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[rebel-builders] engine mount design

Posted: Sun Feb 19, 2012 8:50 pm
by Ken
Rob

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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[rebel-builders] engine mount design

Posted: Sun Feb 19, 2012 8:50 pm
by Aero Propulsion Technolog
Hi!
I am frequentely concepting engine mounth mainely for Rotax engine,
To optimize CG I have my customer weight their project without engine, when
I have those number I find the CG of the engine with it's mass, from there
it's easy to fix aircraft CG where I wanted to be on the cord of the wing in
the case of Rebel I use 20% of the wing cord.
Hope it help.
Daniel.

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Ken
Sent: 10 mai 2011 12:59
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] engine mount design

Rob

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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[rebel-builders] engine mount design

Posted: Sun Feb 19, 2012 8:50 pm
by Hank & Vickie Balch
Have you checked with William Wynne? I know he was working on a
Corvair/Rebel setup when I talked to him at Sun N Fun.

Hank
307R

On Tue, May 10, 2011 at 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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[rebel-builders] engine mount design

Posted: Sun Feb 19, 2012 8:50 pm
by schaumr
Hank, Ken, and others

Thanks for your replies.

William Wynne and I have been chatting about the Rebel/Corvair combination
since I bought the Rebel kit in 2006, and even as recently as last January.
Recent favorable press about the corvair engine in Sport Aviation and
Kitplanes magazines has him overloaded with requests from Zenith
enthusiasts, so I imagine he hasn't had much time to develop a new engine
mount for an airframe he doesn't readily have access to. So, since I just so
happen to have a Rebel in the garage, I've decided to tackle the job myself
(as we builders so often do). :) One thing William does provide is "stock"
engine mount "trays" that are already set up and finish-welded to accept the
engine block. This is a big help in completing the project.

Through research, and responses from all of you, I am coming to the
realization that there is a fudge-factor in the placement of the engine fore-
aft, as long as the thrust-line (and to a lesser extent, prop hub location) is
maintained. Consequently, building the jig for the mount is actually a
relatively straightforward procedure, and I am making steady progress. In
fact, I'm willing to bet it's easier to mock it up on a standing fuselage than to
work off paper diagrams and dimensions.

I should be lighting up the torch by the end of the month, and I might even
reverse-engineer a metal jig from my completed mount in case others end up
choosing the corvair for their Rebels.

So if anyone has additional comments or information regarding engine mount
design for the Rebel, please go ahead and pass it on. As they say,
knowledge is power.
Cheers,
Rob


On 5/10/2011 5:13 PM, cwfarm1@gmail.com wrote to rebel-builders:

-> Have you checked with William Wynne? I know he was working on a
-> Corvair/Rebel setup when I talked to him at Sun N Fun.
->
-> Hank
-> 307R
->
-> On Tue, May 10, 2011 at 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
-> >
-> >
-> >
-> > -----------------------------------------------------------------
-> > 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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[rebel-builders] engine mount design

Posted: Sun Feb 19, 2012 8:50 pm
by Ken
I think you are on the right path.
Exact placement is not very critical so adjust it as necessary to suit
your installation. I added a few ounces by using .058 tubing to make it
easier to weld for a first timer. Richard Finch has a couple of books on
aircraft welding for about $20. if you need more.
Enjoy the end result
Ken
snip
So if anyone has additional comments or information regarding engine mount
design for the Rebel, please go ahead and pass it on. As they say,
knowledge is power.
Cheers,
Rob

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