I think EASA approved the Sea State 6 flotation a few months ago.

Norsk/Bristow Norway were also waiting for the EASA certification to go through. Then suddenly all of their 92´s had the new flotation installed/connected, and its been fully operational for several months now.

Are you sure of this? It is news to me, and I know that SS6 is not yet fully installed on other operators machines - with the Tech log annotated "awaiting EASA approval".

212 man

OK so in your opinion, can all the hours the Blackhawk has flown be used to quantify the "extremely remote" possibility of having to fly with no oil in the MGB of the S92 seeing they do use a different but simlilar MGB

Horror box wrote:
Positive!
We were told that SS6 was approved, and would be connected/fitted to the fleet. I cant remember when this was but it´s several months ago, and as I mentioned earlier, all of our 92´s now have SS6.

Thanks for that. Very interesting. Can anyone shed any light as to why other S92's are still awaiting approval, and have not had SS6 connected?

Maybe the local CAA also has to approve on this, I don´t know.

If the 92 came without the SS6, its a major modification to install them. If it came with the system, i suspect it´s only to fill the bottles and connect the wires.

I know that some companies have a flex/progressive maintanance program. By the time the aircraft has flown, lets say 1250 hrs, all the boxes on the list are checked and the components that needs to be replaced are replaced. The advantage is that the airframe has less down-time and more time available to the customer.

Other companies take the helicopter out of service for the whole duration of a 1250 hrs inspection and it stays in the hangar for a week. Less time available to the customer, but it allows enough down-time to do the major modifications, if there are any to be done that is.

Both maintenance methods are safe, but they both have their advantages and disadvantages.

Maybe this explains it.

Isnt this like having seat belts in a car but saying you cant use them . I cannot understand how a transport catagory helicopter would be allowed to fly offshore without fully functioning floats.

Murph,
No! they are not the same gearbox - they are SIMILAR. Where do you draw the line between similar and same? They are both modular, they both have a similar configuration, they both use similar philosophies, they both look vaguely similar, but they are not the same. To some degree or other, all large twin engined helicopters have 'similar' gearboxes.

SS5 is up to 4m (rough,) SS6 is 4-6m (very rough.) Personally, I don't believe anyone would consider their float certification basis when considering the option to ditch, and if they do then they clearly don't understand the criteria for 'land immediately' (That's not in any way a comment on the Cougar crew - just the remarks above.)

Floats
 

Just to clarify, the original standard was sea state 5 (nose and tail floats). The sea state 6 add-on floats in the sponsons were certified by FAA in late 2007 and by EASA in 2008. Aircraft delivered off the production line from late 2007 had the SS6 installed (but not wired pending certification). Those aircraft should now have the system fully operational (as Rotordude says). Older aircraft require structural and avionic modification and that will depend on the scheduled maintenance downtime.

Any update on the revised anti-vibration system apparently being designed for the military versions according to another thread? I take it the existing system was not up to spec for long-haul flights, or was it due to the recent component failure modes of the titanium filter housing studs?

Would be nice to have on the S-92s, especially when you're on a 3-hour boomerang coming back from offshore, quite a common occurence in the Grand Banks.

Max,
it is a misconception to believe that the anti-vibration systems in use will have any effect on the vibration levels experienced by MGB componants. The S-92 uses a system of 'Force Generators' - either 3 or 6 depending on customer option - which are strategically placed to counter the vibrations experienced within the fuselage. Bear in mind that the fuselage has nodes and anti-nodes and there is not one constant level of vibration experienced throughout. The force generators systems (Active Vibration Control) are tuned to the individual signatures of the aircraft they are installed in.

Other aircraft use diffenet systems (if at all) and the EH-101 uses hydraulic struts between the MGB and the fuselage, thereby stopping the vibration transfer in the first place.

Cheers 212man

I should have been more specific in my question, assuming that the S-92 force generators are being used primarily for pilot/PAX comfort in order to counter-act the 4-blade main rotor (IMO under-rated) design, do they also assist at all in reducing strong vibratory nodes at the helo's critical components such as the MGB?

If the answer in no, then what is being done to improve the situation? I'm sure there is an answer within historical posts...

