DRick5961
Topic Author
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Joined: Fri Oct 05, 2018 6:55 am

Common IDG issue

Mon Nov 05, 2018 9:18 am

Hi Experts,

May I know what is the common IDG issue? Is it copper chelation and what is the main cause of copper chelation?

Thanks in advance
 
Apprentice
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Re: Common IDG issue

Sat Nov 10, 2018 7:01 pm

Hi: Just Line Mx,. More common defects are related to Oil System, which is independent from Engine Oil System and is very “picky” concerning service,
Oil should be serviced to an area between two marks. Desirable to the upper mark.In that Way, device will mantain a constant output speed to generator independent of engine rpm., which will allow for frequency to be 400 hits +/- 1%.
If oil is out of the requiered area, frecuencia will move out of green range and will be disconnected in flight.

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tb727
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Re: Common IDG issue

Sat Nov 10, 2018 8:12 pm

Duplicate post......blah blah
Last edited by tb727 on Sat Nov 10, 2018 8:13 pm, edited 1 time in total.
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tb727
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Re: Common IDG issue

Sat Nov 10, 2018 8:13 pm

Oil being over serviced is the only thing I've noticed. Every CSD I disconnected in flight when on the 727 was due to this and last week I had an IDG on an A320 deferred due to over servicing. Too much oil doesn't allow it to cool and you get high temps requiring disconnect.
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wingscrubber
Posts: 823
Joined: Fri Sep 07, 2001 1:38 am

Re: Common IDG issue

Mon Nov 12, 2018 2:57 pm

IDGs / CSDs are basically just generators with miniature hydrostatic-drives being the interface with the engine ancillary gearbox.

Hydrostatic drives are also used on lawn tractors and big earth movers - all susceptible to the same issues; leakage, fluid degradation due to heat, particulate contamination due to wear - in theory the variable displacement control piston (governor) can stick as well.

It would be interesting to hear from any mechs who've overhauled IDGs/CSDs - I've heard they're quite the pig to put together, kinda like a mini automatic transmission, it's basically a closed loop hydraulic circuit - a variable displacement pump/motor and a fixed displacement pump/motor plus a small gearbox. Probably only gets done at the supplier's facilities e.g. hamilton sundstrand (now UTAS)

Finally shouldn't forget the generator part itself - AC generators are probably maintenance free except for bearings? DC generators (which you won't find in any airliner) may need to have their brushes replaced occasionally I suppose. and I suppose the windings might get checked, plus magnet strength during a generator overhaul... or maybe even just a quick bench test and nothing more.

Oh, and 'copper chelation' sounds like a red herring - google says that's something to do with cancer treatment!?
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fr8mech
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Re: Common IDG issue

Mon Nov 12, 2018 4:15 pm

wingscrubber wrote:
IDGs / CSDs are basically just generators with miniature hydrostatic-drives being the interface with the engine ancillary gearbox.


One correction, a CSD is a constant speed drive. It drives the generator, which is a separate component, and can be replaced independent of the drive. In an IDG (integral or integrated drive generator), the generator is integral to the unit.

tb727 wrote:
Oil being over serviced is the only thing I've noticed.


That's the big thing right there. CSD's tended to be easy to service, and verify the correct service, because they had big sight glasses that where bolted onto the side of the reservoir. IDG's are a different animal. The "sight-glass" is actually a prizm that looks into the sump. It could be a pain in the ass to get the angle right, and the "sight-ball" may be stuck. Early in my career, the "sight-ball" had the letters "OK" imprinted on it...if you saw that, then the IDG was NOT under-serviced, but it said nothing about over-service.

Now, at least where I work, we no longer check service on our IDG's. We service them and ignore the sight glass. In fact, I think ours are painted over. We install an overflow hose, install the service hose, and pump oil in until we get a pint out of the overflow. Then keep the overflow hose connected until there isn't anymore oil coming out.


As an operator, I think you'd rather see an slightly under-serviced IDG (frequency issues), than an over-serviced one (over-heat and internal damage).
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EasternSon
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Re: Common IDG issue

Mon Nov 12, 2018 7:06 pm

From my experience with IDGs, mostly from CRJ200 and Challenger aircraft, the largest problems are due to the wear of the piston slippers. The brass coating on the piston slippers first begins to wear and chip, mostly because the brass is much softer than the steel variable wobbler plate they slid around. Those brass flakes will be pumped around the inside of the closed-loop system, and block oil passages that are minute, causing overheating and disconnect.The flakes appear in the oil when drained as gold flecks.

