Tracy Crook wrote:
Paul Yaw wrote:
Tracy Crook wrote:
At the risk of injuring some sacred cows I'll put in my $.02 here.
Lots of snips
Another factor in ignition is energy in the spark. CD (especially
msd type)
is potentially the highest here but there are exceptions. The Ducati
CD
used on Rotax engines is so weak that its hard to see the spark in
daylight.
I know people who have spent days trouble shooting this ignition
system
(because they couldn't see the spark) when there was nothing wrong
with it.
The energy in Inductive coil & magneto type systems depends on the
particular coil involved. Magnetos are usually at a disadvantage
here
because of the small coil size. The 86 - 92 Mazda coils are
relatively
high energy type (and this is reflected in their weight).
Paul Yaw wrote:
The spark energy form an inductive discharge system is also somewhat rpm
dependant. The '86-'92 have a very low primary resistance which helps
in this situation.
True. I have measured the saturation time on the Mazda coils and verified
that they can maintain full energy up to about 7000 rpm which is why I think
they work fine for aircraft use.
My advice to those using the Mazda rotary for aircraft use is to use
the
stock coils unless you have a very compelling reason not to. In the
RPM
ranges we are interested in (about 6500 rpm max), there is very
little
advantage to using anything else. Those who claim that there is a
world of
difference when using something else are either talking about
operation at
the far end of the performance spectrum or they are dreaming.
Paul Y wrote:
When I say that an ignition upgrade improves fuel
economy, I don't mean that the BSFC was
better at 9000 rpm. I have yet to see anything but an improvement
across the powerband. Aside from full throttle operation, there are
gains to be had at low manifold pressures as well. If they didn't work
better, I would not recommend them. I do not sell them, and I do not
make any money when MSD sells them.
Keep in mind that my reply was addressed to someone thinking that a magneto
would be an improvement. I would take an MSD system over a mag ANY day.
I have not seen any reason not to believe you Paul. I'm sure there is a
measurable difference and I would be very interested to hear what that
difference is. I have not personally tried the MSD system so of course I
can't say for a fact but I'm guessing that if that is the ONLY change
(compared to the stock 86 - 92 system) there would not be a "world of
difference" at 6500 rpm.
I am also keenly aware that there is a huge difference between racing and
what I assume most people here are interested in (aircraft use). A 3 HP
gain (arbitrary number) can be the difference between winning & loosing
(everything) in a race but this would make less difference than cleaning the
dead bugs off your prop on an airplane.
Gains due to
ignition changes are purely due to improvements in efficiency (which
is
wonderful) so don't you think Mazda would have done this is the
improvements
were this dramatic? They were so desperate for efficiency gains
during the
design of the second generation RX7 (1986 - 1992) that the project
was going
to be cancelled if they didn't find a way to reduce the car weight by
ONE
GRAM per design team member. They sweat bullets and spend millions
to do
that. Trust me, if a better ignition system would have done the job,
they
would have done that instead.
First of all, we are ASSUMING that the engineers who
designed the rattle trap piece of shit second generation RX-7 did
everything right. Why ASSUME that? If these guys made efficiency their
number one priority, and then proceeded to do everything right, they
would have scrapped that heavy inefficient POS exhaust manifold. Major
manufacturers have many priorities that we will never understand.
Without knowing everything that was of importance to the design, it is
foolish to ASSUME that we know exactly what their priorities were, and
then ASSUME that they met all of their objectives based on what we THINK
they had in mind.
Aside from that, my buddy Sven Talo says that "trust me" is Swedish for
"#&$@ you"
Rattle trap piece of shit, Ouch! True, there are many compromises made on
a production car. That manifold & secondary port valve on the 13B is a
prime example. BUT, my point is that the average airplane builder assumes
that Mazda didn't know what they were doing in way too many things. Case in
point -- replacing the stock coils on the 86 - 92 13B with mags. Pardon
the expression, but trust me on this Paul, your knowledge of the Mazda
rotary (and engines in general) is NOT represenative of the average airplane
builder. It's OK to change something the factory did, I'm just saying that
we need to understand the relavent facts before doing so.
True, there IS a big difference if you are going to run at 9000 rpm
(like
the Racing Beat 3 rotor project)
The Racing Beat three rotor project makes peak horsepower at 7500 rpm.
Just repeating a number thrown about here on this newsletter. I really know
nothing about the Racing Beat engine.
but the average airplane builder would be
wasting their time (& money) going on a quest for the ultimate
ignition
system. But, (as Dennis Miller says) that's just my opinion, I could
be
wrong :-)
Tracy
Paul Yaw reply:
Without actually going on that quest, how do you know? Starting a fire
is not an easy thing to do in a rotary engine. Complete combustion
NEVER happens in a rotary, or a piston engine that runs on liquid fuel.
The situation is actually worse in a side port engine because the
"fresh" intake mixture is highly diluted with exhaust gasses. A good
ignition system certainly helps.
Again, I was addressing the "average airplane builder". I know because I
once went on that quest (in a previous airplane, not rotary powered) and
busted myself up so bad I can no longer walk straight. A total of 6
different systems were tried. The CD system I installed (piece of shit (to
borrow a phrase) Delta Mark 10B) failed and I crashed. I did get a few
more static rpm using the CD system but the effect on aircraft performance
was not noticible (until it died anyway). A Dyno is a fine place to go on
that quest, an airplane is not.
The turbo 13B that I just finished used a direct fire inductive
discharge ignition system. I did back to back passes with the inductive
system, and two MSD 6A's because I thought I heard a slight bit of
misfire above 5800 rpm. As it turns out, it was not misfiring, but it
did show an improvement in horsepower throughout the powerband. I
wasn't surprised. I will bring these runs home with me tomorrow so that
I can post them for you to look at.
Hope you didn't mind the "trust me" joke.
Paul Yaw
Not at all, without a sense of humor we are all lost. Look forward to
seeing the dyno figures. I also agree that boost places much higher
demands on ignition systems. BTW, I assume that direct fire inductive
system was the stock 86 - 92 system? I do not have much confidence in the
earlier system. Inquiring minds ..................
Tracy Crook rws@altavista.net
Web site: http://www.rotaryaviation.com
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