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

[Chuck Wagoner]

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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