[NSRCA-discussion] Outrunners and structural failures

[Chad Northeast]

Very interesting...and here I was going to get Pletty to make me a front 
mounted 30-10 Evo....I guess there goes that idea :)

What is being used for the front mount?

I have always rear mounted (without a front support), and you can always 
hear some vibration when you get large AOA changes...like in snaps, or 
hard corners with slight rudder application.  Always figured it was the 
prop deflecting and vibrating the motor since is cantilivered so far 
away from the rotational axis.  I had figured a front mount would solve 
this.

I did grab a couple of front mount setups while at the Nats and they all 
felt like they had more movement than my rear mount setup has, which 
surprised me somewhat.

Chad

Chris Moon wrote:

>Several of us have been collecting info on the many (upwards of a dozen) 
>fuse structural failures with people running the larger outrunners.  The 
>common theme is that they are all front mounted to the nose ring without 
>any support at the rear of the motor.  There have been some who have 
>mounted their motors this way that have not had failures, but all that 
>have failed were nose ring mounted without support for the back. Except 
>for one, and that looks like it was a problem with the fuse 
>manufacturer.  In that case (today) the seam split due to a poorly glued 
>seam without good adhesion by the fiberglass seam tape.  The problem 
>seems to be explained by a phenomenon called "whirl flutter" and 
>basically is caused by an outside force causing the prop and motor to 
>oscillate to the point where the structure will fail.  Here is a video 
>of the phenomenon:
>
>http://www.airspacemag.com/ASM/Web/Site/QT/PWFlutter.html
>
>(Thanks to Jerry Budd for the research and video link)
>
>So, if you are planning to use the big outrunners like the Axi or Hacker 
>A60, the evidence is showing that a rear support of some kind is 
>necessary to prevent failure.  I had 2 failures with my A60 set up until 
>I added a rear support.  My first failure was on the 2nd flight and the 
>2nd failure was on the 15th flight (at the NATS).I now have almost 20 
>flight with the rear support and everything seems fine now.  Of course 
>you can also mount the Axi to a firewall and we have not heard of any 
>failures with that set up.  I spoke with Jerry Budd and he is planning 
>to be making a rear support available for the outrunners similar to the 
>one he now makes for the Hacker C50. Please if you are planning on using 
>a front mount outrunner consider the rear support before you get too far 
>along.  I was going to write a KFactor article on this, but it seems 
>like a better idea to get this out more quickly via the mail list.
>
>
>
>Chris Moon
>D5 VP
>
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