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Exhaust in Cockpit

N

N24YW

Well Known Member
I have a RV-6 with a smoke system. When I turn it on for more than 5 seconds I start to get smoke in the canopy. If I am seeing smoke I beleive I am getting CO all of the time. I have a Forsling exhast system. Has anyone else encounted this problem.

Jim Knight
Burlington Iowa
RV6
 
Smoke on

N24YW said:
I have a RV-6 with a smoke system. When I turn it on for more than 5 seconds I start to get smoke in the canopy. If I am seeing smoke I beleive I am getting CO all of the time. I have a Forsling exhaust system. Has anyone else encounted this problem. Jim Knight, Burlington Iowa, RV6
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I have not herd of a big CO problem with RV's. Forsling, I have heard of the brand, but not sure about the design. It's pretty good quality from what I know and assume its like most exhaust. To answer your question most RV'ers don't have a CO problem, despite the pipes leaving just under the cockpit. I suppose you could have a leak somewhere.

I don't know many RV'ers who have a smoke system. Not sure how that might affect CO getting into the cockpit. I understand most smoke systems just blow mineral oil into the exhaust pipe through a tube to get smoke. Is there a way for exhaust to back-feed in the cabin through that oil line?

How do you know you are getting CO? Do you have a meter?

CO is a serious issue so you should check it out before flying.

I would look for any exhaust pipe leaks from the cylinders flange to the exit as a good start. Also consider looking for openings in the firewall to seal.
 
Naw George,

He is getting smoke into the cockpit so therefore he PRESUMES that CO (and other ancillary gases) are entering as well.

I am interested in hearing the responses as well.

:) CJ
 
N24YW said:
I have a RV-6 with a smoke system. When I turn it on for more than 5 seconds I start to get smoke in the canopy. If I am seeing smoke I beleive I am getting CO all of the time. I have a Forsling exhast system...
Click to expand...
I am not familiar with the Forsling but if there is smoke in the cockpit that would seem to be a good reason to wonder about CO.

I have a Vetterman exhaust and had the opportunity for Louise Hose to check my CO using the good gas monitors that she uses in extreme caving. I found there was some CO in my RV-6 pretty much all the time. If I recall correctly it was worst during climb and very low in cruise. I think the levels were somewhere around 6 to 12 PPM during taxi and climb. That is pretty low and not really a cause for concern. She can correct me if I am misremembering the numbers.

I believe Louise's airplane had even lower levels. It has an exhaust system of unknown origin.

I sometimes get a headache after a long flight and was glad to get the actual data for my airplane.
 
In working on my fuselage I can think of places where gases can possibly enter. Among those are:

* Aileron pushrod holes
* Around the wing spar(s)
* The side skin conical bend
* Possibly the emp attach area (Probably not as likely as the others)

What is the permissible exposure limitation for continuous occupation? Is there such a level?

Louise?

:confused: CJ
 
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CO in my RV9A

I have been fighting CO in my 9A ever since first flight. I have a meter that reads down to 1 PPM.

The only way I found to keep it at zero was to take a Y off of the passenger side fresh air inlet tube and duct it to the radio stack to help cool that.

Then I squeezed the outlet of the "radio vent tube" to regulate the volume of air coming in.

Solved two problems for me. CO and overheating sl-30. Only drawback is that if I fly in the rain I get a little bit of water dripping in through the radio vent tube.

Some of the things that I tried that didn't work to well were:

1) tried to seal all the holes in the bulkhead behind the baggage compartment.

2) Seal the flap actuating rod holes

3) Leave the fresh air vents open and or the heater on.

I took the meter and held it under the inst panel and the CO level would drop to zero If I put the meter in the baggage area it rises to about 18 PPM.

Talked to Doug at Vans when he took a look at my plane and he was concerned that I had sealed the canopy to well, there are no gaps for air to seep in to the cockpit between the tip up canopy rails and the deck.

I am interested in what you find in your situation.

Duane
 
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Captain_John said:
What is the permissible exposure limitation for continuous occupation? Is there such a level?

Louise?

:confused: CJ
Click to expand...

OSHA puts the current permissible exposure limit (PEL) for carbon monoxide at 50 parts per million (ppm) of air as an 8-hour time-weighted average (TWA) concentration.

The National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) for carbon monoxide of 35 ppm as an 8-hour TWA.

The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned carbon monoxide a threshold limit value (TLV) of 25 ppm (29 mg/m(3)) as a TWA for a normal 8-hour workday and a 40-hour workweek.

