ORIGINAL: Tired Old Man
Thanks!
Pe:
Since I was in a destructive mood today, and the fact another propeller was tossed with a different failure mode, I got to hacking up some propellers.
The prop you depicted is the same make as two that failed. The difference between yours and one of the ones that failed is ...nothing. Pics of a stock prop core are attached.
Over the counter production propeller with a fiberglass core. It just looks like carbon under casual inspection. The lay up has no "tow" to limit compression. The core strength is determined by the resin content. A 'dry' lay up (does happen) and core compression resistance is severely compromised. That was one of the failure factors in the prop in my first post. I'm starting to like the wood core composite props better. Just don't hunker down on the screws.
Now that I'm thinking about it, a PT or Air Models prop hasn't been failed yet. I hate it when one is missed. Got another mission
The ones I have used so far all had sound hubs, with a hub core of polyester, filled with glass fibres and talcum powder. This gives the prop hub an excellent compression resistance, even when hot.
A dry lay-up that results in any form of delamination should be cause for warranty. This particular manufacturer has the hubs marked, so they can trace any error to the guy who made the prop.
I do not like wood cores so much. Wood compression strength is a variable that can hardly be controlled, unless it is resin impregnated under vacuum, or laminated using very thin hardwood plies. If inferior wood is used in the core of a carbon prop, failure can't be seen like in standard wood props, and a dry lay-up willcause delams as well.
I felt destructive too, so anoher two crash damage props was inspected. Clearly visible are the sound evenlayup, and the extra ring in the core, where the bolt holes are positioned. This particular 3-blade prop had the drilling done very tight (3D milling 4.9mm, M5 bolts). I normally drill 0.5mm oversize. In this case, all 6 bolts max torqued to M5 8.8 quality, at 10Nm. I normally use only 5 - 6 Nm on M5 prop bolts. With wood 3Nm, which already causes some crushing.