light twins?

On Tue, 26 Jul 2005 23:58:12 -0400, "Gordon Arnaut"
wrote:

However the wankel engine has some incredible advantages, including
smoothness simplicity, ruggedness and power potential that truly puts it a
class above the piston engine. There is no question about that, as
rotary-powered race cars have proven over and over -- until they are banned
because they simply have an unfair advantage.

Regards,

Gordon.

It's true that the rotory offers some interesting advantages, one of
which is the ability to continue to run and produce power after the
engine has lost compression due to overheating and warped side seals.

It will make power right to point where you shut it down, but you
won't get it started again because of low compression.

I guessing that it's disadvantages were enough that it never appealed
to big auto makers to work on them. Wankel itself was unable to make
it a success and it's hard to argue that Mazda has either. It's fuel
consumption and inherently dirty emissions which require a lot of
technology to clean up plus the investment in machine tools to create
it just didn't seem worth it to the bean counters, I suppose.

And the public did not seem to care much that it was available. When
Mazda first brought it out, it had a number of quirks that the buying
public had trouble getting used to. It had a cold temperature
starting assist that consisted of an injector that added pure
antifreeze from a seperate tank into the intake manifold. This of
course created a dense white cloud of smoke, which the owner was told
was normal, and it was, but it sure made owners nervous to see it.
And the owner had to refill the tank, which they often did not do,
which resulted in hard cold weather starting. Add this to the manual
choke, which the RX-7's had for many years and which the public had
difficulty using and it's easy to see why it was popular only for a
limited number of people.

Then there was the stench of the exhaust. Nothing smelled worse, not
even a diesel, and you could not tune it away. When properly adjusted
for emissions, it stank most powerfully, it felt like it was actually
burning your nostrils.

Mechanics didn't like it because it had two ignitions called a leading
and trailing ignition and originally, the distributer held three sets
of points in two layers. Not easy to adjust and naturally
problematic.

That of course went away with the advent of electronic ignition, and
eventually the engine was fuel injected and everything was computer
controlled. But converting such an engine for use in an airplane is
not without it's challenges.

Corky Scott

I guessing that it's disadvantages were enough that it never appealed
to big auto makers to work on them. Wankel itself was unable to make
it a success and it's hard to argue that Mazda has either.

How can you say that Mazda hasn't made this successful? Sure, the initial
introduction had it's share of problems, but since the RX-7 made the
re-introduction of the rotary here in the US, the engine has been as
troublefree as any engine produced. Emissions was one of the biggest
problems, but the newly redesigned Renesis engine cleaned that up, as well
as taming a bit of the bark, and overly hot exhaust. Fuel consumption in
aircraft use does not seem to be any worse than any other engine of the same
power range. The truth is that other manufacturers tried the rotary, but
didn't feel like it was worth developing, since they were perfectly happy to
churn out piston engines. Only Mazda seems to have had the willingness to
stick with it, and make it successful.

But converting such an engine for use in an airplane is
not without it's challenges.

Corky Scott

What challenges does it present, that aren't shared by any other auto
engine? Heck, it already has dual ignition. These days, two rotor engines
are not nearly the challenge that some engines would be, because Tracy Crook
sells engine controllers, monitors, and gear drives. Conversion Concepts
makes excellent mounts. About the only thing missing is an off the shelf
intake, and exhaust, which aren't far behind.

Cheers,
Rusty
13B powered RV-3 flying (2500+ fpm climb, 200 mph cruise)
Kolb Slingshot being converted from 912S to single rotor almost as I type

Earlier, Bellsouth News Server wrote:

How can you say that Mazda hasn't made
this successful? Sure, the initial
introduction had it's share of problems,
but since the RX-7 made the re-
introduction of the rotary here in the
US, the engine has been as troublefree
as any engine produced.

Well, Corky didn't say that Mazda hasn't made the Wankel rotary a
success. He only said that it's hard to argue it:

Earlier, Corky Scott wrote:

: Wankel itself was unable to make it a
: success and it's hard to argue that
: Mazda has either.

That the vast majority of Mazda cars are powered by conventional piston
engines supports Corky, at least when you consider the aspect of
commercial success. And it is undeniably commercial success by which
car manufacturers measure themselves and each other. Sure, the RX-7 and
RX-8 motors seem to be trouble-free, but at what cost?

And further, since most of the patents that cover the Wankel
innovations are now expired or are about to expire, you'd expect to see
other manufacturers adopting the Wankel. That you don't see this tends
to support Corky's argument that for the vast majority of engine
applications the Wankel's disadvantages outweigh its advantages.

