I happened to Google Dr. Feng Hsu. If I've got the right person, his
credentials are impressive in the field of high tech risk assessment. I
would also like to add that the other people who have contributed to the
discussion are also not lightweights. I'm probably in the lightweight
category, but I've been around experimental aviation for about 50 years.
Flying, to me, is a matter of risk assessment. Or, as the book about
Jimmy Doolittle put it, "the calculated risk". In terms of different
ignition systems, all have their advantages and disadvantages.
As I understand it, the discussion has been mostly about ignitions for
VWs and engines designed for aircraft. Many have their roots based in
the 1930's and subsequent years, when 80 octane was readily available.
With 100LL, lead fouling has become a real problem for many piston
powered aircraft based on earlier designs.
On Corvairs, designed in the late 50's/early 60's when fuel with high
lead content was used, IIRC, William Wynne claims that lead fouling is
not a problem on them, but that the ignition systems, coils, condensers,
and electronic circuits, are the weak points. As a consequence, his
system only has one ignition plug per cylinder, but two separate
ignition systems with their own coils that feed into a coil switcher
before the distributor and plugs.
IIRC, His system IS powered electrically separate from the unit itself,
unlike mags, which generate their own power. He points out (pun
intended) that Kettering (points, coil) will continue to function at a
much lower voltage than for electronic ignition. The Kettering types
also give warning that they are about to fail. When the voltage to them
falls off, their performance falls off, especially in starting, whereas
an electronic ignition doesn't give warning with low voltage, they just
quit.
Many Corvair flyers have a second battery that just powers the ignition
for several hours if power is lost from the main battery or from the
generator or alternator.
William now sells a dual system for Corvair engines with an electronic
ignition as the 'primary' one, with a Kettering system (like the Corvair
automobiles have) for a backup. As a backup, there is little pitting or
electrical wear on the Kettering points because they aren't powering the
plugs when the electronic system is on. Yes, they are both on the same
shaft from the engine, and he builds in a heavier bearing on the
distributor shaft, as I recall, but there's been no problems that I know
of with distributor shaft failures. There is also no engine coupling to
fail.
Correct me if I'm wrong, but in the early years of e-mag use, there were
several reported failures. Apparently, they are more reliable now. Their
self-generating power puts them in a separate category from regular mags
and totally electronic ignition systems.
I've heard it reported that with electronic systems in general that if
they're going to fail, they do it early in the use cycle (less than 25
hours). As people in the experimental aircraft world, we have to be
careful who we follow because the sample size for other than magneto
systems is relatively small, so that may skew any statistics. IMO,
events are important, but there may not be enough to make them
statistically relevant.
I had a friend who built a KR-1 with a single mag. The thing that caused
him to do a rebuild before even 50 hours were up was that he got a
Brazilian, instead of a German-made cam for his VW. He built it
according to plans, and he found the CG was way aft.
What you choose to be your ignition system is a matter of personal
choice. I appreciate the reasoning expressed by the various people on
this forum, and that there's been on flaming or disparaging in the
discussion.
It behooves us to do a thorough inspection and run-up before we take to
the air, and to monitor the performance of our engines as much as
possible. They do seem to talk to us, if we 'listen'.
Dan Branstrom
On 7/8/2022 9:56 AM, Dr. Feng Hsu via KRnet wrote:
Good morning all,
I enjoyed reading all the excellent stories, failure event
descriptions, arguments of pros & cons and thoughts (from John, Chris
and Luis etc.) pertaining the debate of safety on dual mags, dual
E-ignition or one meg plus one E-ignition redundant aircraft engine
systems.... Well, I am glad to see this discussion actually got us
into a classical technical debate on pros & cons in safety between
conventional engineering vs digital engineering, which has been going
on for several decades across all the so called "high integrity and
high reliability" industries, such as nuclear, aerospace, chemical and
medical ....A famous topic debate on this issue in the aerospace or
aviation industry for example is the debate on "flying by wire"!!
Frankly, I am on the camp of opposing the concept of "flying by wire"
within the safety/reliability & risk assessment academic community,
and this is simply because the folks who have been advocating the
concept of "flying by wire" are the "extremist" in engineering
design... For the same reason, I am a none believer of a truly
autonomous and safe unmanned cars & trucks or ground-based
transportation system based on AI technology due to theoretically
obstacles or limitations in coding highly reliable and safe software
packages based on human brains. The chilling fact is that over 75%
catastrophic accidents from all high-integrity industries were
contributed by software and human errors combined! Guess what, the
single most "unreliable component" in our man-machine systems (such
as aviation) is the human brain itself!