My recollection of Larry's data matches his memory. It topped around 10 or 12 ppm on climb-out and hovered around 2-3 ppm in cruise. My plane was something like half the value of his on climb out and less than 1 ppm in cruise. It didn't seem to be an issue in either of our RV-6 tip-ups.
 
Wow Louise!

That was a FAST response!

Thanks!

Now that we have successfully hijacked this thread, do you have any idea about Jim's smoke issue?

:confused: CJ
 
Later in the week I will try to get some readings on gas levels. We have a couple of meters at work the we use for going into confined spaces. I will keep everone posted of what I find out. I have a tip canopy and Forsling exhaust looks just like the Vetterman.

Jim Knight
Burlington Iowa
RV6
 
CO testing

My experience is primarily with forensic engineering and have had to check on a number of CO poisoning issues. Since you know the source, the problem comes down to differential pressures inside the cockpit. One of the solutions mentioned pressurizes the inside of the cabin with the passenger vent.

I'd check the ppm levels on climb out, descent and cruise. I suspect the climb out CO is due to rich conditions and more CO in the exhaust. Using the smoker may also produce more CO, as smoke usually results from incomplete combustion and one of the byproducts is CO. If you have the means, compare the CO2 levels as well during the different flight phases, with and without the smoker on.

If the cockpit is too well sealed, then there will be greater pressure differentials between inside and outside. During descent I would suspect that the "exhaust gases" inside the cabin may increase, although CO levels may actually decrease. On climbout, I would suspect that levels would be influenced by slightly higher cockpit pressure than outside, however, there may be other leaks with different pressure profiles due to the angle of attack.

Good luck.
 
I any tip up that I have flown the air escapes out under the rail. Next time you are up flying take a piece of tissue paper and see for yourself. With the cabin fresh air vents closed you will find a lot of air coming in the joystick holes and also the baggage compartment bulkhead. One place you can check for exhaust coming in is at the bottom of the firewall if it isn't seal properly otherwise check the CO levels in the air at the joysticks and the rear baggage bulk head by the corregations.
 
Remember that turning on your smoke system and geting smoke in the cockpit DOES NOT mean your getting CO in when its off. The expansion of the smoke oil from liquid to gas, it like 8 to 1 or something along those lines. I got smoke in the cockpit in my 6 enough to go IFR in the cockpit, but a digital co meter showed nothing.

Best,
 
How?

Norman CYYJ said:
........... One place you can check for exhaust coming in is at the bottom of the firewall if it isn't seal properly otherwise check the CO levels in the air at the joysticks and the rear baggage bulk head by the corregations.
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Could you explain how exhaust can get in through the bottom of the firewall since at 180 MPH + and the exhausts pointing aft past the firewall lower lip? Along those lines, how could the exhaust migrate out to the wing roots in flight? Same deal......the forward speed would not allow fumes to go sideways. All the underbelly streaks in my -6A go pretty much straight back to the tail.

????
 
Tail Pump

pierre smith said:
All the underbelly streaks in my -6A go pretty much straight back to the tail.
????
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This has been run into the ground on matronics list numerous times in the past. Theory is that low pressure in the tailcone sucks the exhaust into the cabin. That's the theory. Lots of guys have created some pretty fancy fixes for this theory.

Just the messenger.
 
Smoke and CO2 in the cockpit

It is very likely that both smoke and CO2 are being brought in though the tail section of the airplane. None other than the Cessna folks discovered this in their Skywagons years ago, and after much headscratching and "fixes" by the engineering department, someone figured that the tailcone area was relatively lower in ambient pressure, due to the aerodynamics of the relative wind in the trailing portion of the airframe. This actually "sucked" exhaust gases in, which then migrated forward to the cockpit. They then added some (rather draggy) scoops on the upper sections of the tailcone which, even though counterintuitive at first glance, worked beautifully in presurizing the aft section; thus keeping the exhaust gases from entering the fuselage.
Check this out next time you see a 180 or 185 on the ground. An idea would be to install a small NACA scoop near the tailcone, or experimentally "Y" off a lenght of scat from the cabin vent to the tailcone, and measure the results.
Tom Navar
RV8QB
Cessna Skywagon
Pitts S2A
 
Scary

I watched a Cherokee being annualed today and they found two broken exhaust pipes! This was the fancy four-into-one kind that is supposed to give an extra bunch of horsepower. Don't recall the brand name. The pipes were broken inside the heat muff. Sounds like a really good way to get your minimum daily adult requirement of CO. Pull on the heater and just go to sleep. Out of warranty to boot.

