Adapter plate failed !!!

[PA1195]

Re: Adapter plate failed !!!

I have heard many times about the metal prop being possible issue but I don't so.

I bet the prop hub and rear flange is comparable to say an O-200 flange.

Will measure one tomorrow.

Hmmm, good. Please note any surfacing differences, for example finish and chamfering of offset surface intersections like around the holes...does this suggest that the SAE 0 hub, for the tapered crank, is dimensionally similar to the SAE 1, for the flanged crank, in lateral flange and adapter/prop interference fit and component thickness?

There's also the centerline dimensional fit between the tapered adapter and the internal spec of the prop. Clamp all you want front to back...if the C/L clearance is too loose then what? Only speculation here.

GN from Alaska.

Gary

Re: Adapter plate failed !!!

I have heard many times about the metal prop being possible issue but I don't so.

I bet the prop hub and rear flange is comparable to say an O-200 flange.

Will measure one tomorrow.

[PA1195]

Re: Adapter plate failed !!!

Good analysis Dave...any more from me is way above my knowledge. But I have been known to observe and speculate with the best at times. Part of my former work life I suppose.

I suggest Eddie and his mechanic Fred allow some more picture taking so we can document the event for future reference and continued airworthiness. It would also be a positive move to capture the adapter and maybe have someone who knows about these matters examine it and offer an opinion.

I did note (see the pic again) that the edges of the lightening holes were relatively un-chamfered. I have been led to believe that can create a focus for local stress as I see mechanics taking care to round the edges of stuff. Perhaps whatever surface hardening or anti-corrosion layer is there would be compromised by later machining (?).

EDIT: I wonder if these adapters were initially designed for wooden props and no starter adapters...would adding a metal prop and an adapter complicate things?

Gary

Re: Adapter plate failed !!!

Interesting Gary, thanks.

My conjecture has been that the points that you noted were nearly centered on the the lightening holes and that they were the start of the crack.

The corrosion that you noticed may reinforce my conjecture.

The reason that I take that path of thought is because I imagined the outer portion of the hub (where the bolts are) as the rim of a bike wheel.

Then I imagine the next portion inward toward the center (where the lightening holes are) as the portion of a bike wheel where the spokes are and the "spoke" as being the metal between the lightening holes.

So then I imagine that if the hole in the ring gear plate has a diameter that is large enough such that the edge of that hole contacts the hub at a point that is adjacent to or outboard of the innermost edge of lightening hole (where the crack "point" is) then maybe something odd happens.

Maybe the entire prop load is transferred to the hub center thru the "spokes" which are not as well braced as they would be when a prop alone was installed and the hub is acting more nearly like a rim of bolts connected to a center than a round plate.

If the suspected activity took place one might expect the flexing of the spokes to result in a crack starting at the most inboard point of the lightening hole.

Sorry for all the words, hope it is discernible, picture is worth a thousand words, I may have used that many!

Having seen little of it I was interested in your observation of the cracks.

No doubt there are other possibilities.

Thanks for the observations, Dave.

[PA1195]

Re: Adapter plate failed !!!

If you look at Eddie's pic above pay particular attention to the separation pattern and exposed cracks. Each hole has a pointed separation; the exposed cracks I saw on the actual unit were oxidized, not shiny, and displayed a layer of brown (corrosion?). There was surface fretting on the adapter>starter gear interface (haven't seen the gear itself yet) and ring marks on the bolts (possibly from twisting from removal of the prop). I assume the prop had the rear internal spacer bushings but didn't see if it did.

I'd guess the cracks had some time to corrode as they developed; whatever time it takes to do that. I'd also guess the assembly may have lost fastener torque over some unknown period that allowed things to eventually go bad.

Gary

Re: Adapter plate failed !!!

I flew my BC12D Wednesday and had read this thread before that so I looked for ways to check the back of the hub during pre-flight inspection.

Turns out to be quite easy.

You can see the back of the prop hub by opening and lifting the top cowl on either side and looking forward thru the hole in the nose bowl.

Very easy, might need so cleaning tools like cloth, tooth brush, butter spreader to scrape with...

Dave

[mike bc12d]

Re: Adapter plate failed !!!

Awhile back i had a taper crank overhauled and the man at the shop asked if i already had my prop which i did not and his advise for the taper shaft engines was to use a wood prop only his theory was the weight of the metal prop and the power pulses are what caused the cracking in the shafts on these engines at the keyway area. Not this particlier problem but one to throw out.

