Eurocopter 350/550 airframe problems!!!

[mickjoebill]

Exactly how is the FLIR attached?

In Europe I've seen AS350 brackets where considerable weight and force is born by the cabin fuselage.
ie
1/ A nose mount that attaches to the windscreen pillar.
2/ A purpose built mass stabilised camera rig (like steady cam) hanging from the sliding door runner.

Both camera mounts apparently approved by local authorities.


Mickjoebill

[regency]

350 ariframe problems

Sir, if you fly your aircraft a lot each month you need to put a balance machine on the aircraft once a month or 100 hours which ever comes first. The dampening quality of the aircraft will cause the aircraft to come apart with out the pilot ever feeling it. It is a great machine but you have to keep it in balance.

good luck

[wrench1]

Euro - have no fear on the cracks - very old news on the canopy with any AS350/355 that flies a lot or makes a high number of landings. Door posts, rain gutters, pitot tube mount, etc......

PHI and ERA came up with a number of repairs back in the day when these aircraft had a big presence in the GOM. A company, Mesh (?) Composites out of Lake Charles, LA, came out with a method of repairing the canopies that really worked back then
.
As for the vibration issues - I had an opportunity to sit in on a class given by the guru of vibrations at Aerospaitiale - George (?) - and his take was to balance the M/R, T/R, etc. on a regular basis and you could get 2000 hrs out of M/R P/C link bearings, etc., etc... However, it was a little difficult to weekly balance all these items sitting out at Vermillion 2 million!!! Don't get me wrong about George - he was brilliant when it came to balancing things - especially the infamous AS355 oil cooler blower!! And wrote a manual about it.

Just remember this about the AS350/355 canopy - it is just a bug shield. All the primary structure is behind you except for the two beams under the floor. Heck, I don't think it is even secondary structure, just that mysterious tertitary (?) structure??!?!!

Keep the blue side up.

W1

[farmpilot]

Which STC's are Eurocopter talking about? We fly with a Cineflex a lot and would be interested to know what their take on it is.

[widgeon]

Eurocopter concerned about safety of STCs: AINonline

Here is the article, EC's concern is that the STC holder may not have sufficent Technical information ( complete flight load spectrum etc.) to justify continued airworthiness of the equipment. Of course if they were a little less reticent about providing this information then everyones life would be easier.

[blakmax]

Enough bovine excrement

I tried to contact Eurocrapter off line but got no response. WAKE UP!
There are serious issues here that are not necessarily load related but may be driven by materials and process decisions by the OEM and have nothing to do with the way the items have been operated/loaded/abused. If any of the disbonds are occurring at the interface between the adherends, then this is a processing issue. If any of the disbonds are occurring through the adhesive, then this is a design issue.
IN EITHER CASE it is an OEM problem, NOT A USER CAUSED PROBLEM.
Inadequate processess (contamination, ineffective processes) produce failure at the interface; inadequate designs (inadequate overlap, thermal stresses, inadequate bond strength) produce failures through the adhesive material. These are all factors under the control of the OEM.
Eurocrapter, show me the photographs of the failures and I will provide at least an initial assessment of the probable cause.
It is time that OEMS and certification regulators are held to account for deficient bonding processes. Please read Deficiencies in Regulations for Certification and Continuing Airworthiness of Bonded Structure, at Adhesion Associates
Please understand that these concerns relate to the certification regulations for adhesive bonded structures and are NOT specific to any specific OEM.

It is actually possible to design bonded joints that will NEVER fail. But these designs rely on the use of processes that produce strong and durable bonds. For my initial guess, I will bet that EC used peel plies on their composite bonding surfaces and no other post peel ply removal surface preparation for their bonded joints. Peel plies are a sacrificial layer ripped off at the last moment to remove contamination prior to bonding to produce a "clean" surface for bonding. Peel plies must by necessity be easier to remove from the surface than the underlying composite plies. There are two broadly grouped methods for facilitating the removal of peel plies:
1 Use a release agent such as silicone or
2 Use a heat scoured system that glazes the fibres so they don't bond.
In both cases, the bond is deficient, see Hart-Smith, L.J., Redmond, G, Davis, M.J., The Curse of the Nylon Peel Ply, 41st. Int SAMPE Symp. and Exhib., Anaheim, 25-28 Mar 1996.
I may be wrong, but let anyone from EC refute my assessment. I'd be only to happy to back down and totally retract. If however I am right there may be serious legal implications that operators may wish to discuss further by contacting me off line.

To demonstrate the deficiencies in regulations, please review FAR 23.573 and ask why there is no equivalent for rotary wing aircraft. Then realise that even FAR 23.573 does not provide adequate assurance of bond integrity ANYWAY. Static strength and fatigue resistance are not assurances against interfacial failures, which are processing issues. Unless the FARs are amended to mandate testing to validate THE LONG TERM DURABILITY of composite and adhesive bonding processes, we will continue to see failure of bonded structures. Static strength and fatigue tests do not interogate resistance to interfacial degradation of adhesive bonds.

