X-Mozilla-Keys:
norm doty wrote:
hi guys, im really confused.
why dont we use a frame or bed mount directly bolted to the firewall like
everyone else's airplane. then put the cushions between the motor and mount.
this way we dont have the other problems that seem to be developing.
norm & monda
cozy IV #202
ford v-6 powered
Paul wrote:
There are plenty of examples of bed mounts on the ACRE NL web site.
http://home.earthlink.net/~rotaryeng/
The idea with this mount is it is somewhat simpler to build than a bed
mount as the rotary in general does not have suitable motor mounts built
in
like an aircraft engine. It is much easier just to bolt a few tubes
to it and put the rubber biscuits someplace else. The best place is the
firewall because all you need is about a 1-1/2 inch hole and the
firewall
itself serves as part of the mount. There is also an advantage in that
the loads going into the firewall are not as concentrated as they
are with bolt hard points. They are fed into the firewall over
an area of about a three inch diameter circle. This becomes a large
advantage for a composite airplane as the materials used are not
as hard as those used in metal airplanes.
snips....
norm doty wrote:
well thats what i thought, so i put 2 extra layers of unt where the landing
gear attachec to the fuse, now its a real bear to get the gear into place.
im just saying that 1 change no matter how inocent sounding has
ramifications later on down the line.
btw the post i got said 3" holes not 1.5".
but for a 1.5" hole i think youd need at least 4.5" sq. alum slug in the
firewall.
The slug is not reguired norm as you are not compressing the hard point
with
a large bolt. The only thing in contact with the fiberglass and plywood
is rubber. PL
and when you add more and wider glass for the attach points you stiffen it
up, if it gets too stiff instead of flexing when required it will take the
load until it snaps or something its attached to snaps.
Fiber glass is not, by nature, a stiff material. It is much more
flexible than
aluminum and way more flexible than steel or carbon fiber. No way are
you going to feed loads into it with rubber mounts to cause a brittle
failure. PL
thats why i used a bed mount on the ford and would also on the mazda.
ive had two(2) mazda engines snap their glass mounts and go to the bottom of
the river thru the hull's of the racing boats i was running. both engines
after salvaging from the river(fresh water) ran fine.
norm
I think you had another problem there norm. The mounts were
probably just not strong enough.
You don't have to use this type of firewall mounts. We have many
examples
of a bed type mounts using the Questair Venture system. The advantage
of that system is it will easily fit any year Mazda engine and it gets
the rubber parts away from the conducted heat of the engine. It also
gives
a softer mounting as the loads on the rubber bushings are less and
most of the motor mount tubes are not subjected to the vibration of
the engine directly.
This last point may be over rated as Perry Mick has a bunch
of long skinny tubes supporting his duct; as in ducted fan, directly
connected to his 13B.
Paul Lamar
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