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Worth Checking the CO

sj

sj

Staff member
Northwest Arkansas
Laura and I took a quick flight down to see some friends 150 miles away in the C-180. On a whim, I brought my two CO meters with me. Sure enough, when the heater was on we were getting close to 40ppm CO and the alarm was going off on the one meter. Turn off the heat, goes away instantly. Not enough to knock you out, but certainly enough to give you a nasty headache. It was a cold flight, and now I am going to have to dig into this issue - which I suspect means getting the muffler rebuilt.

While 40 is not very high, I would prefer it to be a lot closer to zero.

I have a Fluke CO-220 and an Aeromedix (looks like smoke alarm). If you are relying on those little "dead stop" dots, they are really not good enough - especially if they are outdated.

fluke.jpg

Just a reminder about the levels and their effects.

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Good reminder. I've been exposed in flight, and it's no fun, and can kill you dead. I had a few days of pretty nasty headaches.

MTV
 
SJ said:
Laura and I took a quick flight down to see some friends 150 miles away in the C-180. On a whim, I brought my two CO meters with me. Sure enough, when the heater was on we were getting close to 40ppm CO and the alarm was going off on the one meter. Turn off the heat, goes away instantly. Not enough to knock you out, but certainly enough to give you a nasty headache. It was a cold flight, and now I am going to have to dig into this issue - which I suspect means getting the muffler rebuilt.

While 40 is not very high, I would prefer it to be a lot closer to zero.

I have a Fluke CO-220 and an Aeromedix (looks like smoke alarm). If you are relying on those little "dead stop" dots, they are really not good enough - especially if they are outdated.

View attachment 41148

Just a reminder about the levels and their effects.

View attachment 41150
Click to expand...

So you had no threat at the levels you saw according to the chart you posted?

I hear it’s about to get cold down there. The CO levels inside your car in stop and go traffic on a cold morning would be interesting to know.
 
Technically, no, but after eight hours of exposure it is considered too high, and of course what ever is causing it is likely to get worse rather than better. I had to change the exhaust pipe on the super cub from bent (Sutton) to straight as the back seat was getting a LOT of CO (through the leaks in the door).

BTW, where are people getting exhausts rebuilt now? It used to be Dawley, is that still the preferred choice?

sj
 
SJ said:
I had to change the exhaust pipe on the super cub from bent (Sutton) to straight as the back seat was getting a LOT of CO (through the leaks in the door).


sj
Click to expand...

My wife would complain about that also, but I don't think it was that bad because after awhile she would get quiet and stop complaining :roll:

Glenn
 
A second for Aerospace Welding. They “rebuilt” an exhaust manifold for me a while back. Fast, and excellent workmanship.

One of the problems with CO is that even a little bit can be bad. The 206 I was flying when I got “gassed” had given the pilot headaches for some time, but he didn’t tumble to what was causing them. Then, temps got COLD as opposed to cool and I flew the thing three hours.....not good.

MTV
 
Remember CO poisoning is cumulative. You can poison your self a little more everyday. But it takes like 6 weeks for it to release from your blood.


Sent from my iPhone using SuperCub.Org
 
  • CO is eliminated unchanged from the lungs in an exponential manner
  • The biological half-life of CO in a sedentary healthy adult is 4–5 hours
  • This half-life decreases with oxygen administration
    • ~ 40–80 minutes with administration of 100% oxygen
    • ~ 23 minutes with hyperbaric oxygen (2 atmospheres)
  • eliminiation is affected by the factors as absorption (aee above) and is likely faster in many CO poisoned patients due to compensatory measures (e.g. hyperventilation, increased cardia output)

This means that 50% remains in 4-5 hours
25% in 8-10 hours
12.5% in 16-20 hours, etc.

But if you are exposed to it daily, the effect can be cumulative.
 
I've wondered how pilots on preflight deal with obvious points of exhaust leaks. There's sometimes unplugged holes or gaps in the firewall, lower boot cowling, or around the landing gear fittings. That plus white exhaust stains from leaded fuel at the slip joints, cylinder flanges, or engine heater box outlet dump if there's an interest to have a look. Plus the open tail to cockpit flow of exhaust like in some Pipers.

I asked one pilot this summer about the leaks on his engine exhaust and openings behind the lower cowling...yea, well, maybe, and so on. One condition can lead to another and sometimes someone needs to be the a-hole that points out the connection.

Edit: There's a good reason to periodically have a look inside the heater's SCAT ducting for exhaust stains as well.

Gary
 
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One thing I really like about the maintenance outfit I currently use is that they thoroughly leak check everything in the exhaust and heat system. Everyone should, but,,,

MTV
 
My 185 is the opposite. If I have everything shut off, I get intermittent 3-8ppm readings. If I open any air source (heater, vent, wing root vents, etc.) the reading almost immediately drops to 0. I’m assuming it’s a small leak in the firewall, but there’s no obvious open holes and I haven’t spent too much time looking as I almost always have an air source opened.
 
