500C (369HS) TR Chip have a look at this!

[nouseforaname]

http://i242.photobucket.com/albums/ff112/nole9126/chip4.jpg

http://i242.photobucket.com/albums/ff112/nole9126/chip2.jpg

http://i242.photobucket.com/albums/ff112/nole9126/chip1.jpg

I got a chip light illuminated and got it back to home base which was about 2 miles. This is the input shaft cog wheel which has now been replaced.

Anyone ever seen anythign like this in a TR gearbox before?

[Hell Man]

Only in Nam with the Loach but that was after a direct hit to the tailboom (small arms fire) which caused an imbalance in the trds which resulted, so the mechanics informed, in a fracture to the same cog!

I would get your maintenance dept. to contact MDH pretty smartly in case there is an issue with the integrity of these cogs. Has this ship had any sudden stoppages?

HM

[nouseforaname]

yeh it's had a tail boom strike some years ago before we had it. Everything was overhauld though. Don't think it would have gone down well if it had gone into the rest of the gears, luckily they said it had just settled at the bottom of the gearbox.

[Hughes500]

Had a tooth come off on a 300C main transmission ( looks just the same as the pix), only knew as there was a clicking on rundown. AAIB looked at the ring gear and came to the conclusion that it was bad manufacturing. SAC werent interested as they said I had misstreated the ac !! Which led to a very excitable phone call between myself and a certain director of SAC.
Other possiblity is corrosion espically if the machine has stood idle and running on mobile 254. 254 seems to strip off the case hardening letting corrosion in. Make sure when the box is overhauled it goes on to Mobil shc626

[nouseforaname]

Yes it is on some form of different oil now in the g/b can't remember exactly the numbers, but its on stuff different to the engine which is on m254. They seem to think that it was corrosion but there is no realy evidence of it when you look, but i wouldn't be an expert on looking at these either.

[chopjock]

254 seems to strip off the case hardening letting corrosion in:eek: I have Mobil 254 in my tail rotor gearbox. Should I be worried then?

[nigelh]

Jump Man for Gods sake before its too late :eek:

[noooby]

Yep, seen this years ago on an AS350BA where a complete tooth came off the bevel gear in a tail gearbox. We got the police involved as we thought it had to be some sort of sabotage (dropped something in the gearbox perhaps?) Metallurgist confirmed that it was a failure from natural causes! Yeesh.

[Hell Man]

Metallurgist confirmed that it was a failure from natural causes! Metallurgist? An aviation matallurgist claiming 'natural causes'! No such thing in the aviation industry. :confused:

If an aircraft has been operated and maintained in compliance with the prescribed flight and maintenance manual directives and a dynamic component fails through no external influence then the failure, if strcutural or through fatigue, is the liability of the manufacturer.

That components become worn and fail is normal but, the manufacturer sets established parameters defined by time (either days or hours or both).

In nouseforaname's situation (and in my view) there may be an obstacle in challenging MDH inasmuch as the airframe suffered a sudden stoppage and which the manufacture will always cite as being an 'out' for them because (and this is understandable) they cannot accept liability for the consequences of a situation in which the integrity of dynamic components (more vulnerable) are influenced by forces which occur while everything is running.

However, nouseforaname's mechanic should still contact MDH but the only way they could accept liability is if it can be demonstrated that there was a fault in the manufacture of the cog.

The answer for operators is of course HUMS which is on the bigger ships.

HM

[500e]

If main GB rebuilt and 626 used from start I understand life is extended, will look to see how long and check on TRgb as well.

[captyankee]

I was flying a Huey for the Mexican Gov. down in the state of Sinaloa when I got the dreaded chip light . (Shares with the 42 & 90) I pulled the plug in the field and it didn't look too bad, so I cleaned it off an flew back to base (light came on right at landing). Mex. mechanics climbed up, peeked in thru the oil filler, and there was a toothless grin, just like yours, to greet them. Just was overhauled by this bloody bugger in San Diego. I pulled it off and opened her up and dam if I could find the broken half of the tooth. And it was big enough to carry a part number so no way it came out the drain and no smaller pieces in there either. Flew back and showed it to the "Sleazy" who overhauled it. His answer "sneaky Mexicans pulled it apart in the middle of the night and swapped shafts" Only problem with that was the sealant had the original paint from overhaul that was never broken before I opened it. Guess 'Sleazy" just had no respect for the mexicans! :=

[riff_raff]

nouseforaname,

Looking at the photo you posted of that bevel gear, the first thing that caught my attention was not the gear tooth that fractured across the roots. That should have been expected. Instead, what caught my attention was the gear's rim thickness. That's the thickness from the gear tooth root fillet to the adjacent rim surface. As a rule of thumb, good gear design dictates that this thickness should be equal to or greater than the gear tooth whole depth. Your example looks to be only about one-third of this.

The reason for maintaining this minimum gear rim thickness is so that any gear tooth root fracture will propagate through the tooth, instead of through the rim. A rim fracture would almost always be catastrophic, while a tooth fracture would be less so. In fact, if the gear mesh has a high enough contact ratio, it may even continue to operate with a missing tooth.

Your gear suffered an unusual tooth fracture. Looking closely at the photos, it appears the fracture started at the tooth root and then (logically) propagated towards the rim. But then it strangely turned around and finally broke out at the adjacent tooth root.

It's just my opinion, but I'd have a serious chat with the guys that designed that gear. Because that gear doesn't seem to have a safe rim thickness based on what I'm used to seeing on rotorcraft drivetrains. Here's a good reference from NASA:

NASA Technical Reports Server (http://ntrs.nasa.gov/search.jsp?R=141845&id=7&as=false&or=false&qs=Ntt%3Dgear%2Brim%2Bthickness%26Ntk%3Dall%26Ntx%3Dmode%2Bm atchall%26Ns%3DHarvestDate%257c1%26N%3D0)

Regards,
riff_raff

[RVDT]

A little trap that comes with the "Hughes" legacy of these parts.

It is possible that input shaft and the whole TRGB for that matter can be fitted to either a 269 OR 369.

The life limit is LOWER on the 269 most probably due to the uneven power pulses of the piston engine.

In days of old you could swap these items between models as long as the lowest life was taken into consideration. This practice is now prohibited by TCDS.

If this shaft has history of being fitted to a 269 it may be the issue. Life on a 269C of a 369A5425-5 is only ~ 8600 hours yet on a 369 it is "on condition."

I would look closely at the previous "history" of this shaft.

As for the tooth dropping off, it is not the first and probably not the last one!

We are talking 50 year old design here. :rolleyes: