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As Walter Atkinson wrote, there is little likelihood of CO getting into the cabin of a pressurized IV once the cabin door is closed and sealed. Some review of the airflow into the cabin helps to understand this. Once the door is closed and the door seal inflated, air can only enter the cabin through the mixer valve on the top of the firewall in the engine compartment and exit through the outflow valve under the rear seat. It's possible to get reverse flow through the outflow valve back into the cabin with the door open, but very unlikely with the door closed and the engine running, as even at idle the turbos are pumping some air, at positive pressure, through the inlet manifold and the cabin pressurization system.
All air entering the cabin pressurization system comes through the engine air filter from the air scoop just under the propeller (or through the alternate air door in the lower cowl when the filter is obstructed). The only parts of the system--from the air scoop back--under reduced pressure that would allow CO to enter--are the SCAT hoses connecting the air filter to the turbochargers, the air filter enclosure and the alternate air source. If these are in good condition, I can't see how any CO, or other contaminants, could enter the cabin through the pressurization system. Any leaks--tubing, controller, etc, will result in a loss of pressurized air to the cabin--outward flow--preventing any introduction of CO or other contaminants.
I said "little likelihood" when I started because there are some possibilities of contaminated air entry into the system. I think the most likely is when the engine inlet filter becomes clogged and the alternate air door opens. (I have an indicator light on my panel that tells me when this happens, and have seen it open when flying in precip at or a little above the freezing level) Even so, this alternate inlet is located well forward in the lower cowl and has a significant cooling airflow across it when in flight.
So, I wouldn't discourage anyone from installing a CO detector. CO Guardian makes several models that work reliably, take little space, and can be easily connected to any warning/indicator system you have already installed. There are likely others that provide a similar function. After researching this, I sold my CO detector to a friend with an unpressurized IV. In an unpressurized airplane, I'd consider this a necessary item.
Bob
- my CO detector goes off reliably on the ground if I have the door slightly cracked. I'm not sure exactly what is going on but I think it has to do with air flowing backwards through the wheel wells into the outflow valve.
- if you had an exhaust leak in the cowl AND some leak in the induction system (e.g. hoses that lead into the turbos) that would eventually get to your cabin pressurized air.
- if you have an engine fire, depending on what fails, you could get CO in the cabin pressurized air.
I would take it very seriously, especially since the flow rate through the cabin is so much lower than an unpressurized plane that the CO could build up.
On Aug 31, 2011, at 7:42 AM, Dico Reijers wrote:
> Hi All,
>
> Since I'm new to the IV-P, I am wondering what the level of worry is of carbon monoxide getting into a pressurized cabin. I know with my old Cherokee or Mooney, I always had CO detectors (either electronic of that little cardboard thing that changes colour)... but with the pressurized cabin, I would think there may be less chance, perhaps close to no chance, of it getting into the cabin.
>
> Can someone please shed some light on this for me?
>
> Thanks,
>
> -Dico
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