Cockpit smoke from smoke system

dsmith1055 · #1 03-22-2015, 08:47 PM

I got my smoke system installed and working well except for getting smoke in the cockpit after about 20 seconds. I have read everything I can search out on the site regarding this. Lots of discussion on sealing cockpits, negative cockpit & tailcone pressure etc., but no reports of solutions. I would like to hear from anyone who has found a solution that allows for extended smoke time without a cockpit full of smoke. My plane is an RV4 with Vetterman 4 pipe exhaust.

fixnflyguy · #2 03-23-2015, 05:00 AM

I have a -4, with Vetterman 4 pipe, 2 injectors located on the inboard 2 pipes, about 12 inches from the exits. I have the angled turn down tips, all turned slightly inward. I have done no unique sealing to my cockpit, and I have never had any smoke/smell in the cockpit. Even with air vents closed and no forced circulation, I have no reverse airflow that I can detect. I do get some residual oil migrating into the aft belly skin near the tailwheel fitting/vertical fin spar and plan to seal all that eventually, so there is some negative pressure there. Depending on your tips, I would possibly suggest looking into your flap rod pass throughs. I do have interior close-out panels that cover those areas, but my smoke is "angled" inward and converges into the centerline.

Andy Hill · #3 03-23-2015, 05:52 AM

I would suggest you check/fit a CO detector? I cannot see how smoke getting into the cockpit is any different from exhaust products when smoke is not running

dsmith1055 · #4 03-23-2015, 06:33 AM

Thanks guys. 400 hrs. on the plane before adding smoke with no apparent CO ill effects. Cockpit clears in a few secs after smoke shut off. I'll check with a CO detector nevertheless.

My pipes are not angled inward and sitting here at my computer I am not sure which 2 pipes I used. I was more concerned with under cowl clearance and hose routing. I do have the turn down tips. I'll follow your example & see how it works or me. How did you go about sealing the flap actuator rods?

fixnflyguy · #5 03-23-2015, 06:47 AM

I didn't seal the flap actuator rods directly, but have a side panel/armrest that completely covers the mechanism I fabricated from .020" sheet metal. No air flows through to the cockpit.

dsmith1055 · #6 03-23-2015, 07:21 AM

Thanks Bill. I'll take a look at that too. Good info from everybody.

PerfTech · #7 03-23-2015, 09:24 AM

Quote:

Originally Posted by dsmith1055

I got my smoke system installed and working well except for getting smoke in the cockpit after about 20 seconds. I have read everything I can search out on the site regarding this. Lots of discussion on sealing cockpits, negative cockpit & tailcone pressure etc., but no reports of solutions. I would like to hear from anyone who has found a solution that allows for extended smoke time without a cockpit full of smoke. My plane is an RV4 with Vetterman 4 pipe exhaust.

...We build and have installed on RVs 25 or so custom smoke systems. This problem is common to all and in a little more complex than just sealing up a couple of places. The open areas where aileron control linkage exits to wing, gaps and leakage around fuselage etc. all contribute to a low pressure situation in the cockpit area. This has a tendency to draw air in from the flap actuator rod openings, but mostly from behind the rear passenger bulkhead. Sealing these up helps but the real solution is to open your fresh air vents when operating your smoke. It is very difficult to eliminate the smell when smoke is on for an extended period. One of our customers says, the answer for him is to use his old french fryer oil from his restaurant as smoke oil. It smells good and the only down side is he gets very hungry when it is in operation. He reported gaining a lot of weight when using his smoke for extended periods.

Thanks, Allan...

Smilin' Jack · #8 03-23-2015, 09:10 PM

I too have experienced this with my smoke system.. Installed on a 4 pipe Vetterman exhaust on the back two cylinders. I do have a CO2 detector and have never had an issue but under certain conditions The cockpit does get some smoke in it. I have sealed up the lightening holes in the tail area and am working on other spots. Open the vents and providing a positive air pressure does help.

Jack

rvmills · #9 03-24-2015, 01:18 AM

Dwight,

I was the brunt of many jokes about being IFR in the cockpit during our formation practice and shows, and had very good success with cockpit sealing. Honestly, it made the difference, and it continue to work well. You may have seen this thread with several good sealing techniques...but it's linked there for you, just in case.

I used weatherstripping along my roll bar, the rubber strips along the sides of the slider, and foam in the baggage wall triangles. I have not yet sealed my flap openings or my aileron push tubes openings, and still have had good results in cockpit smoke mitigation. My feeling is that if you reduce, or nearly eliminate, the cockpit outflow leaks, you'll reduce the airflow into the cockpit from the tailcone, which appears to be where the smoke comes from...at least in my case at any rate.

I realize you may need to develop techniques for the tip over on your 4, but that's where I'd recommend starting. Good luck!

Cheers,
Bob

dsmith1055 · #10 03-24-2015, 05:21 AM

Quote:

Originally Posted by Smilin' Jack

I too have experienced this with my smoke system.. Installed on a 4 pipe Vetterman exhaust on the back two cylinders. I do have a CO2 detector and have never had an issue but under certain conditions The cockpit does get some smoke in it. I have sealed up the lightening holes in the tail area and am working on other spots. Open the vents and providing a positive air pressure does help.

Jack

Jack, Thanks for the reply. I would like to seal the tail cone as best I can and as far back as possible. What technique did you use to seal the the lightening holes?