It’s not just the timing changes that make EI interesting. There is also benefit in having a higher energy spark, as it can ignite weaker mixtures for LOP operation. G3i is a company making an EI for experimentals that doesn’t change the ignition timing. They claim (but they would) that the gains from variable timing are minimal, because the speed range of our engines is narrow (say 2,000 to 2,700 rpm).
There is another company working on a similar electronic mag for certified aircraft – Surefly. It’s not got a TSO yet but they claim it advances the ignition compared to a mag.
Shorrick_Mk2 wrote:
Says who?
EASA and the FAA. Didn’t know they had certified the Electroair system. It has also been around for ages for homebuilts, but requires battery power.
LOP should need the spark to be advanced, because the mixture burns slower.
That is why, with LOP, running at a lower RPM (say 2200 rather than 2400) does deliver a better MPG. LOP itself doesn’t deliver a better MPG because anything beyond peak EGT is burning up all the fuel molecules anyway. This is all very measurable in flight. However, lower RPM itself also delivers a better MPG…
The problem with advancing the spark for LOP is that I don’t think there is a sensor for the depth of the LOP condition. You can detect peak EGT (minimal oxygen) with a sensor in the exhaust but I don’t think any petrol aircraft system does that.
@LeSving, so EASA and FAA forbid ignition timing changes on the one hand and certify a system that does exactly that on the other?
That is interesting.
Peter wrote:
You can detect peak EGT (minimal oxygen) with a sensor in the exhaust but I don’t think any petrol aircraft system does that.
In fact you could swap an EGT probe with a wide range AFR sensor and achieve that quite easily. Nowadays wide-range sensors are plenty cheap (cheaper than a EGT probe in fact). Only downside – they do not like lead.
Shorrick_Mk2 wrote:
That is interesting.
No it’s not. That’s certification. I see that Electroair didn’t get it certified until 2015. They have been making these systems for 20-30 years. The e-mag/p-mag is still not certified. The reasons is as I have understood it, the variable timing combined with manually adjusted mixture.
What is the polished diaphragm looking unit? Is that a vacuum hose fitting?
It looks exactly like the vacuum diaphragms that used to be fitted to the distributors of car engines 30 years ago, which strongly suggests a mechanical vacuum advance mechanism. In cars, they used throttle vacuum, acting via a diaphragm, to operate a mechanical ignition advance mechanism. I’m just guessing (and shamelessly plagiarising the previous ideas 
) but I imagine this sort of mechanism has limited authority, because it can only move between physical stops and that might be why they’ve used it.
The LAA forbid dual ECI because of some unquantified suspicion of destructive harmonic resonance from the prop. I think.
Stick & rudder, I am told that the LAA are moving away from that position and some aircraft have been flying with two Pmags fitted.
