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engine cooling
engine cooling
Bob
Yes there are a couple of differences, but minor! The Lyc. has a carb air box
and a slightly higher hump over the starter ring gear. The air intakes and
exit air shoot are about the same as the Cont. cowl. They both bolt to the
same firewall. If there is other differences that i am not aware of then
maybe they should be incorporated into the Lyc. cowling. Bottom line the Lyc.
cowling has as much air going into and out of as the Cont. cowl for a given
speed.
In my opinion a portion of the cooling problems is related to the turbulence
behind the propeller hub and the air intake area( my reason for moving the
prop forward ) air leaks in the baffles, and the exit air air shoot not
extending far enough aft of the firewall causing a reverse air flow back up
into the lower cowl.( my reason for the cowl flap ) Most of the areodynamic
reference books address the above.
I have observed the air flow patterns over about 80% of my Rebel to date and
some of the directions the air flows is amazing.
Steve Sloan 536R
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Yes there are a couple of differences, but minor! The Lyc. has a carb air box
and a slightly higher hump over the starter ring gear. The air intakes and
exit air shoot are about the same as the Cont. cowl. They both bolt to the
same firewall. If there is other differences that i am not aware of then
maybe they should be incorporated into the Lyc. cowling. Bottom line the Lyc.
cowling has as much air going into and out of as the Cont. cowl for a given
speed.
In my opinion a portion of the cooling problems is related to the turbulence
behind the propeller hub and the air intake area( my reason for moving the
prop forward ) air leaks in the baffles, and the exit air air shoot not
extending far enough aft of the firewall causing a reverse air flow back up
into the lower cowl.( my reason for the cowl flap ) Most of the areodynamic
reference books address the above.
I have observed the air flow patterns over about 80% of my Rebel to date and
some of the directions the air flows is amazing.
Steve Sloan 536R
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engine cooling
HI Bob
I do not agreee that the speed cowl is cursed. We talked about this earlier
today, and, if done properly it is not a problem in any way. Do not
appreciate you slamming my airplane.
Brian #328R
-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
Bob Patterson
Sent: Sunday, June 17, 2001 10:23 PM
To: murphy-rebel@dcsol.com
Subject: Re: engine cooling
*-------------------------------------------------------------------------*
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*-------------------------------------------------------------------------*
Hi B & B !!
Gee, 220 degrees isn't much for CHT !! Or is that OIL temp ??
Do you by any chance have that cursed "Speed Cowl" ?? If so,
you will need a LARGER opening at the bottom, and possibly a lip
added at the back. Some have made a hinged bottom to the whole
channel behind the carb, as a 'cowl flap'.
Do you have an oil cooler - it is absolutely necessary !
Don't know ANYONE who has baffled on top - how tight are
you to the tops of the cylinders ???
If you have the speed cowl, make sure that there is no gap
in front of the carb filter, as air entering there will reverse-
pressurize the cowl.
Last thought - if it's a brand-new engine, you will have to
fly it HARD for a couple of hours to seat the rings. Temperatures
will then come down ....
....bobp
PS
One more thought - you might want to check your guages by
putting the temp. probe into a pail of boiling water. It wouldn't
be the first time a guage was inaccurate !! ;-)
-------------------------------orig.------------------------------------
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I do not agreee that the speed cowl is cursed. We talked about this earlier
today, and, if done properly it is not a problem in any way. Do not
appreciate you slamming my airplane.
Brian #328R
-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
Bob Patterson
Sent: Sunday, June 17, 2001 10:23 PM
To: murphy-rebel@dcsol.com
Subject: Re: engine cooling
*-------------------------------------------------------------------------*
The list archives are located at:
http://www.dcsol.com:81/public/default.htm
username: rebel password: builder
*-------------------------------------------------------------------------*
Hi B & B !!
Gee, 220 degrees isn't much for CHT !! Or is that OIL temp ??
Do you by any chance have that cursed "Speed Cowl" ?? If so,
you will need a LARGER opening at the bottom, and possibly a lip
added at the back. Some have made a hinged bottom to the whole
channel behind the carb, as a 'cowl flap'.
Do you have an oil cooler - it is absolutely necessary !
Don't know ANYONE who has baffled on top - how tight are
you to the tops of the cylinders ???
If you have the speed cowl, make sure that there is no gap
in front of the carb filter, as air entering there will reverse-
pressurize the cowl.
