Lycoming New Electronic Mag Osh 2019

[71459]

Originally Posted by scard

It does work (rough, simplistic statement). The one that successfully lights the fire first wins.

Thanks for the clarification. So the e-mag does all the work and the mechanical mag is there firing away, but really only serves as a backup ignition source? Interesting - I never would have thought it would work like that.

And the e-mags single plug firing is still better than 2 conventional mags firing 2 plugs?

It's too bad they cost what they do. They would never pay for themselves verses conventional mags.

[pecanflyboy]

Originally Posted by RONSIM

I have my Surefly on order to replace my Bendix impulse mag -- also have a "Slick-type) harness on order. I have run the power wire with the 10A fuse from the battery, and ready to go on the install ----

My choices are to hook it up as "fixed" timing (25*) or hook up the MAP for automatic timing advance. My engine is a Lyc O360A1A with added FI and Hartzell CS. My average flying is mostly hamburger runs, instrument currency, "play-time" and the occasional cross country -- most everything at less than 10K MSL. I average 50-60hrs /yr on this machine.

So, question for those with EIs with and without advance -- for my profile, any advantage/disadvantage to going with the timing advance hookup?

Thanks for the help,

Ron

I would suggest you contact Surefly, and ask the questions. My understanding is that when you have the SIM set up for advanced timing, it will not advance until the engine is well within the safety margins for advance. Unlike an automobile, we do not have anti-knock (detonation) sensors to protect from over-advancing the ignition. So, until you get the engine below a certain power via reduced manifold pressure (because of throttle or altitude), the SIM stays in a fixed timing mode just like a MAG. The philosophy being that in cruise, the SIM will safely advance the timing and give you a more efficient burn in the cylinder.

This system is the most tested electronic ignition in the industry. I suspect the ignition curve is proprietary, and that the previously illustrated curve is out of date (it was published with the initial announcement, before development was complete). It will run for hours on just your battery, and a back up battery is being developed. I run dual SIM's on my RV6 with IO360, CS prop, and Gami's. Starts better, runs smoother, and LOP at cruise is as smooth as reducing the throttle.

[pecanflyboy]

BTW, I think Surefly having a COVID sale. 15% off, last I checked. April2020

[DanH]

Originally Posted by 71459

So the e-mag does all the work and the mechanical mag is there firing away, but really only serves as a backup ignition source?

I would say no. The fixed timing magneto only becomes irrelevant if the opposing flame front has already passed when it sparks.

The initial inflammation and subsequent flame spread requires time. For illustration, let's ignore spark rise time and the relatively slow growth of the initial flame kernel, the zero to 10% mass fraction burned period in the textbooks. Start at the 10% burned point and consider only the travel speed of the subsequent flame front, somewhere around 25 m/sec (i.e. 985 inches per sec), for an engine like the parallel valve Lycoming. Bore is 5.25", with the plugs roughly 3.5", maybe 4" apart.

2700 RPM is 0.00006 seconds per degree of rotation, thus a 13 degree difference in timing (i.e 38 BTDC for the EI and 25 for the mag) means the mag would lag 0.00078 seconds behind the EI. 985" x 0.00078 seconds = 0.7683". The EI's 13 degree head start moved the flame front less than an inch across the chamber...not yet to the other plug.

So goes theory; an experiment is required to prove or disprove. Fly a fixed pitch RV with magneto and EI at some altitude which significantly advances the EI. Ground the magneto. Is there an RPM drop? If so, the magneto was contributing to the combustion process.

Reports welcome.

[71459]

Originally Posted by DanH

I would say no. The fixed timing magneto only becomes irrelevant if the opposing flame front has already passed when it sparks.

Hmmmmm this is getting messier. The next question then becomes why is it so important that we time our 2 conventional mags to fire simultaneously? Your post makes it sound as though that isn't particularly important.

[DanH]

Originally Posted by 71459

Hmmmmm this is getting messier. The next question then becomes why is it so important that we time our 2 conventional mags to fire simultaneously? Your post makes it sound as though that isn't particularly important.

Not messy at all.

Mag/mag, mag/EI, and EI/EI combinations all spark simultaneously at high power. At high power, if one is too far advanced, one or more cylinders may tip into detonation. If one is grossly retarded, the engine may not make rated power.

All the advanced timing stuff happens at low power.

[Onewinglo]

Thanks everyone for this discussion. I read every post I encounter about electronic ignition closely. The EI, magneto, spark advance, MP relationship makes sense to me now.
I love some VAF.

[71459]

Originally Posted by DanH

All the advanced timing stuff happens at low power

OK I see. So, compared to a standard mechanical mag, these mags provide a RETARDED timing. Whereas a standard mag is fixed at an advanced time, these mags can time the spark at less than or equal to that (as appropriate).

The nomenclature used had me confused. They should call their system "Advanced Retarded Timing". OK, maybe not..

[DanH]

Originally Posted by 71459

OK I see. So, compared to a standard mechanical mag, these mags provide a RETARDED timing. Whereas a standard mag is fixed at an advanced time, these mags can time the spark at less than or equal to that (as appropriate).

The nomenclature used had me confused. They should call their system "Advanced Retarded Timing". OK, maybe not..

Most EI's provide the same timing as a standard magneto at high power, plus advanced timing with decreased manifold pressure. Some have the option of modifying or eliminating the advance function. Any EI, with or without an advance function, provides easier starting, generally better idle, and the ability to run leaner mixtures.

[71459]

Originally Posted by DanH

plus advanced timing with decreased manifold pressure.

The phrase "advanced timing" used here means the system is retarding (not advancing) the timing with decreased manifold pressure. Right?

If it is said that the system is providing "advanced timing" with lower power, one would read that to mean it advances the timing, when apparently it's doing exactly the opposite of that.