[PA1195]

Re: Adapter plate failed !!!

The previous prop may have been longer than recommended Eddie but who knows why and what happened, just like all this thread. Don't beat yourself up...continued airworthiness is a shared and often foggy experience. Your alive and aware..."pay attention" a 26,000 hr pilot said when asked by me how he'd survived. The rest is FAR's and locating and hiring the best you can for maintenance.

The issue is what the owner has as responsibilities versus the maintenance person. Choose wisely is simple to say but that takes more than most owner/operator/pilots know. We're all still learning.

Gary

[ERicter]

Re: Adapter plate failed !!!

What if the previous prop was not certified for this craft??

Throw another twist to the tale. Thanks for all.
FYI. Another adapter has been found in anchorage by my mech. Am going to check prop out.

To most of these questions I do not know the answers, Gary knows more than I do. He is correct on prop. I leave it up to mech. But I am learning for sure. I can not help but think that my preflight was not good enuf!!! Will be putting more torque on prop, will find out how much is acceptable, I always pushed and pulled, like one old pilot said as we were gathered around the Craft, "Congratulations, this will make you a better pilot". I will tighten up the prefilight, I take responsibility for this one, I believe it was there before takeoff and didn't find it.

[ERicter]

Re: Adapter plate failed !!!

What if the previous prop was not certified for this craft??

Throw another twist to the tale. Thanks for all.
FYI. Another adapter has been found in anchorage by my mech. Am going to check prop out.

To most of these questions I do not know the answers, Gary knows more than I do. He is correct on prop. I leave it up to mech. But I am learning for sure. I can not help but think that my preflight was not good enuf!!! Will be putting more torque on prop, will find out how much is acceptable, I always pushed and pulled, like one old pilot said as we were gathered around the Craft, "Congratulations, this will make you a better pilot". I will tighten up the prefilight, I take responsibility for this one, I believe it was there before takeoff and didn't find it.

[PA1195]

Re: Adapter plate failed !!!

Bolt torque? For discussion and not being an A&P I looked up what I could in the most recent C-85 Overhaul Manual I have, and both Sensenich and McCauley's data on prop torque for the SAE 0 tapered crankshaft that I could find.

Continental's O/H Manual calls for 200-220 in/# or 16.7-18.3 ft/# for the SAE 0 tapered crank.
McCauley lists 25-30 ft/# but that may be for a SAE 1 flanged crank as I couldn't find a specific listing for the SAE 0.
Sensenich lists 23-23 ft/# for their SAE 0 tapered crank installation.
Taylorcraft lists 65-75in/# but I assume it's for a wooden prop in their Service Manual subject to crushing.

Once the hub is mounted to the prop I can't see where the differences these torque values are that critical for metal props...it's a bolt torque that sets a pre-tension stress value on the bolt and nut fasteners and a compression value for the mated components. However if initially under tightened or if a loose condition develops through wear between adjacent components, then unwanted movement may occur and stresses develop.

It may be wrong so please correct as required.

Gary

[Ragwing nut]

Re: Adapter plate failed !!!

yeah, that's not normal failure for those. You either had a bolt torque related failure or at some point in its life that hub had been in an accident.

[PA1195]

Re: Adapter plate failed !!!

This plane with the C-85 upgrade: http://gallery.taylorcraft.org/main....3332&g2_page=1

Gary

Re: Adapter plate failed !!!

Yes I agree it needs to be examined, and the how of best to do that is out of my frame of reference and training. I suggested to Eddie he have the prop looked at for conformity (maybe as you noted via TCDS compliance plus balance and pitch). The other components...hub assembly, starter gear, and crank runout would be good to look at.

Having it done with his mechanic's agreement is important.

I guess a question needs to be asked: Where would someone find similar reports of failure? I looked on the FAA's "broken or defective stuff reports" but couldn't bring up anything regarding the failed A-3745 part.

And yes going forward safety is #1 even if it takes some form of suggested or mandatory inspection procedure or interval. If it doesn't depart the plane a broken part and excessive vibration can create a hazard in flight and a distraction to the plane's occupants. Think "auto rough" over bad terrain or water.

EDIT: I believe Eddie has a McCauley 1A90 round tip @ 71/42. It's Item 7 in TCDS A-696 I think so's that ok for a C-85 with tapered crank?

Gary

I assumed it was an A65, was that a bad assumption?

[astjp2]

Re: Adapter plate failed !!!

I see another AD in the works......