Last thought - if it's a brand-new engine, you will have to
fly it HARD for a couple of hours to seat the rings. Temperatures
will then come down ....
....bobp
PS
One more thought - you might want to check your guages by
putting the temp. probe into a pail of boiling water. It wouldn't
be the first time a guage was inaccurate !! ;-)
-------------------------------orig.------------------------------------
At 12:10 PM 6/17/01 -0700, you wrote:
and*-------------------------------------------------------------------------*
The list archives are located at:
http://www.dcsol.com:81/public/default.htm
username: rebel password: builder
*-------------------------------------------------------------------------*
Builders, we just finished our murphy rebel on floats and are having
cooling problems. we are running a 160 horsepower O-320 and can only taxi
for about five minutes at around 1300 rpm and the engine temp will rise to
220 degrees C. we baffled with standard side and rear baffling, but also
ran baffling over the top front of the enging (just behind the fly wheel).
we also cut two reverse scoops in the bottom of the cowling for more air
escape, but haven't tested it yet. we are wondering how the rest of the
builders have baffled their 0-320's and if they ran the baffling over the
top of the engine like we did, or ran it down below the fly wheel and left
the top more open, like Cessna does. if anyone has had cooling problems
*-------------------------------------------------------------------------*has found fixes for them, whether it be with baffling or changes in the
cowling, we would appreciate it if you would let us know.
thanks,
Brian and Brian
_________________________________________________________________
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engine cooling
Brian There was a cessna150 aerobat at the airport here that had the cowlas usual will be greatly appreciated. Do I need to fair the firewall, fair
the inlets?
inlet and firewall faired. It also had a centre baffle down the lenghth of
the case. The engine ran so cool that the owner kept reducing the size of
the intakes until he was left with 2 slits about 1 1/2" tall. This plane
never had any problems even when doing aerobatics. Drew
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engine cooling
Sorry Brian !
I didn't mean to offend ANYONE ! I'm just VERY unhappy with
MY 'speed cowl'.
I'm getting a bit happier now, as I managed to feed the wires
in from the back this week. This locks them in, and eliminates any
possibility of them coming forward and chewing up my prop AGAIN !
I still find it extremely awkward to handle that one huge chunk of
firberglass, instead of just swinging up an aluminum side panel.
Maybe one day. I'll take a hacksaw to it and convert it into 2
hinged panels with aluminum reinforcing strips around the edges !!
I agree - YOUR cowling setup is wonderful compared to mine.
Unfortunately, mine is done according to the manual ! The world
needs to hear about your method - it IS much better...
Brian added aluminum strips to the bottom of his fuselage
to create standoffs to mount the cowl. This gives about a 1" gap
all the way across the back bottom of the cowling, dramatically
increasing the outlet area, AND leaving the cowl 'chute' extending
back behind the firewall. This arrangement seems to work very
well for him, with no cooling problems. It certainly looks a lot
better than the huge hole in the bottom of mine.
.......bobp
-----------------------------orig.----------------------------------------
At 12:39 AM 6/24/01 -0400, you wrote:
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-----------------------------------------------------------------
I didn't mean to offend ANYONE ! I'm just VERY unhappy with
MY 'speed cowl'.
I'm getting a bit happier now, as I managed to feed the wires
in from the back this week. This locks them in, and eliminates any
possibility of them coming forward and chewing up my prop AGAIN !
I still find it extremely awkward to handle that one huge chunk of
firberglass, instead of just swinging up an aluminum side panel.
Maybe one day. I'll take a hacksaw to it and convert it into 2
hinged panels with aluminum reinforcing strips around the edges !!
I agree - YOUR cowling setup is wonderful compared to mine.
Unfortunately, mine is done according to the manual ! The world
needs to hear about your method - it IS much better...
Brian added aluminum strips to the bottom of his fuselage
to create standoffs to mount the cowl. This gives about a 1" gap
all the way across the back bottom of the cowling, dramatically
increasing the outlet area, AND leaving the cowl 'chute' extending
back behind the firewall. This arrangement seems to work very
well for him, with no cooling problems. It certainly looks a lot
better than the huge hole in the bottom of mine.
