jbudd
Posts: 42
Joined: 12/6/2002
From: Quartz Hill,
CA, USA
Status: offline
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quote:
ORIGINAL: shannah
After re-reading Jerry's post a few times, I think my failure may have been the same as his shaft failure. I noticed that the pin had left an imprint on the dualsky prop adapter, so a similar issue may have been at fault. My motor snapped out of there cleanly and pulled the nose ring with it.
Steve, after looking at your photo of the shaft in the spinner it's clear to me this was a motor shaft failure, same as what happened to my 12T. Given that the loads put on the airframe from such a failure are going to be similar at times to that of a thrown prop blade all bets are off as to whether a firewall mounted motor would better protect the airframe. However, since you'd be using the rear shaft prop adapter you won't have the problem of the hole in the shaft so it's a moot point. 
quote:
Oh well, I'll probably never know for sure. But, one thing is for certain, no more nose mounted and unsupported outrunners for me. I am wondering whether a firewall mounted motor is going to be any better. Do these things need to be supported at both ends no matter what?
I don't see the need to support the front of a rear mounted out-runner as the loads are spread out over a greater portion of the structure (assuming your firewall is very stiff and securely attached to the fuselage). Basically what the firewall does is provide mechanical leverage to transfer the inertial loads from the prop/motor into the outer skin of the fuselage. Front mounted those loads are concentrated into a smaller area that's also weaker (all those cooling air holes in the nose) with minimal mechanical leverage so the attachment loads are higher at the fuselage skin. A rear support (when front mounted) also spreads the loads out over two locations reducing the loads being transfered into the fuselage skin considerably (not to mention the benefit of the mechanical leverage it provides).
FYI - A couple of years ago Jon Carter had an electric Angels Shadow that had a factory installed rear support brace for his Hacker C50 in-runner (which is considered mandatory by all who use them). The rear support wasn't robust enough and failed on his first or second flight. You should have seen it, it nearly ripped the nose off his plane before he got the power pulled off. My point is, it's not just an out-runner problem, it's just that nobody considers only front mounting an in-runner so you nearly never hear of it being a problem with them.
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Thx, Jerry
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RE: Dualsky 6360-12T props - 