Obviously, my views on this topic is taking a balance between the two
approaches and avoid going for both extreme ends of the argument! In
other words, I believe an one mag (mechanical) plus one E-ignition
redundancy makes a lot of sense in risk reduction based on theorems &
reliability engineering principles. I understand what's in the mind of
Luis on dual "independent e-ignition" component and DC power
channels... The issue here is that the two e-ignition channels are not
truly independent as you would believed! Yes, it looks independent in
a physical sense but it is inherently connected or identical due to
the design and manufacturing processes! Although I have not done a
model based risk assessment myself to compare the trade-offs in risk &
reliability of these two ignition configurations, but I am confident
(based on expert judgement) that a meg plus e-ignition configuration
would highly likely to be the winner in terms of safety risk
concerns... I am sure other people in the aviation industry have done
a rigorous model based risk assignment comparison on this matter.
Just to offer some food for thoughts for folks here who might be
interested in this topic debate...!
Best of luck!
Dr. Hsu
On Fri, Jul 8, 2022, 8:07 AM Luis Claudio via KRnet
<krnet@list.krnet.org> wrote:
I think these discussions are healthy and welcoming. I read them
and go "hmmm" then I make my own decisions. I have been flying
since 1966 when I took my first ride as a civil air patrol cadet
in High School in a PA-22 108HP. As a student at Embry-Riddle, I
was an understudy of Dr. Richie (RIP) a true pioneer in failure
analysis (FMEA) of everything aviation-related. I understand
failure modes, and most importantly how to mitigate the risk for
each independent system or collectively (through risk priority
number= severity x occurrence x detection...) I am also very
familiar with E-Mags and other electronic ignitions which is why
after careful consideration I chose a dual SDS ignition system.
It wasn't by "gosh or by golly" that I arrived at my conclusion.
Considering that my initial choice of ignition system was a Dual
Bendix D3000 mag with a single failure mode (the main coupling), I
asked what else is out there... and here is what I considered
1. A dual mag setup such as the aforementioned dual mag - Four
points, four capacitors, one coupling = Total 5 points of failure
minimum
2. An independent mag with an electronic ignition driven by the
timing gears - Minimum of four points of failure (points,
capacitor, two couplings)
3. An "E-Mag like" with an electronic ignition driven by the
timing gears - Engine couplings = two points of failure (minimum)
4. Two independent electronic ignitions with no mechanical moving
parts - dual independent battery backups - Component failure
5. Just screw it and go sailing...
My most predictable component failure is the spark plugs. So
moving forward I then wrote a proactive maintenance schedule in my
POH and annotated it in my conditional inspection form to reduce
the risk of component failure. Additionally, during my selection
process, I prioritized the failure modes of each system,
mechanical and electronic... from highest RPN to lowest RPN noting
that it’s worth emphasizing that it’s nearly impossible to address
every potential failure. Instead, I focused on addressing the
potential failures that would most jeopardize the safe outcome of
my flights and I chose from analysis and not from bells and
whistles... just my rambling thoughts here trying to justify that
$50K I spent on getting educated at Embry-Riddle back in the
day... keep building
Luis R Claudio, KR2S N8981S
On Friday, July 8, 2022 at 06:23:13 AM CDT, victor taylor via
KRnet <krnet@list.krnet.org> wrote:
To answer Chris yes I do have a flying KR2 with a single
electronic ignition though I was actually talking to Dan Diehl
yesterday about adding a magneto for a backup.
I do contract work for Velocity Aircraft as a pilot. We love
electronic ignitions and put them on every airplane. They are the
way to go and in the past have gone 100% electronic ignition but
over time have had enough failures that we went back to having one
mag. I also test fly new airplanes for M-Square who builds the
Zenith CH-750 SLSA. I actually have had two electronic ignition
failures with brand new aircraft there in the last couple of
years. M-Square is still committed to 100% electronic at this
point. Just to be clear I’m not knocking electronic ignitions nor
their reliability. If you have dual electronic ignitions though
you likely are relying on the same electrical system to run both
systems. Up until four months ago I had never had a magneto
failure in my 40 years of flying but recently I lost a magneto
while ferrying a Grumman AA1A. Fortunately the other one got me to
the nearest airport where a safe landing was made. There is a
reason why aircraft manufacturers such as Velocity have reversed
their positions on going 100% electronic. And that reason is
failures in the past and accidents such as the one in Kissimmee.
