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mr.sun
Joined: 30 Jan 2007
Posts: 85
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 Posted: Sat May 19, 2012 7:31 am Post subject: Exit Fairing |
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Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
Do not archive
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kcflyrv(at)comcast.net
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| Posted: Sat May 19, 2012 8:37 am Post subject: Exit Fairing |
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Hello,
I finished my RV6 just over 10 years ago and this was being done by some of my builder friends at that time and I assume a long time before that. I never did add the fairing myself but thought I should have. When I saw your picture, my first thought was to copy your fairing but if you’re not seeing positive results, maybe I won’t waist the effort.???
Ken Cantrell
Lodi, CA
1275 hrs
From: owner-rv-list-server(at)matronics.com [mailto:owner-rv-list-server(at)matronics.com] On Behalf Of mr.gsun(at)gmail.com
Sent: Saturday, May 19, 2012 8:30 AM
To: rv-list(at)matronics.com
Subject: Exit Fairing
Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
Do not archive
[quote][b]
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mr.sun
Joined: 30 Jan 2007
Posts: 85
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| Posted: Sat May 19, 2012 8:54 am Post subject: Exit Fairing |
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Ken
I just can't measure any results.
Greg On May 19, 2012 9:46 AM, "Ken Cantrell" <kcflyrv(at)comcast.net (kcflyrv(at)comcast.net)> wrote:[quote]
Hello,
I finished my RV6 just over 10 years ago and this was being done by some of my builder friends at that time and I assume a long time before that. I never did add the fairing myself but thought I should have. When I saw your picture, my first thought was to copy your fairing but if you’re not seeing positive results, maybe I won’t waist the effort.???
Ken Cantrell
Lodi, CA
1275 hrs
From: owner-rv-list-server(at)matronics.com (owner-rv-list-server(at)matronics.com) [mailto:owner-rv-list-server(at)matronics.com (owner-rv-list-server(at)matronics.com)] On Behalf Of mr.gsun(at)gmail.com (mr.gsun(at)gmail.com)
Sent: Saturday, May 19, 2012 8:30 AM
To: rv-list(at)matronics.com (rv-list(at)matronics.com)
Subject: Exit Fairing
Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
Do not archive
| Quote: |
t="_blank">http://www.matronics.com/Navigator?RV-List
tp://forums.matronics.com
_blank">http://www.matronics.com/contribution
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[b]
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Larry Bowen
Joined: 09 Jan 2006
Posts: 802
Location: NC, USA
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| Posted: Sat May 19, 2012 9:03 am Post subject: Exit Fairing |
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That's the same ramp that is on the RV8, per plans and prefabricated, as you probably already knew. Not sure why the 7 is different.
-
Larry Bowen
Larry(at)BowenAero.com
mr.gsun(at)gmail.com (mr.gsun(at)gmail.com)> wrote:[quote]
Ken
I just can't measure any results.
Greg On May 19, 2012 9:46 AM, "Ken Cantrell" <kcflyrv(at)comcast.net (kcflyrv(at)comcast.net)> wrote: | Quote: |
Hello,
I finished my RV6 just over 10 years ago and this was being done by some of my builder friends at that time and I assume a long time before that. I never did add the fairing myself but thought I should have. When I saw your picture, my first thought was to copy your fairing but if you’re not seeing positive results, maybe I won’t waist the effort.???
Ken Cantrell
Lodi, CA
1275 hrs
From: owner-rv-list-server(at)matronics.com (owner-rv-list-server(at)matronics.com) [mailto:owner-rv-list-server(at)matronics.com (owner-rv-list-server(at)matronics.com)] On Behalf Of mr.gsun(at)gmail.com (mr.gsun(at)gmail.com)
Sent: Saturday, May 19, 2012 8:30 AM
To: rv-list(at)matronics.com (rv-list(at)matronics.com)
Subject: Exit Fairing
Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
Do not archive
t="_blank">http://www.matronics.com/Navigator?RV-List
tp://forums.matronics.com
_blank">http://www.matronics.com/contribution
|
[b]
| | - The Matronics RV-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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Larry Bowen
RV-8 SOLD,
RV-7QB in progress... |
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ceengland(at)bellsouth.ne
Guest
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| Posted: Sat May 19, 2012 4:38 pm Post subject: Exit Fairing |
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On 05/19/2012 10:30 AM, mr.gsun(at)gmail.com (mr.gsun(at)gmail.com) wrote: | Quote: | Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
Do not archive
|
There's a very long and on-going discussion on the VAF forum about cowl exit experiments (with not much useful info).
