Dual ignition homebuilts

How many of you have dual ignition systems?

Just about anyone using an engine originally manufactured for a certified aircraft will have dual ignition. It gives you an increase in power, better combustion, and system redundancy.

Bruce

For my big biplane project I intend using a Chevrolet small block engine. Now there have been people who made heads with dual plug holes, but I have no idea if these are still available. Likely they would be hideously expensive too.
My intention is to use two coils with a switch between them, two sets of magnetic pickups inside a single distributor, a back-up battery and a single set of plugs. I feel automotive sparkplugs have reached such a level of reliability, duplication is simply unnecessary. (100,000 miles service intervals on platinum plugs!)

Personally, I had ignition failures in cars in many different modes, mostly due to bad wires, but also rotor arms coming off and destroying the distributor (This happened twice to me in different vehices). I will be paying special attention to making that part reliable.

Would I fly single ignition? Given a thoroughly thought out system, sure. You can carry duplication to an extreme. I think it is a left-over from days when electrics were just plain unreliable.

We don't fly with dual carbs either...

You're right Peter, a dual ignition source is probably fine without having to go with dual plugs.

Originally Posted by PTAirco

We don't fly with dual carbs either...

Don't need to. 90% of engine troubles are electrical. When I was 15 or so, my high-school mechanics teacher told us that and in the 41 years since I have found it to be abundantly true.

Ignition is the biggest headache. Magnetos are somewhat less reliable than battery-powered distributor ignition systems, but they're self-contained and don't rely on the electrical system that tends to fail more often than the mags so we still see them on new airplanes.

Some homebuilders are using dual ignition based on a traditional distributor as well as a crank pickup, firing two systems that feed one set of plugs through arc blocks. The blocks are made of epoxy or something similar and have three electrodes: two for the spark inputs, one on each side of the third which feeds the plugs.

Dan

Some years ago I owned an '84 Nissan pickup truck that had two spark plugs per cylinder... a strange setup with a weird looking distributor and used two different types of spark plugs, one of each type per cylinder. Never was quite sure what the reason was (probably emissions), but it always ran good, up until the day it threw a rod through the crankcase.

-Dana

If at first you don't succeed, skydiving is not for you.

Originally Posted by bmcj

Just about anyone using an engine originally manufactured for a certified aircraft will have dual ignition. It gives you an increase in power, better combustion, and system redundancy.

Bruce

Are both systems are working at the same time?

Originally Posted by Alan Waters

Are both systems are working at the same time?

With dual plugs... yes.

With single plugs... optional (unless you need a hotter spark).

Very confusing. I assumed when a plane had dual ignition systems, one was being used and one was a backup which could be turned on if and when needed. Why wear out two systems at the same time and how do you know when one has failed?

Why have them both operating all the time? Murphy's Law. Sure as heck, the system you're using will fail at the worst possible time - just after takeoff, on very short final over powerlines (in case of a go-around), etc. Right when you already have your hands full with flying the airplane and you need the power right now, not five or ten seconds later when you've figured out what's wrong and manually switched systems.

With both systems operating all the time, there's no need for pilot action when one fails. You just keep on flying.

Originally Posted by Topaz

Why have them both operating all the time? Murphy's Law. Sure as heck, the system you're using will fail at the worst possible time - just after takeoff, on very short final over powerlines (in case of a go-around), etc. Right when you already have your hands full with flying the airplane and you need the power right now, not five or ten seconds later when you've figured out what's wrong and manually switched systems.

With both systems operating all the time, there's no need for pilot action when one fails. You just keep on flying.

If a mag begins to fail the engine will often start running roughly. Failure isn't always immediate and complete. A mag can start sparking early or late (mag timing slip or impulse spring failure) or start sending the spark to the wrong cylinder (distributor gearing failure) or arcing internally (moisture, carbon residue, oil) or the points can burn; firing intermittently is the result. Some of these are worse than a completely dead mag; spark to the wrong cylinder at the right time is a good way to kill the engine. So that's why we have the mag switch handy: not just to test the mags at runup, but to shut down a renegade mag so we can get down safely.

Mags need occasional inspection. I've seen a mag come off the engine and come apart in my hands, with rusty balls falling out of the bearings. There's no good reason for that sort of neglect.

Dual ignition increases power output. Two flame fronts allow more complete burn before the exhaust valve opens. We can see that on the tach during the mag checks. Aircraft engines typically have rather large cylinders that take longer to burn than the smaller cylinders of auto engines.

Dan

On the nissan's the reason the plugs were two different sizes was the temp's of the plugs were different. The intake side plug was a hotter heat range and the exhaust side was a cooler heat range. In theory both plugs would run at the same temperature and hence spark the same amount of voltage for a more even burn.

Personally i like the EC-2 by Tracy Cook. It does not run both system at the same time but does just take 1 flip of a switch to transfer to the other ignition controller. It shares plugs, plug wires and coils, but almost all other components have redundant systems that run continously and ready to switch over at any time.

http://www.rotaryaviation.com/eficont.html

If a plug or plug wire goes out you don't lose the entire engine just some power. Systems with multible coils have some redundancy and most likely would also lose only partial power with a failure.

skeeter

Originally Posted by Dan Thomas

If a mag begins to fail the engine will often start running roughly. Failure isn't always immediate and complete. A mag can start sparking early or late (mag timing slip or impulse spring failure) or start sending the spark to the wrong cylinder (distributor gearing failure) or arcing internally (moisture, carbon residue, oil) or the points can burn; firing intermittently is the result.

Remember though, we are not restricting our conversation to mags. Coils, condensors, distributors and various electronic ignitions are also possible.

Bruce

My G109 has single ignition. Never had a major problem with mag. I have had plenty of spark plug issues. But with just 4 sparkplugs, the easiest thing is just install new plugs more often. only need 4 instead of 8.
I have heard that the Limbach (VW based) does not need two sparks because the cylinder is small.
BB