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Here's an idea that DIDN'T work
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Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Tue Sep 08, 2009 7:28 pm Post subject: Here's an idea that DIDN'T work

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



 --

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Tue Sep 08, 2009 8:24 pm Post subject: Here's an idea that DIDN'T work

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

Posted: Wed Sep 09, 2009 5:14 am Post subject: Here's an idea that DIDN'T work

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

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

Clive J

Joined: 03 Nov 2007
Posts: 340
Location: UK

Posted: Wed Sep 09, 2009 8:18 am Post subject: Here's an idea that DIDN'T work

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!



--

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Wed Sep 09, 2009 2:41 pm Post subject: Here's an idea that DIDN'T work

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

Posted: Wed Sep 09, 2009 2:41 pm Post subject: Here's an idea that DIDN'T work

Lynn have you got a link to details on the Rotec TBI?

Thanks

Peter



--

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Wed Sep 09, 2009 5:56 pm Post subject: Here's an idea that DIDN'T work

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

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

Clive J

Joined: 03 Nov 2007
Posts: 340
Location: UK

Posted: Wed Sep 09, 2009 8:54 pm Post subject: Here's an idea that DIDN'T work

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

Posted: Wed Sep 09, 2009 10:38 pm Post subject: Here's an idea that DIDN'T work

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



--

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Wed Sep 09, 2009 10:38 pm Post subject: Here's an idea that DIDN'T work

I would like to know how you find the result Clive when you get the time.

Peter



--

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Thu Sep 10, 2009 5:14 am Post subject: Here's an idea that DIDN'T work

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

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Thu Sep 10, 2009 1:24 pm Post subject: Here's an idea that DIDN'T work

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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