Mark;
You raise a good point. The solid state components
are ‘potted’ into the housing; so vibration is not likely a factor,
but internally generated heat definitely is. Heat transfer out is likely
rather poor. At these spark rates the internal components could be
considerably hotter than the 150-180F environment.
So higher re-drive ratio equals more need for coil
cooling?
And do you really cruise down the highway at only 1500
rpm?
Al G
Subject: [FlyRotary] Re:
LS1 Coil Failures
Ed,
I was thinking about this
a while back and was astounded at how many “firings” per second
these coils are producing. Each rotor fires once/revolution of the
eccentric shaft. Cruising along at 6000rpm, that’s 600 sparks/second/coil.
My 5.3L Chevy truck (with LS1 coils), cruising down the highway at 1500 rpm,
each coil fires once every other revolution, or 750 times/minute, or 12.5
times/second. So, we’re really pushing these coils to the
limit. I find it amazing that they don’t fail more often than
this. By the way, in 126,000 miles, I have yet to have a coil fail on my
LS1.
Mark S.
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Wednesday, January 18, 2006
9:09 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] LS1 Coil
Failures
Hummm,
think I will hold off swapping my stock Mazda Coils for the LS1s sitting on my
work bench until we have a better handle on the coil "problem".
Have now flow for 300 + hours and over six years with the stock coils with the
only problem being the early failure of the leading module because of a
resistor opening in its base.
The
wattage of the resistor is apparently too low to carry the load of the ignition
continuously running at 6000+ rpm. Replaced the resistor with a higher
wattage one and no more problem. At least three people have had this
resistor fail using the stock coils - it may well be that the auto folks don't
design for their coils to be run at high continuous rpms unlike the MSD type
ignitions for racing.
I
wonder what the automobile circle are experiencing with their LS1 coils -
anyone know?
-----
Original Message -----
Sent: Wednesday, January 18,
2006 9:57 AM
Subject:
[FlyRotary] Re: Coil & Alt cooling, Buly's input shaft
I'm
wondering if 180f under hood is really the main cause for coil fail? Auto's
shut off hot in desert, black steel hood, must see temps way beyond anything we
can throw at them. You can't get those puppies to fail regardless of
environment. Perhaps there are one or two other significant causes. I'd be real
quick to abandon that manufacturer.
On
Tue, 17 Jan 2006 22:39:15 -0500 "Tracy Crook" <lors01@msn.com> writes:
During
my preflight tests this morning I found the third failed ignition coil in
the last 150 hours so I finally got serious about dropping the temps around my
coils and alternator.
I've
been concerned about this since the under-cowl temps are as high as 180
deg F (delta T through rads is 70 - 90 deg F). The attached photo
shows the solution (hopefully). The alternator plenum is made from a
Tupperware container pirated from the kitchen with a skirt made from sheet silicone
rubber. A 5/8" ID vinyl hose routes cool air from the oil cooler
plenum to it. ( 3/8" ID hose was tried first, not quite good
enough) This was tried prior to today's scrubbed flight and a temp
probe shows that air inlet temps to the alternator are only 3 - 5 degrees above
ambient. Nice.
I
had recently added a cooling plenum around the coils (also made of tupperware)
and fed by a 3/8" ID hose but it was pretty leaky and only dropped
temps about 10 - 15 degrees. After replacing the coil today I built a
better fitting plenum and fed it with 5/8" ID hose. This one is made
of space-age cardboard and I'll build a more permanent one from fiberglass if
it works OK. Will test tomorrow if wx allows.
Buly,
got your input shaft today and checked it out. The thrust bearing rollers
& races look a little stressed but the roller cage has been completely
trashed. I do not think the .005" out of flatness on your
bellhousing would explain this and the odd wear pattern on the plate. The
marks and discoloration (heat) on the bearing and shaft look as if there is
misalignment between the E-shaft and the gear drive. When you built
the plate & bellhousing adapter for the drive, how did you verify
concentricity? This is much harder to do than verifying the parallelism
of the bellhousing and plate but is absolutely vital. There is no
question that the drive would have soon failed if you had continued to run
it. Glad this showed up before flight.
Tracy
(Happy to hear that Dave L. is safe! Good flying. )
-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk assessment, Glass panel design info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html