[NSRCA-discussion] Outrunners and structural failures

[Chris Moon]

Chad:
    I have seen 1/4" aircraft ply to cf flex plate to soft mounts used 
for nose ring setups.  All have had failures.  We had some suspicion 
after my first failure (soft mounted) that a solid mount would solve the 
problem. It didn't.  The soft mount should work just as well as the 
rigid setup as long as you have a back support. But as of now, I am not 
aware of anyone who has done this with an outrunner.


Chris



Chad Northeast wrote:
> 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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>>  
>>
>>     
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