Double electronic Leburg ignition for my VW aero engine
The VW aero engine for my RJ.03 IBIS is going to get a double Leburg electronic ignition system.
After starting the engine, the system advances the timing automatically, adjusting it to the instantaneous RPM.
As long as the engine idles (up to 1000 RPM) the timing advance is set to appr. -7° TDC.
At the lower end of the idle range (around 500 RPM) the timing is advanced a bit more (up to appr. -9° TDC) to ensure a stable engine idle.
From 1000 RPM on, the timing is gradually advanced from appr. -7° TDC up to -27° TDC, which is reached at 3000 RPM. Above 3000 RPM, the timing stays constant at -27° TDC. This is true up to 4000 RPM, above that the timing is reduced to 0°, so from here on there is a bit of automatic rev-limiting going on as well.
The system also gives you a bit of leeway to adapt the maximum advance to your own requirements, as it's not set in stone that the initial timing is +3° TDC. The timing disc could be rotated a bit, so I could also end up with an ignition timing between, say, -1°TDC (zero RPM) and -31°TDC (from 3000 RPM upwards). In this hypothetical setting, I'd not end up with an excellent protection against backfiring, but if I'm going for a system with a starter after all, this might not be much of an issue.
By the way, each of these controllers weigh a mere 200 grams.
Each of the Leburg electronic ignition controllers drive an automotive Visteon (Ford USA) coil unit. These units are vacuum impregnated with epoxy and have a sealed EHT connector. This makes them very robust and water proof. A Visteon igntion coil unit as used on my VW aircraft engine weighs 626 grams. I know, lighter solutions do exists...
2 Leburg electronic ignition controllers and two Visteon coils weigh some 1.6 kgs. The whole lot, including mounting hardware and plug leads for eight spark plugs will weigh less than 2 kgs, which compares favorably against even a single magneto. Alas, this is not the entire equation, there's a bit more to it, see the next paragraph:
Leburg double electronic ignition system
Not shown on this assembly: timing disc with magnets; Wiring loom which contains power supply, ignition key, ignition status signals and RPM signal.
Most of the weight savings compared to using a single magneto I need to put back on board by installing a backup battery for the Leburg electronic ignition. For about the same weight, I'm going to end up with a modern double electronic ignition though, and one that will be much more dependable than a magneto. Did I mention that this setup is going to be virtually maintainance free?
One undeniable advantage of a magneto is that it is self-exciting, i.e. as it turns it produces the energy needed to feed the ignition.
An electronic ignition doesn't have this advantage. The backup battery is one that is big enough to power the double ignition system long enough to be able to fly as long as fuel is left on board. This second battery will have a capacity of 2.8Ah (or a bit bigger, depending on the rest of my systems design) and will be separated from the main battery by a diode.
Most likely I'm going to configure an 'engine bus' or 'ignition bus' that is going to be separated from the normal 'services bus' or 'essential bus'. It shows: I'm still fighting over how I'm going to name - and think about - these busses.... :)
Separating the two will allow the ignition system to continue to do its thing, even in the unlikely case that the other bus gets shorted and/or the generator is down.
This section is going to be considerably updated as my systems design evolves. You might want to re-visit this page occasionally...
Sadly, in February 2009 David Mickleburg - the designer and producer of this ignition system - deceased in a crash while flying his single seater Leburg Sparrow. Even if as of this writing a detailed accident report was not available yet, it was suggested that there might have been a stall and/or spin after an engine failure directly after take-off.
David's son Henry decided to continue or rather re-start the production of this double ignition system. Henry can be contacted on www.leburg.com.
According to some posts on a Yahoo VW group, the latest news is that David's son Henry is not really really continuing the tradition his father set. Rumour has it that he's roaming around in France and that he might just perhaps set up shop on the continent. At any rate, he is no longer responding responding to email messages, which of course is utterly unsatisfying...
Also check out: VW-derived Aero Engine >> Induction