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nukeflyboy
Joined: 05 Jan 2008
Posts: 162
Location: Granbury, TX
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 Posted: Thu Jun 18, 2015 3:59 pm Post subject: Carbon Monoxide |
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I bought a carbon monoxide detector from Aeromedix that appears to work well. It measures CO levels to the ppm level on a real time basis. My experience with it has been interesting and I wonder if you are unknowingly being exposed to high level of carbon monoxide.
If you are in a line of airplanes waiting to take off, say at Oshkosh for example, it is not uncommon for the monitor to alarm (set at 30 ppm). It is picking up the exhaust form the airplane in front of you coming into your vents.
I also recently installed an Icebox air conditioner to help with the Texas summer heat. To work you have to shut off outside ventilation. I have tried this several times and each time at takeoff, and while in a climb, the CO monitor goes into alarm: 30 to 45 ppm have been noticed. This can be alleviated by opening the fresh air vents, but negates the use of the air conditioner.
Thinking that some exhaust may be coming into the cockpit from the tailcone (high AOA puts the exhaust on the belly), I sealed the corrugations in the baggage compartment bulkhead. If you have not checked, there is a considerable amount of air that enters the cabin from the tailcone through these small openings. This is due to the high negative pressure that is normally present in the cabin relative to the tailcone.
On the next flight with the a/c on and vents closed, the CO detector went above 70 ppm. So much for the idea that it is coming in through the tailcone.
Looking at previous posts there does not appear to be a related discussion thread. One thing that I picked up is that I need to seal the small opening near the leading edge of the wing where it meets the fuselage at the floor level. Looking at the geometry it is difficult to see how this could be the source.
Have any of you noticed high CO levels and looked at CO entry into the cabin to figure out where it is coming from?
I generally climb (at least initially) with mixture full rich in order to keep cylinder temps below 400 degrees. I know this is not good from a CO perspective but at high power the full mixture is needed. Airspeed in the climb is typically 130 kts. Once stable at altitude and in level flight the CO problem goes away.
I have standard exhaust tailpipes and the air vents are Van's.
Any thoughts?
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Lew Gallagher
Joined: 04 Jan 2008
Posts: 402
Location: Greenville , SC
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| Posted: Thu Jun 18, 2015 4:41 pm Post subject: Carbon Monoxide |
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Hey Dave,
We have not done any CO monitoring, but I thought I'd pass along that we and
many others have added a 45 degree exhaust tip to angle the exhaust away
from the belly. At the time we were only trying to keep the belly clean (it
works) ... now you’ve got me thinking!
Later, - Lew
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bcondrey
Joined: 03 Apr 2006
Posts: 580
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| Posted: Thu Jun 18, 2015 5:03 pm Post subject: Carbon Monoxide |
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I had a similar situation in an RV-10 and traced the issue to an are along the upper edge of the firewall that hadn't been sealed well. A little goo and never saw the issue again. Only thing I could figure is that a little exhaust was somehow getting in the area behind the engine when in relatively high AOA situations.
Bob
On Thursday, June 18, 2015, <lewgall(at)charter.net (lewgall(at)charter.net)> wrote:
[quote]--> RV10-List message posted by: <lewgall(at)charter.net>
Hey Dave,
We have not done any CO monitoring, but I thought I'd pass along that we and many others have added a 45 degree exhaust tip to angle the exhaust away from the belly. At the time we were only trying to keep the belly clean (it works) ... now you’ve got me thinking!
Later, - Lew
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rv10(at)texasrv10.com
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| Posted: Thu Jun 18, 2015 5:24 pm Post subject: Carbon Monoxide |
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This is interesting... I have the fully installed compressor driven Flightline AC. System I have never had CO issues in any of the various flight phases or high AOA. I fly with the AC on most all times as it really pulls out the humidity from the cabin nicely.
But...
