SR Chevy Cowl/Cooling design and cabin heat

Mike Kimball · Post by **Mike Kimball** » Sat Feb 18, 2012 9:50 am

I heartily agree with the frequent comments about keeping the subject line
appropriate for list submissions so I have changed it with this response,
but I still want to thank the folks that responded with Rebel firewall
dimensions.

I found some photos of the Rotax V6 installation on the MAM website. It
appears as if the inlet is indeed a giant NACA scoop and the radiator
appears to be mounted horizontally clear back against the firewall and seems
to be the only outlet. It doesn't look ducted. It looks as if the air just
comes in the NACA scoop and wants to get out and the only way out is through
the radiator. I wonder about general air circulation around the rest of the
engine compartment in this configuration. Of course, the pictures aren't
very revealing and there could be a lot you can't see in the pictures.
Interestingly, the ROTAX site shows the radiator way up front. I have read
that positioning close to the prop isn't the best idea due to the turbulent
air flow and impulses from each prop blade as they pass by. MAM's radiator
position is better but with the NACA scoop directly behind the prop I wonder
if there is still a problem with turbulent air and prop pulses. It wouldn't
look as clean but theoretically it would be better to keep the radiator
where it is, or even farther back, but lower it, placed in it's own scoop
with the inlet farther away from the prop. However, the bottom line is,
does MAM's design work? If it does, I'd like to go that route for the
simplicity and clean look.

I also had another idea. If I mounted the radiator in it's own scoop behind
the firewall on the bottom of the fuselage could I then somehow direct hot
air into the cabin from there or tap off the cooling lines to a separate
heat exchager in the cabin for cabin heat and avoid the already crowded
firewall area to get heat into the cabin? If I could redirect the air from
the scoop outlet into the cabin I could do away with a separate heat
exchanger. But the design would have to be such that I didn't interfere
with the airflow through the radiator.

I was thinking about general air circulation around the rest of the engine
because I was not planning on ducting air to the carburetor. I was going to
just take air in from the engine compartment just like my 1968 Mustang
California Special/GT. I was trying to figure out why I have never
encountered carburetor ice in the many old carbureted cars I have owned,
driving in perfect conditions for carb ice, yet I have encountered carb ice
in airplanes. One thing I came up with is that airplanes duct air from
outside the engine compartment to the carb and old cars do not. (Many new
cars do, but they generally are either throttle body or multi-port
injected.) I was hoping that by taking air in from inside the engine
compartment, combined with the top mounted carb (heat rises) I would not
have to add a carb heat provision. I would be giving up the temperature and
RAM induced air density increase a ducted system would give me but I have
surplus horsepower and I continue to follow the KISS (keep it simple stupid)
philosophy.

Mike Kimball
SR044

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]
Sent: Saturday, December 11, 2004 8:36 PM
To: rebel-builders@dcsol.com
Subject: Re: Rebel firewall dimensions

Mike, you should give MAM a call and ask what they used on the "Rotax" V6
plane... that seems like it should be similar to what you're trying to do
with the V8.

Mike

----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: "Rebel List" <rebel-builders@dcsol.com>
Sent: Saturday, December 11, 2004 2:57 PM
Subject: Rebel firewall dimensions

Can someone tell me what the dimensions are for a Rebel firewall? I'm
trying
to see if the Aircraft Spruce MC-3B nosebowl will work for my Super Rebel.
If the Super Rebel firewall is not much bigger than a Rebel I think it
will
work without looking too funny with a sharp angle from the firewall to the
nosebowl. My Chevy is only about 24" across at the widest and the MC-3B
is
35 inches across. Plus, the PSRU is much smaller in width up where the
nosebowl sits.

Mike

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Nielsenbe · Post by **Nielsenbe** » Sat Feb 18, 2012 9:50 am

For cabin heat why not just run a heater core in the cabin like in a car. It
would be a little extra weight but heat control just like in a car. I am just
asking because some day in a land far far away I plan on doing that.

Brad

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Legeorgen · Post by **Legeorgen** » Sat Feb 18, 2012 9:50 am

Hi Brad,

that is how we heat the cabin on my 912S Rotax Kitfox. Just like a car and
it works great.

Bruce

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Legeorgen · Post by **Legeorgen** » Sat Feb 18, 2012 9:50 am

To heat the cabin just use a computer fan and a small radiator available at
Skystar.com.

