S-300C (Lycoming HIO-360-D1A) > 2000rpm w/o load => overspeed
 

The S-300C has a four cylinder Lycoming HIO-360-D1A engine.
Engine rpm green arc sits around 3200 rpms.

Why is exceeding 2000 rpm without load considered overspeeding?

FM:What engine parts might be damaged?

I find that very astonishing, considering that all cams, crank and shafts are built for sustained 3200 rpm;
and I do like to understand the reason for a rule, helps memorizing it a lot.

Quote: Why is exceeding 2000 rpm without load considered overspeeding?

Because it is stated in the manual.

HOW DARE YOU QUESTION SIKORSKY!!! (just kidding)

In my recollection from my training days I believe it is the short-shaft that needs to be inspected. It's the shaft that comes out of the engine connected to the lower pulley that you turn each way and listen if there is a clanking noise (metal on metal). Not sure why in a no load situation it needs to be checked.

RTFQ
 

None.

It is the little drive shaft between the engine and lower pulley that requires a crack check and visual inspection. P/No. 269A5559-003 as indicated below.

http://farm8.staticflickr.com/7030/6...c17b8328_b.jpg

I'm not sure exactly what happens that causes damage, but I do know the drive shaft (they always called it the "short shaft") has to be inspected by doing a magnaflux test to check for cracking. On newer models, the mags will short out if you try to roll the throttle on without the rotors engaged. You can expect the aircraft to be down for a couple of days, minimum.

BTW- Don't break it as Schweizer lists the part for $20,077.33!

While I do believe y'all to be right, I have a hard time seeing why that "lower pulley coupling shaft" so urgently needs inspection when it only sees a minimum load (drag of the lower pulley bearing) while hitting 2200 rpms.
We recently had anohter 300C "completely apart" (600h, recently bought from foreign owner G-xxx) and the mechanic showed us that very shaft, with its funny curved sprockets, and dumped it into the waste bin together with the splined "axle" of the lower pulley, as their visible wear was way off spec, on both.

Of course I can imagine that compensating for tiny engine movements relative to the frame while transmitting 190 ponies will be hard on the shaft and the splines it connects to.

Could it be that w/o load the shaft would be rattling in the pulley from the engines uneven running, having no big flywheel and lacking load?

btw. our 300C indeed does have that overrevv ignition cut off *cough* :O
and the FI needs a sturdy device (smartpone will do) to whack the starter relais, to make sure it actually sends electricity to the brand new, shiny high revv starter. Hence that 300C currently requires a crew of two, for startup :rolleyes:

Quote: BTW- Don't break it as Schweizer lists the part for $20,077.33!

From a business point of view those R22's are looking good.

So when you are practicing auto rotation, splitting and rejoining the needles involves the engine running over 2,000 rpm and off load too.
So how come you don't need an inspection for this??:confused:

So, R22/R44s don't have any overspeed issues :confused:

269A5559-003 is more like 2796,68

We sure would have had a major "party" complete with pics and gals
when the mechanic would drop a part costing 20 Grand into the bin
in the cause of a 600h inspection :ugh:

Short answer: you don't.
I'm required to split needles at 2500 rpm during preflight engine check to verify correct function of the freewheeling clutch, but then again the rotor has to be engage before doing that check.

That is exactly what puzzles me:
Only when exceeding 2000 rpm w/o having engaged the rotor requires the inspection.

There are students who accidentally switch the ignition to off when testing "left", talk about major needle split :uhoh:
And of course after the magneto check you do freewheeling clutch check mentioned above.

All of that at 2500 rpm, w/o forcing an inspection.
That is was has me puzzled, what the danger/mechanical damage is, with exceeding 2000 rpm, disengaged.

The driveshaft will oscillate, bend and take the shape of a banana.:{

Cool, got pics?

This is the only correct answer.

Because there is no load on the lower pulley, the pulley will start oscilating on the frequency of the engine. This causes extreme load on the splines of the lower pulley drive shaft (short shaft), resulting in exessive wear and possible creating cracks at the splines.

Why doesn't his happen when i'm perfoming an autorotation?(engine running 1500-2000 rpm);
Because the clutch is still engaged, so there is the drag of the free running clutch and drag of the bearings and that will damp the oscilation(Solid triangle of the drivetrain).

Obviously because it damages the PFM circuits.

Twinstar is correct if memory serves.

All I would add is that I was once told by one of the tech reps that it was predominately a characteristic of the earlier short shafts that were a bit lighter in design hence easier to damage. I've never heard of one of the beefier ones being damaged, still, follow the manual! :ok:

The explanation given to me was that the shaft would behave like a skipping rope during an overspeed but would normally return to shape after the event.
However the damage would manifest itself as hairline cracks along the shaft midway between the splined ends i.e at the point of maximum whip.
Hence a requirement for a magnaflux NDT inspection.

I suppose that if the overspeed was large enough then it might indeed assume the shape of a banana, but then you wouldn't need an NDT!!!

I guess Gordy would have pictures.

During autorotation the shaft is under tension from the drive belts being engaged.