OS 140 RX with Dual Plug Conversion plus Webra Memories <Long>

[David Harmon]

Chuck....this is exactly what was happening on the YS 61 Long Stroke
with a 
Tettra filter on the intake. I had a hellova difficult time with that
engine
so I put it on a test stand and after awhile discovered that the filter
was causing all
the wierd problems. It was just like a light switch...put it on...have
problems...take it off
without even stopping the engine...no problems. After that revelation I
called Futaba
and was told kinda like....'where you been??? Everybody knows that!! 
Yeah RIGHT.
    Regards
        Dave 586

-----Original Message-----
From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]
On Behalf Of Chuck Wagoner
Sent: Wednesday, September 18, 2002 11:48 AM
To: discussion at nsrca.org
Subject: RE: OS 140 RX with Dual Plug Conversion plus Webra Memories
<Long>


Matt,
Your point:"The idea is to get uninterrupted air flow in the throat of
the venturi, by moving the spray-bar against the wall of the venturi.
Better breathing results in more power for a given set of parameters."
is a very good one, and I think "uninterrupted" deserves several
additional comments, especially for those who have not seen a slide
valve function. 
With the slide valve the air flow is straight through  the variable
orifice to the spray bar. However, for the purpose of comparison
consider air flowing toward a spray bar through a carb with openings in
a rotating barrel inside a fixed cylinder. The flow path of the air has
somewhat of a 'Z' or 'S" shape. This means two relatively gradual
changes in direction of air flow occur at half throttle and increasingly
severe changes in direction happen as the idle position is approached.
This rapidly reduces the velocity and energy of the stream of incoming
air and it's ability to spray the fuel via high quality external
atomization from the spray bar. Quality of atomization decreases at the
critical idle position. Local air-to-ATOMIZED-FUEL-ratio (rich/lean
etc.) could bounce around in a non-linear fashion and reduce combustion
stability, heat release rates, and efficiency. This could cause a
richening-mixture effect on throttle up as atomization improved and
efficiency increased. Also it could promote unwanted combustion
quenching (chilling) at or near idle. 
 
I feel that a slide valve carb retrofit in combination  with dual plugs
could give very serious top and carefree performance without
significantly-increased weight, electronic complexity, or small diameter
fuel injection ports. The Webra slide valve was not at all sensitive to
fuel properties over my one-year period of heavy use back then with fun
fly contests almost every weekend in the 
Ohio, Pennsylvania, and West Virginia circuit. Zero problems of any
kind. My total engine back up on the road consisted of a spare prop nut
and some wooden props. At that time I paid $100 for the new engine. 
 
Chuck

-----Original Message-----
From: discussion-request at nsrca.org
[mailto:discussion-request at nsrca.org]On Behalf Of Rcmaster199 at aol.com
Sent: Tuesday, September 17, 2002 10:11 PM
To: discussion at nsrca.org
Subject: Re: OS 140 RX with Dual Plug Conversion plus Webra Memories 


In a message dated 9/17/2002 12:44:23 PM Eastern Daylight Time,
chuckwagon at charter.net writes:




Subj:OS 140 RX with Dual Plug Conversion plus Webra Memories  
Date:9/17/2002 12:44:23 PM Eastern Daylight Time
From:chuckwagon at charter.net
Reply-to:discussion at nsrca.org
To:pattern at rcmailinglists.com, discussion at nsrca.org
CC:lee at piedmontmodels.com
File:winmail.dat (1784 bytes) DL Time (203344 bps): < 1 minute
Sent from the Internet 



Dual plugs
anyone?http://www.rcaerosport.com/articles/reviews/evolis/crino/e10.htm
(I
remember my very smooth running dual-plug Merco 60.)

Also another 2-stroke memory... the great Webra slide valve carb. Mine
seemed to give INSTANT RPM up from an all-day idle with my stock single
plug
Webra black head engine! It had almost zero spool-up or spool-down time
to
or from any level(s) I chose. Blip...blip...blip <happy smile>. Once I
made
an adaptor and tried the slide valve with a ST blue head. Same dynamics.
Also gave more HP than the stock ST carb. Just some thoughts.
Chuck 



Chuck 

the Dynamix carb, or slide valve carb, that you mention worked extremely
well for me also. Duke Fox first used the concept in model engines back
in the sixties I believe. The concept was not lost on Webra, since their
Dynamix carb was a most effective device.

The idea is to get uninterrupted air flow in the throat of the venturi,
by moving the spray-bar against the wall of the venturi. Better
breathing results in more power for a given set of parameters.

Matt Kebabjian 

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