Paul,
Years ago there were two brothers from Venezuela with a Cozy powered by
two
Suzuki Swift engines that were Siamesed together. They didn't share
the
same prop, but instead used two counter-rotating props. The prop
shafts
shared the same centerline. In cruise, they could shut down one engine
and
greatly reduce the fuel burn. I don't see why this idea couldn't be
applied to the rotary using two 13b engines. It would require the use
of
belt drives. I believe Wankel GMBH developed one along these lines
they
called the Wankel Twin-pack. (discussed in your YouTube video) I
always
thought that would make a great package for a larger plane if someone
wanted to spend the time and money to work out all the details.
Mark
I've been tossing this idea around in my head, and I really like it.
(This is why I was asking about reverse rotation and 3d models a few
days ago). It seems so neat to be able to have an almost completely
independent twin setup in a single engine sized package. The only
interlink really is the sharing of the engine mount and perhaps some
bearings in the prop shafts. Both of those can be designed to a very
low failure rate.
I've roughly sketched out a few things, and it seems to me that the
best way to go about it would be to face one engine forward, and the
other backwards. The backwards engine would drive a countershaft off
the similar to some supercharger setups except off the flywheel side,
and the forward facing engine could drive the external co-axial shaft.
I think Mark was right that a belt drive setup would be best. This
setup has a couple of benefits over facing both engines the same way.
First is that you can have the plugs all facing inwards and the
exhaust and intake facing outwards. This will make mounting of coil
packs a bit easier, and will prevent exhaust from one engine heating
the other up. The intakes could possibly share a common filter and/or
plenum depending on how you set them up. Depending on the mounting
setup, you may be able to keep the engines a little closer together.
The countershaft could also provide a great moment arm to resist the
bending moment from the props
If one did want to keep both engines pointing the same direction, a
gearbox type setup with a reverse idler would certainly work. I think
it would be more expensive to do that way, and possibly a little
heavier as well. You'd have to worry with oiling too.
Anyone have any thoughts?
Josh
Are you talking about twin engines driving a single prop, or a twin
setup
with independent engines, props, etc?
Kevin Alderman
I'm talking about twins driving separate contra-rotating props.
Basically everything would be independent. It's all the advantages of
a twin in with single engine drag, no yaw on engine out, and no torque
steering on the ground... like the Cessna 337 except both engines and
props are at the same location.
Joshua Jacobs
Hi Josh
I also like the Idea of having 2 independent drive engines
and being able to shut one down for cruise economy. If you use 2
contra-rotating props one driven by each engine, what will be the
effect of shutting one down ( drag and interference of the running
prop). This will also require purchasing 2 props but the belt drive
will also work as a psru. have a look at this system
http://ezycopter.powweb.com/cds.htm it is for a helo but you get the
idea, may fit with 2x single rotor engines and also works as a psru.
Or you could use 2 single rotor engines inline with
coaxial output to a single prop with a disengaging coupler for one of
the engines. I think I saw that somewhere in the newsletter, using a
tc on the single rotor, similar to this
http://www.rotaryeng.net/RX8-TC-eng3.html , just can't find it right
now.
Graeme Riley
Bell helicopter came out with the twin pack long ago. It uses twin engines
driving a common transmission through overrun clutches. I like the
redundancy of the twins, but the dual props would add a lot of complexity.
I think a simpler solution is twin engines input to a common psru, with a
controllable pitch prop.
Kevin Alderman
I like the idea that you guys are tossing around, but without the contra
rotating
prop. Contra props are extremely noisy, and a bit problematic, the Rusky's
had one in
a long range bomber, apparently you could hear it coming from the next
country.
Chris in NZ.
While I can't speak to the noise problem, I believe it would be
minimal compared to our engine muffling requirements. The cozy spoken of
was a very interesting design. One engine faced forward, one backward. The
effect was to create a V8 with 2 crankshafts, the engines had an end plate
on both ends that fastened the engines together. There were bearings for
the prop shafts in about what would be the camshaft location of a
conventional pushrod V8. There were sealed bearings supporting a solid
shaft in the center with a hollow shaft with bearings that supported both
shafts on the outside. The only thing I would have wondered about was if
the inside bearings were supported inside the hollow shaft they would see
double the surface speed. they could have avoided that with two full length
shafts with independent sets of bearings. It was a very interesting set up.
And the brothers thought enough of it to fly all the way to Oshkosh. They
used multiple sets of v-belts for both drive and reduction, like one of the
Rotorway helecopters, oil pressure hydraulic belt tensioner. A rotary
version would need a gear reduction on both ends as the pulleys for a 3:1
reduction would be hard to make and huge. The small pulley would need to be
around 6 inch minimum diameter. I wonder if it is still flying, It was a
very neat job.
Bill Jepson
I did a 3D or two on the subject.
RX8 electric power steering rack landing gear retraction mechanism.
Paul Lamar
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