.......bobp
-----------------------------orig.----------------------------------------
At 12:39 AM 6/24/01 -0400, you wrote:
*-------------------------------------------------------------------------*
The list archives are located at:
http://www.dcsol.com:81/public/default.htm
username: rebel password: builder
*-------------------------------------------------------------------------*
HI Bob
I do not agreee that the speed cowl is cursed. We talked about this earlier
today, and, if done properly it is not a problem in any way. Do not
appreciate you slamming my airplane.
Brian #328R
-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
Bob Patterson
Sent: Sunday, June 17, 2001 10:23 PM
To: murphy-rebel@dcsol.com
Subject: Re: engine cooling
*-------------------------------------------------------------------------*
The list archives are located at:
http://www.dcsol.com:81/public/default.htm
username: rebel password: builder
*-------------------------------------------------------------------------*
Hi B & B !!
Gee, 220 degrees isn't much for CHT !! Or is that OIL temp ??
Do you by any chance have that cursed "Speed Cowl" ?? If so,
you will need a LARGER opening at the bottom, and possibly a lip
added at the back. Some have made a hinged bottom to the whole
channel behind the carb, as a 'cowl flap'.
Do you have an oil cooler - it is absolutely necessary !
Don't know ANYONE who has baffled on top - how tight are
you to the tops of the cylinders ???
If you have the speed cowl, make sure that there is no gap
in front of the carb filter, as air entering there will reverse-
pressurize the cowl.
Last thought - if it's a brand-new engine, you will have to
fly it HARD for a couple of hours to seat the rings. Temperatures
will then come down ....
....bobp
PS
One more thought - you might want to check your guages by
putting the temp. probe into a pail of boiling water. It wouldn't
be the first time a guage was inaccurate !! ;-)
-------------------------------orig.------------------------------------
At 12:10 PM 6/17/01 -0700, you wrote:and*-------------------------------------------------------------------------*
The list archives are located at:
http://www.dcsol.com:81/public/default.htm
username: rebel password: builder
*-------------------------------------------------------------------------*
Builders, we just finished our murphy rebel on floats and are having
cooling problems. we are running a 160 horsepower O-320 and can only taxi
for about five minutes at around 1300 rpm and the engine temp will rise to
220 degrees C. we baffled with standard side and rear baffling, but also
ran baffling over the top front of the enging (just behind the fly wheel).
we also cut two reverse scoops in the bottom of the cowling for more air
escape, but haven't tested it yet. we are wondering how the rest of the
builders have baffled their 0-320's and if they ran the baffling over the
top of the engine like we did, or ran it down below the fly wheel and left
the top more open, like Cessna does. if anyone has had cooling problems*-------------------------------------------------------------------------*has found fixes for them, whether it be with baffling or changes in the
cowling, we would appreciate it if you would let us know.
thanks,
Brian and Brian
_________________________________________________________________
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-----------------------------------------------------------------
engine cooling
Hi Steve !
There's no doubt that there is a lot of interaction between
the prop and the front of the cowling - I was surprised to learn
several years ago just how much computer simulation time a big
company (De Havilland) spends on this area. Moving the prop forward
definitely helps, but can do un-nice things to the c of g, and
the crankshaft, if you're not careful.
Hadn't thought much about extending the air chute. You're
right - I can see how you would get reverse flow there !
Not "A Good Thing"(tm) !! ;-) Looking at Brian Cross's cowling
yesterday really reinforced that thinking - he seems to have the
answer, and all it takes is a few standoff brackets to open up
the bottom of the cowl. Of course, this must be done when building,
before trimming the cowl. (Although I'm tempted to try a retro-fit !)
I'm sure some of the air flows ARE amazing !! I've heard about
some tuft testing results ....
How did you manage to observe 80% of the Rebel ??? With
tufts and a mirror ?? or a video camera taped outside ??? This
could be VERY useful information for all of us !! You certainly
are getting much higher cruise speeds/hp than the rest of us !!
.....bobp
-----------------------------------orig.----------------------------------
At 10:00 PM 6/22/01 EDT, you wrote:
-----------------------------------------------------------------
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-----------------------------------------------------------------
There's no doubt that there is a lot of interaction between
the prop and the front of the cowling - I was surprised to learn
several years ago just how much computer simulation time a big
company (De Havilland) spends on this area. Moving the prop forward
definitely helps, but can do un-nice things to the c of g, and
the crankshaft, if you're not careful.