When Teladyne Continental first built their full FADEC engine
system it kept experiencing total ignition failures in flight.
After over a year of flight testing with multiple in flight
failures yet not a single one in the test cell they finally got to
the bottom of it. The problems was found to be the frequency that
the US government uses to communicate with submarines was
interfering with the FADAC system. The fix was simple by shielding
the system.
One of the functions of this group is to make the KR’s safer.
That’s done by discussions and experience. Mostly bad experiences
and I’ve personally had those bad experiences as a professional
test pilot. All of us in this group look at canopy latches a
little closer today than we did a year ago. Controls have gotten
balanced, fifth bearings have been added to engines, fuel tanks
are being moved to the wings etc. You would think that over the
years we’ve fixed every possible failure point. Have we?
It’s our duty in this group to be devils advocate at times and to
point out past failures of similar systems.
Victor
> On Jul 8, 2022, at 00:24, John Gotschall via KRnet
<krnet@list.krnet.org> wrote:
>
>
> Hi all,
>
> Quite a bit of commentary about risk, system failure etc.
>
> So I am convinced everything will fail sooner than later. I
make my living on failing machines, so I may appear a pessimist
about machines, or an optimist about future employment fixing
them. On the upside there is so much failed stuff I get paid more
than just several times every day since 1988 to set those broken
machines straight.
>
> I find it particularly interesting to see the failures that come
in groups or waves. I experienced such an odd failure scenerio in
aviation recently.
>
> I bought an experimental flying boat, a volmer home built, OMG,
what a pretty unit! And a blast to fly! A cub can't touch a
volmer for fun. Sadly I broke that and am still working to fix it.
>
> Anyway there is an annual seaplane fly in at NW Idaho, and I and
a friend went in the volmer. What a blast! the mountain
crossing, middle of nowhere overnight camping, etc. However the
alternator quit near Idaho and we made our way there and home by
never turning on the battery switch the whole time, except to run
the starter motor, and then to cross under the Seattle class B.
Needed adsb working for that.
>
> I found the High current alternator output wire had failed by
vibration fatigue and had simply broken off that big alternator
output post. Simple to fix, and I replaced the entire wire with
welding cable, better for vibration. No big deal.
>
> Then I broke the Volmer (another story), and needed another
flying boat so bought a lake LA-4. We found it in Arkansas and
flew it home to the Seattle area.
>
> The same seaplane fly in came up in Idaho this year, and we went
again this time in the lake. A complete blast for all the same
reasons, but on the way home the alternator quit outputting
current! This time the plane has heavy electrical laods that
quickly consumed and flattened the battery in short order (less
than 40 minutes) on the final leg home. instead of panic we just
turned west to get out from under the class B, shut all the
electrical off and used the hand hydraulic backup pump to operate
the gear and flaps. Made the uneventful landing at home in the
backyard and went digging for the fault.
>
> Dang if it wasn't the SAME DAMN WIRE that broke in the Volmer!
On the second occurrence of the same trip. Except this time the
wire pulled out of a bad crimp rather than broke off. Pulled out
of a bad crimp on a certified factory built plane. hmmm.
>
> Well, both the Volmer and the Lake are dual mag lycomings. An
o290 and o360.
>
> So I will say mags are a great choice, from experience. In both
cases mags brought us all the way home. My kr has one mag and one
electric ignition. It'll probably make it home without an
electrical system.
>
> cheers!
>
>
> jg
>
>
>
> --
> KRnet mailing list
> KRnet@list.krnet.org
> https://list.krnet.org/mailman/listinfo/krnet
--
KRnet mailing list
KRnet@list.krnet.org
https://list.krnet.org/mailman/listinfo/krnet
--
KRnet mailing list
KRnet@list.krnet.org
https://list.krnet.org/mailman/listinfo/krnet
--
KRnet mailing list
KRnet@list.krnet.org
https://list.krnet.org/mailman/listinfo/krnet
