Exhaust smells

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Exhaust smells

Postby ghostflyer » Fri Feb 09, 2018 1:14 am

For years now I have had exhaust smells in the cockpit on descent and more so when flaps down. BUT this has happen on a number of Cessna aircraft that I have flown and just thought it was norm especially Cardinals. This was more pronounced when the the 180 hp was fitted. It was now to the point I had to do something and was looking everywhere. [it was suggested by a somebody that a forward facing scoop be fitted to the rear of the fuselage to pressurised the cabin in a fashion .] I have checked on the 170 the door seals ,window seals , upper windscreen where it joins the wing , and also the undercarriage entry point into the fuselage .So on long descents I have cracked the LH window which helps . The other day I fitted aerodynamic cuffs to the lower end of the strut to the fuselage. As per a standard 172.
Well on descents now no smells , then the exhaust must have been entering via the strut attach point to the fuselage . I thought I had that area well Sealed up. The jury is still out if putting aerodynamic cuffs at both ends of the struts has made any performance difference .
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Re: Exhaust smells

Postby GAHorn » Fri Feb 09, 2018 4:21 pm

The lower-left <edit> LANDING GEAR-attach area is a common entry point for exhaust. The <EDIT> landing gear fillet seal at that point should be carefully maintained.
Exhaust has also been known to travel FORWARD from the tailcone to the cabin. Another entry point has been reported at lower beacon-mount areas.

No amount of exhaust should be tolerated in the cabin. IF you can SMELL it.... you've got a PROBLEM. If you CANNOT smell it.... you may STILL HAVE A PROBLEM! (My recent experience in ferrying a 172 has made believer of me with regard to CO-detectors/monitors. Forget those little paper "dots" ...they're useless. Get a REAL ONE.)

Several articles on aircraft-CO detectors have been written over the years. They are expensive ...because they are sensitive. But ANY common detector is better than no detector. Here's the one I have purchased for installation in our 170 and 172 airplanes...to be installed below the instrument panel. (From tests run by others, generally, High wing aircraft have the highest readings below the instrument panel. Low wing aircraft have the highest readings on the left sidewall, beside the pilot's left leg.)
This one has good performance even tho' not "aircraft". It also has a readout of past levels. Less than $25. I suggest it be installed where it can be easily viewed below the panel.
https://www.amazon.com/gp/product/B004Y ... UTF8&psc=1
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Re: Exhaust smells

Postby DaveF » Fri Feb 09, 2018 5:11 pm

I have a Sensorcon CO monitor (https://sensorcon.com/) and have never seen more than about 2ppm in the cabin, and then only briefly. The strut isn't sealed against the fuselage. I also have a 180hp.
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Re: Exhaust smells

Postby GAHorn » Fri Feb 09, 2018 6:15 pm

DaveF wrote:I have a Sensorcon CO monitor (https://sensorcon.com/) and have never seen more than about 2ppm in the cabin, and then only briefly. The strut isn't sealed against the fuselage. I also have a 180hp.


I misspoke... I meant the landing gear seal.
Dave, your exhaust tailpipe is quite different than the OEM "fangs". The OEM tailpipes allowed the propeller "swirl" to bring the left "fang" exhaust directly to the lower/left landing gear attach (which should have a nitrile-rubber or other seal (170B IPC, Item 2, Fig 26 PN 0511125) beneath the "fillet" to prevent ingress of exhaust to the cabin.

LandingGearFillet.jpg
Item 2, PN 0511125, Seal, Landing Gear Fillet
'53 B-model N146YS SN:25713
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Re: Exhaust smells

Postby ghostflyer » Fri Feb 09, 2018 10:47 pm

Thankyou George for that reference for purchasing that co detector. Those paper dot ones are useless as they would turn black after a couple of flights . Maybe it was excessive CO. After very long high altitude flights I do get a grey soot[dust]in the area of the undercarriage leg and strut entry area to the fuselage. Due to the high temperatures in our area all overhead vents are always open and a L/H mounted fuselage side vent is permanently open and often fly with the L/H window open . Except when it rains .
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Re: Exhaust smells

Postby wabuchanan » Mon Feb 12, 2018 8:49 am

Because I have been a Firefighter as well as a Paramedic, I was suspicious of the orange dot detector that was in the plane when I bought it. So I purchased a Sensorcon CO detector like we use at work.

Initial readings showed CO as high as 170-180 in the cabin, mounted on the pouch on passengers side panel. Those high readings were present specifically on descent/approach with flaps down and nose up and eventually led me ( and the IA ) to find the missing exhaust stud during annual. During cruise, levels were much lower.

After replacing the stud and tightening up all the exhaust clamps I was still seeing 35 to mid 80's in the cabin during descent and taxi. No real holes in firewall, but a lot of little holes along belly of plane so filled all those in.

Now it will occasionally hit the alarm at 35 when taxiing, and in the pattern with the nose up and flaps down, but it is transient. I do not have seals where the landing gear enter the belly, and this plane never has had them so this thread is most helpful in that I will put seals there and see how the levels go when taxiing. Current cruise levels rarely exceed 8ppm now.