Hadn't thought much about extending the air chute. You're
right - I can see how you would get reverse flow there !
Not "A Good Thing"(tm) !! ;-) Looking at Brian Cross's cowling
yesterday really reinforced that thinking - he seems to have the
answer, and all it takes is a few standoff brackets to open up
the bottom of the cowl. Of course, this must be done when building,
before trimming the cowl. (Although I'm tempted to try a retro-fit !)
I'm sure some of the air flows ARE amazing !! I've heard about
some tuft testing results ....
How did you manage to observe 80% of the Rebel ??? With
tufts and a mirror ?? or a video camera taped outside ??? This
could be VERY useful information for all of us !! You certainly
are getting much higher cruise speeds/hp than the rest of us !!
.....bobp
-----------------------------------orig.----------------------------------
At 10:00 PM 6/22/01 EDT, you wrote:
*-------------------------------------------------------------------------*
The list archives are located at:
http://www.dcsol.com:81/public/default.htm
username: rebel password: builder
*-------------------------------------------------------------------------*
Bob
Yes there are a couple of differences, but minor! The Lyc. has a carb air box
and a slightly higher hump over the starter ring gear. The air intakes and
exit air shoot are about the same as the Cont. cowl. They both bolt to the
same firewall. If there is other differences that i am not aware of then
maybe they should be incorporated into the Lyc. cowling. Bottom line the Lyc.
cowling has as much air going into and out of as the Cont. cowl for a given
speed.
In my opinion a portion of the cooling problems is related to the turbulence
behind the propeller hub and the air intake area( my reason for moving the
prop forward ) air leaks in the baffles, and the exit air air shoot not
extending far enough aft of the firewall causing a reverse air flow back up
into the lower cowl.( my reason for the cowl flap ) Most of the areodynamic
reference books address the above.
I have observed the air flow patterns over about 80% of my Rebel to date and
some of the directions the air flows is amazing.
Steve Sloan 536R
*-------------------------------------------------------------------------*
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To unsubscribe from this list, send an e-mail to: list-server@dcsol.com
with "unsubscribe murphy-rebel" in the body of the message.
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*-------------------------------------------------------------------------*
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-----------------------------------------------------------------
engine cooling
WHAT IS THE CHANCE OF A FEW PHOTOS
-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of Bob
Patterson
Sent: Monday, June 25, 2001 11:22 AM
To: murphy-rebel@dcsol.com
Subject: Re: engine cooling
*-------------------------------------------------------------------------*
The list archives are located at:
http://www.dcsol.com:81/public/default.htm
username: rebel password: builder
*-------------------------------------------------------------------------*
Hi Steve !
There's no doubt that there is a lot of interaction between
the prop and the front of the cowling - I was surprised to learn
several years ago just how much computer simulation time a big
company (De Havilland) spends on this area. Moving the prop forward
definitely helps, but can do un-nice things to the c of g, and
the crankshaft, if you're not careful.
Hadn't thought much about extending the air chute. You're
right - I can see how you would get reverse flow there !
Not "A Good Thing"(tm) !! ;-) Looking at Brian Cross's cowling
yesterday really reinforced that thinking - he seems to have the
answer, and all it takes is a few standoff brackets to open up
the bottom of the cowl. Of course, this must be done when building,
before trimming the cowl. (Although I'm tempted to try a retro-fit !)
I'm sure some of the air flows ARE amazing !! I've heard about
some tuft testing results ....
How did you manage to observe 80% of the Rebel ??? With
tufts and a mirror ?? or a video camera taped outside ??? This
could be VERY useful information for all of us !! You certainly
are getting much higher cruise speeds/hp than the rest of us !!
.....bobp
-----------------------------------orig.----------------------------------
At 10:00 PM 6/22/01 EDT, you wrote:
You have received this message because you have subscribed to the
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*-------------------------------------------------------------------------*
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-----------------------------------------------------------------
-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of Bob
Patterson
Sent: Monday, June 25, 2001 11:22 AM
To: murphy-rebel@dcsol.com
Subject: Re: engine cooling
*-------------------------------------------------------------------------*
The list archives are located at:
http://www.dcsol.com:81/public/default.htm
username: rebel password: builder
*-------------------------------------------------------------------------*
Hi Steve !
