From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: Ada Cooling - Grayhawk's Pictures - More details
To: lml
Date: Wed, 06 Oct 2004 13:04:07 -0400
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Posted for "Mike Hutchins" <mhutchins@attglobal.net>:

  Thanks Scott for posting the pictures.
   
  Here are some additional comments related to Scott’s pictures in the order
  they occurred. All cylinders are referenced bases on the TCM cylinder
  ordering, i.e. pilot side front to back = 6-4-2 and copilot side front to
  back = 5-3-1. All of the comments apply only to the cylinder head; it is not
  necessary to provide additional cooling to the barrel.
  
   Photo 1. Polar plot of CHT taken at several positions on the head. The BLUE
  trace is cylinder #6. For all of the traces, the exhaust port corresponds to
  the 8:30 position and the intake port is at the 4:30 position. Note that the
  exhaust port area is the hottest area for all of the heads, except #6. Also
  note that the top of #6, at the 10:30 position is substantially cooler than
  the rest of the cylinders. This is related to the blast effect of air as it
  enters the cowling with baffles that leave most of the head exposed to the
  incoming air.
  
   Photo 2. Important details – the baffle has walls on both sides of the fins
  to sandwich the fins in between to prevent the escape of cooling air out the
  sides. The small step-off in the bottom portion of the baffle provides
  adequate exit area for the cooling air. This step-off is necessary to
  prevent choking off the air flow, thus reducing the cooling obtained. George
  told me that the pushrod tube can substantially block the air flow;
  therefore the step-off is a necessary detail. Alternatively, you can forego
  the step-off and leave the medial half of the cooling fins exposed
  (corresponding to the medial most bend in the baffle shown) with nearly the
  same cooling efficiency.
   
  Photo 3. The “curved wing” Scott refers to would be mounted on the shelf
  just above the oil cooler and would extend forward of the slanted surface of
  the oil cooler so it can “catch” some of the upward deflected air stream.
  The “curved wing” would extend rearward to the cylinder head cooling fins
  and would curve downward to deflect the air down the forward face of the
  cylinder head cooling fins. Recall the polar plot of cylinder #6 and
  consider this mod only if #6 is running hot and/or the front baffle covers
  most of the forward facing fins of #6.
   
  Photo 4. Essentially, George created a separate air compartment under the
  cowl just for the intercooler air.
   
  Photos 3 & 4. Think about radiant heat from the exhaust system. It can be a
  more significant contributor to cylinder head heating than you realize. The
  exhaust system is running red-orange hot during cruise conditions and can
  radiate A LOT of heat into the head. George told us that IR radiation
  increases with the 4th power of temperature (my guess is on the Kelvin
  scale). To block the IR heat path into the head, fabricate a small heat
  shield for each of the exhaust runners under the head. The heat shield can
  be mounted to the exhaust pipe with hose clamps and should allow a small Ľ”
  – ˝” airspace between the exhaust pipe and the heat shield. If the heat
  shield spans a slip joint, make sure there is adequate flexibility in the
  stand off legs to allow movement of the slip joint. The portion of the
  exhaust pipe stub or down-tube exiting the exhaust port can also radiate a
  lot of heat into the flat surfaces of the fins just behind the exhaust
  stack. This area can also benefit from a heat shield. The insulating wraps
  for exhaust systems were NOT recommended for this application because of the
  very high temperatures involved. The stainless steel beneath the insulating
  wrap can readily reach its phase-transition temperature and disintegrate.
  Now you are really having a bad day!
  
   Photo 5. The “baffle work” Grayhawk mentions is a bypass channel that gets
  the air around the flat spot and down to the lower cooling fins on the
  intake side of the head. I think it was Carl Cadwell that recently posted an
  elegant fix to this problem for the #2 cylinder. This is also the reason why
  you DO NOT want to place any material between the heads in this area.
   
  Photo #6. Make sure the hole is wide enough to get air past the full width
  of the flat spot in your cylinder head. There seems to be a fair amount of
  variability in the dimensions of this flat spot from engine-to-engine so you
  should not rely on dimensions from another installation. Similarly, be sure
  to extend the opening down far enough to expose enough fin area for adequate
  airflow through the hole and into the fins. Lastly, the “roof” or “awning”
  referred to in association with this opening in the baffle is suggested to
  redirect the airflow. The airflow in the area of this forward facing baffle
  is from bottom-to-top as the incoming air is redirected from its
  front-to-back direction into a bottom-to-top direction before it once again
  resumes its forward-to-back path. The “roof” is therefore placed above the
  hole and extends forward, perpendicular to the baffle and parallel to the
  horizon. The purpose is to create a high pressure area under the “roof” that
  will encourage air to flow through the hole and thus through the exhaust
  port-side cooling fins under the head.
   
  Thanks again Scott for providing some of the more critical pictures from the
  seminar.
   
  I hope this helps some of you who were unable to attend. The “Devil is in
  the Details” was an often quoted remark, as was the impact of that red-hot
  exhaust system just inches away from the bottom of the heads.
   
  Best Regards,
  
  Mike
  
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