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Fresh air from engine baffles.

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I own a lovely little 6 that was finished in 1992. Currently in the midst of a panel update and refurbish, addressing safety items as well. The cockpit fresh air comes from the back of the upper engine baffle - it works very well but I wonder about the safety of this setup. What say you? Is this as bad as it seems? If it’s not broke don’t fix it but I’ll put naca vents somewhere in a minute if it’s a safety issue. Im sure you guys know precisely, couldn’t find much after an hour of searching.
 
I would think the NACA inlets external to the engine compartment that pull in fresh air would be much more preferable. Depending on your setup, the chance exists for the current system to allow heat, CO, fuel vapors, or oil mist into the cockpit. Not to mention it's pulling air away from the engine that should be used for cooling. Just my two cents...
 
D-Dubya said:
I would think the NACA inlets external to the engine compartment that pull in fresh air would be much more preferable. Depending on your setup, the chance exists for the current system to allow heat, CO, fuel vapors, or oil mist into the cockpit. Not to mention it's pulling air away from the engine that should be used for cooling. Just my two cents...
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What he said......
 
I've seen that on another 6 as well.

I can't figure out what keeps an engine fire from going through (in both senses of the word) the flex duct and into the cockpit. Really poor idea I think.
 
Take it for what its worth. I built my RV4 and My Rocket with that set up. I saw no draw back with the RV4 as it was not injected and the chance of fire up that high unlikely. The Rocket is injected so I incorporated a stainless steel shut off valve at the firewall as an in case. The set up works fantastic and it saves a couple of extra holes in the side of your airplane.
Ryan
 
The plans show for heated air to come from the same area, but it goes through the exhaust heat exchanger, sometimes called a "cabin heat muffler."

I would not be too worried about fresh air coming from that area on top of the engine since it's on the cool side of the engine, and at speed, it would be pretty cool. If you feel like taking on a project, adding a NACA vent into the side of the aircraft just behind the FW is pretty easy.
 
131RB said:
Take it for what its worth. I built my RV4 and My Rocket with that set up. I saw no draw back with the RV4 as it was not injected and the chance of fire up that high unlikely. The Rocket is injected so I incorporated a stainless steel shut off valve at the firewall as an in case. The set up works fantastic and it saves a couple of extra holes in the side of your airplane.
Ryan
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At first I thought about your logic and agreed... doing this baffle fresh air vent on an injected plane would be a much worse idea. And on a carb system it would be OK... ?

BUT, I assume the line from the rear of the baffle to the firewall is SCAT? And the valve is at the panel, not at the firewall? So what happens with a lower cowl fire... how long do we expect the SCAT to last before it burns through? And then the only thing keeping the fire from coming into the panel is... lack of airflow? Just the radiant heat is going to light off the SCAT. Time for Dan H to do another test?
 
rv8ch said:
The plans show for heated air to come from the same area, but it goes through the exhaust heat exchanger, sometimes called a "cabin heat muffler."

I would not be too worried about fresh air coming from that area on top of the engine since it's on the cool side of the engine, and at speed, it would be pretty cool. If you feel like taking on a project, adding a NACA vent into the side of the aircraft just behind the FW is pretty easy.
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It Does work very well, the air is nice and cool. I just worry about say, a blown cylinder that suddenly pumps my cabin full of smoke and hot oil vapor. I just don’t know how much of a concern that should be. One of the purposes of fresh air is to provide outside air in the event of smoke, not to add more, especially in an RV where you’re in a fishbowl already…
 
a blown cylinder that suddenly pumps my cabin full of smoke and hot oil vapor
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Well, I've had this very scenario, though it was a conrod failure that punched a hefty hole on the bottom, and another one on top of the case. In my case the engine stopped by itself in a matter of maybe 4 seconds... so the smoke was not really a factor, but more the oil on the windshield, and the lack of landing space.

Installing a shut-off flap on the firewall might be a good idea...
 