There's no doubt that there is a lot of interaction between
the prop and the front of the cowling - I was surprised to learn
several years ago just how much computer simulation time a big
company (De Havilland) spends on this area. Moving the prop forward
definitely helps, but can do un-nice things to the c of g, and
the crankshaft, if you're not careful.
Hadn't thought much about extending the air chute. You're
right - I can see how you would get reverse flow there !
Not "A Good Thing"(tm) !! ;-) Looking at Brian Cross's cowling
yesterday really reinforced that thinking - he seems to have the
answer, and all it takes is a few standoff brackets to open up
the bottom of the cowl. Of course, this must be done when building,
before trimming the cowl. (Although I'm tempted to try a retro-fit !)
I'm sure some of the air flows ARE amazing !! I've heard about
some tuft testing results ....
How did you manage to observe 80% of the Rebel ??? With
tufts and a mirror ?? or a video camera taped outside ??? This
could be VERY useful information for all of us !! You certainly
are getting much higher cruise speeds/hp than the rest of us !!
.....bobp
-----------------------------------orig.----------------------------------
At 10:00 PM 6/22/01 EDT, you wrote:
box*-------------------------------------------------------------------------*
The list archives are located at:
http://www.dcsol.com:81/public/default.htm
username: rebel password: builder
*-------------------------------------------------------------------------*
Bob
Yes there are a couple of differences, but minor! The Lyc. has a carb air
Lyc.and a slightly higher hump over the starter ring gear. The air intakes and
exit air shoot are about the same as the Cont. cowl. They both bolt to the
same firewall. If there is other differences that i am not aware of then
maybe they should be incorporated into the Lyc. cowling. Bottom line the
turbulencecowling has as much air going into and out of as the Cont. cowl for a given
speed.
In my opinion a portion of the cooling problems is related to the
andbehind the propeller hub and the air intake area( my reason for moving the
prop forward ) air leaks in the baffles, and the exit air air shoot not
extending far enough aft of the firewall causing a reverse air flow back up
into the lower cowl.( my reason for the cowl flap ) Most of the areodynamic
reference books address the above.
I have observed the air flow patterns over about 80% of my Rebel to date
*-------------------------------------------------------------------------*some of the directions the air flows is amazing.
Steve Sloan 536R
*-------------------------------------------------------------------------*
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-----------------------------------------------------------------
engine cooling
Hi Bob
I checked with Continental on the extention, it is OK. As to changes to the c
of g, my planes current c of g is 10.169 inches aft of the leading edge. If i
moved the prop and spinner ( 42.5 lbs ) back to the origional position on the
cowl the c of g would be 10.240 inches aft of the leading edge. Not much of a
change for a more efficent propeller and better cooling.
The air chute extends 1 3/4 inchs aft of the lower lip in the open position
and about 2 inches in the closed position. From the open position to the half
closed position i gain 1 1/2 to 2 mph
I used tufts on various areas on the under side of the wing, Wing struts and
the wheel fairings. On some of the landing gear fairings, bottom and lower
tail area i used a mixture of powered charcoal and JP4 painted on just prior
to take off.( Lots of clean up! ) Being the plane is waxed alu. any dust on
it will leave a air flow trail if the plane is flown in damp weather. This is
the best source for the information i have gathered. With a light shining
just right you can follow the airflow from every rivit , fitting or gap.
Steve Sloan 536R
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-----------------------------------------------------------------
I checked with Continental on the extention, it is OK. As to changes to the c
of g, my planes current c of g is 10.169 inches aft of the leading edge. If i
moved the prop and spinner ( 42.5 lbs ) back to the origional position on the
cowl the c of g would be 10.240 inches aft of the leading edge. Not much of a
change for a more efficent propeller and better cooling.
The air chute extends 1 3/4 inchs aft of the lower lip in the open position
and about 2 inches in the closed position. From the open position to the half
closed position i gain 1 1/2 to 2 mph
I used tufts on various areas on the under side of the wing, Wing struts and
the wheel fairings. On some of the landing gear fairings, bottom and lower
tail area i used a mixture of powered charcoal and JP4 painted on just prior
to take off.( Lots of clean up! ) Being the plane is waxed alu. any dust on
it will leave a air flow trail if the plane is flown in damp weather. This is
the best source for the information i have gathered. With a light shining
just right you can follow the airflow from every rivit , fitting or gap.
