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In a message dated 12/21/2006 1:44:38 A.M. Central Standard Time,
fredmoreno@optusnet.com.au writes:
I originally ordered my engine
with dual Lightspeed ignition systems and designed my electrical supply system
accordingly. I have since learned that Lightspeed no longer ships dual
ignition systems, and only recommends a single Lightspeed and a single magneto
as backup. It was reported to me that the problem was NOT the Lightspeed
ignition systems, but rather the LACK of reliability with experimental
aircraft power systems. Apparently too many forced landings have
occurred because of total electrical
failures.
Fred,
Well, I am ready to comment.
This morning I sent the following email to Klaus:
<<<<<<<<<<
Klaus,
It was reported on the Lancair Mail List that Light Speed Engineering
is no longer shipping/selling dual ignition systems and only recommends a single
system with a mag backup because of too many experimental aircraft's
unreliable electrical systems.
I find this hard to believe.
Can you tell me if this is true?
Scott Krueger
Lancair 320 N92EX, Dual Plasma III System with crank sensor, Essential bus
arrangement and backup battery for the primary ignition.
1st Place, 2006 Air Venture Cup Race Formula RG Red Division. 232.8
mph.
1st Place, 2006 Redmond 100 (Lancair factory), 320 Division and beat 6 of
the 7 360 powered Lancairs, 242 mph.
>>>>>>>>>>>>>>>>
His reply was just received:
{{{{{{{{{{{{{{{{{
Thanks for letting me know and also for your support on the List(s). I
can't monitor them and set things straight, that would be a full time
job.
There was a concern for a while when we had a few sensor failures on the
Continentals used on Lancairs. The engine builder would set up the proper
clearance per our instructions, test run the engine and deliver it. The proud
owner would then install his own baffeling between the case and our mounting
bracket. This would reduce the clearance to the point that the sensors could get
damaged.
We are now shipping all Direct Crank Sensor boards with the new "Skip
plate" that will protect the sensors when there is interference. This makes the
DCS board practically indestructible.
Now that we have these components available, we are shipping single and
dual Plasma Systems on a daily basis. There never was an issue with the Lycoming
engines.
Please see the service bulletin on our web page also.
Keep up the good work.
Klaus Savier
Light Speed Engineering
P.O. Box 549
416 E. Santa Maria St. #15
Santa Paula, CA 93060
Tel: (805) 933-3299 Fax: (805) 525-0199
}}}}}}}}}}}}}}}}}}}}}}}}}}
The lack of reliability is sometimes in the reporting of
problems, causes and solutions. Here it was the failure of the builders to
understand the TCM engine package that was bought and the importance of the
sensor position.
I have no problem with my dual LSE ignition by relying on the
Essential Bus distribution system and a backup battery for 1/2 of the
ignition system in case there is some weird sort of unforeseen total
electrical failure. That is also why the header tank is
automatically maintained with at least 8 gallons of fuel at all times as it
is the single non selectable 100LL source for the
engine.
It would be interesting to know
the causes of total electrical system failures in experimental aircraft, but
we shall probably never know. My guess: a combination of poor system
architecture coupled with poor workmanship standards on things like
connectors, couplings, joints, wire chaffing protection and
such.
Is that because you already know the causes and consequences
of TOTAL electrical failures in STC SEL aircraft, like Cessnas? From
my perspective, they are the same except that an experimental builder has the
opportunity to do better and often does. Elder* Cessna aircraft (I have
some experience) use crappy components and connectors and are frequently
full of architecture and design shortcuts used to save MONEY, not
lives. Of course, it would cost even more money to improve those faults
that become known. It seems that the most frequent total
electrical system loss in an old standard aircraft is usually because of
alternator failure and complete battery depletion - not usually seen
in time by the pilot because there were no idiot lights like "ALT
OUT". Instead there has been reliance on scanning the ammeter
(if present). Everybody includes the obscurely placed ammeter in
their 30 second scan, don't they?
*Elder aircraft = those produced before modern
competition (like Cirrus, Columbia, Diamond, etc.) began to
appear.
The correct approach to system
architecture has been demonstrated by the FAA approval of all-electric single
engine night/IFR airplanes such as Columbia. I attach (which
I have done before) the system architecture for the Columbia from the pilot’s operating
handbook. You can go to the www.fly-columbia.com web site and
download the POH, a PDF document, for a cleaner
copy.