Bruce

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Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Sat Feb 18, 2012 9:50 am

Don't forget to run some alum pipes for a rear passenger heater as well
while you're at it ! "

)

----- Original Message -----
From: <Legeorgen@aol.com>
To: <rebel-builders@dcsol.com>
Sent: Sunday, December 12, 2004 8:08 PM
Subject: Re: SR Chevy Cowl/Cooling design and cabin heat

Hi Brad,

that is how we heat the cabin on my 912S Rotax Kitfox. Just like a car

and

it works great.

Bruce

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larry173 · Post by **larry173** » Sat Feb 18, 2012 9:50 am

I found the Rotax Moose on the Rotax site and see that they have changed the
rad to mount on the bottom of the fuselage. It must not have worked with the
naca scoop.

The reason that you don't get carb ice on the Mustang is because it has a
heat riser that directs heat from the exhaust manifold when it gets cold.
You need the same on a carbureted engine whether is automatic or manual.

I checked with Mam and the Moose cowling is one of a kind and they do not
have a mould.

I am putting a V8 in my Moose also I think that the rad mounted under the
engine would work but you would have to use a chin scoop and they are ugly.
I have also seen two rads mounted on the side of the engine by the manifolds
and the air ducted from the nose inlets. Most people are using fans on the
rad to cool the engine during taxiing.

----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: <rebel-builders@dcsol.com>
Sent: Sunday, December 12, 2004 4:23 PM
Subject: SR Chevy Cowl/Cooling design and cabin heat

I heartily agree with the frequent comments about keeping the subject line
appropriate for list submissions so I have changed it with this response,
but I still want to thank the folks that responded with Rebel firewall
dimensions.

I found some photos of the Rotax V6 installation on the MAM website. It
appears as if the inlet is indeed a giant NACA scoop and the radiator
appears to be mounted horizontally clear back against the firewall and
seems
to be the only outlet. It doesn't look ducted. It looks as if the air
just
comes in the NACA scoop and wants to get out and the only way out is
through
the radiator. I wonder about general air circulation around the rest of
the
engine compartment in this configuration. Of course, the pictures aren't
very revealing and there could be a lot you can't see in the pictures.
Interestingly, the ROTAX site shows the radiator way up front. I have
read
that positioning close to the prop isn't the best idea due to the
turbulent
air flow and impulses from each prop blade as they pass by. MAM's
radiator
position is better but with the NACA scoop directly behind the prop I
wonder
if there is still a problem with turbulent air and prop pulses. It
wouldn't
look as clean but theoretically it would be better to keep the radiator
where it is, or even farther back, but lower it, placed in it's own scoop
with the inlet farther away from the prop. However, the bottom line is,
does MAM's design work? If it does, I'd like to go that route for the
simplicity and clean look.

I also had another idea. If I mounted the radiator in it's own scoop
behind
the firewall on the bottom of the fuselage could I then somehow direct hot
air into the cabin from there or tap off the cooling lines to a separate
heat exchager in the cabin for cabin heat and avoid the already crowded
firewall area to get heat into the cabin? If I could redirect the air
from
the scoop outlet into the cabin I could do away with a separate heat
exchanger. But the design would have to be such that I didn't interfere
with the airflow through the radiator.

I was thinking about general air circulation around the rest of the engine
because I was not planning on ducting air to the carburetor. I was going
to
just take air in from the engine compartment just like my 1968 Mustang
California Special/GT. I was trying to figure out why I have never
encountered carburetor ice in the many old carbureted cars I have owned,
driving in perfect conditions for carb ice, yet I have encountered carb
ice
in airplanes. One thing I came up with is that airplanes duct air from
outside the engine compartment to the carb and old cars do not. (Many new
cars do, but they generally are either throttle body or multi-port
injected.) I was hoping that by taking air in from inside the engine
compartment, combined with the top mounted carb (heat rises) I would not
have to add a carb heat provision. I would be giving up the temperature
and
RAM induced air density increase a ducted system would give me but I have
surplus horsepower and I continue to follow the KISS (keep it simple
stupid)
philosophy.

Mike Kimball
SR044

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]
Sent: Saturday, December 11, 2004 8:36 PM
To: rebel-builders@dcsol.com
Subject: Re: Rebel firewall dimensions

Mike, you should give MAM a call and ask what they used on the "Rotax" V6
plane... that seems like it should be similar to what you're trying to do
with the V8.

