Ok Guys,
Some of the comments seem to be a little off base. The Smaller plugs should
require the same amount of energy to jump the GAP. The smaller loop-over
sidewire should allow the plug to be a bit closer to the combustion chamber.
That would make the gap a bit more accessible to the mixture, which MAY help
the combustion. The smaller recess should make for a tiny bit higher compression.

The best thing would be for NEW housings to be DESIGNED for the smaller plugs
which would allow the water jacket to be closer to the plug well and it might
help prevent cracking in that area under extreme power use. Mazda versions having
some small trouble cooling that area.I do like the idea of being able to run the
tiny coil-on-plug coils used on the modern motorcycles. Those coils are super light,
and usually are a ferrofluidic type which is great for low hesterisis. These coils
need to work on machines that have a 13,500 RPM redline on the street! They seem a
perfect choice for the multiple spark regimen of the rotary. Take a look at the
newest Honda or Yamaha 600's for good examples.
Bill Jepson

Bill you're exactly right. There is a small group of us that
are intending to mfg. a rotor housing using the small plugs
based on testing results we have accumulated.

Skip

This I got to see :)

Paul Lamar

Dave, Skip,

Thanks for the idea.I noticed that the inside of the trailing plug hole
had a little bevel on it where the factory no doubt took off the burr
after drilling. Wouldn't this small depression still allow some gas
to move from the compression stroke to the exhaust stroke

Bill

Thanks for the lead to the 10mm bike coil on plug info.About the
leading plugs.I was thinking about making a step shaped rectangular
stainless 303 insert with radius ends.It would have dualplug holes
and slip inside a milled out leading plug area of the housing, TIG
welded on the inside, and interface fit on the outside. Another plate
with gasket and plug holes is then bolted both to the outer housing as
well as the insert providing a water tight seal and mechanical strength
between the inner and outer housing. If the stainless insert had
grooves machined onto the outside where contacting coolant so much the
better for heat transfer.CHT sensor could be built into the insert as
well.Existing hole and boss is pretty muchmilled out with this
operation. Water passages should be a few millimeters wider on each side.

It would send you a Rhino file, except the by Windows based lap top just
died.

Doug in Japan

Doug,
I'll look forward to seeing the drawing when you getyou computer running again
Bill Jepson

By the way Doug, if you were able to weld in an insert you would probably need
to do some annealing of the welded area. This is a hot area which gets locally
much hotter than the area around the intake port. I am not sure why to run two
plugs in the leading position anyway,unless it is to ensure lighting a lean
mixture. I believe that running the multiple spark system Paul was talking about
would be more productive. Running a conformal insert with the small plug in it
in BOTH of the conventional locations makes more sense to me. I would like to
see a dyno chart report of improved function with dual plugs in the leading
position before I would do it.All of the information that I have seen in the
past shows that losing the leading plug was a 80% loss of power, and the loss of
the trailing plug caused a 20% power loss. The key here is that non-turbo at
least the trailing plugs are NEEDED and sagnifigant. Filling the area close to
the rotor and getting the plug as close as posible are the only idea that I
think works. The idea of the "side fire" modification allows you to put the
conventional plug closer to the combustion chamber safely, that is all it does.
Bill Jepson

Bill,

I guess the question is can you fly with twenty percent power if you
loose the leading

That's why the side by side spark plugs. The Wankel engine has dual
plugs but they feed the same hole. That's a good method as well.

Skip

As I recall people say loss of the top plug has little effect
on power. IMHO it was done for emissions primarily.

The dual side by side plugs have little effect on the BSFC
as those that have them show no advantage. On the other hand they are
either air cooled rotors or charged cooled rotor engines so it is not
a real back to back test.

Paul Lamar

Paul,
I would logically conclude the twined leading plugs are simply for standard
redundancy.BTW Mazda terms, lower plug LEADING, higher plug TRAILING. This was a
bit confusing to me at first. To answer Skip, I wouldn't want either plug failing
since you lose power either way.One answer for that is redundant COILS on the
same plug.You can get a'Y' to tee two coils into one plug. Electronics is the
likely failure, so I would feel safe with a single leading plug personally.I
will have 3 rotors though soI could probably limp home on2+20%. The single
rotor guys might have more to say about this. We aren't drag racers here
though. Once run for a while, say 20 hours, you have passed infant mortality
and if your temps are under control you will probably run for years. That is
why the FAA has the 40 hour fly off mark to begin with. Most of us won't even be
asking our engines to develop full automotive level HP! My 20B will be loafing to
produce the 250-260 HP max recommended for my RV-10. The twin turbo cosmo made 345
HP stock. I am not going out on a limb thinking that factors other than the
engine itself will be my likely failure modes. Paul has beating this into the
ground but it is true none the less, design your external systems carefully and
the rotary won't let you down.
Bill Jepson

Just forget leading and trailing. Use top or upper and bottom or lower
much less confusing.

Paul Lamar

Yeah you're right. It's wierd to say the bottom plugs fire
first (leading) then the top(trailing).

Skip

Bill you are absolutely right about annealing the area around the weld
would be ideal though how that would be done without warping the
housing Pinpoint torch Yes dual plugs in the leading (bottom location
for all you guys that still believe that Australia is at the bottom of
the Earth) are a necessity in my opinion for long flights over large
oceans. This implies redundant ignition systems. My engine will be
boosted and the trailing plug is not that important but I will probably
keep it in for testing purposes. Multi firing plugs on any leading plug
is good in theory but would require extensive research to determine the
best plug to use. As you well know, heat values of plugs is critical
for engine performance and multiple firing may change the heat index.
Yes I thought about Y-ing dual ignition systems into one plug but that
doesn't change the fact that the Achillies tendon of the rotary
aviation engine is that it has only one leading plug. If one goes out
in a 13B or even 20B the engine is probably going to be running so rough
that we would shut it down.

