Cowl baffling

[Don Ramsey]

I recently completed my Smaragd.  The first 12 flights resulted in 8 engine failures.  Rebuilting the fuel system and changing the engine had no effect.  Finally I flew without the cowl and everything was OK.  Baffles solved the problem.  I don't know why but I seem to be the only one around with an air flow problem in the Smaragd.

Don
  ----- Original Message ----- 
  From: Bob Pastorello 
  To: discussion at nsrca.org 
  Sent: Sunday, March 21, 2004 6:42 AM
  Subject: Re: Cowl baffling


  Ed, others have run gassers on this list, maybe they'll chime in.  I have also.  I found the gasser to be much hotter overall than the glow motor.  Don't know why, but that was my experience.  That could explain the lack of ducts on pattern planes.  (Ducklessness?)
      Over the past few seasons, folks have been adding air scoops to cool the crankcase area around the main bearing, as there seems to be credible evidence (although mostly anecdotal) that our 2C bearing failures are due in part to high internal temperatures.
      I have had my past three ships so scooped, and after hot runs, the crankcase is measuring 165-170F.  Significantly cooler than without the airscoop.  
      There also is some benefit, particularly if running Bolly pipes, to cooling the pipe along it's length, which is usually accomodated by the exit hole around the stinger.  If it's large enough (I usually try for at least 2x the inlet hole at the front of the tunnel) my experience has been that couplers, and pipes, last far longer.
      My experience is that directing flow over the glow head hasn't been necessary, given the inverted-engine/tunnel designs that are in favor now.  The inlet hole at the front points the air to the fins, at we all know it's CLOSE around there on most designs...Hope this helps.  Just my .02

  Bob Pastorello, Oklahoma
  NSRCA 199, AMA 46373
  rcaerobob at cox.net
  www.rcaerobats.net


    ----- Original Message ----- 
    From: Ed Alt 
    To: discussion at nsrca.org 
    Sent: Saturday, March 20, 2004 8:53 PM
    Subject: Cowl baffling


    Just wondering what's commonly done to direct proper airflow in pattern birds with 2C engines.  I'm used to creating very close fitting baffling to direct air right at the cylinders of large 2 cycle gasoline fed engines and keeping the baffling so close to the fins as to force it through them.  Even the space over the heads is baffled to force air through the head fins.  After that, I make the area of the air exhaust opening at least 3X that of the total intake area.  

    So far, in studying various setups of pattern ships, I haven't seen anyone going to this kind of trouble.  Not wishing to go to any uneccesary work, but is there a reason why no one adds baffling for 2C glow engines?  I've got a Focus II with a Webra 1.60 if that helps with the answer.

    Thanks
    Ed
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