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Lynn Matteson
Joined: 10 Jan 2006 Posts: 2778 Location: Grass Lake, Michigan
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Posted: Tue Sep 08, 2009 7:28 pm Post subject: Here's an idea that DIDN'T work |
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Have you had a look at the Rotec TBI? It is similar to the A'carb,
but in my opinion, it is better built, and looks like it has better
atomization. It almost HAS to have better fuel atomization, being
that the fuel is being introduced to the air through 50-some tiny
holes in the metering tube. I've had an Aerocarb in my hands, and
although I've not used it, I just like the way the Rotec is built,
and the way the slide feels when operated. And given the fact that
the Rotec I bought and installed has worked right from the first
flight, and reading the stories...yours included....of those who have
tried the A'carb and hated it, I'd have to say that the Rotec is a
better/easier unit to use.
Where would I find info on the "NACA principle"? I may at some future
point have to remove my muffler as well, but I'd rather keep my
engine quieter, rather than go for more horsepower. I don't want to
overstress the engine, just make it more efficient in operation, so
I'm not looking at producing more horsepower or rpm's, just
reliability and smooth operation.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 760.3 hrs
Sensenich 62"x46" Wood prop
Electroair direct-fire ignition system
Rotec TBI-40 injection
Status: flying
On Sep 8, 2009, at 9:01 PM, Peter Harris wrote:
[quote]
<peterjfharris(at)bigpond.com>
Pete Disher.
Pete D has made a beautiful symmetrical updraft plenum close to
what I have
in mind.
To make space for my (end fed) plenum I have removed the silencer.
I used the NACA principle to shape the pipe ends and this has
softened the
exhaust note and theoretically reduced exhaust back pressure.
Without a balance pipe it beats a little but they say it sounds
like a V8.
Re multipoint fuel injection it was beyond my budget as the
injectors I am
using are $100 each and any alteration to the induction pipes I
have found
is very time consuming.
In retrospect I am inclined to think that the use of a GOOD slide
carb like
a Posa or the Revmaster and feeding a symmetrical plenum by updraft
may give
as much power as fuel injection although the advantage of fuel
injection is
better atomization. A slide good carb would be cheaper and maybe
safer.It
may be significant to know that I made no gain in static RPM when I
fuel
injected after removing the Bing.
At some future stage I may modify my Aerocarb and try it in place
of my
throttle body but apart from the faulty cable actuation ,the
mixture control
and atomization seems primitive.
I had a Posa fitted to a Revmaster some years ago and it worked
perfectly
but I don't think they are available now.
Some time it would be good to try to quantify all these ideas by
looking at
max. static RPM for a given prop.
Peter
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_________________ Lynn
Kitfox IV-Jabiru 2200
N369LM |
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Peter H
Joined: 20 Mar 2007 Posts: 197
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Posted: Tue Sep 08, 2009 8:24 pm Post subject: Here's an idea that DIDN'T work |
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Lynn,
I have attached a pic of the modified tail pipes. You will be familiar with
the shape. There is a progressive reduction in pressure as the exhaust
progresses out the pipe. This eliminates the "bark" and should make for
reduced back pressure. It was one of those ideas you get in the middle of
the night. (Normally this NACA shape is used as an air inlet)
I found it softened the tone and is comfortable noise level in flight.
I will look into the Rotec but at present I am running fuel injection with a
Jenvey throttle body.
The Aerocarb suffers from basic design faults because of the offset leverage
from the cable attachment. At low throttle settings it can jam and the
harder you pull the cable the harder it jams.
Peter
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Lynn Matteson
Joined: 10 Jan 2006 Posts: 2778 Location: Grass Lake, Michigan
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Posted: Wed Sep 09, 2009 5:14 am Post subject: Here's an idea that DIDN'T work |
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Oh, THAT NACA shape...yes, I am familiar with that shape. I never
gave it a thought as to using it for exhaust pipes. I thought when
you mentioned NACA yesterday, that there was another shape that I
wasn't familiar with....and there are plenty, I'm sure....so I
Googled NACA and didn't find much on exhausts. I wonder how the
"fishmouth" pipes like were used on the P-40 Allison's would work,
and why did they shape those like they did? Seems like I recall it
was for reduced visibility at night, but maybe not.
The Rotec TBI also has a slight offset to the actuation of the slide,
but not as bad as the Aerocarb, and there is no jamming that I've
been able to detect. Mine is smooth, and it is a push wire throttle
control right up to my homemade bellcrank.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 760.3 hrs
Sensenich 62"x46" Wood prop
Electroair direct-fire ignition system
Rotec TBI-40 injection
Status: flying
On Sep 9, 2009, at 12:21 AM, Peter Harris wrote:
Quote: | Lynn,
I have attached a pic of the modified tail pipes. You will be
familiar with
the shape. There is a progressive reduction in pressure as the exhaust
progresses out the pipe. This eliminates the "bark" and should make
for
reduced back pressure. It was one of those ideas you get in the
middle of
the night. (Normally this NACA shape is used as an air inlet)
I found it softened the tone and is comfortable noise level in flight.
I will look into the Rotec but at present I am running fuel
injection with a
Jenvey throttle body.
The Aerocarb suffers from basic design faults because of the offset
leverage
from the cable attachment. At low throttle settings it can jam and the
harder you pull the cable the harder it jams.
Peter
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_________________ Lynn
Kitfox IV-Jabiru 2200
N369LM |
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Clive J
Joined: 03 Nov 2007 Posts: 340 Location: UK
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Posted: Wed Sep 09, 2009 8:18 am Post subject: Here's an idea that DIDN'T work |
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Pete, that looks an interesting idea, do you have a picture from a
different angle?
