What can you tell me about polishing my prop and spinner?
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Technical Editor:
If you polish your prop, you will need to commit to doing repetitive polishing in order to preserve the prop’s surface finish, and prevent corrosion pitting. There are some additional considerations as well. For example, bare aluminum is treated with an Alodine solution to help protect the prop from corrosion, and to create a better bond for paint. Polishing will remove the Alodine, along with any remaining prop paint.
This is particularly true of the leading edge, which really needs to be wiped with LPS-2 after each flight (whether polished or painted), if you want to prevent the erosion-triggered pitting corrosion. That’s what you are seeing when you go out to the plane in the morning and see what looks like little white specks that disappear when you run your finger over them. Those corrosion pits can drive a need for excessive edge dressing (filing), which ruins prop balance and shortens prop life.
Unfortunately, to the best of my knowledge there is nothing in the way of a clear coating that will hold up on the leading edge or the thrust face (aft side of the blade). Not even the 2-part epoxy paint that is applied by a prop shop (and the OEM) will hold up there for long. You can try keeping the whole prop wiped lightly with LPS-2, then just clean it and lightly re-polish it, prior to flights when you need to have it looking good. I would think that this would prevent surface etching, but I have not tried it. I do know that the LPS-2 will positively prevent corrosion for weeks on end.
To wrap up, the polish job is unlikely to survive the prop’s first visit to a prop overhaul shop/FAA Repair Station. As far as I have found, none of our props have OEM approval for a polished finish. Each prop manufacturer provides a series of Service Bulletins that spell out what has to be done to a prop during overhaul, in order for the shop to classify the repair as an overhaul. One of those SBs provides instructions for surface treatment and coatings for preservation of the aluminum. No reputable shop will take the risk with the FAA of releasing a prop as Overhauled without complying will ALL of the applicable SBs. They would be risking their shop license if they did. For the same reason, they will all decline to provide prop polishing during overhaul.
As an aside related to the Hartzell constant-speed props that have the original hub subject to the eddy-current inspection, this is why you need to be careful with terminology. You can send the prop to a shop for ‘re-sealing’ (new o-rings) or repair, and they can do it and return the prop with the original hub. But if you send the prop in for overhaul, they will be forced to install the latest ‘B-hub’, in order to release the prop as overhauled. This is despite the fact that the applicable Airworthiness Directive provides three options for compliance; the ECI, an A-hub, or a B-hub. The manufacturer’s Service Bulletins call for replacement during overhaul if the hub is not a B-hub, and the shop will be forced to comply.
There were a few props on some antique/classic planes that came from the manufacturer with a polished finish. If the manufacturers of those props did not subsequently issue revised SBs regarding surface finish, and a prop shop has the approved data to service those props (they are included in their Repair Station authorizations), then the prop shop can legally restore the polished finish on an OH prop. I’m afraid that none of our Aero Center aircraft props fall into that category.
Here is a link to an FAQ on spinner polishing:
Spinner Polishing