REFLECTOR: High Oil Temps

steve korney s_korney at hotmail.com
Sun Jun 23 22:09:52 CDT 2013


It will take about 8 square inches of inlet to get enough air to each oil cooler at 150 knots...


Steve 

Date: Sun, 23 Jun 2013 21:35:47 -0500
From: michalk at awpi.com
To: reflector at tvbf.org
Subject: Re: REFLECTOR: High Oil Temps


  
    
  
  
    They are the stock coolers, about 4.5"
      x 6" face area.  The inlet duct is not a real NACA scoop.  I
      extended the face of the cooler to the skin of the plane.  Once I
      have enough hours, I will experiment with closing down the aft lip
      of the inlet, making a diverging duct.

      

      I've already closed down my armpit scoops a little based upon oil
      flows on the fuselage.  I have variable armpit scoops, but at the
      moment they are only ground adjustable.

      

      On 06/23/2013 09:29 PM, steve korney wrote:

    
    
      
      Hey
          Brian...how big are the oil coolers and how much inlet scoop
          area do you have...?
        

        

        

        Steve 

        

        > Date: Sun, 23 Jun 2013 17:42:44 -0500

          > From: michalk at awpi.com

          > To: reflector at tvbf.org

          > Subject: REFLECTOR: High Oil Temps

          > 

          > Today I had a very good test flight.

          > 

          > I've been battling high CHT and oil temps, and made the
          decision to 

          > increase my prop pitch for todays flight to bring down
          RPM's. That made 

          > a marked difference in CHT temps, and I could fly without
          redlining the 

          > CHT's.

          > 

          > Now, I still have high oil temps. My oil cooler
          arrangement is two oil 

          > coolers in the nose in parallel. The secondary cooler has
          a radiator 

          > fan attached with a flapper valve that doubles for ground
          operations and 

          > cabin heat. Needless to say, the fan doesn't do a very
          good job, and I 

          > think is the source of my high oil temps.

          > For this thought game, assume two identical oil coolers
          with equal oil 

          > flow in parallel. This means that each cooler gets 50% of
          the oil. 

          > Now, assume no cooling air flows through one of the
          coolers. The result 

          > is that half the oil is cooled, and the other half gets
          returned at the 

          > same temperature it began. The result is that I get 50%
          of the cooling 

          > that's available.

          > 

          > What I've done in the meantime is I've capped off my
          second cooler. I 

          > have not flown with this configuration, and will do so
          this coming 

          > weekend. I really do think this will get me within the
          temperature 

          > ranges to get around to some serious flight testing.

          > 

          > Now, the real question:

          > Given two identical coolers that flow equal parts oil,
          and also have 

          > equal amounts of airflow, is it better to plumb them in
          series or in 

          > parallel for maximum heat rejection? It seems to me that
          parallel is 

          > like having more frontal cooler area, while in series
          would be like 

          > having a thicker cooler, with the larger frontal area
          being the more 

          > efficient design.

          > 

          > Does anyone have any info on this?

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