I I
Nice to hear that SK are supplying Free casings I expect they are reimbursing down time & engineering costs as well ??

Has anyone seen a vibratory analysis on the Gearbox feet as they relate to the airframe?

500e. I have not heard of those costs being reimbursed to our company. However, all recent product improvements have been free, not just the MGB related ones. We never got that from EC with the 332L or the EC225.

IFSKNT
Nice to hear about casing and product improvements?? so your Co are standing ENG costs and loss of revenue on a multi million $ product that appears to be faulty, makes you wonder.
I am not saying that it is only SK EC or only the helicopter industry that charge indirectly the end user for design shortcomings, and expect them to pick up the bill.

immaengineer.
On the HUMS down load, which in the company I work for, we down load after every flight, which is normally about 4 to 5 hrs duration the gearbox foot vibration analysis can be viewed, although I can't make head nor tail of it, ( awaiting the company course). It is then sent away, electronically, direct from the laptops, to our main base and SAC for proper analysis, along with the TGB shaft info, T/Rotor pivot bearing retainer, info, and also the other vibration reports for all the rest of the aircraft.
During Gearbox changes the airframe mount holes are measured for rotation of the bushings and also a maximum/minimum dimensions between holes.

Understood... Thanks... I look forward to seeing the data on the specific foot that seems to be the focal point of the cracking...

If SAC knew I doubt they would share. All indications are they have no real understanding of the failure mode.

Grunt92
Surely, you have hit the spot, bushings shouldn't rotate, holes shouldn't change dimensions, must be something wrong with the designed interference fits/clearances.

Or it could be a supplier problem, and SAC didn't inspect properly... The supplier could be fudging things up. From my research I found out this box is a derivative from the Black Hawk. The Black Hawk has been in service for decades so I think any little problems should have been worked out over the years...

No !!!!! Sherlock!

Thanks for the sarcasm, I can tell you are very well liked... and SAC doesn't build their own MGB housings... They are supplied

And while the foot print is the same and the overall appearance is similar, totally different design gear box.....

EASA S92 Gearbox EAD Issued 17 Aug 2010
 

http://www.caa.co.uk/docs/33/EASA_EA...E_1%5B1%5D.pdf


Posted just for info, probably woth merging with the S92 Gearbox Crack Thread in a few days.

Found out recently that the Navy is looking to go from Mag to Al main gear boxes (and I think Intermediate/Tail rotor as well) in the next few years, even though it created a small weight penalty to do so. (Something less than 50 lb, I think, but I may be wrong about that).

Given that S-92 operators seem to operate quite a bit in salt water environment, is a switch to Aluminum gear boxes a design option under consideration for later production?

If that's close hold/company info, apologies if it seems out of order to ask.

Gear Box Case Coatings
 

I believe that Sikorsky uses either Rockhard or Sermatech coatings on all main and tail gear box housings. This was incorporated during S-92 development to improve the durability of the housings. The initial concept behind the development of the S-92 was for all of the major dynamic components to be capable of being retro-fitted on future Blackhawk/Seahawk models. As such the basic layout (i.e. foot print) would match that of the Hawk line. This design constraint may in part be responsible for some of the on going problems. The Blackhawk’s design gross weight was 18600 lbs. and its maximum all up weight of was approximately 24000 lbs. 28000 lbs may be a stretch for the present configuration.

But Sikorsky sold the S-92 boasting that it was based on Blackhawk dynamics which therefore gave it strong lineage and assured quality - clearly not true:ugh:

Switching from MAg to ALm will be a great weight penalty... 150lbs IMO... With addition of all the other upgrades 200lbs wouldn't be farfetched to me...

Not exactly a great weight penalty over 26500lbs. Get rid of three of the six FG's if you really want to save weight, as they don't make much difference anyway. Alternatively take approximately seven minutes less fuel, either way it is not going to be a huge show stopper.

Introducing the increased MGW (somewhere North of 27,200) will obviously help offset any additional weight, too. Though whether that's on hold pending the phase 3 MGB I've no idea.

"Switching from MAg to ALm will be a great weight penalty... 150lbs IMO"

immaengineer,

The weight difference between a sand cast aluminum or magnesium gearbox housing is usually not much. There are several reasons for this.

First, while magnesium is less dense than aluminum (.064 vs .098 lb/cu.in.), the minimum wall thickness most sand foundries will pour is .16 inch for mag and .12 inch for aluminum. Lightweight aircraft gearbox housings tend to have lots of surface area (especially with cast lube system pipes) with minimum thickness. So that extra .04 inch of mag can make a difference with a large housing.

Second, maintaining accurate gear geometry under load is very important. Housing deflections can cause problems with gear and bearing life, so having a stiff housing structure is critical. Aluminum has a higher modulus than mag (10.3 vs. 6.5 x 10^6 lb/sq.in.), so it gives better stiffness for a similar structural configuration.

Third, if the gearbox is in an area that must meet a fire rating, large thin wall areas in a mag housing must sometimes be thickened to meet the burn through requirement.

As for using cast mag in a marine environment, this is something that the Navy (NAVAIR) usually frowns on, mostly due to corrosion/maintenance issues. There are some newer sand cast mag alloys (WE43) that have decent corrosion resistance, but they are much harder to cast than the more common mag alloys such as ZE41.

riff_raff