Belly Pods and CO levels

[Dan L]

Incremental improvements with my setup. With the tape as shown in post 77 below, I made a 20 minute flight and saw single digits in cruise and a high teens in landing profile. Not much of a change.

As I was landing I wondered if the two top cowl vents I closed off with pipe insulation could be changing things? Could the reduced airflow behind the engine and out the bottom of the cowl be changing the overall flow enough to make a difference? So I pulled them out. And they're not needed right now anyway, it was 50 degrees.

Headed back home I still had single digits in cruise but in the landing configuration it never got above 13. That is the lowest I've seen while landing and the changed flow seems to have made an improvement.

I'll keep puttering with it. I'd like to see zero all of the time.

[Andy]

I'll keep puttering with it. I'd like to see zero all of the time.

I wonder if you are setting the bar a bit too high -

https://tinyurl.com/ak5s4b6v

https://tinyurl.com/3cwbv53n

Interesting discussion though. I must remember to put my Kidde CO monitor in my FX-3 for my next flight. Standard build leaves a few holes for cockpit ventilation.

[turbopilot]

I wonder if you are setting the bar a bit too high -

The combination of altitude exposure and CO exposure has to be viewed very differently than the typical ppm limits at sea level. CO displaces oxygen from the hemoglobin so a pilot with CO exposure at altitude is significantly more hypoxic than would be anticipated by just looking at the current altitude. Even more insidious, pulse oximeters will give a false high oxygen saturation in a pilot at altitude with CO exposure.

Bottom line is that you have to be obsessively concerned any time you experience carbon monoxide at altitude. The higher the altitude the bigger the problem with even what would be considered "low" CO readings at sea level.

[Andy]

The combination of altitude exposure and CO exposure has to be viewed very differently than the typical ppm limits at sea level. CO displaces oxygen from the hemoglobin so a pilot with CO exposure at altitude is significantly more hypoxic than would be anticipated by just looking at the current altitude. Even more insidious, pulse oximeters will give a false high oxygen saturation in a pilot at altitude with CO exposure.

Bottom line is that you have to be obsessively concerned any time you experience carbon monoxide at altitude. The higher the altitude the bigger the problem with even what would be considered "low" CO readings at sea level.

Thanks, that's a factor I had not considered. I'm familiar with my hypoxia symptoms as I have 2 "chamber rides" and lots of time in gliders at high altitude with and without supplemental oxygen.

If a pulse oximeter lies when pilot is exposed to CO do hypoxia symptoms also get modified? I don't remember any mention of CO during high altitude training at Edwards but it was a long time ago.

[turbopilot]

Thanks, that's a factor I had not considered. I'm familiar with my hypoxia symptoms as I have 2 "chamber rides" and lots of time in gliders at high altitude with and without supplemental oxygen.

If a pulse oximeter lies when pilot is exposed to CO do hypoxia symptoms also get modified? I don't remember any mention of CO during high altitude training at Edwards but it was a long time ago.

It has been a long time for me since I have dealt with these issues. I am Board Certified in Aerospace Medicine and even had a tour of two years as a flight surgeon at Edwards. My office was next door to the altitude chamber and our hyperbaric chamber (sometimes used to treat CO poisoning).

Hypoxia symptoms will be related to the oxygen available to the tissues. CO blocks oxygen update into the hemoglobin. CO and altitude was never an issue for us in the Air Force. CO is a special problem related to gas burning engines. There have been many events of CO aggrivated hypoxia in high altitude climbers who crowded into tight spaces to keep warm around a fire.

Bottom line best to keep CO as low as possible in any machine that goes to altitude.

[mikemacon]

I wonder if you are setting the bar a bit too high -

https://tinyurl.com/ak5s4b6v

https://tinyurl.com/3cwbv53n

Interesting discussion though. I must remember to put my Kidde CO monitor in my FX-3 for my next flight. Standard build leaves a few holes for cockpit ventilation.

I have had my CO condition for a couple of years. I get 5 to 15 ppm in cruise and 75 to 125 ppm while landing and for a brief time on the ground. I looked at a chart similar to yours, showing what the levels meant, and put myself at ease that I probably would live. I would still like to know how the CO is entering the cockpit. I know the CO is odorless but I get a good shot of exhaust smell when I land. I hope the pilots that are searching for the cause will continue to update this thread.