Mike

----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: "Rebel List" <rebel-builders@dcsol.com>
Sent: Saturday, December 11, 2004 2:57 PM
Subject: Rebel firewall dimensions

Can someone tell me what the dimensions are for a Rebel firewall? I'm
trying
to see if the Aircraft Spruce MC-3B nosebowl will work for my Super
Rebel.
If the Super Rebel firewall is not much bigger than a Rebel I think it
will
work without looking too funny with a sharp angle from the firewall to
the
nosebowl. My Chevy is only about 24" across at the widest and the MC-3B
is
35 inches across. Plus, the PSRU is much smaller in width up where the
nosebowl sits.

Mike

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Ken · Post by **Ken** » Sat Feb 18, 2012 9:50 am

I would be very hesitant to assume that experience with the specific
carbs that are on a 912 is transferable to other carbs or engines as far
as carb icing liklihood.

I could not come up with a design for a 912 type of cowl that I felt
confident would provided sufficient cooling for 150 hp and be moderate
or low drag. The actual cooling on the liquid circuit of a 912 is pretty
modest after you subtract the air cooled load and the oil cooler load.
No doubt there is someone who could make it work but I also dislike the
high drag brute force air exits which is the same problem many Lycs
have. It helps keep drag low if the air does no or little bending from
inlet to outlet of course. The main thing is making it work regardless
of drag but it is always nice to get both.

Ken

Bob Patterson wrote:

Hi Mike !

Take a good look at the cowling Murphy supplies for the Rebel
for the Rotax 912 - the radiator mounts horizontally under the engine,
with a sealed plenum above it, and a duct under it formed by the bottom
of the cowl, leading back to the outlet at the back rear. This works
VERY well, and is reasonably clean. No problems with prop disturbing
airflow, and no fancy NACA scoop ! ;-)

While you <could> arrange a flapper & ducting to use for heat,
just using an automotive water heater would be cleaner and safer -
no chance of fumes getting in ! Brian Robinson (www.v8seabee.com)
leaves everything on the engines, and has automotive heating AND
air conditioning !!! He has supplied a mount & engine with re-drive
setup for a Moose - it's installed already, and cowl work is progressing.
I've heard comments that his price is too high - BUT, from the money
and time some folks have ALREADY spent TRYING to DIY, I'd say he
offers a very good deal !!! For those who just want to get flying,
I wouldn't even think about doing it yourself !!!! :-)

Of course, for those who like to tinker - go ahead !! :-)

You're on the right track with the carb heat - the Rotax in the
Murphy cowl NEVER had a problem with carb ice !! We had an OAT
( an indoor/outdoor remote from Radio Shack ;-) ) installed near the
carbs, and the temp in there was always about 30 degrees Centipede -
NO fear of ice !! You MAY run into an inspector who insists you
have a heating setup, though - I think ALL Canadian inspectors now
demand some mechanism for providing carb heat..... :-(

.............bobp

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Barnhart · Post by **Barnhart** » Sat Feb 18, 2012 9:50 am

Mike,

Will be putting my radiator for water and oil directly under the oil pan of
the engine. The prop hub is going to be in the same place as the data for
the Lycoming. The inlet will be about 25% of the outlet side. How deep the
radiator is depends on your speed and how much room you have. You want to
keep at least 10 inches of clearance from the outlet for best results. Some
don't use the thermostat, some go with cowl flaps or build them into the
design of the cowl. I can get you more data if you want. The other problem
is if you can have that much weight in the engine compartment. This system
works. There are lots of people out there to make cabin heaters. Ed Klepis
in Ky. has a unit and will doing my radiators.
Klepeis, Ed
E-mail Address(es):
techwelding@comcast.net

I was underwhelmed with the cooling on Rotax V-6.

Barny
MGDQ 20bt SR 103

----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: <rebel-builders@dcsol.com>
Sent: Sunday, December 12, 2004 3:23 PM
Subject: SR Chevy Cowl/Cooling design and cabin heat

I heartily agree with the frequent comments about keeping the subject line
appropriate for list submissions so I have changed it with this response,
but I still want to thank the folks that responded with Rebel firewall
dimensions.