As someone else said, the firewall treatment is standard on the -8. I think that all the really fast RV's have something similar to that, or something much more elaborate (ramps that extend all the way up to the cylinders, in a lot of cases).
One thing to think about in your installation is the horizontal brace on the exhaust pipes. It's round (plus the hose clamps), meaning that you've got a really draggy structure directly in the exit path. Could you run separate braces from each pipe outward, instead of across the exit?
Charlie
[quote][b]
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khorton02(at)gmail.com
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| Posted: Sat May 19, 2012 4:50 pm Post subject: Exit Fairing |
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A smooth, rounded ramp like that should lead to a decrease in CHTs, in theory. But, the devil is in the details. I can't tell from the picture, but is it possible that the bottom of that fairing extends down far enough to decrease the exit area from what it would be if the fairing was not installed? If so, it is quite possible that you have less air flowing than before, and thus may see an increase in CHTs. Normally, if there is less air flowing, there should be less cooling drag, and a speed increase. But, the decrease in air flow, with the same frontal area from the part of the cowling that is dropped down where the exhaust pipes exit, would give extra wake drag which may cancel out the decrease in cooling drag.
Ideally, the rounded radius would end on a tangent to the bottom of the fuselage. If the radius keeps going so there is a sharp corner where it meets the bottom of the fuselage, there May be some flow separation behind the radius, leading to extra drag.
Kevin Horton
Sent from my iPad
On 2012-05-19, at 11:30 AM, mr.gsun(at)gmail.com wrote:
| Quote: | Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
Do not archive
<exit fairing RV7.jpg>
|
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http://www.matronics.com/Navigator?RV-List |
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pilots2(at)yahoo.com
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| Posted: Sat May 19, 2012 9:06 pm Post subject: Exit Fairing |
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Cooling is an art, science, and black magic all rolled into one. If your looking for efficient cooling read LoPersit or Lazlo Pazmany's stuff. You can also Google aircraft piston engine cooling and you will get pages of stuff.
If you having problems with one cyl look from the top down between the cooling fins in and around the spark plug and top the the cyl and clean out all the casting slag.
Reuven Silberman
Enjoy life now
It has an expiration date.
From: Kevin Horton <khorton02(at)gmail.com>
To: "rv-list(at)matronics.com" <rv-list(at)matronics.com>
Sent: Saturday, May 19, 2012 5:49 PM
Subject: Re: Exit Fairing
--> RV-List message posted by: Kevin Horton <khorton02(at)gmail.com (khorton02(at)gmail.com)>
A smooth, rounded ramp like that should lead to a decrease in CHTs, in theory. But, the devil is in the details. I can't tell from the picture, but is it possible that the bottom of that fairing extends down far enough to decrease the exit area from what it would be if the fairing was not installed? If so, it is quite possible that you have less air flowing than before, and thus may see an increase in CHTs. Normally, if there is less air flowing, there should be less cooling drag, and a speed increase. But, the decrease in air flow, with the same frontal area from the part of the cowling that is dropped down where the exhaust pipes exit, would give extra wake drag which may cancel out the decrease in cooling drag.
Ideally, the rounded radius would end on a tangent to the bottom of the fuselage. If the radius keeps going so there is a sharp corner where it meets the bottom of the fuselage, there May be some flow separation behind the radius, leading to extra drag.
Kevin Horton
Sent from my iPad
On 2012-05-19, at 11:30 AM, mr.gsun(at)gmail.com (mr.gsun(at)gmail.com) wrote:
| Quote: | Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
>/www.matronics.com/Navigator?RV-List" sp; - List Contribution Web Site -
|
_; &nb====================
[quote][b]
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Doug Gray
Joined: 10 Jan 2006
Posts: 112
Location: Sydney, Australia
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| Posted: Mon May 21, 2012 5:01 am Post subject: Exit Fairing |
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My #3 CHT is also higher than it should really be - I have been contemplating an addition just like your modification, but I just realized that I have a cabin heater muff on the RHS exhaust pipe. Perhaps this is blocking the airflow from this cylinder.