I have a single down pipe on my 3300 and there's a 2200 at the field,
they are both noisy in comparison with the twin pipe engines, if this
style of outlet reduces the 'bark' I'll change it on mine.
I have my 2200 pipes cut at an angle and that's really quiet, I didn't
do it for the noise rather to stop the floor from getting so
warm....pipe were very short.
Regards, Clive
Jabiru SP 2200
Esqual LS 3300
Both pretty standard!
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Peter H
Joined: 20 Mar 2007 Posts: 197
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Posted: Wed Sep 09, 2009 2:41 pm Post subject: Here's an idea that DIDN'T work |
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Clive,
I have only the three pics attached but here also is a paper on NACA inlet
design.
Using a felt pen on the pipes and an angle grinder I just made it look like
a NACA inlet.
Regards
Peter
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Peter H
Joined: 20 Mar 2007 Posts: 197
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Posted: Wed Sep 09, 2009 2:41 pm Post subject: Here's an idea that DIDN'T work |
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Lynn have you got a link to details on the Rotec TBI?
Thanks
Peter
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Lynn Matteson
Joined: 10 Jan 2006 Posts: 2778 Location: Grass Lake, Michigan
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Posted: Wed Sep 09, 2009 5:56 pm Post subject: Here's an idea that DIDN'T work |
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Here ya go, Peter-
http://www.rotecradialengines.com/TBI/TBI.htm
Are your pipes made of aluminum? They look like it...at least from
the collector to the NACA cut.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 761.4 hrs
Countdown to 1000 hrs~239 to go
Sensenich 62"x46" Wood prop
Electroair direct-fire ignition system
Rotec TBI-40 injection
Status: flying
On Sep 9, 2009, at 6:37 PM, Peter Harris wrote:
Quote: |
<peterjfharris(at)bigpond.com>
Lynn have you got a link to details on the Rotec TBI?
Thanks
Peter
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_________________ Lynn
Kitfox IV-Jabiru 2200
N369LM |
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Clive J
Joined: 03 Nov 2007 Posts: 340 Location: UK
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Posted: Wed Sep 09, 2009 8:54 pm Post subject: Here's an idea that DIDN'T work |
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That's great thanks Pete, felt pen and grinder and I'm off to the
hangar!
If nothing else they look really trendy!
Will match the 4 Naca scoops I have on the new cowling.
Regards, Clive
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Peter H
Joined: 20 Mar 2007 Posts: 197
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Posted: Wed Sep 09, 2009 10:38 pm Post subject: Here's an idea that DIDN'T work |
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Lynn they are Stainless steel.
I see that the Rotec cable attachment is offset but not so bad as the
Aerocarb. It looks well made but is expensive.
Peter
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Peter H
Joined: 20 Mar 2007 Posts: 197
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Posted: Wed Sep 09, 2009 10:38 pm Post subject: Here's an idea that DIDN'T work |
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I would like to know how you find the result Clive when you get the time.
Peter
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Lynn Matteson
Joined: 10 Jan 2006 Posts: 2778 Location: Grass Lake, Michigan
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Posted: Thu Sep 10, 2009 5:14 am Post subject: Here's an idea that DIDN'T work |
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The centrally-located fuel discharge tube has about 50 .010" holes
in it. They are about 1/16" apart at first, then get closer together
as you go up the tube, then when they can't get much closer, they
offset or staggr them, then further up they are set at an angle to
one another. So looking at the tube when the slide is set on idle,
only about one or two holes are revealed, then as the slide is
opened, more and more of the holes are revealed. When I hooked mine
up and turned on the main fuel valve, nothing dripped from the
discharge tube even though I had the slide wide open. Then...just as
Paul (the Rotec rep at Oshkosh) said it would...I pressed the "primer
button" on the regulator body, and all of those holes began to flow
fuel. It was quite impressive. Paul was quite honest in telling us
that they stole that idea right from Ellison. And by the way, when I
released the primer button, the fuel quit right now and did not leak
a drop. The mixture control arm rotates that discharge tube so that
the holes are facing the incoming air at lean, and at 90 degrees to
the air when set on rich, so that the air passing over the tube draws
the fuel out, like any siphon device would....an old bug sprayer
comes to mind as the simplest of this application, or a paint sprayer.
The discharge tube sits in the middle of the slide, and has a teflon
seal around it so that at any position of the slide, there is no
leakage from the holes that are "hidden" inside the slide. There is
also a teflon seal around the rod that operates the slide, and a
teflon sheet that is positioned under the slide on the suction
side....apparently what Aerocarb did not have at first.
I bought mine at Oshkosh for 595 US dollars, and they were to go
higher as of the first of August or so. It looks like they went up a
couple of hundred US, or thereabouts.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 761.4 hrs
Countdown to 1000 hrs~239 to go
Sensenich 62"x46" Wood prop
Electroair direct-fire ignition system
Rotec TBI-40 injection
Status: flying
On Sep 10, 2009, at 2:37 AM, Peter Harris wrote:
Quote: |
<peterjfharris(at)bigpond.com>
Lynn they are Stainless steel.
I see that the Rotec cable attachment is offset but not so bad as the
Aerocarb. It looks well made but is expensive.
Peter
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_________________ Lynn
Kitfox IV-Jabiru 2200
N369LM |
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Peter H
Joined: 20 Mar 2007 Posts: 197
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Posted: Thu Sep 10, 2009 1:24 pm Post subject: Here's an idea that DIDN'T work |
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Lynn,
It seems very similar to the Ellison.
The aerocarb slide is also fitted with a compound gasket to reduce friction
on the suction side, but the offset action of the cable is enough to twist
and at the same time angle the slide so that the other three surfaces
contact metal to metal and there is a high coefficient of friction between
any two anodized Al surfaces.
Peter
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