Hi Paul.
1) Aside from perceived poor fuel economy of rotary
engines, what are its disadvantages ?
2) You advised carbs and magnetos.Why are they not
discussed here? Are they not suitable for rotaries ? If
suitable, Let's have more discussions.
3) Can there be carb icing in tropical countries below 3,
000 feet ?
Best regards.
Ben
Fuel economy is only 5% higher than an aircraft piston engine.
This is more than made up for by the 25% lower cost of auto gas.
Magnetos are suitable. They will work fine. They are just too costly.
$2000 each new
and $400 to $800 re manufactured plus cores. People don't want to
pay as much for two aircraft magnetos as they pay for the rest of
the engine. In some cases much more than they payed for the
engine. RX8 ignition coils are $25 each for a total of $100. One
coil per plug.
However if I were certifying a rotary I would use aircraft magnetos
and an aircraft carb. The FAA is much more comfortable with that
they they are with EFI and electronic ignition. In that case the
rotary engine would pass certification in a heart beat.
The best carb (cost verses power) to use is a two barrel 500 CFM Holley
with a
leaning kit.
The FAA will not sign off on your carb engine unless it has carb heat.
Paul Lamar
Thanks Paul.
I'm glad there is someone like you who
has the knowledge and patience to answer
our questions.
Can there be carb icing in tropical countries at an
altitude up to 4,000 feet ?
Best regards.
Ben
At the higher altitudes for sure. The evaporation of the fuel in
the carb venturi causes a cooling effect.
Paul Lamar
Paul,
My Continental IO 520D has fuel injection- but it is a very basic system
indeed. One inj per cyl, a regulator, and a mechanical "TPS". It
looks like it all related back to the manual leaning valve and
quite possibly the manifold pressure. This system seems remarkably like
the old FI on the corvettes in the early 60s. Regulators and manual
flow metering.
Why would this be a difficult system for the rotary? Before I sell
my Connie, I might inventory the system and see about maybe a prototype.
Kevin Alderman
http://www.vette-vues.com/parts_for_sale.html
Early Power Sport used mech fuel injection.
It is still sold for aircraft.
http://www.airflowperformance.com/html/site_html.html
Paul Lamar
These early Rochester FI systems were not received well due to a
couple of things. The dual quad made more power the next year and
the injection was very sensitive to atmospheric conditions. It
required almost daily tuning unless someone really knowledgeable
worked on it. Att 1. The "throttle" in the center is not the
throttle. It is the choke plate. The throttle can be more easily
seen in Att 4. This works similar to the Bosch/Volkswagon FI and
the Mazda MCES systems, that use a special volute and flapper to
measure air flow. The Rochester used the cone in the intake to
create a pressure drop like a venturi. This was fed over to the
diaphragm to lift the metering "rod" to add fuel. At idle there
would be no "vacuum" on the sensing line. As the throttle is
depressed, the air flow causes a vacuum at the venturi and lifts the
diaphragm. Different air densities and humidity affected the fuel
required which was not well compensated for. The Mazda MCES works
fairly well as the sensor is a form of mass flow and is compensated
with the computer. The Bosch also works as a basic mass meter, but
did not have a computer (Rabbit system. different from K-jetronic).
Any AC system will have compensation for atmospheric condition as a
requirement for altitude changes.
Dale Davies
Hi Paul,
No FI system I have ever flown with has allowance for
temperature or density, only have experience with Cont and Lyc. My
understanding is they are both a engine speed/throttle/mixture
position, ie if you have the mixture,prop,throttle to the wall you
will always get the same fuel flow, regardless of temperature and,or
altitude. But I love 'em, no carby icing!! BUT if you have clogged
injectors your fuel flow gauge will tell you you have say 36 gallons
pre hour at take-off, you will have something less than that,
because it is not a fuel flow meter but purely a pressure gauge!
calibrated to indicate fuel flow in gallons per hour. Where it
become bad is if you have only one injector, you may not notice the
fuel flow is lower than it should be for that engine, unless you
have EGT probes in each exhaust outlet. John Burey
Hi Paul, I was half asleep last missive I think, I had said "if
you have only one injector", I really wanted to say was that if you
had
(one injector partly clogged), you would have a lower fuel flow to
that cylinder, which you can pick up with a EGT in each exhaust
outlet. Fuel injection is much better than carbys every time, as
for the spark, I cannot see why one could not use a electronic
ignition as a previous writer described (B&S), one for each
cylinder with wasted spark, ie two plug wires on each coil, then if
one coil failed you would be only drop out one plug on opposing
cylinders, plus you would have a very hot spark with about .040" gap
not the pillidy .015" to .020" with a magneto, just the correct size
gap to catch a bit of carbon, I am surprised that the FAA still
allow magneto's to be used, I have had more failures with magnetos
in engines than any other single thing. I know all the reasons they
are used (no external power) ect., ect.. John Burey
Be careful with wasted spark. Only the bottom plugs will tolerate that.
Paul Lamar
Hi Paul, what is the reason for not tolerating wasted spark on
the top plugs? as you know I nothing, nothing, (in a high pitched
voice),about Rotarys. John Burey
Waste spark fires two plugs at the same time.
The problem is rotor 2 is always 180 degrees out of phase with
rotor 1 so when rotor 1 is on the firing stroke rotor 2 is on the
compressing stroke with a combustible fuel air mixture that might
pre ignite causing a negative torque on the e-shaft. You can see
that with this picture of a transparent model engine.
In a 2 cylinder or more piston engine, the firing stroke is 180 our
of phase with an exhaust stroke so the waste spark has no effect on
the spent exhaust mixture.
Paul Lamar back from China.
What if you hooked the waste spark return to the 2nd plug on the
same rotor? Is there enough power to fire both?
We are running Klaus' Lightspeed on the little Continental and it
works like a charm.
Chris Cosman
That should work. Is Klaus using waste spark coils? I think that is
a CD system.
Paul Lamar
The only problem I see is that the plug gap resistance is doubled.
This could lead to misfires. A normal waste spark has a very low
resistance on the plug that is firing across the exhaust gap.
Dale Davies
Does not seem to bother them as waste spark is widely used on auto engines.
Paul Lamar
Yes they work fine when the one plug is firing in the exhaust on the running
mate of the cylinder you expect to ignite. Of course 360 degrees later the
plug firing in the exhaust is reversed. If you use one waste spark coil to
fire both plugs in one rotor, the plug resistance may be too high. Remember
that this is a circuit and total resistance has to be considered. Also one of
the plugs will always be firing in reverse polarity (backwards) which it does
not want to do as well. If someone wants to experiment with this, I would
recommend putting the reverse polarity side on the trailing plugs. If the coil
can create enough energy this could be used. I have not tried this. Also a
supercharged engine will require higher spark energy. Turbo normalized engines
are like naturally aspirated in that the air molecules in the plug gap are the
same as at low altitude when at higher altitude.
Dale Davies
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