavily on the design. TR's are typically small and light so adding additional weight to the tail rotor in terms of more structural strength is quite insignificant in terms of the overall weight of the aircraft (assuming CG is OK). Therefore, TR could be designed to be relatively tougher - without significant weight penalty. However they do operate in a more uncertain aerodynamic environment - so its hard to predict the loads. Hence the design dependency.

Hope this helps
CRAN
:)

[widgeon]

My question is if the A119 is around the same MGW as the A109E , why would the TR be giving so much more of a problem ?.
The fuselage is the same except for the Landing gear and probably the engine cowlings , would that change the airflow around the TR to such a degree ?. Does the PW have a hotter exhaust than the Turbomecas ?.
On the Eurocopter side I believe the twin star and A star share the same TR .

[Lu Zuckerman]

The tests described by CRAN are mainly to verify the production integrity of the blades. When I first became involved with the production testing of blades at Sikorsky many moons ago these elaborate testing methods were not even conceived. The main tests to verify the production integrity of the blades was performed by striking the blades with a coin or a small hammer in the area of the pocket bond to the spar. This was performed to verify the integrity of the bond. To verify the design integrity, they would produce several sample blades that had an attachment at the tip of the spar and the entire blade was subjected to tension loads and then subjected to cyclical twisting and bending as well as sending a traveling wave down the blade from the tip to the root. This test would subject the blade sample to a lifetime of aerodynamic and aeromechanical abuse. The test also verified that the blade would meet its’ required life cycle with a safety margin of 50%. The tail rotor blades were tested in a similar manner.

Once the design was verified and the blades placed in production the only testing other than the tapping test was to mass balance the blade and then place it on a whirl stand where it was dynamically balanced against a master blade that had all of the desired flight characteristics. The tail rotors were mass balanced as a set and installed on the helicopter where it would be rigged for basic pitch. The verification test for the design integrity of the tail rotor blades did not always reflect the actual forces on the blades. A case in point was the tail rotor for the first S-58 helicopter. What the design and test engineers did not consider was the tendency for the blades to lead and lag when they flapped. This leading and lagging was constrained within the blade structure and the pivot bolts in the flapping hinge. The flapping bushings would wear and in some cases the blades would crack. Once this phenomenon was understood the blades were redesigned and the problem went away. Not to get anyone upset but the Robinson main rotor blades have a similar problem. The leading and lagging is restrained by the cone bushings and they eventually wear in an elliptical pattern and the leading and lagging is absorbed by the flexibility of the blades in a spanwise direction. Perhaps Agusta is overlooking something relative to the dynamics of the blade system and how the aerodynamic flow around the fuselage effects those dynamics. If you look at certain Hughes designs and Some Sikorsky designs this aerodynamic flow is controlled by the incorporation of the “Doghouse” on the upper fuselage.

:rolleyes:

[flygunz]

widgeon, the AUWs of the 109 and 119 are similar mainly because the basic structure is the same. The 109E has a MAUM of 130kg more than the 119 which isn't a lot when you consider its a twin v a single. The 119 is much stiffer and solid due to the high position of the P&W PT6b. Most of this stiffness is absorbed in the tail which in my humble opinion is where the problem may lie. Agusta produce helicopters that vibrate more than most I've flown, the 119 has vibration attenuaters behind the crew seats to absorb low freq vib but it is still very evident. Ever heard pilots talk about the Agusta rumble during transition?
The 109 had T/R blade cracking problems but I think the same blades on the 119 suffer a higher proportion of vib due to that vib being transmitted straight down the tail. It has to go somewhere.
Eventually, Agusta will beef up a T/R that is man enough for the job. Its only a theory but I dont think i'm far out here.

[Capn Notarious]

I know more now than I did earlier.
But does the weight of air against the edge open the blade bondings, or is it mostly the failure of adhesion.

[Shawn Coyle]

My two cents worth on the testing etc. of the blades.

To quote Ray Prouty- Anything that happens aft of the main rotor is magic - meaning that no-one really has it modeled mathematically or aerodynamically.
The A109E and A119 are different aerodynamic beasts behind the main rotor, and hence the airflow back to the tail rotor is going to be very different.
If you look at the fairings and cowlings around the transmissions and engines of any more than two bladed helicopter you will see a lot of different things that have been done to clean up the airflow. Some of these result in some pretty unusual airflow around the back of the machine, and these could be causing the problems on the A119.
I say could be, because no-one will really know for sure without a lot of testing and analysis. Aeromechanical stability for tail rotors is way beyond my ability to analyze - heck I can barely say the words.
This testing and analysis may have been done for certification, and then again, it may not have been done.
You can be sure that Agusta, like any other manufacturer is pretty interested in solving the problem. It just may not appear like it on the surface.
Hope this helps the discussions.
Shawn