How to fix a broken prop
If the blade is snapped off close to the hub (most common place to break) it's a s simple as drilling a small hole in the blade and the hub and super glue a small piece of brass wire between them. I've had a couple of repairs I had to do that way and none have come apart again. If the break is in mid-blade, the choices are pretty narrow. Best bet is to cast another good blade or find (or cast) another entire prop.
US Army MP Corps combat veteran Operation Desert Shield/Desert Storm
Depending on the type of break, there are a couple of ways to do it. If the break is jagged, and the pieces fit together perfectly, the added area of the jagged parts would allow CA glue to give a strong bond. If the break is fairley clean, the best way to fix it would be to drill a small hole in each piece, use a thread a small shaft between the holes, and use CA glue on both the shaft and the broken surfaces. I have done this on several of my planes and it will provide a very strong bond.