I suppose CHTs to be primarily dependent on power setting and OAT. For day to day comparisons, my EFIS provides good % power analysis in real time (using Kevin Horton's interpolation of the Lycoming performance charts), so I fly my tests at a consistent altitude & same lean % power setting.
To compare I normalize the temperatures to an OAT of 25c (77f). For example if the CHT is 360 for an OAT of 60f the temperature differential is 300f; the corrected value I use for any comparison is 377f.
This does seem to give comparative results but are there any other factors I should consider? I'm no test pilot, the most difficult part for me is mustering the discipline to take the measurements.
Doug Gray
Sent from my iPad
On 20/05/2012, at 1:30 AM, mr.gsun(at)gmail.com wrote:
| Quote: | Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
Do not archive
<exit fairing RV7.jpg>
|
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http://www.matronics.com/Navigator?RV-List |
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Kellym
Joined: 10 Jan 2006
Posts: 1704
Location: Sun Lakes AZ
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| Posted: Mon May 21, 2012 6:15 am Post subject: Exit Fairing |
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The main issue with #3 cylinder on 4 cyl Lycomings is that the cyl. head
is cast with no cooling fins on the intake port side. Testing on
certified aircraft have shown that you do in fact need air passing over
that side of the head. Many baffling installations do not leave room for
air to get by that side of the head (rear of #3). Providing a 1/8 to
1/4 gap behind the cylinder head can lower the CHT as much as 30
degrees. This can also be an issue on front of #2, depending on baffle
design.
On 5/21/2012 6:00 AM, Doug Gray wrote:
| Quote: |
My #3 CHT is also higher than it should really be - I have been contemplating an addition just like your modification, but I just realized that I have a cabin heater muff on the RHS exhaust pipe. Perhaps this is blocking the airflow from this cylinder.
I suppose CHTs to be primarily dependent on power setting and OAT. For day to day comparisons, my EFIS provides good % power analysis in real time (using Kevin Horton's interpolation of the Lycoming performance charts), so I fly my tests at a consistent altitude& same lean % power setting.
To compare I normalize the temperatures to an OAT of 25c (77f). For example if the CHT is 360 for an OAT of 60f the temperature differential is 300f; the corrected value I use for any comparison is 377f.
This does seem to give comparative results but are there any other factors I should consider? I'm no test pilot, the most difficult part for me is mustering the discipline to take the measurements.
Doug Gray
Sent from my iPad
On 20/05/2012, at 1:30 AM, mr.gsun(at)gmail.com wrote:
> Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
>
> It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
>
> The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
>
> Do not archive
> <exit fairing RV7.jpg>
|
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| | - The Matronics RV-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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A&P/IA, EAA Tech Counselor # 5286
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mr.sun
Joined: 30 Jan 2007
Posts: 85
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| Posted: Mon May 21, 2012 6:26 am Post subject: Exit Fairing |
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I put a 1/8" gap behind #3. Now that warmer weather is here, will see if any change occurred. Will also clean injectors soon and try the coke bottle test to see if they are flowing about the same. Not sure what I should be looking for though...
Greg On May 21, 2012 7:19 AM, "Kelly McMullen" <kellym(at)aviating.com (kellym(at)aviating.com)> wrote:[quote] --> RV-List message posted by: Kelly McMullen <kellym(at)aviating.com (kellym(at)aviating.com)>
The main issue with #3 cylinder on 4 cyl Lycomings is that the cyl. head is cast with no cooling fins on the intake port side. Testing on certified aircraft have shown that you do in fact need air passing over that side of the head. Many baffling installations do not leave room for air to get by that side of the head (rear of #3). Providing a 1/8 to 1/4 gap behind the cylinder head can lower the CHT as much as 30 degrees. This can also be an issue on front of #2, depending on baffle design.