Bob Kelly
 
Interesting..

Tom Navar said:
It is very likely that both smoke and CO2 are being brought in though the tail section of the airplane. None other than the Cessna folks discovered this in their Skywagons years ago, and after much headscratching and "fixes" by the engineering department, someone figured that the tailcone area was relatively lower in ambient pressure, due to the aerodynamics of the relative wind in the trailing portion of the airframe. This actually "sucked" exhaust gases in, which then migrated forward to the cockpit.
Tom Navar
RV8QB
Cessna Skywagon
Pitts S2A
Click to expand...

Exactly right. Tom,
My Air Tractor has a big scoop on the left side of the forward tailcone to pressurize it, keeping chemical mist out and preventing corrosion. So you reckon CO is coming in around the elevator horn area?

Would a reverse Naca scoop on top of the RV's turtledeck evacuate air/co?

Regards,
 
I can attest to the fact that it(smoke oil smoke) does in fact come in through the tail and through the baggage of a 6. It was amazing to watch my cockpit go VMC.
This happened cause like a dumb A@#, I cut my stacks off flush with the bottom of the cowl to gain speed. No speed gain. What an idiot. While I was not getting and CO2 from it, the smoke oil smoke filled my cockpit in less than 10 seconds. AHHH!:eek:
I proceeded to weld the stacks back on and all was well again.
 
pierre smith said:
Could you explain how exhaust can get in through the bottom of the firewall since at 180 MPH + and the exhausts pointing aft past the firewall lower lip? Along those lines, how could the exhaust migrate out to the wing roots in flight? Same deal......the forward speed would not allow fumes to go sideways. All the underbelly streaks in my -6A go pretty much straight back to the tail.

????
Click to expand...

I think I remember a different thread about exhaust tube length and also internal cowl pressure gradients, with Van's(?) doing some testing. The tufted strings were placed at different spots along the belly, near the stacks and cowl opening. The tufts would point back into the engine compartment due to lower pressure in the bottom of the cowl. If the stacks are too short, it follows that the exhaust would back-flow into the cowl and could then enter the cabin through any firewall openings that are poorly sealed.

Just regurgitating stuff I read - my fuselage is still on the jig :eek:
 
Multi Gas Detector

I did some test today with a ProGard MultiGas Detector and found some interesting things. First thing I did was drive around with my 92 Dodge Caravan. The tail pipe fell off in front of the rear axle a while back so when I drive with the right window down I smell exhaust. This would give me a reading of 14-18 parts per mil. I believe you can live all day at this level but it really stinks. (It is my airport work van 290,000 miles on it.)

When I went flying I climbed to 5500 feet and my O2 went to 17.5% the alarm went off at 19%. I beleive that to be in a safe confined space Osha requires oxegen to be between 19.5-22.

As far as the CO I never seen any reading get over the 8 parts per million even when I was on short final low power setting and turned on the smoke and filled the cockpit with smoke. Some one said that smoke expands so the would justify why thier can be smoke but not high CO levels.

Jim Knight
Burlington Iowa
 
N24YW said:
...When I went flying I climbed to 5500 feet and my O2 went to 17.5% the alarm went off at 19%. I beleive that to be in a safe confined space Osha requires oxegen to be between 19.5-22...
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Jim, glad to hear you don't seem to have a problem.

The O2 readings you got don't make sense to me. When we checked my airplane we also got O2 readings that didn't make sense. I can't remember if they were way too high or way too low, but the false readings seemed to be related to the sudden pressure changes of climbing and descending.

This was with a pretty sophisticated and calibrated monitor, but with one apparently not intended for that kind of use.
 
Swiss cheese

This has been an interesting thread with some good observations. My personal observation is that many RVs are built with firewalls that are like swiss cheese....and in that condition any leakage of the exhaust system could result in serious levels of CO in the cabin.

Many RV builders don't even seal the firewall where it meets the fuselage skins (bottom, sides, and top). Not good.

Proper sealing of the firewall is a first line defence against heat, CO, and smoke streaming into the cabin.
 
Air Tractor

Monsieur Pierre Smith: My wife's family are in the aerial application industry in Hart, Texas, also using Air Tractors. I've seen the pressurization device you have in yours, and yes, plan to pressurize the tailcone area with a reverse NACA scoop. Thank you for your input.
Tom Navar
RV-8 QB
Cessna 180
Pitts S2A
 
Humm so what will kill you and why.