I found some photos of the Rotax V6 installation on the MAM website. It
appears as if the inlet is indeed a giant NACA scoop and the radiator
appears to be mounted horizontally clear back against the firewall and

seems

to be the only outlet. It doesn't look ducted. It looks as if the air

just

comes in the NACA scoop and wants to get out and the only way out is

through

the radiator. I wonder about general air circulation around the rest of

the

engine compartment in this configuration. Of course, the pictures aren't
very revealing and there could be a lot you can't see in the pictures.
Interestingly, the ROTAX site shows the radiator way up front. I have

read

that positioning close to the prop isn't the best idea due to the

turbulent

air flow and impulses from each prop blade as they pass by. MAM's

radiator

position is better but with the NACA scoop directly behind the prop I

wonder

if there is still a problem with turbulent air and prop pulses. It

wouldn't

look as clean but theoretically it would be better to keep the radiator
where it is, or even farther back, but lower it, placed in it's own scoop
with the inlet farther away from the prop. However, the bottom line is,
does MAM's design work? If it does, I'd like to go that route for the
simplicity and clean look.

I also had another idea. If I mounted the radiator in it's own scoop

behind

the firewall on the bottom of the fuselage could I then somehow direct hot
air into the cabin from there or tap off the cooling lines to a separate
heat exchager in the cabin for cabin heat and avoid the already crowded
firewall area to get heat into the cabin? If I could redirect the air

from

the scoop outlet into the cabin I could do away with a separate heat
exchanger. But the design would have to be such that I didn't interfere
with the airflow through the radiator.

I was thinking about general air circulation around the rest of the engine
because I was not planning on ducting air to the carburetor. I was going

to

just take air in from the engine compartment just like my 1968 Mustang
California Special/GT. I was trying to figure out why I have never
encountered carburetor ice in the many old carbureted cars I have owned,
driving in perfect conditions for carb ice, yet I have encountered carb

ice

in airplanes. One thing I came up with is that airplanes duct air from
outside the engine compartment to the carb and old cars do not. (Many new
cars do, but they generally are either throttle body or multi-port
injected.) I was hoping that by taking air in from inside the engine
compartment, combined with the top mounted carb (heat rises) I would not
have to add a carb heat provision. I would be giving up the temperature

and

RAM induced air density increase a ducted system would give me but I have
surplus horsepower and I continue to follow the KISS (keep it simple

stupid)

philosophy.

Mike Kimball
SR044

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]
Sent: Saturday, December 11, 2004 8:36 PM
To: rebel-builders@dcsol.com
Subject: Re: Rebel firewall dimensions

Mike, you should give MAM a call and ask what they used on the "Rotax" V6
plane... that seems like it should be similar to what you're trying to do
with the V8.

Mike

----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: "Rebel List" <rebel-builders@dcsol.com>
Sent: Saturday, December 11, 2004 2:57 PM
Subject: Rebel firewall dimensions

Can someone tell me what the dimensions are for a Rebel firewall? I'm
trying
to see if the Aircraft Spruce MC-3B nosebowl will work for my Super

Rebel.

If the Super Rebel firewall is not much bigger than a Rebel I think it
will
work without looking too funny with a sharp angle from the firewall to

the

nosebowl. My Chevy is only about 24" across at the widest and the MC-3B
is
35 inches across. Plus, the PSRU is much smaller in width up where the
nosebowl sits.

Mike

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Ken · Post by **Ken** » Sat Feb 18, 2012 9:50 am

Mike Kimball wrote:

I heartily agree with the frequent comments about keeping the subject line
appropriate for list submissions so I have changed it with this response,
but I still want to thank the folks that responded with Rebel firewall
dimensions.

I found some photos of the Rotax V6 installation on the MAM website. It
appears as if the inlet is indeed a giant NACA scoop and the radiator
appears to be mounted horizontally clear back against the firewall and

seems

to be the only outlet. It doesn't look ducted. It looks as if the

air just

comes in the NACA scoop and wants to get out and the only way out is

through

the radiator. I wonder about general air circulation around the rest

of the

engine compartment in this configuration.

I would seal the duct to the rad and provide a little bit of separate
airflow around the engine. Then you can control things better and reduce
drag. I exited the separate engine compartment air through tapered flush
side cowl exits (acceleration ramps) since that was the most conveniant
area for me with reasonably low pressure. I expect to reduce the flow
even more after I document temperatures.

Of course, the pictures aren't
very revealing and there could be a lot you can't see in the pictures.
Interestingly, the ROTAX site shows the radiator way up front. I have

read

that positioning close to the prop isn't the best idea due to the

turbulent

air flow and impulses from each prop blade as they pass by. MAM's

radiator

position is better but with the NACA scoop directly behind the prop I

wonder

if there is still a problem with turbulent air and prop pulses.

No. As long as you are back a couple (3) of prop blade chord widths
behind the prop disk you are fine. For ground cooling it can help a lot
to have to the inlet far enough from the spinner that the prop can blow
some air into it. The Rotax has a fairly large oil cooler and a good
size intercooler on the blown version. I had to look twice to see which
was which.