Steve Sloan 536R
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engine cooling
Could you please expand on the turbulence at the front and the exit being
BEHIND the firewall? My exit started about an inch IN FRONT of the firewall
and I have since been cutting it slowly forward. It is now a trapezoid
cuttout at the bottom of cowl about 10" x 8". I have even cut out an inch at
the top of the inlets. I have atleast got it down now to 430
F....Thanks....Brian
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BEHIND the firewall? My exit started about an inch IN FRONT of the firewall
and I have since been cutting it slowly forward. It is now a trapezoid
cuttout at the bottom of cowl about 10" x 8". I have even cut out an inch at
the top of the inlets. I have atleast got it down now to 430
F....Thanks....Brian
_________________________________________________________________From: SWSLOANLK@aol.com
Reply-To: <murphy-rebel@dcsol.com>
To: murphy-rebel@dcsol.com
Subject: Re: engine cooling
Date: Fri, 22 Jun 2001 22:00:45 EDT
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Bob
Yes there are a couple of differences, but minor! The Lyc. has a carb air
box
and a slightly higher hump over the starter ring gear. The air intakes and
exit air shoot are about the same as the Cont. cowl. They both bolt to the
same firewall. If there is other differences that i am not aware of then
maybe they should be incorporated into the Lyc. cowling. Bottom line the
Lyc.
cowling has as much air going into and out of as the Cont. cowl for a given
speed.
In my opinion a portion of the cooling problems is related to the
turbulence
behind the propeller hub and the air intake area( my reason for moving the
prop forward ) air leaks in the baffles, and the exit air air shoot not
extending far enough aft of the firewall causing a reverse air flow back up
into the lower cowl.( my reason for the cowl flap ) Most of the areodynamic
reference books address the above.
I have observed the air flow patterns over about 80% of my Rebel to date
and
some of the directions the air flows is amazing.
Steve Sloan 536R
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engine cooling
Brian
Steve likely has more useful info but your could try looking up some
cooling references such as the one on the RAAC site. There are some
examples of intakes working poorly if too close to the prop where the
wake of the prop actually sucks some air back out of the intake as the
blade goes past. Generally a prop extension helps the situation.
Similarly a radiator intake often works better if it is situated a foot
or two back from the prop.
Exit air ideally should be arranged to flow parallel to the airstream. A
protruding lip below the cowl will generate more suction but it also
introduces unwanted turbulence which is somewhat counterproductive to
airflow and is relatively high drag.
Ken
brian amendala wrote:
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Steve likely has more useful info but your could try looking up some
cooling references such as the one on the RAAC site. There are some
examples of intakes working poorly if too close to the prop where the
wake of the prop actually sucks some air back out of the intake as the
blade goes past. Generally a prop extension helps the situation.
Similarly a radiator intake often works better if it is situated a foot
or two back from the prop.
Exit air ideally should be arranged to flow parallel to the airstream. A
protruding lip below the cowl will generate more suction but it also
introduces unwanted turbulence which is somewhat counterproductive to
airflow and is relatively high drag.
Ken
brian amendala wrote:
Could you please expand on the turbulence at the front and the exit being
BEHIND the firewall? My exit started about an inch IN FRONT of the firewall
and I have since been cutting it slowly forward. It is now a trapezoid
cuttout at the bottom of cowl about 10" x 8". I have even cut out an inch at
the top of the inlets. I have atleast got it down now to 430
F....Thanks....Brian
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Engine Cooling
Brian
I will try to add a little more information to the cooling problem, as Ken's
comments were right on target.
As ken said the propeller wake can suck some air back out of the air intake,
the air also can stall as it piles up between the aft propeller face and the
face of the cowl, blocking the air flow from going into the air inlets and
reducing the propeller efficiency. Moving the propeller forward with a prop
extension can sometimes help in letting the air escape to the sides, top, and
bottom and of course into the air inlets.Some of the new cowling designs with
round air inlets on both production and experimental planes address this
problem.
The exit air chute on the Rebel cowl is more or less a straight flat surface
sloping down at a 22 to 25 degree angle in relation to the air flow over the
plane. If the cowl lip is cut off near or ahead of the firewall and bottom,
the high pressure air as it leaves the lip rolls upward into the engine
compartment which is at lower pressure. If the cowl exit air lip is gently
curved up so it parallels and extends 2 to 3 inches over the bottom this will
allow the air flow to leave the cowling parallel to the airstream and
generate more suction. Take a look at the lower cowl on various planes the
next time you are on the flight line and I think you will see that the Rebel
cowl can use a little curving upward in this area.