It is only be a matter of time before the lawyers drive the changes that should have been made years ago. I'd be only to happy to make a lot of money as an expert witness, but I'd rather work with regulators and OEMs to correct problems before the lawyers get involved.

[Heliarctic]

350

Hey Guy´s
that sounds like a lot of cracks right there.
The company that i work for owns 2-B2´s and 9-B3`s
They pull in between 400 and 600 hrs a year. two of them have less that 1000 hrs on them the hightimers 8000 hrs.I´ve only ever seen cracks 3 times in the years that i´ve worked with them, which is 7 years.
And they´ve been minor cracks.
The fleet does everything from heavy slingjobs to pax.transport.
I´ve been to Marignane and seen how they join the parts together, and just above the upper door fitting is where the upper and lower part of the canopy comes together, and it is paperthin. I´m actually amazed that there isn´t anymore cracks than usual.
Can´t really come with a guess, not knowing the type of ops.you do, but i feel your pain with OEM support which is sometimes non-existing!
Regards.

[RotaryRat]

I was thinking along the same lines as vaibronco, perhaps the environment your in may be having an adverse effect on the fleet - high humidity/high temperatures, operating in a coastal environment.. must not be good for composite materials with expansion/contraction and water ingress.

Just a thought.

[dvclama]

Nose mount and vibrations

Hi sir,
Your nose amount could be a factor also, if you stay in vibrations phases of flight.
I don't know 550, I know 350; 550 are military ones, and are differents may be.
I mainly fly 350 B2 and B3 with external load with all right side doors removed all the time for long line work. It doesn't seems to affect the frame if you respect the a good vibration level environment for the machine; rotors have to be well balanced.
Try to find the good compromise between speed and comfort, and avoid full power aply on cruise, specialy when heavy, you will see your machine in a better condition.
Those 2 or 3 knots gain, won't worth for the cost and duration of your machines.
peace
Philippe

[gumbyk]

We have had the same issues with some of our fleet, except they were approaching 18,000 hours.
We balance everything on a 100 hour basis. That works out to once a month on our high utilisation aricraft (which, like yours have a FLIR mounted under the nose, as well as some other equipmentfurther back) to every 4 months for some of our lower utilisation aricraft.
After this period of time, we either repair them if hte cracks are minor, or exchange them with a company in Canada (the name escapes me) who do a good repair job.

As for the EC scare-mongering regarding STC's, I think they're looking for ways out of warranty claims on new helicopters.

[blakmax]

Cat amongst the pigeons

OK Guys

with a company in Canada (the name escapes me) who do a good repair job.

Does the "repair job" involve resin infiltration/injection into delaminations or disbonds?

blakmax

[PapaEcho]

Develop of little and superficial cracks over canopy and in door upper mount area is a known probem. Anyway, normally, the cracks will not result in main structure cracks or damage. If you use the aircraft a lot without cabin door installed be carefully on VNe values as stated in Flight Manual.
Also, if you operate hooking within the limits no crack should be developed in that area.
Anyway if you have a FLIR installed you must have an STC application and a FLIR Supplement in your customized Flight Manual.
Have you found also some crakcs in the lower left-hand zone where the FLIR is mounted in the proximity of the mounting tube?

I'm not a Eurocopter Engineer, but an Young HelPilot still working in engineering department of a CAMO which sometimes I receive these issues.

Regards,
PapaEcho

[scomp]

AS350 Canopy

Hi Everyone,

This is my first post here...I stumbled upon this by accident and couldn't help but post a response.
I have a CAMO that has done a lot of repairs to the canopy structure and this is what we have found and know:
1) the canopy is "Polycarbonate" that is "ultrasonic fused" hence the wire mesh that is between the two layers.
2) the canopy is considered secondary structure.
3) the cracks at the upper door post is due to water ingress that breaks down the bond between the fused poly and wire.
4) the MRR fix is to inject resin up into the crack, allow to cure and then perform the stated repair with resin and glass. If you read it carefully they also tell you to apply vacuum.

the door post joggles and goes under the upper section by approx 4" but the bond is only 1/2" wide throughout the entire structure. To tell you the truth I am very impressed that bond is as strong as it is, and from our experience environmental issues are its biggest concern.

I hope this helps

[blakmax]

How to waste time: do injection repairs

So the repair is to inject resin?

the MRR fix is to inject resin up into the crack, allow to cure and then perform the stated repair with resin and glass. If you read it carefully they also tell you to apply vacuum.

Let me assure you that this is totally futile. To achieve a bond, chemical reactions must occur at the interface between the resin and the surface. For these reactions to happen, the surface must be clean AND chemically active. The injected resin will cure but it will not bond to the surface. The only things achieved by resin injection is that the air gap is filled so it appears that the joint has bonded and you get the opportunity to sign off that the repair has been completed IAW the MRR. You will not make one ounce of difference to the strength of the component.

The Australian Air Force prohibited injection repairs in 1996. [DEF (AUST) 9005 Chapter 11].

I invite all manufacturers who use resin injection for MRR repair of disbonds to show any experimental or other evidence whatsoever that this method restores any bond strength.

