Flying quite a bit out of grass airfields, the back of my prop has started to develop a rather rough surface, so much so that going over it with a cloth is virtually impossible. I guess caused by small stones/lrage sand crystals drawn in and tearing out a bit of the surface.
Does it make sense / does it have an expected effect on the performance to smoothen the surface (with 320 or 400 grit ?) and apply some satin finish spray paint ?
I am NOT looking for extra work, will only do if effective. I have not noticed a decrease in performance (yet – and it might be a gradual decline which is discovered over longer periods only?).
Thanks for any input.
What is your prop made of? Metal, wood, composite? I’d be wary of painting due to balance. I’ve rubbed the metal leading edge of a composite prop with very gentle abrasive.
Massive aluminium.
Mmmh never thought of balancing issues with some spray paint… applied sparingly at least
Would definitely need more than light rubbing to get a smooth surface
I don’t think any paint will work against stones and those are the only real risk.
The ~3mm deep dings are your worst long-term enemy, and one gets them from a lot of hard runway places where nobody wants to buy a broom because it would benefit somebody else 
I heard of a leading edge protector which you stick on; not sure how well it works and whether it does anything on aluminium. On wood, the case is much easier to see.
Mmmh need to rephrase.
Dings in the leading edge is a different aspect. Have only1 or 2 of those.
My question is about a rough back of the prop.
And the paint is not to protect against stones, but to make it look better after possibly sanding it.
Question thus – is the sanding of a rough back of prop worth the effort ?
I would certainly keep it sanded and smooth. Remember how you cut glass, it only needs a small scratch with a diamond to break it clean.
The reason why prop blades are made from pure aluminium is to almost totally prevent that sort of failure mode – crack propagation.
Metals generally don’t fail in the way glass does.
I suggest you try to mark a sheet of scrap aluminium sheet with a graphite pencil and see what happens after a while.
Corrosion of aluminium caused by the effect graphite has on the oxide layer has absolutely nothing in common with brittle fracture of glass….
Furthermore, ‘scrap aluminium sheet’ would probably consist of hardenable aluminium alloy (20xx series) rather than soft (nearly pure) aluminium used in props. The former has a greater ultimate tensile strength when undamaged, but a lot more ways to fail or get damaged than the latter.