I highly recommend the Sensorcon line of detectors. Low alarm comes on at 35, and high alarm is 200.
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Re: Exhaust smells

Postby GAHorn » Mon Feb 12, 2018 5:02 pm

wabuchanan wrote:Because I have been a Firefighter as well as a Paramedic, I was suspicious of the orange dot detector that was in the plane when I bought it. So I purchased a Sensorcon CO detector like we use at work.

Initial readings showed CO as high as 170-180 in the cabin, mounted on the pouch on passengers side panel. Those high readings were present specifically on descent/approach with flaps down and nose up and eventually led me ( and the IA ) to find the missing exhaust stud during annual. During cruise, levels were much lower.

After replacing the stud and tightening up all the exhaust clamps I was still seeing 35 to mid 80's in the cabin during descent and taxi. No real holes in firewall, but a lot of little holes along belly of plane so filled all those in.

Now it will occasionally hit the alarm at 35 when taxiing, and in the pattern with the nose up and flaps down, but it is transient. I do not have seals where the landing gear enter the belly, and this plane never has had them so this thread is most helpful in that I will put seals there and see how the levels go when taxiing. Current cruise levels rarely exceed 8ppm now.

I highly recommend the Sensorcon line of detectors. Low alarm comes on at 35, and high alarm is 200.


I don't know which little "holes" in the belly you plugged... but be aware that drain holes are an important part of the design. Airplanes not only corrode...but increase weight even in flight in rain.... unless the water drains out. "Seaplane grommets" might be a consideration if you truly believe they are a source/problem.
I once inspected an airplane which had been tied down outside for a few months and when the tail tiedown ring was untied the airplane refused to "come up" level. We had first thought it was tied down too tightly...then wondered if the nose oleo was overpressurized...but... Removing the bag compartment bulkhead revealed about twenty gallons of water entrapped in the aft fuselage with clogged drains. Imagine if someone had attempted to take it airborne.
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Re: Exhaust smells

Postby wabuchanan » Mon Feb 12, 2018 6:42 pm

Yes, you are correct.

I do know about the drain holes, generally in front of the bulkheads. I utilized those when I first bought the plane and was washing all the AZ dust out of the tail. :lol: These are, I believe, some old antenna holes, slightly larger.
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Re: Exhaust smells

Postby IA DPE » Sat Dec 01, 2018 4:41 pm

gahorn wrote:No amount of exhaust should be tolerated in the cabin. IF you can SMELL it.... you've got a PROBLEM. If you CANNOT smell it.... you may STILL HAVE A PROBLEM!


https://www.desmoinesregister.com/story ... 042715002/
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Re: Exhaust smells

Postby lowNslow » Sun Dec 02, 2018 1:32 am

To George's point here is a picture of the exhaust flow on a 170. As you can see it goes right over landing gear/cabin entry, also doors seals may also be leaking.
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Exhaust Stain.png
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Re: Exhaust smells

Postby edbooth » Sun Dec 02, 2018 3:06 pm

lowNslow wrote:To George's point here is a picture of the exhaust flow on a 170. As you can see it goes right over landing gear/cabin entry, also doors seals may also be leaking.


Another reason for the Bartone type exhaust. :D
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Re: Exhaust smells

Postby ghostflyer » Mon Dec 03, 2018 4:53 am

Wow!!! That would be a good start for corrosion to start on the skin plus it looks like the aluminum has a heat issue also . I have only one exhaust on the right hand side [4 banger engine] and it sticks out about 6 ins away from the cowl,but the smell was coming basically from the L/H side of the cabin . It didn’t appear to be stronger near the floor area just overall. The fairings on the struts have stopped the smell but now worried about the CO that I can’t smell. Have ordered a electronic Carbon monoxide detector.
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Re: Exhaust smells

Postby prairiechicken » Thu Apr 16, 2020 2:48 am

Does anyone know if the gear leg seal P/N 0611064 for an L-19 Bird Dog can be used to replace P/N 0511125 gear leg seal for our 170's?
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Re: Exhaust smells

Postby GAHorn » Thu Apr 16, 2020 2:02 pm

prairiechicken wrote:Does anyone know if the gear leg seal P/N 0611064 for an L-19 Bird Dog can be used to replace P/N 0511125 gear leg seal for our 170's?


The L-19 gear leg is slightly larger, so it may not seal as well as the 0511125 (but you can make your own out of ordinary nitrile sheet gasket material.)
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Re: Exhaust smells

Postby dstates » Thu Apr 16, 2020 2:53 pm

gahorn wrote:
prairiechicken wrote:Does anyone know if the gear leg seal P/N 0611064 for an L-19 Bird Dog can be used to replace P/N 0511125 gear leg seal for our 170's?


The L-19 gear leg is slightly larger, so it may not seal as well as the 0511125 (but you can make your own out of ordinary nitrile sheet gasket material.)


I just recently took these covers off for my annual inspection and there was no seal there, but a lot of black residue stuck to the cover. Now that makes sense. There must have been a seal there at one time.

Is the seal just the same shape as the aluminum cover except tighter on the leg?
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