Personally, I think that Wankel rotaries continue to be part of Mazda's
automobile offerings only because it would be harder sell an RX-series
car without them. I believe that Mazda decided to continue the Wankel
heritage of the RX only after carefully balancing the greater cost per
unit horsepower of their rotary against the whizz-bang (Okay,
whizz-hummm in this case) technical appeal in the RX package. An RX
without a rotary would be like a Mustang without three-element
taillights or a Buick without fake exhaust portholes.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

I think there are theoetical factors against the Wankel-type rotary.

The combustion chamber shape is far from ideal and there isn't a straight
forward way to correct that. As a result, the engine leaks a lot of heat in
exhaust gasses as well as through the cooling system so there is less energy
going into producing power. All else equal (and it rarely is), the rotary
will have worse specific fuel consumption than a crank and piston.

Old pistons have one rarely discussed advantage. In the interval between
ignition and the beginning of the power stroke, piston motion is very low
and the volume of the combustion chamber is close to constant. This allows
combustion to run to completion under near ideal conditions of temperature
and pressure. That squeezes more heat calories, and therefore power, out of
the fuel-air mixture.

Bill Daniels
(I loved my RX-7)

Bill Daniels wrote:
I think there are theoetical factors against the Wankel-type rotary.

The combustion chamber shape is far from ideal and there isn't a straight
forward way to correct that. As a result, the engine leaks a lot of heat in
exhaust gasses as well as through the cooling system so there is less energy
going into producing power. All else equal (and it rarely is), the rotary
will have worse specific fuel consumption than a crank and piston.

Old pistons have one rarely discussed advantage. In the interval between
ignition and the beginning of the power stroke, piston motion is very low
and the volume of the combustion chamber is close to constant. This allows
combustion to run to completion under near ideal conditions of temperature
and pressure. That squeezes more heat calories, and therefore power, out of
the fuel-air mixture.

Bill Daniels
(I loved my RX-7)


Any loss of BSFC at speed is nearly all compensated for through extreme
leaning made possible by charge stratification (centrifugal force throws
gas fumes to the outside of the chamber, where the plugs just happen to
be). In real world airplane (vs. imaginary ones), there is no
difference in rotaries vs pistons. Furthermore, the BSFC Lycoming
et.al. publish is for a engine running on a test stand. In the real
world, most pilots run rich to protect valves.



--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Bob Kuykendall wrote:

And further, since most of the patents that cover the Wankel
innovations are now expired or are about to expire, you'd expect to see
other manufacturers adopting the Wankel. That you don't see this tends
to support Corky's argument that for the vast majority of engine
applications the Wankel's disadvantages outweigh its advantages.


If by "vast majority", you mean automobiles, then you a absolutely
correct. An automobile is one of the worst possible applications for a
rotary. The low end torque isn't there, and Mazda has to go through all
sorts of contortions to get some. Rotaries like to rev fast and stay
that way, and really suck at the low end.

Where the engine will shine is situations where the low end grunt is
unecessary, and they can rev to 6000RPM or more and stay there..
Airplanes and power generation are two examples that come to mind.
Expect to see more AIRPLANE ENGINES using the rotary concepts as the
patents run out.

The biggest disadvantages right now is low volume. GM or Ford won't
touch a design that is meant for a few thousand per year. Mechanics
have neither the time nor inclination to learn about an engine they'll
very rarely see. But Lycoming is already working at those sorts of
volumes. It becomes a non issue.

The second quoted problem is a red herring. BSFC. The rotary leans MUCH
better than any piston engine. In actual practice in real airplanes,
fuel burn is indistinguishable.

But the advantages. An engine that will sacrifice itself to get you
home. A $500 rebuild that takes a weekend. Power to weight ratios that
already beat pistons and continue to climb. Did I mention, an engine
that will sacrifice itself to get you home.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

On Wed, 27 Jul 2005 22:47:34 GMT, Ernest Christley
wrote:

The second quoted problem is a red herring. BSFC. The rotary leans MUCH
better than any piston engine. In actual practice in real airplanes,
fuel burn is indistinguishable.

But the advantages. An engine that will sacrifice itself to get you
home. A $500 rebuild that takes a weekend. Power to weight ratios that
already beat pistons and continue to climb. Did I mention, an engine
that will sacrifice itself to get you home.

All good points. I didn't mention this (at least not recently) but I
had a 13B in my shop at one time that I was going to use for my
airplane.

This was a number of years ago before Tracy began developing his
rotory. I had started with a Buick/Olds 215 cid aluminum V8 but had
sold it because it was too hard to find parts for it.

I was getting increasingly nervous about using the 13B because I knew
I had to fabricate my own intake manifold and exaust system. I had
been an auto mechanic who worked on Mazda's, including the RX7's so I
knew something about them. The intake manifold looked to be almost as
big as the engine, which is why all the folks I'd been talking with
were recommending it be junked and a smaller one fabricated.

