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
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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
Josh,
I also considered this approach. It is certainly do-able. It may be very
noisy, however…wikipedia says
Contra-rotating propellers have been found to be between 6% and
16% more efficient than normal propellers.[1] However they can
be very noisy, with increases in noise in the axial (forward and aft)
direction of up to 30 dB, and tangentially 10 dB.[1] Most of this
extra noise can be found in the higher frequencies. These sub-
stantial noise problems will limit commercial applications unless
solutions can be found. One possibility is to enclose the contra-
rotating propellers in a shroud. It is also helpful if the two propellers
have a different number of blades (e.g. four blades on the forward
propeller and five on the aft)
Also, read about the Air Force's XF-84H in wikipedia…
The XF-84H was quite possibly the loudest aircraft ever built
(rivalled only by the Russian Tupolev Tu-95 bomber [13]), earning
the nickname "Thunderscreech" as well as the "Mighty Ear Banger".
On the ground "run ups", the prototypes could reportedly be heard
25 miles (40 km) away.
Gene Kahn
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http://www.rotaryeng.net
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Copyright 1998-2012 All world wide rights reserved.