I have the Smart Sensor carbon monoxide meter model AS8700A. I do not care for this meter because every time I key my mike it causes the alarm to go off on the meter while giving a false reading on numbers. I'm guessing the Fluke meter doesn't have those type of issues? I would appreciate any feedback on units that you are using and are happy with. Thanks, Eddy
 
I continue to use the disposable dots because as long as I open a new one every few months they're current. My Aeromedix meter? Not so much.
 
Mine is the electronic one from Sporty’s. Seems to work quite well. It’s sensitive enough that if I fly through the wake of my buddy’s Husky, it sets off my detector.
 
We can minimize (but not completely eliminate) CO production by running the engine lean. Too much fuel vs intake air creates incomplete combustion. What should ideally exhaust as CO2 gets produced as CO from insufficient oxygen. Clean air filters and good ignition or fuel components help combustion. Leaks (airframe/exhaust) are still our main enemies.

The only plane I had that would turn a CO spot dark quick in winter was my PA-11. There was an exhaust shroud mod over a slip joint that had been installed to extract more cockpit heat. We sealed the joint with high temp RTV (Ultra Copper) but it persisted. I finally had the heat muff returned to factory design. Later we reformed the leaking connections with a muffler pipe expansion tool as they were deformed but left the extra heat mod alone.

Tool: https://www.classiccarrestorationclub.com/video/exhaust-pipe-expander-015257/ He doesn't show it but placing hose clamps over a deformed fitting can reduce overall expansion but still allow for reforming the metal for a better fit.

Gary
 
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In some aircraft, there can be a fair bit of air flow from the tail forward into the cockpit. In Cubs, I suspect this "induction" comes through the shroud around the stabilizer cross tube.

That forward moving air comes forward through the tail cone, and into the cockpit from under the rear seat. I've placed a shroud that goes under the rear seat cushion, and snaps or velcros to the floorboards to reduce that flow of air. Its surprising how much this one thing increases cabin temps in many Cubs. It also reduces the amount of CO entering the cabin via that route.

Simple, cheap and no STC required

MTV
 
We can minimize (but not completely eliminate) CO production by running the engine lean.
Click to expand...

With carburettor equiped aircraft, my understanding is that Lean Of Peak, leaning is not an option. (Thank god, that arguement makes the heal verses toe brake one look small)

So I do what I did 30 years ago. Lean to 50 rich of peak. Is this what everybody else does in their C180?

I'm also re-doing the dash on mine, and didn't think I'd install an engine monitor but I am installing a fuel flow meter. My arguement is that the aircraft has been operating perfectly fine without it for the last fifty years and I like a simple dash without gadgets flashing and dinging.
I would like a engine digital monitor that was behind the dash and just used a downloadable device.
(Am I doing the right thing here? PM welcome if you like)

I am however installing a dash mounted CO detector.
 
texmex said:
With carburettor equiped aircraft, my understanding is that Lean Of Peak, leaning is not an option.
Click to expand...

It depends - some engine types naturally have more consistent mixtures between cylinders and are happy for a small range of LOP operations. Some specific engines do better than others, whether it's a good engine type or not.

There's also some tricks to making LOP work better on carb'd engines such as pulling on some carb heat and cracking the throttle valve to increase turbulence/fuel-air mixing.
 
Putting a belly pod on my Cub changed exhaust flow enough that CO quickly became a problem. 6” tail pipe extensions on the crossover system helped a lot.
 
If there's airspace between your brake line exit holes and belly fabric or inspection covers seal the gap. Might help reduce CO.

Gary
 
Good advice. I looked for potential gaps and holes. None in the area around the pod. My Brake lines use a bulkhead fitting with no fabric hole at all.
 
Any inspection covers that can leak> Maybe take some pics of that area and we can look for leak spots? But the tail if open above the spring and trim slots are others. Easy to seal them better.

Gary
 
spinner2 said:
Putting a belly pod on my Cub changed exhaust flow enough that CO quickly became a problem. 6” tail pipe extensions on the crossover system helped a lot.
Click to expand...

we ran into this also... we used to not fabric tail shut at rear, but once belly pods appeared, we started having issues.. so now we cover that rear portion(we only cover to the diagonal by spring bolt)
 
I use this device. Seems to work well.
Available on Amazon.
$99 3 yr life

E51535F7-376A-41B6-873A-812170156681.jpeg
 

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texmex said:
With carburettor equiped aircraft, my understanding is that Lean Of Peak, leaning is not an option. (Thank god, that arguement makes the heal verses toe brake one look small)

So I do what I did 30 years ago. Lean to 50 rich of peak. Is this what everybody else does in their C180?

I'm also re-doing the dash on mine, and didn't think I'd install an engine monitor but I am installing a fuel flow meter. My arguement is that the aircraft has been operating perfectly fine without it for the last fifty years and I like a simple dash without gadgets flashing and dinging.
I would like a engine digital monitor that was behind the dash and just used a downloadable device.
(Am I doing the right thing here? PM welcome if you like)

I am however installing a dash mounted CO detector.
Click to expand...



Hopefully there arn't many 180/185 drivers running 50d ROP. It is arguably the worst mixture setting.
 
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