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  #11  
Old 01-14-2018, 03:32 PM
bob888 bob888 is offline
 
Join Date: Jul 2012
Location: Fresno, CA
Posts: 204
Default CO update

Upon careful inspection of the firewall, I noticed there are numerous small gaps around the perimeter of the firewall between the flanges. I did not seal these during construction but plan to do so now as I could find no other way for the CO to get into the cockpit. What have others done about these small gaps and does this sound like a reasonable explanation for the low level CO that I am detecting? I expect just putting a bead of red silicone around the perimeter may solve this....any better or alternative ideas?
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  #12  
Old 01-14-2018, 03:57 PM
rocketman1988 rocketman1988 is offline
 
Join Date: Jun 2010
Location: Sunman, IN
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Default Uh, oh...

I'm pretty sure someone will chime in why as to NOT use Red RTV...

I used 3m Fire Barrier 2000+...
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  #13  
Old 01-14-2018, 04:22 PM
SuperCubDriver SuperCubDriver is offline
 
Join Date: Feb 2011
Location: Germany
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Default

On my RV-7 during test flights I measured around 20 ppm CO during climb with mixture enriched. I got 0 ppm during cruise mixture leaned. The CO almost certainly came in through openings in the empennage.
I believe the exhaust gases out of the exhaust pipes only can get inside the cabin somewhere behind them. Of course there can be leaks somewhere in the engine bay allowing fumes to penetrate the cabin through the firewall.
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  #14  
Old 01-15-2018, 03:06 PM
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RV10inOz RV10inOz is offline
 
Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,122
Default More or less CO?

Interesting fact for your consideration.

ROP operations such as takeoff and climb will produce the highest % of CO, compared to LOP in the cruise which produces hardly any.

So it is likely that you will see radically different CO levels depending on phase of flight if you have any exhaust gases finding their way in. And they may not be coming in the firewall points. Air flow is a funny thing.
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  #15  
Old 01-16-2018, 12:44 AM
rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGG
Posts: 2,316
Default CO inside the cowl

It seems like with any kind of airflow over the engine that there should not be any CO under the cowl at all, so even leaks in the firewall would not cause CO in the cabin, unless you have a cracked exhaust. Do I have this right?
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  #16  
Old 01-16-2018, 07:41 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by rv8ch View Post
It seems like with any kind of airflow over the engine that there should not be any CO under the cowl at all, so even leaks in the firewall would not cause CO in the cabin, unless you have a cracked exhaust. Do I have this right?
There can be slip joints in the exhaust system that are not 100% sealed (depending on what manufacturers system is installed).
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  #17  
Old 02-15-2018, 07:58 AM
Kellym Kellym is offline
 
Join Date: Aug 2005
Posts: 82
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Quote:
Originally Posted by leok View Post
Does the level change from start up/Taxi to flight?

Recommended 8 hour exposure limit (REL) is 35 ppm. Permissible Exposure Limit is 50 ppm. These are from NIOSH and are for continuous exposure.

Short Term Exposure Limit (STEL) of 400 ppm. STEL is typically 20 min time weighted average (TWA).
I would recommend adhering to MUCH lower limits for flight. EPA outdoor ambient air limits are 35 ppm for ONE hour, and 9 PPM for 8 hours.
Your body is much more sensitive to CO at altitude, and first effects will be slower thinking and impaired judgement.
NIOSH is for healthy workers that are not exposed during none work hours, and a lot of other caveats.
If you suspect any exposure while in flight (as opposed to taxi) I would recommend going on O2 mask and landing at nearest reasonable airport to check it out. It is nothing to fool around with.
JMHO from over 25 yrs of monitoring, forecasting and modeling air pollution.
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  #18  
Old 02-17-2018, 08:57 AM
bob888 bob888 is offline
 
Join Date: Jul 2012
Location: Fresno, CA
Posts: 204
Default CO persists

I am continuing to pursue the low level CO in my cockpit. At this point, I suspect it may be coming in from the open areas at the rear of the empennage. There is some exhaust staining on the lower edge of the rudder and if there is somewhat lower pressure inside the fuselage then the exhaust may be moving forward in the fuselage. Anyone have thoughts about this theory? Solutions?
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  #19  
Old 02-17-2018, 09:49 AM
sblack sblack is offline
 
Join Date: Dec 2009
Location: Montreal
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Default

Quote:
Originally Posted by bob888 View Post
I am continuing to pursue the low level CO in my cockpit. At this point, I suspect it may be coming in from the open areas at the rear of the empennage. There is some exhaust staining on the lower edge of the rudder and if there is somewhat lower pressure inside the fuselage then the exhaust may be moving forward in the fuselage. Anyone have thoughts about this theory? Solutions?
In terms of identifying the smoking gun, my first step would be to see the difference made when you turn on the cockpit vents. If you think it is coming through the tail then pressurizing the cockpit should stop it. Are there leaks in the cockpit, like around the canopy, that are creating suction? Do you have boots on the aileron pushrods? In order to have exhaust gases in the cockpit the pressure there has to be lower than where ever it is coming in. So either stop the suction in the cockpit so that it stays at ambient, or boost the cockpit pressure with positive ventilation that has to exit through the tail (nowhere else). I think the ey here is to stop any leaks so that you can start to control the direction of flow. If you have leaks everywhere then you have chaos.
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  #20  
Old 02-17-2018, 10:48 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by bob888 View Post
I am continuing to pursue the low level CO in my cockpit. At this point, I suspect it may be coming in from the open areas at the rear of the empennage. There is some exhaust staining on the lower edge of the rudder and if there is somewhat lower pressure inside the fuselage then the exhaust may be moving forward in the fuselage. Anyone have thoughts about this theory? Solutions?
Your suspicions are possible.

Undesirable airflow entering the cockpit, besides effecting cabin heat performance, can bring engine exhaust with it as well.

A possibly relevant post from another thread.....

http://www.vansairforce.com/communit...8&postcount=42
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