It wouldn't
look as clean but theoretically it would be better to keep the radiator
where it is, or even farther back, but lower it, placed in it's own scoop
with the inlet farther away from the prop. However, the bottom line is,
does MAM's design work? If it does, I'd like to go that route for the
simplicity and clean look.

I've done the separate scoop thing but only because I did not have room
for the rad in the cowl. If done carefully it should be possible to have
lower drag than an air cooled engine with either of these methods. When
they first flew it at Sun'n fun they claimed that the cooling was
working wonderfully. I'd be interested to know if they still feel that
way but I rather suspect they got it right.

I also had another idea. If I mounted the radiator in it's own scoop

behind

the firewall on the bottom of the fuselage could I then somehow direct hot
air into the cabin from there or tap off the cooling lines to a separate
heat exchager in the cabin for cabin heat and avoid the already crowded
firewall area to get heat into the cabin? If I could redirect the air

from

the scoop outlet into the cabin I could do away with a separate heat
exchanger. But the design would have to be such that I didn't interfere
with the airflow through the radiator.

That has been done successfully but you may have to control the
rad air exit temperature with a cowl flap.

I was thinking about general air circulation around the rest of the engine
because I was not planning on ducting air to the carburetor. I was

going to

just take air in from the engine compartment just like my 1968 Mustang
California Special/GT. I was trying to figure out why I have never
encountered carburetor ice in the many old carbureted cars I have owned,
driving in perfect conditions for carb ice, yet I have encountered

carb ice

in airplanes. One thing I came up with is that airplanes duct air from
outside the engine compartment to the carb and old cars do not. (Many new
cars do, but they generally are either throttle body or multi-port
injected.) I was hoping that by taking air in from inside the engine
compartment, combined with the top mounted carb (heat rises) I would not
have to add a carb heat provision. I would be giving up the

temperature and

RAM induced air density increase a ducted system would give me but I have
surplus horsepower and I continue to follow the KISS (keep it simple

stupid)

philosophy.

Actually you do not have to give up the ram pressure, I believe the
entire cowl can be pressurized a bit and provide more rise than the
Lycoming external inlet. Ideally you will minimise airflow out of the
cowl in order to minimise drag. I had an interesting small discussion
this week about throttle body icing on port injected Soobs. They ice at
low throttle behind the butterfly in humid conditions and mild
temperatures if the 5/16" coolant line through the TBI plugs. Apparently
the part throttle air pressure drop and resultant cooling is sufficient
to form ice. Reports of automotive carb ice are very dependant on
location but I wouldn't dream of flying a carby without real carb heat.
I do intend to fly my port injected engine without carb heat.

I haven't flown mine yet so can't claim success but I did a lot of
research. Interestingly the only non-conflicting info I found was the
stuff written during the war. A lot of the modern rules of thumb and
popular advice on cooling is ambiguous. They often won't explain why one
system works and the next apparently identical setup doesn't. For fun I
based my inlet and outlet on wartime streamline work and it shouldn't
work according to many current homebuilt theories ;) I'm looking
forward to trying it out! Cooling is definately something to spend some
time on...

Ken

Mike Kimball
SR044

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Ken · Post by **Ken** » Sat Feb 18, 2012 9:50 am

Issues include - are you comfortable with hot water in the cabin
- will you need fresh heated air to control the
humidity and window fogging or will you just recirculate cabin air
- air through the firewall should have a fire shutoff
whereas air up through the belly may not
- does the engine require an always flowing heater line
to wash the thermostat and are you using a thermostat
- can you find or make an aluminum core heater or stand
the weight of a copper unit and are you comfortable with a copper heater
core in an otherwise all aluminum cooling system
- will you use a water bypass valve on the heater core for summer if
the core is in the cabin

Despite having a rad under the cockpit I went with a heater core on the
forward side of the firewall but with a stainless guilotine air shutoff
on the firewall.

Ken

Nielsenbe@aol.com wrote:

For cabin heat why not just run a heater core in the cabin like in a car. It
would be a little extra weight but heat control just like in a car. I am just
asking because some day in a land far far away I plan on doing that.

Brad

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Bob Patterson · Post by **Bob Patterson** » Sat Feb 18, 2012 9:50 am

Hi Mike !

