Ken Powell wrote:
I have been working on a similar motor mount crossbracing arrangement
as you described in your earlier post today. As you know I am working on the
firewall-forward for the RV-4 along with Mike Wills.
This is what I am attempting (will it provide adequate crossbracing???):
I am going to use the front cover from a 85 SE (w/13b) so I can use the front
motor mount on this cover to bolt 1/2" tubing that will extend ~ 5" past the
right side of the engine and another tube that runs from this point to the
center housing engine mount. Note that the intersection of these tubes will
have a motor mount 'rubber' installed. This forms a triangle that is bolted
to the engine. Next insert a piece of 1/2" tubing from the top left
motor/airframe mount across the engine compartment to the tip of the triangle
formed in the previous step. The last step is to insert 1/2" tubing from
this new engine mount position to the upper right airframe and the lower
right airframe mounts. This creates a 3 sided triangle in the motor mount
that is bolted to the airframe. Note that we now have a triangulated
crossbrace running across the engine compartment that mounts to the engine
thru a 5th motor mount rubber. This should effectively crossbrace the engine
against side loads - is the flex in the rubber motor mount a problem?
This is necessary in order to mount the muffler under the footbox.
This allows the radiator to be mounted under the engine; it will be level
with the top of the footbox and slope downward toward the front of the engine
(this radiator location is why such an elaborate crossbracing scheme). The
cowling will be pressurized. The stock oil cooler will be mounted on the
spark plug side of the engine in a fore and aft configuration and the exhaust
air will exit thru the right side of the cowling thru louvers. This will
also allow 31" exhaust pipes. You will not believe how tight everything is
in a fuselage only 24.5" across. I am attempting to emulate Steve Beckham's
RV-4, but no one seems to know the size of his radiator or how he mounted it.
BTW, my mockup uses a radiator 15.75" x 17.5" x 2" at this time. I have to
have a muffler; I already have poor hearing without the abuse of an unmuffled
rotary.
Will this work or am I wasting my time?
Ken Powell
The lateral brace above the rad below the engine is why I suggested tilting
the rad up at the front instead of up at the rear. Up at the rear means
the lateral brace wants to go through the rad. Why not mount the muff
above the foot box and out the side? I Would also move the motor mounts
forward and up to a 1/2 plate around the flywheel in front of the rear
end housing. This will give you more room for the rad and rubber bushing
flex.
Where are the RV4 gear legs?
Paul Lamar
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