REBEL O-320 ENGINE MOUNT, HELP!!!
Posted: Fri Feb 17, 2012 5:38 pm
I had a look at Wyne O'Shea's firewall fix and a memory came to mind. Last
summer I visited a Rebel builder who had the engine mount bolted on the wall
ready to hang his gorgeous Canadian Aero O-320. He said the mount was
purchased from Murphy and designed for the O-320. What I did not like about
it were the two uppermost tubes extending from the upper firewall bolts with
the other end hanging in the breeze. I could easily flex each of the tubes
with one hand and see the wall flex and this is supposed to support a 160 hp
engine!!! Wow!!!! All the other tubes were triangulated or crossbraced to
others and they did not flex.
The argument was that the upper tubes would stop flexing once tied to the
engine. I did not buy that because the junction at the engine is not rigid,
it is through flexing rubber mounts. These tubes can never be rigid like the
rest. I would always expect to see them spread out a bit and cause the
firewall to locally bulge out.
Wayne's photos don't show the engine end of the mount so I don't know where
the wall flex was comming from on his installation but with the mount I
described above there should be a way to address the problem at the source
and tie the flexing tubes to other ones. Perhaps a firewall fix would not
even be required then although direct pulling loads out of the wall at this
location must be very high just from the moment generated by this heavy
engine.
I understand that once in flight the tubes will not flex nearly as much as
when bouncing on the ground (or water) but still that would not be a good
excuse for leaving the tubes flex.
Can anyone shed some light on this? Has anyone done any beefing up of this
flexing mount and how did it effect the firewall?
Paul Kucera
Rebel builder, 453R
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summer I visited a Rebel builder who had the engine mount bolted on the wall
ready to hang his gorgeous Canadian Aero O-320. He said the mount was
purchased from Murphy and designed for the O-320. What I did not like about
it were the two uppermost tubes extending from the upper firewall bolts with
the other end hanging in the breeze. I could easily flex each of the tubes
with one hand and see the wall flex and this is supposed to support a 160 hp
engine!!! Wow!!!! All the other tubes were triangulated or crossbraced to
others and they did not flex.
The argument was that the upper tubes would stop flexing once tied to the
engine. I did not buy that because the junction at the engine is not rigid,
it is through flexing rubber mounts. These tubes can never be rigid like the
rest. I would always expect to see them spread out a bit and cause the
firewall to locally bulge out.
Wayne's photos don't show the engine end of the mount so I don't know where
the wall flex was comming from on his installation but with the mount I
described above there should be a way to address the problem at the source
and tie the flexing tubes to other ones. Perhaps a firewall fix would not
even be required then although direct pulling loads out of the wall at this
location must be very high just from the moment generated by this heavy
engine.
I understand that once in flight the tubes will not flex nearly as much as
when bouncing on the ground (or water) but still that would not be a good
excuse for leaving the tubes flex.
Can anyone shed some light on this? Has anyone done any beefing up of this
flexing mount and how did it effect the firewall?
Paul Kucera
Rebel builder, 453R
*----------------------------------------------------*
The Murphy Rebel Builders List is for the discussion
between builders and owners of Murphy Rebel aircraft.
Archives located at:
http://www.dcsol.com/murphy-rebel/lists/default.htm
*----------------------------------------------------*
-----------------------------------------------------------------
List archives located at: https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe: rebel-builders-unsubscribe@dcsol.com
List administrator: mike.davis@dcsol.com
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