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Cox Engine of The Month
Inspect your Cox black 5x3 propellers
Page 1 of 1
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.
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.
Ken Cook- Top Poster
- Posts : 5591
Join date : 2012-03-27
Location : pennsylvania
Re: Inspect your Cox black 5x3 propellers
great warning and advice Ken. thanks. I will check my props as you advised in future. I always wear sunglasses when starting and running engines as some level of protection, but had never thought about how to check the prop.
Yabby- Platinum Member
-
Posts : 711
Join date : 2021-06-08
Location : Yorke Peninsula South Australia
Re: Inspect your Cox black 5x3 propellers
I've worn eyeglasses for decades. I have "Lazy Eye" (my left). A condition where, at birth; the brain recognizes only one eye to focus. The other eye has blurred-vision, but is otherwise perfectly healthy. If I had or rather; if my parents had forced me to wear an eye-patch when I was little, the condition could have been corrected. Once past early childhood, those chances are less. Later in life; an eye doctor told me that he hadn't known of a case that was corrected past age 12. He also told me that; although I didn't need a corrective lens for my "good" eye.. that I should consider wearing eyeglasses with Plano lenses.. to protect my good eye. "Loosing sight in that eye will change your life dramatically.." he said.
Fast forward a few years.. and I started wearing "readers" to correct my near-sight.. and eventually needed a prescription lens. Contact lenses are "off the table" though.. because they don't offer the protection of eyeglasses.
I always wear safety-glasses with side-shields whenever I run my model engines.. and when using tools.
Fast forward a few years.. and I started wearing "readers" to correct my near-sight.. and eventually needed a prescription lens. Contact lenses are "off the table" though.. because they don't offer the protection of eyeglasses.
I always wear safety-glasses with side-shields whenever I run my model engines.. and when using tools.
Re: Inspect your Cox black 5x3 propellers
Glad no one got hurt ,Thanks i will pre flight check mine next time running one .
getback- Top Poster
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Posts : 10355
Join date : 2013-01-18
Age : 67
Location : julian , NC
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