Take a good look at the cowling Murphy supplies for the Rebel
for the Rotax 912 - the radiator mounts horizontally under the engine,
with a sealed plenum above it, and a duct under it formed by the bottom
of the cowl, leading back to the outlet at the back rear. This works
VERY well, and is reasonably clean. No problems with prop disturbing
airflow, and no fancy NACA scoop ! ;-)

While you <could> arrange a flapper & ducting to use for heat,
just using an automotive water heater would be cleaner and safer -
no chance of fumes getting in ! Brian Robinson (www.v8seabee.com)
leaves everything on the engines, and has automotive heating AND
air conditioning !!! He has supplied a mount & engine with re-drive
setup for a Moose - it's installed already, and cowl work is progressing.
I've heard comments that his price is too high - BUT, from the money
and time some folks have ALREADY spent TRYING to DIY, I'd say he
offers a very good deal !!! For those who just want to get flying,
I wouldn't even think about doing it yourself !!!! :-)

Of course, for those who like to tinker - go ahead !! :-)

You're on the right track with the carb heat - the Rotax in the
Murphy cowl NEVER had a problem with carb ice !! We had an OAT
( an indoor/outdoor remote from Radio Shack ;-) ) installed near the
carbs, and the temp in there was always about 30 degrees Centipede -
NO fear of ice !! You MAY run into an inspector who insists you
have a heating setup, though - I think ALL Canadian inspectors now
demand some mechanism for providing carb heat..... :-(

.............bobp

-------------------------------orig.-------------------------
On Sunday 12 December 2004 04:23 pm, Mike Kimball wrote:

I heartily agree with the frequent comments about keeping the subject line
appropriate for list submissions so I have changed it with this response,
but I still want to thank the folks that responded with Rebel firewall
dimensions.

I found some photos of the Rotax V6 installation on the MAM website. It
appears as if the inlet is indeed a giant NACA scoop and the radiator
appears to be mounted horizontally clear back against the firewall and
seems to be the only outlet. It doesn't look ducted. It looks as if the
air just comes in the NACA scoop and wants to get out and the only way out
is through the radiator. I wonder about general air circulation around the
rest of the engine compartment in this configuration. Of course, the
pictures aren't very revealing and there could be a lot you can't see in
the pictures. Interestingly, the ROTAX site shows the radiator way up
front. I have read that positioning close to the prop isn't the best idea
due to the turbulent air flow and impulses from each prop blade as they
pass by. MAM's radiator position is better but with the NACA scoop
directly behind the prop I wonder if there is still a problem with
turbulent air and prop pulses. It wouldn't look as clean but theoretically
it would be better to keep the radiator where it is, or even farther back,
but lower it, placed in it's own scoop with the inlet farther away from the
prop. However, the bottom line is, does MAM's design work? If it does,
I'd like to go that route for the simplicity and clean look.

I also had another idea. If I mounted the radiator in it's own scoop
behind the firewall on the bottom of the fuselage could I then somehow
direct hot air into the cabin from there or tap off the cooling lines to a
separate heat exchager in the cabin for cabin heat and avoid the already
crowded firewall area to get heat into the cabin? If I could redirect the
air from the scoop outlet into the cabin I could do away with a separate
heat exchanger. But the design would have to be such that I didn't
interfere with the airflow through the radiator.

I was thinking about general air circulation around the rest of the engine
because I was not planning on ducting air to the carburetor. I was going
to just take air in from the engine compartment just like my 1968 Mustang
California Special/GT. I was trying to figure out why I have never
encountered carburetor ice in the many old carbureted cars I have owned,
driving in perfect conditions for carb ice, yet I have encountered carb ice
in airplanes. One thing I came up with is that airplanes duct air from
outside the engine compartment to the carb and old cars do not. (Many new
cars do, but they generally are either throttle body or multi-port
injected.) I was hoping that by taking air in from inside the engine
compartment, combined with the top mounted carb (heat rises) I would not
have to add a carb heat provision. I would be giving up the temperature
and RAM induced air density increase a ducted system would give me but I
have surplus horsepower and I continue to follow the KISS (keep it simple
stupid) philosophy.

Mike Kimball
SR044

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]
Sent: Saturday, December 11, 2004 8:36 PM
To: rebel-builders@dcsol.com
Subject: Re: Rebel firewall dimensions

Mike, you should give MAM a call and ask what they used on the "Rotax" V6
plane... that seems like it should be similar to what you're trying to do
with the V8.

