One EI or Two EI
jonbakerok said:
I'm not thinking about swapping my mags, but this discussion about combining electronic ignition with a mag made me wonder about something.
Isn't the whole point of electronic ignition to be able to vary the timing like a car does? Well how does that work if the EI plug is sparking well in advance of the mag-driven plug? Seems like you'd lose the performance advantage of dual plugs, because by the time the mag fires, the show's over. Wouldn't it be sort of like flying around all the time on one mag? Just curious.
Dear Just curious: Great question. One EI (w/ one mag) for discussion sake will give 4% more efficiency. The second EI will only give an additional 1-2%.
Well what is the single magneto doing with the one EI, one Mag set-up? Not much. At power above 70-75% the timing of the EI will be approx at the same 25 BTDC, however the EI with its much hotter and longer spark will overpower the Mag even if they fire together. At lower power setting the EI will start to advance, so by the time the relatively weak Mag fires late the show is over.
The Mag is just going along for the ride. However even with this mismatch the single EI is so much better than dual Mags, it is a benefit. The question is if you want to pay for the 1-2% extra benefit the second EI gives.
For me it was a case of practicality. I had old Mags that needed to be overhauled. I was able to sell the mags and impulse couple and make some money. I kept the single no impulse mag gear for my EI hall effect trigger.
The down side of dual EI is the dependence of electrical power. There are work-around's such as a second battery. In fact they use so little power a healthy single ships battery should keep you in the air until you run out of gas. Some do use only a single battery. It is still an issue that has to be addressed that you do not with need to with Mags. The P-mag is a self powered EI, independent of the aircraft electrical system. Others go some elaborate means to prove DC power that seems to rival a B747.
My point is if you are going to get that extra 1-2% you think you are going to get with a second EI for more performance you need to match EI brands. If you are not going to add a matching second EI, which might not get much added benefit, my feeling is you might as well keep the magneto and save the money. As a side note Lycoming list a 2% differnce between single Mag and dual Mag operations.
The question of which brand is better, since they all cost the same?
LSE: From pure performance minded standpoint the LSE has the best features in my opinion. It is the only CDI (capacitor discharge) ignition and they have race minded features such as user adjustable cockpit advanced control and indication. CDI (multi spark) has a slight performance advantage over Induction Coil ignition, which is what the other systems use. As well you can display MAP and RPM with optional LCD displays. Also, the CDI can work on lower voltage. The down side may be the installation, box, wires, coils and dependence on aircraft electrical system. For most the racing features are not necessary. LSE offers crank trigger and all effect trigger (mounted in mag hole).
E-mag/P-mag: Is an induction coil system like the Electoair system. Works very well and has the best form/fit factor, which means self-contained units that mount on the engine like mags, without seperate coils and control box. Also with the self-powered version, the P-mag, you have less electrical redundancy issues (needs electrical power to start with). Although it does not have some of the LSE features it does have easier installation and the timing curve can be adjustable or customized by the factory, including reduced advanced for high compression engines. Timing advance above 70% power for more performance is always at the risk of detonation and engine damage. Therefore most are best served by the stock conservative timing advance, which works primarily in cruise. All the EI use a conservative stock advance curved to protect the engine.
Electroair: Also an induction ignition system. Jeff Rose sold the company I believe and is now being marketed again. The new design features separate controller, coils and hall effect trigger (fits in the mag hole). There are 1000's flying around. I would put it between the LSE and E/P-mag in performance and installation. Electro-air states you must have two batteries for dual EI configuration.
Performance and cost are all close. You have to look at features, installation and your needs. I will also say there is nothing wrong with Mags. However if you are starting from scratch, buying new you sould consider at least one EI.
Cheers George