[Dan L]

I was able to make another flight today with the tape as shown earlier. I flew into the Idaho backcountry on skis and it was about an hour flight to Moose Creek. The NW is having a beautiful start to March and I went up to 9500' and saw 3 PPM in cruise. The lowest continual reading I've had so far. The climb out was around 15 PPM. In the hangar before leaving I also added some tape around the inspection hole covers on the bottom side behind the belly pod. And also where the quick drain penetrates the fabric back there.

IMG_9121.jpg

I landed at MC and decided to remove the tape from the tear drop front elevator cover and the joint between the boot cowl and the front of the triangle belly access panel.

IMG_9146.jpg

I left MC and flew on up to Fish Lake and landed and snowshoed around. I'd say there is about 12' of snow up there. When I got back to the plane I was thinking about the testing and taping while I ate some elk jerky. In the picture at FL you can see I've got blue tape on the inside too trying to pinpoint gas entry points.

On the flight back home at 8500' I saw a steady 8 PPM - up from the 3 PPM earlier in the day when the teardrop and boot cowl were still taped.

Climbing and descending still shows readings in the high teens - up to about 20 at times.

So far the biggest change came when I sealed up the seaplane grommet water drain openings back near the tail and the small fabric opening directly in front of the T3 attach point. These are the biggest contributors. But they aren't the only ones. Some other less obvious gaps and cracks and openings are allowing some gas to enter too.

The Aithre portable detector has been a game changer in getting to the bottom of this. I'm very glad I purchased it.

[Springloaded]

I was able to make another flight today with the tape as shown earlier. I flew into the Idaho backcountry on skis and it was about an hour flight to Moose Creek. The NW is having a beautiful start to March and I went up to 9500' and saw 3 PPM in cruise. The lowest continual reading I've had so far. The climb out was around 15 PPM. In the hangar before leaving I also added some tape around the inspection hole covers on the bottom side behind the belly pod. And also where the quick drain penetrates the fabric back there.

IMG_9121.jpg

I landed at MC and decided to remove the tape from the tear drop front elevator cover and the joint between the boot cowl and the front of the triangle belly access panel.

IMG_9146.jpg

I left MC and flew on up to Fish Lake and landed and snowshoed around. I'd say there is about 12' of snow up there. When I got back to the plane I was thinking about the testing and taping while I ate some elk jerky. In the picture at FL you can see I've got blue tape on the inside too trying to pinpoint gas entry points.

On the flight back home at 8500' I saw a steady 8 PPM - up from the 3 PPM earlier in the day when the teardrop and boot cowl were still taped.

Climbing and descending still shows readings in the high teens - up to about 20 at times.

So far the biggest change came when I sealed up the seaplane grommet water drain openings back near the tail and the small fabric opening directly in front of the T3 attach point. These are the biggest contributors. But they aren't the only ones. Some other less obvious gaps and cracks and openings are allowing some gas to enter too.

The Aithre portable detector has been a game changer in getting to the bottom of this. I'm very glad I purchased it.

Nice picture👍

[Andy]

So far the biggest change came when I sealed up the seaplane grommet water drain openings back near the tail and the small fabric opening directly in front of the T3 attach point. These are the biggest contributors. But they aren't the only ones. Some other less obvious gaps and cracks and openings are allowing some gas to enter too.

I would have thought these tail openings would be insignificant compared to the huge holes provided for trim movement of horizontal stab.

Isn't the likely solution to get the exhaust gas flow away from the fuselage? It's a while since I towed with Pawnees but I think there was an exhaust pipe extension that was intended to reduce cockpit CO levels. How does the exhaust outlet position compare between different CC models?

Your snow pictures are making me wonder what I'm missing. Only 1 landing and 2 takeoffs on skis and no reason to buy them living in Arizona.

[hawgdrvr]

I don't know the flow of air but a thought is if there could be a vent in the aft of the fuselage that would cause any air within to flow out the aft may help vent it so it is not recirculating forward into the cockpit? Depending on items being covered up it may cause air to flow in an unintended direction.