In the worst-case scenarios, which I've seen many times, the slippers separate entirely from the piston itself. They're ground to bits by the cylinder block, and again the metal chunks are distributed through the CSD. They get ingested by the gears, destroying teeth, and causing additional metal contamination. The entire CSD portion can quickly "hand grenade" in a very short time, as these failures usually occur at the highest RPMs. It gets ugly. We've had IDGs come in with fist-sized holes in the CSD housings.
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stratclub
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Re: Common IDG issue

Tue Nov 13, 2018 3:53 am

What is great about the 787 is that it has no IDG's. What the 787 has are called VFSG's (Variable Frequency Starter Generators) which are not speed regulated so there is no reason for a CSD.
 
strfyr51
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Re: Common IDG issue

Tue Nov 13, 2018 9:54 am

wingscrubber wrote:
IDGs / CSDs are basically just generators with miniature hydrostatic-drives being the interface with the engine ancillary gearbox.

Hydrostatic drives are also used on lawn tractors and big earth movers - all susceptible to the same issues; leakage, fluid degradation due to heat, particulate contamination due to wear - in theory the variable displacement control piston (governor) can stick as well.

It would be interesting to hear from any mechs who've overhauled IDGs/CSDs - I've heard they're quite the pig to put together, kinda like a mini automatic transmission, it's basically a closed loop hydraulic circuit - a variable displacement pump/motor and a fixed displacement pump/motor plus a small gearbox. Probably only gets done at the supplier's facilities e.g. hamilton sundstrand (now UTAS)
Overservice is just as bad as underservice
Finally shouldn't forget the generator part itself - AC generators are probably maintenance free except for bearings? DC generators (which you won't find in any airliner) may need to have their brushes replaced occasionally I suppose. and I suppose the windings might get checked, plus magnet strength during a generator overhaul... or maybe even just a quick bench test and nothing more.

Oh, and 'copper chelation' sounds like a red herring - google says that's something to do with cancer treatment!?

The CSD and the IDG are basically automatic Transmissions that Drive Alternators, Just BIG damn Alternators in the KVA range. They're VERY picky about how they're serviced. You want one to cause you a LOT of problems? over service it!!
 
Lpbri
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Re: Common IDG issue

Tue Nov 13, 2018 10:57 pm

stratclub wrote:
What is great about the 787 is that it has no IDG's. What the 787 has are called VFSG's (Variable Frequency Starter Generators) which are not speed regulated so there is no reason for a CSD.

But they are almost as big and heavy and require the same servicing as an IDG.
 
LMP737
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Re: Common IDG issue

Wed Nov 14, 2018 3:06 am

fr8mech wrote:

That's the big thing right there. CSD's tended to be easy to service, and verify the correct service, because they had big sight glasses that where bolted onto the side of the reservoir. IDG's are a different animal. The "sight-glass" is actually a prizm that looks into the sump. It could be a pain in the ass to get the angle right, and the "sight-ball" may be stuck. Early in my career, the "sight-ball" had the letters "OK" imprinted on it...if you saw that, then the IDG was NOT under-serviced, but it said nothing about over-service.

Now, at least where I work, we no longer check service on our IDG's. We service them and ignore the sight glass. In fact, I think ours are painted over. We install an overflow hose, install the service hose, and pump oil in until we get a pint out of the overflow. Then keep the overflow hose connected until there isn't anymore oil coming out. .


The IDG's on GE along with PW powered MD-11 I've worked on have CSD style vertical sight gauges. Comes in handy when checking the number one and three. Not so much on the number two, lol. The biggest mistake people make is service an IDG to full on a cold engine. Oil expands when it gets hot after all. On more than one occasion when I've hooked up a drain bottle to the remote service hookup for the number two I've gotten like half a quart come out, under pressure.
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fr8mech
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Re: Common IDG issue

Wed Nov 14, 2018 5:41 am

LMP737 wrote:
The IDG's on GE along with PW powered MD-11 I've worked on have CSD style vertical sight gauges.


You know, whenever I make a statement that implies "all" or "every", I am reminded that there is rarely an "all" or "every" in aircraft configurations. Now, I'm trying my damnedest to remember what the L1011 IDG was like.

I just checked our MD11 IPC, and there is the sight-glass, big as day.

Makes checking the service easy, doesn't it?
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Unless it's expressly prohibited, it's allowed.
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stratclub
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Re: Common IDG issue

Wed Nov 14, 2018 12:04 pm

Lpbri wrote:
stratclub wrote:
What is great about the 787 is that it has no IDG's. What the 787 has are called VFSG's (Variable Frequency Starter Generators) which are not speed regulated so there is no reason for a CSD.

But they are almost as big and heavy and require the same servicing as an IDG.

Oh heck no. While you service them just like an IDG (fill and overflow lines), they are way bigger. An IDG is 90 KVA while a 787 VFSG is 250 KVA with 2 per engine.
 
AA737-823
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Re: Common IDG issue

Thu Nov 15, 2018 3:49 am

I've seen two IDG failures in my career thus far.
1. Metallic failure of drive structures, which caused an in-flight disconnect. The teardown report showed that it was well and truly buggered.
2. An electrical short in the field. Which caused a failure to connect during startup. Which caused a delay.

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