Adapter plate failed !!!

[Guest]

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 !!!

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

[Guest]

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 !!!

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

[astjp2]

Re: Adapter plate failed !!!

The ones that I have seen that were cracked in the keyway was because of improper torqueing. Tim

[Ragwing nut]

Re: Adapter plate failed !!!

Ring marks are from what suspect was some type of spacer and the prop was not properly seated to the flange of the hub. You are correct that the cracks are not fresh and had been developing for quite some time. I find it interesting at this point there are no more pics posted and that there may be something else going on that may have been questionable in this installation. The more I look at it the sketchier it gets.

[Guest]

Re: Adapter plate failed !!!

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

Here is what I found today.

---------C90/O200 late crank------Tapershaft Hub

Hub o.d. ----------2.25"-----------2.25"
Flange o.d. --------5.5"------------5.2"
Hub length ---------1" ------------3.86"
flange thickness ---.28" ----------.18"


hub info
diameter of inner most edge of lightening holes =>2.93" (see picture)

prop info
i.d. of hole in prop => 2.23"
i.d of chamfer on rear face of prop. => 2.87" (see picture)

[PA1195]

Re: Adapter plate failed !!!

Eddie the OP may post more pics if asked for what's of interest. Note it here somewhere or send him a personal request.

The Hamp starter ring gear assembly may be the unknown (it goes between the forward face of the adapter flange and the rear of the prop face by using longer bolts).

Can we assume it hasn't been involved with some previous hub flange failures? If not, then torque, prop fit to the tapered crank adapter, or uneven prop balance and pitch may be issues. With the adapter in place and the prop moved forward on the hub is there sufficient contact to stabilize the unit? Just some random questions.

Gary

[ERicter]

Re: Adapter plate failed !!!

Just checking in again, been normal Alaska summer and work till 10 up at 530. Life is good. Will get back with you guys when I know more, Mech. Is away to airshow and will be back Monday. Will let him see what you all have said. Been building an airstrip for Tcraft (hopefullY) have 1000 ft by 100ft cleared, work in progress, just have to get Gary over there to give it his blessing.

Eddie

[ERicter]

Re: Adapter plate failed !!!

Just checking in again, been normal Alaska summer and work till 10 up at 530. Life is good. Will get back with you guys when I know more, Mech. Is away to airshow and will be back Monday. Will let him see what you all have said. Been building an airstrip for Tcraft (hopefullY) have 1000 ft by 100ft cleared, work in progress, just have to get Gary over there to give it his blessing.

Eddie

[PA1195]

Re: Adapter plate failed !!!

My blessing would be a herd of grass eating goats or geese...never become a slave to your creations, like a runway and airpark...for example Eddie International Airport with bed and breakfast. Goat and goose omelets with feather beds and a commanding view of Alaska?

Your best mechanic (Fred's seen it all) will have a fix I'm sure and all will be revealed in time.

Gary

[ERicter]

Re: Adapter plate failed !!!

So the latest on the plate, one was found and bought and was put under the inspection of manga flux and couple of mech and was decided not to use. Maybe one small crack, and wallered out holes etc. We are trying to locate a new one. Fred contacted the FAA about the situation after a discussion and not sure what will become of that. As of right now trying to get a new adapter plate and get the Lady back in the air, I am looking forward to it. The starter assembly is under suspicion.

Eddie

[PA1195]

Re: Adapter plate failed !!!

Hi Eddie, sorry the new adapter failed inspection. There has to be more available somewhere but hopefully tested and tagged as airworthy. If not then eventually a conversion to a flanged crankshaft may be needed. The flanged one that came out of my engine may still be with the former owner or Custom Aircraft Engines in Palmer.

I'd consider the following as an owner/operator. The experienced mechanics here may have better suggestions:

1. Contact the current holder of the starter STC and ask about continued maintenance instructions and any know issues after other installations. They may know of a source for adapters as well.
2. Ask for previous service difficulty or malfunction/defect reports regarding the flange adapter, starter, or in a combination of both. The FAA should have them available.
3. Try to determine the time in service of both the adapter and starter, and whether any prior damage was recorded or inferred in the logs reflecting unusual or unexpected maintenance.
4. Inspect the prop hub and propeller. Make sure the prop is within manufacturer's specs.

Hopefully all involved will work to resolve the problem so you can safely fly soon.

Gary

[Guest]

Re: Adapter plate failed !!!

So the latest on the plate, one was found and bought and was put under the inspection of manga flux and couple of mech and was decided not to use. Maybe one small crack, and wallered out holes etc. We are trying to locate a new one. Fred contacted the FAA about the situation after a discussion and not sure what will become of that. As of right now trying to get a new adapter plate and get the Lady back in the air, I am looking forward to it. The starter assembly is under suspicion.

Eddie

There is a new one on Ebay for $600. Actually there are 3 on Ebay. Try Barsntormers too.

[astjp2]

Re: Adapter plate failed !!!

I have 3, 2 at the shop and 1 in my spare parts pile at home...

Note: FAA announced Emergency AD to all owners of Continental A-65 engine with tapered flange crankshaft. The engines must be removed from service until deemed safe as per instruction described and approved per the administrator. Further action will be pending upon further investigation!

Sorry, I can see it happening now with the panic mode that the FAA has for 70+ year old airplane....