So I will be the spoiler

Lets see. 1992 to 2023 is 31 years give or take. If you like it, leave it. It works.
Popcorn:)
 
Fresh air source....

131RB said:
Take it for what its worth. I built my RV4 and My Rocket with that set up. I saw no draw back with the RV4 as it was not injected and the chance of fire up that high unlikely. The Rocket is injected so I incorporated a stainless steel shut off valve at the firewall as an in case. The set up works fantastic and it saves a couple of extra holes in the side of your airplane. Ryan
Click to expand...

That is what I did. Cylinder cooling was definitely not an issue. I have never smelled any vapors from the engine compartment. The air might have been slightly warmed by going over the engine but not enough to make a difference and would blow your hat off, if you wore one. In the -4, it is difficult to find a great place to put NACA intake vents to be effective. Ones on the canopy skirt are notorious for doing not much.

I am experimenting with a ducted way to get air from the cowling air intakes to the baffles. My shutoff is a stainless steel gate on the firewall, not panel. The eyeball vents on the panel can also be shut off, of course. I always start the airplane with the firewall vent shut....
 
We (some) go through great lengths to isolate the engine compartment from the space behind the firewall, maybe to extremes, but your system allows a Scat size hole to exist that routes directly from the potential fire source to your seat.

This routing appears to be an early/easy attempt to solve a problem, and likely has worked well for a long time. Does this mean it's a good idea? I don't think so, but rather a reflection of how infrequently a catastrophic fire occurs FWF in our craft. Just like carrying a fire extinguisher, having airtight firewall sealing is mostly a waste of time until you need it (I'm not talking about smells and CO here).

I would at the very least recommend a skookum shutoff valve in line with your scat tube at the firewall, maybe one of the stainless steel ones available out there, connected to a cable with a big red knob. You may never put it to use, but boy, it would be a really bad day if you didn't have it!

Cheers
 
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YET ANOTHER PERSPECTIVE .....

Assuming that you don't see fire being any worse a situation, I would say REALLY consider **smoke**!

During airshows, I have had the situation where "SMOKE-ON!" (intermittently, I will say) caused the cabin to get filled with "smoke" from my smoke system (lower pressure sucking it in through holes in fuselage). The good stuff doesn't bother you that much but bad stuff will burn your eyes and affect visibility.

I remember one time when it happened (over the Gulf of Mexico), my team members reminding me to MAKE SURE that my "fresh air vents were fully open" so that I have the potential for positive pressure inside the cabin to blow out the smoke (and thus continue in the airshow).

Now, assume that you have a BIGGER problem of oil leaking from somewhere and THAT SMOKE is being blown in. You have no outside air to clear it out. I assume that you can close the vent that caused the cabin to fill up, but you have nothing to get rid of it.

Now, further assume that your engine eventually quits due to this problem, your eyes and breathing may have been compromised past the point of being able to land.

I would consider the NACA vents.
 
blaplante said:
At first I thought about your logic and agreed... doing this baffle fresh air vent on an injected plane would be a much worse idea. And on a carb system it would be OK... ?

BUT, I assume the line from the rear of the baffle to the firewall is SCAT? And the valve is at the panel, not at the firewall? So what happens with a lower cowl fire... how long do we expect the SCAT to last before it burns through? And then the only thing keeping the fire from coming into the panel is... lack of airflow? Just the radiant heat is going to light off the SCAT. Time for Dan H to do another test?
Click to expand...

As stated before I have a stainless steel shutoff on the firewall (engine side) I see no negative. Take it FWIW.
 
131RB said:
As stated before I have a stainless steel shutoff on the firewall (engine side) I see no negative. Take it FWIW.
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Ah. Indeed. Sorry. I was conflating your setup with one I've seen on a 6. Carb system, SCAT from top aft baffle through the firewall to the plastic eyeball vent. I see a negative with that :)
 
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