Sorry, I cannot trust that the FAA knows any better than an experimental
aircraft builder that actually built his/her airplane and studied available
information on how-to-do-it. Uh, aircraft built for personal education and
recreational use (I know I have read that phrase somewhere). Yes, the
current FAA requirements seem better - maybe they learned something from
experimental builders. I know Cessna has for their LSA entry.
I concur with most of your succeeding points - one should consider the
environment and mission of the plane and its systems when one is
designing in safety and redundancy - to some reasonable
level. One of the things the builder cannot fix with hardware is
the loss of life from serious lapses of judgement, training and
knowledge in the other single-point failure, the pilot.
Thanks for the brain tickler,
Scott Krueger
AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)
A man
has got to know his limitations.
As noted elsewhere, the key to best
reliability is redundancy and absence of single point failures that by
themselves can bring you to grief.
Common (and not so common) single
point electrical failure sources can include
- batteries,
- relays,
- circuit breakers,
- wire terminations,
- chaffed wires causing tripped
circuit breakers,
- attachment nuts or screws coming
off,
- vibration-induced mechanical
failures of attachments and structures,
- etc.
If the probability of a
single point failure is one in one thousand per flight hour (vacuum pumps are
worse), the probability of two such independent failures occurring
in the same hour is one in one million. Here we presume the
failures are not linked. Linkage might include two
alternators driven by a common belt, a lightning strike, failure of the
crankshaft, etc.
My recollection is that FAR 23
requires a quantitative safety case to be made that shows the probability of a
failure or set of failures causing loss of aircraft is less than one in ten
million. I presume that the Columbia electrical system was
able to satisfy this type of analytical scrutiny. Thus the architecture
used offers us an excellent starting point to design our own systems for
maximum safety and reliability.
I tried to simplify
Columbia diagram with the sketch attached.
Please forgive my lack of Autocad drafting skill. The sketch suggests a
simplified architecture that builders might start with as a basis for their
electrical power distribution systems. I would suggest that we kick it
around a bit, and then perhaps somebody with greater skills than mine can
generate a clean drawing that includes the collective wisdom gathered from
multiple inputs. It could then be referred to in the community as a
well-conceived starting point for electrical system
design.
Some notes: Diode feed of avionics
buss and essential buss provides automatic supply of power in the event of a
buss failure, but the pilot could remain unaware of the bus failure because of
this automatic operation. Therefore, I believe that an integral element
must be pilot notification of a buss failure via a low voltage
alarm.
In my case, electrical system
design started with the recommendations of Bob Nuckolls’ in Aeroelectric
Connection. I then revised it to incorporate some of the features of the
Columbia system, modified to reflect limitations
and options on my own aircraft.
As an example, Columbia carries two large alternators. My
IO-550 is configured to carry one large alternator (70 amp) and one smaller
B&C alternator (20 amps). So I use the big alternator on the A buss
and connect the high current stuff like hydraulic pump, landing lights and
such, and put smaller loads on the B buss. If the A buss fails
(alternator failure, for example) I know immediately to shed load to get the
total system load under 20 amps to prevent the excess being drawn from the B
battery. During the load shedding, I can keep the airplane upright at
night in IFR because the essential instruments remain operational throughout
the event. For my airplane, this includes the Chelton primary flight
display, back up instruments (including RC Allen electric attitude indicator)
and their night lighting, and the single Lightspeed ignition
system.
I would not treat a single buss
failure as an emergency, but I would put the airplane on the ground ASAP
before another failure occurs. Going back to the earlier example,
if you are working with one in one thousand failure rates, and one system
dies, then the chances of the rest of the system dying is one in one
thousand in the next flight hour, not one in one million. One in
a million applies to both systems failing (a total system failure) in
the same flight hour. So when one system fails, you have used a
good portion of your nine lives already. Conserve those that are
left.
Personally I think one in one
thousand is lousy odds, so it is time to put the airplane on the ground
quickly when the odds have slid this far as would happen if one system
fails.
As another adaptation, a lot of
folks here are using Chelton flight displays. When equipped with the
Pinpoint GADAHRS and magnetic sensing units, you will find that they are
designed to permit dual independent power supplies from separate busses.
So you can connect only one of these supply lines to the essential buss
(forgetting the other) or (preferably) connect each individual supply line to
each buss to get as close as possible to the electrical supply (battery and
alternator).
With our complex and high
performance experimental aircraft, I think it is high time to propose some
“experimental standards” for system designs that provide enhanced
reliability. I would suggest that some attention to the electrical
system design and development of a “recommended electrical architecture” is a
good place to start.
Your comments, please.
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