Carbon Monoxide reading on ground

[carusoam]

I have the most recent....

Dan is doing a great job telling the story from a factual point of view....

And supplying a great discount on meters to everyone that follows along...

And has the tools to calibrate the users monitors each year at Mooney Summit...
 

Dan is also a Mooney specific CFII...

and works with other cool machines in his other job... 

Go Dan!

Best regards,

-a-

 

 

[Adi]

Oh, I remember this story now! I listened to the "There I Was" episode a while ago.

I'd heard of CO poisoning before then, and I had been thinking of getting a CO monitor, but listening to that episode made me get one immediately (initially a Sentry, and then a Sensorcon once I bought my Mooney).

If I didn't have the detector today, I probably would have taken off none the wiser. Thank you @DanM20C for sharing your story! It may have saved my life!

 

[carusoam]

Basic flight training often covers CO...

it is expected that you would smell the exhaust... if it were that much entering the cabin...

I like to ask the question because from my experience... people don’t notice the elevated level of exhaust...

More when you are 20, not so much when you are 40, by 60... I can tell if there is smoke, or a skunk... 

Not shades in between...

Opening the heater valve should show a significant change in the CO reading if the muffler is cracked...  but, if the heater valve isn’t in top condition... it might not be closing all the way either...

You might get a twofer while working on your heat system... 

+1 for having a Sensorcon...

Best regards,

-a-

[ijs12fly]

@Adi So you never mentioned what happened with your CO issue?  Did you ever figure out the cause?

 

I have a 77 M20C and see high CO during climb (sometimes 20-50 ppm) and then it goes to <5 in cruise 24^2.  In cruise if I push the RPM and MP up to 25 or 26 squared then the CO climbs.  Had two shops leak test the exhaust and so far can't figure it out.

 

 

[Adi]

Oh, I thought I had posted an update! My bad.

What eventually happened was that the shop took off the entire exhaust system and shipped it to a specialized company for overhaul. During overhaul they found some tiny cracks that would only open up when warmed up (probably contributing to the flaky reproduction steps / getting worse during runup). After they shipped the overhauled system (took 2+ weeks) it seemed okay - it would still sometimes go to 10-15-20ppm on the ground, seemed to depend mostly on wind, but never the high values I used to get before.

Then I bounced a landing a few months later. It wasn't a terrible bounce but it must have dislocated something because on the next run-up I got higher than normal PPM values, in the 80 range. I got the plane looked at again and the mechanics found that one of the ball joints in the exhaust system had become non-round and was leaking CO. They shipped part of the system to the overhaul company again and they fixed it free of charge.

I haven't had big problems after that, but it's still not perfect. The worst I've seen it go is to about 50ppm on the ground, opening the door vents the CO and it doesn't come back. Most of the time it stays <15ppm on the ground.

I am still getting 10-20ppm when I trail or open the cowl flaps. This can be reproduced reliably - in climb, I get 10-20; in cruise, if I have cowl flaps closed, I get 0; if I trail the cowl flaps, I get ~10+. I cross-checked this reading with another Sensorcon instrument and they seem to be correct.

I moved the Sensorcon above my main instruments to be in my primary scan and given that I can cruise with 0ppm, I've accepted this for now. I plan to get another pressure test at the next annual. 

The cowl flaps affecting the reading so much seems very relevant to me, but I don't know what to make of it. If anyone has any idea what to check, I would appreciate it.

[Ragsf15e]

Not sure about your cowl flaps changing the reading, but your ground and cruise readings are the same as mine.  Less than 20 on the ground, 0 in cruise.  Last week I saw 60 during runup but I had a quartering tailwind and elected to takeoff.  As soon as I turned to point down the runway it started decreasing.  The airplanes are sort of leaky.  No way to fix that perfectly.  However, I have also found a significant exhaust issue based on high readings on the ground, so the sensorcon has paid for itself.

[ijs12fly]

On 5/13/2021 at 10:54 PM, ijs12fly said:

@Adi So you never mentioned what happened with your CO issue?  Did you ever figure out the cause?

 

I have a 77 M20C and see high CO during climb (sometimes 20-50 ppm) and then it goes to <5 in cruise 24^2.  In cruise if I push the RPM and MP up to 25 or 26 squared then the CO climbs.  Had two shops leak test the exhaust and so far can't figure it out.

 

 

I finally (after 2 years) resolved my CO issue.  When looking for the cause I tried all combos of Vents open/closed, heat on/off,  no matter what I did the CO would be high in take off/climb/full power as well as when straight and level with power above 24^2.    Pressure tested heat system,  nothing.  I even removed scat tube and put HVAC tape on my heat valve on the firewall to eliminate anything coming in from the muffler / heat exchanger.   At the last annual I had all of the exhaust gaskets replaced, and engine shock mounts replaced.  Turns out that this fixed the issue 100%.   So the lesson learned is if there is CO under the cowling, it will find its way into the cockpit.   None of my issue was related to holes in heat exchanger, rat boots,  rudder boots,  door seal, loose body panels, slip stream into main gear area, etc...

I'm not certain why the high CO was only noticeable under high power if it were coming from leaking exhaust gaskets, I would have assumed it should have also happened at 24^2 as well, but it didn't.  Also not sure if the shock mounts added to the improvement, maybe relieving some pressure on the exhaust slip joints.    

Edited April 29 by ijs12fly

[carusoam]

Great follow-up IJS!

The open ended exhaust apparently builds enough pressure at high power settings to get CO to leak…

Thanks for sharing the details.

