The Murphy Builders Site

I was reinforcing the firewall the other day and getting ready to drill the
flanges when I took a look at the construction pictures on the CD-ROM version
of the manual. Lo and behold, the flanges were facing aft! I talked with
Brian Godden at MAM about this, and he said that a builder had accidentally
installed his firewall backward, and -- Felix Culpa! -- he discovered an
unexpected benefit, a better cooling engine. Brian thought it might actually
be advisable to install this way.

I can understand how this would improve the exiting airflow. But I imagine it
would make cowl installation a bear. And add a half-inch of forward moment.
Brian suggested that it might be a good idea to put this one out for
discussion.

Jeffrey Steenson
E714





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Same issue for Rebel builders.

On 9/6/02 4:38 AM, STEENSON wrote to MURPHY-REBEL:

-> I was reinforcing the firewall the other day and getting ready to drill the
-> flanges when I took a look at the construction pictures on the CD-ROM
version
-> of the manual. Lo and behold, the flanges were facing aft! I talked with
-> Brian Godden at MAM about this, and he said that a builder had accidentally
-> installed his firewall backward, and -- Felix Culpa! -- he discovered an
-> unexpected benefit, a better cooling engine. Brian thought it might
actually
-> be advisable to install this way.
->
-> I can understand how this would improve the exiting airflow. But I imagine
it
-> would make cowl installation a bear. And add a half-inch of forward
moment.
-> Brian suggested that it might be a good idea to put this one out for
-> discussion.
->
-> Jeffrey Steenson
-> E714
->
->





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Hi Jeffery
Most Rebels tend towards being nose heavy so I don't think moving
everything in front of the firewall forward 1/2" is going to help things at
all. Daryl once told me that there wasn't really any horsepower
restrictions on the rebel but the limiting factor was the bending moment of
heavier engines. Has he done a stress analysis on the extra lenghth? If
you're planning to use the factory cowling are you going to need a
different lenghth prop extension? If so is one the right lenghth even
available?
Theres a whole lot of variables that determine how well an engine cools
itself. I don't think you can say that it cools better unless you tried the
exact same instalation with the firewall both ways or had a large number of
planes to compare.
Personally I think that the factory is jumping the gun a bit on this one
and if I was building another plane I'd stick with the tried and true until
the factory builds another demo plane and test flies it.
Drew Dalgleish

At 04:39 AM 9/6/2002 -0800, you wrote:

Same issue for Rebel builders.

On 9/6/02 4:38 AM, STEENSON wrote to MURPHY-REBEL:

-> I was reinforcing the firewall the other day and getting ready to drill

the

-> flanges when I took a look at the construction pictures on the CD-ROM
version
-> of the manual. Lo and behold, the flanges were facing aft! I talked

with

-> Brian Godden at MAM about this, and he said that a builder had

accidentally

-> installed his firewall backward, and -- Felix Culpa! -- he discovered an
-> unexpected benefit, a better cooling engine. Brian thought it might
actually
-> be advisable to install this way.
->
-> I can understand how this would improve the exiting airflow. But I

imagine

it
-> would make cowl installation a bear. And add a half-inch of forward
moment.
-> Brian suggested that it might be a good idea to put this one out for
-> discussion.
->
-> Jeffrey Steenson
-> E714
->
->



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Hi Jeff, I don't feel that the 1/2 moment will be somthing to even think about, but the cooling issue is. I ended up fairing the bottom of my firewall to cover the flange and the bottom tube of my conical mount. It made almost 35degf difference in cht's. I would also look at the interference created with the flange and the motor mounts overlap with the firewall facing aft. (It might not be an issue). Anyway, keep at it, it's worth it!! Curt N97MR



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