In the post have read CO2, CO and O2 in post (O2 must be typo?). Chemistry is not my strong subject, but its mostly CO or carbon monoxide we are worried about, right? There are lots of bad things in engine exhaust I see: LINK.

Exhaust is being whipped and wrapped around the fuselage with the prop wash. The cockpit sit in a cocoon of exhaust gas. It would be nice to get CO and other byproducts to zero. With the engine and exhaust at your feet, separated with sheet metal, I guess some particles are going to get in the cabin. May be its time for the full crash helmet and oxygen mask ala fighter pilot. :rolleyes:

In cars the solution is run the TAIL PIPES to the rear bumper. I agree a tight leak free firewall is defense one. One week point of the cabin vent system is there is no dedicated vent or exit.
 
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gmcjetpilot said:
In the post have read CO2, CO and O2 in post (O2 must be typo?)...
Click to expand...
No, O2 is not a typo just a limitation of ASCII. O subscript 2 is the notation for molecular oxygen (two oxygen atoms bound together). O3 is the famous ozone. O2 is about 21% of normal air.
 
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n5lp said:
Jim, glad to hear you don't seem to have a problem.

The O2 readings you got don't make sense to me. When we checked my airplane we also got O2 readings that didn't make sense. I can't remember if they were way too high or way too low, but the false readings seemed to be related to the sudden pressure changes of climbing and descending.

This was with a pretty sophisticated and calibrated monitor, but with one apparently not intended for that kind of use.
Click to expand...

Larry et al.,
My monitors (and, I'd guess, most or all personal monitors) calibrates O2 every time it is removed from its charger and assumes 20.9% (at least, I think that's the default). Unlike H2S and some other gases which are calibrated with sample gases, the monitors assume O2 is ambient where you turn the monitor on.....and that you will not significantly change altitudes. (As a side note, this caused me some problems once when we had a diesel truck outside the window where we had our chargers. I had to run down the street quickly to not calibrated it to those conditions.) When the partial pressure of O2 drops on climb-out (and increased altitude), it apparently assumes that the %O2 has dropped. Thus, the readings we got on climb-out in your and my planes read inaccurately low %O2. Apparently, the monitors really read partial pressure but reports it as %O2.
 
ppO2

The commercial gas monitors that we use on board spacecraft for emergencies read the partial pressure of O2, not the percentage....I assume that is the case for most all of them, so yes, the % would (falsely) go down with altitude.

Paul
 
I just bought the RV6 that was advertised here. Red and white 2002 with the Vetterman exhaust system. I get exhaust smell in the cockpit at slow speeds. At one point a CO alarm went off. Previous owner (he rebuilt the engine) says that’s normal, just open the vents. That does not seem safe or correct. Opening vents help but at slow speeds the smell comes back. Any suggestions?

[email protected]
 
Exhaust smell at low speeds

My understanding is that at low speeds the angle of the attack is higher and the negative pressure in the tail cone combine to pull CO into the fuselage that then moves forward through the bulkhead at the back of the luggage area into the cabin. Not an ideal situation, but one that is overcome by increasing the pressure in the cabin by opening the vents.
Pointing the vent stream at your face during these times is also helpful as you will be breathing more fresh air.
You can test my hypothesis by purchasing a hand held CO monitor and holding it in different areas of the cockpit to see if there is indeed a concentration differential as I suggest.
My levels never got above 10 PPM which is considered safe. I think that up to 40 PPM is OK, but check me on that one.
If possible check and see what your alarm limit is set at.


Duane
 
jimkwalton said:
I just bought the RV6 that was advertised here. Red and white 2002 with the Vetterman exhaust system. I get exhaust smell in the cockpit at slow speeds. At one point a CO alarm went off. Previous owner (he rebuilt the engine) says that’s normal, just open the vents. That does not seem safe or correct. Opening vents help but at slow speeds the smell comes back. Any suggestions?
Click to expand...
Hi Jim, welcome to VAF. Can you post a picture of the ends of your exhaust pipes? Just wondering if they are very short, or not pointing down, or something else unusual. I would guess the exhaust is getting in via the flap holes or perhaps from the tail area - not sure if there are many more places for it to come in.

When you are at "slow speeds", are flaps deployed?

The best number for CO is 0, even small amounts of CO are cumulative, and will decrease your brain's performance over time. Short term having the vents blow on your face is a good idea, but I recommend fixing this more permanently.
 
The exhaust stacks are cut very short. Just forward of the the bulkhead/firewall under the belly with strikes on each side going back several feet.
 
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