Mike

----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: "Rebel List" <rebel-builders@dcsol.com>
Sent: Saturday, December 11, 2004 2:57 PM
Subject: Rebel firewall dimensions

Can someone tell me what the dimensions are for a Rebel firewall? I'm
trying
to see if the Aircraft Spruce MC-3B nosebowl will work for my Super
Rebel. If the Super Rebel firewall is not much bigger than a Rebel I
think it will
work without looking too funny with a sharp angle from the firewall to
the nosebowl. My Chevy is only about 24" across at the widest and the
MC-3B is
35 inches across. Plus, the PSRU is much smaller in width up where the
nosebowl sits.

Mike

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Ken · Post by **Ken** » Sat Feb 18, 2012 9:50 am

You might find this read and conclusion interesting if you haven't seen it.
http://www.sdsefi.com/air41.htm
Ken

larry173 wrote:

I found the Rotax Moose on the Rotax site and see that they have changed the
rad to mount on the bottom of the fuselage. It must not have worked with the
naca scoop.

The reason that you don't get carb ice on the Mustang is because it has a
heat riser that directs heat from the exhaust manifold when it gets cold.
You need the same on a carbureted engine whether is automatic or manual.

I checked with Mam and the Moose cowling is one of a kind and they do not
have a mould.

I am putting a V8 in my Moose also I think that the rad mounted under the
engine would work but you would have to use a chin scoop and they are ugly.
I have also seen two rads mounted on the side of the engine by the manifolds
and the air ducted from the nose inlets. Most people are using fans on the
rad to cool the engine during taxiing.

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Mike Kimball · Post by **Mike Kimball** » Sat Feb 18, 2012 9:50 am

Heater core in the cabin just like a car was my first thought. All those
other thoughts came later. After all your comments and more thought I think
the ideal system would be to have the heater core and the fan in the cabin.
(At first I was trying to avoid coolant in the cabin since I can still smell
leaked coolant in my Mustang's carpet when it's warm outside.) Then I would
just need two holes in the firewall for the coolant hoses. But looking at
the available space on the cold side of the firewall I don't know if there
is enough room. I am excited about the comment on using a computer fan. I
had been envisioning much larger fans as found on cars. I could probably
even rig a rheostat to vary the fan speed. I will also check out the heater
core sources mentioned by a couple of contributors. I would like to run
dedicated ducting to the back seat area but right now I'm putting that in
the "too hard and I want to get flying" box. So I am going to progress with
the idea of mounting the fan and heater core in the middle of the firewall,
inside, with an air box with five outlets. One pointing right down the
middle to hopefully send warm air towards the back, two outlets to the side
for the front passengers, and two outlets for the windshield defrost. If
humidity from using inside air is a problem I'll have to cross that bridge
when I come to it. By circulating air from inside the cabin that should
pretty much eliminate the possibility of CO.

As for the radiator - I think I'll progress with mounting it below the oil
pan somewhere. I think the comment about ducting air to it and then having
a separate system for general air circulation around the engine is good.
About the "tapered flush side cowl exits (acceleration ramps)", do you have
any pictures Ken? It's probably similar to the ones used on the RV-6A in
the article you pointed out for me to read. Thanks.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
Nielsenbe@aol.com
Sent: Sunday, December 12, 2004 3:32 PM
To: rebel-builders@dcsol.com
Subject: Re: SR Chevy Cowl/Cooling design and cabin heat

For cabin heat why not just run a heater core in the cabin like in a car.
It
would be a little extra weight but heat control just like in a car. I am
just
asking because some day in a land far far away I plan on doing that.

Brad

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Ken · Post by **Ken** » Sat Feb 18, 2012 9:50 am

Actually I'm not sure what the RV6 did but I have uploaded two of my old
pix. The backs (inside?) of the side ramps continues forward inside the
cowl about 6 or 8" so hopefully the exit air picks up speed as it nears
the exit. The rads in the nosebowl thing on the RV6 has packaging
advantages but it doesn't seem to work for everyone and it is a far from
optimum solution. There is not enough room (length) for reliable
pressure recovery in the intake duct and the intake is closer than
usually desireable to the prop among other things.

The opening just below my spinner is ducted to the heater core and there
is a 5" muffin fan to assist while on the ground to make sure the
windshield stays clear. It was the highest power 5" muffin that I could
put my hands on and I think it draws about 0.8 amp.

Yes I'd have also put the rad below the oil pan if I could have fit it
in but now that it is done I do like not having the rad in the way when
working on the engine. I had to exit the exhaust out the far side of the
cowl to keep it away from the cooling air intake.

