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.