I have uploaded three photos of some tuft tests on various propeller cowl
combinations in the Rebel cowl section for your viewing. They are not of very
good quality and are not oriented in the right direction so you may want to
down load them. You should be able to see the disturbed air near the
propeller hubs and the different directions the air flows on the cowl face.
With that said, it is my opinion with regard to the Murphy speed cowl that
the air intake is not the major portion of the cooling problem it is the exit
air.
Steve Sloan 536R
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I will try to add a little more information to the cooling problem, as Ken's
comments were right on target.
As ken said the propeller wake can suck some air back out of the air intake,
the air also can stall as it piles up between the aft propeller face and the
face of the cowl, blocking the air flow from going into the air inlets and
reducing the propeller efficiency. Moving the propeller forward with a prop
extension can sometimes help in letting the air escape to the sides, top, and
bottom and of course into the air inlets.Some of the new cowling designs with
round air inlets on both production and experimental planes address this
problem.
The exit air chute on the Rebel cowl is more or less a straight flat surface
sloping down at a 22 to 25 degree angle in relation to the air flow over the
plane. If the cowl lip is cut off near or ahead of the firewall and bottom,
the high pressure air as it leaves the lip rolls upward into the engine
compartment which is at lower pressure. If the cowl exit air lip is gently
curved up so it parallels and extends 2 to 3 inches over the bottom this will
allow the air flow to leave the cowling parallel to the airstream and
generate more suction. Take a look at the lower cowl on various planes the
next time you are on the flight line and I think you will see that the Rebel
cowl can use a little curving upward in this area.
I have uploaded three photos of some tuft tests on various propeller cowl
combinations in the Rebel cowl section for your viewing. They are not of very
good quality and are not oriented in the right direction so you may want to
down load them. You should be able to see the disturbed air near the
propeller hubs and the different directions the air flows on the cowl face.
With that said, it is my opinion with regard to the Murphy speed cowl that
the air intake is not the major portion of the cooling problem it is the exit
air.
Steve Sloan 536R
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Engine Cooling
Great photos and commentary Steve!
Ken
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Ken
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Engine Cooling
Brian
Something you may want to try is taping some 1 1/2 inch long yarn tufts say
three or four wide in rows working down to the exit air chute with the last
row overhanging the lip. Also run a couple of rows on the bottom starting at
the firewall and work aft.
With the plane tied down run the engine up with a safety pilot and you can
observe the air flow by laying down under the plane well aft of the
propeller. BE CAREFULL!
Steve Sloan 536R
Something you may want to try is taping some 1 1/2 inch long yarn tufts say
three or four wide in rows working down to the exit air chute with the last
row overhanging the lip. Also run a couple of rows on the bottom starting at
the firewall and work aft.
With the plane tied down run the engine up with a safety pilot and you can
observe the air flow by laying down under the plane well aft of the
propeller. BE CAREFULL!
Steve Sloan 536R
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Engine Cooling
Thanks, I really appreciate all the help I am receiving from everyone. If
there is a problem with the prop being too close to the inlet then I am
guilty as I only have 1/4 inch clearance between my spinner and cowl. That
could be my problem. And as I already have the 2 1/2 inch spacer in place I
would have to buy a longer spacer....Brian
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there is a problem with the prop being too close to the inlet then I am
guilty as I only have 1/4 inch clearance between my spinner and cowl. That
could be my problem. And as I already have the 2 1/2 inch spacer in place I
would have to buy a longer spacer....Brian
_________________________________________________________________From: SWSLOANLK@aol.com
Reply-To: <murphy-rebel@dcsol.com>
To: murphy-rebel@dcsol.com
Subject: Engine Cooling
Date: Sat, 30 Jun 2001 09:20:11 EDT
Brian
Something you may want to try is taping some 1 1/2 inch long yarn tufts
say
three or four wide in rows working down to the exit air chute with the
last
row overhanging the lip. Also run a couple of rows on the bottom starting
at
the firewall and work aft.
With the plane tied down run the engine up with a safety pilot and you can
observe the air flow by laying down under the plane well aft of the
propeller. BE CAREFULL!
Steve Sloan 536R
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