Paul, everyone.
In the interest of redundancy and safety I have been doing drawings
on
the
possibility of installing two leading plugs. Each would be fired
by
independent ignition systems. One a mag, the other a C.D. system.
The leading plugs are the critical ones. Therefore I've look at two
plugs
angled in towards the middle which would result in two angled
intersecting
holes at the housing middle. Another way to do it would be to
plug
the
center hole and drill two new holes side by side.
The first way would bring the fire into the middle but would create
a
chamber of about 1 cc cubed.
The second case is obviously easier and like Paul suggested in an
earlier
post there is enough metal (almost 10mm in the inner housing to tap
and
thread a aluminum insert into it. The outer housing has enough
thickness
so
it could be stepped for an 0-ring seal or epoxied in.
On the straight through approach the pitch of the holes would be
30mm
on
center or in other words 15mm offset. I am concerned if one
ignition
system
goes down would the remaining firing plug cause rotor imbalance
because
the
center of combustion is offset? Lycs and Continentals obviously
can
run
on
one ignition system and the distance between plugs is two to three
times
greater.
Any comments would be appreciated as I can't find any material to
suggest
Mazda or anyone has ever tried this.
Doug Fir
I can see how this would add to the electrical reliability
of the ignition system. Unfortunately this is the most critical
area of the Wankel rotor housing as far as cooling is concerned.
Mazda is still doing research and changing this area as far as
the exact configuration of the water jacket is concerned.
The early one rotor NSU Wankel Spyder got it wrong and
the rotor housing would crack straight through the spark
plug hole.
When the rotor housing melts after you run it at high power
without coolant for awhile this is where it starts melting.
Therefore it is highly risky to modify this area.
On the other hand it might help if a little R&D was done by
installing some thermocouples.
BTW This is another reason you don't want to nickel and
dime the cooling system plumbing by using automotive hose
and hose clamps. Use only silicone rubber hose and constant
torque hose clamps or better yet -20 or -24 AN lines.
Baker Precision down the street from Mazdatrix now has
forty five degree and ninety degree bends in the one inch
size silicone hose. They don't have constant torque hose
clamps yet but you can buy those in every truck stop
in the country. When I need AN fittings and hose Baker is
where I go.
http://www.bakerprecision.com/splsilicone.htm
I know you know all this Doug but it is worth repeating
for the new subscribers from time to time.
Paul Lamar ...No rotor no motor.
Paul,
Yes you brought up one of the points I was concerned with and that
is
adding
more restriction to the water passage in the most critical cooling
area.
I
hadn't heard about the physical weakness of the housing in that area
but
it
does makes sense not to add addition stress risers. Come to think of
it
roughness in castings often causes stress risers. That might be why
the
cooling passages are so smooth. That and low water flow resistance
of
course.
Still for the rotary powered airplanes, failure of the either of the
leading
plugs is probably the main issue I'm not completely happy with. JB
Weld
is
the other but I am coming around on that one. Only 499 more
freeze/boil
cycles to go:)
If the plug is considered a super reliable item then dual ignitions
systems
could be pulsed out of phase through the same plug. IE: one of the
FET
gate
closes as the other one opens. Granted this would cause even more
wear
and
elevated temperatures on the plug but at least it is something that
could
be
easily dyno tested.
I did a little research on plug design today and suspect size has
been
influenced to some extent by ham handed mechanics like Paul has
mentioned
earlier.
Food for thought is shown below:
\\ Since the inside of a spark plug is a relatively slim 3mm dia.
rod
with
a iridium tip welded on, couldn't two of these rods enter at an
angle
and
then travel straight down a 14mm diameter thin wall threaded
stainless
tube
and be epoxy potted in place? Of course the epoxy would have to be
a
high
temp non conductive type. The face that is next to the inner
housing
would
have a stainless cap with two holes surrounding the 0.4mm diameter
iridium
electrodes. The iridium 0.4 mm tip, now currently used in plugs,
would
fire to the stainless 2mm dia. hole surrounding it. The hole shape
could
be
enhanced if need be. Ie star shape. The electrodes would still be
timed
to
fire in sequence.
The loss of compression would be minuscule and might even be better
than
the
standard recessed plugs. The idea might work for the trailing plug
as
well
eliminating fussing with the far trailing plug. This would give us
four
spark events as the rotor travels by.
The inner electrodes could be supplied by Nippon Densu down the road
a
bit
from here, and the stainless and epoxy cases made up without too
much
trouble. Sure they would be more expensive than regular plugs but
with
a
little development effort we may be able to come up with a way to
tap
the
epoxy and screw the electrodes in as well so the cases could be
reusable.
Doug,
Use JB Weld, you could tap that.
John
I don't think JB Weld is high temp enough for this application.
--
Paul Lamar ...No rotor no motor.
Doug,
I appreciate your reasoning for looking into dual leading plugs, but my
gut feeling as an engineer/pilot is that you would be in the area of
diminishing returns.
As I understand it, if the lead plug goes dead for whatever reason, we
still should have 90+% power.
Now I know we can work up a scenario where that 10% might make the
difference between an inconvenience and tragedy, but unless I missed
something in the discussions, I really don't believe an additional
ignition system actually gets us much besides a "warm fuzzy",
complication and expense.
Currently, I feel quite comfortable flying w/ two independent "antique"
ignition systems (mags) sparking an "antique" engine (C-145).
A rotary w/ dual, well designed solid state ignitions system should be a
vast improvement by itself.
Just an opinion.....
Smooth air,
Steve Webre
Broussard, LA.
N3812V
Steve,
Thanks for your opinion. For some reason I thought running on the trailing
plugs alone caused a major loss in power, and elevated exhaust temperatures
due to incomplete combustion. Ie fuel burning in the exhaust or turbo
charger. I just assumed that we were then dealing with a critical situation.
If that is not the case then I completely agree with you. It complicates the
issue. I still want two ignition systems and one of them will be a mag.
About the C-145. That must be the tail dragger father of my plane.
Doug Fir
C-150
N6686T
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