[NSRCA-discussion] Outrunners and structural failures

[Jerry Stebbins]

Chad we are getting ready to try the EVO in the spinner mount. My guess is 
the location of the prop relative to the rear mount-plus all the prop 
related influences is the primary generation source. With the prop right at 
the mount (in the spinner) there would be a very moment short arm. I guess I 
need to look at Jerry B's whirl flutter info trail and see what I find. Hope 
he finds his lost parts and then has time to educate us on what he has 
found.
Jerry S
----- Original Message ----- 
From: "Chad Northeast" <chad at f3acanada.org>
To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
Sent: Saturday, August 12, 2006 10:46 PM
Subject: Re: [NSRCA-discussion] Outrunners and structural failures


> 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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