Best regards,

-a-

[PT20J]

On 8/21/2021 at 2:54 PM, ijs12fly said:

I'm not certain why the high CO was only noticeable under high power if it were coming from leaking exhaust gaskets, I would have assumed it should have also happened at 24^2 as well, but it didn't.

At high power the engine is running on a rich mixture. CO production in an internal combustion engine is heavily mixture dependent. Rich mixtures produce a lot of CO because the combustion of the excess fuel is not complete. As the mixture is leaned, CO production goes down rather precipitously. LOP there is so much excess air that relatively little CO is produced.

Skip

[Ragsf15e]

7 hours ago, PT20J said:

At high power the engine is running on a rich mixture. CO production in an internal combustion engine is heavily mixture dependent. Rich mixtures produce a lot of CO because the combustion of the excess fuel is not complete. As the mixture is leaned, CO production goes down rather precipitously. LOP there is so much excess air that relatively little CO is produced.

Skip

Yet another reason to lean aggressively on the ground.

[carusoam]

4 minutes ago, JohnZ said:

All,

Here is a very well written informational piece about carbon monoxide in general aviation aircraft published by the FAA. Per the article: "CO was monitored over a 12-month period from several single-engine GA aircraft during student flights of the Aviation Department of the Kansas State University at Salina."

I thought this document provided a lot of insight on both "normal" and "excessive" CO readings during ground operation and flight in GA aircraft. The Kansas State University study placed several CO detectors in various locations around flight training aircraft to determine which locations were the most effective at detecting CO readings and it even went so far as to differentiate between phases of flight and high wing/low wing aircraft. The article is lengthy but browse through it and you should easily be able to locate the highlights. 

http://www.tc.faa.gov/its/worldpac/techrpt/ar0949.pdf

Interesting resource John.

See if Dan @DanM20C is familiar with that FAA document (CO detection and prevention)

Best regards,

-a-

[DanM20C]

15 hours ago, carusoam said:

Interesting resource John.

See if Dan @DanM20C is familiar with that FAA document (CO detection and prevention)

Best regards,

-a-

Thanks Anthony, I don't think I have seen that one.  I'll comb through it tonight.

Cheers,

Dan

[A64Pilot]

On 4/26/2020 at 12:15 PM, GeeBee said:

I know some boats that in a strong wind will have CO collect below the swim platform with the generator set running, but in a calm wind, no problem. 

 

 

That has killed a surprising number of swimmers, CO can’t be taken too seriously.

‘I’m surprised the numbers are as high as they are in a Mooney, I’ve not experienced that before. I just ordered a detector, in a month or so when my new knee heals enough so I can fly I’ll find out what mine is. 

What is average in flight?

[exM20K]

2 hours ago, A64Pilot said:

What is average in flight?

I see 0-5 ppm on the Tocsin which was just overhauled by them.  I have no good explanation for where it's coming from, but I know it's not the heat.  I run LOP, which I thought took care of CO, but evidently it doesn't.  I suspect various cabin leaks create low pressure that draw exhaust into the cabin and also let me cheat on airspeed reports by using the alt static like @mike_elliott does lol.

-dan

[A64Pilot]

lean mixtures will reduce CO I believe, but of course not eliminate it. a Diesel engine which has no throttle valve so it runs super lean at part power because the intake is wide open produces little CO I think for example.

In doing production certification test  flights I had to check every third airplane for CO, it was easier to just check them all. and I never got any CO in flight, these were turbines and exhaust was out the side, maybe that’s why? I used a Scott Mini-SA and clipped it to the shoulder harness, that put it close to my face.

I never checked the Maule or 210

On a Mooney I wonder if it’s coming in through the Naca vent on the tail, or the belly? Easy to tape that vent off and see.

Airflow does swirl around the airframe from the prop. this is easy to see on a turbine by the soot from the exhaust.

Edited August 26, 2021 by A64Pilot

[carusoam]

Running LOP is great at minimizing CO… lowering the number is a nicety…

unfortunately, once you ingest the CO, it takes several hours to excrete it… lots of CO can accumulate over hours in flight…

A short exhaust stack, hard plumbed, directly out the side of the cowl would be great for eliminating CO issues in the cabin… not ideal for an efficient airplane that uses heat in the winter… or has a muffler for the neighbors…

Flexible seals, sliding couplings, worn pipes, cracked welds, re-used V-bands, burnt sheet metal in the heat system… all under the cowl right in front of the cabin… adds to the possibilities of CO being available, in the right place…

The cabin is running a vacuum compared to the outside…  it will try to draw in exhaust that is placed anywhere near the skin…

Any CO deposited anywhere that isn’t the exhaust pipe tip… is a potential hazard…

So…. Be on the lookout for exhaust stains anywhere that isn’t the exhaust pipe tip…

Find any missing fasteners and get them replaced sooner rather than later…

The hidden delivery system… is the cable pathways at the back of the cabin… this is where all of the avionics and antenna wires pass through into the interior of the cabin… often, this doesn’t get sealed properly for blocking out CO…. It gets stuffed with things to cut down on cold air from coming in… but not get sealed air tight like we would prefer…

PP thoughts only, not an HVAC technician…

Best regards,

-a-

[mike_elliott]

1 hour ago, exM20K said:

I see 0-5 ppm on the Tocsin which was just overhauled by them.  I have no good explanation for where it's coming from, but I know it's not the heat.  I run LOP, which I thought took care of CO, but evidently it doesn't.  I suspect various cabin leaks create low pressure that draw exhaust into the cabin and also let me cheat on airspeed reports by using the alt static like @mike_elliott does lol.

-dan

Dan, your plane would be faster too if not for the FIKI and you flying it with your foot on the left rudder all the time, making it dog walk thru the sky