Been through this with the soob but I've never seen the kind of numbers
you would need. Installed engine weights are generally above what folks
think so working backward is still only guessing at the bare airframe c
of g. And of course there are all those mods/paint/etc on the airframe.
Your engine c of g may well be aft of the Lyc. engine c of g. unless you
have a heavy flywheel at the prop or a metal prop. Nevertheless from
what I've seen I'd mount the prop in the same place as the Lyc or
farther forward if you need the firewall clearance. Then plan to put the
battery on the firewall. Personally I'd aim for a farther aft c of g
than most Rebels come out at anyway. That also gives the option of a
electric variable prop in the future and a little better cruise with
less likelihood of needing nose up trim in cruise. I imagine someone
will respond to Rob and give some rotax912 numbers to compare. I do know
that Jim moved his 912S several inches forward and is happier than some
912's mounted per the manual.
For my mount I should have made the jig at least a sixteenth inch larger
than the firewall hole spacing as it definitely shrunk as the welds
cooled. I gas welded it which may have helped extra shrinkage but it was
a very solid steel jig. Also I recommend the same green or white epoxy
primer that you used on the airframe. The light color won't hide any
cracks that might develop and it is better than most paints for stopping
rust.
Ken
On 5/10/2011 10:17 AM, schaumr@dcsol.com wrote:
Hello all,
I am in the process of designing the engine mount for my rebel/corvair engine
combination. I am using the MAM prescribed bolt hole locations on the
firewall, and currently building a wood jig a-la-EAA for the fitting and welding
tasks.
I have the document (from the plans) that describes the position of the O-
235 on the rebel which provides the thrust line and the position of the prop
hub for this engine. However, the corvair could weigh about 20-50 lbs less
than a O-235, so I would really like to be able to calculate exactly where the
engine needs to be from the firewall.
Does anyone know if there are more detailed data/calculations for the rebel
that I can use to calculate appropriate CG placement of my engine?
Thanks
Rob
Rebel 786 / Connencticut
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