diamondaviators.net

Anyone else here have bad luck with flywheels failing their 600 inspections? We've gone through four now. Prices went up to $5000 each, we're out of warranty, and parts come from Europe, so you're not getting your plane out of annual in a week or two.

Tried emailing Diamond to see if there are some operational recommendations or best practices. Maybe something along the lines of what geared Continentals call out for: ensuring the engine always drives the prop, not letting lumpy engine idle torture gearbox bouncing back and forth between gear lash. That seems more of a gearbox issue rather than TVD issue, though, but haven't heard back yet from Diamond.

If they both go bad again at 1800 hours/overhaul, it'll be roughly $30,000 in TVD replacements during the life of engines. Essentially the cost of a third engine being overhauled.

For the uninitiated...what is "failing"? Is it cracked or out of balance or....?

Great question: failing the 600 hour inspection. Not in flight failure rate.

Tim H wrote: ↑Thu Mar 12, 2020 11:30 pm For the uninitiated...what is "failing"? Is it cracked or out of balance or....?

The inspection is quite thorough and requires an expensive tool, which is why many shops ship the mass flywheel off to the London factory or one of the other properly equipped Austro qualified shops to be accomplished for a reasonable fee. The inspection might require replacement of the assembly for any of the following reasons:

• Traces of thermal damage at the rear side or at the outside coverage
  Residual molten plastic between primary and secondary mass of the two-mass flywheel
  Excessive wear of inner rivet heads
  Traces of wear at the surface of the primary mass, caused by friction of the secondary mass
  Bearing friction ring broken or width less than 50%
  Bent teeth on the pick-up ring
  Any gear tooth of the starter ring worn to less than 95% of initial volume
  Missing balance weights or broken weld points of balance weights
  Deflection between primary and secondary mass out of tolerance at any of 14 torque values measured on the test rig (AEP-0061):

Back to the OPs question, has anyone else experienced this? His failed at both 600hr inspections.

Are other inspections less thorough? Is his shop overly careful?

As the OP suggests, is this problem more a factor of the gearbox than the engine? Did Diamond respond to the question about "best practices"? Maybe the question should go to Austro rather than Diamond?

neema wrote: ↑Thu Mar 12, 2020 4:59 pm...ensuring the engine always drives the prop...

I got to thinking about this and possible stress on the Torsion Vibration Damper/Dual Mass Flywheel during normal ops. For obvious reasons, Austro no longer allows windmill restarts for training purposes. I have to wonder if pulling power to idle for awesome 3,000+ fpm descents, or even pulling to idle quickly upon landing might unduly stress the dual mass flywheel, leading to early replacement.

On the E4P engine (DA62), the flywheel gets inspected at 300 hours, and replaced at 600 hours no matter what. Basically the same hardware, potentially stressed ~8% more. I have my first 300 hour inspection in another 55 hours. I'll let you know how it goes.

Interesting topic. For my DA42-VI I had both flywheels replaced on my 600 hr as well. Cost each including 12 hrs of labour = USD5k.

Before the 600 hr inspection I separately asked a freelance mechanic as well as a large maintenance organisation on their experiences.

The freelancer said he'd never seen a flywheel fail the 600 hr inspection.

The large maintenance organization said they'd never seen a flywheel pass the 600 hr inspection.

In this particular case, my confidence tilted heavily towards the maintenance organisation as they've always been doing stellar work for me previously and always working strictly by the book.

But perhaps it does indicate how the 600 hr flywheel inspection might set very narrow, literal tolerances & somewhat open to interpretation.

To me it does seem like the flywheels generally do need to be replaced at 600 hr.

Another component that seems to cause issues are the prop governors. They seem to be involved in a lot of interrelated issues with the engine & ECU's. I've had both of my governors replaced within the past 600-700 hrs as well, both times caused by having the engine RPM pegged at max-2300+ RPM regardless of power setting. Whether it's narrow tolerances on the ECU sensors or genunine mechanical issues of the governors, I couldn't tell.

ultraturtle wrote: ↑Fri Mar 13, 2020 11:36 pm or even pulling to idle quickly upon landing might unduly stress the dual mass flywheel, leading to early replacement.

Yep, I certainly work the props as a speed brake once in a while...

Henrik wrote: ↑Sat Mar 14, 2020 3:37 am Another component that seems to cause issues are the prop governors. They seem to be involved in a lot of interrelated issues with the engine & ECU's. I've had both of my governors replaced within the past 600-700 hrs as well, both times caused by having the engine RPM pegged at max-2300+ RPM regardless of power setting. Whether it's narrow tolerances on the ECU sensors or genunine mechanical issues of the governors, I couldn't tell.

Be sure to update EECU software to version 23 (Nov 2019). My guy tells me that it helps with governor issues.

Boatguy wrote: ↑Fri Mar 13, 2020 9:35 pm Back to the OPs question, has anyone else experienced this? His failed at both 600hr inspections.

Are other inspections less thorough? Is his shop overly careful?

As the OP suggests, is this problem more a factor of the gearbox than the engine? Did Diamond respond to the question about "best practices"? Maybe the question should go to Austro rather than Diamond?

I haven't gotten a response yet from Diamond. Hopefully something comes through. I can ping Austro too to see if I get anything sooner.

Since very few maintenance shops own the expensive red jig shown in the post above, they need to send the flywheel(s) to Diamond for inspection -- which can leave your plane unflyable for awhile.

One shop (SouthTec Aviation at KRUQ) addresses this issue by keeping a spare set of flywheels in stock. When you take your Diamond twin to them for flywheel inspection, they'll send your units in to Diamond for inspection, but immediately install the spare set of flywheels on your plane. Then when your original flywheels come back from Canada, they're available to be installed on the next aircraft that comes into the shop.