[NSRCA-discussion] How to minimize exhaust trail?

[David Lockhart]

I've been using Karls exhaust diffuser since spring of 2005 on my Webra 160.

My setup -
Webra 160 MC, Asano pipe, S&W 15/17/2 (nitro/synth/castor), 15.75-10 3 blade ~8200 RPM.  A 12 oz tank is plenty for a full F3A schedule, and in calm air I can fly 2 complete schedules on one tank (about 14-15 minutes of air time).  The smoke trail behind my plane is not a thick and visible as many other planes - mostly because the mixture is very close to perfect across the throttle range with the MC carb, and low rate of fuel consumption.

What I noticed when I added the exhaust diffuser - 
- very slightly quieter
- very slightly different tone
- noise was less directional (ie, more constant in rolling manuevers)
- on days when the smoke trail was very visible, the exhaust diffuser definitely reduced the smoke trail - mostly through the midrange, but also a little bit at full throttle.

My setup is very quiet and smooth sounding without the exhaust diffuser, and the diffuser makes it just a little bit better.  If used on a plane with lots of prop noise or airframe rattles, I suspect the improvement in exhaust sound quality may not be audible above the other noises.

Regards,

Dave Lockhart
DaveL322 at comcast.net

  ----- Original Message ----- 
  From: Karl G. Mueller 
  To: NSRCA Mailing List 
  Sent: Saturday, December 17, 2005 4:34 PM
  Subject: Re: [NSRCA-discussion] How to minimize exhaust trail?


  Glen,

  Here is what I use. It does disperse the smoke a certain amount, just
  getting away from the heavy concentrated stream. It also changes the
  exhaust noise. Dave Lockhart tried one and he claims that it reduces
  the noise by maybe 1db and makes it more non-directional. This is
  noticeable in rolling maneuvers when the exhaust is pointing at you
  or away from you.
  The amount of smoke does depend on  the climatic conditions as well.
  Some days you will have more smoke showing, especially against a
  nice blue sky while on other days, against a hazy background, it will
  not be as visible.


  Karl G. Mueller
  kgamueller at rogers.com

    ----- Original Message ----- 
    From: Glen Watson 
    To: nsrca-discussion at lists.nsrca.org 
    Sent: Saturday, December 17, 2005 1:50 PM
    Subject: [NSRCA-discussion] How to minimize exhaust trail?


    Dear list,

     

    Anyone using a diffuser, if that is the correct term to use, at the end of a muffled pipe to minimize/cloak the visual effect of the exhaust trail?  I am interested in knowing what you used and if it is commercially available or homemade and how effective it worked. 

     

    Regards,

    Glen Watson

    http://www.geocities.com/rcprecision/pah.html

     



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