Inspect your Cox black 5x3 propellers

Yesterday my son and I were dusting off some cobwebs and flew a little 1/2A combat. Norvel .061 powered, not really 1/2A but we use them because these can fly equal to high powered ball bearing .049's. Regardless, I prefer bushed engines because if you have a ground strike with a ball bearing engine, your going to wipe it out if you restart it and go back in the air. A bushed engine can quickly be flushed with a syringe of fuel whereas a ball bearing engine pushes the debris into the bearing cage.

         In general, most of us have experienced the dreaded small stress cracks in the Cox black props. For those unaware, flex the prop hard back on itself and look closely to reveal spider webs of crack perpendicular to the blade. You can audibly hear this as well when flexed. I usually offer a quick bend prior to running and inspect for both. Yesterday, I didn't do this because I was using a prop I've used for quite some time.

          All went well, both planes up in the air but I heard a vibration coming from one of them and couldn't quite pin point which. Within about a minute and half, a very bad noise came from my son's plane and it essentially came to a complete stall in the air. It made about 1 lap making this noise and he intentionally stuffed it in. Upon landing, one blade was completely missing while the other essentially fell off when I flexed it. No damage other then the prop thankfully. The point is, due to the planes sitting for some time, I spent a fair amount of time with my head around those props tuning them. That could've resulted in a major injury.