[scomp]

No the injected resin is not the "only fix" the layup of the fiberglass and resin over the cracked area helps restore strength to the area as well as sealing this area off from any more ingress. If you don't inject resin before the repair you will not be able to apply vacuum to this area. I totally agree injecting resin into a void or dis-bonded area is a quick fix and nothing else.

[500e]

bonding

Hi Scomp.
Do I understand you inject a resin filler mix and then beef up the damaged aria ?.
To me this is a waste of time as there is still little or no bond with the underlying structure.
I fully understand the use of vacuum to remove voids\air & excess resin from the lay up but it will not improve the bond strength.

[blakmax]

Repair of delaminations

there is still little or no bond with the underlying structure

You are dead set right 500e. It is actually possible to repair cracks using bonded patches, but such designs rely on the bond being effective both sides of the crack. In this case as I understand the descriptions of the structure the frame has disbonded and separated from the underlying structure. (Correct me if I am wrong. A photo would help.) In that case, the repair would be bonded on one side of the crack and the frame would still remain disbonded.

There is an issues that must be addressed: Why did the structure disbond in the first place? To answer that would require examination of the disbond surfaces. There are three possibilities:

1. The adhesive has fractured through the body of the adhesive layer. This is a design/load driven failure, in which case the discussion by others about the FLIR attachment may be relevant. It also raises the question of the original certification process.
2. The composite layer has pulled off the structure or the frame. This again is a design/load driven failure, in which case the discussion by others about the FLIR attachment may be relevant. It again raises the question of the original certification process.
3. The failure is through the interface between the adhesive and the substrate (either the structure ir the frame). This is a far more serious issue that is 100% related to processing at the time of manufacture.

Many manufacturers rely on the use of sacrificial layers known as "peel plies" to remove contamination prior to bonding and that is the only preparation specified for the bonding surfaces. To enable the peel ply to be removed, the fibres in the cloth must be treated by the cloth manufacturer to provide a weak bond, otherwise the process of removing the peel ply would reult in undesirable peeling off the first ply of the composite. There are two broad methods for treating the cloth: heat scouring which creates a glazed surface on the fibres which is slick and does not bond, or coating the fibres with a release material such as silicone. Unfortunately the glazed fibres create a cast impression in the resin of a glazed surface which is also slick and will not bond. The coated fibres transfer the release material onto the bonding surfaces. (see Hart-Smith, L.J., Redmond, G, Davis, M.J., The Curse of the Nylon Peel Ply, 41st. Int SAMPE Symp. and Exhib., Anaheim, 25-28 Mar 1996.)

In both cases, unless there has been further treatment of the bonding surface, the result will be disbonds in service.
The questions are, in the manufacture of these aircraft, a. were peel plies used? b. was there any secondary bond preparation if peel plies were used?
Anyone know the answers to these questions?

While we are on the subject, Scomp, what was the preparation used before bonding the fibregalss patch?

Blakmax

[scomp]

I am only talking about the canopy structure not any other type of bonding. As I wrote before the canopy is polycarbonate and is ultrasonic fused with a wire mesh between the two parts, this process heats the wire and "melts" the polycarbonate so that the mesh becomes imbedded in the Poly. We have taken numerous canopy's apart at the "bondline" and discovered this. There is no need for peel plies from the manufacturer as there is no adhesive used in this process. I am not saying it isn't flawed. To answer your question Blakmax our lay-ups are done in a temp controlled room, surface is prepped and cleaned using the manufacturers recommendations. we have to follow this for certification reasons. However we have generated numerous RDC's for repairs that are outside of the SRM, such as bird strike damage, ect. In any lay-ups that we perform we never bond directly to a surface that has had peel ply removed for the reasons that you stated, surface prep is the key to a good bond.

[blakmax]

OOPS

OK Scomp, my mistake re the canopy. I guess I was focussing on the thread title of airframe problems. I'd be interested in any MRR procedures for the airframe cracks. Is there anyone out there actually repairing airframe cracks?

The thought of using fibre glass patches to repair canopy delaminations is interesting. I presume the delaminations are planar in the plane of the canopy, and the glass patches are bonded on the outside of the canopy? Or is the canopy removed, the delamination injected and the glass patch applied to wrap the delaminated end of the canopy on both sides and the edge of the canopy?

Regards

Blakmax

[victor papa]

blakmax, you seem to have taken over from eurocrapter in insisting these cracks are a daily occurense on the 350 and a OEM manufacture fault. When last did you check how many Ecureuils are flying in this world and how many hours they have accumulated? As most agree, these crecks can be ops related and also environmental related. If it is/was as you suggest a major problem and oEM related, how did the Ecureuil get to where it is? As I have suggested before, in my experience we have had no major problems as long as you keep the paint and protective layers well sealed-in other words fix it when you see it following the Composite repair manual procedures and all is fine. If it was a alluminium alclad canopy or al honeycomb the complaint would have been corrosion and/or cracks on some aircraft, as I have experienced on various other types, but never on all of a type. It is important to note that the canopy is polycarbonate as described by scomp.