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Hi Dave,
The induction and exhaust system of any engine plays a (the?) major role in
producing good power. When I first started flying with an 86 N/A 13B using
a "Racers' induction" system, I was probably not producing over 130 HP on a
good day. After developing a bit better understanding of induction systems
match with engine operating regime, I ditched the "Racers" induction system
and build one of my own.
I now consistently and reliably produce 175-185 HP on take off. I turn a
fairly large prop 74x88 and get 6000-6200 static rpm with a fuel flow of
from 17.5 to 20 gph (depending at least partly on OAT). A key factor in
producing good power is to match your operating rpm and induction system
parameters - that was my failing early on.
I had a undoubtedly good 9000+rpm induction system (I mean the rotary racers
were using it successfully), but I was only turning 5200-5500 rpm on take
off. So the induction system best operating region was poorly match to my
operating regime (or vice versa). It simply was not producing the air/fuel
mixture velocity at that rpm needed for good "stuffing" of the combustion
chambers.
After I got rid of the short large diameter induction system and switched to
a set of longer, smaller diameter runners, power increased remarkably. One
reason is, of course, the lower operating rpm I desired maximum power at (I
designed my system for max power at take off) needed a smaller diameter set
of induction tubes to create and maintain good runner mixture velocity.
So, while the Renesis is capable of producing more power than the older 13B
out of the box, you will fail to achieve this potential if your induction
and exhaust system are not well matched to your operating regime. For
example, the 6 port Renesis can wind to 9000 rpm in the automobile
installation producing gobs of HP. However, in aircraft use a more likely
top end is 7500 rpm (that's the limit listed for the 4 port Renesis.) For
that reason, I would opt for the 4 port over the six port Renesis, as the
six port is really not going to buy you much (in aircraft usage) except more
difficult in trying to build a six port induction system rather than a 4
port. Just my opinion, of course.
I do not plan on putting Renesis in my aircraft simply because it would
really not buy me anything over the older 13B (other than perhaps more
available parts) because my induction system is tuned for max power at 6000
rpm (take off). I don't fly at max power in cruise so there was no reason
for me to tune for max power at 6800 rpm (my max rpm). So design your
system for the operating regime you most want the power. Some folks want it
at WOT in cruise, as for myself - getting in and out of small grass strips,
I wanted the power at take off. Therefore, the next rotary I hope to put in
my bird with be the new developmental engine the 16X. Hopefully it will be
out in the 2011 model year.
Your mileage may vary.
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://www.dmack.net/mazda/index.html
http://www.flyrotary.com/
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.rotaryaviation.com/Rotorhead%20Truth.htm
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Dave Wilenius
Sent: Tuesday, March 10, 2009 9:54 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Ground Testing
"A normally aspired Renesis will work well, but I think will need very
careful attention to intake and exhaust optimization to get the power
you're probably hoping for."
This seems to go against what I thought was conventional wisdom where the
Renesis is lighter and doesn't have the same level of exhaust bark, making
it a good choice. If you want between 180-200 hp is this really that
difficult?
I was also under the impression that the placement of the exhaust ports on
the side
housings improved fuel efficiency.
If you design goal was fuel economy with 180hp would you still opt for a
turbo REW?
regards,
Dave
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]On
Behalf Of John Slade
Sent: 2009-03-09 01:20
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Ground Testing
Welcome, Jim.
You will get differing answers to that question. Mine is "not much
beyond the integrity of the engine itself".
Installation of a rotary in a Cozy is fairly tight and, by the way, in
my opinion a 20b is a little too big, long and heavy. Apart from test
running the engine to be sure that it's been correctly rebuilt, most of
what you do on a test stand will be a waste of time and effort. When
installed on the plane the engine is dependent on many systems that
either can't be effectively duplicated on a test stand, or will have to
be re-engineered when installed in the plane. Sure, if you can get your
hands on a dyno you can test power and tune, but once you put the engine
on the plane you'll have to wire the engine into the plane's systems and
implement fuel, ignition, injection, cooling and exhaust systems that
fit in the cowl. Testing those systems in the "real world" is really
only possible with air flowing through (and over) the cowl into a prop
at 200 mph and at various attitudes.
A normally aspired Renesis will work well, but I think will need very
careful attention to intake and exhaust optimization to get the power
you're probably hoping for. Next you will need some sort of muffler that
can hold up. I wasn't keen on hanging a muffler below the fuselage like
the RV guys do. There isn't much room for that in a Cozy and it would
look very ugly and draggy. Putting a red hot muffler inside the cowl is
a heat radiation problem, plus there's very little room. A turbo is
relatively small, circular and easily screened for heat. My approach was
that the easiest way to silence the roar was to install a turbo. This
way you don't have to bother with an exhaust system, and the intake
system is much less critical. This gives added (and exciting) benefits
in take-off and cruise power, but comes with its own complexity. The
trick seems to be to use the right turbo. Then, if you use a turbo, the
Renesis is a little high in compression ratio and you might be better
with a 3rd generation 13B. I'm working with another builder right now on
his Cozy project. We are duplicating my 13B exactly. That might be a
useful indication of whether I consider it a success. The Cozy Girrrls
are very knowledgeable on this rotary stuff, and they also are
installing a 3rd gen 13B with a big turbo.
In general, I'd say the rotary is more risky to start with - say the
first 50 hours - because every installation is different and errors WILL
occur. After the first 50 hours I think the rotary is well worth it.
It's safer, faster, quieter, very much smoother, and much cheaper to
maintain. The devil is in the peripherals. Redundancy is key. I have
redundant fuel tanks, filters, pumps, injectors, plugs, ignition
computers, batteries. Failure of any item is survivable because I have a
spare. The problem is that redundancy breeds complexity - this is where
the extra build and testing time comes from. I'd recommend the IVO
in-flight adjustable prop.
I've seen too many failed rebuilds by people who have much more
experience and talent than I, to risk applying my skills to this most
critical part. Also, there's enough to do with the peripherals and I
didn't need the learning curve. Unless you're determined to rebuild your
own you might consider using an expert who's done it 1000 times and
knows what to modify for aviation build your engine. Given your
investment in the plane, a professionally rebuilt engine is cheap
insurance. Instead, I'd suggest concentrating your effort on getting the
peripherals perfect, adding redundancy everywhere you can get it.
Having said all this, my take, for what its worth, would be to forget
the engine for a while and spend every spare waking moment building
yourself an airframe. Given that you have a few years to make the engine
decision, use those years to see what happens with other installations.
I hope this helps in your decision process, or at least starts yet
another heated discussion you can learn from :).
Regards,
John Slade
Turbo Rotary Cozy, N96PM.
98 hours and purring like a kitten.
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