When I put on the belly pod, MotoPod, I have experienced CO situations. As mentioned before in another post straight and level cruise cleans out the cabin without needing to open the fresh air vents. I did add the 45 degree tips and have experimented with the direction "I thought" would solve the issue. Not.. Tried various directions most obvious and none worked showing me I obviously didn't understand the issue. Turned them both to point towards center (not down) and that did help. Seemed to solve the issue then it reappeared after 4 hours. Then I noticed the muffler hanger hose clamps that supports the muffler had become loose allowing the tail pipe and muffler to relocate itself further outboard thus causing the exhaust to flow more to the left wing root. I tightened up the hanger clamps with muffler in correct location but haven't flown with pod on since then. Prior to this coming loose no CO..next time will tell..
Again this is only with the pod on. I think each of our situations might be different but regardless it's an issue likely solved differently per our installations.
Gaylon Koenning
| Quote: | On Jun 18, 2015, at 7:38 PM, <lewgall(at)charter.net> <lewgall(at)charter.net> wrote:
Hey Dave,
We have not done any CO monitoring, but I thought I'd pass along that we and many others have added a 45 degree exhaust tip to angle the exhaust away from the belly. At the time we were only trying to keep the belly clean (it works) ... now you’ve got me thinking!
Later, - Lew
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Kellym
Joined: 10 Jan 2006
Posts: 1700
Location: Sun Lakes AZ
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| Posted: Thu Jun 18, 2015 8:06 pm Post subject: Carbon Monoxide |
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While I agree that CO is likely in the climb, it really depends on what
you did or didn't do to seal the belly, doors, vents, etc. While full
rich produces a high level, perhaps 3-5% CO in the exhaust, you would
have to go fully lean of peak, say 80 degrees to be able to get CO down
enough to make much difference. On the rich side I suggest you keep EGT
fairly close to 1250. Otherwise, once above pattern altitude, pull
mixture back to a value known to be lean of peak, say 11-12 gph, and
continue climb. At 75% power lean of peak you should be burning 13gph,
so anything less than that will reduce power some but is lean enough you
won't hurt anything regardless of throttle position. Other wise known as
the big mixture pull. Besides reducing CO it will get you much cooler
CHT, since your output will be a bit under 70%.
On 6/18/2015 4:59 PM, nukeflyboy wrote:
| Quote: |
I bought a carbon monoxide detector from Aeromedix that appears to work well. It measures CO levels to the ppm level on a real time basis. My experience with it has been interesting and I wonder if you are unknowingly being exposed to high level of carbon monoxide.
If you are in a line of airplanes waiting to take off, say at Oshkosh for example, it is not uncommon for the monitor to alarm (set at 30 ppm). It is picking up the exhaust form the airplane in front of you coming into your vents.
I also recently installed an Icebox air conditioner to help with the Texas summer heat. To work you have to shut off outside ventilation. I have tried this several times and each time at takeoff, and while in a climb, the CO monitor goes into alarm: 30 to 45 ppm have been noticed. This can be alleviated by opening the fresh air vents, but negates the use of the air conditioner.
Thinking that some exhaust may be coming into the cockpit from the tailcone (high AOA puts the exhaust on the belly), I sealed the corrugations in the baggage compartment bulkhead. If you have not checked, there is a considerable amount of air that enters the cabin from the tailcone through these small openings. This is due to the high negative pressure that is normally present in the cabin relative to the tailcone.
On the next flight with the a/c on and vents closed, the CO detector went above 70 ppm. So much for the idea that it is coming in through the tailcone.
Looking at previous posts there does not appear to be a related discussion thread. One thing that I picked up is that I need to seal the small opening near the leading edge of the wing where it meets the fuselage at the floor level. Looking at the geometry it is difficult to see how this could be the source.
Have any of you noticed high CO levels and looked at CO entry into the cabin to figure out where it is coming from?
I generally climb (at least initially) with mixture full rich in order to keep cylinder temps below 400 degrees. I know this is not good from a CO perspective but at high power the full mixture is needed. Airspeed in the climb is typically 130 kts. Once stable at altitude and in level flight the CO problem goes away.
I have standard exhaust tailpipes and the air vents are Van's.
Any thoughts?
--------
Dave Moore
RV-6 flying
RV-10 QB - flying
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