[NSRCA-discussion] Outrunners and structural failures

[Jerry Budd]

Actually credit for finding that link should properly be given to 
Chris Atwood, Don Atwood's son (that and Google - it's the first link 
when you search on "whirl flutter").  Chris sent me an email with the 
link suggesting it might be a possible causal factor in the mishap. 
I had been considering "whirl flutter" but the info Chris sent along 
with additional info I've uncovered in researching the phenomenon has 
me pretty well convinced that it's the root cause.

For those that are interested in what happened I'm planning on 
writing something up with a lot more detail, but not tonight - way 
too late to stay up and do that (besides, I have to get up early and 
go walk around in the desert and see if I can find my motor and 
battery pack!).

Suffice to say, Abbra#2 is now officially retired after 10-1/2 
flights.  Here's some photos of the aftermath:

http://209.221.206.182/~jbudd/Photos/Abbra%20Mishap/Abbra%20Mishap.html

Thx, Jerry


>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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-- 
___________
Jerry Budd
Budd Engineering
(661) 722-5669 Voice/Fax
(661) 435-0358 Cell Phone
mailto:jerry at buddengineering.com
http://www.buddengineering.com