On 5/21/2012 6:00 AM, Doug Gray wrote:
| Quote: | --> RV-List message posted by: Doug Gray<dgra1233(at)bigpond.net.au (dgra1233(at)bigpond.net.au)>
My #3 CHT is also higher than it should really be - I have been contemplating an addition just like your modification, but I just realized that I have a cabin heater muff on the RHS exhaust pipe. Perhaps this is blocking the airflow from this cylinder.
I suppose CHTs to be primarily dependent on power setting and OAT. For day to day comparisons, my EFIS provides good % power analysis in real time (using Kevin Horton's interpolation of the Lycoming performance charts), so I fly my tests at a consistent altitude& same lean % power setting.
To compare I normalize the temperatures to an OAT of 25c (77f). For example if the CHT is 360 for an OAT of 60f the temperature differential is 300f; the corrected value I use for any comparison is 377f.
This does seem to give comparative results but are there any other factors I should consider? I'm no test pilot, the most difficult part for me is mustering the discipline to take the measurements.
Doug Gray
Sent from my iPad
On 20/05/2012, at 1:30 AM, mr.gsun(at)gmail.com (mr.gsun(at)gmail.com) wrote:
| Quote: | Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
Do not archive
<exit fairing RV7.jpg>
|
|
-----
No virus found in this message.
Checked by AVG - www.avg.com
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get="_blank">http://www.matronics.com/Navigator?RV-List
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http://forums.matronics.com
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le, List Admin.
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[b]
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Doug Gray
Joined: 10 Jan 2006
Posts: 112
Location: Sydney, Australia
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| Posted: Mon May 21, 2012 10:07 pm Post subject: Exit Fairing |
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I do have a .062" spacer on the #3 baffle.
Doug
Sent from my iPad
On 22/05/2012, at 12:14 AM, Kelly McMullen <kellym(at)aviating.com> wrote:
| Quote: |
The main issue with #3 cylinder on 4 cyl Lycomings is that the cyl. head is cast with no cooling fins on the intake port side. Testing on certified aircraft have shown that you do in fact need air passing over that side of the head. Many baffling installations do not leave room for air to get by that side of the head (rear of #3). Providing a 1/8 to 1/4 gap behind the cylinder head can lower the CHT as much as 30 degrees. This can also be an issue on front of #2, depending on baffle design.
On 5/21/2012 6:00 AM, Doug Gray wrote:
>
>
> My #3 CHT is also higher than it should really be - I have been contemplating an addition just like your modification, but I just realized that I have a cabin heater muff on the RHS exhaust pipe. Perhaps this is blocking the airflow from this cylinder.
>
> I suppose CHTs to be primarily dependent on power setting and OAT. For day to day comparisons, my EFIS provides good % power analysis in real time (using Kevin Horton's interpolation of the Lycoming performance charts), so I fly my tests at a consistent altitude& same lean % power setting.
>
> To compare I normalize the temperatures to an OAT of 25c (77f). For example if the CHT is 360 for an OAT of 60f the temperature differential is 300f; the corrected value I use for any comparison is 377f.
>
> This does seem to give comparative results but are there any other factors I should consider? I'm no test pilot, the most difficult part for me is mustering the discipline to take the measurements.
>
> Doug Gray
>
>
>
> Sent from my iPad
>
> On 20/05/2012, at 1:30 AM, mr.gsun(at)gmail.com wrote:
>
>> Hey RV posters, In my never ending quest for another ounce of velocity, I installed a cooling air exit fairing at the bottom of the firewall in my RV-7. IO-360. 4 into 2 Vetterman Exhaust pipes. The idea is to straighten the exiting cooling airflow to more closely align with the slipstream. It was one of those easy to install mods that an experienced RV builder told me about.
>>
>> It is a curved piece of aluminum about 4" diameter and approximately 10" long. The lower surface is in line with the bottom of the fuselage. A photo is attached.
>>
>> The question is: Has anyone installed this sort of thing before? Did you get the same ZERO results? Did it cause increased CHTs? My #3 continues to be too hot but I can't tell if it was affected by this mod. Haven't decided if it is worth removing it.
>>
>> Do not archive
>> <exit fairing RV7.jpg>
>
>
>
>
-----
No virus found in this message.
Checked by AVG - www.avg.com
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