Carbon Monoxide contamination

[sonexsteve]

Hi everyone,

I’ve just started flight test of a newly complete Sonex A model, tailwheel, Jabiru 3300. I’ve done two flights so far, generally going well, but getting repeated CO alarms from a domestic battery powered detector sitting on the glareshield.

I know some time ago there was a fair bit of discussion on the Forum about just this, but I can’t get the search function to work.

I recall suggestions involving confirming sealing of the firewall, the wing root edges and installing a bulkhead to seal off the rear fuselage aft of the baggage bay.

Can anyone with experience of solving this problem please let me know what worked best?

Thanks,

Steve Moody
Leamington Spa, England.

[WaiexN143NM]

hi steve,
is the exhaust the 3 into one collector ? those 3 slip joints are leaky. dave amsler made some tools to help fix this,
but your’re accross the pond. other suggestions for that joint is fiber wrap (auto parts store) , w stainless wire, and muffler paste.
things i did:
1) sealed wing roots w white caulk silicone (our plane is painted white w stewart white water based epoxy)
2) sealed firewall good , all rivets and corners.
3) filled all rivets on bottom of plane w caulk.
4) make sure you have a fuel. drip pan installed, another area where co could easily enter cockpit.
5) is the area on bottom of cowl opened up enough for good cooling or airflow?
6) sealed area on bulkhead behind baggage area.

good luck, let us know of you success!

WaiexN143NN
Michael

[fastj22]

hi steve,
is the exhaust the 3 into one collector ? those 3 slip joints are leaky. dave amsler made some tools to help fix this,
but your’re accross the pond. other suggestions for that joint is fiber wrap (auto parts store) , w stainless wire, and muffler paste.
things i did:
1) sealed wing roots w white caulk silicone (our plane is painted white w stewart white water based epoxy)
2) sealed firewall good , all rivets and corners.
3) filled all rivets on bottom of plane w caulk.
4) make sure you have a fuel. drip pan installed, another area where co could easily enter cockpit.
5) is the area on bottom of cowl opened up enough for good cooling or airflow?
6) sealed area on bulkhead behind baggage area.

good luck, let us know of you success!

WaiexN143NN
Michael1

Michael, are you measuring your CO levels? If so, what are they at run up, taxi, climb and cruise? I was alarmed at the high levels at in anything but cruise.

[WaiexN143NM]

hi john,
Good to hear from you. hope you and family are well and safe.
Sorry i cant tell you the numbers, plane is in our hangar at tucson, Kryn ryan field. notes are there.
i do remember after all the work sealing up stuff it helped. i have a digital yellow co monitor i got thru walmart online.
about $30.
i read kathrynsreport daily . there have been accidents caused by high co into the cabin. usually muffler cracks.
i suggest everyone invest in a digital co monitor. protect your health.
good to hear the story of you and gary returning from osh last yr and had a co monitor. it saved you guys!
a portable co monitor many avbl from amazon.
take along on a fbo rental or your own plane.

take care,

WaiexN143NM (stuck in SF since early march)
michael

[GraemeSmith]

I know some time ago there was a fair bit of discussion on the Forum about just this, but I can’t get the search function to work.

Steve,

Here is the thread:

viewtopic.php?f=25&t=5644&hilit=co

[inventor]

From other posts I have read in the past much CO can get into the cabin from the tail area. Just like leaving the rear window open in a station wagon. Anyone remember those?

Richard

[DCASonex]

I did make a tool to improve the seal at the three into one exhaust junctions and it kept things cleaner under the cowl. but found that CO was getting in cockpit mostly through the small holes in the tail. plunged those and no more CO alarms.

David A.

[lpaaruule]

While not a solution, one way to keep CO levels lower is to not run rich. I think Michael is still using a Rotec TBI, which may allow his engine's cylinders to run more evenly in terms of richness, which would allow him to run leaner, and more efficient. It's supposed to atomize the fuel better.

I won't get into everything I've done to reduce CO here, but it's not entirely gone. When in cruise, I can usually get it below 10ppm by fairly aggressive leaning.

In the winter there were times when my CO levels in cruise were 1 to 3 ppm. However, once the weather warmed, and my engine was running richer, the levels rose to the low teens.

My "fresh air" vents will even pull in a little CO, usually around 6ppm or less.

I haven't re-tuned the aerocarb this summer, and thought that I'd just lean the mixture knob. Leaning this way doesn't seem to be as effective though. I don't have any proof of this, but my guess is that when you tune the carb itself, you're actually making the needle orifice smaller, and the fuel can atomize better, whereas just leaning in the cockpit just slows down the rate of bigger droplets.

Anyway, when I go full rich for landing, I've seen my CO rise to the low 20s. It will probably only rise to the low teens when I retune the Aerocarb for summer.

[sonexsteve]

Thanks everyone for your thoughts and suggestions, very helpful.

The builder had installed a extension to the lower rear cowl cooling air exit airflow dams in an attempt to draw more air out of the cowling and so reduce elevated CHTs. He’d also added the crossover air tube from above cylinder 2 to above cylinder 5.

When we removed the air dam extension from the lower cowl as if by magic the CO contamination disappeared completely, a digital detector readout showing zero throughout a 2 hour flight, just registering 11 ppm during taxi back in after landing.

So in some aerodynamically magic way the dam extension had been drawing exhaust flow into the cabin.

All fine now, thanks again for your help.

Steve.

[Area 51%]

From other posts I have read in the past much CO can get into the cabin from the tail area. Just like leaving the rear window open in a station wagon. Anyone remember those?

Richard

Still drive one. 1996 Buick Century Custom. While folks in the Home Depot parking lot are scratching their heads on how they are going to get a 4X8 sheet of plywood home in their Chevy Colorado, I just slide it in through the back glass. Two 3/4in sheets will fit. Sticks out about a foot. I do keep the fan on high to keep the cabin pressurized.