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
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