smoke in cockpit causes

[bmellis11]

I’m working on the design for my RV-8’s electrical system, which will include a rear battery and battery contactor. I plan on having a B&C alternator (and regulator) and the main bus feed hooked up to the starter contactor on the firewall (the B lead will be hooked up to ANL fuse). I also plan to have something similar to an endurance bus, which will be fed by the main bus and a separate relay from the hot side of the battery contactor, to which the Monkworkz generator will also be connected (via a contactor a la Dan H.’s simplified approach). I will have a G3X system and intend to do IFR in IMC and want plenty of redundancy. So the avionics will, for the most part, be on the endurance bus.

What I’ve been thinking about is how to design for smoke in the cockpit scenarios, since I really want to avoid having to shut off the endurance bus. And to answer that question, I need a better understanding of what is usually going up in smoke in those scenarios.

If every device is on its own circuit, and each wire to these devices is hooked up to the right sized breaker/fuse (which should blow if there is a fault on that circuit before the wire burns), then what is most likely going to be smoking? Is it the bus feeds, the starter contactor feed, or something else, like the devices themselves?

 

[Mich48041]

The devices themselves are most likely to smoke. Fuses protect wires, not
devices (except for low resistance shorts to ground). In case of smoke in the
cockpit, the pilot might not know which device is smoking. So if the smoke is
bad enough, the best option is to shut everything off with the master switch.

 

[rv8ch]

Very interesting topic - it would be great to know what kinds of things cause smoke. I only have experience with one off-field landing due to smoke, and that was a capacitor blowing up in a rotax-powered tecnam in our flying club. The pilot got it down safely.

What kinds of things have caused smoke in RVs?

 

[Dugaru]

One source

What kinds of things have caused smoke in RVs?

When my flap motor burned up, it created no smoke that I saw, but the distinct smell was very strong. My first thought was that I was flying through smoke from some sort of fire on the ground.

 

[Strikhedonia]

During phase 1 I had smoke in the cockpit from Klixon 40A breaker. I thought that was a quality brand, maybe it is and I had bad luck. Regardless I replaced with a more robust E-T-A circuit breaker.

 

[Carl Froehlich]

SNIP….I also plan to have something similar to an endurance bus, which will be fed by the main bus and a separate relay from the hot side of the battery contactor, to which the Monkworkz generator will also be connected (via a contactor a la Dan H.’s simplified approach).

One option is to wire your panel power (I assume this is your “endurance” buss) directly from your battery via a separate relay. Doing this you can maintain your POH immediate action for electrical faults of opening the Master Solenoid.
Now - expand this to a two battery system and you open up many new options.

To date, the only smoke in the cockpit issue has been a failed breaker. Take power away - done.

Carl

 

[bmellis11]

One option is to wire your panel power (I assume this is your “endurance” buss) directly from your battery via a separate relay. Doing this you can maintain your POH immediate action for electrical faults of opening the Master Solenoid.
Now - expand this to a two battery system and you open up many new options.
Carl

Yes, the panel/avionics/endurance bus power will come from the battery via relay and also through the main bus, which is on the switched side of the master contactor. If I had smoke, I would switch off the master and turn on the alternate feed for the avionics, but this isn't guaranteed to fix the problem because it could be one of the avionics smoking. For this reason, I'm thinking about a relay feed from the main bus to the avionics/endurance bus instead of a diode feed (like Nuckolls uses) so I can keep the main bus hot and disconnect the avionics bus from the main bus and battery if it has a device that is smoking. But having to turn off avionics would be bad news.

That's why I'm also toying with the setup you mention -- two batteries + alternator + backup generator -- for redundancy, expandability to fully electric ignition/FI, and as a more useful setup than a main battery + smaller backup/brownout battery for the avionics. Also, from a safety perspective, the smaller backup battery is lithium and is not supposed to go FWF, so I worry about it smoking in the cockpit and not being vented.

In that dual battery setup, my initial thought is that I would feed the Garmin avionics that have dual power inputs from two independent busses. But I wonder whether that really helps the smoke in cockpit problem. If there's smoke, it seems like I would have to turn off all buses because it wouldn't be clear immediately what was causing issues. If it was one of the dual fed devices that was smoking then I couldn't turn either avionics bus back on without first pulling the breakers/fuses for that device (which may not be accessible) and I would be left with no avionics power.

Thinking further about this, maybe the better solution is to split up and isolate the avionics to independent buses (without the dual independent power feeds to equipment that would support it), and just try to divide up the avionics across the two busses in a way that either bus working alone would have enough equipment to get me home.

What do you think the best option is?

 

[Walt]

Smoke in the CP is the worst scenario I can think of, I've seen how fast burning wires can fill a CP with smoke.

There is simply no time for troubleshooting in this case, only one thing you can think about is how fast you can get this thing on the ground.

For me, and the way I build all my panels (and my own), the master is just that, turn it off and it cuts all power to the aircraft. The only thing that will remain operational in that case are the units tied to the backup battery(s).

So, I always install a TCW BU bat to power primary AHRS, display unit and engine monitor box, turn off the master and those items keep running.
The next unit is the G5 which has it's own BU bat so it keeps going.

I won't do a panel or electrical system with EFII or such where you are required to have dual busses/batteries to stay alive. Risk vs Reward.

I'm a real die-hard KISS fan.

 

[lukejb]

I recently had a lightspeed ignition box smoke in my RV8 cockpit in flight. I was unaware of what it was at the time but when I pulled the ignition box out and opened it up it was burned up on the inside. Had about 400 hours on it. After a little research I learned that it is not uncommon for these to burn up and smoke if they get hot. It was a hot day, close to 100f the day it happened. Luckily I was close to home and able to land safely.