Bob,
This is one of my pet subjects, so allow me to give you my very biased
opinion, and my personal solution.
Magnetos date back to the stone age of the automotive industry. Being a
geared system, they are, by essence, very unreliable. This is the very
reason why there are two of them on an aircraft (Other engine components,
like the carburetor, are not redundant, right?).
Magnetos are a pain: they are very expensive, they fail a lot, have a
short service life, are difficult to set, and have a very hazardous
failure mode (remember the "P" lead story?)
In the automotive industry, magnetos have long been replaced. First, in
the 1930's, by distributors, which were much more reliable. Then, in the
1970's, by electronic ignition.
Unfortunately, the aircraft industry, with its wonderful certification
process, is much more conservative, and so, we can keep the magnetos
alive, at great expenses; and our reward is that we can show off when
visiting a car museum! ;-).
The reason that is always mentioned in favour of magnetos is that magnetos
produce their own ignition current, so the engine can still run in case of
total electrical failure (master off, the engine still runs). Trouble is,
dual magneto failures are much more frequent than total electrical
failures, especially if the electrical system is well designed.
I know of at least one company that solved the problem, and that's Jabiru
of Australia. If I am not mistaken, they have an electronic ignition that
creates its own current from the crankshaft rotation.
We, as experimental builders, can go around that, and go for electronic
ignition that is fed from the electrical system. But it is wise, in that
case, to design your system so as to make sure that an electrical failure
is highly unlikely. Basically, you can rely on the alternator or the
battery, provided failure of the one is not going to cause failure of the
other; also, you must make sure that failure of either source is
immediately detected (through annunciators, or whatever). You must also
make sure that in case of alternator failure, the battery gives you enough
time to react before the engine dies.
Electronic ignition is not only highly reliable; it is also very stable:
no periodical setting whatsoever, and pinpoint timing accuracy.
Now, my solution.
On my 2.0 liter Type 4 VW, recently replaced by a 2.4 liter Type 4 VW, I
run a fully dual redundant electronic ignition system. This consists of
two solid state electronic ignitions, salvaged from 1980's motorcycles.
These are nice, because:
1 - They have very few components;
2 - They were designed for a very hot, very vibrating environment;
3 - They run from the crankshaft, not the camshaft; no gears involved;
4 - The timing pick-up is magnetic; no mechanical contact, friction, etc.
5 - They are extremely light and compact
6 - They come straight from the junkyard, and cost almost nothing.
If one of them fails, I get a warning through engine RPM drop.
If my alternator fails, I am warned by an annunciator, plus the ammeter;
If my battery fails, I am warned by an annunciator, plus the ammeter;
I also have a couple of diodes protecting the electrical circuit .
This setting has logged 400 hours on my KR2, without a single glitch. I
have no starter, and it does not matter: the engine starts beautifully
every time.
More sophisticated systems exist, but I doubt if any electronic ignition
system can be more reliable or cheaper than that.
Now, let's dig quickly, before the magneto fan club attacks...
Serge Vidal
KR2 "Kilimanjaro Cloud"
Paris, France
"Robert L. Stone" <rsto...@hot.rr.com>
Envoyé par : krnet-boun...@mylist.net
2005-02-22 18:51
Veuillez répondre à KRnet
Remis le : 2005-02-22 18:53
Pour : "KR Builders Pilots" <kr...@mylist.net>
cc : (ccc : Serge VIDAL/DNSA/SAGEM)
Objet : KR> Electronic Ignition
Netters,
I have heard that the modern electronic ignition system is more
reliable than the conventional two magneto set-up in all aircraft engines.
Assuming this is true, opinions from any of you who are knowledgeable in
this area would be welcome. Also does anyone know where if at all an
electronic ignition to use on a VW engine is available.
Bob Stone, Harker Heights, Tx
rsto...@hot.rr.com
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