Ken

Mike Kimball wrote:

Heater core in the cabin just like a car was my first thought. All those
other thoughts came later. After all your comments and more thought I think
the ideal system would be to have the heater core and the fan in the cabin.
(At first I was trying to avoid coolant in the cabin since I can still smell
leaked coolant in my Mustang's carpet when it's warm outside.) Then I would
just need two holes in the firewall for the coolant hoses. But looking at
the available space on the cold side of the firewall I don't know if there
is enough room. I am excited about the comment on using a computer fan. I
had been envisioning much larger fans as found on cars. I could probably
even rig a rheostat to vary the fan speed. I will also check out the heater
core sources mentioned by a couple of contributors. I would like to run
dedicated ducting to the back seat area but right now I'm putting that in
the "too hard and I want to get flying" box. So I am going to progress with
the idea of mounting the fan and heater core in the middle of the firewall,
inside, with an air box with five outlets. One pointing right down the
middle to hopefully send warm air towards the back, two outlets to the side
for the front passengers, and two outlets for the windshield defrost. If
humidity from using inside air is a problem I'll have to cross that bridge
when I come to it. By circulating air from inside the cabin that should
pretty much eliminate the possibility of CO.

As for the radiator - I think I'll progress with mounting it below the oil
pan somewhere. I think the comment about ducting air to it and then having
a separate system for general air circulation around the engine is good.
About the "tapered flush side cowl exits (acceleration ramps)", do you have
any pictures Ken? It's probably similar to the ones used on the RV-6A in
the article you pointed out for me to read. Thanks.

Mike

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rickhm · Post by **rickhm** » Sat Feb 18, 2012 9:50 am

A question that I have long pondered is how do you determine the size (widthxheight) of your radiator. There are so many variables here that are hard to predict. Thickness of the radiator, density of cooling fins within the radiator, airflow, etc. I finally concluded you just give it a try and see what you get. A more analytical approach I would prefer. Any thoughts?

-------------- Original message --------------

Actually I'm not sure what the RV6 did but I have uploaded two of my old
pix. The backs (inside?) of the side ramps continues forward inside the
cowl about 6 or 8" so hopefully the exit air picks up speed as it nears
the exit. The rads in the nosebowl thing on the RV6 has packaging
advantages but it doesn't seem to work for everyone and it is a far from
optimum solution. There is not enough room (length) for reliable
pressure recovery in the intake duct and the intake is closer than
usually desireable to the prop among other things.

The opening just below my spinner is ducted to the heater core and there
is a 5" muffin fan to assist while on the ground to make sure the
windshield stays clear. It was the highest power 5" muffin that I could
put my hands on and I think it draws about 0.8 amp.

Yes I'd have also put the rad below the oil pan if I could have fit it
in but now that it is done I do like not having the rad in the way when
working on the engine. I had to exit the exhaust out the far side of the
cowl to keep it away from the cooling air intake.

Ken

Mike Kimball wrote:

Heater core in the cabin just like a car was my first thought. All those
other thoughts came later. After all your comments and more thought I think
the ideal system would be to have the heater core and the fan in the cabin.
(At first I was trying to avoid coolant in the cabin since I can still smell
leaked coolant in my Mustang's carpet when it's warm outside.) Then I would
just need two holes in the firewall for the coolant hoses. But looking at
the available space on the cold side of the firewall I don't know if there
is enough room. I am excited about the comment on using a computer fan. I
had been envisioning much larger fans as found on cars. I could probably
even rig a rheostat to vary the fan speed. I will also check out the heater
core sources mentioned by a couple of contributors. I would like to run
dedicated ducting to the back seat area but right now I'm putting that in
the "too hard and I want to get flying" box. So I am going to progress with
the idea of mounting the fan and heater core in the middle of the firewall,
inside, with an air box with five outlets. One pointing right down the
middle to hopefully send warm air towards the back, two outlets to the side
for the front passengers, and two outlets for the windshield defrost. If
humidity from using inside air is a problem I'll have to cross that bridge
when I come to it. By circulating air from inside the cabin that should
pretty much eliminate the possibility of CO.

As for the radiator - I think I'll progress with mounting it below the oil
pan somewhere. I think the comment about ducting air to it and then having
a separate system for general air circulation around the engine is good.
About the "tapered flush side cowl exits (acceleration ramps)", do you have
any pictures Ken? It's probably similar to the ones used on the RV-6A in
the article you pointed out for me to read. Thanks.

Mike

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