Dual plugs can also be fired in an alternating or staggered pattern.
Megasquirt has the code to do this with injectors, so it stands to
reason it can also be done with plugs. The code is called Kurt staging.
Each plug can still fire at least once per cycle, which together
actually equates to a total of two firing event per cycle. Following
your advice and experimenting with plugs found on high revving 16,000rpm
engines it would stand to reason that these plugs can be fired at twice
the rate that we need at max. power in the rotary. More at 6,000 rpm.
That gives us 4 -5 firing events per combustion cycle.

This is all fine and dandy on paper but it really takes a working
relationship with a spark plug manufacturer to come up with a plug that
can handle the heat of the rotary. We are at the bleeding edge here.
The latest BOSCH plugs with the four prong cage around the central
emitter look to be the most promising technology for us. The spark has
four possible pathways. Plugs come pre gapped.

Perhaps like Skip mentioned two 10mm plugs angled into a central screw-in
insert might work. Actually I am loathe to do any welding on the rotor
housing if another alternative is out there. Speaking of which. Anyone
know if a stainless boss is welded (in the manufacturing process)
outside the housing liner and just inside the leading spark plug hole
It doesn't appear to be aluminum. If so I wonder if it was annealed
before the liner was formed.

Doug in Japan.

If you fired the plug with 4 sparks .2 ms long 1 ms apart might be the same
effect on the plugs as one inductive spark 1 ms long.

I re read K.Y.'s book on the subject and there is little advantage to the
upper plug. What they published was BMEP data at only several lean mixture
settings. No BSFC data.

I think two lower plugs side by side are not worth it. Too risky! Could damage
the rotor housing but I have no objection to it if you are going
to carefully measure the BSFC change (if any) on a good dyno.

IMHO your better off spending your time and money on TC.
BTW how is that coming

Paul Lamar

Doug,
I believe that your best bet for annealling would be inductive. I have seen
this done on machine tool ways, but usually for hardening. I don't think the
risk of the two plug modification is worth it. Plug fouling is your biggest
worry. I have seen the "Y" adapter to run 2 coils on one plug on summit racing
web-site. Really I don't think you need to worry about fouling as much running
alcohol anyway. Also what fouls the first plug usually fouls the second.
Ignition failure could be covered by a separate EMS box. The thing is that I
really think you would find anything that knocks out the first EMS will also
probably kill the second. Exception possibly being lightening strike. Sometimes
I think we get way too worked up about redundancy. We are far more likely to
cause a engine stoppage by running a fuel tank dry than ever having an ignition
failure while flying. That assumes of course that the basic wiring harness and
components are sound. Those are the things that you are testing durring the
fly-off time right We get way to clever about all these things and tend to
ignore the basics. Ignoriong good wiring practices and good hoses and clamps
and radiator volumes are what will stop the rotary. Get that done right then
you can start on a second engine core to experiment on. I am a mechanical
engineer and total motorhead so don't think I don't think of these things too,
but I want the standard setup flying first.

Bill Jepson

Bill

Well said. It sounds like my cure might be more harmful than the
percieved illness. Spark plugs are pretty basic technology without any
moving parts. The only failure besides ham handing an installation is a
manufacturing mistake such in the internal resistor or crack in the
insulator. Yes I have seen the Y system on Summit Racing as well and
leave that route open as a good option.

On the other hand I don't feel so confidient about driving one plug
with multiple strikes. That is a research project in itself. Give me a
week to think about it as I have machine shop time next Thursday.

Thanks

Doug in Japan

Doug,
Why are you worried about one plug with multiple strikes That is what a MDS
system does right now. Note for everybody: The spark discharge doesn't govern
the heat range of the plug, the combustion temperature does. Having multiple
spark discharges adds almost nothing to the temperature of the combustion event
other than making it more reliable. If your ignition system has proper control
of coil kickback you could make a hundred sparks and not cause any additional
wear either. 3-5 sparks effect will be negligible with reguards to wear. I am
mentioning this because for some reason people think this is new technology. It
isn't, only using multiple caps is. The use of multiple caps is just to
ensurethat you get multiple sparks all the time, it isn't new technology. If
fact the unit that Paul has in hand would only require very minor changes to do
what he wants it to. Changes that could be made by the manufacturer if we are
willing to buy some of them.

Let me now make what I consider the defining statement about this thread. NONE
OF THIS STUFF IS REQUIRED TO MAKE A PERFECTLY FINE AND FLYABLE ROTARY AIRCRAFT
ENGINE. Everything we are talking about here is to IMPROVE the performance of
that same engine. By improve I mean better fuel consumption or better power on
the same fuel,(BSFC), not needed to make the engine run or the system work. Ed
Anderson has been flying his NA 13B engine for years without ANY of this stuff.
When considering any of these changes use the physicians mantra: First do no
harm!TC offers REAL improvement, as does a better FI or safer PSRU. I really
want a hyd. constant speed capability too. When designing a mod or improvement
always think what is the return for this change P-ports make real sense for us
because thay WORK BETTER in the speed ranges we want to use. The twin plug mod
may require mods that compromise engine integrity for longterm flight. Be sure
you are ready to do a proper test program with many HOURS of operation before
you call it good. As I mentioned before this is not a drag race, and there is
always theZ axis tobe concerned about.

Bill Jepson

Bill,

OK you convinced me.  In light of what you just said what merit would
smaller plugs have?
I was only interested in them because they would fit better in a dual
plug insert.
Obviously a smaller plug means a smaller cavity in the area near the
inner liner.  Is that such a
big deal.  For instance when the leading apex seal crosses that hole is
there a transfer of gases   from the presiding exhaust cycle?

Doug in Japan