Remember, this was in the early 90's, not now.

But the thing that really put me off was the heat of the exhaust
system. It ran something like 500 degrees hotter than piston type
exhaust systems and required a thick wall stainless steel system.
Even with such a system, all that heat seemed a little scary to me.

So I sold that and now have the Ford V6 which is running well at this
point and seems to have all the power I need.

Corky Scott

On Wed, 27 Jul 2005 10:08:35 -0500, "Bellsouth News Server"
wrote:

How can you say that Mazda hasn't made this successful? Sure, the initial
introduction had it's share of problems, but since the RX-7 made the
re-introduction of the rotary here in the US, the engine has been as
troublefree as any engine produced. Emissions was one of the biggest
problems, but the newly redesigned Renesis engine cleaned that up, as well
as taming a bit of the bark, and overly hot exhaust. Fuel consumption in
aircraft use does not seem to be any worse than any other engine of the same
power range. The truth is that other manufacturers tried the rotary, but
didn't feel like it was worth developing, since they were perfectly happy to
churn out piston engines. Only Mazda seems to have had the willingness to
stick with it, and make it successful.

Now now Bellsouth, let's not get too worked up over this. I agree on
most aspects of the rotory but a raging success in the automotive
world it has not ever been. Sure you can get it in old RX-7's and new
RX-8's, but that's it. If it were such a great alternative, everyone
would be trying to build one.

I don't quite understand how Tracy manages to get the kind of fuel
burn he claims but I suspect he isn't running it very hard because the
amount of surface area the rotors are exposed to as they rotate is
much greater than that in a piston type engine. This much greater
combustion chamber exposed surface area means much more fuel can
condense on the surface. It means it's going to get poorer gas milage
inherently, unless you unleash the electronics engineers to do their
magic with fuel injection and all the other gadgets that are used to
emeliorate the situation.

The problem is, you don't get that stuff when you put it in a
homebuilt airplane unless you rip out all the sensors and the entire
wiring harness to go along with it.

So yes, it's a very very solid engine but like so many things in
aviation, it has it's compromises.

Corky Scott

Now now Bellsouth, let's not get too worked up over this. I agree on
most aspects of the rotory but a raging success in the automotive
world it has not ever been. Sure you can get it in old RX-7's and new
RX-8's, but that's it. If it were such a great alternative, everyone
would be trying to build one.

Hi Corky,

Finally fixed the "Bellsouth News Server" name. I left that all generic
after the last time I got spam attacked on one of these groups. We'll see
if it comes up as my real name this time.

Certainly the rotary cost's Mazda a bit more to make, but I would assume
that's true of any automakers flagship engine. They also don't put their
top engine in everything they make. Ever heard of a Dodge Hemi Neon :-)
Seriously, the rotary is a bit of a specialty engine, but those of us who
bet our lives on them believe that those special qualities are what makes
them the best choice. Still, if they have to be in every vehicle on the
road to be a raging success in the automotive world, then I guess they're
not :-)

Breaks over, back to the single rotor in the garage.

Cheers,
Rusty

Corky Scott wrote:

I don't quite understand how Tracy manages to get the kind of fuel
burn he claims

he reaches up and turns down that mixture button. The charge stratifies
in a rotary, pushing the fuel charge out to the plugs.

but I suspect he isn't running it very hard because the
amount of surface area the rotors are exposed to as they rotate is
much greater than that in a piston type engine. This much greater
combustion chamber exposed surface area means much more fuel can
condense on the surface.

Running at 6000RPM vs 2500 doesn't leave much time for fuel condensing.
It is true, though. The rotary doesn't get complete fuel burn,
especially at the little pointy ends of the chamber. But the
counterpoint is that most pilot run rich to keep from cooking their
valves. No valves in a rotary.

Besides, all that extra energy left in the exhaust need not be wasted in
an airplane engine.

It means it's going to get poorer gas milage
inherently, unless you unleash the electronics engineers to do their
magic with fuel injection and all the other gadgets that are used to
emeliorate the situation.

The problem is, you don't get that stuff when you put it in a
homebuilt airplane unless you rip out all the sensors and the entire
wiring harness to go along with it.

Tracy is an electronics engineer 8*)
I bought 42lb Ford injectors, still have to get LS1 (from GM I believe)
coils. Tracy's controller is around $800. All the other sensor you
need are attached to the engine when you pull it out of the car. You
get them unless you go through a lot of trouble to leave them behind.


So yes, it's a very very solid engine but like so many things in
aviation, it has it's compromises.

Have I mentioned in this thread that it will sacrifice itself to get you
home. Even on one rotor, it will keep making enough power to keep most
GA planes in the air until you shut it off. To me, it takes a lot to
compromise away that much safety.


--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."