Max

maxwelg

The answer is certainly no - the force generators are only to improve passenger comfort. In fact where the vibration (from the rotor system etc) and the anti-phase vibration (from the force generators) collide and cancel out, there is an increased stress on the structure since the vibration energy is dissipated by flexing of the structure, whereupon its converted to heat.

The only way to reduce vibration at the critical parts is to have an intrinsically smooth rotor system or cancel out the vibration at source (eg rotor head bifilars, L2 oscillating weights etc). Even the 101's active struts do not reduce vibration at the gearbox, only within the fuselage (the gearbox is mounted directly onto the head).

However, I think this line of thought is a bit of a red herring, the high mass of a main gearbox means that vibration acceleration levels are quite low, and such a low acceleration level on a light piece of structure such as an oil filter housing is likely to be very small unless there is some resonance involved. Forces on the housing from pulsing oil pressure, for example, are likely to be much higher than those arising from MGB vibration.

HC

Bad Vibes??
 

Helicomparator:
With the info from your last post I see more clearly what John Dixson meant when he wrote that the vibration at the filter attachment point could not be deduced by the vibes in the cockpit or passenger cabin. Is it fair to say that the level or intensity of the vibes induced into the passenger cabin are of similar intensity to the vibes originating at the rotor head and travelling down through the gearbox into the fuselage?

So all the force generators are doing, even with the 6 unit VIP setup is leveling out the vibration in the passenger cabin only for the sake of passenger comfort. Will the vibration present at the rotor head and gearbox remain as severe, unaffected by the dampening of the vibes in the fuselage below?

I know we're talking about a heavier transmission medium with much lower acceleration rates but there are still just three M8 studs to hold the vibrating mass of the filter bowl and the column of fluid within, in addition to the axial loading from the internal gearbox pressure. It doesn't seem like enough fasteners given that the design ensures that one broken stud can cause catastrophic loss of the MGB lubricant.

NL, I think you'll see that HC and I are saying the same thing. The AVC has no effect at all on anything other than the cabin structure (and any companants contained therein) in the adjacent areas to the force generators.

Similarly, I agree with HC that the forces encountered by the filter bowl as a consequence of fluctuations in oil pressure are likely to be far more significant than the vibration. It is not vibration per se that is a problem - it's the resultant forces it generates, with the attendant cyclic stress fatigue.

Frankly, I think the whole subject (of vibration and the filter mounting) is a red herring.

I'll second that.

And with my vote the motion is passed.

But will the "Newfie SLF expert panel" actually listen :ugh::ugh:

But just suppose, for argument's sake, that the vibrations caused by the rotors and transmitted to the MRGB do, in fact, create a resonance in the filter assembly - not only would that have helped to cause the failure of the titanium bolts but might do the same to the steel ones.

I know it is unlikely but since modern helicopter designers haven't dealt with the problem of the source of vibration but have been more creative in how they mask it maybe there is something in it.

The vibration/fatigue theory has also been postulated elsewhere ,following the Norwegian Flight Safety institute report .Helidata News suggested that the vibration levels could contribute to stud failure ,either over time or suddenly.
This was followed up recently in the Globe and Mail .

The problem is that I don't think we know how the studs failed. Did the stud pull out? Did the stud shear off? Did the nut come off? Until we know that, its all pointless speculation.

Titanium is a funny material, very hard and doesn't stretch much. Stretching is important because it affects the relation ship of tensile force to rotational position of the nut etc. Stretchy steel is good in this respect - a bit of stretching ( not beyond its elastic limit of course) means that tensile force is maintained when other factors such as expansion/contraction of the casing, slight rotation of the nut etc are in play. Being very hard, I would expect titanium to be quite good at stripping the threads on the MGB case if its over-torqued, and bearing in mind its lack of stretching, correct torqueing is much more critical that with steel.

Overall, its hard to understand why titanium was chosen - presumably only for its lighter weight for the same strength?

But to suggest that 3 studs is a fundamentally flawed design, would be quite wrong. 3 studs of the correct grade for the job in hand is perfectly adequate - you just need to be sure that you have chosen the correct material and size, thread etc for the loads to be encountered.

HC